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 

Christopher Nelson, P.E. 

Manager Strategic Projects Sector 

Industrial Division 

Minnesota Pollution Control Agency 

520 Lafayette Road North 

St. Paul, MN 55155 

Re: Final Pilot Test Results- Low NOx Main Burner 

As per your 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 pilot testing of the Low NOx Main Burner. 

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 this goal, pilot 

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

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

Low NOx Main Burners. The SNCR pilot testing was conducted and a repmt 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 that was installed in May 2010 on Agglomerator Line 7. 

Summary 

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

and proper flame shape to minimize the generation ofNOx. Upon statt-up, initial testing 

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

test core and annual gas to dete1mine the optimum percentages, and determine optimum 

air to fuel ratios. 

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

biomass/gas. Burner design issues were identified while utilizing the solid fuels, so the 

majority of the testing has 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 on Line 7 facilitated design changes for the 

Low NOx Main Burner that was installed on Line 6 in April 2011. These included 

ensuring adequate combustion air for the proper air to fuel ratio and reconfiguring the 

placement of the combustion air to improve the flame shape. 
The following criteria will be used to evaluate the control technology: 

technical feasibility or impact to pellet quality; significant NOx 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 information since installation of the burner on 

Line 7, this is a technically feasible NOx control technology. Some initial 

concerns were identified with lower compressions, however, effort continued with 

optimizing the burner. There are no negative impacts to pellet quality currently 

identified. 

• Significant NOx reduction 

Based on performance 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 information 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 

A fuel penalty of 10.5% was realized after installation of the new burner. Efforts 

continue to optimize the performance and minimize the fuel penalty. 

• Economic Feasibility 

Due to design changes being incorporated into the next burner, an actual cost per 

ton of pollutant removed would be preliminary. Based on the capital cost for the 

burner and ancillary equipment, design changes and the preliminary emissions 

reductions this technology is economically feasible. 

Path Forward 

Performance ofthe Line 7 LowNOx 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 were addressed for the next generation burner design 

that was installed in April2011 on Line 6 during its major outage. Updates on the pilot 

testing on new burner's perfotmance will be provided as per the approved schedule. 
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, 

Chrissy Bartovich 

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, 2011 
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 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 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 burner was 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 burner to have adequate 

combustion air to achieve the proper stoichiometric ratio while burning 

natural gas. 

• Re-designed the new Line 6 low NOx main burner to have a longer and 

tighter flame shape while burning coal. This was 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 bushy flame. 

• 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 of the low NOx 

main burner. A process fuel increase of 10.5% was realized after the installation 

of the 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 blast furnace. 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 per year 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 * 1 year * 2000 lbs * day * 1 = 182.21bs/hr for each induration line 

year 365 days ton 24 hours 5 induration lines 

NOx emissions 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 Test Audits (RAT As) were 

conducted in May 2010 with acceptable results. 

In the Spring of 2010 procurement was initiated for replacing the in-situ GEMS for 

Lines 6 and 7 with new Ametek 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 NOx emissions 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 burner was 

installed on Line 7 in May 2010. 

A general outline of the 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 of combustion 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 scanner for the 

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 NATURAL GA£>--0----------,-1--,1 OPERATING 

~6~--------------~ 

:\FLEX :t;FLEX 

) LINE 5 LINE 

l". J 

3 

Line 7 KILN 
The Line 7 low NOx burner 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 of the major repair outage. 

Below is an outline of the issues that have occurred during start-up of the 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 of the refractory on the discharge end of the 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 of the 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 
NOx Testing 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 deliver the required 

amount of air 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 November 2010. 

The burner inlet was 20" in diameter and was increased to 26" to reduce 

the friction loss. 

A summary of the 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 air to reduce NOx. The NOx was measured on-line by Line 7's 

GEMS. The goal of <182.2 lb/hr was 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 while Testing 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 

0.97 
A 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 Burner with 1 00% Gas: NOx vs. Stoich Ratio 

1,000 

900 - 800 

700 

~ 600 

- ""' .a 

)( 500 

0 

z 400 - ~ 

300 ~ 

200 ~ 

100 

0 

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 

Stoichiometric Ratio 

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

- 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 effect to the system 

resulted in the pellets exiting the cooler to be excessively hot and creating 

excess steam. This created poor visibility on the burner floor 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 3A fan 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 gas testing involved optimizing the process to balance 

safety, NOx emissions, pellet quality, mechanical wear, and production. Graph 

1.2, is a process behavior chart for Line 7's daily NOx when running 100% natural 

gas. The chart shows Line 7's process is capable of a 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 of the 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 - · - - - - - - - - · - - - - - - - - - - - - - - · - - - - - - · - - - - - - - - - · · - - - - - - - · +2 a = 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/hr when 

combusting a coal and natural gas mix. In addition, the flame has been observed 

to be bushy instead of a longer and tighter flame shape. The following items 

were implemented in an attempt to correct this issue: 

• A coal tip insert was installed in July 2010 to restrict the coal displacement 

at the burner tip. The addition of the 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 after the 

modification. 

• A coal cone was installed in November 2010 to deflect the coal to the 

center of the flame. A 20% improvement was anticipated, however, the 

NOx did not decrease after the 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 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) (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 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) {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 

It was 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/hr was not achieved during any of the 

testing. This is attributed to the improvement needed with respect to the flame 

shape, which is being addressed in the next burner design on Line 6. 

8 
Graph 1.3 

450 

400 

-.::- 350 .s:: 

~ 300 

>< 250 

0 

z 200 

150 

100 

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 Vvtlile Testing on 12,500 lb/hr Coal Rates (8/11/10)) 

- Poly. (New Low NOx Main Burner Vvtlile Testing on 7,600 lb/hr Coal Rates (1 0/13/1 0)) 

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 that the biomass is settling in the burner 

pipe due low flow 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 burner was installed in May 2010 during 

the major repair outage. Process fuel increased by 10.5% after the 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 in Fuel 

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 
Impact to Pellet Quality 

The only quality issue found to date has been lower compressive strength. 

Compressive strength is a measurement of the 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 

·u; 400 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 per the MPCA approved schedule. 

Due to the 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 air to achieve the proper stoichiometric ratio while burning 

natural gas. 

• Designed the new Line 6 low NOx main burner to achieve a longer and 

tighter flame shape while burning coal. This was accomplished by 

reconfiguring the position of the 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 bushy flame. 

• Improved the design of the biomass line so that the biomass is not settling 

out in the burner pipe. 

12 
Conclusions 

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 is a technically 

feasible method to achieve the goal of a 70% NOx reduction, averaging 181.5 

lbs/hr of NOx for the period of December 6, 2010 - March 8, 2011, achieving the 

goal. 

Information from the Line 7 low NOx main burner was 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 burner to have sufficient 

combustion air to achieve the proper stoichiometric ratio while burning 

natural gas. 

• Designed the new Line 6 low NOx main burner to have a longer and tighter 

flame shape while burning coal by reconfiguring the position of the 

combustion air versus Line 7. 

• Improved the design of the biomass supply line so that the biomass is not 

settling out in the burner pipe. 

A 1 0% increase in process fuel was predicted with the installation of the low NOx 

main burner. The process fuel increased by 1 0.5% after the installation of the 

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