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 

Christopher Nelson, P.E. 

Manager Strategic Projects Sector 

Industrial Division 

Minnesota Pollution Control Agency 

520 Lafayette Road North 

St. Paul, MN 55155 

Re: Preliminary Pilot Test Results- Low NOx Main Burner 

As per your letter dated September 23, 2010, United States Steel Corporation, Minnesota 

Ore Operations- Minntac is providing preliminary results from the Line 7 pilot testing of 

the Low NOx Main Burner, a schedule for continued pilot testing, and a pilot testing 

schedule for Line 6. 

Background 

The air emissions permit for Minntac contains requirements for a NOx reduction goal of 

at least 70% from the baseline limit of 13,300 tons per year. To achieve tllis goal, pilot 

testing ofNOx technologies are to be conducted. Minntac submitted a pilot testing 

schedule in April 2009 to the MPCA for approval whlch included pilot testing SNCR and 

Low NOx Main Burners. The SNCR pilot testing was conducted and a report submitted 

on December 9, 2009 detailing the results. The second pilot test proposed was 

installation of a Low NOx Main Burner. Minntac commissioned the design of a multifuel burner and it was installed in May 2010 on Agglomerator Line 7. 

Summary 

The concept behlnd the Low NOx Main Burner is to obtain the proper air to fuel ratios 

and flame shape to minimize the generation ofNOx. Upon start-up, initial testing was 

conducted on each fuel blend to: ensure there were no operational or quality issues, test 

core and annual gas to determine the optimum percentages, and deternline optimum air to 

fuel ratios. 

Testing has been conducted on 100% natural gas, and fuel blends of coaVgas and 

biomass/gas. Burner design issues have been identified while utilizing the solids fuels, so 

the majority of the testing has been conducted on optimizing the burner while burning 

1 00% natural gas. Details on the 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 October due to 

issues with the Line 7 CEMS. Further optimization of the burner was not achlevable 

without accurate real-time NOx values. 
The following criteria will be used to evaluate the control technology: 

technical feasibility or impact to pellet quality; significant NO, reduction; cross media 

impacts; multi-pollutant co-control benefits; energy efficiency or consumption impact; 

and economic feasibility. The following is a brief discussion on each of the criteria based 

upon the pilot testing conducted to date. 

• Technical feasibility or impact to pellet quality 

In an indurating line green balls are oxidized and heat hardened into pellets. The 

process involves preheating, drying, hardening, oxidizing and cooling. Excess air 

is needed in order for the process to work. The furnace is designed to operate at 

2400 oF in order to meet product quality specifications. The process temperature 

requirements result in some NOx reduction technologies being technically 

infeasible. Based on operating infotmation since installation of the bumer on 

Line 7, this is a technically feasible NOx control technology. In addition, 

negative impacts to pellet quality have not been identified as a result of this 

technology. 

• Significant NOx reduction 

Based on initial test data, this technology has proven a 70% NOx reduction is 

achievable, which is a significant reduction in NOx emissions. 

• Cross media impacts 

Several NOx control technologies while reducing NOx emissions have a negative 

impact to either other pollutants or media. Based on infotmation gathered to date, 

no cross media impacts have been identified. 

• Multi-pollutant co-control benefits: 

Based on information gathered to date, no multi-pollutant benefits have been 

identified. In theory operating the burner at the proper air to fuel ratio improves 

combustion and therefore could potentially have a benefit to products of 

combustion. 

• Energy Efficiency or consumption impact 

Optimization of the burner is still being conducted, therefore this is still being 

evaluated. However it is not anticipated to have a greater than 10% impact on fuel 

consumption. 

• Economic Feasibility 

Due to design changes being incorporated into the next burner, full evaluation of a 

potential fuel penalty, and optimization activities still on-going, an actual cost per 

ton of pollutant removed is preliminary. Based on the capital cost for the butner 

and ancillary equipment and the preliminary emissions reductions this technology 

is economically feasible. 

Path Forward 

Preliminary testing on the Line 7 Low NO, Main Burner has proven that this technology 

is capable of achieving the permit goal. Although some design issues have been 

identified for the solid fuels, these changes are being incorporated into the next 

generation butner design that will be installed in the Spring of2011 on Line 6 during its 
major outage. A schedule for continued pilot testing on Line 7 and the pilot testing 

schedule for Line 6 is included below. 

If you should have any additional questions regarding this submittal, please feel free to 

contact me at 218-749-7364 or clbartovich@uss.com. 

Sincerely, 

0----;&~-v~ Chrissy Bartovich 

Manager - Environmental Services 

cc: Suzanne Baumann, MPCA 

Tishie Woodwell, USS 

Mike Dzurinko, USS 

James Jarvi, USS 
United States Steel Corporation 

Minnesota Ore Operations- Minntac 

NOx Pilot Testing Schedule 

October 22, 2010 

Continued Pilot Testing L 7 Low NOx Main Burner 

1. Installation of new coal tip design 

2. Perfotm evaluation of performance on coal 

3. Provide an update to the MPCA 

4. Perform evaluation of performance on biomass** 

5. Complete full scale evaluation 

6. Submit final report to MPCA 

L6 Low NOx Main Burner Pilot Testing 

1. Install bumer during major repair 

2. Initial startup after installation 

3. Perform initial evaluation of performance 

4. Provide an update to the MPCA 

5. Complete full scale evaluation 

6. Submit final report to MPCA 

Milestone Date* 

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 if missed, is not a violation provided that the final 

compliance date(s) are met. 

**As noted in the attached technical report, U. S. Steel continues to work with the bumer 

vendor on a solution to 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 

October 22, 2010 
Executive 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 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 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 burner to have a longer and tighter 

flame shape while burning coal. This will be accomplished by reconfiguring the position 

of the 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 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 • 1 year • 2000 lbs • 

year 365 days ton 

• ___ 1'----

24 hours 5 induration lines 

day 182.21bs/hr for 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 of total 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 Burner while Testing on 100% Natural Gas (6/11/1 0) 

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 0.97 
Graph 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% 100"A 

Stoichiometric Ratio 

- New Low NOx Main Burner after VFD Speed Increase (9/23/201 0) 

- New Low NOx Main Burner (6/11/201 0) 

- 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 Burner while 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 Burner while 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 Burners 
Graph 1.2 shows the NOx is lowest at around a stoichiometric ratio of 66%, 

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 Burner with Coal: NOx vs. Stoich Ratio 

' 

""'" ............ ~ 

~ "-.,. 

----- 20% 40% 60% 

Stoichiometric Ratio 

__..,. 

~ 

80% 100% 

- Poly. (New Low NOx Main Burner vAlile Testing on 12,500 lb/hr Coal Rates (8/11110)) 

- Poly. (New low NOxMain Burnerooile Testing on 7,600 lb/hr Coal 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 burner will 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 burner tip. 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 of the 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 for the 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. 

Impact to 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 burner for Line 6 to be installed 

during the major scheduled for April 2011 . Information from the Line 7 low NOx 

main burner is currently being used to improve the design for the further burner 

optimization. 

Figure 1.1, shows the current Line 7 low NOx main burner has the coal on the 

outer most ring of the burner and the combustion air in inside of the coal burner. 

The combustion air will be placed on the very outer most position of the new Line 

6 low NOx main burner (this figure is not shown). 

Figure 1.1 

r---Coil I Annllllls 

r---Milke-up Air Annul lis Annulus Gas 
Conclusions 

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 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.