U. S. Steel Corporation Minnesota Ore Operations P

.O. Box 417 Mt. Iron, MN 55768 CERTIFIED MAIL 7009 0820 0001 3944 4252 May 13,2011 ChristopherNelson, P.E. Manager Strategic Projects Sector Industrial Division MinnesotaPollution ControlAgency 520 LafayetteRoadNorth St. Paul, MN 55155 Re: Final Pilot Test Results- Low

### NOxMain Burner As peryour letter dated January 18,2011 and the approved schedule, United States Steel Corporation, Minnesota Ore Operations

- Minntac is providing a final repmt for the Line 7 pilottesting ofthe LowNOxMain Burner. Background The air emissions permitfor Minntac contains requirements for aNOx reduction goal of at least 70% from the baseline limit of 13,300 tons per year. To achieve this goal, pilot testing ofNOxtechnologies are to be conducted. Minntac submitted a pilottesting schedule in April 2009 to the MPCAfor approval which includedpilottesting SNCR and LowNOx MainBurners. The SNCRpilottesting was conducted and a repmt submitted onDecember 9, 2009 detailingthe results
. The secondpilottestproposedwas installation ofa LowNOx MainBurner. Minntac commissioned the design ofa multifuel burnerthatwas installed inMay 2010 onAgglomerator Line 7. Summary The conceptbehind the LowNOx Main Burneris to obtainthe proper air to fuel ratios andproperflame shape to minimize the generation ofNOx
. Upon statt-up, initial testing was conducted oneach fuel blendto: ensure there were no operational or quality issues, test core and annual gas to dete1mine the optimumpercentages, and determine optimum air to fuel ratios. Testinghas been conducted on 100% natural gas, andfuel blends ofcoal/gas and biomass/gas. Burner design issues were identified while utilizing the solidfuels, so the majority ofthe testinghas been conducted to optimize the burner while burning 100% natural gas. Results indicate that the 70% reduction goal is achievable. Issues identified while utilizing solid fuels onLine 7 facilitated design changes for the LowNOxMain Burnerthatwas installed on Line 6 inApril 2011. These included ensuring adequate combustion air for theproper air to fuel ratio and reconfiguring the placementofthe combustion air to improve the flame shape
.The following criteriawill be usedto evaluate the controltechnology: technical feasibility or impactto pellet quality; significantNOx reduction; cross media impacts; multi-pollutant co-control benefits; energy efficiency or consumptionimpact; and economic feasibility. The following is abriefdiscussion on each ofthe criteriabased uponthe pilottesting conductedto date.

• Technical feasibility orimpact to pellet quality In an indurating line greenballs are oxidized andheathardened into pellets. The process involvespreheating, drying, hardening, oxidizing and cooling. Excess air is needed in orderfor the processto work. The furnace is designedto operate at 2400

### oF in orderto meetproduct quality specifications. Theprocess temperature requirementsresult in someNOxreductiontechnologies beingtechnically infeasible. Based on operating information since installation ofthe burner on Line 7, this is a technically feasible NOx control technology. Some initial concerns were identified with lower compressions, however, effort continued with optimizingthe burner. There are no negative impacts to pellet quality currently identified. • SignificantNOx reduction Based onperformance data, this technology has proven a 70% NOxreduction is achievable, which is a significantreduction inNOx emissions. • Cross media impacts SeveralNOxcontrol technologies while reducingNOx emissions have a negative impactto either otherpollutants or media. Based oninformation gatheredto date, no cross media impacts have been identified. • Multi-pollutant co-control benefits: Based oninformation gatheredto date, no multi-pollutantbenefits have been identified. Intheory operatingthe burner atthe proper airto fuel ratio improves combustion andtherefore couldpotentiallyhave a benefitto products of combustion. • Energy Efficiency or consumption impact A fuel penalty of 10.5% was realized after installation ofthe newburner. Efforts continueto optimizethe performance and minimizethe fuel penalty. • Economic Feasibility Dueto design changes being incorporatedinto the nextburner, an actual costper ton ofpollutantremoved would be preliminary. Based onthe capital costfor the burner and ancillary equipment, design changes and the preliminary emissions reductions this technology is economically feasible. Path Forward Performance oftheLine 7 LowNOxMainBurnerhas proven thatthis technology is capable ofachievingthe permit goal. Although some designissues have beenidentified for the solidfuels, these changes were addressed for the next generationburner design that was installed inApril2011 onLine 6 during its major outage. Updates onthe pilot testing on newburner'sperfotmance will beprovided as perthe approved schedule.Ifyou should have any additional questions regarding this submittal, please feel free to contactme at 218-749-7364 or clbartovich@uss.com. Sincerely,

ChrissyBartovich Director

- Environmental

cc: Suzanne Baumann, MPCA Tishie Woodwell, USS Mike Dzurinko, USS Stephani Campbell, USS James Jarvi, USS

# U. S. Steel Minntac
Line 

# 7 Low 

# NOx Main Burner
Final Testing Report

May 13, 2011Executive Summary A combination of short term planttesting and process optimization has been conducted on the new Line 7 low NOx main burner since the installation in May 2010. Shortterm testing data concludes the low NOx main burnerto be a technically feasible method to achieve the goal of 70% NOx reduction from the baseline, averaging 181.5 lbs/hr of NOx from December 6, 2010- March 8, 2011. Knowledge gained from the Line 7 low NOx main burnerwas used to improve the design for Line 6's new low NOx main burner installed in April 2011. The following challenges have been identified and progress is ongoing to resolve them:
• Designed the new Line 6 low NOx main burnerto have adequate combustion airto achieve the proper stoichiometric ratio while burning natural gas.
• Re-designed the new Line 6 low NOx main burnerto have a longer and tighter flame shape while burning coal. This was accomplished by reconfiguring the position ofthe combustion air on 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 bushyflame.
• Designed modifications to the biomass supply line so that the biomass is not settling out in the burner pipe. A 10% increase in process fuel was predicted with the installation ofthe low NOx main burner. A process fuel increase of 10.5% was realized afterthe installation ofthe Line 7 low NOx main burner. Process optimization efforts are in progress to minimize this fuel penalty. The only quality issue found to date has been lower compression values. Compression is a key process variable to ensure pellets maintain integrity en route to the blastfurnace. Burner optimization is ongoing to maintain quality specifications.

1

## 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 peryear became 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 * day * 1 = 182.21bs/hrfor each induration line year 365 days ton 24 hours 5 induration lines NOxemissions on Line 7 have been measured with a Sick AG Model GM 31-6 Continuous Emissions Monitoring System (GEMS). This is an in-situ instrument with a 5 foot measurement probe. Relative Accuracy TestAudits (RAT As) were conducted in May 2010 with acceptable results. In the Spring of2010 procurement was initiated for replacing the in-situ GEMS for Lines 6 and 7 with newAmetek extractive units. The new GEMS were installed and passing Certification Tests were completed on February 23 and 24, 2010 for Line 6 and 7, respectively. With their installation, both Keetac and Minntac now have identical GEMS units on all lines, allowing for easier spare parts management and maintenance activities. Also, replacing the previous Sick-Mahik units on Lines 6 and 7 will lead to decreased downtime for monitored emissions. USS continues discussions with the MPCA on a temporary data substitution method for the new GEMS until sufficient data has been generated. In addition, with the utilization of GEMS, USS was able to determine a new lower maximum potential value of NOxemissions for Line 7. Without GEMS, such a reduction may not have been accurately determined.



### 2

### Burner In order to meet the 70% NOx reduction goal, a low NOx main burnerwas installed on Line 7 in May 2010. A general outline ofthe burner is shown in Figure 1.1. The following are major additions and changes that were made to the burner in comparison to the burner previously installed on Line 7:
• Increased the kiln burner opening. The burner is larger in diameter due to the addition ofcombustion air. • Modified the natural gas train. The new burner has a pilot line and two main gas lines versus one gas line on the old burner. • Installed two combustion air fans (operating and spare). The combustion fans have an inlet damper, outlet damper, and VFD. The inlet damper is used for control and the outlet damper is for isolation (open/close). • Installed a flame scanner for the pilot flame and a flame scannerforthe main flame. • Modified the Burner Management System (BMS), which controls and manages the safety interlock system for the burner.

Figure 1.1
FUEL OIL

### )~~"G 

# I NATURALGA£>--0----------,-1--,1
OPERATING

### ~6~--------------~ :\FLEX :t;FLEX ) LINE 

### 5 LINE 

# l". 

# J

3 Line 7 KILNThe Line 7 low NOxburner tip configuration is shown if Figure 1.2. The burner is capable of utilizing natural gas, coal, biomass, and fuel oil. There is a dual gas gun on the burner. The annulus gas is used initially to start-up the burner

. The core gas is used to lengthen the flame and is considered to de-stabilize the flame. 

### Figure 1.2

----- Coal Annulus



### Burner Start-up r---- Combustion Air Annulus**~-** Biomass Annulus

.· Atomizing Air Annulus ...........,. Gas Core Gas Fuel Oil Gun

The burner was started in May 2010 after completion ofthe major repair outage. Below is an outline ofthe issues that have occurred during start-up ofthe burner:
• Problems with lighting the flame. This is due to issues with the flame scanner, pilot light, etc. The issues have been documented and are being worked on to ensure that they are corrected. • Spalling ofthe refractory on the discharge end ofthe kiln occurred during the start-up from the May 2010 and February 2011 major repair outage
. Corrective actions are under investigation. • Losing the flame during heat-up. The Manufacturer has provided assistance with addressing some ofthe issues; however, challenges still exist with heat-up. The operators adjust the gas and combustion air manually during heat-up. The end goal is automate the heat-up.
4

### NOxTesting with Natural Gas The primary means of NOx control with the Line 7 low NOx main burner is accomplished by controlling the stoichiometric ratio of air to fuel. Initially, there were issues with the combustion fans being unable to deliverthe required amount ofair to achieve the proper stoichiometric ratio and achieve the testing target of 182.2 lbs/hr. The following are items that have been done to correct this issue:
• The combustion fan VFD was sped up according to manufacturer recommendations in September 2010. • The combustion air inlet to the burner was increased in November2010. The burner inlet was 20" in diameter and was increased to 26" to reduce the friction loss. A summary ofthe testing on natural gas on 9/23/10 is shown in Table 1.1. The testing parameters consisted of burning 100% natural gas while varying the total combustion airto reduce NOx. The NOx was measured on-line by Line 7's GEMS. The goal of <182.2 lb/hrwas achieved during the testing. The data demonstrates that NOx is reduced when the stoichiometric ratio increases and is crucial to lowering NOx emissions. Table 1.1 Line 7 New Low NOx Main Burner whileTesting on 100% Natural Gas

- VFD Speed Increased (9/23/10)

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

560 0 234 100,460 11,717 611 560 0 233 114,301 11,686 484 560 0 226 158,766 11,327 236 560 0 223 173,519 11,214 177

5 Stoich Ratio 0.54 0.62 0.88 0.97A graphical illustration of how NOx is reduced when the stoichiometric ratio increases is shown on Graph 1.1. 

### Graph 11 

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

900 

# - 800 700**~** 600 

# - 

# ""' .a )( 500

### ~ 0 z 400 -

### ~ 300

### ~ 200 100

00% 10% 20% 30% 40% 50% 60% 70% 80% 90% Stoichiometric Ratio

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

- Line 7's Old Main Burner Historic Performance 

# -

100%

The changes to the combustion fans resulted in more air delivered through the burner, which reduced NOx emissions. However, the overall effectto the system resulted in the pellets exiting the cooler to be excessively hot and creating excess steam. This created poor visibility on the burnerfloor which is a safety concern. Additionally, pellets being too hot can result in a conveyor belt fire which is another safety concern. The reason for the excess steam is the addition of combustion air in the burner offsets the 3Afan which is used for cooling the product. The cooler dumping hot also results in excessive mechanical wear, high fuel rates, and below target pellet quality. The next phase of natural gastesting involved optimizing the process to balance safety, NOxemissions, pellet quality, mechanical wear, and production. Graph 1.2, is a process behavior chartfor Line 7's daily NOx when running 100% natural gas. The chart shows Line 7's process is capable ofa 70% NOx reduction, averaging 181.51bs/hrofNOxfrom December6, 2010-March 8, 2011. There were not any significant safety, quality, mechanical wear, and/or production issues as a direct result ofthe Line 7 low NOx main burner.

6

### Graph 1.2 Line 7- Low NOx Main Burner 100% Natural Gas 260 240
220

--------------- UCL=217

.3 200 - · - - - - - - - - · - - - - - - - - - - - - - - · - - - - - - · - - - - - - - - - · · - - - - - - - · +2a = 205.4 

# i 180 -- - -.- +1 a = 193.5 AVG=181.5

## ~ 160
140 120 100 0 0 0**~**

# ~ ~ ..... C\1

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

## ~ ..... ..... ..... i::::**~** ..... ..... ..... 0**~** -1 a = 169.6 -2 a = 157.7 LCL = 145
.8



### NO!Testing With Coal During testing, Line 7 was unable to achieve the NOx goal of 182.2 lbs/hrwhen combusting a coal and natural gas mix. In addition, the flame has been observed to be bushy instead ofa longer and tighter flame shape. The following items were implemented in an attemptto correctthis issue: • A coal tip insertwas installed in July 2010 to restrict the coal displacement at the burner tip. The addition ofthe coal tip insert did improve the coal mill backpressure to typical levels and allowed testing to determine the proper stoichiometric ratio. However, NOx did not decrease afterthe modification. • A coal cone was installed in November 2010 to deflectthe coal to the center ofthe flame. A 20% improvement was anticipated, however, the NOx did not decrease afterthe installation. Coal testing conducted on 8/11/10 and 10/13/10 is summarized in Table 1.2. The testing parameters consisted of keeping the coal feed rates steady and burning small amounts of kiln gas while varying the stoichiometric ratio to reduce



### 7

### NOx. The 

### NOx emissions were measured on-line by Line 7's CEMS. The flame shape was observed to be bushy in all cases.

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) (lb/hr) (MSCF) (lb/hr) (lb/hr) (lb/hr) 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 BurnerwhileTesting 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) {lb/hr) {MSCF) (lb/hr) (lb/hr) (lb/hr) 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 Burners Itwas determined that 

### NOx is lowest at approximately a stoichiometric ratio of 66%, which is typical for coal combustion. This is depicted by Graph 1.3. The goal to have 

### NOx emissions < 182.2 lb/hrwas not achieved during any ofthe testing. This is attributed to the improvement needed with respect to the flame shape, which is being addressed in the next burnerdesign on Line 6.



### 8Graph 1.3

450 400 -.::- 350 .s::**~** 300 >< 250 0 z 200 150 1000% 

### Line 7Low NOx Main Burnerwith Coal: NOx

### vs. Stoich Ratio 

# '**~**

20% ....

# "'

# ' ..........._ 

# ----

40% 60% Stoichiometric Ratio ..--"'



# -----

80% 100%

-Poly. (New Low NOxMain BurnerVvtlile Testing on 12,500 lb/hr Coal Rates (8/11/10))

- Poly. (New Low NOxMain BurnerVvtlile Testing on 7,600 lb/hr Coal Rates (10/13/10))



### Testing With Biomass 120%

The new Line 7 low NOx main burner has not been able to achieve the desired delivery of over 150 lb/min of biomass due to plugging issues. This issue was investigated and it has been concluded thatthe biomass is settling in the burner pipe due lowflow velocity. A change to the biomass lines has been investigated to resolve the settling.

9

### Impact on Energy Efficiency (Process Fuel Consumption) In industry, low NOx burners have been known to increase fuel consumption by 10%. Graph 1.4, shows the MBTU/ton on Line 7 from November 2009 - September 2010. The low NOx main burnerwas installed in May 2010 during the major repair outage. Process fuel increased by 10.5% afterthe installation of the Line 7 low NOx main burner. Process optimization efforts are in progress to minimize this fuel penalty. Graph 1.4

m 0 0**~** ..... 

# - ..... ..... Line 

### 7 - MMBTU/ton (November 2009- September 2010)
10.5%Increase inFuel

m 0 0 0 0 0 0 ..... ..... ..... ..... ..... 0 0 0 0 0 0**~ ~ ~** **~ ~ ~**  ..... ..... ..... ..... ..... ..... N 

# - N M**~** ;r; ..... .....



### 10 0 0 0
..... c.; ..... 0 0**~ ~** **~** ..... ..... ..... <0**~** co

### Impactto Pellet Quality The only quality issue found to date has been lower compressive strength

. Compressive strength is a measurement ofthe pellets ability to resist breakage under compression. Graph 1.5, shows the Line 7 compressions from November 2009 - February 2011. In mid-August, the compressions decreased on all lines, but Line 7 compressions were the lowest. Burner and process optimization is ongoing to maintain quality specifications.

Graph 1.5 Line 7 -Compressions 500 480 460 

# ! 440 420 c 0 400 ·u; VI 

## e 380 Q. E 360 0 0 340 320 MAJOR 300 Ol Ol 0 0 0 0 0 0 0 0 0 0 0 0 ...... Q Q ...... 

# - ...... ...... :!::: ...... ...... :!::: :!::: :!::: :!::: :!::: :!::: :!::: 

# - - - -

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

# - N 

# -

...... ...... N (;)**~** i?i (0 ;:::: 00 a; 0 

# - N 

# -

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

11

### Line 6 Low NO! Main Burner U. S. Steel installed a new low 

### NOx main burner on Line 6 during the major repair outage in April 2011. The burner is a second generation design based on results from the Line 7 installation. Information on Line 6 testing progress will be reported perthe MPCA approved schedule. Due tothe issues identified on the Line 7 low 

### NOx main burner, design changes were incorporated on the Line 6 low 

### NOx main burner. These changes are:
• Designed the new Line 6 low 

### NOx main burner to have sufficient combustion airto achieve the proper stoichiometric ratio while burning natural gas.
• Designed the new Line 6 low 

### NOx main burnerto achieve a longer and tighterflame shape while burning coal. This was accomplished by reconfiguring the position ofthe combustion air on the outer most position on the new Line 6 low 

### NOx main burner (See Figure 1.21. The Line 7 low 

### NOx main burner currently has coal as the outer most position, resulting in a bushyflame.
• Improved the design ofthe biomass line so that the biomass is not settling out in the burner pipe.



### 12

### Conclusions A combination ofshortterm planttesting and process optimization has been conducted on the new Line 7 low 

### NOx main Burner since its installation in May 2010. Shortterm testing data concludes the low 

### NOx main burner is a technically feasible method to achieve the goal ofa 70% 

### NOx reduction, averaging 181.5 lbs/hr of 

### NOx forthe period of December6, 2010 - March 8, 2011, achieving the goal. Information from the Line 7 low 

### NOx main burnerwas used to improve the design for Line 6's new low 

### NOx main burner, which was installed in April2011. Information on this progress will be reported as required. The following challenges have been identified and progress is ongoing to resolve them:
• Designed the new Line 6 low 

### NOx main burnerto have sufficient combustion airto achieve the proper stoichiometric ratio while burning natural gas.
• Designed the new Line 6 low 

### NOx main burnerto have a longer and tighter flame shape while burning coal by reconfiguring the position ofthe combustion airversus Line 7.
• Improved the design ofthe biomass supply line so thatthe biomass is not settling out in the burner pipe. A 10% increase in process fuel was predicted with the installation ofthe low 

### NOx main burner. The process fuel increased by 10.5% afterthe installation ofthe Line 7 low 

### NOx main burner. Process optimization efforts are in progress to minimize this fuel penalty. The only quality issue found to date has been lower compression values. Burner optimization is ongoing to maintain quality specifications.



### 13