U. S. Steel Corporation Minnesota Ore Operations P 0. Box 417 MI. Iron, MN 55768


### CERTIFIED MAIL 7009 0820 0001 3944 3965 October 22,2010 ChristopherNelson, P.E. Manager Strategic Projects Sector Industrial Division MinnesotaPollution Control Agency 520 Lafayette RoadNorth St. Paul, MN 55155 

### Re: Preliminary Pilot TestResults- Low 

### NOxMain Burner As peryour letter dated September 23, 2010, United States Steel Corporation, Minnesota Ore Operations- Minntac is providingpreliminary results from the Line7 pilottesting of theLowNOx Main Burner, a schedule for continued pilottesting, and a pilottesting schedule for Line 6
. 

### Background Theairemissionspermit for Minntac containsrequirements for a NOx reduction goal of at least70%from the baseline limit of 13,300 tons per year. To achieve tllis goal, pilot testing ofNOx technologies are to beconducted

. Minntac submitted a pilot testing schedule in April 2009 to the MPCA for approval whlch includedpilottesting SNCRand LowNOx MainBurners. The SNCRpilottesting was conducted and a report submitted on December 9, 2009 detailingthe results. The secondpilot testproposed was installation ofa LowNOx MainBurner. Minntac commissioned the design ofa multifuel burner and it was installed in May 2010 onAgglomerator Line 7. 

### Summary The concept behlnd the LowNOx Main Burneris to obtainthe proper airto fuel ratios and flame shape to minimize the generation ofNOx. Upon start-up, initial testing was conducted on each fuel blend to: ensurethere were no operational orquality issues, test core and annual gas to determine the optimumpercentages, and deternline optimum air to fuel ratios. Testinghas been conducted on 100% natural gas, and fuel blends ofcoaVgas and biomass/gas. Burnerdesign issues have been identified while utilizingthe solids fuels, so the majority ofthe testing has been conducted on optimizing the burner while burning 1

00%natural gas. Details onthe pilot testing and identified issues are further outlined in the attached report. However, preliminary results indicate that the 70% reduction goal is achlevable. Additional testing was hindered in late September and early Octoberdue to issues withthe Line 7 CEMS. Further optimization ofthe burner was not achlevable without accuratereal-timeNOx values.The following criteriawill be used to evaluate the control technology: technical feasibility or impact to pellet quality; significantNO,reduction; cross media impacts; multi-pollutant co-control benefits; energy efficiency or consumption impact; and economic feasibility. The following is a briefdiscussion oneach ofthe criteriabased upon the pilottesting conductedto date.

• Technical feasibility or impact to pellet quality In an indurating line greenballs are oxidized and heat hardened into pellets. The process involves preheating, drying, hardening, oxidizing and cooling. Excess air is needed inorderfor the processto work. The furnace is designed to operate at 2400

### oF in orderto meetproduct quality specifications. Theprocess temperature requirements result in someNOxreduction technologies being technically infeasible. Based on operating infotmation since installation ofthe bumer on Line 7, this is a technically feasible NOx control technology. In addition, negative impacts to pellet quality have notbeenidentified as a result ofthis technology. • SignificantNOx reduction Based on initialtest data, this technology has provena 70%NOxreductionis achievable, whichis a significant reduction inNOx emissions. • Cross media impacts SeveralNOx control technologies while reducing NOx emissions have a negative impactto either otherpollutants or media. Based on infotmation gathered to date, no cross media impacts have been identified. • Multi-pollutant co-control benefits: Basedoninformation gathered to date, no multi-pollutant benefits have been identified. Intheory operatingthe burner at the proper air to fuel ratio improves combustion and therefore couldpotentiallyhave a benefitto products of combustion. • Energy Efficiency or consumption impact Optimization ofthe burner is still being conducted, therefore this is still being evaluated. Howeverit is not anticipated to have a greaterthan 10% impact onfuel consumption. • Economic Feasibility Due to design changes being incorporated into the next burner, full evaluationofa potential fuel penalty, and optimization activities still on-going, an actual costper tonofpollutantremoved is preliminary. Based onthe capital costfor the butner and ancillary equipment andthe preliminary emissions reductions this technology is economically feasible. Path Forward Preliminarytesting onthe Line 7 LowNO,MainBurner has proven that this technology is capable ofachieving the permit goal. Although some design issues have been identified for the solid fuels, these changes are being incorporated into the next generationbutner design that will beinstalled inthe Spring of2011 on Line 6 during itsmajor outage. A schedule for continued pilottesting on Line 7 and thepilot testing schedulefor Line 6 is includedbelow. Ifyou should have any additional questionsregardingthis submittal,please feel free to contactme at 218-749-7364 or clbartovich@uss

.com. Sincerely,

# 0----;&~-**v~** ChrissyBartovich Manager

- Environmental Services

cc: SuzanneBaumann, MPCA Tishie Woodwell, USS MikeDzurinko, USS JamesJarvi, USS

### United States Steel Corporation Minnesota Ore Operations- Minntac NOxPilot Testing Schedule October 22, 2010 Continued Pilot Testing L 7 Low NOxMain Burner 1. Installation ofnewcoal tip design 2. Perfotmevaluation ofperformance on coal 3. Provide anupdate to the MPCA 4. Perform evaluation ofperformance onbiomass** 5. Complete full scale evaluation 6. Submit final report to MPCA

L6LowNOxMain BurnerPilot Testing 1. Install bumer during majorrepair 2. Initial startup after installation 3. Performinitial evaluation ofperformance 4. Provide an update to the MPCA 5. Complete full scale evaluation 6. Submit final report to MPCA MilestoneDate* November 2010 30 days after Step 1 30 days after Step 2 30 days after Step 2 60 days after Step 4 60 days after Step 5

Milestone Date* April2011 30 days after Step 1 45 days after Step 2 30 days after Step 3 120 days after Step 3 60 days after Step 5
*An interim milestone date, which ifmissed, is not a violationprovidedthatthe final compliance date(s) are met. **As noted inthe attached technical report, U. S. Steel continues to work with the bumer vendor on a solutionto increasing biomass delivery to the burner. Any delay encountered in biomass will not delay the final repot1.

# U. S. Steel Minntac
Line 7 Low NOx Main Burner Preliminary Pilot Testing Report



# October22, 2010Executive Summary A combination of short term plant testing and process optimization has been conducted on the new Line 7 low NOx main burner since its installation in May 2010. Short term testing data concludes the low NOx main burnerto be a technically feasible method to achieve the goal of 70% NOx reduction. Information from the Line 7 low NOx main burner is currently being used to improve the design for Line 6's new low NOx main burner scheduled for April 2011. The following challenges have been identified and progress is ongoing to resolve them:

• Investigating methods to increase the total combustion air to the new Line 7 low NOx main burner when burning natural gas to achieve the proper stoichiometric ratio.

• Designing the new Line 6 low NOx main burner to have enough combustion air to achieve the proper stoichiometric ratio while burning natural gas.
• Coal flame shape is bushy on the new Line 7 low NOx main burner. Investigating methods to achieve longer and tighter coal flame shape to reduce NOxon Line 7 while burning coal.

• Design modification to the new Line 6 low NOx main burnerto have a longer and tighter flame shape while burning coal. This will be accomplished by reconfiguring the position ofthe combustion airon the outer most position on the new Line 6 low NOx main burner. The Line 7 low NOx main burner currently has coal as the outer most position resulting in a bushier flame.

• Challenges delivering more than 150 lb/min of biomass on the new Line 7 low NOx main burner. Investigating methods to achieve higher rates of biomass for the existing Line 7 low NOx main burner and design the new Line 6 low NOx main burner to achieve higher rates of biomass. The higher rates would be to deliver biomass levels the existing main burners are capable of utilizing. A 10% increase in process fuel was predicted with the installation of the low NOx main burner. At this time the full effects of increased process fuel are not quantified, but it is not anticipated to exceed a 10% increase as a direct cause from the burner. No significant change in pellet quality has been identified as a direct cause from the new low NOx main burner.NOx Reduction Goals At permit issuance, NOx emissions are to be less than or equal to 13,300 tons/year using a 365-day rolling sum from all five waste gas stacks combined. On February 1, 2011 a permit limit of 7,300 tons per year is effective. The goal is to achieve 70% NOx reduction from the 13,300 tons/year baseline to 3,990 tons/year using a 365-day rolling sum from all five waste gas stacks combined. To determine a simplistic approach to identifying a target for the testing, the 70% goal was broken down as follows: 3,990 tons/year goal to reflect one induration line would be 182.2 lb/hr 3,990 tons • 1year • 2000 lbs • year 365 days ton •
___ 1'---- 24 hours 5 induration lines day 182.21bs/hrfor each induration line
NOx emissions on Line? are measured with a Sick AG Model GM 31-6 Continuous Emissions Monitoring System. This is an in-situ instrument with a 5 foot measurement probe. Relative Accuracy Test Audits (RAT As) were conducted in May 2010 with acceptable results.NOx Testing with Natural Gas 

### Table 1.1, summarizes the testing conducted utilizing natural gas on 6/11/10 and 9/23/10. The testing parameters consisted of burning 100% natural gas while varying the total combustion air to reduce NOx. The NOx was measured on-line by Line 7's GEM. On 9/22/10 the combustion air VFD was sped up according to the manufacturer recommendation to achieve more air to the burner. The goal of <182.2 lb/hr was achieved during the 9/23/10 test. Based on the information obtained during the testing it is clear that the stoichiometric ratio is crucial to lowering NOx emissions. As previously discussed we are currently unable to provide the level oftotal combustion air necessary to drive the emissions down lower. U.S. Steel is investigating additional methods to increase the total combustion air.

Table 1.1 Line 7 New Low NOx Main Burnerwhile Testing on 100% Natural Gas (6/11/10)

Feed Set Point Coal Feed Kiln Gas Total Air Total Fuel NOx Stoich (LTPH) (lb/hr) (MSCF) {lb/hr) (lb/hr) (lb/hr) Ratio

540 0 188 86,631 9,424 635 0.58 540 0 190 101,398 9,515 510 0.67 540 0 192 118,241 9,623 398 0.77 540 0 183 116,930 9,151 367 0.80 540 0 172 117,042 8,596 272 0.86 540 0 192 142,207 9,611 220 0.93 Line 7 New Low NOx Mian Burner while Testing on 100% Natural Gas

- VFD Speed Increased (9/23/10)

Feed Set Point Coal Feed Kiln Gas Total Air Total Fuel NOx Stoich (LTPH) (lb/hr) (MSCF) (lb/hr) (lb/hr) (lb/hr) Ratio

560 0 234 100,460 11,717 611 0.54 560 0 233 114,301 11,686 484 0.62 560 0 226 158,766 11,327 236 0.88 560 0 223 173,519 11,214 177 0.97Graph 1.1 further illustrates NOx emissions are reduced as the stoichiometric ratio increases

.



### Graph 11 

# . Line 7 Low NOx Main Burner with 100% Gas: NOx vs. Stoich Ratio 1 ,000

900 

# - 800 r--- - - - 700 1-



# .. 600 ........

### ~ 

# , ...............

## ~ 500

### :.............. 400

# ""' 300**~** 200 

# - 100

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 1 00"A Stoichiometric Ratio

- New Low NOx Main Burner afterVFD Speed Increase (9/23/2010)

- New Low NOx Main Burner (6/11 /2010)



## - Line 7's Old Main Burner with Feed at 540 L TPH (Historic)

### NOx Testing With Coal Table 1.2, summarizes the testing conducted with coal on 8/11/10 and 10/13/10. The testing parameters consisted of holding the coal feed rates steady and burning small amounts of kiln gas while varying the total combustion air to reduce NOx. The NOx was measured on-line by Line 7's CEM. The flame shape was observed to be bushy in all cases. More burner optimization is needed to improve flame shape.

Table 1.2 New Low NOx Main Burnerwhile Testing on 12,500 lb/hr Coal Rates (8/11/10) Feed Set Point Coal Feed Kiln Gas Total Air Total Fuel NOx Stoich Line 7 Line 7 (LTPH) (lblhr) (MSCF) (lblhr) (lblhr) (lblhr) Ratio %Gas %Coal

540 12,506 37 25,425 14,386 321 0.21 48 52 540 12,544 40 33,121 14,473 294 0.27 48 52 540 12,521 40 52,610 14,518 236 0.42 48 52 540 12,453 40 53,225 14,471 226 0.43 49 51 540 12,557 48 62,522 14,951 226 0.48 50 50 540 12,485 43 82,698 14,622 212 0.66 49 51 540 12,516 49 125,046 14,910 247 0.96 50 50 New Low NOx Main Burnerwhile Testing on 7,600 lb/hr Coal Rates (10/13/10) Feed Set Point Coal Feed Kiln Gas Total Air Total Fuel NOx Stoich Line 7 Line 7 (LTPH) (lblhr) (MSCF) (lblhr) (lblhr) (lblhr) Ratio %Gas %Coal

540 7,696 82 51,657 11,802 414 0.42 70 30 540 7,690 79 71,412 11,637 284 0.60 69 31 540 7,703 84 90,988 11,860 267 0.74 70 30 540 7,668 91 111,476 12,254 268 0.86 71 29 540 7,686 105 129,471 12,925 284 0.93 72 28 ** Note: % Natural Gas and Coal includes the Preheat BurnersGraph 1

.2 shows the NOx is lowest at around a stoichiometric ratio of66%, which is typical for coal combustion and expected. The goal to have the NOx < 182.2 lb/hr, which was not achieved during these tests. This is attributed to the improvement needed with respect to the flame shape which is discussed in more detail below

.



### Graph 1.2

450 400 'i:' 350 .c 

### ;e 300 )( 250 0 z 200 150 100 1--

1-

0% Line 7 Low NOx Main Burnerwith Coal: NOx vs. Stoich Ratio
'

# ""'"

............**~**

### ~ 

## "-.,.



# -----

20% 40% 60% Stoichiometric Ratio 

# __..,.**~**

80% 100%

- Poly. (New L ow NOx Main BurnervAlile Testing on 12,500 lb /hr Coal Rates (8 /11110))

- Poly. (New lowNOxMain B urnerooile Testing on7,600 lb/hrCoal Rates (10/13/10 )) 120%Burner Optimization to Reduce NOx The following activities are on-going to optimize NOx reduction: Increase Stoichiometric Ratio • Currently investigating methods to increase total combustion air on Line 7. • The Line 6 low NOx main burnerwill have increased total combustion air. Improve Coal Flame Shape On 7/28/10 the new coal tip insert was installed on Line 7 to restrict the coal displacement at the burnertip. Prior to the new insert, when testing with coal at various rates of combustion air atypical results were found and there was no consistent relationship to NOx and the stoichiometric ratio. The coal exhaust pressure was identified to be significantly lower. Since the coal insert tip has been installed the typical coal mill backpressure has been obtained. By maintaining the historical coal mill back pressure, typical NOx vs. Stoichiometric Ratio curves have been developed, meaning the new coal insert is maintaining a more consistent process which will help to optimize the coal burner. Before the burner tip was installed, one test showed NOx at 174 lb/hr with a minimum coal rate and natural gas. This result has not been repeated with the new coal tip. To further improve the flame shape, the burner manufacturer has designed a new coal cone to replace the existing tip which will allow proper backpressure and deflect the coal to the center ofthe flame. The burner manufacture has predicted this new coal cone will reduce NOx by 20% from current levels while utilizing coal. The coal tip is scheduled to be installed during the November outage.

Testing With Biomass The new Line 7 low NOx main burner has not been able to achieve significant delivery of over 150 lb/min of biomass due to plugging issues. These issues are currently under investigation to develop a solution forthe new Line 6 low NOx main burner.

Impact on Energy Efficiency (Process Fuel Consumption) In industry, low NOx main burners have been known to increase fuel by 10%. At this time the full effects of increased process fuel are not quantified, but they do not exceed a 10% increase as a direct cause from the burner.
Impactto Pellet Quality No significant change in pellet quality has been identified as a direct cause from the new low NOx main burner.Line 6 Low NOx Main Burner U

.S

. Steel has authorized a new low NOx main burnerfor Line 6 to be installed during the major scheduled forApril 2011

. Information from the Line 7 low NOx main burner is currently being used to improve the design forthe further burner optimization

. Figure 1.1, shows the current Line 7 low NOx main burner has the coal on the outer most ring ofthe burner and the combustion air in inside ofthe coal burner

. The combustion air will be placed on the very outer most position ofthe new Line 6 low NOx main burner (this figure is not shown)

. Figure 1.1

r- --CoilI Annllllls r---Milke-up Ai r Annullis Annulus GasConclusions A combination of short term plant testing and process optimization has been conducted on the new Line 7 Low NOx Main Burner since the installation in May 2010. Short term testing data concludes the low NOx main burner to be a technically feasible method to achieve the goal of 70% NOx reduction. Information from the Line 7 low NOx main burner is currently being used to improve the design for Line 6's new low NOx main burner scheduled for April 2011. The following challenges have been identified and progress is on-going to resolve them:
• Increasing combustion air when burning natural gas to achieve the proper stoichiometric ratio.

• Improve coal flame shape on the new Line 7 low NOx main burner. Investigating methods to achieve longer and tighter coal flame shape to reduce NOxon Line 7 while burning coal.

• Design modification to the new Line 6 low NOx main burner to have a longer and tighter flame shape while burning coal.

• Challenges delivering more than 150 lb/min of biomass on the new Line 7 low NOx main burner. A 10% increase in process fuel was predicted with the installation ofthe low NOx main burner. At this time the full effects of increased process fuel are not quantified, but it is not anticipated to exceed a 10% increase as a direct cause from the burner. No significant change in pellet quality has been identified as a direct cause from the new low NOx main burner.