## U. S. Steel Minntac

Line 6 Low NOx Main Burner

Final Report

& Facility NOx Management

December 1 , 2011U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 2 of 23 

### Introduction

Title V permit 13700005

- 005 was issued to U. S. Steel Minntac on December 22, 2008. This permit action i ncluded not only NOx limits on a 24

- hour block average and 365

- rolling sum basis, but also put forth requirements to incrementally take steps towards proving a NOx control technology for indurating lines, as nothing was currently installed for this purpose anywhere in the taconite industry. The requirements included Computational Fluid Dynamics (CFD) modeling, a technology review, and ultimately selection of technologies to pilot test. The goal was to find a technically and economically feasible NOx contro l or reduction technology which would be successful on taconite facilities.

In 2009 Minntac conducted a trial of the Nalco Mobotec technology, which is

Selective Non

- Catalytic Reduction, or SNCR. Through the testing it was

determined that the technolo gy was not technically feasible. After further evaluating other technologies, U. S. Steel elected to pilot test a low NOx main burner. This is a NOx reduction technology which has significant cross media benefits as compared to post

- combustion controls i n that the pollutant is reduced

versus removed and transferred to another media

.

The first installation occurred on Minntac Agglomerator Line 7 in May of 2010. Some design issues were encountered and incorporated into a second generation burner which was installed on Agglomerator Line 6 in April of 2011. The purpose of this report is not only to provide a report on the status of the Line 6 burner, but also to discuss NOx management at the facility as a whole. Based on concepts learned both from the theo ry, design and operation of the new burners, Minntac was able to implement additional projects at the facility which

resulted in NOx reductions.U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 3 of 23 

### NOx Reduction Goals

The permit contains a goal of a 70% NOx reductio n from a baseline of 1 3,300 tons/year using a 365

- day rolling sum from all five waste gas stacks combined. Since not all five lines operate exactly the same, or with the same fuel blend, it was initially a struggle to decide how to evaluate a 70% reduction. A simplistic
way t o evaluate this is to assume the lines operate 100% of the year and would have equal emissions. This would be a worst case scenario since the lines do not operate at that high of an operational uptime. Therefore, to be ultimately

conservative the intern al NOx target for short term testing, was broken down as

fol low s: 3,990 tons/year (13,300 * 0.3 ) goal to reflect one induration line would be

182.2 lb/hr

On February 1, 2011 a permit limit of 7,300 tons per year became effective that replaced the 13,300 tons/year limit. Although the pound per hour target is used for short term evaluation, the form of the limit being all five waste gas lines combined is critical. This allows for operational flexibility while ensuring compliance. The combined limit is especially important as additional controls are installed. This allows for a start up and shake down period with the new equipment while minimizing emissions from the facility and ensuring compliance.



### Continuous Emission s Monitori ng System (CEMS)

In order to reduce NOx emissions it is necessary to know what the emissions are on a short term basis. This enables real time data to be used when testing and tuning the equipment to better understand and evaluate how the changes are

aff ecting NOx performance. As a result of having reliable CEMS on all of the lines, Minnesota Ore Operations has been effectively measuring NOx continuously. With this information, baseline NOx values are known which allows for effectively testing NOx reduc tion technologies.

NOx emissions are measured by CEMS that are located in the waste gas stacks. CEMS have been installed on all the operating lines at Minnesota Ore Operation. The following is an outline of the CEMs installation:

 CEMS units were init ially installed on Minntac lines 6 and 7 around 2000.

The measurement was done with a Sick AG Model GM 31

- 6 which is an

in

- situ instrument with a 5 foot measurement probe.

 CEMS were installed on Minntac lines 3, 4, and 5 in 2006 . The

measurement is don e with an Ametek model 920 extractive analyzer. TheU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 4 of 23 decision was made to go to a different analyzer type because it was a newer technology which appeared to be more reliable.

 CEMS unit was installed at Keetac in 2008. Keetac uses the same

measurement in strument as Minntac Lines 3, 4, and 5 , the Ametek extractive analyzer

.

 I n spring 2010

, procurement was initiated for replacing the CEMS on Minntac lines 6 and 7 with the same equipment as the other lines. The purpose of the installation was to improve CEM S reliability. In addition, having identical CEMS on all lines allows for standardization across the two facilities (six lines total) which improved spare parts management. The new CEMS have been installed and passing Certification Tests were completed on February 23 and 24, 2011 for Line 6 and 7, respectively.

o Prior to the installation of the new CEMS, the Line 7 CEMS failed in

October of 2010 . A rental CEMS was procured and installed to ensure continuous NOx readings. This quick action enabled testin g to continue with the Line 7 burner without risk of inaccurate data.

o Since the installation of the new CEMS on Line 6 and 7, the

downtime has been reduced. The downtime since installations has

been excellent . The 2011 third quarter NOx CEMS downtime

rep ort contained zero percent downtime for both Lines 6 and 7.U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 5 of 23 

### Line 7 Low NOx Main Burner

The first low NOx main burner was installed on Line 7 in May 2010. As previously stated, this was the first installation of a NOx technology on an indurating line in the United States. This was also the first design and installation of a quad fuel burner of this size by the manufacturer. Figure 1 shows the burner tip configuration of the Line 7 burner.

Figure 1: Line 7 Low NOx Burner Tip

During the evaluation of the burner on Line 7 some issues were encountered

. This was expected given that this was an initial design for an operation not currently utilizing the technology. The following outlines the issues , concerns, and actions ta ken to improve the line 7 burner NOx performance.

 Issue #1 : Unable to achieve desired combustion airflow

 Concern: Sufficient air volumes are an essential element to reach the proper stoichiometric ratio to maximize NOx emission reduction.

 Actions take n:

o Oversped the combust ion air fan VFD according to manufacturer

recommendations

o Increased the combustion air inlet duct to the burner to reduce

fric tion loss

o Design modification made on the Line 6 low NOx burnerU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 6 of 23  Issue #2 : Unable to meet the NOx reducti on goal on coal

 Concern: Fuel flexibility is a critical component to the successful operation of the facility.

 Action taken:

o Installed coal insert to restrict the coal displacement at the burner tip

o Installed a coal co ne that was anticipated to improve NO x performance by 20%, however NOx performance did not improve

o Design modification made on the Line 6 low NOx main burner

 Issue #3 : Unable to achieve steady rates of biomass at higher flow rates

due to the biomass settling out in the burner pipe

 Concern: Fuel flexibility is a critical component to the successful operation of the facility.

 Actions taken:

o Design modification made on the Line 6 low NOx main burner

Figure 2 shows the timeline of the modifications that were made.

Figure 2: Line 7 Low NOx Burner Timeline of ModificationsU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 7 of 23 The short term testing results on Line 7 showed that the low NOx main burner is a technically feasible method to achieve the goal of a 70% NOx reduction. Graph 1 shows the burner achieving the NOx reduction target when combusting

100% natural gas. Based on the successful NOx reductions achieved on Line 7,

U. S. Steel made the decision to move forward with a low NOx main burner on Agglomerator Line 6. In addition, t he i nformation from the Line 7 low NOx main

burner was used to improve the design for the Line 6 low NOx main burner.

Graph 1: Line 7 Low NOx Main Burner NOx Performance Running 100%

Natural Gas Average = 18 1 lbs/hrU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 8 of 23 

### Line 6 Low NOx Main Burner

The Line 6 low NOx main burner was installed in April 2011

. There were 3 sign ificant design changes that were made when compared to the Line 7 low

NOx main burner. The first modification was increasing the size of the combustion air fans. The fan capacity was increased by 25% to ensure there

was sufficient combustion air to ensur e the appropriate stoichiometric ratio to

achieve the NOx reductions

. This required a n addition to the north side of the Step 3 Agglomerator building in order to house the combustion fans.

The second modification was switching the locations of the combus tion air and coal annulus. Figure 3 shows the Line 6 burner tip. The goal of relocating the

combustion air on the outside was to improve the flame shape and NOx performance when combusting coal.

Figure 3: Line 6 Low NOx Burner Tip

The third modification was modifying the biomass annulus to eliminate the issue of plugging when running increased flow rates of biomass. Combustion Air

Coal

Biomass

Atomizing

Air Annulus Gas

Core Gas Fuel OilU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 9 of 23 

### Variables to Control NOx

The primary means of NOx control with the low NOx main burners is by controlling the stoichiometric ratio of air to fuel. This is accomplished by adjusting the combustion air. The combustion air lengthens the flame and reduces the flame temperature which reduces NOx.

The other means of NOx control is by adj usting the atomizing air and the gas split between the core and annulus gas. The atomizing air adds swirl to the

flame and affects the flame length and shape. The split between the core and annulus gas is also monitored because the core gas lengthens the flame and annulus gas stabilizes the flame.

All three variables were adjusted during burner testing to determine the optimum settings to meet the NOx goal. The optimum settings are different for each fuel
type , therefore significant testing is necessary in order to fully understand the technical aspects of the system and ensure NOx minimization while meeting other obligations such as pellet quality and a safe working environment

.



### NOx Testing with Natural Gas

Similar to the success observed on the Line 7 burner, the Line 6 main burner is

able to achieve the internal NOx target of <182.2 lbs/hr. However, i n order to

achieve the same level of NOx reduction

, the Line 6 bur ner required more combustion air when compared to the Line 7 burner

. It was determin ed that L ine

6 combustion air had 40% less thrust than L ine 7 combustion air. The decrease in air thrust resulted in a poorer flame shape and higher NOx emissions at the

same stoichiometric r atios when compared to Line 7. The goal is to have a long tigh t flame shape in order to minimize NOx while ensur ing proper process operation. The burner manufacturer was consulted about this issue to recommend changes.

As a result, the manufacturer recommended installing rings on inner and outer edges of the combus tion air annulus to increase the air thrust. The modification

, which took several days, was made to the burn er in mid September 2011. F igure

4 shows the burner after the modification. The modification did provide the benefit of improved NOx performance.U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 10 of 23 Figure 4: Line 6 Low NOx Burner after the Burner

Modification

A summary of the testing on natural gas on 9/26/11 is shown in Table 1. The testing parameters consisted of burning 100% natural gas while varying the total

combustion air to reduce NOx.

Table 1: Line 6 Low NOx Burner Testing with 100% Natural Gas Inner Ring

Outer RingU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 11 of 23 Graph 2 illustrates NOx emission levels versus the stoichiometric ratio. The graph demonstrates that NOx is reduced when the stoichiometric r atio increases. Therefore, the stoichiometric ratio is crucial to lowering NOx emissions.

Graph 2: Line 6 Low NOx Burner with 100% Natural Gas: NOx versus

Stoic h iometric Ratio (9/26/11)

Graph 3 confirms that the Line 6 low NOx burner can meet the 70% NOx reduction, averaging 182 lbs/hr from October 28, 2011

– November 7, 2011.

Graph 3: Line 6

– Low NOx Main Burner 100% Natural Gas Average = 182 lbs/hrU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 12 of 23 

### NOx Testing With Coal

Coal testing was delayed on Line 6 due to safety issues related to the coal mill.

Onc e t he safety issues were re ctified

, coal was able to be utilized as a fuel again

. However, after re starting the coal

, a leak was found in the pipe. The line was shutdown and the flame was shut off in order to repair the coal pipe . Coal testing

was the n able to be started in early June.

Line 6 has been unable to achieve the NOx target goal of 182.2 lbs/hr of NOx when running a mix of coal and natural gas. The burner manufacturer was

consulted multiple times about this issue. It was determined that L i ne 6

combustion air had 20% less thrust than L ine 7 combustion air when running

coal

. Similar to the issue when running natural gas, t he decrease in air thrust resulted in a poorer flame shape and higher NOx emissions

.

Therefore, the rings the manufactur er recommended installing on the inner and outer edges of the combustion air annulus were to improve NOx performance when running coal and natural gas. Figure 4 shows the burner after the rings

were installed.

Table 2 shows the results of the testing on Line 6 low NOx burner on 10/7/11 when running 10,000 lbs/hr of coal and on 11/18/11 when running 8,000 lbs/hr of

coal . The testing parameters consisted of holding the coal feed rates steady and burning reduced amount of kiln gas while varying the stoichio metric ratio to reduce NOx. After the modification there was an improvement in the coal flame shape ; however, Line 6 is still unable to achieve the NOx goal when running a mix of coal and natural gas.

Table 2: Line 6 Low NOx burner

– Running CoalU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 13 of 23 It was determined that NOx is the lowest at approximately a stoic h iometric ratio of 1. This is depicted in Graph 4. As previously shown and discussed, this is different than how the burner operates on 100% gas to maximize NOx

reductions.

Graph 4: Line 6 Low NOx Burner with Coal: NOx versus Stoichiometric

Ratio



### NOx Testing With Biomass

The Line 6 low NOx burner was designed to burn 300 lbs/min of biomass.
However, consistent biomass feed rates at levels greater than 125 lbs/min were unable to be achiev ed. The manufacturer was consulted on this issue and they recommended that changes be made to the biomass system to improve delivery

. The biomass supplier completed the recommendations in June, but no improvements were seen in the volume of biomass throu gh the burner . In addition, the biomass supplier assisted in additional testing by supplying a

constant material of oat hulls , which has a more consistent size distribution . Thi s is different than typical biomass feed which is not a constant ma terial. A gain, this did not improve performance.

Due to these issues, the burner tip was inspected in July to determine if there was plugging and it wa s found that the biomass line was deformed. Figure 5 shows the burner tip at the July inspection. The burner manufacturer investigated the cause of the deformation and found that is was a design malfunction. The biomass pipe was designed to be a division plate, but the location of the tabs resulted in the thin biomass pipe wall to see excessive

stresses which ca used it to deform.U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 14 of 23 No further biomass testing is planned until the biomass line is repaired. The repair will be extensive as the burner will need to be removed from the kiln

, disassembled

, reassembled and reinstalled . The burner manufacturer is provid ing the recommendations for the repair. Due to the time necessary to design the modification and lead time to construct, the modification is planned to coincide with the Line 6 major repair in early 2012.

Figure 5: Line 6 Low NOx Burner Tip after Biomass Line

Deformation Biomass pipe

TabsU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 15 of 23 

### NOx Testing With Fuel Oil

F uel oil is used as a back

- up fuel for when natural gas is curtailed . As a result, only a short test was conducted on the Line 6 low NOx main burner with fuel oil.

Fuel oil was tested on 8/4/11 and was run for approximately two hours. Graph 5 shows that fuel oil can meet the can meet the 70% NOx reduction, averaging 165

lbs/hr.

Graph 5: Line 6

– Low NOx Main Burner with Running 100% Fuel Oil.



### Process Issues

The addi tion of combustion air from the low NOx main burners has had two negative affects on the process. The first is an increase in process fu el consumption. After the installation of the Line 7 low NOx burner, the pr ocess fuel increased by 10.5%. As a result of the fuel increase, a change was made to

increase the waste gas fans on lines 6 and 7 to balance the air flow through the
system to maintain fuel rates at values prior to the instal lation of the low NOx burners. The waste gas fans on both lines were ru n at maximum before the

burner installations and with the addition of combustion air, the process efficiency decreased. Now with the increase in waste gas fan flow, the air in and out of the system is balanced.

The second issue that has been encountered is pellets dumping hot from the

cooler. This created steam and poor visibility on the burner floor which is a safety concern. The reason for dumping hot from the cooler is the 3A and 3B cooling fans decrease with the addition of combustion air. Figure 6 shows the Average = 1 65 l bs/hrU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 16 of 23 kiln and cooler section of the Agglomerator process. The 3A and 3B fans are

controlled by kiln hood pressure.

Figure 6: Kiln and Cooler Section of the Agglomerator Process

With the addition of the combustion air through the burner, the pressure

increas e s and forc e s the 3A and 3B cooling fans to decrease their airflow. The 3A and 3B fans cannot increase because the pressure would increase which is also a safety concern. The cooler dumping hot also results in excessive mechanical wear, high fuel rates, and below target pellet quality. Projects have

been completed in order to eliminate this issue.

With the projects implemented and through process optimization, L ine 6 has not seen an increase in process fuel co nsumption and dumping hot from the cooler

has been corrected.



### Impact to Pellet Quality

Four quality parameters were examined to determine if there was an impact to final pellet quality. The four quality parameters are after tumble, compressions,

reduci bility, and low temperature disintegration (LTD). Table 3 shows the values

before and after the installation of the Line 6 low NOx burner.

Table 3: Line 6 Quality Before and After the low NOx Burner Installation

An improvement was seen in the reduc ibility and is believed to be due to improved heat distribution in the kiln from the low NOx burner.

A decreased in LTD was seen and is due to the issues of dumping hot from the cooler. When material is dumping hot, water is added and the hot pellets a re cooled too quickly. When pellets are not allowed to cool slowly enough, the LTD

decreases . Graph 6 shows that the LTD has been increasing since the Line 6 KILN HOOD

PRESSUREU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 17 of 23 low NOx burner installation in April 2011. This is due to resolving the issues of dumping hot f rom the cooler.

Graph 6: Line 6 Low Temperature Disintegration Monthly Quality Averages



### Additional NOx Education

In addition to the installation of the low NOx main burners, the manufacturer was procured to provide training to the key facility pers onnel to develop a better understanding of the technology. This included an extensive three day course that covered fundamentals of heat transfer, fluid dynamics

, and chemistry to provide the rudiments of the technology. Furthermore, a short course was

p rovided to the operators and maintenance personnel on the floor to provide them of a basic understanding of the burner operation. This time was also used to provide the burner design engineer an opportunity to view both lines in operation and evaluate the ir flame properties.U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 18 of 23 

### Other NOx Proj

ects

In addition to the installation of the low NOx main burners, other projects have been completed at Minntac to reduce overall NOx emissions. The following is the list of projects:

 CEMS Management (Lines 3, 4, 5, 6, and 7)

o Alarms have been added to the control room to alert the operators

that the CEMS are not workin g properly. Technicians are the n called out to correct the issue. This reduces the usage of

substitution NOx values.

 Process Optimization (Lines 3, 4 , 5, 6, and 7)

o By optimization the process, the line runs more efficiently and less

NOx is emitted.

 Coal Management (Lines 6 and 7)

o A modification was made to the coal mills to alleviate the issue of plugging the coal pipes and stopping coal. When the co al pipes plugged, it created a process upset and increased NOx emissions.

o A new coal was procured and managed to improve performance

.

 Biomass Management (Lines 3, 4, and 5)

o The biomass supplier has improved their biomass delivery by ensuring there is suff icient biomass to burn steady rates on the lines. Before, especially during holidays, biomass would run out and 100% natural gas would be used which increases NOx on lines

without the new burners

.

 Blowers Installed on the Burners (Lines 3, 4, and 5)

o Simi lar to the concept of the Line 6 and 7 low NOx main burners,

blowers were installed on the other lines to improve the air to fuel ratio, thus reduc ing NOx.

 Burner Modifications (Lines 4 and 5)

o The burner draft tubes were modified so that additional air co uld be put through the existing burner.

 OCS© Installation ( Line 4 )

o OCS©, and expert control system, was installed and programmed

to reduce NOx emissions.

 OCS© Upgrade (Line 5)

o Line 5 OCS © was upgraded with the same programming as Line 4

to reduce NOx em issions.U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 19 of 23  Ovation Upgrade (Lines 3, 4, and 5)

o The Lines 3, 4, and 5 computer control system was reaching capacity where no new control logic could be installed. To ensure that there is sufficient capacity for future NOx projects, the computer control sys tem was upgraded.

Graph 7 below shows t he Minntac NOx model. This model is discussed frequently with the management team to ensure all are aware of the NOx emission levels we are currently at, and where we are projected to be. The assumptions for the mo del are as follows:

1. Continue to Optimize Line 6&7 Low NOx Burner

a. Operate Safe

- Don't Dump Hot

b. Maintain NOx at 180 lb/hr

c. Reduce Process Fuel

d. Avoid Excess Wear to Equip ment

e. Produce pellet tons within quality parameters to meet business plans

2. Increase Util ization of OCS

3. Minimize CEM Downtime

Minntac’s NOx compliance has been and continues to be on target. This was accomplished by the installation and optimization of the low NOx main burners

on Lines 6 and 7 ; in addition to all of the other NOx projects that have been completed on all five induration lines as discussed above

. Graphs 8

- 12 show the

NOx reductions on the individual ind uration line

. As you will see when viewing the graphs, the Agglomerator lines have each shown a steady decrease in NOx

emi ssions, and the NOx intensity level from the facility has reached record lows.U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 20 of 23 Graph 7: Minntac NOx ModelU. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 21 of 23 Graph 8: Line 3 NOx Performance August 2009

– October 2011

Graph 9: Line 4 NOx Performance August 2009

– October 2011U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 22 of 23 Graph 1 0: Line 5 NOx Performance August 2009

– October 2011

Graph 11: Line 6 NOx Performance August 2009

– October 2011U. S. Steel Minntac

- Line 6 Low NO x Main Burner Final Report and Facility NOx Management

Page 23 of 23 Graph 12: Line 7 NOx Performance January 2009

– October 2011



### Conclusions

Minntac has committed significant time, money and resou rces to not only meet permit requirements by complying with emission limits and moving forward with technology evaluations. Based on testing conducted to date, Minntac is confident that low NOx main burners are a technically and economically feasible

mech anism to achieve NOx reductions. The installation of two of these burners, along with a significant amount of other projects has resulted in dramatic reductions in NOx emissions from the facility as a whole.