NALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 1 of 10 

# US Steel Minn Tac Line 7 Final Report October 2 7 , 2009NALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 2 of 10 

## Table of Contents

Table of Contents 2 1. Project Background 3
1.1. Contract Description 3 1.2. Unit Description 3 1.3. CFD Modeling 3 2. Nalco Mobotec System Description 4
3. Summary of engineering, construction and testing performed. 4
4. Summary of Tuning results 6 5. Temperature Traverse 7
6. SNCR applicability Summary 8
7. Recommendations 9
7.1 Cooling the kiln exit flue gas temperature by injecting water spray into the kiln 9 7.2 Flue gas recirculation into kiln burner 9 7.3 Low

- NOx kiln burner 9 8

. Conclusion 10NALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 3 of 10 1. Project Backg round 1.1. Contract Description US Steel Issued Purchase Order 00797286 to Nalco Mobotec to perform Computation Fluid Dynamic Modeling on agglomerator line 5 per Nalco Mobotec Proposal dated March 25 , 2009. Nalco Mobotec performed the contracted CFD modeling and presented the results to US Steel at the plant on March 17, 2009. Following CFD presentation, Nalco Mobotec submitted a revised proposal dated April 3, 2009 to e ngineer, s upply , start up andtune a NOx only demonstration. USS Steel awarded purchase order00824682 dated April 7, 2009 to Nalco Mobotec to install SNCR System on line 6 or line 7 . In later discussions, US Steel clarified that the SNCR demonstratio n would be applied to line 7

. 1.2. Unit Description US Steel operates an iron ore pelletizing plant at their Minnesota Ore Operation (Minntac) facility, inclu ding five pelletizing lines designated as Nos. 3, 4, 5, 6 and 7. These facilities emit tremendous NOx from fuel combustion and mercury from iron ore pelletizing process. To meet pollutant emission limitations, US Steel is currently investigating the feasib ility of reducing NOx and mercury emissions from these indurating processes, focusing initially on Line No.5. NOx emission control would be installed onthe other lines once the technologies prove to be effective. The indurating process at Line No.5 is a “grate

- kiln” type system,which employs a traveling grate, a rotary kiln and an annular cooler. The green pellets are dried and heated in an oxidizing atmosphere at an incipient fusion temperature of approx. 2400

- 2600 F depending on the type of pellet. Aci d pellets are generally heated to the lower end of the temperature range, while flux pellets are heated to the higher end of the temperature range. Drying of the green pellets and partial induration occurs at the grate, while final induration is finished i n the rotary kiln. The pellets are cooled in an annular cooler that is designed to operate with counter

- current cooling air flow. 1.3. CFD Modeling The objective of the CFD study was to analyze combustion performance and NOx/Hg reduction resulting from the ap plication of Nalco Mobotec Rotamix ® designed for Minntac pelletizing lines. Multiple CFD models have been performed for baseline and Rotamix ® cases. All models focused on Line 5 only. The accuracy of the baseline modelNALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 4 of 10 results have been validated against t he testing data. Through careful study, analysis and review the following conclusions have been drawn from the CFD study:

• Rotamix ® system designed for NOx reduction has multiple injection ports on the furnace walls between rotary kiln and preheater. The Rotamix ® air pressure is designed for 15 inwg.

• The modeling results showed that more than 50% NOx reduction can be achieved by Rotamix ® urea injection with an NSR of 1.0

- 1.3. Further reduction is possible by injecting more urea.
2. Nalco Mobote c System D escript io n Follow ing award of purchase order 00824682, Nalco Mobotec began engineering of the Nalco Mobotec Rotamix ® SNCR System for application on Line 7 . The s ystem consist s of a Rotamix ® Air system and a urea pumping and delivery system. Components included:

 Rotamix ® fan

 Ductwork and supports

 Trailer tanker for temporary u rea storage
 Dilution tank for mixing demineralized water with the urea.

 Pump station.

 Distribution piping

 Rotamix ® Injection lateral and lances.

 Instrumentation. US Steel provided electrical design and a ll installation labor.
3. Summary of e ngineering, construction and testing performed. Nalco Mobotec began Engineering on April 8, 200 9 and mobilized the site for beginning of construction the week of June 22, 2009. Construction was completed and commissio ning began the week on July 21, 2009. Nalco Mobotec performed tuning Summary of Tuning Performed From July 24 through August 7, Nalco Mobotec performed SNCR tuning. Following tuning period, Nalco Mobotec and US Steel had several conference calls to exp lore what systems modifications could be made to improve the NOx reduction. Nalco Mobotec and US Steel agreed that additional temperature data was required . As a result, Nalco Mobotec remobilized and on September 24, 2009 performed a temperature traverse of the injection plane. Details of testing are discussed below.NALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 5 of 10NALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 6 of 10 4. Sum mary of Tuning results - line 7 The urea injection ports are located at the entrance of the preheater (exit of the kiln)

. The ports are adjacent to the Zone 2 burners. Ten ports are installed for the urea injection: four ports are located on top of the preheat entrance and three ports are located on each of the side walls. Figure 1 shows the general location of the ports and in reference to the burne rs. Port numbering is also presented in the figure.

Figure 1 : Port position and numbering Nalco Mobotec performed the tuning from July 26 to August 7, 2009. The variables that were adjusted during the tuning include  diffe rent combinations of lance injection  air pressure of Rotamix ® fan  urea concentration in the solution  solution flow rates
N o NOx reductions were seen with Zone 3 burners in service. The best NOx reduction was realized with Lances9 and 10 in service. The other ports showed no significant NOx reduction. Under most operating conditions, the NOx reduction was in the range of 8

– 10%. A final test using a 10% urea concentration resulted in a 15% reduction. However, the test was held for a relatively short time and should be repeated to validate the results.NALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 7 of 10 Nalco Mobotec also tested injecting urea solution through the view ports located above the grate in the preheat section. In all cases, the urea injection resulted in an increase in NOx production. The temperature of the gas above the grate is elevated because of its proximity to the Zone 1 and Zone 2 natural gas burners. The high temperature caused the urea to react with the high O 2 concentration and produce NOx.
5. Temperature Traverse During the tuni ng, Nalco Mobotec used its IRthermocouple to measure the flue gas in the preheat section of line 7 through the numerous view ports. The temperatures were higher than desired, mainly ranging between 2100 and 2500 o F. (The ideal temperature range for SNCR is 1900 to 2100 o F.) The view portswere downstream of the injection location. Also, a limitation of the IR thermocouple is that the reading is an average temperature value. To determine the actual flue gas temperature around the injection location, Nalco Mobote c brought an 8

- foot thermocouple totraverse the preheat duct through the injection ports. The temperature results are presente d in Table 1 , with Zone 3 burners out of service.
Table 1 : Temperature readings of traverse measurement

Top Ports West Ports East Ports Port # 4 5 6 7 2 1 3 8 9 10 Time Start 10:06 10:20 10:38 11:28 14:21 14:37 15:31 8 1933 1965 1979 2019 2141 2185 2157 7 1920 1938 1959 20 02 2133 2146 2143 6 1909 1913 1934 1998 2110 2031 2077 5 1910 1906 1929 1994 2095 1982 2023 4 1874 1852 1933 1980 1980 1964 2010 3 <1000 <1000 <1500 2Depth(ft)

1 End Time 10:20 10:38 10:50 11:44 14:37 14:56Plugged

15:54PluggedPlugged

The first three feet of the probe were in the refractory section. Therefore, the temperature readings were of the five feet closest to the preheat walls, which has dimensions of 16 X 10 ft. Three portswere plugged and could not be traversed, incl uding ports 9 and 10, which resulted in the bulk of NOx reduction when urea was injected.NALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 8 of 10 The temperatures measured from the top ports were between 1900 and 2020 o F, which is the desired temperature range for urea injection. However, the side ports show t emperatures higher than 2100 o F. The temperature is higher deeper inside the duct. Therefore, the gas temperature away from the preheat walls is expected to be even higher than the measured values (i.e. greater than 2100 o F). This temperature is beyond th e best temperature windows for SNCR which is between 1900

- 2100 o F, which is believed to be the main reason for low NOx reduction achieved. The lack of NOx reduction from the ports on the top of the preheater is due to short residence time for the urea react ion before reaching preheat burners in Zone 2, while the limited NOx reduction from the side ports is due tothe higher flue gas temperatures.
6. SNCR applicability Summary Nalco Mobotec installed ten ports for urea injection to reduce the NOx emissions o f Line 7. The portswere located at the entrance of the preheat section. Two important factors forthe SNCR effectiveness in NOx reduction are flue gas temperature (ideally between 1900 and 2100 o F) and sufficiently long residence time. In the majority of the flue gas duct, the temperatures are believed to be too high for SNCR to effectively reduce NOx. When Zone 3 burners are out of service, only the top five feet of the duct (approximately the top third of the duct) appears to be in the right tempera ture regime. In the region of elevated temperatures, NOx reduction was limited to only 8

– 10% (from Ports 9 and 10). The flue gas at the top of the duct travels longer distances(through length of the preheater) before finally passing through the grate. The required reaction time for SNCR is short (fractions of a second). However, because of the fast flue gas velocities in the preheater and the presence of natural gas heaters, the residence time may not be sufficient for complete SNCR reaction. Any urea that does not react to reduce NOx will quickly react in the presence of high temperatures and high O 2 concentrations to produce NOx, resulting in an overall negligible NOx reduction. The conditions necessary for SNCR were not present to reduce NOx suff iciently. NOx was reduced by 8

– 10%, with one short test yielding a 15% reduction. SNCR is more like ly to work if more burners in the preheat were taken out of service. Unfortunately that would greatly affect the quality of the taconite green balls and is therefore not a viable solution. SNCR may still be possible in taconite lines where preheaters do not have burners (such as lines where there are no limestone fluxing, and therefore a lower heat requirement). It is noted from the historical plant ope rational data that the kiln exit temperature ofNALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 9 of 10 Line 7 that we injected urea in is hotter than Line 5 that was originally tested by HVT and modeled . Line 5 is much suitable for SNCR injection from temperature standpoint.
7. Recommendations With the discus sions Nalco Mobotec has hadwith US Steel, finding an effective NOx reduction strategy will be a challenge. The economics, technical difficulty and operating issues of an SCR clearly make that technology seem unreasonable. We still believe that there are potential solutions tothe US Steel NOx reduction goals that may be economically and technically feasible. However; additional time and investigation will be required. Some of the options we consider possible are as follows: 7.1 Cooling the kiln exit flue g as temperature by injecting water spray into the kiln Mixing water spray with flue gas will cool down the gas temperature to an appropriate point for SNCR injection. In order for flue gasto be well mixed, the water injection points have to be upstream 5

- 10 ft from the kiln exit, and the injection ports shall be on the kiln cylinder. To maintain the same heat flux to the pellets in the preheater, the preheater burners have to burn harderto compensate for the loss of flue gas heat capacity due to water in jection. We understandthat injection of water into a gas stream to then reheat it is an efficiency loss, however; the temperature drop required making SNCR work appears to be relatively small compared to the overall temperature. This layout can be field tested. US Steel needs to consider whether this is acceptable by the process operation. 7.2 Flue gas recirculation into kiln burner The majority of NOx is formed from thermal NOx when natural gas is fired through the kiln burner. One way to reduce the NOx i s to reduce the flame temperature of kiln burner. Kiln burner is a diffusion flame; flue gas recirculation has proved to be able to effectively reduce the peak flame temperature by reducing the O2 concentration of the secondary air before its mixing with f uel from the kiln burner. This design is not overly complicated and can be designed and implemented in a relatively short time frame. 7.3 Low

- NOx kiln burner A conventional low

- NOx burnercan be applied to the kiln. If US Steel desired Nalco Mobotec would work with a burner manufacturer to provide a burnerNALCO Mobotec Nalco Mobotec Final Report October 2 6 , 2009

**Confidential & Proprietary Informa tion** This information is proprietary and confidential and shall not be copied, discl osedor shared with parties other than those addressed without specific written authorization by NALCO Mobotec. All state and federal laws governing such information, copy writes, and trademarks shall apply. All rights reserved. 10 of 10 design appropriate for the process. It is important to keep in mind that Nalco Mobotec has done low NOx burner modifications in conjunction with combustion modifications in order to optimize NOx reductio n. Nalco Mobotec’s ROFA system is an alternative to typical low

- NOx burners that has always shown higher NOx reduction while maintaining good combustion (recognized by the US EPA) and may be an option, but due to the rotation of the kiln and configuration it would be a challenging design that requires detailed design up front and cannot be pilot scale tested as the SNCR application was.
8. Conclusion Nalco Mobotec is more than willing to work with US Steel on a solution if US Steel desires. Investigation of the options stated above may yield additional solutions not yet examined, but potentially highly successful.