NO X 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-15 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, 2000i 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 XEMISSIONS FROM CEMENT KILNS

........... 2 2.2 NO XCONTROL TECHNOLOGY FOR CEMENT KILNS

................. 4 2.2.1 Process Control Modifications

................................... 4 2.2.2 Combustion Modifications

..................................... 5 2.2.3 NO XRemoval Control

......................................... 6 2.2.4 NO XControl 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 XEMISSIONS

........................................ 29 4.1 MECHANISMS OF NO XFORMATION IN CEMENT MANUFACTURING

... 29 4.1.1 Thermal NO XFormation

..................................... 29 4.1.2 Fuel NO XFormation

........................................ 31 4.1.3 Feed NO XFormation

........................................ 32ii TABLE OF CONTENTS (continued)
4.2 FACTORS AFFECTING NO XEMISSIONS IN CEMENT MANUFACTURING

. 32 4.2.1 NO XFormation in the Kiln Burning Zone

........................ 33 4.2.2 NO XFormation 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 XEMISSIONS FROM CEMENT MANUFACTURING FACILITIES

................................... 36 4.4 REFERENCES

..................................................... 44
5.0 NO XCONTROL 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 XPrecalciners

................................ 64 5.2.2.3 Mid-Kiln Firing

...................................... 65 5.3 NO XREMOVAL 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 XCONTROL TECHNOLOGIES

.......... 76 5.6 REFERENCES

..................................................... 78
6.0 COSTS OF NO XCONTROL TECHNIQUES

................................... 84 6.1 COST CALCULATION METHODOLOGY

.............................. 84 6.1.1 Model Plants

............................................... 84 6.1.2 Capital Cost Estimation

....................................... 84iii 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 XCONTROL 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 XBurners

.................................... 91 6.2.2.2 Mid-Kiln Firing

...................................... 95 6.2.3 NO XRemoval 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 XCONTROLS

......................... 102 6.3.1 CemStar

.................................................. 102 6.3.2 Low NO XBurner

........................................... 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

.................................................... 110iv LIST OF TABLES Table 2-1. Summary of Updated Uncontrolled NO XEmissions Data and the Corresponding 1994 Act Document Estimates

................................. 3 Table 2-2. Comparison of 1994 Act Document and Current NO XControl 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 XEmissions Data Used to Develop 1994 Act Document

.................. 38 Table 4-3. Summary of Additional NO XEmission Data for Different Kiln Types

.......... 48 Table 4-4. Comparison of Emission Rates

......................................... 49 Table 4-5. NO XEmission Factors for Different Kiln Types

............................ 49 Table 5-1. Results of Short-term Cemstar Tests on a Preheater/precalciner Kiln

........... 56 Table 5-2. Results of Cemstar Tests on a Wet Kiln

.................................. 57 Table 5-3. NO XEmissions from a Precalciner Equipped with a Low-NO XBurner

.......... 60 Table 5-4. NO XEmissions Before and after Installation of Pyro-jet Low-NO XBurners

...... 61 Table 5-5. NO XEmissions with 3 Channel and Rotaflam ® Low-NO XBurners

............. 61 Table 5-6. Emissions Before and after Installation of a Rotaflam ® 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 XControl Techniques Summary from European Best Available Techniques Report 75 Table 5-10. NO XControl Techniques and Applicable Types of Cement Kilns

............. 76 Table 5-11. Comparison of 1994 Act NO XEmissions Reductions with Newly Available Emissions Data

......................................................... 77v LIST OF TABLES (continued)

Table 6-1. Cement Kiln Model Plants for Cost Calculations

........................... 85 Table 6-2. Capital Investment Components for Emission Control 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 XBurners in an Existing Indirect-fired Kiln

... 93 Table 6-6. Annualized Costs for Retrofit Low-NO XBurners in an Existing Indirect-fired Kiln 94 Table 6-7. Capital Costs for Retrofit Low-NO XBurners in an Existing Direct-fired Kiln

..... 96 Table 6-8. Annualized Costs for Retrofit Low-NO XBurners 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 Conversion

......................... 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 XBurners in an Existing Indirect-fired Kiln

................................................................ 106 Table 6-16. Cost Effectiveness of Retrofit Low-NO XBurners 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

....................................... 110vi LIST OF FIGURES Figure 3-1. Annual clinker production.

............................................ 15 Figure 3-2. United States and Canadian Portland Cement Locations (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 in gas from combustion sustained in air.

........................................................ 31 Figure 5-1. Schematic of low-NO Xburner.

......................................... 59 Figure 5-2. Schematic of preheater.

.............................................. 63 Figure 5-3. Schematic of precalciner.

............................................. 63 Figure 5-4. Reduction of NO Xemissions 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.

.................................. 711

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 the 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 document 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, including CemStar, low-NO Xburners, 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 visits at cement kiln facilities; contacts with control technology vendors, portland cement industry representatives, and state regulatory agencies; and a literature search. Additional information was obtained through seeking out useful sites on the internet.
1.3 ORGANIZATION Chapter 2 presents a summary of the findings of this study. Chapter 3 provides a description of the portland cement industry. Chapter 4 examines uncontrolled NO Xemissions. Chapter 5 presents an update on selected NO Xcontrol technologies. Chapter 6 presents an update on control costs and cost effectiveness.
1.4 REFERENCE FOR CHAPTER 12 2.0 SUMMARY This report addresses nitrogen oxides (NO X ) emissions from portland cement kilns and the current use, effectiveness, and cost of applicable control technologies. This chapter presents a summary of updated information on uncontrolled NO Xemissions from kilns and the applicability, effectiveness, and costs of NO Xcontrol technologies. Information that is summarized in this chapter is presented in greater depth in subsequent chapters. Section 2.1 includes a summary of current uncontrolled NO Xemissions data from the four kiln types. Section 2.2 summarizes NO Xcontrol technology emissions data. Section 2.3 presents a summary of updated control costs and cost effectiveness for these control technologies.
2.1 UNCONTROLLED NO X EMISSIONS FROM CEMENT KILNS In cement manufacturing, conditions favorable for formation of NO Xare reached routinely because of high process temperatures. Essentially all NO Xemissions associated with cement manufacturing are generated in cement kilns. In cement kilns, NO Xemissions 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 significant amount of nitrogen compounds which may lead to feed NO Xformation similar to fuel NO Xformation. Because of the high temperatures involved in the burning or clinker formation step, thermal NO Xformation provides the dominant mechanism for NO Xformation in cement manufacturing. There are four different types of cement kilns used in the industry: wet kilns, long dry kilns, kilns with a preheater, and kilns with a preheater/precalciner. All cement kiln systems contain a rotary kiln. The wet, long dry, and most preheater kilns have only one fuel combustion zone; whereas, the newer preheater/precalciner kilns and preheater kilns with a riser duct have two fuel combustion zones. Some precalciner kilns have a third combustion zone. Since the typical temperatures in the combustion zones are different, the factors affecting NO Xformation are also somewhat different in the different kiln types. In the primary combustion zone at the hot end of a kiln, the high temperatures lead predominantly to thermal NO Xformation; whereas, in secondary combustion zones lower gas-phase temperatures suppress thermal NO Xformation. In addition to the specific NO Xformation mechanisms, the energy efficiency of the cement making process is also important as it determines the amount of heat input needed to3

produce a unit quantity of cement. A high thermal efficiency would lead to less consumption of heat and fuel, and should produce lower NO Xemissions per ton of clinker, the product of the rotary kiln. EC/R obtained emissions data for cement kilns from state regulatory 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 summary 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 XEMISSIONS 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 Xemissions with significant overlap for different kiln types. The four different cement kiln types, however, do appear to have different levels of NO Xemissions and different characteristics influencing NO Xformation. Information used to calculate NO Xuncontrolled emission rates come from air emission tests at various cement manufacturing facilities in the United States. Twenty-two tests were used to calculate the AP-42 NO Xemission factors and all of the tests are over ten years old. In addition, the majority of these are short-term emissions tests, which do not capture the inherent variability of kiln NO X emissions. As a result, the AP-42 NO Xemission factors have a quality rating of “D” (relatively low quality - limited data, or highly variable). When one reviews the original data summarized in the 1994 ACT document, it is clear that the average emission 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 1994 ACT document NO Xemission rates are newer, these average emission rates may be more representative of modern kilns than the factors presented in AP-42. 4 Seven of the states that were contacted reported emissions in 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 hours/year at maximum production capacity. The resulting average emission rates are generally lower than the average emission4

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 actual kiln production values. Because of the uncertainty surrounding the production values for the state data and because the AP-42 data have a “D” rating, the 1994 ACT document values for uncontrolled NO Xemissions from cement kilns are used in this document. However, it should be noted that 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 Xemission values.
2.2 NO X CONTROL TECHNOLOGY FOR CEMENT KILNS
NO Xcontrol approaches applicable to the cement industry may be grouped in three categories: process modifications, where the emphasis is on increased energy efficiency and productivity; combustion control approaches, where the emphasis is on reducing NO Xformation; and NO Xreduction controls, which remove the NO Xformed in the combustion process.
2.2.1 Process Control Modifications Process modifications are usually done to reduce heat consumption, 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 operators, homogenizing raw material, ensuring uniform coal dosing, improving the cooler’s operation, and installing new equipment. Process modifications improve fuel efficiency, reduce operating costs, increase capacity and kiln operational stability. Since NO Xformation is directly related to the amount of energy consumed in cement-making, improving fuel efficiency and productivity will reduce NO Xemissions. Continuous monitoring of oxygen and carbon monoxide emissions in the cement kiln exhaust gases indicates the amount of excess air. At a given excess air level, NO Xemissions increase as the temperature of the combustion zone increases. A typical kiln combustion zone solids temperature range is about 1430 to 1540 E C (2600 to 2800 E F) for completion of clinkering reactions and to maintain the quality of the cement produced. 6 The corresponding gasphase temperature is usually greater than 1700 E C (3100 E F). 7 Maintaining the combustion zone temperature at the minimum necessary value would minimize both the process energy requirement and the NO Xemissions. Along with the appropriate temperature, it is also necessary 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 desired oxidizing conditions in the clinker burning zone. An experimental test on a cement kiln showed that by reducing excess air from 10 to 5 percent (i.e., reducing exhaust oxygen levels from 2 to 1 percent), NO Xemissions per unit time can be reduced by approximately 15 percent. 8 , 95

With state-of-the-art continuous emissions monitoring systems (CEMS) and feedback control, excess air can be accurately controlled to maintain a level that promotes optimum combustion and burning conditions in addition to lowering NO Xemissions. Reducing excess air levels also results in increased productivity per unit of energy consumed and thus results in an indirect reduction of NO Xemissions 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 modifications and combustion control measures are implemented simultaneously. Process modifications can reduce NO Xemissions in cement kilns without any specific NO Xcontrol equipment. Some plants rely on process monitoring and control and process modifications as a means to maintain NO Xemissions within their allowable limits. Although process controls will reduce NO Xemissions in poorly operated kilns, for the purposes of this document, such approaches are considered necessary for proper kiln operation and are not specifically considered as NO Xcontrol techniques, except as noted below for CemStar. One process modification that can be quantified is the CemStar process, which can reduce NO Xemissions 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 chemically very similar to clinker. Since many of the chemical reactions required to convert steel slag 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 thermal efficiency of the process both contribute to reduced thermal NO Xand carbon dioxide emissions. 10 CemStar is currently being used or is in the process of being incorporated at 11 cement facilities 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 sources, such as shale or clay. This process can decrease NO Xemissions by 30% and can also increase production by 15 percent. 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 focus on staging the combustion to minimize the amount of combustion that must occur at the maximum temperatures. This can be accomplished by modifying the way oxygen or fuel is provided for combustion.
Low-NO Xburner systems are available for all kiln types and rely on the staged combustion of air. Technical literature and industry publications report NO Xreduction rates of 23 to 47 percent with the installation of low-NO Xburners, depending on the baseline emissions, type of kiln, type of low-NO Xburner, and operating conditions. 11 , 12 , 13 , 14 , 15 In January 2000, the Portland Cement Association (PCA) and American Portland Cement Alliance (APCA) provided results of a survey of cement facilities where the respondents indicated 14% of the operating U.S. kilns have already installed a low-NO Xburner (81% of the facilities representing 81% of the operating U.S. kilns responded to the survey). 16 , 176

Staged combustion of fuel includes the use of preheaters/precalciners and mid-kiln firing. Mid-kiln firing of fuels is currently installed in 21 U.S. wet and long dry cement kilns, and whole tires are most frequently used for the mid-kiln fuel. Technical literature, industry publications, and state emissions data for several kilns that have used or tested mid-kiln firing demonstrate NO Xreductions 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 shown to decrease NO Xemissions by 30-40 percent. 25
2.2.3 NO X Removal Control
NO Xremoval controls destroy NO Xthat is formed in the combustion process. Selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) are two types of NO X removal controls. Biosolids injection technology is not technically 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 Xemissions from exhaust gases. SCR technology has not been used on any cement kilns in the United States, although pilot plant trials and feasibility studies have been conducted in Europe.
SNCR relies on the reduction of NO Xin exhaust gases by ammonia or urea without using any catalyst and can achieve NO Xemission reductions of 30 to 70 percent. This approach avoids the problems related to catalyst fouling, as in SCR technology, but requires injection of the reagents in the kiln at a temperature between 870 to 1090 E C (1600 to 2000 E F). At these temperatures urea decomposes to produce ammonia which is responsible for NO Xreduction. Because of the temperature constraint, SNCR technology is only 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, for 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 the 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 Southern 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. The mixing chamber offers the benefits of good residence time in the appropriate temperature window and high mixing effectiveness. Biosolids injection is achieving a 50 percent NO Xemission reduction at this facility.
2.2.4 NO X Control Efficiencies An assortment of industry data, literature, and professional publications, as well as some of the state data described above, was used to develop an estimate of emissions from cement7

kilns using NO Xcontrol technologies. Table 2-2 presents a summary of updated control technology emission rates alongside the emission estimates used in the 1994 ACT document. The new emissions rates are all within or very close to the ranges established in the 1994 ACT document. CemStar, a relatively new process that involves adding steel slag to the feed mix in a long kiln, was not discussed in the 1994 ACT document. Emission rate reductions from the use of CemStar averaged 33 percent. New data on low-NO Xburners 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 Xemissions from cement kilns and improved performance using mid-kiln firing technology has been obtained. 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. Additional information on SCR was not obtained during the development of this report. Chapter 5 contains a more detailed discussion of the NO Xcontrol technologies.
TABLE 2-2. COMPARISON OF 1994 ACT DOCUMENT AND CURRENT

NO XCONTROL 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

aOnly 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 reduction 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 effectiveness were determined for technologies for which detailed costs could be developed. Costs for low-NO Xburners and midkiln firing were developed for applicable model plants. Since 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 were not developed for model plants for purposes of this report. Costs for SCR were developed in the 1994 ACT document and are presented again in this report. The SCR costs have not been updated or revised. All of the capital and annualized operating costs developed for this report 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 Standards (EPA/OAQPS) Control Cost Manual. The cost of a commercially available kiln process control system, based on existing installations, is approximately $750,000. The resulting savings 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 reduced cost of producing cement is expected to recover process control installation costs in less than 2 years. Costs for CemStar were estimated for a long wet kiln. Approximate capital investment in 1997 dollars was estimated at $1,176,000 and annualized costs estimated to be $220,000. Cost savings associated with CemStar due to the resulting production 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 kilns because the amount of steel slag added is completely dependent on plant-specific variables. Biosolids injection has been installed on one kiln. The total 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. Total capital investment were $1.06 million and $1.2 million. The annualized costs for these kilns are $560,000 and $2,000,000 per year. Cost analysis was performed for low-NO Xburners and mid-kiln firing on up to eight different model kilns. Models 1 and 2 were wet kilns with 30 and 50 tons of clinker per hour (ton/hour) respective capacities, models 3 and 4 were long dry kilns with 25 and 40 ton/hour respective capacities, models 5 and 6 were preheater kilns with 40 and 70 ton/hour respective capacities, and models 7 and 8 were precalciner kilns with 100 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 Sources. 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 and cost effectiveness estimates is presented in Chapter 6.

TABLE 2-3. SUMMARY OF COST EFFECTIVENESS

(1997 Dollars/ton NO XReduced)
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 IndirectFired 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

aThe 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 REFERENCES10

3. Memo from Battye, R., and S. Walsh, EC/R Incorporated, Chapel Hill, NC to D. Sanders, U.S. EPA, RTP, NC. Derivation and data supporting development 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 October 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. Greening. 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 Oxides 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 for Process Control,” 27 th IEEE Cement Industry Technical Conference Proceedings, May 1985.
10. Andover Technology Partners. NO X Reduction from Cement Kilns Using the CemStar Process, Evaluation of CemStar Technology - Final Report to Texas Industries. 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 California . 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 Combustion 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 September 1995, on the proposed alternative NO XRACT 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. Neuffer, U.S. EPA. Results of PCA Survey - Preliminary NO XControl Technology Questionnaire. January 2000.
17. Letter from R. Battye and S. Edgerton, EC/R Incorporated, Chapel Hill, NC, to B. Neuffer, USEPA, RTP, NC. Summary of February 4, 2000 conference call on PCA Survey - Preliminary NO XControl Technology Questionnaire. February 11, 2000.
18. Walquist, C., Cadence Environmental Energy. “Cadence system leads to fall in NO X emissions,” World Cement , Dec 1997, pp. 26, 27.
19. Cadence Environmental Energy and Ash Grove Cement. “Mid-Kiln 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 Neuffer, EPA, Feb 8, 2000. Minutes from Dec 16, 1999 meeting with representatives from EPA and Cadence.
21. Texas Natural Resources Conservation Commission. A list of permitted NO Xlevels for cement plants in the state, CEMS data as reported by the facilities for 1994 - 1999, and information on the control technology in use at each facility.
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 Corporation.” 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 Waste 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) Reference Document on Best Available Techniques in the Cement and Lime Manufacturing Industries. Joint Research Centre, Institute for Prospective Technological Studies, Technologies for Sustainable Development, European IPPC Bureau, World Trade Center, Seville, Spain. March 2000.
29. Battye, R., and S. Edgerton, EC/R Incorporated, Chapel Hill, 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-98-026, work assignment No. 2-28. July 5, 2000.
30. Biggs, H.O., Plant Manager, Mitsubishi Cement Corporation. 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, its annual production rates, and the various manufacturing processes used. Process and operating parameters most influential for NO Xformation in the various processes are discussed. The cement industry is a vital industry for a modern society because cement is an essential ingredient in concrete. One need only mention reinforced-concrete walls and girders, tunnels, dams, and roads to realize the dependence of our society upon cement products. Hydraulic portland cement, the primary product of the cement industry, is made from clinker blended with gypsum. Clinker is produced by heating a mixture of limestone, clay, and other ingredients to incipient fusion at a high temperature. Limestone is the single largest ingredient required in the cement-making process, and most cement plants are located near large limestone deposits. Portland cement is used in almost all construction applications including homes, public buildings, roads, industrial plants, dams, bridges, and many other structures. In the cement-making process, the solid raw materials are heated to their fusion temperature, typically 1400 to 1500 E C (2550 to 2750 E F), by burning various fuels such as coal.Portland cement has been defined as “a hydraulic cement produced by pulverizing portlandcement clinker and usually containing calcium sulfate.” 1 Portland-cement clinker has been defined as “a clinker, partially fused by pyroprocessing, consisting predominantly of crystalline hydraulic calcium silicates.” 1 Burning an appropriately proportioned mixture of raw materials at a suitable temperature produces hard fused nodules called clinker which are further ground to a desired fineness. Five types of portland cement are recognized in the United States which contain varying amounts of the basic clinker compounds given 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 Xemissions from cement kilns.
3.2 TYPES OF CEMENT PRODUCED The five basic types of portland cement recognized and produced in the United States are described below. 2, 3 In addition, different varieties are prepared by using various blending formulations. 4 Type I portland cement is a normal, general-purpose cement suitable for all uses. It is used in general construction projects such as buildings, bridges, floors, pavements, and other precast concrete products. Type I is also known as regular cement and most commonly known as gray cement because of its color. White cement typically contains less ferric oxide and is used for special applications. There are other types of cements in 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- calcium silicate lattice. Type II portland cement generates less heat at a slower rate and 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 moderate sulfate action. Type IIA portland cement is identical to Type II and produces air-entrained concrete. Type III portland cement is a high-early-strength cement and causes concrete to set and gain strength rapidly. Type III is chemically and physically similar to Type I, except that its particles have been ground finer. It is made from raw materials with a lime to silica ratio higher than that of Type I cement. They contain a higher proportion of tricalcium silicate (3Ca0 @ Si0 2 ) than regular portland cements. Type IIIA is an air-entraining, high-early-strength cement. Type IV portland cement has a low heat of hydration and develops strength at a slower rate than other cement types, making it ideal for use in dams and other massive concrete structures where there is little chance for heat to escape. Type 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 tetracalcium 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 that will be exposed to severe sulfate action, principally where concrete is exposed to soil and groundwater with a high sulfate content. Type V portland cement are those which, by their composition or processing, resist sulfates better than the other four types. The use of air-entraining agents increases the resistance of the hardened concrete to scaling from alternate freezing and thawing. By adding these 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 ingredients: masonry cement, expansive cement, oil-well cement, etc. Masonry cements are commonly finely ground mixtures of15 Figure 3-1. Annual clinker production. 5 portland cement, limestone, and air-entraining agents. Granulated blast furnace slags and natural or artificial pozzolans are mixed and interground with portland 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 reached 393,000 metric tons. Although 42 cement companies produced clinker in 1998, the top 5 companies provided about 44.2 percent of the total finish grinding capacity. This is evidence of a high 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. Table 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 in terms of clinker capacity with Pennsylvania, Missouri, and Alabama rounding out the top five. 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 CorporationTABLE 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 CaliforniaTABLE 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 AlabamaTABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE (continued) (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 NevadaTABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE (continued) (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 states:
Alaska Connecticut Delaware Dist. of Columbia Hawaii Louisiana Massachusetts Minnesota New Hampshire New Jersey North Carolina North Dakota Rhode Island Vermont Wisconsin20Figure 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 percent using oil as the primary fuel. 5 The remaining 13.9 percent of the plants used other combinations, e.g. coal/waste as primary fuel. In 1998, 11 plants used waste as a primary fuel with 49 plants reporting 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 fineness,

• Subjecting the raw mix to pyroprocessing in a rotary kiln, and

• Grinding the resulting clinker to a fine powder. A layout of a typical plant is shown in Figure 3-3 which also illustrates differences between the two primary types of cement processes: wet process 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 efficiency of the cement plant. 6 Figure 3-4 is an illustration of a preheater/precalciner type of dry process system. 7 The choice between the wet or dry process for cement manufacturing often depends upon the moisture content in the raw feed materials mined from quarries. If the moisture content of the feed materials is already very high (15 to 20 percent), a wet process may be attractive. The recent trend, however, has been toward the dry process with preheater/precalciner systems. In 1998, about 20.6 million metric tons of clinker were produced 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 preheater system and 26.1 million metric tons were produced by facilities equipped with a precalciner system. 5 The different steps involved in the cement manufacturing process are described in the following subsections.
3.3.3 Raw Materials and Kiln Feed Preparation Calcium carbonate and the oxides of silicon, aluminum, and iron comprise the basic ingredients of cement raw mix. Because of the large requirement for calcium, the plants are generally located near the source of the calcareous material. The requisite silica and alumina may be derived from a clay, shale, or overburden from a limestone quarry. Such materials usually contain some of the required iron oxide, but many plants need to supplement the iron with mill scale, pyrite cinders, or iron ore. Silica may be supplemented by adding sand to the22 Figure 3-3. Steps in the manufacture of portland cement. 723 Figure 3-4. Preheater/precalciner cement kiln. 724

raw mix, whereas alumina can be furnished by bauxites and alumina-rich flint clays. 6 Industrial byproducts are becoming more widely used as raw materials for cement, e.g., slags contain carbonate-free lime, as well as substantial levels of silica and alumina. Fly ash from utility boilers can often be a suitable feed component, since it is already finely divided and provides silica and alumina. The bulk of raw materials originates in the plant quarry. A primary jaw or roll crusher is frequently located within the quarry and reduces the quarried 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 gases from the kiln or clinker cooler to dry wet material during crushing. Each of the raw materials is stored separately and proportioned into the grinding mills separately using weigh feeders or volumetric measurements. Ball mills are used for both wet and dry processes to grind the material to a fineness such that only 15 to 30 wt% is retained on a 74- F m (200 mesh) sieve. In the wet process the raw materials are ground with about 30 to 40 percent water, producing a well-homogenized mixture called slurry. Raw material for dry process plants is ground in closed-circuit ball mills with air separators, which may be adjusted for the desired fineness. Drying may be carried out in separate units, but most often is accomplished in the raw mill simultaneously with grinding. Waste heat can be utilized directly in the mill by coupling the raw mill to the kiln or clinker cooler exhaust. For suspension preheater-type kilns, a roller mill utilizes the exit gas from the preheater to dry the material in suspension in the mill. A blending system provides the kiln with a homogeneous raw feed. In the wet process the mill slurry isblended in a series of continuously agitated tanks in which the composition, usually the calciumoxide 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 longitudinal axis at 1 to 3 rpm. It is a countercurrent heating device slightly inclined to the horizontal 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 materials in succession as it passes upward toward the feed end. Refractory bricks of magnesia, alumina, or chrome-magnesite combinations line the firing end. In the less heat-intensive midsection of the kiln, bricks of lower thermal conductivity are often used. Abrasion-resistant bricks or monolithic castable linings are used at the feed end. 625

Pyroprocessing may be conveniently divided into four stages, as a function of location and temperature of the materials in the rotary kiln. 8
1. Evaporation of uncombined water from raw materials, as material temperature increases to 100 E C (212 E F);
2. Dehydration, as the material temperature increases from 100 E C to approximately 430 E C (800 E 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 E C (1650 E F) and 982 E C (1800 E F); and
4. Reaction, of the oxides in the burning zone of the rotary kiln, to form cement clinker at temperatures of approximately 1510 E C (2750 E F). The duration and location of these stages in an actual kiln depend upon the type of process used, e.g., wet or dry, and the use of preheaters and precalciners as discussed in the following section. It is desirable to cool the clinker rapidly as it leaves the burning zone. Heat recovery, preheating of combustion air, and fast clinker cooling are achieved by clinker coolers of the reciprocating-grate, planetary, rotary, or shaft type. Most commonly used are grate coolers where the clinker is conveyed along the grate and subjected to cooling 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 E C (700 to 1500 E F) at the hot end of cooler. A portion of the heated air serves as secondary combustion air in the kiln. Primary air is that portion of the combustion air needed to carry the fuel into 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 feed end first undergoes simultaneous heating and drying. The refractory lining is alternately heated by the gases when exposed and cooled by the slurry when immersed; thus, the lining serves to transfer heat as do the gases themselves. Large quantities of water must evaporated, thus most wet kilns are equipped with chains suspended across the cross section of the kiln to maximize heat transfer from the gases to the slurry. After most of the moisture has been evaporated, the nodules, which still contain combined water, move down the kiln and are gradually heated to about 550 E C (1022 E F) where the calcination reactions commence. The calcined material further undergoes clinkering reactions. As the charge leaves the burning zone and begins to cool, clinker minerals crystallize from the melt, and the liquid phase solidifies. The granular clinker material drops into the clinker cooler for further cooling by air. 6 Wet kilns typically represent an older cement technology with smaller capacity kilns. In the United States wet cement kiln capacities range from 77,000 to 1,179,000 metric tons/year with an average of 307,000 metric tons/year. 526

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 quantities of waste heat in the exit gases from such kilns were frequently used in boilers to generate electric power which often satisfied all electrical needs of the plant. In one modification, the kiln has been lengthened to nearly thelength of wet-process kilns and chains were added. The chains serve almost exclusively a heatexchange function. Refractory heat -recuperative devices, such as crosses, lifters, and trefoils, have also been installed. So equipped, the long dry kiln is capable 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 discussed in the next sections. 6 Long dry process kilns are generally of a smaller capacity compared to long wet kilns. In the United States dry cement kiln capacities range from 50,000 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 cyclones in a vertical arrangement where it is separated and preheated several times, typically in a four-stage cyclone system. The partially (40 to 50 percent) calcined feed exits the preheater tower into the kiln at about 800 to 900 E C (1500 to 1650 E F). The kiln length required for completion of the cement formation is considerably shorter than that of conventional kilns, and heat 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 condensation of alkalies and sulfur on the feed which sometimes results in objectionable high alkali and sulfur contents in the clinker. To alleviate this problem, some of the kiln exit gases can bypass 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 technology compared to the long dry kilns. They are also somewhat larger in production capacity than the long conventional rotary kilns. In the United States the preheater type kiln capacities 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 out 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 burns about 60 percent of the total kiln fuel. Most often coal is used as a fuel in a calciner furnace; however, almost any fuel may be used including chipped tires. The raw material is calcined 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 permits the use of smaller dimension kilns since only actual clinkering is carried out in the rotary kiln. Energy efficiency is even better than that of a preheater kiln, and the energy penalty for bypass of kiln exit gases is reduced since27

only about 40 percent of the fuel is being burned in the kiln. The 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 manufacturing technology and almost all of the newer cement plants are based on these designs. Precalciner kilns are also much larger in capacity than the conventional rotary kilns. The precalciner type kilns in the United States range from 449,000 to 1,580,000 metric tons/year with 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 average 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 subsequently mixed with 4 to 6 percent gypsum and introduced directly into the finish mills. These are large, steel cylinders [2 to 5 m (7 to 16 ft) in diameter] containing a charge of steel balls, 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 F m in diameter. This grinding may be accomplished by two different mill systems. In open-circuit milling, the material passes directly through the mill without any separation. A wide particle size distribution range is usually obtained with substantial amounts of very fine and rather coarse particles. Open circuit grinding is, however, rarely practiced in U.S. cement plants. In closed-circuit grinding, the mill product is carried to a cyclonic air separator in which the coarse particles 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 product is maintained by adjustments of composition, burning conditions, and finish grinding. Control checks are made for fineness of materials, chemical composition, and uniformity. 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 absorption, or flame photometry. Standard cement samples are available from the National Institute of Standards and Technology. Fineness of the cement is most commonly measured by the air permeability method. Finally, standardized performance tests are conducted on the finished 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 clinker cooler exhaust gases. Several small dust collectors are also installed at various dust emission points throughout the28

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 Association. 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. Greening. Kirk-Othmer Encyclopedia of Chemical Technology. Vol. 5. Fourth Edition. 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 Sources. Research Triangle Park, NC. January 1995. pp. 11.6-1 - 11.6-26. plant such as material transfer points and grinding operations. 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 States uses any flue gas treatment for reducing NO X , emissions.
3.4 REFERENCES29 4.0 UNCONTROLLED NO X EMISSIONS
4.1 MECHANISMS OF NO X FORMATION IN CEMENT MANUFACTURING In cement manufacturing, conditions favorable for formation of nitrogen oxides (NO X ) are reached routinely because of the high process temperatures involved. Essentially, all of the NO Xemissions associated with cement manufacturing are generated in the cement kilns. Although, there are other heating operations in a cement plant, such as drying of raw feed or coal, often the heat from the kiln exhaust gases is used for these operations making their contribution to NO Xemissions negligible. In cement kilns, NO Xemissions are formed during fuel combustion by two primary mechanisms:

• Oxidation of the molecular nitrogen present in the combustion air which is termed thermal NO Xformation, and

• Oxidation of the nitrogen compounds present in the fuel which is termed fuel NO X formation. Sometimes the raw material feed to the kiln may also contain nitrogen compounds which may lead to feed NO Xformation similar to fuel NO Xformation. Because of the high temperatures involved in the burning or clinker formation step, the thermal NO Xformation provides the dominant mechanism for NO Xformation in cement manufacturing. The term NO Xincludes 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 Xare, however, typically expressed in equivalent NO 2 form.
4.1.1 Thermal NO X Formation
Thermal NO Xis formed by the homogeneous reaction of oxygen and nitrogen in the gas phase at high temperatures. In the overall reaction mechanism proposed by Zeldovich, 2 the two important steps in NO formation are given as:
N 2 + O X NO + N k f

= 2 x 10 14 exp(-76500/RT) (4-1)
N + O 2 X 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 activation energy of reaction (4-1), 76.5 kcal/mol, means that this reaction is the most temperature 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 are lower than those for ambient conditions due to the lower O 2 concentration. The excess air used during fuel combustion can substantially affect NO formation by determining the amount 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 the 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 typical kiln solids temperatures of 1430 to 1480 E C (2600 to 2700 E F) as the corresponding gas-phase temperatures are on the order of 1650 E C (3000 E 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 E 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 source of thermal NO X , formation in cement kilns due to temperatures well above 1400 E C (2550 E F). In contrast, the fuel combustion temperature in a precalciner or in a kiln riser duct is well below 1200 E C (2200 E F), suppressing thermal NO Xformation. 4 Mainly fuel and feed NO Xmay 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 available oxygen concentration in the high temperature kiln burning zone are important parameters. Longer residence times at the high temperatures will allow the NO to be formed in the equilibrium quantities. Greater amounts of oxygen in the combustion zone will of course lead to greater amounts of NO formation. Once formed, the decomposition of NO at lower temperatures, although thermodynamically favorable, is kinetically limited. Thus, strategies to reduce NO Xemissions need to be based upon reducing formation of NO Xwhich may be achieved by reducing combustion temperature, oxygen 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 Xis 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 oiland natural gas have relatively low fuelbound 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 burned. The maximum possible fuel NO Xformation may be estimated from the fuel nitrogen content by assuming 100 percent nitrogen conversion. As discussed in section 4.3, the typical heat requirement for a wet process is estimated to be about 6 million Btu for a ton of clinker and the corresponding requirement for a dry process is estimated to be about 4.5 million Btu for a ton of clinker. Assuming an average heat requirement of 5.3 million 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, approximately 9.5 lb of NO (14.5 lb expressed as NO 2 ) would be produced per ton of clinker with 100 percent nitrogen conversion. Thus, even with only 10 percent conversion of coal nitrogen to 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 Xformed is difficult to identify separately from thermal NO Xas measurements indicate the overall NO Xformed. In general, however, thermal NO Xis 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 produced by coal burners. Thus, gas-fired kilns may be expected to produce greater thermal NO Xas compared to coal-fired kilns. Coal, on32

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 thus be expected to produce more fuel NO Xthan gas-fired kilns. A study of gas- and coal-fired kilns, however, clearly indicated that gas-fired, dry-process kilns typically produce almost three times more NO Xthan the coal-fired, dry-process kilns. 7 This fact indicates the dominance of thermal NO Xin overall NO Xformation.
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. Various 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 displaying noticeable kerogen contents. Since 100 ppm N in a kiln feed is equivalent to about 1 lb NO Xper ton of clinker (if it all converted), NO Xemissions from the kiln feed may represent a major source of NO Xfrom cement kilns. Nevertheless, it is probably less important than thermal NO Xand fuel NO Xin most cases. The same study indicated that conversion of feed nitrogen to NO Xoccurs mainly in the 300 to 800 E C (570 to 1470 E F) temperature range and depends upon the feed heating rate. 8 Rapid heating rates (~1000 E C flash heating) of the kiln feed mixtures were found to give much lower conversion efficiencies, whereas slow heating rates of kiln feed mixtures (~60 E C/min) gave fairly high conversion of about 50 percent of bound nitrogen to NO. These results were explained by assuming that the organic nitrogen must vaporize from the sample prior to oxidation if high conversion efficiencies to NO Xare to be achieved. If heating rates are rapid, "cracking" of these volatile compounds may occur in situ, and this may result in conversion of the bound nitrogen directly to N 2 before it comes into contact with gaseous oxygen, thus reducing the fraction converted to NO X . Such a hypothesis is also consistent with the observation that, during coal combustion, the involatile or "char" nitrogen is converted to NO Xmuch 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 used in the industry: wet kilns, long dry kilns, kilns with a preheater, and kilns with a preheater/precalciner. The wet and long dry kilns typically have only one fuel combustion zone, whereas the newer preheater and precalciner kiln designs have two or three fuel combustion zones: kiln burning zone, riser duct and precalciner. Because the typical temperatures present in the combustion zones are different, the factors affecting NO Xformation are also somewhat different in different kiln types and are discussed in the following sections. In addition to the specific NO Xformation mechanisms, the energy efficiency of the cement-making process is also important as it determines the amount of33

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 produce lower NO Xemissions.
4.2.1 NO X Formation in the Kiln Burning Zone In the kiln burning zone, thermal NO Xprovides the primary mechanism for NO X formation. Thermal NO Xformation depends upon the combustion zone temperature, the gasphase residence time and the oxygen concentration in the high 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 burners. 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 produce 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 Xformation. The firing system used in the kiln affects the proportion of primary and secondary combustion air. Direct firing systems introduce a large proportion of combustion air with the fuel being burned. This produces two conflicting effects for NO Xemissions: higher oxygen concentration or fuel lean combustion and lower gas temperature. Indirect firing systems on the other hand use only a small portion of combustion air to convey fuel and thus use less primary air. In general, direct fired systems may be expected to produce greater NO Xemissions compared to indirect fired systems. The majority of kilns in the United States are direct fired. The flame shape and the theoretical flame temperature are important factors in thermal NO Xformation as these factors determine the hottest points in the flame. A long "lazy" flame will produce less NO than a short intense flame. The flame shape 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 coal burning. The lower the secondary air temperature and the greater the dust content in 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 the burning zone (insufflation) may also reduce NO Xformation. With increasing excess air percentage, the NO Xformation 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 temperature.
Process conditions that can affect NO Xemissions substantially are: temperature stability, stability of raw mix feed rate, burnability of raw mix, and alkali and sulfur control. Temperature stability is important to maintain the quality of clinker and is achieved by stable-flame conditions and energy efficiency. Clinker formation reactions require temperatures of 2650 to 2800 E F (1450 to 1540 E C ) 10 and an oxidizing environment. Sometimes natural gas or liquid wastederived fuel is used to control flame conditions and improve clinker quality. The excess air used during combustion has a substantial influence on NO Xemissions. Oxygen levels of 4 to 5 percent in kiln exhaust gases would correspond to high NO Xemissions, whereas oxygen levels of34

only 0.5 to 1.5 percent would mean lower NO Xemissions. Thus, NO Xemissions 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 clinker formation reactions are exothermic and represent a dynamic process that requires constant operator adjustments which can vary NO X formation. The heating value of the fuel burned may also affect NO Xemissions. High heating value fuels, such as petroleum coke, require less combustion air and produce less NO Xper ton of clinker. Different raw material compositions require different burning conditions to maintain the quality of clinker produced. Thus, similar types of kilns with different feed materials may produce different levels of NO Xemissions. The alkali content of finished cement needs to be below a certain acceptable level. Low alkali requirements may require higher kiln temperatures and longer residence times at high temperatures to volatilize 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 produce greater NO Xemissions. Increased volatilization of alkali results in increased alkali emissions in kiln exhaust gases. To control 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 particulate matter collector. This alkali-rich particulate matter is removed from the process and disposed. The bypass of kiln exhaust gases typically involves a fuel penalty, e.g., about 20,000 Btu/ton of clinker for every 1 percent gas bypass. The additional heat requirement will contribute to increased NO Xemissions. 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 production. On the other hand, the greater amount of combustion air will also mean a somewhat lower secondary air temperature. Based on these contradicting factors, one might expect the NO Xemissions from a wet process kiln to be similar to the dry and preheater kilns without riser 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 E C (1500 to 2000 E 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 compounds in the fuel. 1 Reaction (4-3) shows that NO formation in the secondary firing zone will depend upon the nitrogen content in the fuel and the oxygen level in the firing zone. Reaction (4-4) indicates that, if there is already35

NO present in the gas introduced into the secondary firing zone, a reduction of this NO may occur with the fuel nitrogen compounds acting as reducing agents. 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 that the volatile content in the solid fuel and the temperature in the secondary firing zone also influence the NO formation in the secondary firing zone. 11 With increased volatile content in the fuel, the ratio of fuel nitrogen conversion into NO seems to decrease and, as the reaction rate 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 Xformation. 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 duct. The preheater systems are more energy efficient compared to long dry kilns. The increased energy efficiency and the reduction in the amount of fuel burned at the higher clinker burning temperature may be expected to reduce the NO Xemissions from preheater kilns when compared with the long dry and wet kilns. Measurements at several riser-duct fired kiln systems indicate that firing coarse fuel (e.g., tires) into the kiln riser duct will reduce NO Xemissions from the kiln systems. 12 This may be explained by the fact that a large part of the fuel falls directly down into the kiln charge, creating a reducing atmosphere in the kiln back-end where NO Xfrom the burning zone is reduced. Conversely, when firing finely ground fuel into the kiln riser duct, the NO Xcontent in the exhaust gas may increase on passing through the riser duct. As the NO Xemissions from the kiln may also increase slightly due to an increased excess air rate, the total NO Xemissions from the kiln system may increase when starting up riser duct firing with 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 from 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 and the substantial reduction in the proportion of the fuel burned at clinker burning temperatures may be expected to reduce the NO X emissions from the precalciner kilns as compared to the preheater kilns. On the other hand, the NO Xconcentration (in ppm) in the kiln gas may be considerably higher than in preheater kilns. This is probably due to the shorter material and longer gas retention times in the precalciner kiln burning zone combined with a very high secondary air temperature. 1 When examining the contribution from the calciner firing to the emission of NO X , two basically different types of precalcining kiln systems need to be considered:

• The in-line (ILC) type in which the kiln gas passes through the firing region of the precalciner, and36

• The separate line (SLC) type in which the kiln exhaust gas bypasses the firing region of the precalciner. ILC systems: In these systems, the fuel combustion in the calciner takes place in a mixture of the kiln exhaust gas and hot air from the cooler (tertiary air). Some of the nitrogen in the fuel reacts with NO from the kiln exhaust gas while another part reacts with oxygen to form NO. The result may be a net increase or a net reduction of NO in the calciner. SLC systems: In these systems, the fuel combustion in the calciner takes place in pure hot air. In the case of oil firing, NO production in the calciner is negligible; but when using fuels containing fuel-bound nitrogen, up to 50 percent of the nitrogen 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 Xper ton of clinker as measured in a calciner fired with petroleum coke which has a high nitrogen content and low volatile content. 1 The NO Xin the calciner exhaust gas is added to the NO Xin the gas from the rotary kiln which leaves this type of kiln system without being reduced. When fired with solid fuels, SLC systems may therefore be expected to generate somewhat higher NO Xemissions than the ILC systems. 1
4.2.3 Energy Efficiency of the Cement-Making Process
Since NO Xformation is directly related to fuel combustion, any reduction in the amount of fuel burned per unit amount of clinker produced should reduce NO Xemissions per unit clinker. Attempts to improve energy efficiency of the process by avoiding excessive clinker burning and utilizing waste heat effectively for preheating combustion air, coal, and raw mix is likely to reduce NO Xemissions. Improving heat transfer between hot gases and solid materials, e.g., by chain systems, will improve energy efficiency. The newer preheater and precalciner kilndesigns provide very efficient preheating and precalcining of the raw mix with intimate gassolids contact in cyclone towers. New cement kiln installations or renovations of older kilns thus predominantly involve precalciner designs for their energy efficiency. The inherent energy efficiency of these kiln designs is likely to produce less NO Xemissions 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 exhibit different combustion characteristics as well as energy efficiencies and heat requirements. The available NO X emissions data are therefore generally grouped by these cement kiln types. In January 1995, EPA published a revised AP-42 section for Portland Cement Manufacturing. 13 The revised NO Xemission factors adopted for the AP-42 document for the same four kiln types mentioned above are: 7.4 lb/ton of clinker for wet process kilns, 6.0 lb/ton of clinker for dry process kilns, 4.8 lb/ton of clinker for kilns with preheaters, and 4.2 lb/ton of1 A = Tests are performed by a sound methodology and are reported 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 lacking a significant amount of background information.D = Tests are based on a generally unacceptable method, but the method may provide an orderof-magnitude value for the source.

2 Waste Derived fuels can include scrap tires.
37 clinker for kilns with precalciners. These emission factors were developed from 23 references. All 23 references are over ten years old and primarily represent 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 first step is an appraisal of data quality, the reliability of the basic emission data that will be used to develop the factor. The second step is an appraisal of the ability of the factor to stand as a national annual average emission factor for that source activity. All of the AP-42 NO Xemission factors have a “D” rating which is below average. A “D” rating means the factors were developed from A-, B-, and/or C - rated test data from a small number of facilities, and there may 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 Xemissions data were collected from major cement companies in the United States. Out of 51 cement kilns providing NO Xemissions data, 22 were from wet kilns, 10 were from long dry kilns, 10 were from preheater kilns, and 9 were from precalciner type cement kilns. Table 4-2 presents the NO Xemissions data along with the kiln types and fuels burned. As seen from Table 4-2, in general, wet kilns were found to produce 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 different 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 cases, high secondary combustion air temperatures were present with high NO Xemission rates. Twelve of the wet kilns reported burning WDFs 2 in significant quantities. Five of these kilns used "mid-kiln" firing of the solid and liquid waste fuel and the other seven kilns injected liquid 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 XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

1. 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 14TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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

16TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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 18TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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 18TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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 PreheaterPrecalciner 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

20TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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 

### 24TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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 PreheaterPrecalciner 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 27TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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 28TABLE 4-2. NO XEMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)

Location Kiln # Kiln type Capacity (tons/hr) Fuel burned Heat in MM Btu/ton NO X emissions

(lb/ton clinker) Method and

date of data Reference

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 PreheaterPrecalciner 80 75% - Coal 12% - LWDF 13% - SWDF 3.6 7 CEM Jan-91 2947

The kilns with mid-kiln firing reported much greater NO Xemissions ranging from 9 to 18.3 lb/ton of clinker, whereas other waste-fuel burning wet kilns reported much lower NO X emissions ranging from 3.6 to 8.1 lb NO X/ton of clinker. NO Xemissions data from these kilns prior to introducing waste fuels, however, were not available to directly assess the effect of waste fuel burning on NO Xemissions. The-long dry kilns consume significantly less energy than wet kilns (about 4.5 MM Btu/ton on average) and produce less NO Xemissions 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 Xemission rates may thus be attributed to the difference in the energy consumption rates 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 energy consumption of preheater kilns was much lower, about 3.8 MM Btu/ton. In addition, combustion of a part of the fuel at a lower preheating temperature is expected to reduce the NO Xemissions as compared to burning all the fuel in the hot kiln burning zone. These two factors account for the lower NO Xemissions in preheater kilns as compared to wet or long dry kilns. The precalciner kilns produced the least NO Xemissions 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 with an average energy consumption of 3.3 MM Btu/ton of clinker. Precalciner kilns have lower NO Xemission rates because they burn more fuel at the calcining temperature. There have been many changes in the six years since the 1994 ACT document was published. One of the most interesting from an emissions estimation 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 the respondents indicated 46% of the operating U.S. kilns (74 kilns) have already installed a CEMS (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 Xmeasurements at closely spaced intervals. These measurements are accumulated and averaged by a process control computer at preset time intervals. CEMs data provide a better estimation of average NO X emissions from cement kilns than do short-term tests because of the high degree of variability in NO Xemissions and autocorrelation between sequential NO Xmeasurements. 32 Eight state air pollution control agencies were asked to provide NO Xemissions data for their kilns. These data were supplemented with additional test 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 state agencies are primarily from CEMS and are the reported annual emissions for the facilities. Most of the states did not report production values (because they tend to be confidential) so kiln capacities 5 were used to48

determine emission rates. The kilns were also assumed to operate for an average of 8,000 hours per year. In addition, most of the state agencies did not provide additional information on any NO Xcontrol measures that may have been implemented (e.g., low-NO Xburners). 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 of using kiln capacities rather than actual kiln production values but may also be a result of assumptions regarding the installation of NO Xcontrol devices (approximately 14% of the operating U.S. kilns have installed low-NO X burners - see section 5.2.1.2). 30,31

TABLE 4-3. SUMMARY OF ADDITIONAL NO XEMISSION 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 substantial spread in the reported NO X emissions with significant overlap for different kiln types. Table 4-4 compares the NO Xemission rates from the 1994 ACT document, AP-42, and the data recently collected from the State air agencies. The four different cement kiln types, however, do appear to have different levels of NO Xemissions and different characteristics influencing NO Xformation. As shown, the rates calculated from the State data are generally lower that the values calculated during development of the 1994 ACT document. The new data are not necessarily more representative than the 1994 ACT document data. The lower rates derived from the new data probably result from the assumptions made regarding kiln production and level of NO Xcontrol. It should be noted that the lower emission rates derived from the new data for preheater kilns relative to precalciner kilns is contrary to expectation and could be due to the lack of data points for preheater kilns. The AP-42 factors are also lower than the 1994 ACT document rates but are primarily based on short term emission tests, which do not capture the inherent variability of kiln NO Xemissions, and the data are all over 10 years old. When one reviews the original data summarized in the 1994 ACT document, the maximum or minimum NO Xemission rate for a specific kiln type is about equally greater or less than the calculated average. Because the data used to calculate the 1994 ACT document NO Xemission rates are newer, these average emission rates may be more representative of modern kilns than the factors presented in AP-42. 3449

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 used in estimating uncontrolled emissions from typical cement kilns because these data are newer and include more CEMS data than the data used in AP-42; the NO Xemission rates derived in AP-42 have a “D” quality rating (based on number of tests and variability of emissions from the process); and the data collected from the state agencies are less certain because 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 correlation with the NO Xemission rates.

TABLE 4-5. NO XEMISSION 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 REFERENCES50

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 Workshop. 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 X10. 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 Point 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 Cement Company, to Neuffer, W.J., U.S. Environmental Protection Agency. August 25, 1992. Response to questionnaire on NO Xemissions data.51

15. Letter and attachments from Willis, D.A., Blue Circle Cement, Inc., to Neuffer, W.J., U.S. Environmental Protection Agency. October 2, 1992. Response to questionnaire on NO Xemissions data.
16. Letter and attachments from Bennett, J., California Portland Cement Company, to Neuffer, W.J., U.S. Environmental Protection Agency. November 17, 1992. Response to questionnaire on NO Xemissions data.
17. Letter and attachments from Ellison, J.E., Calaveras Cement Company, to Neuffer, W.J., U.S. Environmental Protection Agency. August 31, 1992. Response to questionnaire on NO Xemissions data.
18. Letter and attachments from Hackett, H.P., Holnam, Inc., to Jordan, B.C., U.S. Environmental Protection Agency. August 28, 1992. Response to questionnaire on NO X emissions data.
19. Letter and attachments from Gandy, M., Lafarge Corporation, to Jordan, B.C., U.S. Environmental Protection Agency. August 20, 1992. Response to questionnaire on NO X emissions data.
20. Letter and attachments from Smith, M.G., Lafarge Corporation, to Jordan, B.C., U.S. Environmental Protection Agency. August 26, 1992. Response to questionnaire on NO X emissions data.
21. Letter and attachments from Smith, R.G., Lafarge Corporation, to Jordan, B.C., U.S. Environmental Protection Agency. July 31, 1992. Response to questionnaire on NO X emissions data.
22. Letter and attachments from Johns, T., Lafarge Corporation, to Jordan, B.C., U.S. Environmental Protection Agency. August 13, 1992. Response to questionnaire on NO X emissions data.
23. Letter and attachments from Wallace, W., Lafarge Corporation, to Jordan, B.C., U.S. Environmental Protection Agency. August 14, 1992. Response to questionnaire on NO X emissions data.
24. Letter and attachments from Collins, B., Lafarge Corporation, 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 Corporation, to Jordan, B.C., U.S. Environmental Protection Agency. August, 1992. Response to questionnaire on NO X emissions data.52

26. Letter and attachments from Harris, M.D., Lafarge Corporation, to Jordan, B.C., U.S. Environmental Protection Agency. September 1, 1992. Response to questionnaire on NO X , emissions data.
27. Letter and attachments from Matz, T.L., Lehigh Portland Cement Company, to Neuffer, W.J., U.S. Environmental Protection Agency. October 27, 1992. Response to questionnaire on NO Xemissions data.
28. Letter and attachments from Johnson, R.M., Lone Star Industries, to Jordan, B.C., U.S. Environmental Protection Agency. October 9, 1992. Response to questionnaire on NO X emissions data.
29. Letter and attachments from Gill, A.S., Southdown, Inc., to Neuffer, W.J., U.S. Environmental Protection Agency. December 3, 1992. Response to questionnaire on NO X emissions data.
30. Email transmission from Hawkins, G., PCA, Skokie, IL to B. Neuffer, 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, Chapel 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 XEmissions 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. Sanders, 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 October 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 thermal NO Xis a function of the flame temperature, flame turbulence, the amount of nitrogen and oxygen available for the thermal reaction, and the gas phase residence time at high temperature. To reduce the amount of thermal NO Xformed, one or more of these variables needs to be minimized. The formation of fuel and feed NO Xis not as well understood as the thermal NO Xformation. In general, however, the greater the concentration of nitrogen in the fuel and feed, the greater the fuel NO Xemissions. Therefore, reducing the amount of fuel and feed-bound nitrogen should reduce the contribution of the fuel and feed NO X . The typical NO Xemissions from a cement plant depend upon the type of the cement kiln as shown in Table 4-6. For any given type of kiln, the amount of NO Xformed is directly related to the amount of energy consumed in the cement-making process. Thus, measures that improve the energy efficiency of this process should reduce NO Xemissions in terms of lb of NO X/ton of clinker. With the rising costs of energy and the very competitive cement market, greaterattention is being paid to increasing overall energy efficiency, such as through reduction of overburning of clinker and improvement in gas-solids heat transfer. Continuous emissions monitoring of CO, NO X , and O 2 provide an indication of kiln conditions and also provide inputs for process control. Newer cement kiln designs are generally based on preheater/precalciner systems which provide very efficient gas-solids contact and greater energy efficiency.
NO Xcontrol approaches applicable to the cement industry may be grouped in three categories:
1. Process modifications where the emphasis is on increased energy efficiency and productivity (section 5.1);
2. Combustion control approaches where the emphasis is on reducing NO X formation (section 5.2); and
3. NO Xreduction controls which remove the NO Xformed in the combustion process (section 5.3). Section 5.4 provides a discussion of the technologies supporting the recent selection of Best Available Techniques (BAT) for NO Xcontrol at European cement kilns. Section 5.5 gives a summary of the applicable NO Xcontrol technologies, and section 5.6 provides the references 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 increase the lifetime of the equipment (such as the refractory lining) by stabilizing process parameters. Reduction of emissions, such as NO X , SO X , and dust, are secondary effects of these modifications. Smooth 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 instruction and training of the kiln operators, homogenizing raw material, ensuring uniform coal dosing, improving the cooler’s operation, and installing new equipment. Process modifications are primarily done to reduce operating costs, increase capacity, and improve product quality. Adopting process modifications usually results in a reduction of operating costs for a kiln. The savings result from reduced fuel and refractory consumption, lower maintenance costs, and higher productivity, among other factors. 1 This section describes process modifications that improve fuel efficiency and kiln operational stability with an emphasis on reducing NO Xformation. Since NO Xformation is directly related to the amount of energy consumed in cement-making, improving fuel efficiency and productivity will reduce NO Xemissions.
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 level, NO Xemissions increase as the temperature of the combustion zone increases. A typical kiln combustion zone solids temperature range is about 1430 to 1540 E C (2600 to 2800 E 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 E C (3100 E F). 3 Maintaining the combustion zone temperature at a necessary minimum value would minimize both the process energy requirement and the NO Xemissions. Along with the appropriate temperature, it is also necessary 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 exhaust oxygen level, typically the kiln operators strive for an oxygen level of 1 to 2 percent to guarantee 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 exhaust oxygen levels from 2 to 1 percent) NO Xemissions per unit time can be reduced by approximately 15 percent. 4 , 5 With state-of-the-art continuous emissions monitoring systems (CEMS) and feedback control, excess air can be accurately controlled to maintain a level that promotes optimum combustion and burning conditions in addition to lowering NO Xemissions. Reducing excess air level also results in increased productivity per unit amount of energy consumed and thus results in an indirect reduction of NO Xemissions per unit amount of clinker product.55

5.1.2 Feed Mix Composition Heat requirements for producing clinker are dependent on the composition of the raw feed which varies among cement plants. Experiments have demonstrated 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 input per ton of clinker, less fuel is burned and less NO Xper unit product is produced. This approach of changing the feed composition may, however, be highly site specific and may not 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 below a certain acceptable level. Low alkali requirements need higher kiln temperatures and longer residence times at high temperatures to volatilize the alkali present in the semi-molten clinker. Raw materials with greater alkali content need to be burned longer at higher temperatures to meet alkali requirements and thus may produce greater NO Xemissions. Increased volatilization of alkali also results in increased alkali emissions in kiln exhaust gases. To control 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 particulate collector. The bypass of kiln exhaust gases typically involves a fuel penalty, e.g., about 20,000 Btu/ton of clinker for every 1 percent gas bypass. The additional heat requirement may also contribute to increased NO X emissions; thus, reducing the alkali content of the raw feed mix may contribute to a reduction in the NO Xemissions.
5.1.2.2 CemStar Process

. Another feed modification that can reduce NO Xemissions is the addition of a small amount of steel slag to the raw kiln feed. This patented technique 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 chemical reactions required to convert steel slag 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 thermal efficiency of the process both contribute to reduced thermal NO Xand CO 2 emissions. 7 Eleven facilities are using or in the process of incorporating CemStar. 8 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 sources, such as shale 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 CemStar process reduces the kiln material temperature in the region of the flame by an average of 200 E F (from 2610 E F to 2405 E F); the lower gas temperature of the flame results in lower NO Xemissions. 9 Another test56

of CemStar technology found an average reduction in burn zone temperature of 160 E F, a six percent reduction. 9 The amount of NO Xemissions 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 Xemissions 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 without 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 emission 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 Xemissions would have less NO Xreductions with CemStar than those with higher baseline emissions. Wet and long-dry kilns would have greater NO Xreductions with CemStar because more energy is used per ton of clinker produced than preheater/precalciner kilns. Wet kilns may achieve the greatest NO Xreductions 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. 757 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 ndtest test 1 = 36 test 2 = 55 Long-Term Test Without CemStar 5.23 no 2 ndtest

- With CemStar 4.00 no 2 ndtest 24

a Percent reductions are relative to the emissions rate without CemStar during the same test period.
5.1.3 Kiln Fuel Changing the primary kiln fuel from natural gas to coal can reduce the flame temperatures significantly, resulting in lower thermal NO Xemissions. 10 , 11 Although nitrogen present in coal may provide greater fuel NO Xcontribution, switching the fuel burned in kilns from natural gas to coal has been shown to provide substantial reduction in the total NO Xemissions in one experimental study. 10 In the dry process kilns tested in this study the average NO Xemissions decreased from 20.4 lb/ton of clinker to 6.2 lb/ton of clinker when the fuel was changed from natural gas to coal. A number of cement kilns have already made the switch from natural gas to coal and currently 87 percent of cement kilns in the United States use coal as the primary fuel. 12 When natural gas (with no nitrogen in the fuel) is used in the burning zone of a cement kiln, the NO Xemissions are significantly higher than when coal is used. There may be additional environmental impacts when coal is burned as opposed to natural gas (e.g., sulfur dioxide and sulphate emissions may increase). Although switching to a lower nitrogen fuel in a precalciner may reduce NO X , the fuel nitrogen content in the burning zone has little or no effect on NO X generation. Some researchers have found no relationship between fuel nitrogen content and the NO Xemissions from a cement kiln. 13 Switching to a fuel with a higher heating value and lower nitrogen content may reduce NO Xemissions in a cement kiln, e.g., petroleum coke has a lower nitrogen 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. However, petroleum coke cannot be burned alone because it does not provide enough volatile matter. 1458

5.1.4 Increasing Thermal Efficiency The thermal efficiency of the cement-making process may be increased by improving gas/solids heat transfer, e.g., using an efficient chain system, increasing heat recovery from clinker cooler, and by minimizing infiltration of cold ambient 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 reduce the energy requirement per ton of a clinker. By increasing the thermal efficiency, NO Xemissions are reduced per ton of clinker produced.
5.2 COMBUSTION MODIFICATION Combustion modifications are generally applicable to all types 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 combustion 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 proceed 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 completion 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 fuel. In the second, fuel-lean zone, additional (secondary) combustion air is added to complete the combustion process. However, the temperature in this second zone is much lower than the first zone because of mixing with the cooler secondary air, so the formation of NO Xis minimized in spite of the excess available oxygen. This staged approach can be used for combustion of all fossil fuels. Staged combustion is typically achieved by using only a part of the combustion air (primary air) for fuel injection in the flame zone, with remaining secondary air being injected in the subsequent cooler zone. For effective staging of combustion air to reduce NO Xemissions, cement plants must have indirect-fired kilns. In a direct-fired cement kiln, air used for conveying pulverized coal from a coal mill, i.e., primary air, is typically 17 to 20 percent of the total combustion air. The amount of primary air may be reduced by separating the coal mill air from coal. A cement kiln using less than 10 percent of primary air is an indirect-fired kiln. Conversion of a direct-fired kiln to an indirect-fired kiln involves adding particle separation equipment such as a cyclone or a baghouse and a fan to provide the primary air used to transport the powdered coal from storage to the kiln. An indirect-firing system increases overall energy efficiency by allowing a greater proportion of hot clinker cooler air to be used as secondary combustion air.59

5.2.1.1 Flue Gas Recirculation In addition to changing the combustion air distribution, the oxygen content of the primary air may be reduced to produce a fuel-rich combustion zone by recycling 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 zone. Direct injection allows more precise control of the amount and location of the flue gas recirculation (FGR). In order for FGR to reduce NO Xformation, recycled flue gas must enter the flame zone. The FGR also reduces the peak flame temperature by heating the inert combustion products contained in the recycled flue gas. The use of FGR may not be a viable method of reducing NO Xin a full-size cement kilnburning zone. FGR’s effectiveness relies on cooling the flame and generating an oxygendeficient (reducing) atmosphere for combustion to reduce NO Xformation, conditions that may not be compatible with cement kiln operation. High flame temperature and an oxidizing atmosphere are process requirements to produce a quality clinker product. A cement kiln differs from a utility boiler and other combustion devices because minimum temperatures and an oxidizing atmosphere are required to initiate chemical reactions in a cement kiln in addition to the providing the required heat (Btu/ton of clinker). Reduced flame temperatures and reducing conditions in the burning zone of a cement kiln may not be compatible with the production of cement clinker. 13 Coupling a low-NO Xstep burner with flue gas recirculation has been shown to reduce NO Xemissions further in a cement kiln. 16 The additional NO Xreduction attributable to FGR was estimated to be about 15 to 38 percent depending upon the proportion 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 Xburners can be installed on any type of kiln. Low-NO Xburners 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 Xburner. 1760

flames resulting from the staged combustion lower flame temperatures 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. Such a low pressure zone, as shown in Figure 5-1, 17 tends to recirculate hot combustion gas which is retrieved through an internal reverse flow zone around the extension of the burner centerline. The recirculated combustion gas is deficient in oxygen, thus producing a similar effect as FGR. Combustion of the fuel in the first stage thus takes place in an oxygen-deficient zone before the fuel is diluted in the secondary air. Installing such a burner reduces NO Xemissions from the kiln-burning zone by up to 30 percent. 17, 19 , 20
Low-NO Xburners have been used by the cement industry for twenty years. 21 Many suppliers offer low-NO Xburners and most of these systems focus on lowering the NO Xformation in the calciner by air or fuel staging, by reburning, or by high temperature combustion. 22 Test data from several different low-NO Xburners are now available. Thomsen, Jensen, and Schomburg reported on tests of a F.L. Smidth in-line calciner low-NO Xsystem in a preheater/precalciner kiln where different percentages of coal were added to the reduction zone of the precalciner (the remaining coal was added to the oxidizing zone). 22 When 100 percent of the coal was added to the reduction zone of the precalciner, the NO Xcontent at the preheater exit was reduced by 44 percent relative to when zero coal was added (see Table 5-3).

TABLE 5-3. NO XEMISSIONS FROM A PRECALCINER EQUIPPED

WITH A LOW-NO XBURNER

Percent Coal Added to Reduction Zone a (lb NO X/ton of clinker) NO XEmissions 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 oxidizing zone. b Emission measurements were taken at the preheater exit.
c Percent reductions are relative to emissions when zero percent of the coal was added; the original measurements were in kg NO X/ton of clinker to the hundredth place - the percent reductions were calculated using the original measurements, which results in slightly different values than when lb NO X/ton of clinker are used. Steinbiß, Bauer, and Breidenstein reported emissions changes for five kilns before and after the installation of Pyro-Jet low-NO Xburners (see Table 5-4). 21 The emission reductions ranged from 15 to 33 percent. Information on kiln-type was not provided.61 TABLE 5-4. NO XEMISSIONS BEFORE AND AFTER INSTALLATION

OF PYRO-JET LOW-NO XBURNERS

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 the use of Rotaflam ® lowNO Xburners. The Pillard Combustion Equipment and Control Systems published data on four kilns, comparing NO Xemissions with a 3 channel burner to emissions when a Rotaflam ® burner was used (see Table 5-5). 23 The emission reductions ranged from 23 to 47 percent. Information on kiln-type was not provided.

TABLE 5-5. NO XEMISSIONS WITH 3 CHANNEL AND ROTAFLAM ® LOW-NO XBURNERS

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 Rotaflam ® low-NO Xburner 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 average NO X emissions, 277.25 lb NO X/hr. b 1991 data were not provided. The Fuller Company low NO XIn-Line Calciner was installed in an RMC Lonestar kiln which reported 30-40 percent reductions in the amount of thermally formed NO Xafter installation. 25 In January 2000, the PCA and PCA provided results of a survey of cement facilities where the respondents indicated 14% of the operating U.S. kilns (22 kilns) have already installed a low-NO Xburner (81% of the facilities representing 81% of the operating U.S. kilns respondedto the survey). The remaining 139 kilns that are represented by the survey have not installed lowNO Xburners. 26 , 27
5.2.2 Staged Combustion of Fuel In conventional long (wet or dry) rotary kilns, all heat required for the cement-making process is supplied in the primary kiln burning zone, where the combustion occurs at the hottest temperature in the kiln. In the cement-making process, the preheating and calcination of the raw materials requires a large amount of heat but are typically at a temperature of 600 to 900 E C (1100 to 1650 E F) which is much lower than the kiln’s clinker-burning temperature of 1200 to 1480 E C (2200 to 2700 E F). 28 In the secondary combustion method, part of the fuel is burned at a much lower temperature in a secondary firing zone to complete 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 preheater/precalciner cement kiln design. Almost all new cement kilns have a preheater/precalciner-type designs. In the preheater kilns, the primary emphasis is on efficient heat recovery from kiln exhaust gases (see63

Figure 5-2). 29 However, up to 15 to 20 percent of the fuel may be fired in the riser duct in preheater designs. 29Precalciner systems typically employ a tower of four-stage cyclones for efficient gassolids contact which improves the energy efficiency of the overall process (see Figure 5-3). 29 In a typical precalciner kiln almost 40 to 50 percent of the fuel is burned at a lower (calcination) temperature which reduces the thermal NO Xformation considerably.

Tire-derived fuel can also be added to the feed end of a preheater or precalciner kiln. The Mitsubishi Cement Company’s Cushenbury Plant in Lucerne Valley, CA began using whole waste tires as a fuel supplement in 1993. The waste tires are delivered in enclosed container trucks and dumped into the plant’s automated handling system. A live bottom hopper and singulator place the waste tires on a conveyor system. This conveyor system transports the tires to the feed end of the kiln and drops the tire into an airlock system 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 waste tires supplements the iron requirements and approximately 2 percent of the iron in the final product comes from the tires. Figure 5-2. Schematic of preheater. 29 Figure 5-3. Schematic of precalciner. 2964

The addition of waste tires reduces NO Xemissions from the kiln by 30 to 40 percent, and there is no significant change in toxic, hydrocarbon, or metal emissions. 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 the fuel into the feed end of the kiln, countercurrent to the exhaust gas flow, as illustrated in Figure 5-4. 33 This fuel is burned in a substoichiometric O 2 environment to create a strongly reducing atmosphere (relatively high concentrations of CO) by following the simplified reactions:
NO + C N + CO (5-1)
and
NO + CO N + CO 2 (5-2) This reducing atmosphere inhibits the formation of fuel NO Xand destroys a portion of the NO Xformed 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 Xper ton of clinker. 13 Up to 46 percent reduction of NO Xemissions 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 Xformation mechanism in the secondary firing is the fuel NO Xformation which depends upon the nitrogen content of the fuel used. In order for the above reactions (5-1) and (5-2) to proceed at reasonable rates the temperature in the reduction zone should be maintained between 1000 and 1200 E C (1830 to 2190 E 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 Xemissions from precalcining kiln system by fuel injection in the

rotary kiln gas outlet. 3365

It is not possible to use “staged combustion” on preheater kilns that are firing fuel in the riser since in staged combustion it is necessary to add the fuel in an oxygen deficient atmosphere and then supply additional combustion air to fully combust the 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 introducing the secondary fuel into an atmosphere with insufficient oxygen for complete combustion. 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 Xemissions 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 conventional wet and long-dry kilns by injecting solid fuel into the calcining zone 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 calcination temperature of 600 to 900 E C (1100 to 1650 E F) which is much lower than the clinker burning temperature of 1200 to 1480 E C (2200 to 2700 E 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 side 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 mechanism 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 Figures 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 investigating a variety of energy containing waste Figure 5-5. Schematic of mid-kiln firing. 2966

materials from carpet scrap to pharmaceutical waste. These energy-bearing waste materials can be containerized or dementionalized into discrete fuel modules 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 ofthe kiln can be improved by adding solid fuels midkiln. 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. The enhanced control has shown to impart better formation of clinker. Reductions in cement fineness have been shown while maintaining similar seven-day strengths. Several facilities 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 Xformation by burning part of the fuel at a lower temperature and by creating reducing conditions at the solid waste injection point which may destroy some of the NO Xformed upstream in the kiln burning zone. MKF may also produce additional fuel NO Xdepending upon the nitrogen content of the fuel. 38 However, as discussed in section 5.1.3, fuel NO Xis unimportant relative to thermal NO Xformation. Additionally the discontinuous fuel feed from MFK can result in increased CO emissions especially if hazardous wastes are used. To control CO emissions, the kiln may have to have increased combustion air which can decrease production capacity. 40 According to literature from Cadence, in tests of its feed fork technology, one kiln reduced NOX emissions by 38%, overall particulate emissions 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 reduction in NOX emissions was 33%, with a range from 11% to 55%. In three tests on the wet kilns, the average reduction in NO Xemissions 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 emissions reductions of 45 percent or more. Figure 5-6. Schematic of fuel injection in kiln. 3867 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 I40 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 economical source of energy for the cement industry and its consumption has been increasing during the past decade. 12 Midkiln firing is a proven technology and so far at least 21 long kilns in the U.S. and nearly 40 kilns worldwide have been modified to allow mid-kiln firing of solid and hazardous waste. 37, 45
5.3 NO X REMOVAL CONTROLS
NO Xremoval controls are intended to destroy NO Xthat is formed in the combustion process. Selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) are described; however, SCR has not been demonstrated on any cement kilns in the United States at68

this time. There have been two demonstrations of SNCR in the United 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 the principles of its operation are similar. For this reason it is discussed with the other NO Xremoval controls.
5.3.1 Selective Catalytic Reduction (SCR) SCR is a process that uses ammonia in the presence of a catalyst to selectively reduce NO Xemissions from exhaust gases. This technology is widely used for NO Xabatement in other industries, such as coal-fired power stations and waste incinerators. The SCR process has been used extensively in Japan to achieve a 90 percent reduction in NO Xemissions from fossil fuelfired boilers. 46 In the United States SCR technology has successfully been used 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 catalyst 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 90 to 95 percent of NO X emissions in the flue gas are in the form of NO. A number of materials 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 Xpoisoning. 47 , 48 Zeolite-based catalyst materials have also been developed capable of operating at higher temperatures 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 base metal (titania-vanadia) and zeolite catalysts often make up the bulk of the substrate material. The catalyst shape and reactor design vary depending upon the manufacturer. The optimum temperature for the catalytic reactions depends upon the specific catalyst used and is usually 300 to 450 E C (570 to 840 E F). This temperature may be higher than typical cement kiln flue gas temperatures, especially in plants using heat recovery systems or baghouses for particulate collection. But it may be possible to reheat the exhaust using heat recovery systems. Ammonia is typically injected to produce a NH3:NO Xmolar ratio of 1.05-1.1:1 to achieve NO Xconversion 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 Xdestruction efficiency depends upon the temperature, NH3:NO Xmolar ratio, and the flue gas residence time (or the space velocity) used69

in the catalyst bed. The SCR reactor system can be designed for a desired NO Xreduction using appropriate reagent ratio, catalyst bed volume, and operating 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 alkalies and lime as well as sulfur dioxide in the exhaust gases is also of concern. Because of fouling problems, 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 considered: 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 cost. 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 applicable to other kiln systems as well. 1 Pilot plant trials on small portions (three percent) of the exhaust gas have shown promising results in Austria, Germany, Italy, and Sweden. There are at least three suppliers in Europe that offer full scale SCR to the cement industry with performance 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 United States cement plants. In 1976, Hitachi Zosen, an SCR manufacturer, conducted three pilot 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 were used to remove particulates before the flue gas entered the SCR unit. Also, a heat recovery system 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 Xremoval efficiencies of 98 percent. However, after 5,400 hours of operation, NO Xremoval efficiencies dropped to about 75 percent due to catalyst coating. Full-scale production runs will have to be carried out in order to remove the technical and economic uncertainties related to upscaling of the SCR technique. 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, lifetime of catalysts, and total investment costs. 1 Feasibility studies have been carried out in Austria, Germany, the Netherlands, and Sweden. The estimated costs vary considerably, with the production costs and lifetime of the catalyst being major variables. 1 Based on the experience in other industries, NO Xreductions in the range of 80 to 90 percent are considered possible, regardless of kiln type. 46 However, further studies are needed to demonstrate the specific NO Xreduction in the cement kiln exhaust gas environment.70

5.3.2 Selective Noncatalytic Reduction (SNCR) This control technique relies on the reduction of NO Xin 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 catalyst fouling, as in SCR technology, but requires injection of the reagents in the kiln at a temperature between 870 to 1090 E C (1600 to 2000 E F). At these temperatures urea decomposes to produce ammonia which is responsible for NO Xreduction. In principle, any of a number of nitrogen compounds may be used, e.g., cyanuric acid, pyridine, and ammonium acetate. However, for 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, the temperature window is critical for conducting this reaction. At higher temperatures, the rate of a competing reaction for the direct oxidation of ammonia which actually forms NO Xbecomes significant. At lower temperatures, the rates of NO Xreduction reactions become too slow resulting in too much unreacted ammonia slip. The effective temperature window range can be lowered to about 700 E C (1300 E 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 reduce ammonia slip and CO and NO 2 formation. In a conventional long kiln the appropriate temperature window is in the middle of a kiln. Because of the rotating nature of a long kiln, continuous injection of ammonia- or urea-based reagents is presently not possible. The technology developed 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 not been used because of the rapid decomposition of such salts. Therefore, SNCR technology has not been applicable for long dry or wet kilns. However, Fuel Tech Inc. is currently evaluating dry dust or pellet injection methods for direct injection into kilns. 52 In preheater/precalciner type cement kilns, the temperatures at the cooler end of the rotating kiln, in the riser duct, and in the lower section of the cyclone preheater tower are likely to be in the temperature window appropriate for SNCR. Such kilns are therefore good candidates for application of SNCR technology.
The NO Xreduction efficiency of SNCR depends upon the temperature, residence time, as well as ammonia and NO Xconcentrations in the flue gas. Injection of ammonia at a NH 3 :3NO X proportion of 1 to 1.5 will reduce NO Xemissions between 60 to 80 percent. Using a molar ratio of 0.5 will give NO Xreductions of approximately 40 percent. 47 The reagent consumption can be significantly higher with greater ammonia slip in SNCR systems 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 ammonium bisulfite scale which is significant for sulfur-containing fuels. SNCR processes also appear to convert some NO to71

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 Xdestruction efficiency also depends upon the flue gas residence 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 the existing gas temperature profile to provide an adequate residence time for a desired NO Xdestruction. Maximum achievable NO X reduction in a cement kiln may thus depend upon the gas temperature profile.The SNCR process was demonstrated in Europe in a preheater type kiln. Both ammoniaand urea-based reagents were investigated. The reagents were 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 Xemissions was observed with ammonia-based reagent and about 35 percent NO Xreduction 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 Xreductions 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 E C (1796 E F). NH 3 escape occurred when temperatures were less than 900 E C (1652 E 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 promising at low NO emissions rates. 13, 56 SNCR is presently being used in 18 cement kilns in Europe. Fifteen kilns are in Germany, two are in Sweden, and one is in Switzerland. These kilns are either suspension preheater kilns or precalciner kilns. The most common reagent used is 25% ammonia water. 1 Figure 5-7. Application of SNCR in

preheater kiln.72

NO Xreduction 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 clinker. Two dry process cyclone preheater/precalciner kilns in Sweden achieve 80 to 85 percent 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/precalciner kiln. 3 Ammonia was injected into the lower cyclone of the preheater tower where temperatures are favorable for the reduction reactions to occur. NO Xemissions reductions during this experiment averaged 40 percent, but NO Xreductions 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 preheater/precalciner kiln in Seattle, Washington during October 1993. NO Xemissions 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 approximately 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 Southern 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 Lucerne 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). The founding participants in the CIEC are Southdown, Inc., Riverside Cement Company, Mitsubishi Cement Corporation, California Department of Commerce (now Trade & Commerce Agency), and the San Bernardino County Air Pollution Control District (now Mojave Desert Air Quality Management District). This technology is covered under U.S. Patent No. 5,586,510 issued December 24, 1996. 13 The basic principle is to utilize the naturally occurring ammonia content of dewatered biosolids as the reagent. The dewatered biosolids are obtained from wastewater treatment plants. Since the biosolids are mechanically dewatered without heat input, the solids content varies between 16 and 30 percent (moisture content of 84 to 70%). Depending on the moisture content, the net Btu content (after evaporating the moisture) of the biosolids varies between -750 and +2200 Btu/lb. Since the biosolids heating value is relatively small, the net effect on kiln fuel combustion is expected to be small. 61
The same conditions that affect NO Xreduction performance in SNCR affect BSI performance: temperature (927 E C / 1700 E F is optimal), residence time (> 0.5 seconds is desirable), inlet NO Xconcentration, inlet CO concentration, and NH 3 /NO Xmolar ratio. Another73

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/precalciner kilns because the temperature window for BSI (927 E C / 1700 E 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 benefits of good residence time in the appropriate temperature window (927 E C / 1700 E F) and high mixing effectiveness. 61 At the Cushenbury plant, BSI underwent long-term testing and 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 difficult to isolate the effects of TDF or BSI on NO Xemissions. The company estimates that the use of TDF reduces NO Xemissions from the kiln by 30 to 40 percent. 62 Before the SNCR technology was adopted, the company estimated NO Xemissions 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 emissions 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 organic HAP emissions. Using the SNCR biosolids technology, the kiln also reduced its fuel consumption 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 Xoccurs at NSR=2; 80% reduction at NSR=1.6; 50% reduction at NSR=1.0, etc. Performance improves with increased turbulence or mixing, residence time, and more favorable temperature conditions. A higher NO X baseline generally leads to a higher percentage of NO Xreduction. 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 E C (1600 to 2000 E 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 of methanol injection downstream of the urea injection point to improve overall NO Xremoval. Nalco also introduced an improved NO X OUT ® PLUS, which is said to further broaden the operating temperature window and to reduce ammonia slip and CO and NO 2 formation. The Ash Grove plant in Seattle is a preheater/precalciner kiln with average processing rates of 160 tons dry feed/hour producing approximately 100 tons clinker/hour. NO X OUT ® was74

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 preheater O 2 (1.8 to 2.9 percent). The baseline NO Xlevels 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/precalciner 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 reasonable indication of what may be achievable with NO X OUT ® . The baseline NO Xrate 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 kiln were contrasted to conditions at the Ash Grove kiln that achieved greater reductions to explain why NO X OUT ® may achieve better results on some kilns than others. Nalco also has conducted a number of demonstrations and commercial projects in preheater/precalciner cement kilns. The fuels have included coal, and coal in combination with No. 6 heavy fuel oil, waste oil, and/or tire chips. The clinker capacity on these kilns ranged from approximately 1000 metric tons to 3200 metric tons per day. The 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 XEmissions

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 measures, such as process control optimization, use of modern, gravimetric solid fuel feed systems, optimized cooler connections and use of power management systems. These measures are usually taken to improve clinker quality and lower production costs but they also reduce the energy use and air emissions. 175

In March 2000, the European Integrated Pollution Prevention and Control (IPPC) Bureau issued a report on Best Available Techniques for European cement kilns. 1 The report collected emissions data from several sources. Emission rates for European 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 Xemissions for a cyclone preheater with heat recovery of 1.2 to 6.2 lb/ton of clinker, for a cyclone preheater without heat recovery of 1.6 to 7.0 lb/ton of clinker, and for a grate preheater of 1.6 to 8.2 lb /ton of clinker. These rates are similar to the averages for preheater and precalciner kilns found by EC/R in the new data presented in Chapter 4 (1.7 and 2.7 lb/ton of clinker respectively), but are less than those reported in the ACT document (5.9 and 3.8 lb/ton of clinker respectively). 1 Table 5-9 presents a summary of NO Xcontrol device applicability, reduction efficiency, and reported average emissions from the IPPC Bureau report on BAT for European cement kilns. 1 There are no emissions data in the IPPC report for kilns with CemStar technology or midkiln firing. For low-NO Xburners, the IPPC report found a lower average NO Xemissions 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 reduction efficiencies for low-NO X burners of up to 30 percent. The reduction efficiencies in the IPPC report for SNCR (10 to 85 percent) and SCR (85 to 95 percent) are close to but slightly greater than those reported in the 1994 ACT document (30 to 70 percent and 80 to 90 percent respectively).
TABLE 5-9. NO XCONTROL 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)

aNormally referring to daily averages, dry gas, 273 K, 101.3 kPa 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 Xemissions are a combination of general primary measures, primary measures to control NO Xemissions, 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 clinker (<200-3000 mg NO X/m 3 ), and that the majority of kilns in the European Union is said to be able to 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 control NO Xemissions, there was an opposing view that the BAT emission level associated with 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 level 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 Xcontrol techniques and the types of kilns on which they are applicable.
TABLE 5-10. NO XCONTROL 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 XBurner 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 Xburners 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 Xreductions identified in the 1994 ACT document and updated emissions data for various control technologies.77

TABLE 5-11. COMPARISON OF 1994 ACT NO XEMISSIONS 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 were calculated using a simple (not weighted) average of the available data. b There was only one source that provided emission rate data for low-NO X burners; the rest of the kilns with lowNO 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. dAt the time the kiln with the 59 percent emission reduction installed 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 reduction data for both biosolids injection (BSI) technology and firing tire derived fuel (TDF) in a precalciner. f The average emissions reduction for NO X OUT ® was estimated from the three tests/demonstrations described 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 increase the energy efficiency and78

1. European Integrated Pollution Prevention and Control Bureau (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 minimizing NO Xemissions. 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 site specific and data from one site cannot be directly translated to other sites. Quite often a number of process modifications and combustion control measures are implemented simultaneously. Process modifications can reduce NO Xemissions in cement kilns without any specific NO Xcontrol equipment. Some plants rely on process monitoring and control and process modifications as a means to maintain NO X emissions within their allowable limits. The CemStar process described in Section 5.1.2.2 is being used or incorporated by 11 facilities in the United States. Several long-term and short-term tests of CemStar have found average NO Xemission reductions of 33 percent.
Combustion modifications to reduce NO Xemissions include the staged combustion of air and of fuel. Low-NO Xburner systems described in Section 5.2.1.2 rely on the staged combustion of air. Technical literature and industry publications report NO Xreduction rates of 4 to 47 percent with the installation of low-NOX burners, depending on the baseline emissions, type of kiln, type of low-NO Xburner, and operating conditions. As described in Section 5.2.2, staged combustion of fuel includes 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-kiln fuel. Data are available for several kilns that have used or tested mid-kiln firing demonstrating NO Xreductions ranging from 11 to over 59 percent.
The NO Xremoval controls discussed in Section 5.3 include selective catalytic reduction, and selective noncatalytic reduction (biosolids injection and NO X OUT). SCR technology has not been used on any cement kilns in the U.S., although pilot plant 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 difficult, if not impossible, to be used in wet and long dry process kilns due to problems in obtaining the 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 is being used on one kiln in Southern California and NO X OUT has been demonstrated on two kilns in the U.S. SNCR technology is widely practiced in Europe.
5.6 REFERENCES79

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4. Miller, F.M. Oxides of Nitrogen . GTC Presentation, Kansas City, MO, September 20, 1977.
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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).
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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 Canada, Contract No. K2035-3-7044. October 1994. Pg.iv.
12. Portland Cement Association. U.S. and Canadian Portland Cement Industry Plant Information Summary . Skokie, IL. December 31, 1998.
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14. Comments on Alternative Control Techniques Document - NO X Emissions from Cement Manufacturing submitted by Greer, W.L. to William Neuffer, U.S. EPA through T.B. Carter, APCA. October 27, 1999.
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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. Procedair 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 California . ZKG International. October 1998. pp. 542 - 550.
23. Letter and attachments from M.H. Vaccaro, Pillard Combustion Equipment and Control Systems, to G.J. Hawkins, Portland Cement Association, re: Low NOX Rotaflam ® burner, dated January 20, 1999.
24. PSM International, “Response to USEPA Comments, 13 September 1995, on the proposed alternative NO XRACT for a portland cement manufacturing plant located in Thomaston, Maine and owned by Dragon Products Company,” Jan 31, 1996.
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 Incorporated, 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.cadencerecycling.com.
30. Battye, R., and S. Edgerton, EC/R Incorporated. “December 2, 1999 Trip Report to Mitsubishi Cement Corporation, Cushenbury Plant.” Lucerne Valley, CA. Submitted to Dave Sanders, US EPA, under contract No. 68-D-98-026, work assignment No. 2-28. August 31, 2000.
31. Shumway, D.C. “Tire Derived Fuel at Mitsubishi Cement Corporation.” 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, CA. 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 Company, to Damle, A.S., Research Triangle Institute. August 4, 1993. Process modifications 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 system 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-Kiln 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 Neuffer, 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 of permitted NO Xlevels for cement plants in the state, CEMS data as reported by the facilities for 1994 - 1999, and information on the control technology in use at each facility.
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.
43. Letter and attachments from Bramble, Kim, Cadence, to Bill Neuffer, USEPA, re: NO X Emission Reducing Technology, dated Feb 14, 2000.
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. Neuffer, U.S. EPA. Results of PCA Survey - Preliminary NO XControl 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. September 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. 115-124. October 1981.
50. Letter from Wax, J., Institute of Clean Air Companies, to Neuffer, W.J., U.S. Environmental Protection Agency. August 27, 1992. Response to ACT Document - Control of NO XEmissions from Process Heaters.
51. Haas, G.A. Selective Noncatalytic Reduction (SNCR): Experience with the Exxon Thermal DeNO X

Process . Presented at the NO XControl V Conference. Council of Industrial Boiler Owners. Long Beach, CA. February 10-11, 1992.
52. Lin, M.L., M.J. Knenlein, Fuel Tech Inc. “Cement Kiln NO XReduction Experience Using the NO X OUT ® Process,” proceedings of the 2000 International Joint Power 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 XControl. 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, Washington . October 28, 1993.
58. Sun, et. al. Reduction of NOX Emissions from Cement Kiln/ Calciner through the Use of the NO X OUT

® Process . Presented at the International Specialty Conference on Waste 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 Corporation. 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, Chapel 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 Xemission control techniques discussed in Chapter 5. Section 6.1 presents the cost methodology 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 plants were developed to perform cost calculations. Section 6.2 presents costs of selected incombustion and postcombustion control approaches. The cost effectiveness of different control approaches 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 definition of model plants and the guidance provided by EPA in the OAQPS Control Cost Manual

. 1 The definition of the model plants, calculation of capital costs and annual operating costs is presented in this section.
6.1.1 Model Plants As discussed in Chapter 3, existing cement kilns in the United 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 portland cement industry to replace coal and reduce NO Xemissions. As seen from data presented in Chapter 4, the NO Xemissions 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 four kiln types has typical energy consumption and NO Xemission rates as shown in Table 6-1 describing model plant parameters. The model plant kilns were assumed to be in continuous-duty operation and were assumed to operate 8,000 hours per year which allows scheduled downtime for maintenance operations. 3 Although waste-derived fuels are finding increasing applications in cement kilns, coal provided more than 82 percent of the energy requirement of the cement industry. 2 Model plants wereassumed to use 100 percent coal as a fuel and where available, a percentage of coal and wastederived fuels (i.e., for mid-kiln firing 85% coal and 15% tire-derived fuel were used).
6.1.2 Capital Cost Estimation The total capital investment is the sum of the direct cost (which is the purchased equipment costs and direct installation costs), indirect installation costs, contingency costs, sales taxes, freight, and production downtime. The purchased equipment costs (PECs) used in this chapter for each control technology are based on cost information provided by vendors or from data provided by existing facilities. Table 6-2 provides a list of various cost elements included in the capital costs. Where installation costs were not provided by vendors, direct and indirect installation costs were developed using the factors 45 and 33 percent, respectively, of PEC, per guidelines in the EPA OAQPS Control Cost Manual

. 1 A contingency factor of 20 percent was85

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 E C (300 E F). Average stack gas moisture content ~12%. Average particulate loading in stack gas ~0.01 grains/dry std 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 Xburners 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 of 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 replacement and disposal and the indirect operating charges, including plant overhead, general administration, and capital recovery charges. Table 6-3 lists the typical values used for these costs. A brief description is provided below for each component of the direct annual operating costs used in the cost evaluation.
6.1.3.1 Utilities
. The utility requirements for the control techniques consist 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 negligible relative to the other operating costs. The credit applied (tipping fee) for burning tires is an average value. 4 Tire tipping fees are highly variable showing a large regional variation and large fluctuations in the market. The average tipping fee used in this analysis is within the 1997 range of $20 to $200 credit/ton of86

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 New York; $125 to $65 in Miami, Florida; $100 to $75 in Atlanta, Georgia; $150 to $75 in Houston, Texas; $85 to $75 in Chicago, Illinois; $85 to $20 in Denver, Colorado; $100 to $42 in Los Angeles; 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 average market value per ton of clinker) *

* Average market value per short ton of clinker is $72.59. 787 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 capital 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 Xcontrol technologies were identified as currently operating on a cement kiln in the United States. Therefore, information for typical operating labor requirements from the cement industry was unavailable. A requirement of 0.5 hour of operator attention was assigned for an 8-hour shift, for88

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 the operating labor costs consistent with the OAQPS Control Cost Manual. 1
6.1.3.3 Maintenance
. Specific maintenance costs were not available from the control system vendors and manufacturers. The guidelines for maintenance costs in the OAQPS Control Cost Manual suggest a maintenance labor cost of 0.5 hours per 8-hour shift 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 cost was used, consistent with guidelines in the OAQPS Control Cost Manual. 1 As described above, the maintenance cost is 0.5 hours per 8-hour shift and a maintenance 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 OAQPS 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 Control 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, consistent 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 calculate equal annual payments over the equipment life.
6.2 COSTS OF NO X CONTROL APPROACHES As discussed in Chapter 5, feasible NO Xcontrol approaches include process modifications, combustion modifications, and NO Xremoval controls. Process modifications include combustion zone control of temperature and excess air, feed mix composition, kiln fuel, and increasing thermal efficiency of the kiln. Combustion modifications include staged89

combustion of air and staged combustion of fuel. NO Xremoval controls that are presented include selective catalytic and noncatalytic reduction of NO Xusing either ammonia or urea. This chapter includes costs for approaches and technologies that will reduce NO Xemissions and focuses on four technologies; changing the feed mix composition (CemStar), installation of a low NO Xburner (staged combustion of air), installation of a mid-kiln firing system (staged combustion of fuel), and noncatalytic reduction of NO Xusing biosolids (biosolids injection).
6.2.1 Process Modifications As discussed in Section 5.1, process modifications can be highly site specific and data from one site cannot be directly translated to other sites. Data are not available to determine costs of individual process modifications. Quite often a number of process modifications and combustion control measures are implemented simultaneously. Similar to combustion process control approaches, process modifications have also shown to reduce energy requirement and increase productivity, thus providing an economic incentive to implement them in addition to NO Xreduction.
6.2.1.1 Combustion Zone Control of Temperature and Excess Air
. Approaches aimed at improving the energy efficiency of the process indirectly reduce NO Xemissions per ton of clinker product. These approaches rely on continuous monitoring of O 2 and CO and in some cases NO Xemissions for controlling the excess air, fuel rate, and the combustion zone temperature. These measures are usually undertaken to increase process energy efficiency by reducing over-burning of the clinker. Maintaining the combustion zone temperature to a necessary minimum value using process control systems minimizes both the process energy requirement and increases refractory life. Because continuous monitoring of emissions is necessary for efficient process control, the cost of monitors is not considered as a NO Xcontrol cost. Further, the information obtained during this study indicated that some plants relied on process monitoring, including NO Xmonitoring, as a means to maintain NO Xemissions 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 estimated 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 installation 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) reduces the kiln temperature in the region of the flame and results in lower NO Xemissions. 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 required to convert a ton of raw materials to clinker. 14 The costs associated with installing this process are primarily 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 $200,000 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

aIncludes cost of steel slag, royalties, and credit for the reduction in raw materials. CemStar model plants costs could not be developed because the addition of steel slag is completely plant dependant. There is no set ratio of steel slag injection to kiln production rate. The amount of steel slag needed depends on the plants raw materials. The ratio can vary anywhere from five to ten percent addition of steel slag, based on kiln production. For the example presented in this document, the addition of steel slag was 7.7 percent of the kiln production prior to production with the CemStar process. The 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 reduction in shale and/or clay may also result from the addition of steel slag. The amount of shale 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 royalties that are paid by the facility installing the technology. The royalties are approximately $16 per ton of steel slag used. 1691

Cost savings associated with the CemStar process are based on production increase with the addition of steel slag compared to the cost benefit. Due to 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 equals $62.59 per ton times increase in production. Most plants increase production by five to ten percent with the addition of the CemStar process.
6.2.2 Combustion Modifications
As discussed in section 5.2 there are several combustion modifications that can be implemented to reduce NO Xemissions. This section presents costs for low NO Xburners (staged combustion of air) and mid-kiln firing (staged combustion of 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 Xburner in an existing direct-fired kiln, it is necessary to convert the kiln-firing system to an indirect firing system. Two sets of costs are therefore developed: (1) to install a low NO Xburner in an existing indirect-fired kiln, and (2) to install a low NO Xburner in an existing direct-fired kiln. In the first case, only the costs of the low NO Xburner equipment are considered, whereas in the second case the costs of conversion of a direct-fired system to an indirect-fired system are added to the low NO Xburner cost. Information was obtained from a supplier of low-NO Xburners regarding costs and heat duty. 17 The cost of a burner depends upon the size or heat duty as well as 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 burner is being installed in a new plant or is a retrofit in an older plant. The PEC of a low NO Xburner retrofit using coal as a fuel is typically about $100,000 for a 200 MM Btu/hr heat duty. For a multi-channel burner the cost is higher. The capital cost of a multi-channel retrofit low NO Xburner 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 function of heat duty is given as: PEC = 172,000 + 152 H
where PEC = Multi-channel low NO Xburner purchase equipment cost in $, and H = Burner heat duty in MM Btu/hr. The cost of a single channel low NO Xburner is obtained by dividing the PEC of a multi-channel burner by 2.92

For each model plant described in Table 6-1 purchase equipment costs for multi-channel burners were determined based on the heat duty needed by the kiln. For wet, long dry, and preheater kilns all the required heat is assumed to be provided by the low NO Xburner, whereas for precalciner kilns only 60 percent of the heat duty is assumed to be provided by the low NO X burner at the hot end of the kiln. The capital costs for retrofiting the eight model plants described in Table 6-1 in an existing indirect-fired kiln are given in Table 6-5. Direct installation, indirect installation, and contingency costs were assumed to be 45, 33, and 20 percent, respectively, as discussed in Section 6.1.2. The capital costs of retrofit low NO Xburners for the eight model plants ranged from $473,000 for the small long dry kiln to $966,000 for the large preheater/precalciner kiln. The capital costs for retrofitting 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 Xburners in an existing indirect-fired kiln are presented in Table 6-6. No additional costs for utilities were deemed necessary for NO Xcontrol purposes. As described in section 6.1.3, 0.5 hours of operating labor were 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 costs were determined as described in Section 6.1.3. The total annualized costs for the eight low NO Xburner retrofits ranged from a low of $130,000/year for the small long dry kiln to a high of $204,000/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 the kiln. The total cost to convert an existing dry process facility with two kilns, with a combined 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 burner and trolley, coal fire detection system, carbon dioxide inerting system, coal conveying blowers, 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 presented in section 6.1 (which adds 8 percent PEC cost for sales tax and freight, 45 percent PEC cost for direct installation, 33 percent PEC cost for indirect installation, and 20 percent PEC cost for 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 for contractor engineering and project management. When the costs are adjusted to include engineering 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 parallel systems, the cost of one conversion system to process coal for a 50 ton/hr dry facility 21 was considered to be $1.88 million in 1997 dollars. The amount of coal processed is proportional to heat requirement. For a dry process, the energy requirement is approximately 4.5 MM Btu/ton. Therefore, the cost of93

TABLE 6-5. CAPITAL COSTS FOR RETROFIT LOW-NO XBURNERS IN AN EXISTING INDIRECT-FIRED KILN (1997 $)

Model no. Kiln type Kiln capacity (tons clinker/hr) Heat duty

(MM Btu/hr) PEC ($) Freight and sales tax ($) Installation costs $ Contingency costs ($) Production

Downtime ($) Total

capital costs ($) 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 43,000 523,000 966,00094

TABLE 6-6. ANNUALIZED COSTS FOR RETROFIT LOW-NO XBURNERS IN AN EXISTING INDIRECT-FIRED KILN (1997 $)

Model no. Kiln type Kiln capacity (tons clinker/hr) Heat duty

(MM Btu/hr) Maintenance

costs ($/yr) Other

labor ($) Overhead

costs ($/yr) Taxes

insurance admin. ($/yr) Capital

recovery ($/yr) Total

annualized costs ($/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 48,600 106,000 204,00095 

### PEC for mo del plant Heat requi rement for model pla nt 835 000 225 0 6



### , .



### =       firing system conversion to process coal to provide 225 MM Btu/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 Xburner. For each model plant described in Table 6-1 the PEC for the firing system conversion as well as for the multi-channel burner was determined based on the heat duty needed by the kiln. For wet, long dry, and preheater kilns all the required heat is assumed to be provided by the low NO Xburner, whereas for precalciner kilns only 60 percent of the heat duty is assumed to be provided by the low NO X burner at the hot end of the kiln. The capital costs for retrofitting the eight model plants in an existing direct-fired kiln are given in Table 6-7. The capital costs ranged from $1.21 million for the small long dry kiln to $2.54 million for the large precalciner kiln.
The annualized costs for low NO Xburners in an existing direct-fired kiln are presented in Table 6-8. Operating labor 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 total annualized costs for the eight low NO Xburner retrofits in existing direct-fired kilns ranged from $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 low-NO Xburner, 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 fuel reduces thermal NO Xformation in cement kilns. Modification of a long kiln for secondary combustion of fuel is termed mid-kiln firing. The amount of fuel NO Xgenerated during the secondary combustion determines the net effectiveness of this technique for NO Xcontrol. The costs associated with this process are those for kiln modifications necessary to facilitate secondary combustion of fuels as well as those for a conveying 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 for four scenarios representing two wet kilns and two dry kilns. 4 Typically, the secondary combustion approach allows burning waste-derived fuels and, as such, reduces the overall cost for 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 injecting tires or containerized solid or liquid fuels and $500,000 for the modifications to the kiln. The cost of a fuel conveying system can be considerably lower for a semiautomatic, labor intensive system and may be expected to depend to a small extent upon the fuel conveying capacity needed. Costs for mid-kiln firing are not applicable to preheater or precalciner type kilns.96

TABLE 6-7. CAPITAL COSTS FOR RETROFIT LOW-NO XBURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)

Model no. Kiln type Kiln capacity (tons clinker/hr) Heat duty

(MM Btu/hr) PEC ($) Freight and sales tax ($) Installation costs $ Contingency costs ($) Production

Downtime ($) Total

capital costs ($) 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 2,540,00097

TABLE 6-8. ANNUALIZED COSTS FOR RETROFIT LOW-NO XBURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)

Model no. Kiln type Kiln capacity (tons clinker/hr) Heat duty

(MM Btu/hr) Maintenance

costs ($/yr) Operating

labor ($) Overhead

costs ($/yr) Taxes

insurance admin. ($/yr) Capital

recovery ($/yr) Total

annualized costs ($/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 22,200 102,000 279,000 439,00098

Approximate capital investment costs were developed by assuming a total of $1.5 million purchased equipment cost for kiln modifications and the fuel conveying and metering system for the four model plants. In this example approximately 15% of the 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 not vary with the heat duty of the kiln, the 0.6 power rule does not apply. Total capital investment was calculated using the methodology presented in section 6.1. It should be noted that the costs estimated are higher than the actual installation costs reported by the vendor. The total capital costs for mid-kiln firing conversion of the four wet and long dry model kilns are given in Table 6-9. The total capital investment costs range from $3.15 million for a small long dry kiln to $3.24 million for a large wet kiln. The annualized costs for the mid-kiln firing conversions are presented in Table 6-10. Operating labor 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 large wet kiln to a high cost of $189,000 for the small long dry kiln. These annualized costs were developed with a fuel credit (for the fuel that was replaced with waste tires) as well as a tire tipping fee. In 1998 270 million scrap tires were generated and the estimates of tires in stockpiles range from 500 million to 3 billion. 24 Although the tipping fees for tires may decline as markets for used tires increases, tire tipping fees are not likely to disappear in the near future. In 1997, average national tipping fees for tires ranged from $20 to $200 per ton (for whole tires). 5 The annualized cost of mid-kiln firing without a tire tipping fee (but including the fuel credit: assuming the tires or other waste 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 Xremoval 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 capital 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 instrumentation. Operating costs include the cost of reagents and additives used, additional electricity cost for reagent pumping, and fuel penalty cost along with operating labor and maintenance requirements.
6.2.3.1 Biosolids Injection Process
. As discussed in section 5.3.2.1, the biosolids injection process (which involves the injection of biosolids into a precalciner kiln) reduces the NO Xthat was formed in the kiln. Biosolids injection has been installed on one kiln in Southern California and the costs of the installation were obtained for that facility. 3, 25 The costs associated with installing this technology include the sludge system and the sludge conveying system and99 TABLE 6-9. CAPITAL COSTS FOR MID-KILN FIRING CONVERSION (1997 $)

Model no. Kiln type Kiln capacity (tons clinker/hr) Heat duty

(MM Btu/hr) PEC ($) Freight and sales tax ($) Installation costs $ Contingency costs ($) Production

Downtime ($) Total

capital costs ($) 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 CONVERSION (1997 $)

Model no. Kiln

type Kiln

capacity (tons clinker/hr) Heat duty

(MM Btu/hr) Maintenance,

other labor, and overhead costs ($/yr) Taxes,

insurance, admin. ($/yr) Capital

recover y ($/yr) Disposal

revenue ($/yr) Fuel Credit

($/yr) Licence

Fee ($/yr) Total

annualized costs ($/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 in a cost savings associated with the tipping fees for the biosolids. The annual costs include operating 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 labor cost), credit for the biosolids tipping fee, and an electricity penalty of an additional 3% increase in fan capacity. Biosolid tipping fees range from $0.00 to $10.00 per wet ton. An average 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

aBased 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 Xemissions 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 currently operating in the United States using this technology. Costs for this technology were obtained from the equipment vendor for two preheater/precalciner kilns and are summarized in Table 6-12. 28 , 29 The costs presented in Table 6-12 are consistent with values previously obtained and 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 much 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 due 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/precalciner 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

aIncludes 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 United States, this control technique has been applied successfully in other industries and pilot plant trials have been conducted in Europe. Capital costs for this control approach would include cost of the SCR unit, ammonia storage tank, and an ammonia heating/ vaporization injection system along with equipment needed for preheating flue gases to an appropriate temperature. Operating 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 the 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 the model plants were not available from any of the SCR control system vendors in the United States. The following information was first presented in the 1994 ACT document and is repeated here. An equipment cost estimate of an SCR system was submitted by a Japanese supplier to a cement company in the United States in 1991. 35 For a dry long kiln with 1,120 tons/day (47 tons/hr) clinker capacity, the estimated equipment cost was 1 billion/Yen. With a 1992 exchange rate of 108 Yen/$ and assuming 5 percent inflation, the estimated cost in 1992 U.S. dollars was about 9.72 million. This equipment cost estimate included SCR catalyst, SCR reactor, gas/gas heat exchanger, heater, ammonia injection grid, ammonia storage tank, ammonia vaporizer and supply unit, induced draft fan, instrumentation and all piping and ductwork. The reactor temperature was assumed to be 350 E C (660 E F) and design NO Xremoval efficiency was 80 percent. Since the reactor, heat exchanger, and gas heater design strongly depend upon the flow rate of flue gas to be treated, the equipment costs for the model plants may be scaled based upon flue gas flow rate:


### PEC for mo del 1 PEC for mo del 2 Gas flow f or model 1 Gas flow f

or model 2 =       0 6

.102

Table 6-13 presents estimated capital costs for the eight model 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 capital cost for the SCR systems. The estimated capital costs range from $9.9 million for the small dry long kiln to $24.6 million for the large precalciner kiln. The estimated annualized costs for SCR systems on the eight model plants are shown in Table 6-14. These include operating labor and maintenance costs, capital recovery, gas reheating, ammonia reagent, and catalyst replacement costs. 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 the 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 three technologies for which detailed costs could be developed as presented in the last section: low NO Xburners (on an existing indirect fired system and with conversion to an indirect firing system), and mid-kiln firing (with a credit for firing tires or just firing coal). Limited 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 technology by the annual NO X reduction likely to be achieved by that technology and is expressed in the units of $/ton of NO X removed. Cost effectiveness was determined for each of the model plant scenarios.
6.3.1 CemStar As discussed in section 6.2.1.2, the costs of installing CemStar were obtained from the vendor for one kiln configuration (a wet kiln) at one facility. Data for other installations of CemStar were not available for this report. The kiln capacity was 42 tons clinker/hour prior to the installation of CemStar and 45 tons clinker/hour after the installation of CemStar. The annualized cost for the conversion was calculated as $220,000. This annualized cost does not include a credit for the increased production of clinker (approximately 3 tons/hour). Uncontrolled emissions were calculated as approximately 1600 tons NO X/year. An average emission reduction of 30% was determined for the installation of CemStar which results in 100 tons NO X/year. The cost effectiveness for this example facility was $550/ton of NO Xreduced.
6.3.2 Low NO X Burner
The NO Xreduction that may be achieved with a low NO Xburner depends mainly on the operating parameters. In fact, no guarantee on the NO Xreduction level is usually provided by burner vendors. With proper operation of the low NO Xburner, 15 to 40 percent reduction in NO Xemissions should be possible. 37 An average NO Xreduction efficiency of 25 percent was used in determining controlled NO Xemissions and cost effectiveness of the low NO Xburner103 TABLE 6-13. CAPITAL COSTS FOR SCR PROCESS (1992 $) 38

Model no. Kiln type Kiln capacity (tons clinker/hr) Heat duty

(MM Btu/hr) PEC ($) Freight and sales tax ($) Installation costs

direct and indirect ($) Contingency

costs ($) Total capital

costs ($)
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 24,600104 TABLE 6-14. ANNUALIZED COSTS FOR SCR(1992 $) 38

Model no. Kiln type Kiln capacity (tons clinker/hr) Operating

labor ($/year) Ammonia

reagent costs ($/year) Maintenance

& overhead costs ($/yr) Energy

and fuel costs ($/year) Catalyst

costs ($/year) Taxes

insurance admin. ($/yr) Capital

recovery ($/yr) Total

annualized costs ($/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 7,180105

technology. For precalciner kilns, although only 60 percent of the heat duty was assumed to be provided by the low NO Xburners, all of the NO Xemissions 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 Xremoval considerably. Table 6-15 presents the uncontrolled and controlled NO Xemissions for the eight model plants along with the cost effectiveness of low NO Xburner in an existing indirect-fired kiln. The cost effectiveness were within a close range for the model plants and ranged from $300/ton of NO Xfor the large wet kiln to $620/ton of NO Xfor the small long dry kiln. Table 6-16 presents the cost effectiveness of low NO Xburner 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 cost effectiveness as compared to those in Table 6-15. The conversion from direct fired to an indirect 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 in 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 Xremoved. A NO Xreduction efficiency of 40 percent was calculated for wet kilns and 30 percent for long dry kilns. This cost effectiveness value includes a fuel credit for using waste-derived fuel and a tipping fee for the tires. If the tire tipping fee is removed (but the fuel credit is retained - assuming waste material is free), the cost effectiveness will range from $150/ton of NO Xto $680/ton of NO Xreduced.
6.3.4 Preheater/Precalciner Tire Derived Fuel Costs for installing a tire derived fuel system at a precalciner kiln were obtained from onefacility. The purchased equipment and total capital investement costs were similar to the midkiln firing costs (the majority of the cost is in the tire handling system). Cost effectiveness for this kiln is based on the annualized costs of ($1,600,000/year), the emission reduction achieved at that facility (emissions decreased approximately 30% from 3.4 lb/ton of clinker to 2.4 lb/ton of clinker), a kiln capacity of 215 tons/hr, and an annual operation of 8,000 hr/yr. Cost effectiveness is a credit of ($1,900/ton) for installing a tire derived fuel system on this kiln. This cost effectiveness value includes a fuel credit for using waste-derived fuel and a tipping fee for the tires. If the tire tipping fee is removed (but the fuel credit is retained - assuming waste material is free), the cost effectiveness is calculated as a credit of ($480/ton) of NO Xreduced.106

TABLE 6-15. COST EFFECTIVENESS OF RETROFIT LOW-NO XBURNERS IN AN EXISTING INDIRECT-FIRED KILN (1997 $)

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

duty (MM Btu/hr) Uncontrolled

NO X emissions (tons/yr) Controlled

NO X emissions (tons/yr) NO X

removed (tons/yr) NO X

reduction (%) Total annualized

costs ($/yr) Cost effectiveness

($/ton NO X removed) 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 XBURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)

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

duty (MM Btu/hr) Uncontrolled

NO X emissions (tons/yr) Controlled

NO X emissions (tons/yr) NO X

removed (tons/yr) NO X

reduction (%) Total annualized

costs ($/yr) Cost effectiveness

($/ton NO X removed) 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 1,100107 TABLE 6-17. COST EFFECTIVENESS OF MID-KILN FIRING

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

duty (MM Btu/hr) Uncontrolled

NO X emissions (tons/yr) Controlled

NO X emissions (tons/yr) NO X

removed (tons/yr) NO X

reduction (%) Total annualized

costs ($/yr) Cost effectiveness

($/ton NO X removed) 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 biosolids injection technology on one preheater/precalciner kiln. Cost effectiveness for this kiln is based on the annualized costs of ($320,000/year), the emission reduction achieved at that facility (emissions decreased from 2.4 lb/ton of clinker to 1.2 lb/ton of clinker), a kiln capacity of 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 Xreduction based on the available test data. Cost effectiveness for the two kilns described in section 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 Xcontrol 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 Xreduction that may be achieved with SCR technology depends upon 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 applications such as utility boilers and gas turbines. 39 The SCR equipment costs developed in Section 6.2.2.2 were based upon SCR costs quoted for application on dry kiln exhaust gases with 80 percent design reduction in NO X emissions. To determine the cost effectiveness of the SCR technology in cement kiln applications, an 80 percent NO Xreduction efficiency was therefore assumed and the results are shown in Table 6-18. The cost effectiveness ranged from $3,140/ton to $4,870/ton of NO Xremoved and are almost five to six times greater than the corresponding values for the ammoniabased SNCR technology.109 TABLE 6-18. COST EFFECTIVENESS OF SCR PROCESS 38

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

duty (MM Btu/hr) Uncontrolled

NO X emissions (tons/yr) Controlled

NO X emissions (tons/yr) NO X

removed (tons/yr) NO X

reduction (%) Total annualized

costs ($/yr) Cost effectiveness

($/ton NO X removed) 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 4,400110

1. Vatavuk, W.M. Cost Estimating Methodology. In: OAQPS Control Cost Manual, Fifth Edition, Vatavuk, W.M. (ed.). U.S. Environmental Protection 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 various technologies. Table 6-19 also presents the ozone season cost effectiveness. The ozone 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 XReduced)
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 IndirectFired 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

aThe 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 REFERENCES111

3. Battye, R., and S. Edgerton, EC/R Incorporated, Chapel Hill, 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-98-026, work assignment No. 2-28. July 5, 2000.
4. Letter with attachments from Bramble, K.J., Cadence Environmental Energy Inc., Michigan City, IN, to W. Neuffer, U.S. EPA, RTP, NC. January 20, 2000. Cost of a mid-kiln firing system.
5. Email from Joe Truini, Waste News to Lee-Greco, J., EC/R Incorporated, 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 $72.59 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/cement/170398.pdf), January 1998.
8. Coal prices based on average price of coal delivered to other industrial plants by census division and state, 1997, nominal dollars per short ton, from the U. S. DOE Energy Information Administration. Website: (http://www.eia.doe.gov/cneaf/coal/cia/html/t94p01p1.html), accessed on 5/22/2000.
9. Electricity prices based on U. S. Average Revenue per Kilowatt-hour by Sector and Class of Ownership, from the U. S. Energy Information Administration/Electric Sales and Revenue for 1997. Website: (http://www.eia.doe.gov/), accessed on 5/22/2000.
10. Natural gas prices based on Average Price of Natural Gas Delivered to U. S. Consumers for 1997, from the U. S. DOE Energy Information Administration/Historical Natural Gas Annual 1930 through 1997. Website: http://www.eia.doe.gov/), accessed on 5/22/2000.
11. Letter with attachments from Bramble, K.J., Cadence Environmental Energy Inc., Michigan City, IN, to W. Neuffer, U.S. EPA, RTP, NC. January 20, 2000. Cost of a mid-kiln firing system.
12. Hourly wage rates are based on the Bureau of Labor Statistics website. Based on March 1997 dollars from Table 41. Website: (http://stats.bls.gov/ecthome.htm), accessed on 7/10/2000.
13. Letter and attachments from Willis, D.A., Blue Circle Cement, Inc., Atlanta, GA, to Damle, A.S., Research Triangle Institute. June 4, 1993. Information 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, December 2, 1999. Prepared for the U.S. EPA, RTP, NC, under contract No. 68-D-98-026, work 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 and 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 LeeGreco, J., EC/R Incorporated, Durham, NC. July 26, 2000. Costs of low-NO Xburners.
18. Letter from Denizeau, J., Lafarge Canada, Inc., Montreal, Quebec, Canada, to Crolius, R.W., American Portland Cement Alliance, Washington, DC, August 24, 1993. Cost of low NO Xburners.
19. Letter and attachments from Bennett, J.H., California Portland 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 California 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 assignment 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, Washington, 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 system conversion.
24. Scrap Tire Recycling. Consumer Energy Information: EREC Reference 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 Kiln NO X Control. Mitsubishi Cement Corporation, Lucerne Valley, CA. Received 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 & Browne 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 Air 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 Cement Company. Prepared for California Portland Cement Company, Glendora, CA. October 26, 1994
35. Letter and attachments from Akita, A., Hitachi Zosen Corporation, 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 Portland Cement Company, Glendora, CA, to Neuffer, W.J., U.S. EPA, RTP, NC. March 16, 1993. Costs for an SCR unit for Colton plant.
37. Memo from Battye, R., and S. Walsh, EC/R Incorporated, Chapel Hill, NC to D. Sanders, U.S. EPA, RTP, NC. Derivation and data supporting development 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 Companies. September 1992.