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	 EPA-457/R-00-002 September 2000



### NOX Control Technologies for the Cement Industry

FINAL REPORT

EPA Contract No. 68-D98-026 Work Assignment No. 2-28 EC/R Project No. ISD-228

Prepared for: Mr. David Sanders Ozone Policy and Strategies Group Air Quality Strategies and Standards Division, MD-1 5 Office of Air Quality Planning and Standards U.S. Environmental Protection Agency Research Triangle Park, NC 27711

Prepared by: Rebecca Battye, Stephanie Walsh, Judy Lee-Greco

EC/R Incorporated 1129 Weaver Dairy Road, Suite AA-1 Chapel Hill, NC 27514

September 19, 2000**i** TABLE OF CONTENTS

**1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1**  **1.1 PURPOSE OF THIS DOCUMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1**  **1.2 METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1**  **1.3 ORGANIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1**  **1.4 REFERENCE FOR CHAPTER 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1** 

**2.0 SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2**  **2.1 UNCONTROLLED NO X**  **EMISSIONS FROM CEMENT KILNS . . . . . . . . . . . 2 2.2 NO**  **X CONTROL TECHNOLOGY FOR CEMENT KILNS . . . . . . . . . . . . . . . . . 4**  **2.2.1 Process Control Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4**  **2.2.2 Combustion Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5**  **2.2.3 NO X**  **Removal Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6**  **2.2.4 NO X**  **Control Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6**  **2.3 CONTROL COSTS AND COST EFFECTIVENESS . . . . . . . . . . . . . . . . . . . . . . 8**  **2.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9** 

**3.0 INDUSTRY DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13**  **3.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13**  **3.2 TYPES OF CEMENT PRODUCED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13**  **3.3 INDUSTRY CHARACTERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15**  **3.3.1 Description of the Cement Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15**  **3.3.2 Overview of Cement Manufacturing Process . . . . . . . . . . . . . . . . . . . . . 21**  **3.3.3 Raw Materials and Kiln Feed Preparation . . . . . . . . . . . . . . . . . . . . . . . . 21**  **3.3.4 Pyroprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24**  **3.3.4.1 Wet Process Kilns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25**  **3.3.4.2 Dry Process Kilns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25**  **3.3.4.3 Suspension Preheaters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26**  **3.3.4.4 Precalciner Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26**  **3.3.5 Finish Grinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27**  **3.3.6 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27**  **3.3.7 Emission Control Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27**  **3.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28** 

**4.0 UNCONTROLLED NO X**  **EMISSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4.1 MECHANISMS OF NO**  **X FORMATION IN CEMENT MANUFACTURING . . . 29**  **4.1.1 Thermal NO X**  **Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29**  **4.1.2 Fuel NO X**  **Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31**  **4.1.3 Feed NO X**  **Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32** **ii** TABLE OF CONTENTS (continued)

**4.2 FACTORS AFFECTING NO X**  **EMISSIONS IN CEMENT MANUFACTURING . 32 4.2.1 NO**  **X Formation in the Kiln Burning Zone**  **. . . . . . . . . . . . . . . . . . . . . . . . 33 4.2.2 NO**  **X Formation in Secondary Firing**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 4.2.2.1 Suspension Preheater (SP) Kilns with Riser Duct Firing**  **. . . . . . 35 4.2.2.2 Precalcining Kiln Systems**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.2.3 Energy Efficiency of the Cement-Making Process**  **. . . . . . . . . . . . . . . . . 36 4.3 AVAILABLE DATA FOR UNCONTROLLED NO**  **X EMISSIONS FROM CEMENT**  **MANUFACTURING FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36**  **4.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44** 

**5.0 NO X**  **CONTROL TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53**  **5.1 PROCESS CONTROL MODIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54**  **5.1.1 Combustion Zone Control of Temperature and Excess Air . . . . . . . . . . . . 54**  **5.1.2 Feed Mix Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55**  **5.1.2.1 Reduction of Alkali Content of Raw Feed . . . . . . . . . . . . . . . . . 55**  **5.1.2.2 CemStar Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55**  **5.1.3 Kiln Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57**  **5.1.4 Increasing Thermal Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58**  **5.2 COMBUSTION MODIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58**  **5.2.1 Staged Combustion of Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58**  **5.2.1.1 Flue Gas Recirculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59**  **5.2.1.2 Low-NOX Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59**  **5.2.2 Staged Combustion of Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62**  **5.2.2.1 Preheater/Precalciner and Tire Derived Fuel . . . . . . . . . . . . . . . 62**  **5.2.2.2 Low-NO X**  **Precalciners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64**  **5.2.2.3 Mid-Kiln Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65**  **5.3 NO X**  **REMOVAL CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67**  **5.3.1 Selective Catalytic Reduction (SCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68**  **5.3.2 Selective Noncatalytic Reduction (SNCR) . . . . . . . . . . . . . . . . . . . . . . . . 70**  **5.3.2.1 Biosolids Injection (BSI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72**  **5.3.2.2 NO X**  **OUT ®**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 5.4 SUMMARY OF EUROPEAN EXPERIENCES . . . . . . . . . . . . . . . . . . . .**  **. . . . . . . 74 5.5 SUMMARY OF APPLICABLE NO**  **X CONTROL TECHNOLOGIES . . . . . . . . . . 76**  **5.6 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78** 

**6.0 COSTS OF NO X**  **CONTROL TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84**  **6.1 COST CALCULATION METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84**  **6.1.1 Model Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84**  **6.1.2 Capital Cost Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84** **iii** TABLE OF CONTENTS (continued)

**6.1.3 Annual Operating Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85**  **6.1.3.1 Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85**  **6.1.3.2 Operating and Supervising Labor . . . . . . . . . . . . . . . . . . . . . . . . 87**  **6.1.3.3 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88**  **6.1.3.4 Overhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88**  **6.1.3.5 Property Taxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88**  **6.1.3.6 Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88**  **6.1.3.7 Administrative Charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88**  **6.1.3.8 Capital Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88**  **6.2 COSTS OF NO X**  **CONTROL APPROACHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 6.2.1 Process Modifications**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.2.1.1 Combustion Zone Control of Temperature and Excess Air**  **. . . . 89 6.2.1.2 CemStar Process**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.2.2 Combustion Modifications**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 6.2.2.1 Low NO**  **X Burners**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 6.2.2.2 Mid-Kiln Firing**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 6.2.3 NO**  **X Removal Controls**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.2.3.1 Biosolids Injection Process**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.2.3.2 NO**  **X OUT**  **®**

**. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100**  **6.2.3.3 Selective Catalytic Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 101**  **6.3 COST EFFECTIVENESS OF NO X**  **CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.3.1 CemStar**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.3.2 Low NO**  **X Burner**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.3.3 Mid-Kiln Firing of Tires**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.3.4 Preheater/Precalciner Tire Derived Fuel**  **. . . . . . . . . . . . . . . . . . . . . . . . . 105 6.3.5 Biosolids Injection**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.3.6 Selective Noncatalytic Reduction**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.3.7 Selective Catalytic Reduction**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.3.8 Summary of Cost Effectiveness**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 6.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .**  **. . . . . . . . . . . . . . 110 iv**  LIST OF TABLES

**Table 2-1. Summary of Updated Uncontrolled NO X**  **Emissions Data and the Corresponding 1994 Act Document Estimates . . . . . . . . . . . . . .**  **. . . . . . . . . . . . . . . . . . . 3 Table 2-2. Comparison of 1994 Act Document and Current NO**  **X Control Technology**  **Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7**  **Table 2-3. Summary of Cost Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9**  **Table 3-1. Basic Clinker Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14**  **Table 3-2. United States Cement Company Capacities in 1998 . . . . . . . . . . . . . . . . . . . . . . . . . 15**  **Table 3-3. United States 1998 Clinker Capacities by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17**  **Table 4-1. Calculated Equilibrium Concentrations (in ppm) of NO and NO**  **2 in Air and Flue Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .**  **. . . . . . . . . . . . . . . . . 30 Table 4-2. NO**  **X Emissions Data Used to Develop 1994 Act Document . . . . . . . . . .**  **. . . . . . . . 38 Table 4-3. Summary of Additional NO**  **X Emission Data for Different Kiln Types . . . . . . . . . . 48**  **Table 4-4. Comparison of Emission Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49**  **Table 4-5. NO X**  **Emission Factors for Different Kiln Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49**  **Table 5-1. Results of Short-term Cemstar Tests on a Preheate r/precalciner Kiln . . . . . . . . . . . 56**  **Table 5-2. Results of Cemstar Tests on a Wet Kiln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57**  **Table 5-3. NO X**  **Emissions from a Precalciner Equipped with a Low-NO X**  **Burner . . . . . . . . . . 60 Table 5-4. NO**  **X Emissions Before and after Installation of Pyro-jet Low-NO**  **X Burners . . . . . . 61**  **Table 5-5. NO X**  **Emissions with 3 Channel and Rotaflam ®**  **Low-NO X**  **Burners . . . . . . . . . . . . . 61 Table 5-6. Emissions Before and after Installation of a Rota**  **flam ®**  **Burner on a Wet Kiln . . . . 62 Table 5-7. Emissions from Kilns with Mid-kiln Firing . . . . . .**  **. . . . . . . . . . . . . . . . . . . . . . . . . 67 Table 5-8. Emission Reductions from Two Kilns Using NO**  **X OUT**  **® . . . . . . . . . . . . . . . . . . . . . 74**  **Table 5-9. NO X**  **Control Techniques Summary from European Best Available Te chniques Report75**  **Table 5-10. NO X**  **Control Techniques and Applicable Types of Cement Kilns . . . . . . . . . . . . . 76**  **Table 5-11. Comparison of 1994 Act NO X**  **Emissions Reductions with Newly Available Emissions Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .**  **. . . . . . . 77 v**  LIST OF TABLES (continued)

**Table 6-1. Cement Kiln Model Plants for Cost Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . 85**  **Table 6-2. Capital Investment Components for Emission Cont rol Device Cost Evaluation . . . 86**  **Table 6-3. Annualized Cost Elements and Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87**  **Table 6-4. Basis for Cost Analysis of Cemstar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90**  **Table 6-5. Capital Costs for Retrofit Low-NO X**  **Burners in an Existing Indirect-fired Kiln . . . 93 Table 6-6. Annualized Costs for Retrofit Low-NO**  **X Burners in an Existing Indirect-fired Kiln 94**  **Table 6-7. Capital Costs for Retrofit Low-NO X**  **Burners in an Existing Direct-fired Kiln . . . . . 96 Table 6-8. Annualized Costs for Retrofit Low-NO**  **X Burners in an Existing Direct-fired Kiln . 97**  **Table 6-9. Capital Costs for Mid-kiln Firing Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99**  **Table 6-10. Annualized Costs for Mid-kiln Firing Conversio n . . . . . . . . . . . . . . . . . . . . . . . . . 99**  **Table 6-11. Basis for Cost Analysis of Biosolids Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . 100**  **Table 6-12. Basis for Cost Analysis of NO X**  **OUT ®**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Table 6-13. Capital Costs for SCR Process . . . . . . . . . . . . . . .**  **. . . . . . . . . . . . . . . . . . . . . . . . 103 Table 6-14. Annualized Costs for SCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104**  **Table 6-15. Cost Effectiveness of Retrofit Low-NO X**  **Burners in an Existing Indirect-fired Kiln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .**  **. . . . . . . . . . . . . . . . . 106 Table 6-16. Cost Effectiveness of Retrofit Low-NO**  **X Burners in an Existing Direct-fired**  **Kiln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106**  **Table 6-17. Cost Effectiveness of Mid-kiln Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107**  **Table 6-18. Cost Effectiveness of SCR Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109**  **Table 6-19. Summary of Cost Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110** **vi** LIST OF FIGURES

**Figure 3-1. Annual clinker production. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15**  **Figure 3-2. United States and Canadian Portland Cement Loca tions**  **(December 31, 1998) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20**  **Figure 3-3. Steps in the manufacture of portland cement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22**  **Figure 3-4. Preheater/precalciner cement kiln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23**  **Figure 4-1. Theoretical equilibrium concentrations of NO i n gas from combustion** 
**sustained in air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31**  **Figure 5-1. Schematic of low-NO X**  **burner. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Figure 5-2. Schematic of preheater. . . . . . . . . . . . . . . . . . . . .**  **. . . . . . . . . . . . . . . . . . . . . . . . . . 63 Figure 5-3. Schematic of precalciner. . . . . . . . . . . . . . . . . . .**  **. . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Figure 5-4. Reduction of NO**  **X emissions from precalcining kiln system by fuel injection**  **in the rotary kiln gas outlet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64**  **Figure 5-5. Schematic of mid-kiln firing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65**  **Figure 5-6. Schematic of fuel injection in kiln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66**  **Figure 5-7. Application of SNCR in preheater kiln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71** **1**

**1. U.S. Environmental Protection Agency.** Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing **. EPA-453/R-94-004. Research Triangle Park, NC. March 1994.**  1.0 INTRODUCTION

1.1 PURPOSE OF THIS DOCUMENT

**The purpose of this document is to update the information in t he document**  Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing **(the 1994 ACT document).**  **1 This update incorporates comments received on the 1994 ACT d**  **ocument and provides more recent data on emission control technologies**  **and their costs.**

**This report examines uncontrolled emissions from four kiln types (wet, long dry,**  **preheater, precalciner). The report focuses on the current use, effectiveness, and cost of several**  **control technologies applicable to all or some kiln types, i ncluding CemStar, low-NO**  **X burners,**  **mid-kiln firing, and selective noncatalytic reduction via biosolids injection and NO**  **X OUT**  **® technology.** 

1.2 METHODS

**Data were collected for this report primarily through site v isits at cement kiln facilities;**  **contacts with control technology vendors, portland cement industry representatives, and state**  **regulatory agencies; and a literature search. Additional i nformation was obtained through**  **seeking out useful sites on the internet.**

1.3 ORGANIZATION

**Chapter 2 presents a summary of the findings of this study. Ch apter 3 provides a**  **description of the portland cement industry. Chapter 4 exam ines uncontrolled NO**  **X emissions.**  **Chapter 5 presents an update on selected NO X**  **control technologies. Chapter 6 presents an update on control costs and cost effectiveness.** 

1.4 REFERENCE FOR CHAPTER 1**2** 2.0 SUMMARY

**This report addresses nitrogen oxides (NO X**  **) emissions from portland cement kilns and the current use, effectiveness, and cost of applicable cont**  **rol technologies. This chapter presents a summary of updated information on uncontrolled NO**  **X emissions from kilns and the**  **applicability, effectiveness, and costs of NO X**  **control technologies. Information that is summarized in this chapter is presented in greater depth in s**  **ubsequent chapters. Section 2.1 includes a summary of current uncontrolled NO**  **X emissions data from the four kiln types.**  **Section 2.2 summarizes NO X**  **control technology emissions data. Section 2.3 presents a s ummary**  **of updated control costs and cost effectiveness for these co ntrol technologies.** 

2.1 UNCONTROLLED NO X EMISSIONS FROM CEMENT KILNS

**In cement manufacturing, conditions favorable for formati on of NO**  **X are reached**  **routinely because of high process temperatures. Essential ly all NO**  **X emissions associated with**  **cement manufacturing are generated in cement kilns.**

**In cement kilns, NO X**  **emissions are formed during fuel combustion by two primary mechanisms:** 

**• Oxidation of molecular nitrogen present in the combustion air, which is termed**  **“thermal NO X**  **” formation, and**

**• Oxidation of nitrogen compounds present in the fuel, which is termed “fuel NO**  **X ”**  **formation.**

**Often the raw material feed to the kiln contains a significan t amount of nitrogen compounds**  **which may lead to feed NO X**  **formation similar to fuel NO X**  **formation. Because of the high temperatures involved in the burning or clinker formation s**  **tep, thermal NO X**  **formation provides the dominant mechanism for NO**  **X formation in cement manufacturing.** 

**There are four different types of cement kilns used in the ind ustry: wet kilns, long dry**  **kilns, kilns with a preheater, and kilns with a preheater/pr ecalciner. All cement kiln systems**  **contain a rotary kiln. The wet, long dry, and most preheater k ilns have only one fuel combustion**  **zone; whereas, the newer preheater/precalciner kilns and p reheater kilns with a riser duct have**  **two fuel combustion zones. Some precalciner kilns have a thi rd combustion zone. Since the**  **typical temperatures in the combustion zones are different , the factors affecting NO**  **X formation**  **are also somewhat different in the different kiln types. In t he primary combustion zone at the hot**  **end of a kiln, the high temperatures lead predominantly to th ermal NO**  **X formation; whereas, in**  **secondary combustion zones lower gas-phase temperatures s uppress thermal NO**  **X formation.** 

**In addition to the specific NO X**  **formation mechanisms, the energy efficiency of the cement making process is also important as it determines the**  **amount of heat input needed to 3** 

**produce a unit quantity of cement. A high thermal efficiency would lead to less consumption of**  **heat and fuel, and should produce lower NO X**  **emissions per ton of clinker, the product of the rotary kiln.** 

**EC/R obtained emissions data for cement kilns from state reg ulatory agencies in eight of**  **the top ten states in terms of clinker capacity: California, Florida, Indiana, Michigan, Missouri,**  **New York, Pennsylvania, and Texas. Table 2-1 presents a summ ary of the recent state emissions**  **data alongside a summary of the estimates used in the 1994 ACT document and the current**  **edition of AP-42.**

**TABLE 2-1. SUMMARY OF UPDATED UNCONTROLLED NO X**  **EMISSIONS DATA AND THE CORRESPONDING 1994 ACT DOCUMENT ESTIMATES** 

**1994 ACT Document 1**  **AP-42 2**  **Recent State Data 3** 

**Cement kiln type Average** 

**(lb/ton of clinker)**  **Range**

**(lb/ton of clinker)**  **(lb/ton of**

**clinker) Average rate** 

**(lb/ton of clinker)**  **Range of rates**

**(lb/ton of clinker)** 

**Wet kiln 9.7 3.6 to 19.5 7.4 6.2 1.9 - 13.4**
**Long dry kiln 8.6 6.1 to 10.5 6.0 4.5 2.5 - 7.1**

**Preheater kiln 5.9 2.5 to 11.7 4.8 1.7 0.4 - 3.7**

**Precalciner kiln 3.8 0.9 to 7.0 4.2 2.9 1.1 - 5.6**

**There is substantial spread in the reported NO X**  **emissions with significant overlap for different kiln types. The four different cement kiln types,**  **however, do appear to have different levels of NO**  **X emissions and different characteristics influencing NO**  **X formation. Information**  **used to calculate NO X**  **uncontrolled emission rates come from air emission tests at various**  **cement manufacturing facilities in the United States. Twen ty-two tests were used to calculate the**  **AP-42 NO X**  **emission factors and all of the tests are over ten years old. I n addition, the majority**  **of these are short-term emissions tests, which do not captur e the inherent variability of kiln NO**  **X emissions. As a result, the AP-42 NO**  **X emission factors have a quality rating of “D” (relatively**  **low quality - limited data, or highly variable). When one rev iews the original data summarized**  **in the 1994 ACT document, it is clear that the average emissio n rates are not unduly influenced**  **by outliers as evidenced by the fact that the average for each kiln type is nearly in the middle of**  **the range. Because the data used in the calculation of the 199 4 ACT document NO**  **X emission**  **rates are newer, these average emission rates may be more rep resentative of modern kilns than**  **the factors presented in AP-42. 4** 

**Seven of the states that were contacted reported emissions i n tons NO**  **X /year. Six of these**  **states did not report production values, so kiln capacities 5**  **were used to determine emission rates. The kilns were assumed to operate for an average of 8,000 hour**  **s/year at maximum production capacity. The resulting average emission rates are general**  **ly lower than the average emission 4** 

**rates calculated in the 1994 ACT document or presented in AP- 42. The lower numbers are**  **probably a result of using kiln capacities rather than actua l kiln production values. Because of**  **the uncertainty surrounding the production values for the s tate data and because the AP-42 data**  **have a “D” rating, the 1994 ACT document values for uncontrol led NO**  **X emissions from cement**  **kilns are used in this document. However, it should be noted t hat the ranges in emissions and the**  **average values for all three data sources generally support one another. Chapter 4 contains more**  **detailed information on the uncontrolled NO X**  **emission values.**

2.2 NO X CONTROL TECHNOLOGY FOR CEMENT KILNS

**NO X**  **control approaches applicable to the cement industry may be grouped in three**  **categories: process modifications, where the emphasis is o n increased energy efficiency and**  **productivity; combustion control approaches, where the em phasis is on reducing NO**  **X formation;**  **and NO X**  **reduction controls, which remove the NO X**  **formed in the combustion process.**

2.2.1 Process Control Modifications

**Process modifications are usually done to reduce heat consu mption, to improve clinker**  **quality, and to increase the lifetime of the equipment (such as the refractory lining) by stabilizing**  **process parameters. Process modifications are applicable to all kilns and can include many**  **elements, such as instruction and training of the kiln opera tors, homogenizing raw material,**  **ensuring uniform coal dosing, improving the cooler’s opera tion, and installing new equipment.**  **Process modifications improve fuel efficiency, reduce ope rating costs, increase capacity and kiln**  **operational stability. Since NO X**  **formation is directly related to the amount of energy consum ed**  **in cement-making, improving fuel efficiency and productiv ity will reduce NO**  **X emissions.** 

**Continuous monitoring of oxygen and carbon monoxide emissi ons in the cement kiln**  **exhaust gases indicates the amount of excess air. At a given e xcess air level, NO**  **X emissions**  **increase as the temperature of the combustion zone increase s. A typical kiln combustion zone**  **solids temperature range is about 1430 to 1540**  **C (2600 to 2800**  **F) for completion of clinkering reactions and to maintain the quality of the ceme**  **nt produced. 6**  **The corresponding gas phase temperature is usually greater than 1700**   **C (3100**  **F). 7**  **Maintaining the combustion zone temperature at the minimum necessary value would minimize b**  **oth the process energy requirement and the NO**  **X emissions.** 

**Along with the appropriate temperature, it is also necessar y to maintain an oxidizing**  **atmosphere in the clinker burning zone to ensure the quality of the clinker produced. Although a**  **kiln could be operated with as little as 0.5 percent oxygen in the exhaust, kiln operators typically**  **strive for an oxygen level of 1 to 2 percent to guarantee the de sired oxidizing conditions in the**  **clinker burning zone. An experimental test on a cement kiln s howed that by reducing excess air**  **from 10 to 5 percent (i.e., reducing exhaust oxygen levels fr om 2 to 1 percent), NO**  **X emissions**  **per unit time can be reduced by approximately 15 percent. 8,9** **5**

**With state-of-the-art continuous emissions monitoring sy stems (CEMS) and feedback**  **control, excess air can be accurately controlled to maintai n a level that promotes optimum**  **combustion and burning conditions in addition to lowering N O**  **X emissions. Reducing excess air**  **levels also results in increased productivity per unit of en ergy consumed and thus results in an**  **indirect reduction of NO X**  **emissions per unit of clinker product.**

**Process modifications can be highly site specific and data from one site cannot be directly**  **translated to other sites. Quite often a number of process mo difications and combustion control**  **measures are implemented simultaneously. Process modific ations can reduce NO**  **X emissions in**  **cement kilns without any specific NO X**  **control equipment. Some plants rely on process monitoring and control and process modifications as a means**  **to maintain NO X**  **emissions within their allowable limits. Although process controls will red**  **uce NO X**  **emissions in poorly operated kilns, for the purposes of this document, such approaches ar**  **e considered necessary for proper kiln operation and are not specifically considered as NO**  **X control techniques, except as noted**  **below for CemStar.**

**One process modification that can be quantified is the CemSt ar process, which can reduce**  **NO X**  **emissions at any type of kiln by the addition of a small amount of steel slag to the raw kiln**  **feed. Steel slag has a low melting temperature and is chemica lly very similar to clinker. Since**  **many of the chemical reactions required to convert steel sla g to clinker have already taken place**  **in a steel furnace, the fuel needed to convert steel slag into clinker is low. The decreased need**  **for limestone calcination per unit product and improved the rmal efficiency of the process both**  **contribute to reduced thermal NO X**  **and carbon dioxide emissions. 10**  **CemStar is currently being used or is in the process of being incorporated at 11 cement fa**  **cilities in the United States. CemStar requires little extra equipment and the addition of**  **steel slag to the feed mix can result in a reduction or elimination of the need for some mineral sourc**  **es, such as shale or clay. This process can decrease NO**  **X emissions by 30% and can also increase production by 15 perce**  **nt. 10** 

2.2.2 Combustion Modifications

**Combustion modifications are an efficient way to reduce the formation of thermal NO**  **X .**  **The combustion modifications discussed in this report focu s on staging the combustion to**  **minimize the amount of combustion that must occur at the maxi mum temperatures. This can be**  **accomplished by modifying the way oxygen or fuel is provided for combustion.** 

**Low-NO X**  **burner systems are available for all kiln types and rely on th e staged**  **combustion of air. Technical literature and industry publi cations report NO**  **X reduction rates of**  **23 to 47 percent with the installation of low-NO X**  **burners, depending on the baseline emissions, type of kiln, type of low-NO**  **X burner, and operating conditions.**  **11,12,13,14,15 In January 2000, the**  **Portland Cement Association (PCA) and American Portland Ce ment Alliance (APCA) provided**  **results of a survey of cement facilities where the responden ts indicated 14% of the operating U.S.**  **kilns have already installed a low-NO X**  **burner (81% of the facilities representing 81% of the operating U.S. kilns responded to the survey).**  **16,17 6** 

**Staged combustion of fuel includes the use of preheaters/pr ecalciners and mid-kiln firing.**  **Mid-kiln firing of fuels is currently installed in 21 U.S. we t and long dry cement kilns, and whole**  **tires are most frequently used for the mid-kiln fuel. Techni cal literature, industry publications,**  **and state emissions data for several kilns that have used or t ested mid-kiln firing demonstrate**  **NO X**  **reductions ranging from 28 to over 50 percent. 18,19,20,21,22,23,24**  **Use of tire derived supplemental fuel at a preheater/precalciner has been show**  **n to decrease NO X**  **emissions by 30-40 percent.**  **25**

2.2.3 NO X Removal Control

**NO X**  **removal controls destroy NO X**  **that is formed in the combustion process. Selective catalytic reduction (SCR) and selective noncatalytic redu**  **ction (SNCR) are two types of NO X**  **removal controls. Biosolids injection technology is not te chnically SNCR, but the chemistry and**  **the principles of its operation are similar. For this reason it is discussed with the other NO**  **X removal controls.** 

**SCR uses ammonia in the presence of a catalyst to selectively reduce NO**  **X emissions**  **from exhaust gases. SCR technology has not been used on any ce ment kilns in the United States,**  **although pilot plant trials and feasibility studies have be en conducted in Europe.** 

**SNCR relies on the reduction of NO X**  **in exhaust gases by ammonia or urea without using any catalyst and can achieve NO**  **X emission reductions of 30 to 70 percent. This approach avoid**  **s the problems related to catalyst fouling, as in SCR technolo**  **gy, but requires injection of the reagents in the kiln at a temperature between 870 to 1090**   **C (1600 to 2000**  **F). At these temperatures urea decomposes to produce ammonia which is re**  **sponsible for NO X**  **reduction. Because of the temperature constraint, SNCR technology is o**  **nly applicable to preheater and precalciner kilns. In principle, any of a number of nitrogen**  **compounds may be used, e.g., cyanuric acid, pyridine, and ammonium acetate. However, fo**  **r reasons of cost, safety, simplicity, and by-product formation, ammonia and urea have been used in**  **most of the SNCR applications. There have been two SNCR demonstration at full size kilns in t**  **he United States using the NO**  **X OUT**  **® process.**  **26,27 SNCR is currently operating on numerous kilns in Europe.**  **28**

**Biosolids injection technology is being used in one kiln in S outhern California.**  **29,30 At**  **this facility, the biosolids (dewatered sewage sludge) are injected into the mixing chamber where**  **the flue gas streams leaving the kiln and precalciner mix. Th e mixing chamber offers the**  **benefits of good residence time in the appropriate temperat ure window and high mixing**  **effectiveness. Biosolids injection is achieving a 50 perce nt NO**  **X emission reduction at this**  **facility.**

2.2.4 NO X Control Efficiencies

**An assortment of industry data, literature, and profession al publications, as well as some**  **of the state data described above, was used to develop an esti mate of emissions from cement** **7**

**kilns using NO X**  **control technologies. Table 2-2 presents a summary of updat ed control**  **technology emission rates alongside the emission estimate s used in the 1994 ACT document.**  **The new emissions rates are all within or very close to the ran ges established in the 1994 ACT**  **document. CemStar, a relatively new process that involves a dding steel slag to the feed mix in a**  **long kiln, was not discussed in the 1994 ACT document. Emissi on rate reductions from the use**  **of CemStar averaged 33 percent. New data on low-NO X**  **burners and mid-kiln firing tend to support the information presented in the 1994 ACT document.**  **Both of these technologies have become more commonplace in controlling NO**  **X emissions from cement kilns and improved**  **performance using mid-kiln firing technology has been obta ined. Data were also obtained on**  **two SNCR technologies, biosolids injection and NO X**  **OUT ®**  **. These technologies showed average emission reductions of 50 and 40 percent, respectively. Add**  **itional information on SCR was not obtained during the development of this report. Chapter 5 co**  **ntains a more detailed discussion of the NO**  **X control technologies.** 

**TABLE 2-2. COMPARISON OF 1994 ACT DOCUMENT AND CURRENT**

**NO X**  **CONTROL TECHNOLOGY PERFORMANCE**

**1994 ACT Updated Emissions Data 3** 

**Possible NO**  **X Emission**  **Reduction (%)**  **Average**

**Emission Reduction**  **(%) Range of** 

**Emission Reductions**  **(%) Average** 

**Emission Rate**  **(lb NO X**  **/ton of clinker)**  **Range of**

**Emission Rates Found**  **(lb NO X**  **/ton of clinker)** 
**Process Control Modifications**  **<25**

**CemStar n/a 33 23 to 40 6.0 3.2 to 11.2 Indirect firing**  **with a low-NO X**  **burner 20 to 30 27 4 to 47 9.0**  **a 9.0**  **a**

**MKF (wet kilns only)**  **20 to 40 41 28 to 59 n/a n/a**

**MKF (dry kilns only)**  **20 to 40 33 11 to 55 3.9 2.0 to 10**

**TDF in a precalciner** 

**b not**  **applicable 35 30 to 40 2.4**  **b 2.4**  **b**

**SNCR 30 to 70 BSI**  **50 NA 1.2 b**  **1.2 b** 

**NO X**  **** **OUT 40 10 to 50 NA NA** 

**n/a - not applicable**

**a Only one facility reported emissions in lb NO**  **X /ton of clinker. The other data were reported in**  **percent. 8**  **b One facility in southern California provided emission redu**  **ction data for both biosolids injection technology and firing tire derived fuel in a precalciner.** 

2.3 CONTROL COSTS AND COST EFFECTIVENESS

**Capital and annualized operating costs as well as cost effec tiveness were determined for**  **technologies for which detailed costs could be developed. C osts for low-NO**  **X burners and mid**  **kiln firing were developed for applicable model plants. Sin ce there are limited cost data**  **available for installations of CemStar and biosolids injection, and no U.S. installations of SNCR, the capital and annualized costs for these technologies wer**  **e not developed for model plants for purposes of this report. Costs for SCR were developed in the 1**  **994 ACT document and are presented again in this report. The SCR costs have not been up**  **dated or revised. All of the capital and annualized operating costs developed for this r**  **eport are based on information provided by vendors, actual installations, and guidelines**  **provided by the U.S. Environmental Protection Agency/Office of Air Quality Planning and Stand**  **ards (EPA/OAQPS) Control Cost Manual.** 

**The cost of a commercially available kiln process control sy stem, based on existing**  **installations, is approximately $750,000. The resulting s avings due to reduced energy and fuel**  **requirements and increased refractory life were estimated to be about $1.37/ton of clinker. Thus,**  **for a kiln producing 300,000 tons/year of clinker, the reduc ed cost of producing cement is**  **expected to recover process control installation costs in l ess than 2 years.** 

**Costs for CemStar were estimated for a long wet kiln. Approxi mate capital investment in**  **1997 dollars was estimated at $1,176,000 and annualized cos ts estimated to be $220,000. Cost**  **savings associated with CemStar due to the resulting produc tion increase are estimated to be**  **approximately $63 per ton times the increase in production, which is usually 5 to 10 percent.**  **The cost of CemStar could not be estimated on a variety of kiln s because the amount of steel slag**  **added is completely dependent on plant-specific variables**

**. Biosolids injection has been installed on one kiln. The tota**  **l capital investment costs for this kiln were $1.2 million with an annual operating cost of (**  **$322,000) per year (which includes tipping fees for the biosolids of $5/ton). Costs for NO**  **X OUT**  **® technology were obtained from the**  **equipment vendor for two preheater/precalciner kilns. Tot al capital investment were $1.06**  **million and $1.2 million. The annualized costs for these kil ns are $560,000 and $2,000,000 per** 
**year.**
**Cost analysis was performed for low-NO X**  **burners and mid-kiln firing on up to eight different model kilns. Models 1 and 2 were wet kilns with 30 an**  **d 50 tons of clinker per hour (ton/hour) respective capacities, models 3 and 4 were long d**  **ry kilns with 25 and 40 ton/hour respective capacities, models 5 and 6 were preheater kilns w**  **ith 40 and 70 ton/hour respective capacities, and models 7 and 8 were precalciner kilns with 10**  **0 and 150 ton/hour respective capacities. The results of the cost analysis in 1997 dollars**  **are summarized in Chapter 6. 9** 

**1. U.S. Environmental Protection Agency.** Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing. **EPA-453/R-94-004. Research Triangle Park, NC. March 1994.** 

**2. U.S. Environmental Protection Agency.** Compilation of Air Pollutant Emission Factors. AP-42. Fifth Edition. Volume I - Stationary Point and Area So urces. **Research Triangle Park, NC. January 1995. pp. 11.6-1 - 11.6-26.**  **Cost effectiveness was also estimated for each technology. A summary of the results is**  **presented in Table 2-3. Greater detail on the cost analysis a nd cost effectiveness estimates is**  **presented in Chapter 6.**

**TABLE 2-3. SUMMARY OF COST EFFECTIVENESS**

**(1997 Dollars/ton NO X**  **Reduced)**

**Technology Range of Annual**

**Cost Effectiveness Average Annual** 

**Cost Effectiveness Average Ozone** 

**Season Cost Effectiveness** 
**CemStar n/a 550 1,100**

**Low-NO X**  **Burners Indirect** 

**Fired Kilns 300 to 620 440 1,060** 

**Direct-Fired Kilns**  **760 to 1200 940 2,260**

**Mid-Kiln Firing (460) to 730 55 130**

**Tire Derived Fuel at a Precalciner**  **a (1,900)**  **b (1,900)**  **b (4,500)**  **b**

**Biosolids Injection n/a (310) b**  **(740) b** 

**NO X**  **OUT ®**  **1,000 to 2,500 1,750 2,160**

**N/A - not applicable ( ) - indicates a negative cost** 

**a The purchased equipment and total capital investment costs**  **for a tire derived fuel installation on a precalciner are very similar to mid-kiln firing.** 

**b Represents a single installation.** 

2.4 REFERENCES**10**

**3. Memo from Battye, R., and S. Walsh, EC/R Incorporated, Chap el Hill, NC to D. Sanders,**  **U.S. EPA, RTP, NC. Derivation and data supporting developme nt of cement plant NO**  **X emission rates. September 5, 2000.** 

**4. Strietman, F.L, T.B. Carter, and G.J. Hawkins.** Regulation and Control of NO X Emission from the Portland Cement Industry. **Presented at the 1999 IEEE Gulf Coast Cement Industry Conference. Charleston, SC. September 30 and Octo**  **ber 1, 1999.**

**5. Portland Cement Association.** U.S. and Canadian Portland Cement Industry: Plant Information Summary **. Skokie, IL. December 31, 1998. 214 pp.**

**6. Helmuth, R.A., F.M. Miller, T.R. O'Connor, and N.R. Greeni ng.**  Kirk-Othmer Encyclopedia of Chemical Technology. Vol. 5. Third Edition **. New York, NY. John Wiley & Sons, Inc. 1979. pp. 163-193.** 

**7. Yee, G.M.** Suggested Control Measure for the Control of Emissions of Ox ides of Nitrogen from Cement Kilns **. Presented to the State of California, Air Resources Board for Discussion on October 21, 1981.** 

**8. Miller, F.M.** Oxides of Nitrogen **. GTC Presentation, Kansas City, MO, September 20, 1977.** 

**9. Hansen, E.R., “The Use of Carbon Monoxide and Other Gases fo r Process Control,” 27**  **th IEEE Cement Industry Technical Conference Proceedings, Ma**  **y 1985.**

**10. Andover Technology Partners.** NO X Reduction from Cement Kilns Using the CemStar Process, **Evaluation of CemStar Technology - Final Report to Texas Ind ustries. Dallas,**  **Texas. April 18, 2000.**

**11. Thomsen, K., L.S. Jensen, and F. Schomburg.** FLS-Fuller ILC-lowNOx calciner commissioning and operation at Lone Star St. Cruz in Califor nia **. ZKG International. October 1998. pp. 542 - 550.** 

**12. Steinbiß, V.E., C. Bauer, and W. Breidenstein.** Current state of development of the PYRO-JET

® burner. **VDZ Kongress. 1993.**

**13. Letter and attachments from M.H. Vaccaro, Pillard Combust ion Equipment and Control**  **Systems, to G.J. Hawkins, Portland Cement Association, re: Low NOX Rotaflam**  **® burner, dated January 20, 1999.** 

**14. PSM International, “Response to USEPA Comments, 13 Septem ber 1995, on the**  **proposed alternative NO X**  **RACT for a portland cement manufacturing plant located in Thomaston, Maine and owned by Dragon Products Company,” Jan**  **31, 1996. 11** 

**15. Renfrew, S, Process Engineer, RMC Lonestar.** Calciner modification highly effective in meeting Northern California Plant’s alkali reduction and emission control requirements

**. no date.** 

**16. Email transmission from Hawkins, G., PCA, Skokie, IL to B. N euffer, U.S. EPA. Results**  **of PCA Survey - Preliminary NO X**  **Control Technology Questionnaire. January 2000.**

**17. Letter from R. Battye and S. Edgerton, EC/R Incorporated, C hapel Hill, NC, to B.**  **Neuffer, USEPA, RTP, NC. Summary of February 4, 2000 confere nce call on PCA**  **Survey - Preliminary NO X**  **Control Technology Questionnaire. February 11, 2000.**

**18. Walquist, C., Cadence Environmental Energy. “Cadence sys tem leads to fall in NO**  **X emissions,”**  World Cement **, Dec 1997, pp. 26, 27.**

**19. Cadence Environmental Energy and Ash Grove Cement. “Mid-K iln Fuel Entry**  **Benefits,” section 3 of the report,** Emission, Reduction, Technology: Resource Conservation & Recovery **. (no date).**

**20. Letter from Edgerton, S. and T. Stobert, EC/R Inc., to Bill N euffer, EPA, Feb 8, 2000.**  **Minutes from Dec 16, 1999 meeting with representatives from EPA and Cadence.** 

**21. Texas Natural Resources Conservation Commission. A list o f permitted NO**  **X levels for**  **cement plants in the state, CEMS data as reported by the facil ities for 1994 - 1999, and**  **information on the control technology in use at each facilit y.** 
**22. May, M. and L. Walters, Jr. "Low NO X**  **& Tire-derived Fuel for the Reduction of NO X**  **from the Portland Cement Manufacturing Process."** Cement Americas **, August 1999, pp. 10-1.** 

**23. Letter and attachments from Bramble, Kim, Cadence, to Bill Neuffer, USEPA, re: NO**  **X Emission Reducing Technology, dated Feb 14, 2000.** 

**24. Radian Corporation, "MDE Air Permit Test Report for Lehigh Portland Cement**  **Company, Union Bridge, Maryland Facility," January 1996.**

**25. Shumway, D.C. “Tire Derived Fuel at Mitsubishi Cement Corp oration.” Received**  **during December 2, 1999 visit to Mitsubishi.**

**26. Sun, et. al.** Reduction of NO X Emissions from Cement Kiln/ Calciner through the Use of the NO

X OUT Process **. Presented at the International Specialty Conference on Wa ste**  **Combustion in Boilers and Industrial Furnaces. Kansas City , MO. April 1994.** 

**27. Interoffice Correspondence from McAnany, L. to H. Knopfel , H, LaFarge Corporation.**  **October 26, 1998. re: Fuel Tech NO X**  **OUT Testing. 12** 

**28. European Commission.** Integrated Pollution Prevention and Control (IPPC) Refere nce Document on Best Available Techniques in the Cement and Lime Manufacturing Industries. **Joint Research Centre, Institute for Prospective Technolo gical Studies,**  **Technologies for Sustainable Development, European IPPC B ureau, World Trade Center,**  **Seville, Spain. March 2000.**

**29. Battye, R., and S. Edgerton, EC/R Incorporated, Chapel Hil l, NC.**  Trip Report to Mitsubishi Cement Corporation, Cushenbury Plant, Lucerne Valley, CA, December 2, 1999. **Prepared for the U.S. EPA, RTP, NC, under contract No. 68-D-9 8-026, work**  **assignment No. 2-28. July 5, 2000.**

**30. Biggs, H.O., Plant Manager, Mitsubishi Cement Corporatio n.**  Biosolids Injection Technology: An Innovation in Cement Kiln NO X Control. **(no date). Received during December 1999 trip report.** **13** 3.0 INDUSTRY DESCRIPTION

3.1 BACKGROUND

**This chapter provides an overview of the cement industry, it s annual production rates, and**  **the various manufacturing processes used. Process and oper ating parameters most influential for**  **NO X**  **formation in the various processes are discussed.**

**The cement industry is a vital industry for a modern society b ecause cement is an**  **essential ingredient in concrete. One need only mention rei nforced-concrete walls and girders,**  **tunnels, dams, and roads to realize the dependence of our soc iety upon cement products.**  **Hydraulic portland cement, the primary product of the cemen t industry, is made from clinker**  **blended with gypsum. Clinker is produced by heating a mixtur e of limestone, clay, and other**  **ingredients to incipient fusion at a high temperature. Lime stone is the single largest ingredient**  **required in the cement-making process, and most cement plan ts are located near large limestone**  **deposits. Portland cement is used in almost all constructio n applications including homes, public**  **buildings, roads, industrial plants, dams, bridges, and ma ny other structures.** 

**In the cement-making process, the solid raw materials are he ated to their fusion**  **temperature, typically 1400 to 1500**  **C (2550 to 2750**  **F), by burning various fuels such as coal. Portland cement has been defined as “a hydraulic cement prod** **uced by pulverizing portland cement clinker and usually containing calcium sulfate.”**  **1 Portland-cement clinker has been**  **defined as “a clinker, partially fused by pyroprocessing, c onsisting predominantly of crystalline**  **hydraulic calcium silicates.” 1**  **Burning an appropriately proportioned mixture of raw mater ials at**  **a suitable temperature produces hard fused nodules called c linker which are further ground to a**  **desired fineness. Five types of portland cement are recogni zed in the United States which**  **contain varying amounts of the basic clinker compounds give n in Table 3-1.**  **2 Different types of**  **cements are produced by starting with appropriate kiln feed composition, blending the clinker**  **with the desired amount of calcium sulfate, and grinding the product mixture to appropriate**  **fineness. Manufacture of cements of all of the various types involves the same basic high**  **temperature fusion and clinkering process responsible for the NO**  **X emissions from cement kilns.** 

3.2 TYPES OF CEMENT PRODUCED

**The five basic types of portland cement recognized and produ ced in the United States are**  **described below. 2,3**  **In addition, different varieties are prepared by using vari ous blending**  **formulations. 4** 

**Type I portland cement is a normal, general-purpose cement s uitable for all uses. It is**  **used in general construction projects such as buildings, br idges, floors, pavements, and other**  **precast concrete products. Type I is also known as regular ce ment and most commonly known as**  **gray cement because of its color. White cement typically con tains less ferric oxide and is used**  **for special applications. There are other types of cements i n general use such as oil-well cement,** **14**

**quick-setting cement, and others for special applications . Type IA portland cement is similar to**  **Type I with the addition of air-entraining properties.**

**TABLE 3-1. BASIC CLINKER COMPOUNDS 2** 

Formula Name

**2CaO**
 **SiO 2**  **Dicalcium silicate**

**3CaO**
 **SiO 2**  **Tricalcium silicate**

**3CaO**
 **AL 2**  **0 3**  **Tricalcium aluminate**

**4Ca0**
 **A1 2**  **0 3**   **Fe 2**  **0 3**  **Tetracalcium aluminoferrite**
**Mg0 Magnesium oxide in free state or combined in di- or tri- ca lcium silicate lattice.** 

**Type II portland cement generates less heat at a slower rate a nd has a moderate resistance**  **to sulfate attack. Type II portland cements are for use where moderate heat of hydration is**  **required or for general concrete construction exposed to mo derate sulfate action. Type IIA**  **portland cement is identical to Type II and produces air-ent rained concrete.** 

**Type III portland cement is a high-early-strength cement an d causes concrete to set and**  **gain strength rapidly. Type III is chemically and physicall y similar to Type I, except that its**  **particles have been ground finer. It is made from raw materia ls with a lime to silica ratio higher**  **than that of Type I cement. They contain a higher proportion o f tricalcium silicate (3Ca0** 
 **Si0 2**  **) than regular portland cements. Type IIIA is an air-entraini**  **ng, high-early-strength cement.**

**Type IV portland cement has a low heat of hydration and develo ps strength at a slower**  **rate than other cement types, making it ideal for use in dams a nd other massive concrete**  **structures where there is little chance for heat to escape. T ype IV portland cement contains a**  **lower percentage of tricalcium silicate (3Ca0**
 **Si0 2**  **) and tricalcium aluminate (3Ca0**
 **A1 2**  **0 3**  **) than type I, thus lowering the heat evolution. Consequently, the**  **percentage of dicalcium silicate is increased substantially and the percentage of tetracalciu**  **m aluminoferrite (4Ca0**
 **A1 2**  **0 3**   **Fe 2**  **0 3**  **) may be increased or may stay the same.** 

**Type V portland cement is used only in concrete structure tha t will be exposed to severe**  **sulfate action, principally where concrete is exposed to so il and groundwater with a high sulfate**  **content. Type V portland cement are those which, by their com position or processing, resist**  **sulfates better than the other four types.**

**The use of air-entraining agents increases the resistance o f the hardened concrete to**  **scaling from alternate freezing and thawing. By adding thes e materials to the first three types of**  **cements, IA, IIA, and IIIA varieties of cements are produced . Additional varieties of cements are**  **produced for special applications by blending different in gredients: masonry cement, expansive**  **cement, oil-well cement, etc. Masonry cements are commonly finely ground mixtures of** **15** Figure 3-1. Annual clinker production. 5 **portland cement, limestone, and air-entraining agents. Gr anulated blast furnace slags and natural**  **or artificial pozzolans are mixed and interground with port land cement to prepare still other**  **varieties such as blended types IP, IS, S, I(PM), and I(SM). 4** 

3.3 INDUSTRY CHARACTERIZATION

3.3.1 Description of the Cement Industry

**About 77.6 million metric tons of gray portland and 274,000 metric tons of**  **white cement were produced in a total of 198 cement kilns at 118 plants in the**  **United States in 1998. 5**  **This was a 6.0 percent increase from the 1990 reported**  **total production of 73.5 million metric tons. As shown in Figure 3-1, cement**  **industry annual clinker capacity steadily declined from the 1975 peak through**  **1990 and has steadily increased since the 1990 low. While the number of kilns has**  **dropped off sharply, average kiln size has increased. Since 1973 when average kiln**  **size was 173,000 metric tons, average kiln size has now reach ed 393,000 metric tons. Although**  **42 cement companies produced clinker in 1998, the top 5 compa nies provided about 44.2 percent**  **of the total finish grinding capacity. This is evidence of a h igh concentration of the U.S.**  **production among a limited number of top producers. Table 3- 2 provides a list of all companies**  **along with their share of the total clinker production. Tabl e 3-3 lists the clinker producing**  **capacity in the United States by States. The locations of the operating kilns are shown in**  **Figure 3-2. California and Texas are the two largest states i n terms of clinker capacity with**  **Pennsylvania, Missouri, and Alabama rounding out the top fi ve. Fourteen states and the District**  **of Columbia had no cement clinker- producing plants in 1998. 5** 

**TABLE 3-2. UNITED STATES CEMENT COMPANY CAPACITIES IN 1998**

**(INCLUDES GRAY AND WHITE PLANTS) 5** 

**Rank Clinker**

**(10 3**  **tons/year) Percent** 

**Industry Company Name** 

**1 2**  **3 9371** 

**8297 6459**  **12.0**

**10.6 8.3**  **Holnam Inc.**

**Southdown Inc. Lafarge Corporation** **TABLE 3-2. UNITED STATES CEMENT COMPANY CAPACITIES IN 1998 ( continued)**  **(INCLUDES GRAY AND WHITE PLANTS) 5** 

**Rank Clinker**

**(10 3**  **tons/year) Percent** 

**Industry Company Name** 

**16 4**  **5 6**  **4738**

**4367 3972**  **6.1**

**5.6 5.1**  **Ash Grove Cement Company**

**Blue Circle Inc. Essroc Cement Corporation** 

**7 8**  **9 3374** 

**3119 3096**  **4.3**

**4.0 4.0**  **Lone Star Industries**

**Lehigh Portland Cement Texas Industries** 

**10 11**  **12 2965** 

**2711 1616**  **3.8**

**3.5 2.1**  **California Portland Cement**

**RC Cement Company, Inc. Centex** 

**13 14**  **15 1580** 

**1457 1387**  **2.0**

**1.9 1.8**  **Mitsubishi Cement Corporation**

**Kaiser Cement Corporation Calaveras Cement Company** 

**16 17**  **18 1358** 

**1075 1047**  **1.7**

**1.4 1.3**  **Giant Cement Holding, Inc.**

**Kosmos Cement Company St. Lawrence Cement Company** 

**19 20**  **21 1003** 

**1003 952**  **1.3**

**1.3 1.2**  **Texas-Lehigh Cement Company**

**Roanoke Cement Company National Cement Company of Alabama** 

**22 23**  **24 870** 

**868 866**  **1.1**

**1.1 1.1**  **Sunbelt Cement Corporation**

**Capitol Cement Corporation Pennsuco Cement Company** 

**25 26**  **27 840** 

**812 788**  **1.1**

**1.0 1.0**  **Allentown Cement Company Inc.**

**Dacotah Cement Alamo Cement Company** 

**28 29**  **30 768** 

**763 755**  **1.0**

**1.0 1.0**  **North Texas Cement**

**Capitol Aggregates, Inc. RMC Lonestar** 

**31 32**  **33 639** 

**567 562**  **0.8**

**0.7 0.7**  **Monarch Cement Company**

**Phoenix Cement Company National Cement Company of California** **TABLE 3-2. UNITED STATES CEMENT COMPANY CAPACITIES IN 1998 ( continued)**  **(INCLUDES GRAY AND WHITE PLANTS) 5** 

**Rank Clinker**

**(10 3**  **tons/year) Percent** 

**Industry Company Name** 

**17 34**  **35 36**  **545**

**545 498**  **0.7**

**0.7 0.6**  **Continental Cement Company, Inc.**

**Florida Crushed Stone Dixon-Marquette** 

**37 38**  **39 494** 

**492 432**  **0.6**

**0.6 0.6**  **Rinker Portland Cement Corporation**

**Glens Falls Cement Company, Inc. Rio Grande Cement Corporation** 

**40 41**  **42 392** 

**294 177**  **0.5**

**0.4 0.2**  **Dragon Products Company**

**Armstrong Cement & Supply Corporation Royal Cement Company, Inc.** 

**Total: 77914**

**TABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE**

**(INCLUDES GRAY AND WHITE PLANTS) 5** 

Clinker (10 3 tons/year) No. of

Facilities Making Clinker No. of Kilns States

**10461 8187**  **6809 4497**  **4233 10** 

**10 10**  **5 5**  **18**

**19 21**  **7 6**  **California Texas**  **Pennsylvania Missouri**  **Alabama TABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE (c**  **ontinued) (INCLUDES GRAY AND WHITE PLANTS)**  **5**

Clinker (10 3 tons/year) No. of

Facilities Making Clinker No. of Kilns States

**18 4228**  **3071 2745**  **2670 2632**  **3**

**4 3**  **4 4**  **8**

**7 4**  **8 8**  **Michigan Florida**  **New York Illinois**  **Indiana**

**2630 2462**  **1748 1728**  **1719 3** 

**3 3**  **2 3**  **7**

**4 7**  **7 7**  **South Carolina Iowa**  **Oklahoma Arizona**  **Maryland**

**1710 1690**  **1259 1127**  **1104 4** 

**3 2**  **2 2**  **11**

**5 2**  **3 3**  **Kansas Colorado**  **Utah Georgia**  **Ohio**

**1060 1044**  **1003 868**  **843 2** 

**2 1**  **1 1**  **3**

**2 1**  **3 1**  **Tennessee Washington**  **Virginia West Virginia**  **Nebraska**

**812 794**  **759 726**  **623 1** 

**1 1**  **1 2**  **3**

**3 1**  **1 3**  **South Dakota Arkansas**  **Oregon Kentucky**  **Nevada TABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE (c**  **ontinued) (INCLUDES GRAY AND WHITE PLANTS)**  **5**

Clinker (10 3 tons/year) No. of

Facilities Making Clinker No. of Kilns States

**19 593**  **585 433**  **432 392**  **2**

**1 1**  **1 1**  **2**

**2 1**  **1 1**  **Montana Wyoming**  **Mississippi New Mexico**  **Maine**

**237 1 2 Idaho**

**77914 105 192**

**There are no clinker producing plants in the following state s:** 

**Alaska Connecticut Delaware Dist. of Columbia Hawaii Louisiana**  **Massachusetts Minnesota New Hampshire New Jersey North Carolina North Dakota**  **Rhode Island Vermont Wisconsin 20** Figure 3-2. United States and Canadian Portland Cement Locations(December 31, 1998)**21**

**The large majority of the cement plants (about 82.4 percent) in the United States are coal**  **fired with about 2.8 percent using natural gas, and 0.9 perce nt using oil as the primary fuel.**  **5 The**  **remaining 13.9 percent of the plants used other combination s, e.g. coal/waste as primary fuel. In**  **1998, 11 plants used waste as a primary fuel with 49 plants rep orting waste as an alternate fuel.** 

3.3.2 Overview of Cement Manufacturing Process

**The process of portland cement manufacture consists of: 6** 

**• Quarrying and crushing the rock,**

**• Grinding the carefully proportioned materials to high fin eness,** 
**• Subjecting the raw mix to pyroprocessing in a rotary kiln, a nd** 

**• Grinding the resulting clinker to a fine powder.**

**A layout of a typical plant is shown in Figure 3-3 which also il lustrates differences**  **between the two primary types of cement processes: wet proce ss and dry process.**  **6 Newer**  **designs of dry process plants are equipped with innovations such as precalciners and/or**  **suspension preheaters to increase the overall energy effic iency of the cement plant.**  **6 Figure 3-4 is**  **an illustration of a preheater/precalciner type of dry proc ess system.**  **7**

**The choice between the wet or dry process for cement manufact uring often depends upon**  **the moisture content in the raw feed materials mined from qua rries. If the moisture content of**  **the feed materials is already very high (15 to 20 percent), a w et process may be attractive. The**  **recent trend, however, has been toward the dry process with p reheater/precalciner systems. In**  **1998, about 20.6 million metric tons of clinker were produce d by the wet process with 57.4**  **million metric tons produced by a dry process. Within the dry process category, 14.2 million**  **metric tons were produced by facilities equipped with a preh eater system and 26.1 million metric**  **tons were produced by facilities equipped with a precalcine r system.**  **5**

**The different steps involved in the cement manufacturing pr ocess are described in the**  **following subsections.**

3.3.3 Raw Materials and Kiln Feed Preparation

**Calcium carbonate and the oxides of silicon, aluminum, and i ron comprise the basic**  **ingredients of cement raw mix. Because of the large requirem ent for calcium, the plants are**  **generally located near the source of the calcareous materia l. The requisite silica and alumina**  **may be derived from a clay, shale, or overburden from a limest one quarry. Such materials**  **usually contain some of the required iron oxide, but many pla nts need to supplement the iron**  **with mill scale, pyrite cinders, or iron ore. Silica may be su pplemented by adding sand to the** **22** Figure 3-3. Steps in the manufacture of portland cement. **7 23**  Figure 3-4. Preheater/precalciner cement kiln. **7 24** 

**raw mix, whereas alumina can be furnished by bauxites and alu mina-rich flint clays.**  **6 Industrial**  **byproducts are becoming more widely used as raw materials fo r cement, e.g., slags contain**  **carbonate-free lime, as well as substantial levels of silic a and alumina. Fly ash from utility**  **boilers can often be a suitable feed component, since it is al ready finely divided and provides**  **silica and alumina.**

**The bulk of raw materials originates in the plant quarry. A pr imary jaw or roll crusher is**  **frequently located within the quarry and reduces the quarri ed limestone or shale to about 100 mm**  **top size. A secondary crusher, usually roll or hammer mills, gives a product of about 10 to 25**  **mm top size. Combination crusher-dryers can utilize exit ga ses from the kiln or clinker cooler to**  **dry wet material during crushing. Each of the raw materials i s stored separately and proportioned**  **into the grinding mills separately using weigh feeders or vo lumetric measurements. Ball mills**  **are used for both wet and dry processes to grind the material t o a fineness such that only 15 to 30**  **wt% is retained on a 74-**  **m (200 mesh) sieve.**

**In the wet process the raw materials are ground with about 30 t o 40 percent water,**  **producing a well-homogenized mixture called slurry. Raw ma terial for dry process plants is**  **ground in closed-circuit ball mills with air separators, wh ich may be adjusted for the desired**  **fineness. Drying may be carried out in separate units, but mo st often is accomplished in the raw**  **mill simultaneously with grinding. Waste heat can be utiliz ed directly in the mill by coupling the**  **raw mill to the kiln or clinker cooler exhaust. For suspensio n preheater-type kilns, a roller mill**  **utilizes the exit gas from the preheater to dry the material i n suspension in the mill. A blending**  **system provides the kiln with a homogeneous raw feed. In the w et process the mill slurry is**  **blended in a series of continuously agitated tanks in which t he composition, usually the calcium**  **oxide content, is adjusted as required. These tanks may also serve as kiln feed tanks or the slurry**  **may be pumped to large kiln feed basins. Dry process blending is usually accomplished in a silo**  **with compressed air. 6** 

3.3.4 Pyroprocessing

**All cement clinker is produced in large rotary kiln systems. The rotary kiln is a refractory**  **brick-lined cylindrical steel shell [3 to 8 m (10 to 25 ft) dia , 50 to 230 m (150 to 750 ft) long]**  **equipped with an electrical drive to rotate the kiln on its lo ngitudinal axis at 1 to 3 rpm. It is a**  **countercurrent heating device slightly inclined to the hor izontal so that material fed into the**  **upper end travels slowly by gravity to be discharged into the clinker cooler at the lower,**  **discharge end. The burners at the firing end, i.e., the lower or discharge end, produce a current of**  **hot gases that heats the clinker, and the calcined and raw mat erials in succession as it passes**  **upward toward the feed end. Refractory bricks of magnesia, a lumina, or chrome-magnesite**  **combinations line the firing end. In the less heat-intensiv e midsection of the kiln, bricks of lower**  **thermal conductivity are often used. Abrasion-resistant b ricks or monolithic castable linings are**  **used at the feed end. 6** **25**

**Pyroprocessing may be conveniently divided into four stage s, as a function of location**  **and temperature of the materials in the rotary kiln. 8** 

**1. Evaporation of uncombined water from raw materials, as mat erial temperature**  **increases to 100**  **C (212**  **F);**

**2. Dehydration, as the material temperature increases from 1 00**   **C to approximately 430**   **C (800**  **F) to form oxides of silicon, aluminum, and iron;**

**3. Calcination, during which carbon dioxide (CO 2**  **) and CaO are formed from calcium carbonates, primarily between 900**   **C (1650**  **F) and 982**  **C (1800**  **F); and**

**4. Reaction, of the oxides in the burning zone of the rotary kil n, to form cement**  **clinker at temperatures of approximately 1510**  **C (2750**  **F).**

**The duration and location of these stages in an actual kiln de pend upon the type of**  **process used, e.g., wet or dry, and the use of preheaters and p recalciners as discussed in the**  **following section.**

**It is desirable to cool the clinker rapidly as it leaves the bu rning zone. Heat recovery,**  **preheating of combustion air, and fast clinker cooling are a chieved by clinker coolers of the**  **reciprocating-grate, planetary, rotary, or shaft type. Mo st commonly used are grate coolers where**  **the clinker is conveyed along the grate and subjected to cool ing by ambient air, which passes**  **through the clinker bed in cross-current heat exchange. The air is moved by a series of**  **undergrate fans and becomes preheated to 370 to 800**  **C (700 to 1500**  **F) at the hot end of cooler. A portion of the heated air serves as secondary combu**  **stion air in the kiln. Primary air is that portion of the combustion air needed to carry the fuel in**  **to the kiln and disperse the fuel. 6** 

3.3.4.1 Wet Process Kilns. **In a long wet-process kiln, the slurry introduced into the fe ed**  **end first undergoes simultaneous heating and drying. The re fractory lining is alternately heated**  **by the gases when exposed and cooled by the slurry when immers ed; thus, the lining serves to**  **transfer heat as do the gases themselves. Large quantities o f water must evaporated, thus most**  **wet kilns are equipped with chains suspended across the cros s section of the kiln to maximize**  **heat transfer from the gases to the slurry. After most of the m oisture has been evaporated, the**  **nodules, which still contain combined water, move down the k iln and are gradually heated to**  **about 550**  **C (1022**  **F) where the calcination reactions commence. The calcined m aterial further**  **undergoes clinkering reactions. As the charge leaves the bu rning zone and begins to cool, clinker**  **minerals crystallize from the melt, and the liquid phase sol idifies. The granular clinker material**  **drops into the clinker cooler for further cooling by air. 6** 

**Wet kilns typically represent an older cement technology wi th smaller capacity kilns. In**  **the United States wet cement kiln capacities range from 77,0 00 to 1,179,000 metric tons/year**  **with an average of 307,000 metric tons/year. 5** **26**

3.3.4.2 Dry Process Kilns. **The dry process utilizes a dry kiln feed rather than a slurry. Early dry process kilns were short, and the substantial quan**  **tities of waste heat in the exit gases from such kilns were frequently used in boilers to generate e**  **lectric power which often satisfied all electrical needs of the plant. In one modification, the k**  **iln has been lengthened to nearly the length of wet-process kilns and chains were added. The chain**  **s serve almost exclusively a heat exchange function. Refractory heat -recuperative devices**  **, such as crosses, lifters, and trefoils, have also been installed. So equipped, the long dry kiln is ca**  **pable of better energy efficiency than wet kilns. Other than the need for evaporation of water,**  **its operation is similar to that of a wet kiln. To improve the energy efficiency of the dry process**  **, variations such as suspension preheaters and precalciners have been introduced as discus**  **sed in the next sections. 6** 

**Long dry process kilns are generally of a smaller capacity co mpared to long wet kilns. In**  **the United States dry cement kiln capacities range from 50,0 00 to 590,000 metric tons/year with**  **an average capacity of 265,000 metric tons/year. 5** 

3.3.4.3 Suspension Preheaters. **In systems with suspension preheaters, the dry, pulverized feed passes by gravity through a series of cyclon**  **es in a vertical arrangement where it is separated and preheated several times, typically in a fou**  **r-stage cyclone system. The partially (40 to 50 percent) calcined feed exits the preheater tower in**  **to the kiln at about 800 to 900**  **C (1500 to 1650**   **F). The kiln length required for completion of the cement for mation is**  **considerably shorter than that of conventional kilns, and h eat exchange is very good. Suspension**  **preheater kilns are very energy efficient compared to wet or long dry kilns. The intimate mixing**  **of the hot gases and feed in the preheaters promotes condensa tion of alkalies and sulfur on the**  **feed which sometimes results in objectionable high alkali a nd sulfur contents in the clinker. To**  **alleviate this problem, some of the kiln exit gases can bypas s the preheater through a slip stream**  **or fewer cyclone stages can be used in the preheater with some sacrifice of efficiency.**  **6**

**Suspension preheater kilns represent a newer cement techno logy compared to the long**  **dry kilns. They are also somewhat larger in production capac ity than the long conventional**  **rotary kilns. In the United States the preheater type kiln ca pacities range from 223,000 to**  **1,237,000 metric tons/year with an average capacity of 406, 000 metric tons/year.**  **5**

3.3.4.4 Precalciner Systems. **The success of preheater kiln systems, led to precalciner kiln systems. These units utilize a second burner to carry ou**  **t calcination in a separate vessel attached to the preheater. The calciner utilizes preheated**  **combustion air drawn from the clinker cooler or kiln exit gases and is equipped with a burner that bu**  **rns about 60 percent of the total kiln fuel. Most often coal is used as a fuel in a calciner furna**  **ce; however, almost any fuel may be used including chipped tires. The raw material is calcine**  **d almost 95 percent, and the gases continue their upward movement through successive cyclone**  **preheater stages in the same manner as in an ordinary preheater. The precalciner system p**  **ermits the use of smaller dimension kilns since only actual clinkering is carried out in the rota**  **ry kiln. Energy efficiency is even better than that of a preheater kiln, and the energy penalty for bypa**  **ss of kiln exit gases is reduced since 27** 

**only about 40 percent of the fuel is being burned in the kiln. T he burning process and the clinker**  **cooling operations for the modern dry-process kilns are the same as for long wet kilns.**  **6**

**The precalciner technology is the most modern cement manufa cturing technology and**  **almost all of the newer cement plants are based on these desig ns. Precalciner kilns are also much**  **larger in capacity than the conventional rotary kilns. The p recalciner type kilns in the United**  **States range from 449,000 to 1,580,000 metric tons/year wit h an average of 869,000 metric**  **tons/year. 5**  **Because of the new large precalciner plants replacing older and smaller plants, the**  **overall average kiln capacity has been steadily increasing in the United States. It has increased**  **from an average of 239,000 metric tons/year in 1980 to an aver age capacity of 393,000 metric**  **tons/year in 1989. 5** 

3.3.5 Finish Grinding

**The cooled clinker is conveyed to clinker storage. It is subs equently mixed with 4 to 6**  **percent gypsum and introduced directly into the finish mill s. These are large, steel cylinders [2**  **to 5 m (7 to 16 ft) in diameter] containing a charge of steel bal ls, that rotate at about 15 to 20**  **rpm. The clinker and gypsum are ground to a fine, homogeneous powder. About 85 to 96**  **percent of the product is in particles less than 44**  **m in diameter. This grinding may be accomplished by two different mill systems. In open-circui**  **t milling, the material passes directly through the mill without any separation. A wide particle siz**  **e distribution range is usually obtained with substantial amounts of very fine and rather co**  **arse particles. Open circuit grinding is, however, rarely practiced in U.S. cement plants. In clos**  **ed-circuit grinding, the mill product is carried to a cyclonic air separator in which the coarse parti**  **cles are rejected from the product and returned to the mill for further grinding.**  **6**

3.3.6 Quality Control

**Beginning at the quarry operation, quality of the end produc t is maintained by**  **adjustments of composition, burning conditions, and finis h grinding. Control checks are made**  **for fineness of materials, chemical composition, and unifo rmity. Clinker burning is monitored**  **by the liter weight test weighing a portion of sized clinker, a free lime test, or checked by**  **microscopic evaluation of the crystalline structure of the clinker compounds. Samples may be**  **analyzed by wet chemistry, X-ray fluorescence, atomic abso rption, or flame photometry.**  **Standard cement samples are available from the National Ins titute of Standards and Technology.**  **Fineness of the cement is most commonly measured by the air pe rmeability method. Finally,**  **standardized performance tests are conducted on the finish ed cement.**  **6**

3.3.7 Emission Control Systems

**All cement plants are equipped with particulate collection devices to remove cement kiln**  **dust (CKD) from the kiln exhaust gases and clinker dust from c linker cooler exhaust gases.**  **Several small dust collectors are also installed at various dust emission points throughout the** **28**

**1. American Society for Testing and Materials.** 1998 Annual Book of ASTM Standards. ASTM Volume 04.01 Cement; Lime; Gypsum. **West Conshohocken, PA. 1998.**

**2. Shreve, R.N., and J.A. Brink.** Chemical Process Industries. Fourth Edition. **New York, NY. McGraw Hill, Inc. 1977. pp. 156-162.** 

**3. Dorris, V.K., A. Gerson, and M.McIntyre. Portland Cement A ssociation.**  Cement and Concrete Reference Guide. **Skokie IL. 1997.**

**4. U.S. Environmental Protection Agency.** Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing **. EPA-453/R-94-004. Research Triangle Park, NC. March 1994.** 

**5. Portland Cement Association.** U.S. and Canadian Portland Cement Industry: Plant Information Summary, December 31, 1998. **Skokie, IL. 214 pp.**

**6. Helmuth, R.A., F.M. Miller, T.R. O'Connor, and N.R. Greeni ng.**  Kirk-Othmer Encyclopedia of Chemical Technology. Vol. 5. Fourth Editio n. **New York, NY. John Wiley & Sons, Inc. 1992. pp. 564-598.** 

**7. Kosmatka, S.H. and W.C. Panarese.** Design and Control of Concrete Mixtures, Thirteenth Edition. **Portland Cement Association. Skokie, IL. 1994.**

**8. U.S. Environmental Protection Agency.** Compilation of Air Pollutant Emission Factors. AP-42. Fifth Edition. Volume I - Stationary Point and Area So urces. **Research Triangle Park, NC. January 1995. pp. 11.6-1 - 11.6-26.**  **plant such as material transfer points and grinding operati ons. The collected CKD is usually**  **recycled with the feed or injected at different points in the kiln depending upon the quality and**  **source of the CKD. None of the cement plants in the United Stat es uses any flue gas treatment**  **for reducing NO X**  **, emissions.**

3.4 REFERENCES**29** 4.0 UNCONTROLLED NO X EMISSIONS

4.1 MECHANISMS OF NO X FORMATION IN CEMENT MANUFACTURING

**In cement manufacturing, conditions favorable for formati on of nitrogen oxides (NO**  **X )**  **are reached routinely because of the high process temperatu res involved. Essentially, all of the**  **NO X**  **emissions associated with cement manufacturing are genera ted in the cement kilns.**  **Although, there are other heating operations in a cement pla nt, such as drying of raw feed or coal,**  **often the heat from the kiln exhaust gases is used for these op erations making their contribution**  **to NO X**  **emissions negligible.**

**In cement kilns, NO X**  **emissions are formed during fuel combustion by two primary mechanisms:** 

**• Oxidation of the molecular nitrogen present in the combust ion air which is termed**  **thermal NO X**  **formation, and**

**• Oxidation of the nitrogen compounds present in the fuel whi ch is termed fuel NO**  **X formation.** 

**Sometimes the raw material feed to the kiln may also contain n itrogen compounds which may**  **lead to feed NO X**  **formation similar to fuel NO X**  **formation. Because of the high temperatures involved in the burning or clinker formation step, the therm**  **al NO X**  **formation provides the dominant mechanism for NO**  **X formation in cement manufacturing. The term NO**  **X includes both**  **NO and NO 2**  **species, although NO 2**  **normally accounts for less than 10 percent of the NO X**  **emissions from a cement kiln exhaust stack. 1**  **The concentration and emission of NO X**  **are, however, typically expressed in equivalent NO**  **2 form.** 

4.1.1 Thermal NO X Formation

**Thermal NO X**  **is formed by the homogeneous reaction of oxygen and nitrogen in the gas**  **phase at high temperatures. In the overall reaction mechani sm proposed by Zeldovich,**  **2 the two**  **important steps in NO formation are given as:**

**N 2**  **+ O**  **NO + N k f** 

**= 2 x 10 14**  **exp(-76500/RT) (4-1)**

**N + O 2**   **NO + O k f** 

**= 6.3 x 10 9**  **exp(-6300/RT) (4-2)**

**where k f**  **are the rate constants for the reactions shown. The high acti vation energy of reaction**  **(4-1), 76.5 kcal/mol, means that this reaction is the most te mperature sensitive. An equilibrium**  **reaction of NO with O 2**  **further results in NO 2**  **formation. 30** 

**The equilibrium concentrations of NO and NO 2**  **formed thus depend strongly upon the gas-phase temperature as well as the concentration of O**  **2 and N**  **2 in the gas phase. Table 4-1**  **shows the equilibrium concentrations of NO and NO 2**  **for two conditions. 3**  **First, the equilibrium concentrations of NO and NO**  **2 for N**  **2 and O**  **2 concentrations found in ambient air are shown.**  **Secondly, Table 4-1 also shows the NO and NO 2**  **concentrations at flue gas conditions where the O**  **2 and N**  **2 concentrations are defined for this table as 3.3 percent O**  **2 and 76 percent N**  **2 . The**  **equilibrium NO concentrations for the flue gas conditions a re lower than those for ambient**  **conditions due to the lower O 2**  **concentration. The excess air used during fuel combustion c an**  **substantially affect NO formation by determining the amoun t of oxygen available for NO**  **reaction. The cement kiln burning zones usually have about 5 to 10 percent excess air while**  **higher excess air levels are not uncommon. Figure 4-1 shows t he theoretical equilibrium**  **concentrations of NO in the flue gas for different excess air levels.**  **1 As can be seen from this**  **figure, over 1000 ppm of NO may possibly be formed at the typic al kiln solids temperatures of**  **1430 to 1480**  **C (2600 to 2700**  **F) as the corresponding gas-phase temperatures are on the or der**  **of 1650**  **C (3000**  **F).**

**TABLE 4-1. CALCULATED EQUILIBRIUM CONCENTRATIONS (in ppm)**

**OF NO AND NO 2**  **IN AIR AND FLUE GAS 3** 

Temperature Air Flue Gas

K  F NO NO 2 NO NO 2 **300 80 3.4 (10) -10**  **2.1 (10) -4**  **1.1 (10) -10**  **3.3 (10) -3** 

**800 980 2.3 0.7 0.8 0.1**

**1440 2060 800 5.6 250 0.9**

**Fuel combustion in the kiln burning zone is the primary sourc e of thermal NO**  **X ,**  **formation in cement kilns due to temperatures well above 140 0**   **C (2550**  **F). In contrast, the fuel combustion temperature in a precalciner or in a kiln ris**  **er duct is well below 1200**  **C (2200**   **F), suppressing thermal NO X**  **formation. 4**  **Mainly fuel and feed NO X**  **may be formed in the secondary firing zone of preheater and precalciner kiln**  **systems. Along with the combustion temperature, the gas-phase residence time and the availabl**  **e oxygen concentration in the high temperature kiln burning zone are important parameters. Lo**  **nger residence times at the high temperatures will allow the NO to be formed in the equilibriu**  **m quantities. Greater amounts of oxygen in the combustion zone will of course lead to greater a**  **mounts of NO formation. Once formed, the decomposition of NO at lower temperatures, alth**  **ough thermodynamically favorable, is kinetically limited. Thus, strategies to reduce NO**  **X emissions need to be based upon reducing**  **formation of NO X**  **which may be achieved by reducing combustion temperature, o xygen**  **concentration in the high temperature combustion zone, and the gas residence time at high**  **temperatures. 31** 

Figure 4-1. Theoretical equilibrium concentrations of NO in gas from combustion sustained in air. **1** 4.1.2 Fuel NO X Formation

**Fuel NO X**  **is formed by the conversion of nitrogen present in the fuel**  **used. A recent survey of the cement industry by Portland Cement Association**  **(PCA) indicates that almost 82 percent of the energy requirement of the cement**  **industry is provided by coal. 5**  **Natural gas contributed about 3 percent of the energy**  **demand, oil about 1 percent, and other fuels such as waste solvents provided**  **about 14 percent of the energy. Both oil and natural gas have relatively low fuel**  **bound nitrogen content, whereas coal may contain 1 to 3 percent of nitrogen by**  **weight depending upon the source of coal. Waste-derived fuels (WDF) such as scrap**  **tires, used motor oils, surplus printing inks, dry-cleaning solvents, paint thinners,**  **sludge from the petroleum industry, agricultural wastes such as almond shells,**  **and even municipal biosolids (dewatered sewage sludge) are finding an increasing**  **application in the cement kilns. 6**  **The nitrogen content in these fuels may be significant depending on the chemicals included in the waste mix being bu**  **rned.**

**The maximum possible fuel NO X**  **formation may be estimated from the fuel nitrogen content by assuming 100 percent nitrogen conversion. As dis**  **cussed in section 4.3, the typical heat requirement for a wet process is estimated to be about 6 m**  **illion Btu for a ton of clinker and the corresponding requirement for a dry process is estimate**  **d to be about 4.5 million Btu for a ton of clinker. Assuming an average heat requirement of 5.3 mill**  **ion Btu for a ton of clinker, and a coal heating value of 12,000 Btu/lb, about 442 lb of coal will**  **be required per ton of clinker produced. With a nitrogen content of 1 percent by weight, app**  **roximately 9.5 lb of NO (14.5 lb expressed as NO**  **2 ) would be produced per ton of clinker with 100 percent nitrog**  **en conversion. Thus, even with only 10 percent conversion of coal nitrogen t**  **o NO X**  **, 1.5 lb of fuel NO X**  **(expressed as NO 2**  **) may be formed per ton of clinker when coal is used as a primary fuel.** 

**The amount of fuel NO X**  **formed is difficult to identify separately from thermal NO X**  **as measurements indicate the overall NO**  **X formed. In general, however, thermal NO**  **X is assumed to**  **be the dominant mechanism in cement kilns. 7**  **Typically, gas burners produce more intense and hot flames compared to the less intense "lazy" flames produc**  **ed by coal burners. Thus, gas-fired kilns may be expected to produce greater thermal NO**  **X as compared to coal-fired kilns. Coal, on** **32**

**the other hand, contains much greater amounts of fuel-bound nitrogen than natural gas which has**  **almost no fuel-bound nitrogen. The coal-fired kilns may thu s be expected to produce more fuel**  **NO X**  **than gas-fired kilns. A study of gas- and coal-fired kilns, h owever, clearly indicated that**  **gas-fired, dry-process kilns typically produce almost thr ee times more NO**  **X than the coal-fired,**  **dry-process kilns. 7**  **This fact indicates the dominance of thermal NO X**  **in overall NO X**  **formation.**

4.1.3 Feed NO X Formation

**Similar to coal, the raw materials used in cement production may contain a significant**  **amount of nitrogen. In most cases, limestone is the major raw material, with the remainder of the**  **raw mix being composed of clays, shales, sandstones, sands, and iron ores. Since most of these**  **raw material components are sedimentary minerals, they may contain small amounts of**  **chemically bound nitrogen, presumably of organic origin. V arious kiln feeds contain appreciable**  **amounts of nitrogen, ranging from about 20 ppm up to as much as 1000 ppm (as N).**  **8 The higher**  **values (>100 ppm) are generally associated with minerals di splaying noticeable kerogen**  **contents. Since 100 ppm N in a kiln feed is equivalent to about 1 lb NO**  **X per ton of clinker (if it**  **all converted), NO X**  **emissions from the kiln feed may represent a major source of N O**  **X from**  **cement kilns. Nevertheless, it is probably less important t han thermal NO**  **X and fuel NO**  **X in most** 

**cases.**
**The same study indicated that conversion of feed nitrogen to NO**  **X occurs mainly in the**  **300 to 800**  **C (570 to 1470**  **F) temperature range and depends upon the feed heating rate. 8**  **Rapid heating rates (~1000**  **C flash heating) of the kiln feed mixtures were found to give m uch**  **lower conversion efficiencies, whereas slow heating rates of kiln feed mixtures (~60**   **C/min) gave fairly high conversion of about 50 percent of bound nitr**  **ogen to NO. These results were explained by assuming that the organic nitrogen must vapori**  **ze from the sample prior to oxidation if high conversion efficiencies to NO**  **X are to be achieved. If heating rates are rapid,**  **"cracking" of these volatile compounds may occur in situ, an d this may result in conversion of**  **the bound nitrogen directly to N 2**  **before it comes into contact with gaseous oxygen, thus reduc ing**  **the fraction converted to NO X**  **. Such a hypothesis is also consistent with the observation t hat,**  **during coal combustion, the involatile or "char" nitrogen i s converted to NO**  **X much less**  **efficiently than the volatile nitrogen. 9** 

4.2 FACTORS AFFECTING NO X EMISSIONS IN CEMENT MANUFACTURING

**Chapter 3 identified four different types of cement kilns us ed in the industry: wet kilns,**  **long dry kilns, kilns with a preheater, and kilns with a prehe ater/precalciner. The wet and long**  **dry kilns typically have only one fuel combustion zone, wher eas the newer preheater and**  **precalciner kiln designs have two or three fuel combustion z ones: kiln burning zone, riser duct**  **and precalciner. Because the typical temperatures present in the combustion zones are different,**  **the factors affecting NO X**  **formation are also somewhat different in different kiln typ es and are**  **discussed in the following sections. In addition to the spec ific NO**  **X formation mechanisms, the**  **energy efficiency of the cement-making process is also impo rtant as it determines the amount of** **33**

**heat input needed to produce a unit quantity of cement. A high thermal efficiency would lead to**  **less consumption of heat and fuel, and would generally produ ce lower NO**  **X emissions.** 

4.2.1 NO X Formation in the Kiln Burning Zone

**In the kiln burning zone, thermal NO X**  **provides the primary mechanism for NO X**  **formation. Thermal NO X**  **formation depends upon the combustion zone temperature, th e gas**  **phase residence time and the oxygen concentration in the hig h temperature combustion zone.**  **The flame temperature strongly depends upon the type of fuel burned. The temperature and**  **intensity are generally greater for gas burners than coal bu rners. The oxygen concentration in the**  **combustion zone depends upon the overall excess air used and on the source and proportion of**  **primary and secondary combustion air. Less primary air may p roduce an initial**  **high-temperature, fuel-rich combustion zone followed by a low-temperature fuel-lean**  **combustion zone. Such a combination is likely to reduce NO X**  **formation.**

**The firing system used in the kiln affects the proportion of p rimary and secondary**  **combustion air. Direct firing systems introduce a large pro portion of combustion air with the**  **fuel being burned. This produces two conflicting effects fo r NO**  **X emissions: higher oxygen**  **concentration or fuel lean combustion and lower gas tempera ture. Indirect firing systems on the**  **other hand use only a small portion of combustion air to conve y fuel and thus use less primary**  **air. In general, direct fired systems may be expected to prod uce greater NO**  **X emissions compared**  **to indirect fired systems. The majority of kilns in the Unite d States are direct fired.** 

**The flame shape and the theoretical flame temperature are im portant factors in thermal**  **NO X**  **formation as these factors determine the hottest points in t he flame. A long "lazy" flame**  **will produce less NO than a short intense flame. The flame sha pe depends on the fuel being**  **burned as well as the proportion of air. For the same amount of primary air, gas burning may be**  **expected to produce a shorter and more intense flame than coa l burning. The lower the**  **secondary air temperature and the greater the dust content i n the secondary air, the lower the NO**  **X formation in the kiln burning zone. A large amount of water in**  **the primary air (from a direct firing coal mill) and injection of cement kiln dust (CKD) in t**  **he burning zone (insufflation) may also reduce NO**  **X formation. With increasing excess air percentage, the NO**  **X formation in the kiln**  **will increase, but only up to a certain point as an increasing excess air rate will reduce the**  **secondary air temperature and, consequently, the flame tem perature.** 

**Process conditions that can affect NO X**  **emissions substantially are: temperature stability, stability of raw mix feed rate, burnability of raw mix, and al**  **kali and sulfur control. Temperature stability is important to maintain the quality of clinker an**  **d is achieved by stable-flame conditions and energy efficiency. Clinker formation reactions requir**  **e temperatures of 2650 to 2800**  **F (1450 to 1540**   **C ) 10**  **and an oxidizing environment. Sometimes natural gas or liqu id waste**  **derived fuel is used to control flame conditions and improve clinker quality. The excess air used**  **during combustion has a substantial influence on NO X**  **emissions. Oxygen levels of 4 to 5 percent in kiln exhaust gases would correspond to high NO**  **X emissions, whereas oxygen levels of** **34**

**only 0.5 to 1.5 percent would mean lower NO X**  **emissions. Thus, NO X**  **emissions in a kiln may depend upon the care exercised by the operator in minimizing**  **excess oxygen needed to maintain the quality of the clinker produced. All but one of the clinke**  **r formation reactions are exothermic and represent a dynamic process that requires constant oper**  **ator adjustments which can vary NO X**  **formation.**

**The heating value of the fuel burned may also affect NO X**  **emissions. High heating value fuels, such as petroleum coke, require less combustion air a**  **nd produce less NO X**  **per ton of clinker.** 

**Different raw material compositions require different bur ning conditions to maintain the**  **quality of clinker produced. Thus, similar types of kilns wi th different feed materials may**  **produce different levels of NO X**  **emissions. The alkali content of finished cement needs to be below a certain acceptable level. Low alkali requirements m**  **ay require higher kiln temperatures and longer residence times at high temperatures to volatili**  **ze the alkali present in the molten clinker. Raw materials with greater alkali content may need**  **to be burned longer at higher temperatures to meet alkali requirements and thus may produ**  **ce greater NO X**  **emissions. Increased volatilization of alkali results in increased al**  **kali emissions in kiln exhaust gases. To control alkali emissions, a part of the kiln exhaust gases ma**  **y be bypassed around a downstream unit, e.g., a precalciner. The bypassed gases are quenched t**  **o remove alkali and sent through a particulate matter collector. This alkali-rich particula**  **te matter is removed from the process and disposed. The bypass of kiln exhaust gases typically involv**  **es a fuel penalty, e.g., about 20,000 Btu/ton of clinker for every 1 percent gas bypass. The additi**  **onal heat requirement will contribute to increased NO**  **X emissions.** 

**Wet kilns require about 33 percent more thermal energy than a dry kiln. This means a**  **greater volume of exhaust gas from a wet kiln for the same prod uction. On the other hand, the**  **greater amount of combustion air will also mean a somewhat lo wer secondary air temperature.**  **Based on these contradicting factors, one might expect the N O**  **X emissions from a wet process**  **kiln to be similar to the dry and preheater kilns without rise r duct firing.** 

4.2.2 NO X Formation in Secondary Firing

**In the secondary firing region of precalcining kilns, where temperatures range from 820 to**  **1100**  **C (1500 to 2000**  **F) , the following reactions may take place:**

**"N" + O NO**  **(4-3)**

**"N" + NO N**  **2 + O (4-4)** 

**where "N" means nitrogen originating from nitrogen compoun ds in the fuel.**  **1 Reaction (4-3)**  **shows that NO formation in the secondary firing zone will dep end upon the nitrogen content in**  **the fuel and the oxygen level in the firing zone. Reaction (4- 4) indicates that, if there is already** **35**

**NO present in the gas introduced into the secondary firing zo ne, a reduction of this NO may**  **occur with the fuel nitrogen compounds acting as reducing ag ents. Accordingly, the net**  **formation of NO in the secondary firing zone will also depend upon the initial NO concentration**  **in the combustion gas. Finally, measurements have shown tha t the volatile content in the solid**  **fuel and the temperature in the secondary firing zone also in fluence the NO formation in the**  **secondary firing zone. 11**  **With increased volatile content in the fuel, the ratio of fue l nitrogen**  **conversion into NO seems to decrease and, as the reaction rat e of reaction (4-4) increases more**  **rapidly with the temperature than that of reaction (4-3), an increase in the temperature of the**  **secondary firing region may reduce-the net NO X**  **formation. 1** 

4.2.2.1 Suspension Preheater (SP) Kilns with Riser Duct Firing

. **In many SP kiln systems 10 to 20 percent of the fuel is fired into the riser duc**  **t. The preheater systems are more energy efficient compared to long dry kilns. The increased e**  **nergy efficiency and the reduction in the amount of fuel burned at the higher clinker burning tempe**  **rature may be expected to reduce the NO**  **X emissions from preheater kilns when compared with the long d**  **ry and wet kilns. Measurements at several riser-duct fired kiln systems indi**  **cate that firing coarse fuel (e.g., tires) into the kiln riser duct will reduce NO**  **X emissions from the kiln systems.**  **12 This may be**  **explained by the fact that a large part of the fuel falls direc tly down into the kiln charge, creating**  **a reducing atmosphere in the kiln back-end where NO X**  **from the burning zone is reduced.**

**Conversely, when firing finely ground fuel into the kiln ris er duct, the NO**  **X content in the**  **exhaust gas may increase on passing through the riser duct. A s the NO**  **X emissions from the kiln**  **may also increase slightly due to an increased excess air rat e, the total NO**  **X emissions from the**  **kiln system may increase when starting up riser duct firing w ith finely ground fuel.**  **1**

4.2.2.2 Precalcining Kiln Systems

. **In precalcining kiln systems with a tertiary air duct, firing into the rotary kiln typically accounts for only 40 to**  **50 percent of the total heat consumption and the specific amount of combustion gases fro**  **m the kiln burning zone is reduced proportionally. Precalciner kilns also typically require**  **the least amount of energy per unit amount of clinker produced. The lower energy requirement an**  **d the substantial reduction in the proportion of the fuel burned at clinker burning temperatur**  **es may be expected to reduce the NO X**  **emissions from the precalciner kilns as compared to the preh eater kilns. On the other hand, the**  **NO X**  **concentration (in ppm) in the kiln gas may be considerably hi gher than in preheater kilns.**  **This is probably due to the shorter material and longer gas re tention times in the precalciner kiln**  **burning zone combined with a very high secondary air tempera ture.**  **1**

**When examining the contribution from the calciner firing to the emission of NO**  **X , two**  **basically different types of precalcining kiln systems nee d to be considered:** 

**• The in-line (ILC) type in which the kiln gas passes through t he firing region of the**  **precalciner, and 36** 

**• The separate line (SLC) type in which the kiln exhaust gas by passes the firing**  **region of the precalciner.**

ILC systems: **In these systems, the fuel combustion in the calciner takes p lace in a**  **mixture of the kiln exhaust gas and hot air from the cooler (te rtiary air). Some of the nitrogen in**  **the fuel reacts with NO from the kiln exhaust gas while anothe r part reacts with oxygen to form**  **NO. The result may be a net increase or a net reduction of NO in t he calciner.** 

SLC systems: **In these systems, the fuel combustion in the calciner takes p lace in pure hot**  **air. In the case of oil firing, NO production in the calciner i s negligible; but when using fuels**  **containing fuel-bound nitrogen, up to 50 percent of the nitr ogen compounds in the fuel may be**  **converted into NO X**  **. The specific NO X**  **, production in an SLC calciner may be as high as 4 lb NO**  **X per ton of clinker as measured in a calciner fired with petrol**  **eum coke which has a high nitrogen content and low volatile content.**  **1 The NO**  **X in the calciner exhaust gas is added to the**  **NO X**  **in the gas from the rotary kiln which leaves this type of kiln s ystem without being reduced.**  **When fired with solid fuels, SLC systems may therefore be exp ected to generate somewhat**  **higher NO X**  **emissions than the ILC systems. 1** 

4.2.3 Energy Efficiency of the Cement-Making Process

**Since NO X**  **formation is directly related to fuel combustion, any reduc tion in the amount**  **of fuel burned per unit amount of clinker produced should red uce NO**  **X emissions per unit**  **clinker. Attempts to improve energy efficiency of the proce ss by avoiding excessive clinker**  **burning and utilizing waste heat effectively for preheatin g combustion air, coal, and raw mix is**  **likely to reduce NO X**  **emissions. Improving heat transfer between hot gases and so lid materials,**  **e.g., by chain systems, will improve energy efficiency. The newer preheater and precalciner kiln**  **designs provide very efficient preheating and precalcinin g of the raw mix with intimate gas**  **solids contact in cyclone towers. New cement kiln installat ions or renovations of older kilns thus**  **predominantly involve precalciner designs for their energ y efficiency. The inherent energy**  **efficiency of these kiln designs is likely to produce less NO X**  **emissions per unit amount of clinker as compared to the wet or long dry kilns.** 

4.3 AVAILABLE DATA FOR UNCONTROLLED NO X EMISSIONS FROM CEMENT MANUFACTURING FACILITIES

**The four types of cement kilns discussed in the last section e xhibit different combustion**  **characteristics as well as energy efficiencies and heat req uirements. The available NO**  **X emissions data are therefore generally grouped by these cem**  **ent kiln types.**

**In January 1995, EPA published a revised AP-42 section for Po rtland Cement**  **Manufacturing. 13**  **The revised NO X**  **emission factors adopted for the AP-42 document for the same four kiln types mentioned above are: 7.4 lb/ton of clink**  **er for wet process kilns, 6.0 lb/ton of clinker for dry process kilns, 4.8 lb/ton of clinker for ki**  **lns with preheaters, and 4.2 lb/ton of 1**  **A = Tests are performed by a sound methodology and are reporte d in enough detail for adequate** 

**validation. B = Tests are performed by a generally sound methodology, but**  **lacking enough detail for adequate validation.**  **C = Tests are based on an unproven or new methodology, or are la cking a significant amount of**  **background information. D = Tests are based on a generally unacceptable method, but th**  **e method may provide an order of-magnitude value for the source.** 

**2 Waste Derived fuels can include scrap tires.** 

**37 clinker for kilns with precalciners. These emission factor**  **s were developed from 23 references. All 23 references are over ten years old and primarily repres**  **ent short-term compliance tests.**

**Each AP-42 emission factor is given a rating from A through E, with A being the best.**  **Two steps are involved in factor rating determination. The f irst step is an appraisal of data**  **quality, the reliability of the basic emission data that wil l be used to develop the factor. The**  **second step is an appraisal of the ability of the factor to sta nd as a national annual average**  **emission factor for that source activity. All of the AP-42 NO X**  **emission factors have a “D” rating which is below average. A “D” rating means the factors were de**  **veloped from A-, B-, and/or C - rated test data from a small number of facilities, and there m**  **ay be reason to suspect that these facilities do no represent a random sample of the industry.**  **1 There also may be evidence of**  **variability with the source population.**

**During preparation of the 1994 ACT document, NO X**  **emissions data were collected from major cement companies in the United States. Out of 51 cement**  **kilns providing NO X**  **emissions data, 22 were from wet kilns, 10 were from long dry kilns, 10 we**  **re from preheater kilns, and 9 were from precalciner type cement kilns. Table 4-2 presents**  **the NO X**  **emissions data along with the kiln types and fuels burned.** 

**As seen from Table 4-2, in general, wet kilns were found to pro duce the highest NO**  **X emissions ranging from 3.6 to 19.5 lb NO**  **X /ton of clinker with an average of 9.7 lb NO**  **X /ton of**  **clinker. Wet kilns also consume the most energy among differ ent cement kiln types. The energy**  **consumption of wet kilns was found to be in the range of 4.9 to 8 .8 MM Btu/ton of clinker with**  **an average of 6.0 MM Btu/ton. Wet kilns burning gas were found to produce greater NO**  **X emissions as compared to those burning coal. Also in some cas**  **es, high secondary combustion air temperatures were present with high NO**  **X emission rates. Twelve of the wet kilns reported**  **burning WDFs 2**  **in significant quantities. Five of these kilns used "mid-ki ln" firing of the solid**  **and liquid waste fuel and the other seven kilns injected liqu id waste in the hot kiln burning zone.** **CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 38** **TABLE 4-2. NO X** **EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT**Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference1. Ash Grove Cement Co.**Foreman, AR 1 2** **3 Wet** **Wet Wet** **36 36** **54 42% - Coal** **42% - LWDF 16% - SWDF** **As above As above** **6.86 7.1** **7.05 13.51** **18.34 15.65** **CEM Jul-92** **CEM Jul-92** **CEM Jul-92** **14 14** **14 Chanute, KS 1 & 2 Wet 30% - Coal** **7.1% - Coke 61.6% - WDF** **1.3% - Gas 6.56 9 CEM** **7/10/92 7/18/92** **14 Durkee, OR 1 Four-stage** **Preheater 68.2 100% - Coal** **during tests 95% - Gas** **Currently 3.88** **during test 3.72** **currently 5.06 CEM** **Method 7 9/15/85** **14 Nephi, UT 1 Precalciner 80 100% - Coal 3.6 3.43** **4.51 1.31** **Nov-82 Jul-88** **Apr-92 14** **TABLE 4-2. NO X** **EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued )** Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 39** 2. Blue Circle Inc.**Calera, AL 1 Dry 38 100% - Coal 3.8 9.58 CEM 15** **Atlanta, GA 1 Dry 38.5 50% - Coal 50% - Coke** **3.95 10.47 CEM 15 Ravena, NY 1 Wet 106.3 40% - Coal** **60% - Coke 4.9 9.38 CEM 15** **Tulsa, OK 1 Dry 38.5 100% - Coal 4 7.5 CEM 15 Harleyville, SC 1 Preheater 85 100% - Coal 3.5 5.87 CEM 15** 3. California Portland Cement Inc.**Rillito, AZ 1 2** **3 Long Dry** **Long Dry Long Dry** **17 17** **17 71% - Coal** **28% - Gas 1% - Coke** **54.2% - Coal 44.8% - Gas** **1% - Coke 66.8% - Coal** **31.8% - Gas 1.2% - Coke** **5 5** **5 7.2 - 11.0** **(9.1) 7.2 - 11.0** **(9.1) 7.2 - 11.0** **(9.1) EPA Method** **7E - CEM Jun-91** **EPA Method 7E - CEM** **Jun-91 EPA Method** **7E - CEM Jun-91** **16 16** **16 TABLE 4-2. NO** **X EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued** **)**Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 40** **4 Precalciner 125 64% - Coal 23.8% - Gas** **3.6% - Coke 3.8% - Used** **oil 5.7% - Tires** **3.4 3.6 - 6.6 (5.1)** **EPA Method 7E - CEM** **Jun-Aug-91 16** **Mojave, CA 1 Precalciner 130 90.8% - Coal 4.7% - Oil** **4.5% - Gas 3.1 3.9 CARB 100** **Compliance Test** **May-92 16** 4. CBR Cement Corporation**Redding, CA 1 Preheater 85 80% - Coal 20% - Tires** **3.1 2.5 CEM Jul-92** **17**5. Holnam, Inc.**Theodore, AL 1 Precalciner 193.8 4 EPA Method 7E** **9/24/91 18** **Florence, CO 3 Wet 60 5.8 EPA Method** **7E 10/24/91** **18 TABLE 4-2. NO** **X EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued** **)**Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 41** **Fort Collins, CO 1 One-stage preheater** **61.7 8.1 CEM Jan-Jun-92** **18 Artesia, MS 1 Wet 62.5 12.5 CEM** **7/16/92 18** **Clarksville, MO 1 Wet 170 6.8 CEM 18 Three Forks, MT 1 Wet 37.7 11.6 EPA Method 7** **2/10/86 18** **Ada, OK 1 2** **Wet Wet** **40 40** **15.9 19.5** **KVB System Jun-92** **KVB System Jun-92** **18 Holly Hill, SC 1** **2 Wet** **Wet 60** **102 5.7** **5.3 CEM** **6/28/92 CEM** **7/9/92 18** **TABLE 4-2. NO X** **EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued )** Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 42** **Morgan, UT 1 2** **Wet Wet** **22 22** **6.61 5.46** **EPA Method 7E 11/21/91** **EPA Method 7E** **11/27/91 18** **18 Seattle, WA 1 Wet 56.2 8.12 EPA Method** **7E 10/15/90** **18**6. Lafarge Corporation**Demopolis, AL 1 Preheater 98 70% - Coal 30% - WDF** **Gas - Preheat 3.2 4.8 EPA Method** **7E 9/5/8/91** **19 Davenport, IA 1 Preheater** **Precalciner 108.3 100% - Coal 3.2 217 lb/hr** **2.61 204.4 lb/hr** **2.07 EPA Method 7** **9/21/82 6/6/84** **20 20** **TABLE 4-2. NO X** **EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued )** Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 43** **Fredonia, KS 1 2** **Wet Wet** **17 28.5** **100% - Coal 100% - Coal** **5.98 6.17** **5.85 ~200 ppm** **4/11/89 ~550 ppm** **9/17/91 ~500 ppm** **9/18/91 EPA Method** **7E 21** **21 21** **Alpena, MI 1 2** **Dry Dry** **70 45** **78% - Coal 22% - WDF** **100% - Coal 5** **4.6 957 ppm avg** **393 ppm avg CEM** **8/7/92 CEM** **8/7/92 22** **22 Sugar Creek, MO 1 & 2 Dry 66.7 71.4% - Coal** **23.8% - Coke 4.8% - Gas** **4.52 6.1 EPA Method 7E** **9/19/91 23** **Paulding, OH 1 & 2 Wet 30 45.3% - Coal 2.5% - Coke** **52.2% - WDF 5.3 3.6 EPA Method** **7E 5/25/82** **24 TABLE 4-2. NO** **X EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued** **)**Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 44** **Whitehall, PA 3 Four-stage preheater** **36 70% - Coal 30% - Coke** **90% - Coal 10% - Tire** **80% - Coal 20% - Tire** **70% - Coal 30% - Tire** **3.3 4.24 3.2** **3.3 4.1** **EPA Method 7E** **Dec-91 25** **25 25** **25 New Braunfels,** **TX 1 Preheater** **Precalciner 122 50.2% - Coal** **40.7% - Coke 9.1% - Gas** **3 4.15 EPA Method 7E** **3/90-5/90 26** 7. Lehigh Portland Cement Co.**Leeds, AL 1 Preheater 83 89% - Coal 11% - Gas** **3.76 3.46 - Mill off** **2.24 - Mill on** **5/23/91 5/21/91** **27 Cementon, NY 1 Wet 77 100% - Coal 5.25 5.9 5/22/90 27** **Buda, TX 1 Precalciner 138 95% - Coal 5% - Gas** **3.63 3.8 6/30/86 27 TABLE 4-2. NO** **X EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued** **)**Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 45** **Waco, TX 1 Wet 10 68% - Gas 32% - Coke** **8.8 17.1 12/5/85 27**8. Lone Star Industries**Oglesby, IL 1 Dry 64.6 8 7.2** **CEM 5/92-6/92** **EPA Method 7 12/13/83** **28 28** **Greencastle, IN 1 Wet 91.7 5 CEM 28 Cape Girardeau,** **MO 1** **1 1** **Precalciner Precalciner** **Precalciner 139.4** **139.4 139.4** **1.4 (178 ppm)** **0.9 (115 ppm)** **1.5 (182 ppm)** **CEM 4/13/92** **CEM 4/15/92** **CEM 6/25/92** **28 28** **28 Sweetwater, TX 3 Preheater 20.8 11.68 EPA Method 7** **Apr-May 1991 28** **TABLE 4-2. NO X** **EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued )** Location Kiln # Kiln type Capacity(tons/hr)Fuel burned Heat inMM Btu/tonNOXemissions(lb/tonclinker)Method anddate of dataReference**CEM = Continuous emissions monitor; WDF - waste derived fuel ; LWDF - liquid waste derived fuel; SWDF - solid waste derived** **fuel; either WDF or SWDF can include waste tires 46** 9. Southdown, Inc.**Brooksville, FL 1 Preheater 80 100% - Coal 3.2 3 CEM Feb-92** **29 Fairborn, OH 1 Preheater 85 80% - Coal** **20% - LWDF 3.9 11 CEM** **Dec-91 29** **Knoxville, TN 1 Preheater Precalciner** **80 75% - Coal 12% - LWDF** **13% - SWDF 3.6 7 CEM** **Jan-91 29** **47**

**The kilns with mid-kiln firing reported much greater NO X**  **emissions ranging from 9 to 18.3 lb/ton of clinker, whereas other waste-fuel burning wet kil**  **ns reported much lower NO X**  **emissions ranging from 3.6 to 8.1 lb NO X**  **/ton of clinker. NO X**  **emissions data from these kilns prior to introducing waste fuels, however, were not availab**  **le to directly assess the effect of waste fuel burning on NO**  **X emissions.** 

**The-long dry kilns consume significantly less energy than w et kilns (about 4.5 MM**  **Btu/ton on average) and produce less NO X**  **emissions in the range of 6.1 to 10.5 lb NO X**  **/ton of clinker with an average of 8.6 lb NO**  **X /ton of clinker. The wet and long dry kilns are similar in**  **terms of structure and firing of fuels. The difference in the NO**  **X emission rates may thus be**  **attributed to the difference in the energy consumption rate s in these two types of kilns.** 

**The preheater kilns reported NO X**  **, emissions in the range of 2.5 to 11.7 lb NO X**  **/ton of clinker with an average of 5.9 lb NO**  **X /ton of clinker. The high values of 8.1 and 11.7 were**  **incidently found in gas burning kilns. As expected, the ener gy consumption of preheater kilns**  **was much lower, about 3.8 MM Btu/ton. In addition, combustio n of a part of the fuel at a lower**  **preheating temperature is expected to reduce the NO X**  **emissions as compared to burning all the fuel in the hot kiln burning zone. These two factors account f**  **or the lower NO X**  **emissions in preheater kilns as compared to wet or long dry kilns.** 

**The precalciner kilns produced the least NO X**  **emissions ranging from 0.9 to 7.0 with an average of 3.8 lb NO**  **X /ton of clinker. These kilns are the most energy efficient wi**  **th an average energy consumption of 3.3 MM Btu/ton of clinker. Precalcine**  **r kilns have lower NO X**  **emission rates because they burn more fuel at the calcining temperatu**  **re.**
**There have been many changes in the six years since the 1994 AC T document was**  **published. One of the most interesting from an emissions est imation perspective is the increased**  **use of continuous emissions monitors (CEM) on cement kilns. In January 2000, the PCA and**  **PCA provided results of a survey of cement facilities where t he respondents indicated 46% of the**  **operating U.S. kilns (74 kilns) have already installed a CEM S (81% of the facilities representing**  **81% of the operating U.S. kilns responded to the survey). The remaining 87 kilns that are**  **represented by the survey have not installed a CEMS. 30,31**  **CEMs record NO X**  **measurements at closely spaced intervals. These measurements are accumula**  **ted and averaged by a process control computer at preset time intervals. CEMs data provid**  **e a better estimation of average NO X**  **emissions from cement kilns than do short-term tests becaus e of the high degree of variability in**  **NO X**  **emissions and autocorrelation between sequential NO X**  **measurements. 32** 

**Eight state air pollution control agencies were asked to pro vide NO**  **X emissions data for**  **their kilns. These data were supplemented with additional t est data, and industry literature to**  **determine average uncontrolled emission rates for the four kiln types.**  **33 These most recent data**  **are summarized in Table 4-3. The emissions data from the stat e agencies are primarily from**  **CEMS and are the reported annual emissions for the facilitie s. Most of the states did not report**  **production values (because they tend to be confidential) so kiln capacities**  **5 were used to** **48**

**determine emission rates. The kilns were also assumed to ope rate for an average of 8,000 hours**  **per year. In addition, most of the state agencies did not prov ide additional information on any**  **NO X**  **control measures that may have been implemented (e.g., low- NO**  **X burners). The resulting**  **average emission rates are generally lower than the average emission rates calculated in 1994 or**  **presented in AP-42. The lower numbers are probably a result o f using kiln capacities rather than**  **actual kiln production values but may also be a result of assu mptions regarding the installation of**  **NO X**  **control devices (approximately 14% of the operating U.S. ki lns have installed low-NO**  **X burners - see section 5.2.1.2).**  **30,31**

**TABLE 4-3. SUMMARY OF ADDITIONAL NO X**  **EMISSION DATA**

**FOR DIFFERENT KILN TYPES**

Cement kiln type Average

rate (lb/ton of clinker) Range of

rates (lb/ton of clinker) Number of

Data Points

**Wet kiln 6.2 1.9 - 13.4 10**
**Long dry kiln 4.5 2.5 - 7.1 6**

**Preheater kiln 1.7 0.4 - 3.7 6**

**Precalciner kiln 2.9 1.1 - 5.6 12**

**All of the literature and data gathered indicate substantia l spread in the reported NO**  **X emissions with significant overlap for different kiln type**  **s. Table 4-4 compares the NO X**  **emission rates from the 1994 ACT document, AP-42, and the data recentl**  **y collected from the State air agencies. The four different cement kiln types, however, do**  **appear to have different levels of NO**  **X emissions and different characteristics influencing NO**  **X formation. As shown, the rates**  **calculated from the State data are generally lower that the v alues calculated during development**  **of the 1994 ACT document. The new data are not necessarily mor e representative than the 1994**  **ACT document data. The lower rates derived from the new data p robably result from the**  **assumptions made regarding kiln production and level of NO X**  **control. It should be noted that the lower emission rates derived from the new data for prehea**  **ter kilns relative to precalciner kilns is contrary to expectation and could be due to the lack o**  **f data points for preheater kilns. The AP-42 factors are also lower than the 1994 ACT document ra**  **tes but are primarily based on short term emission tests, which do not capture the inherent**  **variability of kiln NO X**  **emissions, and the data are all over 10 years old. When one reviews the ori**  **ginal data summarized in the 1994 ACT document, the maximum or minimum NO**  **X emission rate for a specific kiln type is**  **about equally greater or less than the calculated average. B ecause the data used to calculate the**  **1994 ACT document NO X**  **emission rates are newer, these average emission rates may b e more**  **representative of modern kilns than the factors presented i n AP-42.**  **34 49** 

**1. Nielsen, P.B., and O.L. Jepsen.** An Overview of the Formation of SO X and NO

X in Various Pyroprocessing Systems. **Presented at the IEEE Cement Industry Technical Conference XXXII. Tarpon Springs, FL. May 22-24, 1990.** 

**2. Zeldovich, J. The Oxidation of Nitrogen in Combustion and Explosions: Acta. Physiochem. 21(4). 1946.** 

**TABLE 4-4. COMPARISON OF EMISSION RATES**

**Kiln Type Emission Rate (lb NO X**  **/ton clinker)**

**1994 ACT AP-42 New Data**

**Wet 9.7 7.4 6.2**
**Long dry 8.6 6.0 4.5**

**Preheater 5.9 4.8 1.7**

**Precalciner 3.8 4.2 2.9**

**The emission data compiled for the 1994 ACT document will be u sed in estimating**  **uncontrolled emissions from typical cement kilns because t hese data are newer and include more**  **CEMS data than the data used in AP-42; the NO X**  **emission rates derived in AP-42 have a “D” quality rating (based on number of tests and variability of e**  **missions from the process); and the data collected from the state agencies are less certain beca**  **use of lack of production data. These data are presented in Table 4-5. This table also includes the**  **heat input requirement for the different cement kiln types which indicates a good correlat**  **ion with the NO X**  **emission rates.**

**TABLE 4-5. NO X**  **EMISSION FACTORS FOR DIFFERENT KILN TYPES**

Cement kiln type Heat input requirement (MM Btu/ton of clinker) Average NO X emission rate (lb/ton of clinker) Range of NO X emissions (lb/ton of clinker)

**Wet kiln 6.0 9.7 3.6-19.5**
**Long dry kiln 4.5 8.6 6.1-10.5**

**Preheater kiln 3.8 5.9 2.5-11.7**

**Precalciner kiln 3.3 3.8 0.9-7.0**

4.4 REFERENCES**50**

**3. U.S. Environmental Protection Agency.** Control Techniques for Nitrogen Oxide Emissions From Stationary Sources **. Publication AP-47. National Air Pollution Control Administration. Washington D.C. 1970.** 

**4. Shreve, R.N., and J.A. Brink, Jr.** Chemical Process Industries **. New York, NY. Fourth Edition. McGraw Hill, Inc. 1977.** 

**5. Portland Cement Association.** U.S. and Canadian Portland Cement Industry: Plant Information Summary **. December 31, 1998. 1999.**

**6. Portland Cement Association. Website: (**  **http://www.portlandcement.org/env/enviro2.asp). Accessed on July 11, 2000.** 

**7. Hilovsky, R.J.** NO X Reductions in the Portland Cement Industry With Conversion to Coal-Firing. **Presented at the 1977 U.S. EPA Emission Inventory/Factor Wo rkshop.**  **Raleigh, NC. September 13-15, 1977.**

**8. Gartner, E.M.** Nitrogenous Emissions From Cement Kiln Feeds: Portland Cement Association Interim Report on Project HM7140-4330. **Skokie, IL. June 1983.**

**9. Payne, R., T. Akiyama, and J.G. Witkamp.** Aspects of NO X Formation and Reduction in Coal Fired Combustion Systems **. International Flame Research Foundation. Report NO X**  **F37/a/10. Ijmuiden, Netherlands. 1981.**

**10. Penta Engineering Corporation.** Report on NO X Formation and Variability in Portland Cement Kiln Systems Potential Control Techniques and Their Feasibility and Cost Effectiveness **. 1999.**

**11. Johansen, V., A. Egelov, and A. Eirikson.** Emission of NO X and SO 2 , From Cement Clinker Burning Installations **. Zement-KalkGips NO X**  **10. 1986.**

**12. Scheuer, A.** Theoretische und betriebliche untersuchungen zur bildung und zum abbau von stickstoffmonoxid in zementdrehofenanlagen **. Schriftenreihe der Zementindustrie, Heft 49. 1987.** 

**13. U.S. Environmental Protection Agency.** Compilation of Air Pollutant Emission Factors. Publication AP-42. Fifth Edition. Volume I - Stationary Poin t and Area Sources

**. Research Triangle Park, NC. January 1995. pp. 11.6-1 - 11.6-**  **26.**

**14. Letter and attachments from Sweeney, D.M., Ash Grove Cemen t Company, to Neuffer,**  **W.J., U.S. Environmental Protection Agency. August 25, 199 2. Response to**  **questionnaire on NO X**  **emissions data. 51** 

**15. Letter and attachments from Willis, D.A., Blue Circle Ceme nt, Inc., to Neuffer, W.J.,**  **U.S. Environmental Protection Agency. October 2, 1992. Res ponse to questionnaire on**  **NO X**  **emissions data.**

**16. Letter and attachments from Bennett, J., California Portl and Cement Company, to**  **Neuffer, W.J., U.S. Environmental Protection Agency. Nove mber 17, 1992. Response to**  **questionnaire on NO X**  **emissions data.**

**17. Letter and attachments from Ellison, J.E., Calaveras Ceme nt Company, to Neuffer, W.J.,**  **U.S. Environmental Protection Agency. August 31, 1992. Res ponse to questionnaire on**  **NO X**  **emissions data.**

**18. Letter and attachments from Hackett, H.P., Holnam, Inc., t o Jordan, B.C., U.S.**  **Environmental Protection Agency. August 28, 1992. Respons e to questionnaire on NO**  **X emissions data.** 

**19. Letter and attachments from Gandy, M., Lafarge Corporatio n, to Jordan, B.C., U.S.**  **Environmental Protection Agency. August 20, 1992. Respons e to questionnaire on NO**  **X emissions data.** 

**20. Letter and attachments from Smith, M.G., Lafarge Corporat ion, to Jordan, B.C., U.S.**  **Environmental Protection Agency. August 26, 1992. Respons e to questionnaire on NO**  **X emissions data.** 

**21. Letter and attachments from Smith, R.G., Lafarge Corporat ion, to Jordan, B.C., U.S.**  **Environmental Protection Agency. July 31, 1992. Response t o questionnaire on NO**  **X emissions data.** 

**22. Letter and attachments from Johns, T., Lafarge Corporatio n, to Jordan, B.C., U.S.**  **Environmental Protection Agency. August 13, 1992. Respons e to questionnaire on NO**  **X emissions data.** 

**23. Letter and attachments from Wallace, W., Lafarge Corporat ion, to Jordan, B.C., U.S.**  **Environmental Protection Agency. August 14, 1992. Respons e to questionnaire on NO**  **X emissions data.** 

**24. Letter and attachments from Collins, B., Lafarge Corporat ion, to Jordan, B.C., U.S.**  **Environmental Protection Agency. August 4, 1992. Response to questionnaire on NO**  **X emissions data.** 

**25. Letter and attachments from Weiss, R., Lafarge Corporatio n, to Jordan, B.C., U.S.**  **Environmental Protection Agency. August, 1992. Response t o questionnaire on NO**  **X emissions data.** **52**

**26. Letter and attachments from Harris, M.D., Lafarge Corpora tion, to Jordan, B.C., U.S.**  **Environmental Protection Agency. September 1, 1992. Respo nse to questionnaire on**  **NO X**  **, emissions data.**

**27. Letter and attachments from Matz, T.L., Lehigh Portland Ce ment Company, to Neuffer,**  **W.J., U.S. Environmental Protection Agency. October 27, 19 92. Response to**  **questionnaire on NO X**  **emissions data.**

**28. Letter and attachments from Johnson, R.M., Lone Star Indus tries, to Jordan, B.C., U.S.**  **Environmental Protection Agency. October 9, 1992. Respons e to questionnaire on NO**  **X emissions data.** 

**29. Letter and attachments from Gill, A.S., Southdown, Inc., t o Neuffer, W.J., U.S.**  **Environmental Protection Agency. December 3, 1992. Respon se to questionnaire on NO**  **X emissions data.** 

**30. Email transmission from Hawkins, G., PCA, Skokie, IL to B. N euffer, U.S. EPA.**  Results of PCA Survey - Preliminary NO X Control Technology Questionnaire. **January 2000.**

**31. Letter from R. Battye and S. Edgerton, EC/R Incorporated, C hapel Hill, NC, to B.**  **Neuffer, USEPA, RTP, NC.** Summary of February 4, 2000 conference call on PCA Survey - Preliminary NO X Control Technology Questionnaire. **February 11, 2000.**

**32. Walters Jr., L.J., et. al. “Time-Variability of NO X**  **Emissions from Portland Cement Kilns.”**  Environmental Science & Technology **. Vol. 33, No. 5, 1999, pp. 700 - 704.**

**33. Memo from R. Battye and S. Walsh, EC/R Incorporated to D. San ders, U.S. EPA,**  Derivation and data supporting development of cement plant NO X emission rates. **September 15, 2000.**

**34. Strietman, F.L, T.B. Carter, and G.J. Hawkins.** Regulation and Control of NO X Emission from the Portland Cement Industry. **Presented at the 1999 IEEE Gulf Coast Cement Industry Conference. Charleston, SC. September 30 and Octo**  **ber 1, 1999. 53**  5.0 NO X CONTROL TECHNIQUES

**As discussed in Chapter 4, nitrogen oxides (NO X**  **) are formed by the oxidation of nitrogen during the fuel combustion process. The formation of therma**  **l NO X**  **is a function of the flame temperature, flame turbulence, the amount of nitrogen and o**  **xygen available for the thermal reaction, and the gas phase residence time at high temperatu**  **re. To reduce the amount of thermal NO**  **X formed, one or more of these variables needs to be minimized.**  **The formation of fuel and feed NO**  **X is not as well understood as the thermal NO**  **X formation. In general, however, the**  **greater the concentration of nitrogen in the fuel and feed, t he greater the fuel NO**  **X emissions.**  **Therefore, reducing the amount of fuel and feed-bound nitro gen should reduce the contribution**  **of the fuel and feed NO X**  **. The typical NO**  **X emissions from a cement plant depend upon the type of the ceme**  **nt kiln as shown in Table 4-6. For any given type of kiln, the amount of**  **NO X**  **formed is directly related to the amount of energy consumed in the cement-making proces**  **s. Thus, measures that improve the energy efficiency of this process should reduce NO**  **X emissions in terms of lb of NO**  **X /ton of**  **clinker. With the rising costs of energy and the very competi tive cement market, greater**  **attention is being paid to increasing overall energy effici ency, such as through reduction of over**  **burning of clinker and improvement in gas-solids heat trans fer. Continuous emissions**  **monitoring of CO, NO X**  **, and O 2**  **provide an indication of kiln conditions and also provide in puts**  **for process control. Newer cement kiln designs are generall y based on preheater/precalciner**  **systems which provide very efficient gas-solids contact an d greater energy efficiency.** 

**NO X**  **control approaches applicable to the cement industry may be grouped in three**  **categories:**

**1. Process modifications where the emphasis is on increased e nergy efficiency and**  **productivity (section 5.1);**

**2. Combustion control approaches where the emphasis is on red ucing NO**  **X formation (section 5.2); and** 

**3. NO X**  **reduction controls which remove the NO X**  **formed in the combustion process (section 5.3).** 

**Section 5.4 provides a discussion of the technologies suppo rting the recent selection of**  **Best Available Techniques (BAT) for NO X**  **control at European cement kilns. Section 5.5 gives a summary of the applicable NO**  **X control technologies, and section 5.6 provides the referen**  **ces for this entire chapter.** **54**

5.1 PROCESS CONTROL MODIFICATION

**Process modifications are applicable to any type of kiln and are usually done to reduce**  **heat consumption, to improve clinker quality, and to increa se the lifetime of the equipment (such**  **as the refractory lining) by stabilizing process parameter s. Reduction of emissions, such as NO**  **X ,**  **SO X**  **, and dust, are secondary effects of these modifications. Sm ooth and stable kiln operation**  **close to design values for process parameters is beneficial for all kiln emissions. Process**  **modifications can include many elements, such as instructi on and training of the kiln operators,**  **homogenizing raw material, ensuring uniform coal dosing, i mproving the cooler’s operation, and**  **installing new equipment. Process modifications are prima rily done to reduce operating costs,**  **increase capacity, and improve product quality. Adopting p rocess modifications usually results**  **in a reduction of operating costs for a kiln. The savings resu lt from reduced fuel and refractory**  **consumption, lower maintenance costs, and higher producti vity, among other factors.**  **1**

**This section describes process modifications that improve fuel efficiency and kiln**  **operational stability with an emphasis on reducing NO X**  **formation. Since NO X**  **formation is directly related to the amount of energy consumed in cement-**  **making, improving fuel efficiency and productivity will reduce NO**  **X emissions.** 

5.1.1 Combustion Zone Control of Temperature and Excess Air

**Continuous monitoring of O 2**  **and CO emissions in the cement kiln exhaust gases indicates the amount of excess air. At a given excess air leve**  **l, NO X**  **emissions increase as the temperature of the combustion zone increases. A typical kil**  **n combustion zone solids temperature range is about 1430 to 1540**   **C (2600 to 2800**  **F) for completion of clinkering reactions and to maintain the quality of the cement produced** 

**. 2**  **The corresponding gas-phase temperature is usually greater than 1700**   **C (3100**  **F). 3**  **Maintaining the combustion zone temperature at a necessary minimum value would minimize bot**  **h the process energy requirement and the NO**  **X emissions.** 

**Along with the appropriate temperature, it is also necessar y to maintain an oxidizing**  **atmosphere in the clinker burning zone to ensure the quality of the clinker produced. Although a**  **kiln could be operated with as little as 0.5 percent kiln exha ust oxygen level, typically the kiln**  **operators strive for an oxygen level of 1 to 2 percent to guara ntee the desired oxidizing**  **conditions in the kiln burning zone. An experimental test on a cement kiln showed that by**  **reducing excess air from 10 to 5 percent (i.e., reducing exha ust oxygen levels from 2 to 1**  **percent) NO X**  **emissions per unit time can be reduced by approximately 15 pe rcent.**  **4,5**

**With state-of-the-art continuous emissions monitoring sy stems (CEMS) and feedback**  **control, excess air can be accurately controlled to maintai n a level that promotes optimum**  **combustion and burning conditions in addition to lowering N O**  **X emissions. Reducing excess air**  **level also results in increased productivity per unit amoun t of energy consumed and thus results**  **in an indirect reduction of NO X**  **emissions per unit amount of clinker product. 55** 

5.1.2 Feed Mix Composition

**Heat requirements for producing clinker are dependent on th e composition of the raw**  **feed which varies among cement plants. Experiments have dem onstrated that by improving the**  **burnability of the raw feed, the heat requirement of clinker can be reduced by 15 percent.**  **6 If the**  **raw feed composition can be formulated to require less heat i nput per ton of clinker, less fuel is**  **burned and less NO X**  **per unit product is produced. This approach of changing the f eed**  **composition may, however, be highly site specific and may no t be applicable at all locations.** 

5.1.2.1 Reduction of Alkali Content of Raw Feed

**The alkali content of finished cement generally needs to be b elow a certain acceptable**  **level. Low alkali requirements need higher kiln temperatur es and longer residence times at high**  **temperatures to volatilize the alkali present in the semi-m olten clinker. Raw materials with**  **greater alkali content need to be burned longer at higher tem peratures to meet alkali requirements**  **and thus may produce greater NO X**  **emissions. Increased volatilization of alkali also result s in**  **increased alkali emissions in kiln exhaust gases. To contro l alkali emissions, a part of the kiln**  **exhaust gases may be bypassed around a downstream unit, e.g. , a precalciner. The bypassed**  **gases are quenched to remove alkali and sent through a partic ulate collector. The bypass of kiln**  **exhaust gases typically involves a fuel penalty, e.g., abou t 20,000 Btu/ton of clinker for every 1**  **percent gas bypass. The additional heat requirement may als o contribute to increased NO**  **X emissions; thus, reducing the alkali content of the raw feed**  **mix may contribute to a reduction in the NO**  **X emissions.** 

5.1.2.2 CemStar Process

**.**

**Another feed modification that can reduce NO X**  **emissions is the addition of a small amount of steel slag to the raw kiln feed. This patented techn**  **ique is known as the CemStar Process and was developed by TXI Industries. Steel slag has a**  **low melting temperature and is chemically very similar to clinker. Since many of the chemic**  **al reactions required to convert steel slag to clinker have already taken place in a steel furnace, t**  **he fuel needed to convert steel slag into clinker is low. The decreased need for limestone calcin**  **ation per unit product and improved thermal efficiency of the process both contribute to reduce**  **d thermal NO X**  **and CO 2**  **emissions. 7** 

**Eleven facilities are using or in the process of incorporati ng CemStar.**  **8 CemStar requires**  **little extra equipment and the addition of steel slag to the f eed mix can result in a reduction or**  **elimination of the need for some mineral sources, such as sha le or clay. This process can also**  **increase production by 15 percent. 7** 

**According to the En tellect Environmental Services “Evaluation of the Effects**  **of the CemStar Process on a Wet Process Cement Kiln” report, the Cem**  **Star process reduces the kiln material temperature in the region of the flame by an average**  **of 200**  **F (from 2610**  **F to 2405**   **F); the lower gas temperature of the flame results in lower NO X**  **emissions. 9**  **Another test 56** 

**of CemStar technology found an average reduction in burn zon e temperature of 160**   **F, a six percent reduction.**  **9 The amount of NO**  **X emissions reductions achievable with CemStar varies by**  **kiln type but ranges from over 20 to 60 percent. 7**  **Short- and long-term tests of CemStar were conducted at two different types of TXI cement kilns in 1999.**  **Short-term tests (two days) on a preheater/precalciner kiln found NO**  **X emissions reductions in lbs NO**  **X /ton of clinker of 44**  **percent when operated at maximum capacity, and between 9 and 30 percent when operated at**  **normal capacity, depending on the quality of the raw feed mix (see Table 5-1).** 

**TABLE 5-1. RESULTS OF SHORT-TERM CEMSTAR TESTS ON A**

**PREHEATER/PRECALCINER KILN**

**Poor Quality Feed Mix**  **(lb NO X**  **/ton of clinker)**  **Percent**

**Reduction a**  **(%) Ideal Quality** 

**Feed Mix (lb NO**  **X /ton of**  **clinker) Percent** 

**Reduction a**  **(%)**

**Without CemStar 4.98 - 5.59 -**

**With CemStar at normal feed rate**  **b 4.51 9 3.89 30** 

**With CemStar at maximum feed rate**  **c (no test) - 3.15 44** 

**a Percent reductions are relative to the emission rate withou**  **t CemStar.**

**b The normal feed rate is 170 - 180 tons per hour of dry feed.** 

**c The maximum feed rate is 195 tons per hour of dry feed.** 

**Andover Technologies also reported on short-term and long- term tests of a wet kiln using**  **CemStar Technology. The short-term tests (one day) found em ission reductions of 36 to 55**  **percent in lbs NO X**  **/ton of clinker, and the long-term tests (approximately two and a half months)**  **found reductions of 24 percent (see Table 5-2). 7** 

**Kilns with lower initial baseline NO X**  **emissions would have less NO X**  **reductions with CemStar than those with higher baseline emissions. Wet and l**  **ong-dry kilns would have greater NO**  **X reductions with CemStar because more energy is used per ton o**  **f clinker produced than preheater/precalciner kilns. Wet kilns may achieve the gre**  **atest NO X**  **reductions with CemStar because the addition of steel slag would reduce the amount of**  **water needed to create the slurry and consequently decrease the amount of heat needed to dry it** 

**. 7** **57 TABLE 5-2. RESULTS OF CEMSTAR TESTS ON A WET KILN** 

**Test 1 (lb NOX/ton of clinker)**  **Test 2 (lb NOX/ton of clinker)**  **Percent Reduction**  **a (%)** 

Short-Term Test

**Without CemStar 17.53 24.7 -**

**With CemStar 11.24 no 2 nd**  **test test 1 = 36**

**test 2 = 55**
Long-Term Test

**Without CemStar 5.23 no 2 nd**  **test -**

**With CemStar 4.00 no 2 nd**  **test 24**

**a Percent reductions are relative to the emissions rate witho**  **ut CemStar during the same test period.**

5.1.3 Kiln Fuel

**Changing the primary kiln fuel from natural gas to coal can re duce the flame temperatures**  **significantly, resulting in lower thermal NO X**  **emissions. 10,11**  **Although nitrogen present in coal may provide greater fuel NO**  **X contribution, switching the fuel burned in kilns from natur**  **al gas to coal has been shown to provide substantial reduction in the t**  **otal NO X**  **emissions in one experimental study.**  **10 In the dry process kilns tested in this study the average NO**  **X emissions**  **decreased from 20.4 lb/ton of clinker to 6.2 lb/ton of clinke r when the fuel was changed from**  **natural gas to coal. A number of cement kilns have already mad e the switch from natural gas to**  **coal and currently 87 percent of cement kilns in the United St ates use coal as the primary fuel.**  **12**

**When natural gas (with no nitrogen in the fuel) is used in the b urning zone of a cement**  **kiln, the NO X**  **emissions are significantly higher than when coal is used. T here may be additional**  **environmental impacts when coal is burned as opposed to natu ral gas (e.g., sulfur dioxide and**  **sulphate emissions may increase). Although switching to a l ower nitrogen fuel in a precalciner**  **may reduce NO X**  **, the fuel nitrogen content in the burning zone has little or n o effect on NO**  **X generation. Some researchers have found no relationship be**  **tween fuel nitrogen content and the NO**  **X emissions from a cement kiln.**  **13**

**Switching to a fuel with a higher heating value and lower nitr ogen content may reduce**  **NO X**  **emissions in a cement kiln, e.g., petroleum coke has a lower n itrogen content per million**  **Btu than coal. Petroleum coke is also more uniform in terms of heat value, lower in volatile**  **matter content and burns with a lower flame temperature. How ever, petroleum coke cannot be**  **burned alone because it does not provide enough volatile mat ter.**  **14 58** 

5.1.4 Increasing Thermal Efficiency

**The thermal efficiency of the cement-making process may be i ncreased by improving**  **gas/solids heat transfer, e.g., using an efficient chain sy stem, increasing heat recovery from**  **clinker cooler, and by minimizing infiltration of cold ambi ent air leaking into the kiln. Heat**  **recovery from a clinker cooler may be improved by increasing the proportion of secondary air.**  **Recycling cement kiln dust from the dust collectors would re duce the energy requirement per ton**  **of a clinker. By increasing the thermal efficiency, NO X**  **emissions are reduced per ton of clinker produced.** 

5.2 COMBUSTION MODIFICATION

**Combustion modifications are generally applicable to all t ypes of kilns and are an**  **efficient way to reduce the formation of thermal NO X**  **. The combustion modifications discussed in this section focus on staging the combustion to minimize c**  **ombustion at the maximum temperatures. This can be accomplished by modifying the way**  **oxygen or fuel is provided for combustion.** 

5.2.1 Staged Combustion of Air

**Staging of combustion air allows combustion of fuel to proce ed in two distinct zones. In**  **the first zone, the initial combustion is conducted in a fuel -rich, oxygen-poor flame zone. This**  **zone provides the high temperatures necessary for completi on of the clinkering reactions, but the**  **lack of available oxygen minimizes the formation of thermal and fuel NO**  **X . The lack of**  **sufficient oxygen leads to only partial combustion of the fu el.** 

**In the second, fuel-lean zone, additional (secondary) comb ustion air is added to complete**  **the combustion process. However, the temperature in this se cond zone is much lower than the**  **first zone because of mixing with the cooler secondary air, s o the formation of NO**  **X is minimized**  **in spite of the excess available oxygen. This staged approac h can be used for combustion of all**  **fossil fuels. Staged combustion is typically achieved by us ing only a part of the combustion air**  **(primary air) for fuel injection in the flame zone, with rema ining secondary air being injected in**  **the subsequent cooler zone.**

**For effective staging of combustion air to reduce NO X**  **emissions, cement plants must have indirect-fired kilns. In a direct-fired cement kiln, a**  **ir used for conveying pulverized coal from a coal mill, i.e., primary air, is typically 17 to 20 perc**  **ent of the total combustion air. The amount of primary air may be reduced by separating the coal mi**  **ll air from coal. A cement kiln using less than 10 percent of primary air is an indirect-fire**  **d kiln. Conversion of a direct-fired kiln to an indirect-fired kiln involves adding particle sep**  **aration equipment such as a cyclone or a baghouse and a fan to provide the primary air used to transpor**  **t the powdered coal from storage to the kiln. An indirect-firing system increases overall ener**  **gy efficiency by allowing a greater proportion of hot clinker cooler air to be used as secondary c**  **ombustion air. 59** 

5.2.1.1 Flue Gas Recirculation

**In addition to changing the combustion air distribution, th e oxygen content of the primary**  **air may be reduced to produce a fuel-rich combustion zone by r ecycling a portion of the flue gas**  **into the primary combustion zone. 15**  **The recycled flue gas may be premixed with the primary combustion air or may be injected directly into the flame zon**  **e. Direct injection allows more precise control of the amount and location of the flue gas rec**  **irculation (FGR). In order for FGR to reduce NO**  **X formation, recycled flue gas must enter the flame zone. The F**  **GR also reduces the peak flame temperature by heating the inert combustion prod**  **ucts contained in the recycled flue**
**gas.**
**The use of FGR may not be a viable method of reducing NO X**  **in a full-size cement kiln burning zone. FGR’s effectiveness relies on cooling the fla**  **me and generating an oxygen deficient (reducing) atmosphere for combustion to reduce N**  **O X**  **formation, conditions that may not be compatible with cement kiln operation. High flame tem**  **perature and an oxidizing atmosphere are process requirements to produce a quality cl**  **inker product. A cement kiln differs from a utility boiler and other combustion devices because m**  **inimum temperatures and an oxidizing atmosphere are required to initiate chemical rea**  **ctions in a cement kiln in addition to the providing the required heat (Btu/ton of clinker). Reduc**  **ed flame temperatures and reducing conditions in the burning zone of a cement kiln may not be comp**  **atible with the production of cement clinker.**  **13**

**Coupling a low-NO X**  **step burner with flue gas recirculation has been shown to red uce**  **NO X**  **emissions further in a cement kiln. 16**  **The additional NO X**  **reduction attributable to FGR was estimated to be about 15 to 38 percent depending upon the prop**  **ortion of FGR used. 16**  **Incorporation of FGR in a cement kiln also results in somewhat**  **increased power consumption and reduced kiln output.** 

5.2.1.2 Low-NOX Burners

**Some cement kiln burners, specifically marketed as low-NO**  **X ,**  **burners, typically use 5 to 7 percent primary air**  **17,18 and thus can be used**  **only on indirect-fired kiln systems. Low-NO**  **X burners can be installed on**  **any type of kiln. Low-NO X**  **burners are designed to reduce flame**  **turbulence, delay fuel/air mixing, and establish fuel-rich zones for initial**  **combustion. The longer, less intense** Figure 5-1. Schematic of low-NO X burner. **17 60** 

**flames resulting from the staged combustion lower flame tem peratures and reduce thermal NO**  **X formation. Some of the burner designs produce a low pressure**  **zone at the burner center by injecting fuel at high velocities along the burner edges. Su**  **ch a low pressure zone, as shown in Figure 5-1,**  **17 tends to recirculate hot combustion gas which is retrieved t**  **hrough an internal reverse flow zone around the extension of the burner centerl**  **ine. The recirculated combustion gas is deficient in oxygen, thus producing a similar effect as FG**  **R. Combustion of the fuel in the first stage thus takes place in an oxygen-deficient zone before th**  **e fuel is diluted in the secondary air. Installing such a burner reduces NO**  **X emissions from the kiln-burning zone by up to 30**  **percent. 17,19,20** 

**Low-NO X**  **burners have been used by the cement industry for twenty year s.**  **21 Many**  **suppliers offer low-NO X**  **burners and most of these systems focus on lowering the NO X**  **formation in the calciner by air or fuel staging, by reburning, or by hig**  **h temperature combustion. 22**  **Test data from several different low-NO**  **X burners are now available. Thomsen, Jensen, and**  **Schomburg reported on tests of a F.L. Smidth in-line calcine r low-NO**  **X system in a**  **preheater/precalciner kiln where different percentages o f coal were added to the reduction zone**  **of the precalciner (the remaining coal was added to the oxidi zing zone).**  **22 When 100 percent of**  **the coal was added to the reduction zone of the precalciner, t he NO**  **X content at the preheater exit**  **was reduced by 44 percent relative to when zero coal was added (see Table 5-3).** 

**TABLE 5-3. NO X**  **EMISSIONS FROM A PRECALCINER EQUIPPED**

**WITH A LOW-NO X**  **BURNER**

**Percent Coal Added to Reduction Zone**  **a (lb NO**  **X /ton of clinker)**  **NO X**  **Emissions b**  **(lb NO X**  **/ton of clinker) Percent**  **Reduction b**  **(%)**

**0 2.8 -**

**50 1.9 31**

**100 1.6 44**

**a The remaining percentage of the coal was added to the oxidizi**  **ng zone. b**  **Emission measurements were taken at the preheater exit.**

**c Percent reductions are relative to emissions when zero perc**  **ent of the coal was added; the original measurements were in kg NO**  **X /ton of clinker to the hundredth place - the percent reductio**  **ns were calculated using the original measurements, which results in slightly different values t**  **han when lb NO X**  **/ton of clinker are used.**

**Steinbiß, Bauer, and Breidenstein reported emissions chan ges for five kilns before and**  **after the installation of Pyro-Jet low-NO X**  **burners (see Table 5-4). 21**  **The emission reductions ranged from 15 to 33 percent. Information on kiln-type was no**  **t provided. 61**  **TABLE 5-4. NO X**  **EMISSIONS BEFORE AND AFTER INSTALLATION**

**OF PYRO-JET LOW-NO X**  **BURNERS**

**Kiln Before Installation**

**(ppm) After Installation** 

**(ppm) Percent Reduction** 

**(%)**

**A 970 650 33**
**B not given not given 30**

**C 650 460 29**

**D 900 730 19**
**E not given not given 15**

**There are two new data sources on emissions reductions from t he use of Rotaflam**  **® low**  **NO X**  **burners. The Pillard Combustion Equipment and Control Syst ems published data on four**  **kilns, comparing NO X**  **emissions with a 3 channel burner to emissions when a Rotafla m**  **® burner**  **was used (see Table 5-5). 23**  **The emission reductions ranged from 23 to 47 percent. Inform ation**  **on kiln-type was not provided.**

**TABLE 5-5. NO X**  **EMISSIONS WITH 3 CHANNEL AND ROTAFLAM ®**  **LOW-NO X**  **BURNERS**

**Kiln With 3 Channel**

**Burner (ppm) With Rotaflam**  **®**

**Burner (ppm) Percent** 

**Reduction (%)**

**A 774 409 47**

**B 865 664 23**

**C 484 350 28**

**D 487 336 31**

**Emissions data are also available before and after a Rotafla m**  **® low-NO**  **X burner was**  **installed on a long-wet kiln (see Table 5-6). 24**  **The average emissions decreased 14 percent. 62**  **TABLE 5-6. EMISSIONS BEFORE AND AFTER INSTALLATION OF A**

**ROTAFLAM ®**  **BURNER ON A WET KILN**

**Year Average Emissions**

**(lb NO X**  **/ton of clinker) Percent Reduction**  **a (%)** 

**1990 277 -**

**1992 b**  **288 -**

**1993 269 -**

**1994 275 -**

**1995 (Rotaflam**  **® installed)**  **239 14**

**a Percent reduction is relative to the 1990, 1992-1994 averag**  **e NO X**  **emissions, 277.25 lb NO X**  **/hr. b**  **1991 data were not provided.**

**The Fuller Company low NO X**  **In-Line Calciner was installed in an RMC Lonestar kiln which reported 30-40 percent reductions in the amount of the**  **rmally formed NO X**  **after installation.**  **25**

**In January 2000, the PCA and PCA provided results of a survey o f cement facilities**  **where the respondents indicated 14% of the operating U.S. ki lns (22 kilns) have already installed**  **a low-NO X**  **burner (81% of the facilities representing 81% of the operat ing U.S. kilns responded**  **to the survey). The remaining 139 kilns that are represented by the survey have not installed low**  **NO X**  **burners. 26,27** 

5.2.2 Staged Combustion of Fuel

**In conventional long (wet or dry) rotary kilns, all heat requ ired for the cement-making**  **process is supplied in the primary kiln burning zone, where t he combustion occurs at the hottest**  **temperature in the kiln. In the cement-making process, the p reheating and calcination of the raw**  **materials requires a large amount of heat but are typically a t a temperature of 600 to 900**   **C (1100 to 1650**   **F) which is much lower than the kiln’s clinker-burning tempe rature of 1200 to**  **1480**  **C (2200 to 2700**  **F). 28**  **In the secondary combustion method, part of the fuel is burne d at a**  **much lower temperature in a secondary firing zone to complet e the preheating and calcination of**  **the raw materials.**

5.2.2.1 Preheater/Precalciner and Tire Derived Fuel

**This concept of a secondary firing zone is the basis of the pre heater/precalciner cement**  **kiln design. Almost all new cement kilns have a preheater/pr ecalciner-type designs. In the**  **preheater kilns, the primary emphasis is on efficient heat r ecovery from kiln exhaust gases (see** **63**

**Figure 5-2). 29**  **However, up to 15 to 20 percent of the fuel may be fired in the ri ser duct in**  **preheater designs. 29** 

**Precalciner systems typically employ a tower of four-stage cyclones for efficient gas**  **solids contact which improves the energy efficiency of the o verall process (see Figure 5-3).**  **29 In a**  **typical precalciner kiln almost 40 to 50 percent of the fuel i s burned at a lower (calcination)**  **temperature which reduces the thermal NO X**  **formation considerably.**

**Tire-derived fuel can also be added to the feed end of a prehea ter or precalciner kiln. The**  **Mitsubishi Cement Company’s Cushenbury Plant in Lucerne Va lley, CA began using whole**  **waste tires as a fuel supplement in 1993. The waste tires are d elivered in enclosed container**  **trucks and dumped into the plant’s automated handling syste m. A live bottom hopper and**  **singulator place the waste tires on a conveyor system. This c onveyor system transports the tires**  **to the feed end of the kiln and drops the tire into an airlock sy stem that allows the waste tire to**  **fall onto the feed plate inside the kiln at a rate of five to six tires per minute.** 

**Currently, 8,000 to 9,000 tires are burned per day, totaling about 13 percent of the fuel.**  **Tires have a fuel content of approximately 14,000 Btu/lb and a sulfur content that is roughly the**  **same as the coal that would be used. The steel belting in the wa ste tires supplements the iron**  **requirements and approximately 2 percent of the iron in the f inal product comes from the tires.**  Figure 5-2. Schematic of preheater. **29** Figure 5-3. Schematic of precalciner. **29 64** 

**The addition of waste tires reduces NO X**  **emissions from the kiln by 30 to 40 percent, and there is no significant change in toxic, hydrocarbon, or metal emiss**  **ions. 30,31,32** 

5.2.2.2 Low-NO X Precalciners

**Most of the major cement kiln suppliers are now offering “low NO**  **X ” precalciner designs**  **for new kilns. These designs typically inject a portion of th e fuel into the feed end of the kiln,**  **countercurrent to the exhaust gas flow, as illustrated in Fi gure 5-4.**  **33 This fuel is burned in a sub**  **stoichiometric O 2**  **environment to create a strongly reducing atmosphere (rela tively high**  **concentrations of CO) by following the simplified reaction s:** 

**NO + C N + CO (5-1)** 

**and**

**NO + CO N + CO**  **2 (5-2)** 

**This reducing atmosphere inhibits the formation of fuel NO**  **X and destroys a**  **portion of the NO X**  **formed in the kiln burning zone. In some designs, additional**  **fuel is then added, again with insufficient O**  **2 for complete combustion, to create**  **another reducing zone. Several precalciner kilns in the US have recently been**  **retrofitted with these “low NO X**  **” precalciners and preliminary information**  **indicates a noticeable reduction in NO X**  **per ton of clinker.**  **13 Up to 46 percent reduction**  **of NO X**  **emissions have been reported without causing excessive coating**  **difficulties in the kiln. 33** 

**As discussed in Section 4.2.2, nitrogen present in the fuel may also**  **participate in the reduction of NO X**  **. The primary NO**  **X formation mechanism in the**  **secondary firing is the fuel NO X**  **formation which depends upon the nitrogen content of the fuel used. In o**  **rder for the above reactions (5-1) and (5-2) to proceed at reasonable rates the temperature in t**  **he reduction zone should be maintained between 1000 and 1200**   **C (1830 to 2190**  **F). These temperatures may lead to coating difficulties, particularly if the fuel used is coal**  **with high ash content. 34**  Figure 5-4. Reduction of NO X emissions from precalcining kiln system by fuel injection in the

rotary kiln gas outlet. **33 65** 

**It is not possible to use “staged combustion” on preheater ki lns that are firing fuel in the**  **riser since in staged combustion it is necessary to add the fu el in an oxygen deficient atmosphere**  **and then supply additional combustion air to fully combust t he fuel. Preheater kilns do not have**  **tertiary air ducts to supply the additional combustion air. The air for combustion of the**  **secondary fuel must come through the kiln, which precludes i ntroducing the secondary fuel into**  **an atmosphere with insufficient oxygen for complete combus tion.**  **13**

**Emissions reductions have also been found when tire derived fuel was burned in a**  **precalciner. In one case, when 47 percent of the coal fired in the calciner was substituted with**  **tire-derived-fuel, a reduction in NO X**  **emissions of about 29 percent was observed. 35** 

5.2.2.3 Mid-Kiln Firing

**The concept of staged combustion of fuels may also be used in c onventional wet and**  **long-dry kilns by injecting solid fuel into the calcining zo ne of a rotating long kiln using a**  **specially designed feed injection mechanism. 36**  **This system is known as mid-kiln firing (MKF) and allows part of the fuel to be burned at a material calcinat**  **ion temperature of 600 to 900**  **C (1100 to 1650**   **F) which is much lower than the clinker burning temperature o f 1200 to 1480**   **C (2200 to 2700**   **F). 28** 

**To maintain a continuity in the heat input,**  **solid and slow burning fuels (such as tires) are most**  **amenable for MKF. The Cadence feed fork MKF**  **technology was first introduced in 1989. It can be**  **installed during an annual maintenance shutdown. It is**  **comprised of three primary components: (1) a staging arm**  **or ‘feed fork’ that picks up the fuel modules and positions**  **them for entry into the kiln, (2) two pivoting doors that open to allow the fuel modules to drop**  **into the kiln, and (3) a drop tube that extends through the sid e wall of the kiln. In addition to**  **these basic components, feed fork technology also requires a delivery system which positions the**  **fuel models so they can be picked up by the feed fork and a mecha nism for opening the doors so**  **the fuel modules can enter the kiln. 37**  **Due to the rotation of the kiln, fuel can be conveniently injected only once per revolution from the top, as shown in Fi**  **gures 5-5 29**  **and 5-6. 38** 

**Although most feed forks today are dedicated to whole tires, one facility uses baled**  **industrial waste as a fuel, and many others are investigatin g a variety of energy containing waste**  Figure 5-5. Schematic of mid-kiln firing. **29 66** 

**materials from carpet scrap to pharmaceutical waste. These energy-bearing waste materials can**  **be containerized or dementionalized into discrete fuel mod ules to be fed to the kiln using the feed**  **fork. 37** 

**Inserting whole tires into mid-kiln locations can give precalciner stability to the kiln. The operators have**  **two points of control to assist in stabilizing kiln operation. Tires burn for 15 to 20 minutes within the**  **kiln after entry. This is deduced from observations of the rate of change in kiln exit oxygen levels after entry**  **of tires begins. With proper instrumentation, control of the kiln can be improved by adding solid fuels mid**  **kiln. 39** 

**Mid-kiln firing of tires or other waste-derived fuels does not reduce the final product quality; in fact,**  **many of Cadence’s cement kiln partners have reported an improvement in the clinker burnability and mineralogy. T**  **he enhanced control has shown to impart better formation of clinker. Reductions in cement fi**  **neness have been shown while maintaining similar seven-day strengths. Several facilit**  **ies also have reported an extended life of the refractory in the burn zone.**  **37,39**

**By adding fuel in the main flame at mid-kiln, MKF changes both the flame temperature**  **and flame length. These changes may reduce thermal NO X**  **formation by burning part of the fuel at a lower temperature and by creating reducing conditions a**  **t the solid waste injection point which may destroy some of the NO**  **X formed upstream in the kiln burning zone. MKF may also**  **produce additional fuel NO X**  **depending upon the nitrogen content of the fuel. 38**  **However, as discussed in section 5.1.3, fuel NO**  **X is unimportant relative to thermal NO**  **X formation.**  **Additionally the discontinuous fuel feed from MFK can resul t in increased CO emissions**  **especially if hazardous wastes are used. To control CO emiss ions, the kiln may have to have**  **increased combustion air which can decrease production cap acity.**  **40**

**According to literature from Cadence, in tests of its feed fo rk technology, one kiln**  **reduced NOX emissions by 38%, overall particulate emission s by 14%, metal emissions by 30%,**  **SO 2**  **emissions by 36%, and net emissions of all hydrocarbons by 29 %.**  **37,39 In the research**  **conducted for this report, test data were compiled for seven dry kilns and three wet kilns with**  **MKF technology. In nine tests on the dry kilns, the average re duction in NOX emissions was**  **33%, with a range from 11% to 55%. In three tests on the wet kiln s, the average reduction in**  **NO X**  **emissions 40%, with a range from 28% to 59% (see Table 5-7). 40,41,42,43,44**  **It should be noted that the three kilns that are known to have CEMS all reported e**  **missions reductions of 45 percent**

**or more.** Figure 5-6. Schematic of fuel injection in kiln. **38 67**  **TABLE 5-7. EMISSIONS FROM KILNS WITH MID-KILN FIRING**

**Emissions (lb NO**  **X /ton of clinker)**  **Percent Reduction (%)**  **Emissions Based on**

**CEMS Data Dry Kilns**  **a**

**A 40**  **not given 13.6 unknown**

**B 40**  **not given 11.1 unknown**

**C 24, 44**  **not given 45.1 yes**

**C 40**  **not given 55.3 yes**

**D 21, 41**  **2.7 not given unknown**

**E 22, 42**  **10.2 13.9 unknown**

**F 40**  **not given 46.6 unknown**

**F 40**  **not given 50.4 unknown**

**F 40**  **not given 28.3 unknown Average**  **(Dry Kilns) 6.4 33.3** 

**Wet Kilns**

**G 23, 43**  **not given 59.0 yes**

**H 40**  **not given 35.0 unknown**

**I 40**  **not given 27.6 unknown Average**  **(Wet Kilns) n/a 40.5** 

**Average (Dry & Wet Kilns)**  **6.4 35.1**

**a There was more than one test at some kilns.** 

**Waste-derived fuels with high heating values represent an e conomical source of energy**  **for the cement industry and its consumption has been increas ing during the past decade.**  **12 Mid**  **kiln firing is a proven technology and so far at least 21 long k ilns in the U.S. and nearly 40 kilns**  **worldwide have been modified to allow mid-kiln firing of sol id and hazardous waste.**  **37, 45**

5.3 NO X REMOVAL CONTROLS

**NO X**  **removal controls are intended to destroy NO X**  **that is formed in the combustion process. Selective catalytic reduction (SCR) and selectiv**  **e noncatalytic reduction (SNCR) are described; however, SCR has not been demonstrated on any cem**  **ent kilns in the United States at 68** 

**this time. There have been two demonstrations of SNCR in the U nited States and there are 18**  **actual full-scale installations of SNCR for cement kilns in Europe. Biosolids injection**  **technology is not technically SNCR, but the chemistry and th e principles of its operation are**  **similar. For this reason it is discussed with the other NO X**  **removal controls.**

5.3.1 Selective Catalytic Reduction (SCR)

**SCR is a process that uses ammonia in the presence of a catalys t to selectively reduce**  **NO X**  **emissions from exhaust gases. This technology is widely use d for NO**  **X abatement in other**  **industries, such as coal-fired power stations and waste inc inerators. The SCR process has been**  **used extensively in Japan to achieve a 90 percent reduction i n NO**  **X emissions from fossil fuel**  **fired boilers. 46**  **In the United States SCR technology has successfully been us ed for gas turbines,**  **internal combustion engines, and utility boilers. 46** 

**In SCR, anhydrous ammonia, usually diluted with air or steam , is injected through a grid**  **system into hot flue gases which are then passed through a cat alyst bed to carry out NO**  **X reduction reactions. The two principal reactions are:** 

**4 NH 3**  **+ 4 NO + O 2**  **4 N 2**  **+ 6 H 2**  **O (5-3)**

**and**

**4 NH 3**  **+ 2 NO 2**  **+ O 2**  **3 N 2**  **+ 6 H 2**  **O (5-4)**

**Equation (5-3) represents the predominant reaction since 9 0 to 95 percent of NO**  **X emissions in the flue gas are in the form of NO. A number of mate**  **rials have been used for catalysts. Titanium dioxide (TiO**  **2 ) and vanadium pentoxide (V**  **2 O**  **5 ) mixtures are most commonly**  **used as catalysts due to their resistance to SO X**  **poisoning. 47,48**  **Zeolite-based catalyst materials have also been developed capable of operating at higher temp**  **eratures than conventional metal based catalysts.**  **48 The catalyst is typically supported on ceramic materials, e**  **.g., alumina in a honeycomb monolithic form. The active ingredients of the ba**  **se metal (titania-vanadia) and zeolite catalysts often make up the bulk of the substrate mat**  **erial. The catalyst shape and reactor design vary depending upon the manufacturer. The optimum te**  **mperature for the catalytic reactions depends upon the specific catalyst used and is usu**  **ally 300 to 450**  **C (570 to 840**  **F). This temperature may be higher than typical cement kiln flue**  **gas temperatures, especially in plants using heat recovery systems or baghouses for particu**  **late collection. But it may be possible to reheat the exhaust using heat recovery systems.** 

**Ammonia is typically injected to produce a NH3:NO X**  **molar ratio of 1.05-1.1:1 to achieve NO**  **X conversion of 80 to 90 percent with an ammonia "slip" of about**  **10 ppm of unreacted ammonia in the gases leaving the reactor.**  **49 The NO**  **X destruction efficiency depends upon the**  **temperature, NH3:NO X**  **molar ratio, and the flue gas residence time (or the space vel ocity) used** **69**

**in the catalyst bed. The SCR reactor system can be designed fo r a desired NO**  **X reduction using**  **appropriate reagent ratio, catalyst bed volume, and operat ing conditions.** 

**In general, the catalysts may be fouled or deactivated by the particulates present in the**  **flue gas. In the case of cement plants, the presence of alkali es and lime as well as sulfur dioxide**  **in the exhaust gases is also of concern. Because of fouling pr oblems, the SCR system must be**  **installed after the particulate collection device. Recent developments have led to sulfur tolerant**  **SCR catalysts which limit SO 2**  **oxidation to less than 1 percent. 50**  **Soot blowers may be used to prevent dust accumulation on SCR catalysts.** 

**In the cement industry, basically two SCR systems are being c onsidered: low dust exhaust**  **gas and high dust exhaust gas treatment. Low dust exhaust gas systems require reheating of the**  **exhaust gases after dedusting, resulting in additional cos t. High dust systems are considered**  **preferable for technical and economical reasons. 1**  **Up to now SCR has only been tested on preheater and semi-dry kiln systems, but it might be applica**  **ble to other kiln systems as well. 1** 

**Pilot plant trials on small portions (three percent) of the e xhaust gas have shown**  **promising results in Austria, Germany, Italy, and Sweden. T here are at least three suppliers in**  **Europe that offer full scale SCR to the cement industry with p erformance levels of 100 to 200**  **mg/m 3**  **(approximately 0.2 to 0.4 lb/ton of clinker). 1**  **A full-scale SCR demonstration plant is being built in Germany with governmental financial support**  **; a full-scale SCR plant is also under consideration in Austria.**  **1**

**There are currently no installations of SCR units in any Unit ed States cement plants. In**  **1976, Hitachi Zosen, an SCR manufacturer, conducted three p ilot test programs to evaluate SCR**  **on cement kilns. 3**  **During these tests, two suspension preheater kilns and a wet process kiln were**  **tested for 5,400 hours each. Electrostatic precipitators w ere used to remove particulates before**  **the flue gas entered the SCR unit. Also, a heat recovery syste m equipped with supplemental fuel**  **firing was provided to raise the flue gas temperatures to the required reaction temperatures.**  **Slipstreams of about 3,000 scfm were treated with initial NO X**  **removal efficiencies of 98 percent. However, after 5,400 hours of operation, NO**  **X removal efficiencies dropped to about 75 percent**  **due to catalyst coating.**

**Full-scale production runs will have to be carried out in ord er to remove the technical**  **and economic uncertainties related to upscaling of the SCR t echnique. The main uncertainties**  **are related to the high dust concentration in the gases (up to 500 g/Nm**  **3 , approximately 1.0 lb/ton**  **of clinker), the catalyst dust removal techniques, lifetim e of catalysts, and total investment costs.**  **1 Feasibility studies have been carried out in Austria, Germa**  **ny, the Netherlands, and Sweden. The estimated costs vary considerably, with the production cos**  **ts and lifetime of the catalyst being major variables.**  **1 Based on the experience in other industries, NO**  **X reductions in the range of 80**  **to 90 percent are considered possible, regardless of kiln ty pe.**  **46 However, further studies are**  **needed to demonstrate the specific NO X**  **reduction in the cement kiln exhaust gas environment. 70** 

5.3.2 Selective Noncatalytic Reduction (SNCR)

**This control technique relies on the reduction of NO X**  **in exhaust gases by ammonia or urea, without using any catalyst, with the same reactions (5**  **-3) and (5-4) as in the case of the SCR process. This approach avoids the problems related to catal**  **yst fouling, as in SCR technology, but requires injection of the reagents in the kiln at a temper**  **ature between 870 to 1090**  **C (1600 to 2000**   **F). At these temperatures urea decomposes to produce ammoni a which is responsible**  **for NO X**  **reduction. In principle, any of a number of nitrogen compoun ds may be used, e.g.,**  **cyanuric acid, pyridine, and ammonium acetate. However, fo r reasons of cost, safety, simplicity,**  **and by-product formation, ammonia and urea have been used in most of the SNCR applications.** 

**Because no catalyst is used to increase the reaction rate, th e temperature window is**  **critical for conducting this reaction. At higher temperatu res, the rate of a competing reaction for**  **the direct oxidation of ammonia which actually forms NO X**  **becomes significant. At lower temperatures, the rates of NO**  **X reduction reactions become too slow resulting in too much**  **unreacted ammonia slip. The effective temperature window r ange can be lowered to about**  **700**  **C (1300**  **F) by the addition of hydrogen along with the reducing agent. 51**  **Nalco Fuel Tech, the producer of the SNCR technology NO**  **X OUT**  **® , has also introduced NO**  **X OUT**  **® PLUS which is**  **said to broaden the operating temperature window and to redu ce ammonia slip and CO and NO**  **2 formation.** 

**In a conventional long kiln the appropriate temperature win dow is in the middle of a kiln.**  **Because of the rotating nature of a long kiln, continuous inj ection of ammonia- or urea-based**  **reagents is presently not possible. The technology develop ed for mid-kiln firing of containerized**  **solid fuels allows injection of a certain amount of material once during the kiln revolution.**  **Injection of solid ammonium or urea salts in this manner has n ot been used because of the rapid**  **decomposition of such salts. Therefore, SNCR technology ha s not been applicable for long dry**  **or wet kilns. However, Fuel Tech Inc. is currently evaluatin g dry dust or pellet injection methods**  **for direct injection into kilns. 52** 

**In preheater/precalciner type cement kilns, the temperatu res at the cooler end of the**  **rotating kiln, in the riser duct, and in the lower section of t he cyclone preheater tower are likely**  **to be in the temperature window appropriate for SNCR. Such ki lns are therefore good candidates**  **for application of SNCR technology.**

**The NO X**  **reduction efficiency of SNCR depends upon the temperature, residence time, as**  **well as ammonia and NO X**  **concentrations in the flue gas. Injection of ammonia at a NH 3**  **:3NO X**  **proportion of 1 to 1.5 will reduce NO X**  **emissions between 60 to 80 percent. Using a molar ratio of 0.5 will give NO**  **X reductions of approximately 40 percent.**  **47 The reagent consumption can be**  **significantly higher with greater ammonia slip in SNCR syst ems as compared to SCR systems.**  **Operating experience has identified several concerns with both ammonia and urea-based SNCR**  **processes. The most frequently reported is the buildup of am monium bisulfite scale which is**  **significant for sulfur-containing fuels. SNCR processes a lso appear to convert some NO to** **71**

**N 2**  **O. 53**  **The rate of N 2**  **O formation is a weak function of both the reactant and the NO concentration. However, N**  **2 O formation seems to be inherently more prevalent in systems**  **using urea than those using ammonia.**  **54**

**The NO X**  **destruction efficiency also depends upon the flue gas resid ence time in the**  **appropriate temperature window. Unlike an SCR system where the reaction temperature is**  **controlled in a dedicated reactor, an SNCR system relies on t he existing gas temperature profile**  **to provide an adequate residence time for a desired NO X**  **destruction. Maximum achievable NO X**  **reduction in a cement kiln may thus depend upon the gas temper ature profile.** 

**The SNCR process was demonstrated in Europe in a preheater ty pe kiln. Both ammonia**  **and urea-based reagents were investigated. The reagents we re injected in the bottom gas duct as**  **shown in Figure 5-7. 55**  **With a molar ratio of reagent to NO**  **2 of 1:1, about 70 percent reduction in NO**  **X emissions**  **was observed with ammonia-based reagent and about 35 percent NO**  **X reduction was obtained with urea.**  **55 With**  **this reagent ratio, there was no major increase in ammonia emissions in exhaust gases over the**  **background level of ammonia emissions generated by kiln feed material. Greater NO**  **X reductions were**  **observed with more than stoichiometric amount of reagent, although there was increasing ammonia 'slip' in**  **the exhaust gases.**

**Scheuer,of the Research Institute of the Cement Industry in Dusseldorf, Germany, reported on 148 SNCR**  **trials carried out on five different kilns. Three kiln systems had cyclone preheaters and two had grate**  **preheaters. A 25% molar concentration of NH 3**  **in water was the main reagent tested, with some additional testing**  **done with ammonium sulfate solutions and with urea solutions. Scheuer reported that NO reductions with the**  **NH 3**  **/water solution ranged from 15% to 75% and that temperature appeared to be one of the main determinants**  **of the effectiveness of the reagent. Maximum NO reduction occurred at 980**   **C (1796**  **F). NH 3**  **escape occurred when temperatures were less than 900**   **C (1652**  **F) and when the NO concentration fluctuated. NH 3**  **utilization decreased significantly with increasing NH**  **3 :NO molar ratio and with decreasing NO concentration in the**  **exhaust gases, indicating that SNCR appears to be less promi sing at low NO emissions rates.**  **13,56**

**SNCR is presently being used in 18 cement kilns in Europe. Fif teen kilns are in**  **Germany, two are in Sweden, and one is in Switzerland. These k ilns are either suspension**  **preheater kilns or precalciner kilns. The most common reage nt used is 25% ammonia water.**  **1** Figure 5-7. Application of SNCR in

preheater kiln.**72**

**NO X**  **reduction rates vary from 10 to 50 percent with NH 3**  **/NO 2**  **molar ratio of 0.5 to 0.9, NO X**  **emissions at these reductions are 2.4 to 3.8 lb/ton of clinke r. Two dry process cyclone**  **preheater/precalciner kilns in Sweden achieve 80 to 85 perc ent reduction (1.0 lb/ton of clinker) at**  **a NH 3**  **/NO 2**  **molar ratio of 1.0 to 1.1. 1** 

**F. L. Smidth and Company tested SNCR on a preheater/precalci ner kiln.**  **3 Ammonia was**  **injected into the lower cyclone of the preheater tower where temperatures are favorable for the**  **reduction reactions to occur. NO X**  **emissions reductions during this experiment averaged 40 percent, but NO**  **X reductions of over 90 percent were obtained when the ammonia**  **injection rate was 10 to 20 percent in excess of stoichiometric.** 

**In the United States, SNCR has been tested on two kilns. NO X**  **OUT ®**  **technology was tested under ten different operating conditions at a prehea**  **ter/precalciner kiln in Seattle, Washington during October 1993. NO**  **X emissions were effectively reduced from 3.5 to 6.0 lb**  **NO X**  **/ton of clinker to less than 1 lb NO X**  **/ton of clinker. 57, 58**  **Another test of NO X**  **OUT ®**  **technology was conducted during October 1998 in Davenport, Iowa. This test found NO**  **X reductions of 10 to 20 percent from a baseline of approximate**  **ly 350 pounds NO X**  **/hour, although higher levels of reduction are thought to be achievable when**  **the baseline is higher. 59**  **An evaluation of NO**  **X OUT**  **® technology was conducted in 1994 for a long dry kiln in Southe**  **rn California, but the study concluded that application of the**  **NO X**  **OUT ®**  **technology at the subject kiln was technically infeasible.**  **60**

5.3.2.1 Biosolids Injection (BSI)

**The Mitsubishi Cement Corporation’s Cushenbury plant in Lu cerne Valley, CA, uses**  **biosolids injection technology (BSI) to achieve SNCR of NO X**  **. The BSI process was developed by the Cement Industry Environmental Consortium (CIEC). Th**  **e founding participants in the CIEC are Southdown, Inc., Riverside Cement Company, Mitsub**  **ishi Cement Corporation, California Department of Commerce (now Trade & Commerce Age**  **ncy), and the San Bernardino County Air Pollution Control District (now Mojave Desert Ai**  **r Quality Management District). This technology is covered under U.S. Patent No. 5,586,510 i**  **ssued December 24, 1996. 13** 

**The basic principle is to utilize the naturally occurring am monia content of dewatered**  **biosolids as the reagent. The dewatered biosolids are obtai ned from wastewater treatment plants.**  **Since the biosolids are mechanically dewatered without hea t input, the solids content varies**  **between 16 and 30 percent (moisture content of 84 to 70%). Dep ending on the moisture content,**  **the net Btu content (after evaporating the moisture) of the b iosolids varies between -750 and**  **+2200 Btu/lb. Since the biosolids heating value is relative ly small, the net effect on kiln fuel**  **combustion is expected to be small. 61** 

**The same conditions that affect NO X**  **reduction performance in SNCR affect BSI performance: temperature (927**   **C / 1700**  **F is optimal), residence time (> 0.5 seconds is desirable), inlet NO**  **X concentration, inlet CO concentration, and NH**  **3 /NO**  **X molar ratio. Another** **73**

**key issue is mixing effectiveness, which affects the extent of contact and, hence, reaction**  **between NH 3**  **and NO X**  **. The BSI technology is applicable to preheater/precalcine r kilns because**  **the temperature window for BSI (927**  **C / 1700**  **F) occurs in a location where it is feasible to inject biosolids.**  **61**

**The biosolids are injected into the mixing chamber where the flue gas stream leaving the**  **kiln and precalciner mix. The mixing chamber offers the bene fits of good residence time in the**  **appropriate temperature window (927**  **C / 1700**  **F) and high mixing effectiveness. 61** 

**At the Cushenbury plant, BSI underwent long-term testing an d eventual adoption in 1994**  **and 1995. The kiln is fueled with coal (85 percent) and tires ( 15 percent). The plant began**  **using tire-derived fuel (TDF) in mid-1993, so it is difficul t to isolate the effects of TDF or BSI on**  **NO X**  **emissions. The company estimates that the use of TDF reduces NO**  **X emissions from the**  **kiln by 30 to 40 percent. 62**  **Before the SNCR technology was adopted, the company estimat ed**  **NO X**  **emissions averaged 2.4 pounds/ton of clinker; afterwards, the average fell to 1.2 lb/ton of**  **clinker, a 50 percent reduction. The effects of BSI on CO emis sions varies between a large**  **increase and no change at all, but in all cases it has remained below 500 ppm. BSI has not**  **caused any significant changes in either metal HAP or organi c HAP emissions. Using the SNCR**  **biosolids technology, the kiln also reduced its fuel consum ption by 5 percent.**  **61**

5.3.2.2 NO X OUT ®

**An SNCR process using aqueous urea was developed by Electric Power Research**  **Institute (EPRI) and is now marketed by Nalco Fuel Tech, Inc. , under the trade name of**  **NO X**  **OUT ®**  **. In the urea reaction with NO, one mole of urea reacts with two moles of NO to**  **complete the reaction to nitrogen, carbon dioxide and water . Normalized Stoichiometric Ratio**  **(NSR) is used to express the reagent feed rate relative to the reaction stoichiometry. The NSR**  **takes into account the 2:1 mole ratio of the NO:urea reaction as the “normalized” ratio. If 50%**  **of the urea reacts to reduce NO to nitrogen, reduction of 100% NO**  **X occurs at NSR=2; 80%**  **reduction at NSR=1.6; 50% reduction at NSR=1.0, etc. Perfor mance improves with increased**  **turbulence or mixing, residence time, and more favorable te mperature conditions. A higher NO**  **X baseline generally leads to a higher percentage of NO**  **X reduction.**  **52**

**Urea is safer to handle than anhydrous ammonia. Both ammonia and urea need to be**  **injected in a similar temperature window which is 870 to 1090**  **C (1600 to 2000**  **F). Proprietary additives have been developed by Nalco to widen**  **the temperature window. 63**  **One modification of the urea-based SNCR system is the addition o**  **f methanol injection downstream of the urea injection point to improve overall NO**  **X removal. Nalco also introduced an improved**  **NO X**  **OUT ®**  **PLUS, which is said to further broaden the operating tempera ture window and to**  **reduce ammonia slip and CO and NO 2**  **formation.**

**The Ash Grove plant in Seattle is a preheater/precalciner ki ln with average processing**  **rates of 160 tons dry feed/hour producing approximately 100 tons clinker/hour. NO**  **X OUT**  **® was** **74**

**tested on this kiln under varying conditions, including the use of different fuel types (natural gas**  **and coal), heat input to the calciner (5 to 9 percent), and pre heater O**  **2 (1.8 to 2.9 percent). The**  **baseline NO X**  **levels varied from 350 to550 lbs NO X**  **/hour. When NO X**  **OUT ®**  **was used, NO X**  **emission reductions varied significantly depending on the conditions, with a maximum reduction**  **of 90 percent (less than 100 lbs NO X**  **/hour). Typical reductions were greater than 50%. 58** 

**NO X**  **OUT ®**  **was tested for one week in October of 1998 on the preheater/pr ecalciner kiln**  **at the Lafarge-Davenport Plant. Operating conditions were unstable most of that week and only**  **five hours of testing produced results that could provide a r easonable indication of what may be**  **achievable with NO X**  **OUT ®**  **. The baseline NO X**  **rate was approximately 350 lbs NO X**  **/hour. Using NO**  **X OUT**  **® , emission reductions of 10 to 20 percent were achieved.**  **59 Operating conditions such**  **as residence time, temperature, and the use of coal at this ki ln were contrasted to conditions at**  **the Ash Grove kiln that achieved greater reductions to expla in why NO**  **X OUT**  **® may achieve**  **better results on some kilns than others.**

**Nalco also has conducted a number of demonstrations and comm ercial projects in**  **preheater/precalciner cement kilns. The fuels have includ ed coal, and coal in combination with**  **No. 6 heavy fuel oil, waste oil, and/or tire chips. The clinke r capacity on these kilns ranged from**  **approximately 1000 metric tons to 3200 metric tons per day. T he results of two tests with**  **average NOX reductions of approximately 50%, were featured in a recent report (see Table 5-**  **8). 52** 

**TABLE 5-8. EMISSION REDUCTIONS FROM TWO KILNS USING NO X**  **OUT ®** 

**Baseline NO X**  **Emissions (ppm)**  **NO X**  **Emissions**

**with NO X**  **OUT ®**  **(ppm) Percent** 

**Reduction (%)** 
**Kiln A, Test 1 412 203 51**
**Kiln A, Test 2 389 185 53**

**Kiln B 525 284 46**

5.4 SUMMARY OF EUROPEAN EXPERIENCES

**In Europe, many cement plants have adopted general primary m easures, such as process**  **control optimization, use of modern, gravimetric solid fue l feed systems, optimized cooler**  **connections and use of power management systems. These meas ures are usually taken to**  **improve clinker quality and lower production costs but they also reduce the energy use and air**  **emissions. 1** **75**

**In March 2000, the European Integrated Pollution Preventio n and Control (IPPC) Bureau**  **issued a report on Best Available Techniques for European ce ment kilns.**  **1 The report collected**  **emissions data from several sources. Emission rates for Eur opean kilns included in this study**  **range from less than 0.8 to 12 lb NO X**  **/ton of clinker. A set of German kiln emission measurements presented in the European report found NO**  **X emissions for a cyclone preheater**  **with heat recovery of 1.2 to 6.2 lb/ton of clinker, for a cyclo ne preheater without heat recovery of**  **1.6 to 7.0 lb/ton of clinker, and for a grate preheater of 1.6 t o 8.2 lb /ton of clinker. These rates**  **are similar to the averages for preheater and precalciner ki lns found by EC/R in the new data**  **presented in Chapter 4 (1.7 and 2.7 lb/ton of clinker respect ively), but are less than those reported**  **in the ACT document (5.9 and 3.8 lb/ton of clinker respective ly).**  **1**

**Table 5-9 presents a summary of NO X**  **control device applicability, reduction efficiency, and reported average emissions from the IPPC Bureau report o**  **n BAT for European cement kilns.**  **1 There are no emissions data in the IPPC report for kilns with C**  **emStar technology or mid kiln firing. For low-NO**  **X burners, the IPPC report found a lower average NO**  **X emissions rate**  **(1.6 lb/ton of clinker) than EC/R found in the new State data ( 8.98 lb/ton of clinker). Both the**  **IPPC report and the 1994 ACT document had estimated reductio n efficiencies for low-NO**  **X burners of up to 30 percent. The reduction efficiencies in th**  **e IPPC report for SNCR (10 to 85 percent) and SCR (85 to 95 percent) are close to but slightly g**  **reater than those reported in the 1994 ACT document (30 to 70 percent and 80 to 90 percent respec**  **tively).**

**TABLE 5-9. NO X**  **CONTROL TECHNIQUES SUMMARY FROM EUROPEAN**

**BEST AVAILABLE TECHNIQUES REPORT 1** 

**Technique Kiln Systems**

**Applicability Reduction** 

**Efficiency Reported Emissions** 

**mg/Nm 3 a**  **kg/tonne b** 

**(lb/ton) Flame cooling All 0 to 50% 400 0.8**  **(1.6) Low-NO**  **X burner**  **All 0 to 30%**

**Staged combustion**  **Preheater and**

**Precalciner 10 to 50 % <500 to 1000 < 1.0 to 2.0**  **(2.0 to 4.0) Mid-kiln firing Wet and long dry 20 to 40% no info no info** 

**SNCR Preheater and**

**Precalciner 10 to 85% 200 to 800 0.4 to 1.6**  **(0.8 to 3.2)**

**SCR - data from pilot plants only**  **Possibly all 85 to 95% 100 to 200 0.2 to 0.4 (0.4 to 0.8)** 

**a Normally referring to daily averages, dry gas, 273 K, 101.3 k**  **Pa and 10% O 2**  **. b**  **kg/tonne clinker is based on 2000 m 3**  **/tonne of clinker. 76** 

**The IPPC report concludes that BAT for reducing NO X**  **emissions are a combination of general primary measures, primary measures to control NO**  **X emissions, staged combustion and**  **SNCR. The BAT emission level associated with the use of these techniques is 0.4 to 1.0 lb/ton**  **of clinker (200-500 mg NO X**  **/m 3**  **(as NO 2**  **) ). This emission level could be seen in context of the current reported emission range of 0.4 to 6.0 lb/ton of clink**  **er (<200-3000 mg NO X**  **/m 3**  **), and that the majority of kilns in the European Union is said to be able t**  **o achieve less than 2.4 lb/ton of clinker (1200 mg/m**  **3 ) with primary measures.**  **1**

**While there was support for the above concluded BAT to contro l NO**  **X emissions, there**  **was an opposing view that the BAT emission level associated w ith the use of these techniques is**  **1.0 to 1.6 lb/ton of clinker (500-800 mg NO X**  **/m 3**  **(as NO 2**  **)). There was also a view that selective catalytic reduction is BAT with an associated emission leve**  **l of 0.2 to 0.4 lb/ton of clinker (100- 200 mg NO**  **X /m**  **3 (as NO**  **2 )).**  **1**

5.5 SUMMARY OF APPLICABLE NO X CONTROL TECHNOLOGIES

**Table 5-10 presents NO X**  **control techniques and the types of kilns on which they are applicable.** 

**TABLE 5-10. NO X**  **CONTROL TECHNIQUES AND APPLICABLE TYPES OF CEMENT KILNS** 

**NO X**  **Control Technique Applicable Kiln Type** 
**Wet Long-Dry Preheater Precalciner**
**Process Control Systems yes yes yes yes**
**CemStar yes yes yes yes**

**Low-NO X**  **Burner a**  **yes yes yes yes Mid-Kiln Firing yes yes no no** 

**Tire Derived Fuel b**  **yes yes yes yes SNCR no no yes yes** 

**a Low-NO**  **X burners can only be used on kilns that have indirect firing.** 

**b Tire derived fuel can be introduced mid-kiln in a wet or long-**  **dry kiln, or at the feed end of a preheater or precalciner kiln.** 

**Table 5-11 presents a comparison between the NO X**  **reductions identified in the 1994 ACT document and updated emissions data for various control**  **technologies. 77** 

**TABLE 5-11. COMPARISON OF 1994 ACT NO X**  **EMISSIONS REDUCTIONS**

**WITH NEWLY AVAILABLE EMISSIONS DATA**

**1994 ACT 64**  **Updated Emissions Data 65** 

**Possible NO**  **X Emission**  **Reduction (%)**  **Average**

**Emission Reduction**  **(%) a**  **Range of**

**Emission Reductions**  **(%) Average** 

**Emission Rate**  **(lb NO X**  **/ton of clinker)**  **a Range of** 

**Emission Rates**  **(lb NO X**  **/ton of clinker)** 

**Process Control Modifications**  **<25**

**CemStar n/a 33 23 to 40 6.0 3.2 to 11.2**
**Indirect firing with a low-NO**  **X burner**  **20 to 30 27 4 to 47 9.0 b**  **9.0 b** 

**MKF (wet kilns only)**  **20 to 40 c**  **41 28 to 59 d**  **n/a n/a**

**MKF (dry kilns only)**  **20 to 40 c**  **33 11 to 55 3.9 2.0 to 10**

**TDF in a Precalciner**  **e 35 30 to 40 2.4 2.4** 

**SNCR 30 to 70 BSI**  **e 50 1.2 1.2** 

**NO X**  **** **OUT f**  **40 10 to 50**

**n/a - not applicable**

**a The average emission reduction and average emission rate we**  **re calculated using a simple (not weighted) average of the available data.**  **b There was only one source that provided emission rate data fo**  **r low-NO X**  **burners; the rest of the kilns with low NO**  **X burners only provided percent reductions.** 

**c The 1994 ACT document provide one range of possible emission**  **reductions for MKF at both wet and dry kilns. d**  **At the time the kiln with the 59 percent emission reduction in stalled MKF, it also added a Linkman control**  **system; the next largest percent emission reduction at a wet kiln from MKF was 35.0.** 

**e One facility in southern California provided emission redu**  **ction data for both biosolids injection (BSI) technology and firing tire derived fuel (TDF) in a prec**  **alciner.**

**f The average emissions reduction for NO**  **X OUT**  **® was estimated from the three tests/demonstrations describ**  **ed in 5.3.2.2.** 

**Monitoring the temperature and excess air in the combustion zone as discussed in Section**  **5.1.1 provides optimum kiln operating conditions, which in crease the energy efficiency and** **78**

**1. European Integrated Pollution Prevention and Control Bur eau (EIPPCB).**  Reference Document on Best Available Techniques in the Cement and Lime Manufacturing Industries. **World Trade Center, Seville, Spain. March 2000. productivity of the cement-making process while minimizin**  **g NO X**  **emissions. The NO X**  **reduction effect of other process modifications discussed in Section 5.1 is usually difficult to**  **isolate from other factors. These measures can be highly sit e specific and data from one site**  **cannot be directly translated to other sites. Quite often a n umber of process modifications and**  **combustion control measures are implemented simultaneous ly. Process modifications can reduce**  **NO X**  **emissions in cement kilns without any specific NO X**  **control equipment. Some plants rely on process monitoring and control and process modification**  **s as a means to maintain NO X**  **emissions within their allowable limits.**

**The CemStar process described in Section 5.1.2.2 is being us ed or incorporated by 11**  **facilities in the United States. Several long-term and shor t-term tests of CemStar have found**  **average NO X**  **emission reductions of 33 percent.**

**Combustion modifications to reduce NO X**  **emissions include the staged combustion of air and of fuel. Low-NO**  **X burner systems described in Section 5.2.1.2 rely on the stag**  **ed combustion of air. Technical literature and industry publications rep**  **ort NO X**  **reduction rates of 4 to 47 percent with the installation of low-NOX burners, dependin**  **g on the baseline emissions, type of kiln, type of low-NO**  **X burner, and operating conditions.** 

**As described in Section 5.2.2, staged combustion of fuel inc ludes the use of preheaters/**  **precalciners and mid-kiln firing. Mid-kiln firing of fuels is practiced in over 20 U.S. cement**  **kilns and whole tires are most frequently used for the mid-ki ln fuel. Data are available for**  **several kilns that have used or tested mid-kiln firing demon strating NO**  **X reductions ranging from**  **11 to over 59 percent.**

**The NO X**  **removal controls discussed in Section 5.3 include selectiv e catalytic reduction,**  **and selective noncatalytic reduction (biosolids injectio n and NO**  **X OUT). SCR technology has not**  **been used on any cement kilns in the U.S., although pilot plan t trials and feasibility studies have**  **been conducted in Europe. The principles of SNCR technology are applicable to preheater/**  **precalciner kilns. It is believed that SNCR would be difficu lt, if not impossible, to be used in**  **wet and long dry process kilns due to problems in obtaining th e right temperature and retention**  **time. Two SNCR technologies, biosolids injection and NO X**  **OUT ®**  **, have demonstrated NO X**  **emission reductions in cement kilns. Biosolids injection i s being used on one kiln in Southern**  **California and NO X**  **OUT has been demonstrated on two kilns in the U.S. SNCR techno logy is**  **widely practiced in Europe.**

5.6 REFERENCES**79**

**2. Helmuth, R.A., F.M. Miller, T.R. O'Connor, and N.R. Greeni ng.**  Kirk-Othmer Encyclopedia of Chemical Technology. Vol. 5. Third Edition **. New York, NY. John Wiley & Sons, Inc. 1979. pp. 163-193.** 

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**4. Miller, F.M.** Oxides of Nitrogen **. GTC Presentation, Kansas City, MO, September 20, 1977.** 

**5. Hansen, E.R., “The Use of Carbon Monoxide and Other Gases fo r Process Control,” 27**  **th IEEE Cement Industry Technical Conference Proceedings, Ma**  **y 1985.**

**6. Mehta, P.K.** Energy, Resources and the Environment - A Review of the U.S. C ement Industry. **World Cement Technology. July/August 1978.**

**7. Andover Technology Partners.** NOx Reduction from Cement Kilns Using the CemStar Process, **Evaluation of CemStar Technology - Final Report to Texas Ind ustries. Dallas,**  **Texas. April 18, 2000.**

**8. Battye, R., and S. Edgerton, EC/R Incorporated. “December 2, 1999 Trip Report to**  **Texas Industries (TXI) Riverside Cement, Oro Grande facili ty.” Oro Grande, CA.**  **Submitted to Dave Sanders, US EPA, under contract No. 68-D-9 8-026, work assignment**  **No. 2-28. August 31, 2000.**

**9. En-tellect Environmental Services, Inc., “Evaluation of the Effects of the CemStar**  **Process on a Wet Process Cement Kiln,” (no date, but includes data for July-Sept 1999).** 

**10. Hilovsky, R.J.** NO X Reductions in the Portland Cement Industry With Conversion To Coal-Firing **: Presented at the 1977 U.S. EPA Emission Inventory/Factor W orkshop.**  **Raleigh, NC. September 13-15, 1977.**

**11. Radian Canada, Inc.** Assessment of NO X Emission Control Technologies for Cement and Lime Kilns **. Radian Report No. 714-061-01. Prepared for Environment Ca nada, Contract**  **No. K2035-3-7044. October 1994. Pg.iv.**

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**13. Penta Engineering Corporation** Report on NO X Formation and Variability in Portland Cement Kiln Systems Potential Control Techniques and Their Feasibility and Cost Effectiveness. **Penta Project No. 971212. Prepared for the Portland Cement A ssociation.**  **PCA R&D Serial No. 2227. Skokie, IL. 1999. 80** 

**14. Comments on** Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing

**submitted by Greer, W.L. to William Neuffer, U.S. EPA throug h T.B.**  **Carter, APCA. October 27, 1999.**

**15. U.S. Environmental Protection Agency.** Summary of NO X Control Technologies and Their Availability and Extent of Application **. EPA450/3-92-004. Research Triangle Park, NC 27711. February 1992.** 

**16. Xeller, H.** Reducing NO X Formation Using a Step Burner with Exit Gas Recycling from Preheater **. World Cement. 19(3):8492. March 1988.**

**17. Bauer, C.** PYRO-JET Burners to Reduce NO X Emissions Current Developments and Practical Experience **. World Cement. 21(4). April 1990.**

**18. The ROTAFLAM Kiln Burner. Product Information Brochure. P rocedair Industries,**  **Combustion Division, Pillard Products, Louisville, KY. 1992**

**19. Vollan, P., and L. Klingbeil.** Modernization and Capacity Increase of Kiln Line No. 6 at the Dalen Plant, Norway. **World Cement. January 1988.**

**20. Wolter, A.** Fast Gas Trace Analysis Optimizes and Reduces the Emission of Pollutants in Cement Plants **. Zement-KalkGips No. 12, 1987.**

**21. Steinbiß, V.E., C. Bauer, and W. Breidenstein.** Current state of development of the PYRO-JET

® burner. **VDZ Kongress. 1993.**

**22. Thomsen, K., L.S. Jensen, and F. Schomburg.** FLS-Fuller ILC-lowNOx calciner commissioning and operation at Lone Star St. Cruz in Califor nia **. ZKG International. October 1998. pp. 542 - 550.** 

**23. Letter and attachments from M.H. Vaccaro, Pillard Combust ion Equipment and Control**  **Systems, to G.J. Hawkins, Portland Cement Association, re: Low NOX Rotaflam**  **® burner, dated January 20, 1999.** 

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**25. Renfrew, S, Process Engineer, RMC Lonestar.** Calciner modification highly effective in meeting Northern California Plant’s alkali reduction and emission control requirements

**. no date.** 

**26. Portland Cement Association and American Portland Cement Alliance.**  Results of the NO X Control Presurvey Results. **January 2,000. 81** 

**27. Memorandum from Battye, R.E., and S. Edgerton, EC/R Incorp orated, Chapel Hill, NC,**  **to B. Neuffer, U.S. EPA, RTP, NC.** Summary of February 4, 2000 teleconference to discuss results of NO X Control Presurvey Results. **February 11, 2000.**

**28. Portland Cement Association.** A New Stone Age: The Making of Portland Cement

**. Skokie, IL. 1992. pg. 4.** 

**29. Cadence Environmental Energy, Inc. www.cadencerecyclin g.com.** 
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**31. Shumway, D.C. “Tire Derived Fuel at Mitsubishi Cement Corp oration.” Received**  **during December 2, 1999 visit to Mitsubishi.**

**32. Shumway, D.C.** Mitsubishi Cement Corporation’s Cushenbury Plant **presented at the IEEE West Coast Cement Industry Conference. Victorville, C**  **A. Oct 1995.**

**33. Rother, R. and D. Kupper.** Staged Fuel Supply - An Effective Way of Reducing NO X Emissions **. Zement-Kalk-Gips. No. 9. 1989.**

**34. Nielsen, P.B., and O.L. Jepsen.** An Overview of the Formation of SO X and NO

X In Various Pyroprocessing Systems **. Presented at the IEEE Cement Industry Technical Conference XXXII. Tarpon Springs, FL. May 22-24, 1990.** 

**35. Facsimile from Bennett, J., California Portland Cement Co mpany, to Damle, A.S.,**  **Research Triangle Institute. August 4, 1993. Process modif ications in cement kilns.** 

**36. Benoit, M.R., E.R. Hansen, and T.J. Reese.** Method for Energy Recovery from Containerized Hazardous Waste. **U.S. Patent No. 4974529. December 1990.**

**37. Walquist, C., Cadence Environmental Energy. “Cadence sys tem leads to fall in NO**  **X emissions,”**  World Cement **, Dec 1997, pp. 26, 27.**

**38. Hansen, E.R.** New Way to Burn Hazardous Waste **. Rock Products. April 1990.**

**39. Cadence Environmental Energy and Ash Grove Cement. “Mid-K iln Fuel Entry**  **Benefits,” section 3 of the report,** Emission, Reduction, Technology: Resource Conservation & Recovery **. (no date).**

**40. Letter from Edgerton, S. and T. Stobert, EC/R Inc., to Bill N euffer, EPA, Feb 8, 2000.**  **Minutes from Dec 16, 1999 meeting with representatives from EPA and Cadence.** **82**

**41. Texas Natural Resources Conservation Commission. A list o f permitted NO**  **X levels for**  **cement plants in the state, CEMS data as reported by the facil ities for 1994 - 1999, and**  **information on the control technology in use at each facilit y.** 
**42. May, M. and L. Walters, Jr. "Low NO X**  **& Tire-derived Fuel for the Reduction of NO X**  **from the Portland Cement Manufacturing Process."** Cement Americas **, August 1999, pp. 10-1.** 

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**44. Radian Corporation, "MDE Air Permit Test Report for Lehigh Portland Cement**  **Company, Union Bridge, Maryland Facility," January 1996.**

**45. Email transmission from Hawkins, G., PCA, Skokie, IL to B. N euffer, U.S. EPA. Results**  **of PCA Survey - Preliminary NO X**  **Control Technology Questionnaire. January 2000.**

**46. Smith, J.C., and M.J. Wax.** Selective Catalytic Reduction (SCR) Controls to Abate NO X Emissions. **White Paper by Wax, M. J., Institute of Clean Air Companies. S eptember**  **1992.**

**47. Joseph, G.E., and D.S. Beachler.** Student Manual, APTI Course 415 Control of Gaseous Emissions **. U.S. EPA, Air Pollution Training Institute. EPA 450/2-81- 006. December**  **1981.**

**48. Campbell, L.M., D.K. Stone, and G.S. Shareef.** Sourcebook: NO X Control Technology Data **. U.S. EPA, Air and Energy Engineering Research Laboratory. EPA-600/2-91-029.**  **July 1991.**

**49. Siddiqi, A.A., and J.W. Tenini. Hydrocarbon Processing. 1 15-124. October 1981.** 

**50. Letter from Wax, J., Institute of Clean Air Companies, to Ne uffer, W.J., U.S.**  **Environmental Protection Agency. August 27, 1992. Respons e to ACT Document -**  **Control of NO X**  **Emissions from Process Heaters.**

**51. Haas, G.A.** Selective Noncatalytic Reduction (SNCR): Experience with the Exxon Thermal DeNO X Process **. Presented at the NO X**  **Control V Conference. Council of Industrial Boiler Owners. Long Beach, CA. February 10-11, 1**  **992.**

**52. Lin, M.L., M.J. Knenlein, Fuel Tech Inc. “Cement Kiln NO X**  **Reduction Experience Using the NO**  **X OUT**  **® Process,” proceedings of the 2000 International Joint Powe**  **r Generation Conference, Miami Beach, FL, July 23-26, 2000.** **83**

**53. Kokkinos, A., J.E. Cichanowicz, R.E. Hall, and C.B. Sedman.** Stationary Combustion NO X Control: A Summary of the 1991 Symposium **. J. Air Waste Manage. Assoc. 1252. 1991.** 

**54. Teixeira, D.** Widening the Urea Temperature Window. **In Proceedings of 1991 Joint Symposium on Stationary Combustion NO**  **X Control. NTIS. 1991.** 

**55. Kupper, D., and Brentrup, L.** SNCR Technology for NO X Reduction in the Cement Industry **. World Cement 23(3):4-9. March 1992.**

**56. Scheuer, A.,** Non-catalytic reduction of NO with NH 3 in the cement burning process. **Zement-Kalk-Gips, No. 3/1990, Wiesbaden, Germany.**

**57. Sun, William H., Nalco Fuel Tech.** NO X OUT ® Process Demonstration on a Cement Kiln/Calciner, Ash Grove Cement, Seattle Plant, Seattle, W ashington **. October 28, 1993.**

**58. Sun, et. al.** Reduction of NOX Emissions from Cement Kiln/ Calciner throug h the Use of the NO

X OUT ® Process **. Presented at the International Specialty Conference on Wa ste**  **Combustion in Boilers and Industrial Furnaces. Kansas City , MO. April 1994.** 

**59. Interoffice Correspondence from McAnany, L. to H. Knopfel , H, LaFarge Corporation.**  **October 26, 1998. re: Fuel Tech NO X**  **OUT ®**  **Testing.**

**60. PSM International Inc. and Penta Engineering Corp.** Review of Nalco Fuel Tech NO X OUT ® Program for Mid-Kiln Injection Urea to Reduce NO X at the Colton California Plant of California Portland Cement Company **. October 26, 1994.**

**61. Biggs, H.O., Plant Manager, Mitsubishi Cement Corporatio n.**  Biosolids Injection Technology: An Innovation in Cement Kiln NOx Control. **(no date). Received during December 1999 trip report.** 

**62. Shumway, D.C.** Tire Derived Fuel at Mitsubishi Cement Corporation **. (no date) Received during December 1999 site report.** 

**63. McInnes, R., and M.B. von Wormer.** Cleaning Up NO X Emissions. **Chem. Eng. 130-135. September 1990.** 

**64. U.S. Environmental Protection Agency.** Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing **. EPA-453/R-94-004. Research Triangle Park, NC. March 1994.** 

**65. Memo from Battye, R., and S. Walsh, EC/R Incorporated, Chap el Hill, NC to D. Sanders,**  **U.S. EPA, RTP, NC.** Derivation and Data Supporting Development of Cement Plant NO X Emission Rates. **September 15, 2000. 84**  6.0 COSTS OF NO X CONTROL TECHNIQUES

**This chapter presents the cost estimates for the NO X**  **emission control techniques discussed in Chapter 5. Section 6.1 presents the cost method**  **ology used to develop capital and annual operating costs for these techniques. Based upon the**  **distribution of the type of kilns used in the cement industry and their typical capacities, model p**  **lants were developed to perform cost calculations. Section 6.2 presents costs of selected incom**  **bustion and postcombustion control approaches. The cost effectiveness of different control ap**  **proaches is discussed in Section 6.3. All costs presented in this chapter are in 1997 dollars.** 

6.1 COST CALCULATION METHODOLOGY

**The cost calculation methodology is dependent upon the defi nition of model plants and**  **the guidance provided by EPA in the OAQPS Control Cost Manua l** 

**. 1**  **The definition of the model plants, calculation of capital costs and annual operating c**  **osts is presented in this section.**

6.1.1 Model Plants

**As discussed in Chapter 3, existing cement kilns in the Unite d States may be grouped in**  **four types: wet, long dry, preheater, and precalciner types . Coal is the most common fuel used in**  **all types of kilns. 2**  **Several types of waste-derived fuels are being used in the po rtland cement**  **industry to replace coal and reduce NO X**  **emissions. As seen from data presented in Chapter 4, the NO**  **X emissions from individual kilns expressed as lb NO**  **X /ton of clinker do not seem to**  **depend on the kiln capacity. Therefore, only two capacities of the kilns of a given type are used**  **to define model plants for each of the kiln types. Each of the f our kiln types has typical energy**  **consumption and NO X**  **emission rates as shown in Table 6-1 describing model plant p arameters.**  **The model plant kilns were assumed to be in continuous-duty o peration and were assumed to**  **operate 8,000 hours per year which allows scheduled downtim e for maintenance operations.**  **3 Although waste-derived fuels are finding increasing appli**  **cations in cement kilns, coal provided more than 82 percent of the energy requirement of the cement i**  **ndustry. 2**  **Model plants were assumed to use 100 percent coal as a fuel and where available,**  **a percentage of coal and waste derived fuels (i.e., for mid-kiln firing 85% coal and 15% tir**  **e-derived fuel were used).**

6.1.2 Capital Cost Estimation

**The total capital investment is the sum of the direct cost (wh ich is the purchased**  **equipment costs and direct installation costs), indirect i nstallation costs, contingency costs, sales**  **taxes, freight, and production downtime. The purchased equ ipment costs (PECs) used in this**  **chapter for each control technology are based on cost inform ation provided by vendors or from**  **data provided by existing facilities. Table 6-2 provides a l ist of various cost elements included in**  **the capital costs. Where installation costs were not provid ed by vendors, direct and indirect**  **installation costs were developed using the factors 45 and 3 3 percent, respectively, of PEC, per**  **guidelines in the EPA OAQPS Control Cost Manual**

**. 1**  **A contingency factor of 20 percent was 85** 

**TABLE 6-1. CEMENT KILN MODEL PLANTS FOR COST CALCULATIONS**

Model no. Kiln type Capacity (tons clinker/hr) Heat input

rate (MM Btu/ton clinker) Uncontrolled NO X

emissions Gas flow

rate at stack location (dry std ft 3 /min) (lb/ton clinker) (lb/hr)

**1 Wet 30 6.0 9.7 291 59,100**

**2 Wet 50 6.0 9.7 485 98,500**
**3 Long dry 25 4.5 8.6 215 38,500**
**4 Long dry 40 4.5 8.6 344 61,500**

**5 Preheater 40 3.8 5.9 236 53,200**

**6 Preheater 70 3.8 5.9 413 93,000**

**7 Precalciner 100 3.3 3.4 340 118,500**

**8 Precalciner 150 3.3 3.4 510 176,000 Average stack gas temperature ~150**   **C (300**  **F). Average stack gas moisture content ~12%.**  **Average particulate loading in stack gas ~0.01 grains/dry s td ft**  **3**

**. added to the vendor costs in all cases to cover contingencies**  **as listed in Table 6-2. 1**  **The capital costs of in-combustion approaches such as low NO**  **X burners and postcombustion approaches**  **such as selective noncatalytic reduction are related to the clinker production capacity of the kiln**  **as well as the energy requirement of the kiln per unit amount o f clinker production.** 

6.1.3 Annual Operating Costs

**Annual operating costs are composed of the direct operating costs of materials and labor**  **for maintenance, operation, utilities, material replacem ent and disposal and the indirect operating**  **charges, including plant overhead, general administratio n, and capital recovery charges.**  **Table 6-3 lists the typical values used for these costs. A bri ef description is provided below for**  **each component of the direct annual operating costs used in t he cost evaluation.** 

6.1.3.1 Utilities

. **The utility requirements for the control techniques consis t of electricity**  **and/or compressed air to power control instrumentation and auxiliary equipment and the energy**  **requirements for vaporization and injection of ammonia for SCR systems. The cost for**  **electricity and compressed air is considered to be negligib le relative to the other operating costs.** 

**The credit applied (tipping fee) for burning tires is an aver age value.**  **4 Tire tipping fees**  **are highly variable showing a large regional variation and l arge fluctuations in the market. The**  **average tipping fee used in this analysis is within the 1997 r ange of $20 to $200 credit/ton of** **86**

**tires provided by Waste News. 5**  **A direct access of the Waste News - Current Commodity Pricing demonstrated a range in tipping fee credits of $140 to $75 in N**  **ew York; $125 to $65 in Miami, Florida; $100 to $75 in Atlanta, Georgia; $150 to $75 in Houst**  **on, Texas; $85 to $75 in Chicago, Illinois; $85 to $20 in Denver, Colorado; $100 to $42 in Los An**  **geles; California: and $200 to $100 in Seattle, Washington.**  **6**

**TABLE 6-2. CAPITAL INVESTMENT COMPONENTS FOR EMISSION CONTROL DEVICE COST EVALUATION**  **1**

**Capital Investment Cost Elements Direct costs (DC)**  **Purchased equipment costs (PEC): Control device and auxiliary equipment**  **Instrumentation**

**Direct installation costs (DIC) - 45 percent of PEC: Foundations and supports**  **Handling and erection Electrical**  **Piping Insulation for ductwork**  **Painting**

**Indirect installation costs (IIC) - 33 percent of PEC: Engineering**  **Construction and field expenses Contractor fees**  **Startup Performance test**  **Model study**

**Contingencies (C) - 20 percent of PEC: Equipment redesign and modifications**  **Cost escalations Delays in startup** 

**Sales taxes (3 percent of PEC)**

**Freight (5 percent of PEC)**

**Production downtime (two days loss of production times aver age market value per ton of**  **clinker)** *****

***** **Average market value per short ton of clinker is $72.59. 7** **87 TABLE 6-3. ANNUALIZED COST ELEMENTS AND FACTORS**  **1**

Direct annual costs (DC)

1. Utilities:

Coal 8 $32.41 per short ton
Electricity 9 $0.05 per kwh
Natural gas 10 $3.59 per 1000 ft 3

Tires 11 -$42.50 per ton
2. Operating labor
Operator labor 12 $22.12 per hour
Supervising labor 1 15 percent of operator labor

3. Maintenance a
Maintenance labor $24.33 per hour times 0.5 hours per 8 hour shift b

Maintenance materials 100% of maintenance labor
Indirect annual costs (IC) a
Overhead 60% of operating labor, supervisory labor, maintenance labor and materials
Property tax 1% of total capital cost
Insurance 1% of total capital cost
Administrative charges 2% of total capital cost
Capital recovery capital recovery factor times total capit al investment

TOTAL ANNUAL COST DC + IC

**a References for costs are included in Section 6.1.3.** 

**b Maintenance labor is 1.1 times the operator labor.**  **1**

6.1.3.2 Operating and Supervising Labor

. **No postcombustion NO X**  **control technologies were identified as currently operating on a ce**  **ment kiln in the United States. Therefore, information for typical operating labor requir**  **ements from the cement industry was unavailable. A requirement of 0.5 hour of operator attentio**  **n was assigned for an 8-hour shift, for 88** 

**all technologies considered, regardless of the plant size. Operator wage rates were estimated to**  **be $22.12/hr in 1997. 12**  **Supervisory labor costs were estimated to be 15 percent of th e operating**  **labor costs consistent with the OAQPS Control Cost Manual. 1** 

6.1.3.3 Maintenance

. **Specific maintenance costs were not available from the cont rol**  **system vendors and manufacturers. The guidelines for maint enance costs in the OAQPS Control**  **Cost Manual suggest a maintenance labor cost of 0.5 hours per 8-hour shif**  **t and a maintenance material cost equal to this labor cost.**  **1**

6.1.3.4 Overhead

. **An annual overhead charge of 60% of the total maintenance cos t was**  **used, consistent with guidelines in the OAQPS Control Cost M anual.**  **1 As described above, the**  **maintenance cost is 0.5 hours per 8-hour shift and a maintena nce material cost equal to this labor** 
**cost.**

6.1.3.5 Property Taxes

. **The property taxes were calculated as 1 percent of the total capital cost of the control system, as suggested in the OAQP**  **S Control Cost Manual. 1** 

6.1.3.6 Insurance

. **The cost of insurance was calculated as 1 percent of the total capital**  **cost of the control system, as suggested in the OAQPS Contro l Cost Manual.**  **1**

6.1.3.7 Administrative Charges

. **The administrative charges were calculated as 2 percent of the total capital cost of the control system, cons**  **istent with the OAQPS Control Cost Manual.**  **1**

6.1.3.8 Capital Recovery

. **In this cost analysis the capital recovery factor (CRF) is defined as**  **1 :** 

**CRF = i (1 + i) n**  **/ ( (1 + i) n**  **- 1) = 0.1098**

**where**

**i is the annual interest rate = 7 percent, and n is the equipment life = 15 years.** 

**The CRF is used as a multiplier for the total capital cost to ca lculate equal annual payments over**  **the equipment life.**

6.2 COSTS OF NO X CONTROL APPROACHES

**As discussed in Chapter 5, feasible NO X**  **control approaches include process modifications, combustion modifications, and NO**  **X removal controls. Process modifications**  **include combustion zone control of temperature and excess a ir, feed mix composition, kiln fuel,**  **and increasing thermal efficiency of the kiln. Combustion m odifications include staged** **89**

**combustion of air and staged combustion of fuel. NO X**  **removal controls that are presented include selective catalytic and noncatalytic reduction of**  **NO X**  **using either ammonia or urea. This chapter includes costs for approaches and technologies tha**  **t will reduce NO X**  **emissions and focuses on four technologies; changing the feed mix composi**  **tion (CemStar), installation of a low NO**  **X burner (staged combustion of air), installation of a mid-ki**  **ln firing system (staged combustion of fuel), and noncatalytic reduction of NO**  **X using biosolids (biosolids injection).** 

6.2.1 Process Modifications

**As discussed in Section 5.1, process modifications can be hi ghly site specific and data**  **from one site cannot be directly translated to other sites. D ata are not available to determine**  **costs of individual process modifications. Quite often a nu mber of process modifications and**  **combustion control measures are implemented simultaneous ly. Similar to combustion process**  **control approaches, process modifications have also shown to reduce energy requirement and**  **increase productivity, thus providing an economic incenti ve to implement them in addition to**  **NO X**  **reduction.**

6.2.1.1 Combustion Zone Control of Temperature and Excess Air

. **Approaches aimed at improving the energy efficiency of the process indi**  **rectly reduce NO X**  **emissions per ton of clinker product. These approaches rely on continuous mon**  **itoring of O 2**  **and CO and in some cases NO**  **X emissions for controlling the excess air, fuel rate, and the**  **combustion zone temperature. These measures are usually undertaken to incr**  **ease process energy efficiency by reducing over-burning of the clinker. Maintaining the comb**  **ustion zone temperature to a necessary minimum value using process control systems mini**  **mizes both the process energy requirement and increases refractory life. Because conti**  **nuous monitoring of emissions is necessary for efficient process control, the cost of monito**  **rs is not considered as a NO X**  **control cost. Further, the information obtained during this study i**  **ndicated that some plants relied on process monitoring, including NO**  **X monitoring, as a means to maintain NO**  **X emissions within**  **their respective permit limits.**

**Based on existing installations, the cost of a commercially available kiln process control**  **system is in the neighborhood of $750,000. 13**  **The resulting savings due to reduced energy and fuel requirements and increased refractory life were estim**  **ated to be about $1.37 per short ton of clinker. Thus, for a cement kiln facility producing 300,000**  **tons/year of clinker the reduced cost of producing cement is expected to recover process control i**  **nstallation costs in less than 2 years. 90** 

6.2.1.2 CemStar Process

. **As discussed in section 5.1.2.2, the CemStar process (which involves the substitution of steel slag for raw materials) r**  **educes the kiln temperature in the region of the flame and results in lower NO**  **X emissions. In addition, because the chemical**  **composition and structure of steel slag is similar to cement , the heat required to convert a ton of**  **steel slag to clinker is substantially lower than the heat re quired to convert a ton of raw materials**  **to clinker. 14**  **The costs associated with installing this process are prima rily material handling**  **equipment for the steel slag. Cost information was obtained from TXI and are summarized in**  **Table 6-4. 15**  **The cost of the material handling equipment can range from $2 00,000 to $500,000.** 

**TABLE 6-4. BASIS FOR COST ANALYSIS OF CEMSTAR (1997 $)**

**Capital Cost of Material Handling Equipment**  **$500,000**

**Type of Kiln Wet**
**Primary Fuels Coal and natural gas**

**Kiln Production Rate**

**Before CemStar 42 tons/hour**

**After CemStar 45 tons/hour**
**Quantity of Steel Slag 3.2 tons/hour**
**Average kiln heat requirement 5.00 MMBtu/ton**
**Total Capital Investment $1,176,000**

**Annualized Cost a**  **$220,000**

**a Includes cost of steel slag, royalties, and credit for the re**  **duction in raw materials.**

**CemStar model plants costs could not be developed because th e addition of steel slag is**  **completely plant dependant. There is no set ratio of steel sl ag injection to kiln production rate.**  **The amount of steel slag needed depends on the plants raw mate rials. The ratio can vary**  **anywhere from five to ten percent addition of steel slag, bas ed on kiln production. For the**  **example presented in this document, the addition of steel sl ag was 7.7 percent of the kiln**  **production prior to production with the CemStar process. Th e addition of steel slag typically**  **reduces the need for iron used in raw material feed. Monetary savings from the reduction in iron**  **can range from $0.5 to $1.00 per ton of clinker produced. A red uction in shale and/or clay may**  **also result from the addition of steel slag. The amount of sha le and/or clay reduction varies**  **based on each facilities raw materials. Depending on the raw material characteristics, the need**  **for shale and/or clay may be eliminated. CemStar charges roy alties that are paid by the facility**  **installing the technology. The royalties are approximatel y $16 per ton of steel slag used.**  **16 91** 

**Cost savings associated with the CemStar process are based o n production increase with**  **the addition of steel slag compared to the cost benefit. Due t o steel slag addition you get**  **approximately one ton of clinker per ton of steel slag added. Steel slag cost $5-15 per ton,**  **15 whereas clinker cost $72.59 per ton. Average cost savings eq**  **uals $62.59 per ton times increase in production. Most plants increase production by five to te**  **n percent with the addition of the CemStar process.** 

6.2.2 Combustion Modifications

**As discussed in section 5.2 there are several combustion mod ifications that can be**  **implemented to reduce NO X**  **emissions. This section presents costs for low NO X**  **burners (staged combustion of air) and mid-kiln firing (staged combustion o**  **f fuel).**

6.2.2.1 Low NO X Burners

. **Cement kiln burners, specifically marketed as low NO X**  **burners, require an indirect-fired kiln system. Therefore , to install a low NO**  **X burner in an**  **existing direct-fired kiln, it is necessary to convert the k iln-firing system to an indirect firing**  **system. Two sets of costs are therefore developed: (1) to ins tall a low NO**  **X burner in an existing**  **indirect-fired kiln, and (2) to install a low NO X**  **burner in an existing direct-fired kiln. In the first case, only the costs of the low NO**  **X burner equipment are considered, whereas in the second case**  **the costs of conversion of a direct-fired system to an indire ct-fired system are added to the low**  **NO X**  **burner cost.**

**Information was obtained from a supplier of low-NO X**  **burners regarding costs and heat duty.**  **17 The cost of a burner depends upon the size or heat duty as well a**  **s on the number of different types of fuels that can be burned, e.g., only coal,**  **or coal and gas, or coal, waste-derived liquid fuel and gas. The cost also depends on whether the burn**  **er is being installed in a new plant or is a retrofit in an older plant. The PEC of a low NO**  **X burner retrofit using coal as a fuel is**  **typically about $100,000 for a 200 MM Btu/hr heat duty. For a m ulti-channel burner the cost is**  **higher. The capital cost of a multi-channel retrofit low NO X**  **burner is about 100 percent greater than that for a single channel burner for the same heat duty.** 

**From the limited available data a linear correlation (R 2**  **= 0.98) developed for an approximate purchase cost for a retrofit application as a fu**  **nction of heat duty is given as:**

**PEC = 172,000 + 152 H** 

**where PEC = Multi-channel low NO**  **X burner purchase equipment cost in $, and**  **H = Burner heat duty in MM Btu/hr.**

**The cost of a single channel low NO X**  **burner is obtained by dividing the PEC of a multi-channel burner by 2.** **92**

**For each model plant described in Table 6-1 purchase equipme nt costs for multi-channel**  **burners were determined based on the heat duty needed by the k iln. For wet, long dry, and**  **preheater kilns all the required heat is assumed to be provid ed by the low NO**  **X burner, whereas**  **for precalciner kilns only 60 percent of the heat duty is assu med to be provided by the low NO**  **X burner at the hot end of the kiln. The capital costs for retrof**  **iting the eight model plants described in Table 6-1 in an existing indirect-fired kiln are given in T**  **able 6-5. Direct installation, indirect installation, and contingency costs were assumed to be 45, 3**  **3, and 20 percent, respectively, as discussed in Section 6.1.2. The capital costs of retrofit lo**  **w NO X**  **burners for the eight model plants ranged from $473,000 for the small long dry kiln to $96**  **6,000 for the large preheater/precalciner kiln. The capital costs for retrofi**  **tting on a wet kiln compare well with the $500,000 total installed cost estimated by a cement company** 

**. 18** 

**The annualized costs for low NO X**  **burners in an existing indirect-fired kiln are presented in Table 6-6. No additional costs for utilities were deemed n**  **ecessary for NO X**  **control purposes. As described in section 6.1.3, 0.5 hours of operating labor w**  **ere added per 8-hour shift and maintenance costs were estimated as 0.5 hours of labor per 8-**  **hour shift with maintenance material costs equal to this labor cost. Indirect annual cos**  **ts were determined as described in Section 6.1.3. The total annualized costs for the eight low N**  **O X**  **burner retrofits ranged from a low of $130,000/year for the small long dry kiln to a high of $2**  **04,000/year for the large preheater/precalciner kiln.** 

**Conversion of a direct-fired kiln to an indirect-fired kiln reduces the amount of primary**  **air and increases the proportion of secondary air input to th e kiln. The total cost to convert an**  **existing dry process facility with two kilns, with a combine d 100 tons/hr clinker capacity and a**  **225 MM Btu/hr heat duty, was $5.6 million in 1998. 19,20**  **The equipment list included a Pfister coal metering system, coal mill dust collector, Pillard bur**  **ner and trolley, coal fire detection system, carbon dioxide inerting system, coal conveying blo**  **wers, pulverized coal bins, pulverized coal bin dust collector, instrumentation, primary air fan,**  **and ductwork. Using the data provided by the facility and the cost calculation methodology presen**  **ted in section 6.1 (which adds 8 percent PEC cost for sales tax and freight, 45 percent PEC cos**  **t for direct installation, 33 percent PEC cost for indirect installation, and 20 percent PEC cost f**  **or contingencies) the total installed capital cost is estimated at $3.8 million (in 1997 dollars).**  **The actual cost of $5.6 million (in 1998 dollars) for the same facility includes $2.3 million fo**  **r contractor engineering and project management. When the costs are adjusted to include engineer**  **ing and project management as part of the indirect installation costs**  **1 (approximately $550,000), there is agreement between the**  **two estimates.**

**Since the $3.8 million equipment cost estimate was for two pa rallel systems, the cost of**  **one conversion system to process coal for a 50 ton/hr dry faci lity**  **21 was considered to be $1.88**  **million in 1997 dollars. The amount of coal processed is prop ortional to heat requirement. For a**  **dry process, the energy requirement is approximately 4.5 MM Btu/ton. Therefore, the cost of** **93 TABLE 6-5. CAPITAL COSTS FOR RETROFIT LOW-NO** **X BURNERS IN AN EXISTING INDIRECT-FIRED KILN (1997 $)** Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heat duty(MMBtu/hr) PEC ($)Freightand salestax ($)Installation costs $Contingencycosts ($)ProductionDowntime($)Totalcapitalcosts ($)Direct Indirect**1 Wet 30 180 198,000 16,000 89,000 65,000 40,000 105,000 511,000 2 Wet 50 300 216,000 17,000 97,000 71,000 43,000 174,000 618,000** **3 Long dry 25 113 187,000 15,000 84,000 61,000 37,000 87,000 473,000 4 Long dry 40 180 198,000 16,000 89,000 65,000 38,000 139,000 546,000** **5 Preheater 40 152 193,000 15,000 87,000 64,000 39,000 139,000 538,000 6 Preheater 70 266 210,000 17,000 95,000 69,000 42,000 244,000 678,000** **7 Precalciner 100 330 200,000 16,000 90,000 66,000 40,000 348,000 761,000 8 Precalciner 150 495 215,000 17,000 97,000 71,000 43,000 523,000 966,000** **94 TABLE 6-6. ANNUALIZED COSTS FOR RETROFIT LOW-NO** **X BURNERS IN AN EXISTING INDIRECT-FIRED KILN** **(1997 $)**Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heat duty(MMBtu/hr)Maintenancecosts ($/yr)Otherlabor ($)Overheadcosts ($/yr)Taxesinsuranceadmin.($/yr)Capitalrecovery($/yr)Totalannualizedcosts ($/yr)**1 Wet 30 180 24,400 12,700 22,200 20,500 56,200 136,000 2 Wet 50 300 24,400 12,700 22,200 24,700 67,900 152,000** **3 Long dry 25 113 24,400 12,700 22,200 18,900 51,900 130,000 4 Long dry 40 180 24,400 12,700 22,200 21,900 60,000 141,000** **5 Preheater 40 152 24,400 12,700 22,200 21,500 59,000 140,000 6 Preheater 70 266 24,400 12,700 22,200 27,100 74,400 161,000** **7 Precalciner 100 330 24,400 12,700 22,200 30,400 85,600 173,000 8 Precalciner 150 495 24,400 12,700 22,200 48,600 106,000 204,000** **95** 

### PEC for model plant Heat requirement for model plant
**835 000 225 0 6** 



### , **.**



### =       **firing system conversion to process coal to provide 225 MM Bt u/hr equivalent energy is**  **considered to be $835,000. Cost of firing system conversion for other heat capacities was**  **estimated using 0.6 power rule:**

**This cost includes the PEC for installing a low NO X**  **burner. For each model plant described in Table 6-1 the PEC for the firing system conversi**  **on as well as for the multi-channel burner was determined based on the heat duty needed by the kil**  **n. For wet, long dry, and preheater kilns all the required heat is assumed to be provid**  **ed by the low NO X**  **burner, whereas for precalciner kilns only 60 percent of the heat duty is assu**  **med to be provided by the low NO X**  **burner at the hot end of the kiln. The capital costs for retrof itting the eight model plants in an**  **existing direct-fired kiln are given in Table 6-7. The capit al costs ranged from $1.21 million for**  **the small long dry kiln to $2.54 million for the large precalc iner kiln.** 

**The annualized costs for low NO X**  **burners in an existing direct-fired kiln are presented in Table 6-8. Operating labor was assumed to be 0.5 hour per 8-ho**  **ur shift. Maintenance labor costs were assumed to be 0.5 hour per 8-hour shift and mainten**  **ance materials were assumed to be equal to 100% of the maintenance labor cost. The total annu**  **alized costs for the eight low NO**  **X burner retrofits in existing direct-fired kilns ranged fro**  **m $241,000 for the small dry kiln to $439,000 for the large precalciner kiln. These values agree**  **well with the costs, of converting a direct fired kiln to an indirect fired kiln and installing a l**  **ow-NO X**  **burner, presented in the 1994 ACT.**  **18,22,23**

6.2.2.2 Mid-Kiln Firing **As discussed in Section 5.2.2.2, secondary combustion of fu el**  **reduces thermal NO X**  **formation in cement kilns. Modification of a long kiln for se condary**  **combustion of fuel is termed mid-kiln firing. The amount of f uel NO**  **X generated during the**  **secondary combustion determines the net effectiveness of t his technique for NO**  **X control. The**  **costs associated with this process are those for kiln modifi cations necessary to facilitate**  **secondary combustion of fuels as well as those for a conveyin g system required for the secondary**  **fuel. Mid-kiln firing is now a proven technology with twenty one cement kilns in the U.S. that**  **utilize mid-kiln firing. Costs were obtained from a vendor f or four scenarios representing two**  **wet kilns and two dry kilns. 4**  **Typically, the secondary combustion approach allows burni ng**  **waste-derived fuels and, as such, reduces the overall cost f or the fuel. The purchased equipment**  **cost for each of the four kilns is approximately $1.5 million . This cost includes approximately**  **$1.0 million for a completely automated system for injectin g tires or containerized solid or liquid**  **fuels and $500,000 for the modifications to the kiln. The cos t of a fuel conveying system can be**  **considerably lower for a semiautomatic, labor intensive sy stem and may be expected to depend to**  **a small extent upon the fuel conveying capacity needed. Cost s for mid-kiln firing are not**  **applicable to preheater or precalciner type kilns. 96** **TABLE 6-7. CAPITAL COSTS FOR RETROFIT LOW-NO X** **BURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)**Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heat duty(MMBtu/hr) PEC ($)Freightand salestax ($)Installation costs $Contingencycosts ($)ProductionDowntime($)Totalcapitalcosts ($)Direct Indirect**1 Wet 30 180 724,000 58,000 326,000 239,000 145,000 105,000 1,600,000 2 Wet 50 300 984,000 78,700 443,000 325,000 197,000 174,000 2,200,000** **3 Long dry 25 113 546,000 43,700 246,000 180,000 109,000 87,100 1,210,000 4 Long dry 40 180 724,000 60,000 326,000 239,000 145,000 139,000 1,630,000** **5 Preheater 40 152 655,000 52,400 295,000 216,000 131,000 139,000 1,490,000 6 Preheater 70 266 916,000 73,200 412,000 302,000 183,000 244,000 2,130,000** **7 Precalciner 100 330 767,000 61,400 345,000 253,000 153,000 348,000 1,930,000 8 Precalciner 150 495 978,000 78,300 440,000 323,000 196,000 523,000 2,540,000** **97 TABLE 6-8. ANNUALIZED COSTS FOR RETROFIT LOW-NO** **X BURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)** Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heat duty(MMBtu/hr)Maintenancecosts ($/yr)Operatinglabor ($)Overheadcosts ($/yr)Taxesinsuranceadmin.($/yr)Capitalrecovery($/yr)Totalannualizedcosts ($/yr)**1 Wet 30 180 24,300 12,700 22,200 63,900 175,000 298,000 2 Wet 50 300 24,300 12,700 22,200 88,100 242,000 389,000** **3 Long dry 25 113 24,300 12,700 22,200 48,500 133,000 241,000 4 Long dry 40 180 24,300 12,700 22,200 65,300 179,000 304,000** **5 Preheater 40 152 24,300 12,700 22,200 59,500 163,000 282,000 6 Preheater 70 266 24,300 12,700 22,200 85,200 234,000 378,000** **7 Precalciner 100 330 24,300 12,700 22,200 77,100 212,000 348,000 8 Precalciner 150 495 24,300 12,700 22,200 102,000 279,000 439,000** **98**

**Approximate capital investment costs were developed by ass uming a total of $1.5 million**  **purchased equipment cost for kiln modifications and the fue l conveying and metering system for**  **the four model plants. In this example approximately 15% of t he heat duty is from tire derived**  **fuel. This assumption results in a fuel credit (for the coal) as well as a tipping fee for the tires**  **(also a credit). Because the purchased equipment cost does n ot vary with the heat duty of the**  **kiln, the 0.6 power rule does not apply. Total capital invest ment was calculated using the**  **methodology presented in section 6.1. It should be noted tha t the costs estimated are higher than**  **the actual installation costs reported by the vendor.**

**The total capital costs for mid-kiln firing conversion of th e four wet and long dry model**  **kilns are given in Table 6-9. The total capital investment co sts range from $3.15 million for a**  **small long dry kiln to $3.24 million for a large wet kiln. The a nnualized costs for the mid-kiln**  **firing conversions are presented in Table 6-10. Operating l abor was assumed to be 0.5 hour per**  **8-hour shift. Maintenance labor costs were assumed to be 0.5 hour per 8-hour shift and**  **maintenance materials were assumed to be equal to 100% of the maintenance labor cost. The**  **annualized costs ranged from a credit of $370,000 for the lar ge wet kiln to a high cost of**  **$189,000 for the small long dry kiln.**

**These annualized costs were developed with a fuel credit (fo r the fuel that was replaced**  **with waste tires) as well as a tire tipping fee. In 1998 270 mil lion scrap tires were generated and**  **the estimates of tires in stockpiles range from 500 million t o 3 billion.**  **24 Although the tipping**  **fees for tires may decline as markets for used tires increase s, tire tipping fees are not likely to**  **disappear in the near future. In 1997, average national tipp ing fees for tires ranged from $20 to**  **$200 per ton (for whole tires). 5**  **The annualized cost of mid-kiln firing without a tire tippin g fee**  **(but including the fuel credit: assuming the tires or other w aste derived fuels are free) ranges**  **from $140,000 for the large wet kiln to a high cost of $380,000 for the small long dry kiln.** 

6.2.3 NO X Removal Controls

**Two NO X**  **removal controls that are demonstrated in the United States for cement kilns**  **are biosolids injection and NO X**  **OUT ®**  **. As discussed in Section 5.3.2, both of these technologies are only applicable to preheater/precalciner kilns. The ca**  **pital costs of this control technique primarily include the cost of an injection system for either**  **ammonia- or urea-based reagent, delivery system plus storage tanks, and control instrument**  **ation. Operating costs include the cost of reagents and additives used, additional electricity cos**  **t for reagent pumping, and fuel penalty cost along with operating labor and maintenance requiremen**  **ts.**

6.2.3.1 Biosolids Injection Process

. **As discussed in section 5.3.2.1, the biosolids injection process (which involves the injection of biosoli**  **ds into a precalciner kiln) reduces the NO**  **X that was formed in the kiln. Biosolids injection has been ins**  **talled on one kiln in Southern California and the costs of the installation were obtained f**  **or that facility. 3,25**  **The costs associated with installing this technology include the sludge system a**  **nd the sludge conveying system and 99** **TABLE 6-9. CAPITAL COSTS FOR MID-KILN FIRING CONVERSION (19 97 $)** Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heat duty(MMBtu/hr) PEC ($)Freightand salestax ($)Installation costs $Contingencycosts ($)ProductionDowntime($)Totalcapitalcosts ($)Direct Indirect**1 Wet 30 180 1,490,000 119,000 670,000 491,000 298,000 105,000 3,170,000 2 Wet 50 300 1,490,000 119,000 670,000 491,000 298,000 174,000 3,240,000** **3 Long dry 25 113 1,490,000 119,000 670,000 491,000 298,000 87,100 3,150,000 4 Long dry 40 180 1,490,000 119,000 670,000 491,000 298,000 139,000 3,210,000** **TABLE 6-10. ANNUALIZED COSTS FOR MID-KILN FIRING CONVERSIO N (1997 $)** Modelno.KilntypeKilncapacity(tonsclinker/hr)Heat duty(MMBtu/hr)Maintenance,other labor,and overheadcosts ($/yr)Taxes,insurance,admin.($/yr)Capitalrecovery ($/yr)Disposalrevenue($/yr)Fuel Credit($/yr)LicenceFee ($/yr)Totalannualizedcosts ($/yr)**1 Wet 30 180 59,200 127,000 348,000 (306,000) (300,000) 54,000 (14,600) 2 Wet 50 300 59,200 130,000 356,000 (510,000) (500,000) 90,000 (370,000)** **3 Long dry 25 113 59,200 126,000 346,000 (190,000) (185,000) 34,000 189,000 4 Long dry 40 180 59,200 128,000 352,000 (306,000) (300,000) 54,000 (9,340)** **100**

**are summarized in Table 6-11 use of this technology results i n a cost savings associated with the**  **tipping fees for the biosolids. The annual costs include ope rating labor (assumed to be 0.5 hour**  **per 8-hour shift), maintenance labor costs (assumed to be 0. 5 hour per 8-hour shift), maintenance**  **materials (assumed to be equal to 100% of the maintenance lab or cost), credit for the biosolids**  **tipping fee, and an electricity penalty of an additional 3% i ncrease in fan capacity. Biosolid**  **tipping fees range from $0.00 to $10.00 per wet ton. An averag e value of $5.00/ton was used in**  **this analysis.**

**TABLE 6-11. BASIS FOR COST ANALYSIS OF BIOSOLIDS INJECTION (1997 $)** 

**Purchased Equipment Cost $240,000**
**Type of Kiln Preheater/precalciner**
**Primary Fuels Coal and tire derived fuel**

**Kiln Production Rate 215 tons/hour**
**Quantity of Biosolids 20 tons/hour**
**Average kiln heat requirement**  **680 MMBtu/hour**

**Total Capital Investment $1,200,000**
**Annualized Cost ($322,000) a** 

**a Based on a biosolids tipping fee of $5.00/ton.** 

6.2.3.2 NO X OUT ®

. **As discussed in section 5.3.2.2, the NO X**  **OUT ®**  **process using either ammonia or urea to reduce NO**  **X emissions from cement kilns has been used successfully in**  **Europe. Two demonstrations of this technology 26,27**  **for application to cement kilns has been made in the United States but there are no cement kilns curren**  **tly operating in the United States using this technology. Costs for this technology were obtai**  **ned from the equipment vendor for two preheater/precalciner kilns and are summarized in Tabl**  **e 6-12. 28,29**  **The costs presented in Table 6-12 are consistent with values previously obtained a**  **nd presented in the** Alternatives Control Techniques Document – NO X Emissions from Cement Manufacturing. **30,31,32,33**

**In addition to the vendor costs and the published literature , cost analyses were available**  **from two facilities. 27,34**  **The presented costs for both of these installations were muc h higher than**  **the costs presented by the Vendor. It should be noted that the second facility has a long dry kiln**  **and NO X**  **OUT ®**  **is generally not recommended for a mid-kiln installation du e to the difficulties in**  **providing for continuous injection of the reagent. 101**  **TABLE 6-12. BASIS FOR COST ANALYSIS OF NO X**  **OUT ®**  **(1997 $)**

**Capital Cost of Material Handling Equipment**  **Kiln A Kiln B**

**Type of Kiln Preheater/precalciner Preheater/precalcine r** 

**Kiln Production Rate 92 tons clinker/hour 133 tons clinker/hour**
**Average kiln heat requirement**  **320 MMBtu/hour 440 MMBtu/hour**

**Total Capital Investment $1,060,000 $1,200,000**
**Annualized Cost $560,000 a**  **$2,000,000 a** 

**a Includes cost of reagent.** 

6.2.3.3 Selective Catalytic Reduction

. **Although no selective catalytic reduction (SCR) systems are currently being used on cement plants in the Unit**  **ed States, this control technique has been applied successfully in other industries and pilot pla**  **nt trials have been conducted in Europe. Capital costs for this control approach would include cost o**  **f the SCR unit, ammonia storage tank, and an ammonia heating/ vaporization injection syste**  **m along with equipment needed for preheating flue gases to an appropriate temperature. Opera**  **ting costs would include the cost of ammonia reagent, dilution steam, catalyst replacement and**  **disposal costs, and energy cost associated with reheating the kiln exhaust gases as well as t**  **he operating labor and maintenance**
**costs.**

**Since the SCR technology has not been proven in cement plants in the United States,**  **approximate capital and operating costs as applicable to th e model plants were not available from**  **any of the SCR control system vendors in the United States. Th e following information was first**  **presented in the 1994 ACT document and is repeated here. An eq uipment cost estimate of an**  **SCR system was submitted by a Japanese supplier to a cement co mpany in the United States in**  **1991. 35**  **For a dry long kiln with 1,120 tons/day (47 tons/hr) clinker c apacity, the estimated**  **equipment cost was 1 billion/Yen. With a 1992 exchange rate o f 108 Yen/$ and assuming 5**  **percent inflation, the estimated cost in 1992 U.S. dollars w as about 9.72 million. This equipment**  **cost estimate included SCR catalyst, SCR reactor, gas/gas h eat exchanger, heater, ammonia**  **injection grid, ammonia storage tank, ammonia vaporizer an d supply unit, induced draft fan,**  **instrumentation and all piping and ductwork. The reactor te mperature was assumed to be 350**   **C (660**   **F) and design NO X**  **removal efficiency was 80 percent. Since the reactor, heat e xchanger,**  **and gas heater design strongly depend upon the flow rate of fl ue gas to be treated, the equipment**  **costs for the model plants may be scaled based upon flue gas fl ow rate:** 



### PEC for model 1 **PEC for model 2 Gas flow for model 1**  **Gas flow for model 2** =       **0 6. 102** 

**Table 6-13 presents estimated capital costs for the eight mo del plants. Direct and indirect**  **installation costs were assumed to be 45 and 33 percent of PEC , respectively, and an additional**  **20 percent contingency cost was added to determine total cap ital cost for the SCR systems. The**  **estimated capital costs range from $9.9 million for the smal l dry long kiln to $24.6 million for**  **the large precalciner kiln.**

**The estimated annualized costs for SCR systems on the eight m odel plants are shown in**  **Table 6-14. These include operating labor and maintenance c osts, capital recovery, gas**  **reheating, ammonia reagent, and catalyst replacement cost s.**  **35,36 The individual operating costs**  **were obtained by appropriately scaling the vendor provided operating costs to the model plants.**  **The total annualized costs ranged from $2.5 million/yr for t he small long dry kiln to $7.2 million**  **for the large precalciner kiln.**

6.3 COST EFFECTIVENESS OF NO X CONTROLS

**Cost effectiveness for the model plants was determined for t hree technologies for which**  **detailed costs could be developed as presented in the last se ction: low NO**  **X burners (on an**  **existing indirect fired system and with conversion to an ind irect firing system), and mid-kiln**  **firing (with a credit for firing tires or just firing coal). L imited cost data are available for a**  **CemStar, biosolids injection, or NO X**  **OUT ®**  **installation in the U.S. Cost effectiveness was calculated by dividing the total annualized cost of a given t**  **echnology by the annual NO X**  **reduction likely to be achieved by that technology and is exp ressed in the units of $/ton of NO**  **X removed. Cost effectiveness was determined for each of the m**  **odel plant scenarios.**

6.3.1 CemStar

**As discussed in section 6.2.1.2, the costs of installing Cem Star were obtained from the**  **vendor for one kiln configuration (a wet kiln) at one facilit y. Data for other installations of**  **CemStar were not available for this report. The kiln capacit y was 42 tons clinker/hour prior to**  **the installation of CemStar and 45 tons clinker/hour after t he installation of CemStar. The**  **annualized cost for the conversion was calculated as $220,0 00. This annualized cost does not**  **include a credit for the increased production of clinker (ap proximately 3 tons/hour).**  **Uncontrolled emissions were calculated as approximately 1 600 tons NO**  **X /year. An average**  **emission reduction of 30% was determined for the installati on of CemStar which results in 100**  **tons NO X**  **/year. The cost effectiveness for this example facility was $550/ton of NO**  **X reduced.** 

6.3.2 Low NO X Burner

**The NO X**  **reduction that may be achieved with a low NO X**  **burner depends mainly on the operating parameters. In fact, no guarantee on the NO**  **X reduction level is usually provided by**  **burner vendors. With proper operation of the low NO X**  **burner, 15 to 40 percent reduction in NO**  **X emissions should be possible.**  **37 An average NO**  **X reduction efficiency of 25 percent was**  **used in determining controlled NO X**  **emissions and cost effectiveness of the low NO X**  **burner 103** **TABLE 6-13. CAPITAL COSTS FOR SCR PROCESS (1992 $) 38** Modelno. Kiln typeKiln capacity(tonsclinker/hr)Heat duty(MM Btu/hr) PEC ($)Freight andsales tax ($)Installation costsdirect andindirect ($)Contingencycosts ($)Total capitalcosts ($)**1 Wet 30 180 6,200 496,000 4,840,000 1,240 12,800 2 Wet 50 300 8,430 674,000 6,570,000 1,690 17,400** **3 Long dry 25 113 4,790 383,000 3,740,000 958 9,870 4 Long dry 40 180 6,350 508,000 4,950,000 1,270 13,100** **5 Preheater 40 152 5,820 466,000 4,540,000 1,160 12,000 6 Preheater 70 266 8,140 651,000 6,350,000 1,630 16,800** **7 Precalciner 100 330 9,400 749,000 7,310,000 1,870 19,300 8 Precalciner 150 495 11,900 956,000 9,330,000 2,390 24,600** **104 TABLE 6-14. ANNUALIZED COSTS FOR SCR(1992 $)** **38**Modelno. Kiln typeKilncapacity(tonsclinker/hr)Operatinglabor($/year)Ammoniareagentcosts($/year)Maintenance& overheadcosts ($/yr)Energyand fuelcosts($/year)Catalystcosts($/year)Taxesinsuranceadmin.($/yr)Capitalrecovery($/yr)Totalannualizedcosts ($/yr)**1 Wet 30 30,400 287,000 24,300 468,000 326,000 511,000 1,680,000 3,350 2 Wet 50 30,400 485,000 24,300 779,000 544,000 694,000 2,280,000 4,860** **3 Long dry 25 30,400 218,000 24,300 304,000 212,000 395,000 1,300,000 2,510 4 Long dry 40 30,400 337,000 24,300 487,000 339,000 523,000 1,720,000 3,490** **5 Preheater 40 30,400 238,000 24,300 421,000 293,000 480,000 1,580,000 3,090 6 Preheater 70 30,400 406,000 24,300 736,000 513,000 571,000 2,210,000 4,610** **7 Precalciner 100 30,400 337,000 24,300 930,000 649,000 772,000 2,540,000 5,300 8 Precalciner 150 30,400 505,000 24,300 1,400,000 974,000 985,000 3,240,000 7,180** **105**

**technology. For precalciner kilns, although only 60 percen t of the heat duty was assumed to be**  **provided by the low NO X**  **burners, all of the NO X**  **emissions were assumed to result from these burners. For existing direct-fired kiln systems, the costs**  **involved in conversion of the firing system increase the costs of NO**  **X removal considerably. Table 6-15 presents the uncontrolle**  **d and controlled NO**  **X emissions for the eight model plants along with the cost effe**  **ctiveness of low NO**  **X burner in an existing indirect-fired kiln. The cost effecti**  **veness were within a close range for the model plants and ranged from $300/ton of NO**  **X for the large wet kiln to $620/ton of NO**  **X for**  **the small long dry kiln.**

**Table 6-16 presents the cost effectiveness of low NO X**  **burner installed in an existing direct-fired kiln scenario. The cost effectiveness ranges**  **from $760/ton to $1,200/ton of NO X**  **removed. The cost of firing system conversion doubled the co st effectiveness as compared to**  **those in Table 6-15. The conversion from direct fired to an in direct firing system is expected to**  **reduce the energy requirement per ton of clinker. The energy savings associated with the**  **increased efficiency and productivity are not considered i n determining the cost effectiveness.** 

6.3.3 Mid-Kiln Firing of Tires

**The cost effectiveness for the four model plants are given in Table 6-17 which range from**  **a credit of $460/ton to a cost of $730/ton of NO X**  **removed. A NO X**  **reduction efficiency of 40 percent was calculated for wet kilns and 30 percent for long d**  **ry kilns. This cost effectiveness value includes a fuel credit for using waste-derived fuel an**  **d a tipping fee for the tires. If the tire tipping fee is removed (but the fuel credit is retained - assu**  **ming waste material is free), the cost effectiveness will range from $150/ton of NO**  **X to $680/ton of NO**  **X reduced.** 

6.3.4 Preheater/Precalciner Tire Derived Fuel

**Costs for installing a tire derived fuel system at a precalci ner kiln were obtained from one**  **facility. The purchased equipment and total capital invest ement costs were similar to the mid**  **kiln firing costs (the majority of the cost is in the tire hand ling system). Cost effectiveness for**  **this kiln is based on the annualized costs of ($1,600,000/ye ar), the emission reduction achieved**  **at that facility (emissions decreased approximately 30% fr om 3.4 lb/ton of clinker to 2.4 lb/ton of**  **clinker), a kiln capacity of 215 tons/hr, and an annual opera tion of 8,000 hr/yr. Cost**  **effectiveness is a credit of ($1,900/ton) for installing a t ire derived fuel system on this kiln. This**  **cost effectiveness value includes a fuel credit for using wa ste-derived fuel and a tipping fee for**  **the tires. If the tire tipping fee is removed (but the fuel cre dit is retained - assuming waste**  **material is free), the cost effectiveness is calculated as a credit of ($480/ton) of NO**  **X reduced.** **106 TABLE 6-15. COST EFFECTIVENESS OF RETROFIT LOW-NO** **X BURNERS IN AN EXISTING INDIRECT-FIRED KILN** **(1997 $)**Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heatduty(MMBtu/hr)UncontrolledNOXemissions(tons/yr)ControlledNOXemissions(tons/yr)NOXremoved(tons/yr)NOXreduction(%)Total annualizedcosts ($/yr)Cost effectiveness($/ton NOXremoved)**1 Wet 30 180 1,200 880 320 25 136,000 425 2 Wet 50 300 2,000 1,500 500 25 152,000 300** **3 Long dry 25 113 860 650 210 25 130,000 620 4 Long dry 40 180 1,400 1,000 400 25 141,000 350** **5 Preheater 40 152 940 700 240 25 140,000 580 6 Preheater 70 266 1,700 1,200 500 25 161,000 320** **7 Precalciner 100 330 1,400 1,000 400 25 173,000 430 8 Precalciner 150 495 2,000 1,600 400 25 204,000 510** **TABLE 6-16. COST EFFECTIVENESS OF RETROFIT LOW-NO X** **BURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)**Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heatduty(MMBtu/hr)UncontrolledNOXemissions(tons/yr)ControlledNOXemissions(tons/yr)NOXremoved(tons/yr)NOXreduction(%)Total annualizedcosts ($/yr)Cost effectiveness($/ton NOXremoved)**1 Wet 30 180 1,200 880 320 25 298,000 930 2 Wet 50 300 2,000 1,500 500 25 389,000 780** **3 Long dry 25 113 860 650 210 25 241,000 1,100 4 Long dry 40 180 1,400 1,000 400 25 304,000 760** **5 Preheater 40 152 940 700 240 25 282,000 1,200 6 Preheater 70 266 1,700 1,200 500 25 378,000 760** **7 Precalciner 100 330 1,400 1,000 400 25 348,000 870 8 Precalciner 150 495 2,000 1,600 400 25 439,000 1,100** **107 TABLE 6-17. COST EFFECTIVENESS OF MID-KILN FIRING** Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heatduty(MMBtu/hr)UncontrolledNOXemissions(tons/yr)ControlledNOXemissions(tons/yr)NOXremoved(tons/yr)NOXreduction(%)Total annualizedcosts ($/yr)Cost effectiveness($/ton NOXremoved)**1 Wet 30 180 1,200 700 500 40 (14,600) (29) 2 Wet 50 300 2,000 1,200 800 40 (368,000) (460)** **3 Long dry 25 113 860 600 260 30 189,000 730 4 Long dry 40 180 1,400 960 440 30 (9,300) (21)** **108**

6.3.5 Biosolids Injection

**One facility in the United States is currently using biosoli ds injection technology on one**  **preheater/precalciner kiln. Cost effectiveness for this k iln is based on the annualized costs of**  **($320,000/year), the emission reduction achieved at that f acility (emissions decreased from 2.4**  **lb/ton of clinker to 1.2 lb/ton of clinker), a kiln capacity o f 215 tons/hr, and an annual operation**  **of 8,000 hr/yr. Cost effectiveness is a credit of ($310/ton) for installing biosolids injection on**  **this kiln.**

6.3.6 Selective Noncatalytic Reduction

**NO X**  **OUT ®**  **is estimated to provide 40 percent NO X**  **reduction based on the available test data. Cost effectiveness for the two kilns described in sect**  **ion 6.2.3.2, using urea as the reagent, is based on an uncontrolled emission rate of 3.8 lb NO**  **X /ton of clinker, kiln capacities of 92 and**  **130 tons/hr respectively, annual operation of 8,000 hr/yr, and a NO**  **X control efficiency of 40%.**  **Cost effectiveness is $1,000/ton for the smaller kiln and $2 ,500/ton for the larger kiln.** 

6.3.7 Selective Catalytic Reduction

**The NO X**  **reduction that may be achieved with SCR technology depends u pon the reagent**  **stoichiometric ratio used, and the gas phase residence time in the SCR reactor. Although there**  **are no installations of the SCR technology in cement plants, 80 to 90 percent reduction in NO**  **X emissions has been achieved in SCR installations in other ap**  **plications such as utility boilers and gas turbines.**  **39 The SCR equipment costs developed in Section 6.2.2.2 were ba**  **sed upon SCR costs quoted for application on dry kiln exhaust gases with 8**  **0 percent design reduction in NO X**  **emissions. To determine the cost effectiveness of the SCR te chnology in cement kiln**  **applications, an 80 percent NO X**  **reduction efficiency was therefore assumed and the results are**  **shown in Table 6-18. The cost effectiveness ranged from $3,1 40/ton to $4,870/ton of NO**  **X removed and are almost five to six times greater than the corr**  **esponding values for the ammonia based SNCR technology.** **109 TABLE 6-18. COST EFFECTIVENESS OF SCR PROCESS** **38**Modelno. Kiln typeKilncapacity(tonsclinker/hr)Heatduty(MMBtu/hr)UncontrolledNOXemissions(tons/yr)ControlledNOXemissions(tons/yr)NOXremoved(tons/yr)NOXreduction(%)Total annualizedcosts ($/yr)Cost effectiveness($/ton NOXremoved)**1 Wet 30 180 1,160 230 930 80 3,351,000 3,600 2 Wet 50 300 1,940 390 1,550 80 4,864,000 3,140** **3 Long dry 25 113 860 170 690 80 2,506,000 3,630 4 Long dry 40 180 1,380 280 1,100 80 3,486,000 3,170** **5 Preheater 40 152 940 190 750 80 3,087,000 4,120 6 Preheater 70 266 1,650 330 1,320 80 4,610,000 3,490** **7 Precalciner 100 330 1,360 270 1,090 80 5,304,000 4,870 8 Precalciner 150 495 2,040 410 1,630 80 7,179,000 4,400** **110**

**1. Vatavuk, W.M. Cost Estimating Methodology. In: OAQPS Cont rol Cost Manual, Fifth**  **Edition, Vatavuk, W.M. (ed.). U.S. Environmental Protecti on Agency, Research Triangle**  **Park, NC. Publication No. EPA 450/3-90-006. January 1996.**

**2. Portland Cement Association.** U.S. and Canadian Portland Cement Industry: Plant Information Summary **. Skokie, IL. December 31, 1998. 214 pp.** 6.3.8 Summary of Cost Effectiveness

**Table 6-19 summarizes the cost effectiveness for the variou s technologies. Table 6-19**  **also presents the ozone season cost effectiveness. The ozon e season cost effectiveness is based**  **on the emission reduction that will be achieved in the 5 month ozone season (May-September).** 

**TABLE 6-19. SUMMARY OF COST EFFECTIVENESS**

**(1997 $/ton NO X**  **Reduced)**

**Technology Range of Annual**

**Cost Effectiveness Average Annual** 

**Cost Effectiveness Average Ozone** 

**Season Cost Effectiveness** 
**CemStar n/a 550 1,100**

**Low-NO X**  **Burners Indirect** 

**Fired Kilns 300 to 620 440 1,060** 

**Direct-Fired Kilns**  **760 to 1200 940 2,260**

**Mid-Kiln Firing (460) to 730 55 130**

**Tire Derived Fuel at a Precalciner**  **a (1,900)**  **b (1,900)**  **b (4,500)**  **b**

**Biosolids Injection n/a (310) b**  **(740) b** 

**NO X**  **OUT ®**  **1,000 to 2,500 1,740 2,160 N/A - not applicable**  **( ) - indicates a negative cost**

**a The purchased equipment and total capital investment costs**  **for a tire derived fuel installation on a precalciner are very similar to mid-kiln firing.** 

**b Represents a single installation.** 

6.4 REFERENCES**111**

**3. Battye, R., and S. Edgerton, EC/R Incorporated, Chapel Hil l, NC.**  Trip Report to Mitsubishi Cement Corporation, Cushenbury Plant, Lucerne Valley, CA, December 2, 1999. **Prepared for the U.S. EPA, RTP, NC, under contract No. 68-D-9 8-026, work**  **assignment No. 2-28. July 5, 2000.**

**4. Letter with attachments from Bramble, K.J., Cadence Envir onmental Energy Inc.,**  **Michigan City, IN, to W. Neuffer, U.S. EPA, RTP, NC. January 2 0, 2000. Cost of a**  **mid-kiln firing system.**

**5. Email from Joe Truini, Waste News to Lee-Greco, J., EC/R Inc orporated, Durham, NC.**  **July 28, 2000. Average tire tipping fees.**

**6. Waste News - Current Commodity Pricing. Website: (**  **http://www.wastenews.com/current2.html). Accessed on January 21, 2000.** 
**7. Cost of production downtime is based on clinker cost of $72.5 9 per short ton, 1997, from**  **the US Geological Survey Minerals Handbook and time loss of 2 days. Website:**  **(http://minerals.usgs.gov/minerals/pubs/commodity/c ement/170398.pdf), January 1998.** 

**8. Coal prices based on average price of coal delivered to othe r industrial plants by census**  **division and state, 1997, nominal dollars per short ton, fro m the U. S. DOE Energy**  **Information Administration. Website: (http://www.eia.doe.gov/cneaf/coal/cia/html/t94p01p**  **1.html), accessed on 5/22/2000.**

**9. Electricity prices based on U. S. Average Revenue per Kilow att-hour by Sector and Class**  **of Ownership, from the U. S. Energy Information Administrat ion/Electric Sales and**  **Revenue for 1997. Website: (http://www.eia.doe.gov/), ac cessed on 5/22/2000.** 

**10. Natural gas prices based on Average Price of Natural Gas Del ivered to U. S. Consumers**  **for 1997, from the U. S. DOE Energy Information Administrati on/Historical Natural Gas**  **Annual 1930 through 1997. Website: http://www.eia.doe.go v/), accessed on 5/22/2000.** 

**11. Letter with attachments from Bramble, K.J., Cadence Envir onmental Energy Inc.,**  **Michigan City, IN, to W. Neuffer, U.S. EPA, RTP, NC. January 2 0, 2000. Cost of a**  **mid-kiln firing system.**

**12. Hourly wage rates are based on the Bureau of Labor Statistic s website. Based on March**  **1997 dollars from Table 41. Website: (http://stats.bls.go v/ecthome.htm), accessed on**  **7/10/2000.**

**13. Letter and attachments from Willis, D.A., Blue Circle Ceme nt, Inc., Atlanta, GA, to**  **Damle, A.S., Research Triangle Institute. June 4, 1993. Inf ormation on LINKman**  **Process Control System. 112** 

**14. Battye, R., EC/R Incorporated, Chapel Hill, NC.** Trip Report to Texas Industries (TXI) Riverside Cement, Oro Grande facility, Oro Grande, CA, Dece mber 2, 1999. **Prepared for the U.S. EPA, RTP, NC, under contract No. 68-D-98-026, wo**  **rk assignment No. 2-28. August 31, 2000.** 

**15. Telecon. Neuffer, W., US EPA, Durham, NC and Mayes, G., TXI, Dallas, TX. March**  **24, 2000. Information on the CemStar Process.**

**16. Telecons. Lee-Greco, J., EC/R Incorporated, Durham, NC an d Mayes, G., TXI, Dallas,**  **TX. July 20 and 28, 2000. Additional information on the costs of installing CemStar.** 

**17. Electronic mail and telecon. Vaccaro, M., Pillard E.G.C.I ., Marseille, France with Lee**  **Greco, J., EC/R Incorporated, Durham, NC. July 26, 2000. Cos ts of low-NO**  **X burners.** 

**18. Letter from Denizeau, J., Lafarge Canada, Inc., Montreal, Quebec, Canada, to Crolius,**  **R.W., American Portland Cement Alliance, Washington, DC, A ugust 24, 1993. Cost of**  **low NO X**  **burners.**

**19. Letter and attachments from Bennett, J.H., California Por tland Cement, Glendora, CA to**  **Neuffer, W.J., U.S. EPA, RTP, NC. July 2, 1999. Cost of firing system conversion.** 

**20. PSM International, Inc.** Available Control Techniques for NO X Emissions from the Portland Cement Manufacturing Plant of California Portland Cement Company located in Colton, California. **Prepared by PSM International, Inc., Dallas, Texas for Cali fornia**  **Portland Cement, Glendora, CA. March 6, 1995. Heat input for Colton Plant kilns. pg.**  **12.**

**21. Battye, R., EC/R Incorporated, Chapel Hill, NC.** Trip Report to California Portland Cement Company, Colton Plant, Colton, CA, December 2, 1999. **Prepared for the U.S. EPA, RTP, NC, under contract No. 68-D-98-026, work assignme**  **nt No. 2-28. August 31, 2000.** 

**22. Letter and attachments from Novak, L.S., RC Cement Co., Inc ., Bethlemhem, PA, to**  **Crolius, R.W., American Portland Cement Alliance, Washing ton, DC, August 23, 1993.**  **Cost of firing system conversion.**

**23. Letter from Pap, E.S., Willis & Paul Group, Danville, NJ, to Stampf., Hercules Cement**  **Company, Stockerton, PA, April 6, 1988. Cost of firing syste m conversion.** 

**24. Scrap Tire Recycling. Consumer Energy Information: EREC R eference Briefs. Website:**  **(http://www.eren.doe.gove/consumerinfo/rebriefs/ee9 .html), accessed on 7/11/00.** 

**25. Biggs, H.O.** Biosolids Injection Technology: An Innovation in Cement Ki ln NO X Control. **Mitsubishi Cement Corporation, Lucerne Valley, CA. Receiv ed on December 2, 1999**  **during plant trip. 113** 

**26. Sun, W.H.** NO X OUT ® Process Demonstration on a Cement Kiln/Calciner - Ash Grove Cement - Seattle Plant - Seattle Washington. **October 28, 1993.**

**27. Letter and attachments Six, E.B., Spencer Fane britt & Brow ne LLP, Kansas City, MO to**  **P. Hamlin, Iowa Department of Natural Resources, Urbandale , IA.**  Lafarge Corporation Draft Construction Permit for Air Emission Source Plant # 82 -01-006, project # 96-494. **March 10, 1999. Attachment E - SNCR Data Analysis.**

**28. Lin, M.L., and M.J. Knenlein, Fuel Tech, Inc.** Cement Kiln NO X Reduction Experience Using the NO

X OUT ® Process **. Proceedings of 2000 International Joint Power Generation Conference, Miami Beach, FL., July 23-26, 2000.** 

**29. Telecon. Lee-Greco, J., EC/R Incorporated, Durham, NC and Knenlein, M.J., Fuel Tech,**  **Inc. August 17, 2000. Additional cost information for NO X**  **OUT ®**  **process.**
**30. Letter and attachments from Pickens, R.D., Nalco Fueltech , Santa Fe Springs, CA, to**  **Damle, A.S., Research Triangle Institute, October 15, 1992 . Nalco Fueltech's urea-based**  **SNCR technology.**

**31. Letter and attachments from Wax, M.J., Institute of Clean A ir Companies, Washington,**  **DC, to Damle A.S., Research Triangle Institute, December 7, 1992. Costs for application**  **of SNCR systems to cement kilns.**

**32. Letter from Seebach, M.V., Polysius Corporation, Atlanta , GA, to Willis, D., Blue Circle**  **Cement, Inc., Marietta, GA, June 18, 1993. Costs for Ammonia -based SNCR system.** 

**33. Kupper, D., and L. Brentrup.** SNCR Technology for NO X Reduction in the Cement Industry. **World Cement 23(3):4-9. March 1992.**

**34. PSM International, Inc., Dallas, TX and Penta Engineering Corporation, St. Louis, MO.**  Review of Nalco Fuel Tech NO X OUT ® program for Mid-Kiln Injection of urea to Reduce NO X at the Coloton California Plant of California Portland Ceme nt Company. **Prepared for California Portland Cement Company, Glendora, CA. Octo**  **ber 26, 1994**

**35. Letter and attachments from Akita, A., Hitachi Zosen Corpo ration, Tokyo, Japan, to**  **Kohl, R.F., Arizona Portland Cement Company, August 2, 1991 . Costs for an SCR unit**  **for Colton plant.**

**36. Letter and attachments from Bennett, J.H., California Por tland Cement Company,**  **Glendora, CA, to Neuffer, W.J., U.S. EPA, RTP, NC. March 16, 1 993. Costs for an**  **SCR unit for Colton plant.**

**37. Memo from Battye, R., and S. Walsh, EC/R Incorporated, Chap el Hill, NC to D. Sanders,**  **U.S. EPA, RTP, NC. Derivation and data supporting developme nt of cement plant NO**  **X emission rates. August 31, 2000.** **114**

**38. U.S. Environmental Protection Agency.** Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing **. EPA-453/R-94-004. Research Triangle Park, NC. March 1994.** 

**39. Smith, J.C., and M.J. Wax.** Selective Catalytic Reduction (SCR) Controls to Abate NOX Emissions. **White Paper sent by Wax, M.J., Institute of Clean Air Compani es.**  **September 1992.**United States Office of Air Quality Planning and Standards Publication No. EPA-457/R-00-002Environmental Protection Air Quality Strategies andStandards Division September 2000Agency Research Triangle Park, NC