Subject: Technical Support Document For Taconite Settlement FIP 

Date: August 13, 2015 

From: Steven Rosenthal 

To: Docket EPA- RO5-OAR-2015-0196 

Cliffs and ArcelorMittal provided significant additional 

information in their petitions for reconsideration and supplemental 

submittals that EPA finds sufficient to warrant proposing revised 

BART limits. The following discussion details the new information 

upon which EPA is relying to justify its proposal to revise the 

BART emission limits and compliance schedules for these 

facilities. 

1. United Taconite - NOX

A report by Metso dated August 7, 2014, entitled “Technical 

Analysis for applying LNB technology to (United Taconite) UTAC 

Line 2 Grate-Kiln,” provides a detailed analysis of expected 

adverse impacts of using high-stoich LNBs on pellet quality, as 

well as increased fuel use resulting from high-stoich LNBs. 

Metso analyzed the effects of LNB technology on the United 

Taconite Line 2 Grate-Kiln by using simulation modeling in which 

Metso compared Line 2’s normal operating conditions, which 

result in the production of quality pellets, with simulations 

performed using high-stoich LNB burners (which are the basis of 

the 2013 Taconite FIP limits). 
 Three high-stoich simulations were run with 115 percent 

stoichiometric primary air representing updated COEN LNB 

technology while unsuccessfully trying to balance fuel 

requirements and pellet quality issues in one simulation. Steps 

were also taken to mitigate pellet quality issues in two 

simulations. For the simulations in which most airflow, 

temperatures and pressures were maintained for the purpose of 

minimizing pellet quality issues, the results were drastically 

increased fuel rates and particulate releases into the 

atmosphere. A summary of the operational and environmental 

impacts from high-stoich LNB installation follows: 

- Fuel usage rate is expected to increase between 212 

percent and 220 percent when incorporating high-stoich LNB 

technology at UTAC Line 2 with 115 percent stoichiometric air 

while maintaining current pellet quality. 

- Because grate preheat zone gases from the kiln have less 

oxygen concentration, the oxidation reaction will slow down. 

This shifts more reaction heat to the cooler, but the secondary 

cooling fan does not have available capacity to supply the 

volume increase requirements. The resulting reduction in 

oxidation heat on the grate produces lower pellet temperatures 

leaving the grate and entering the kiln and may lead to pellet 

breakage. 
 This evidence from Metso, which became available after EPA 

promulgated NOX emission limits based on use of high-stoich LNBs, 

suggests that this type of control may cause a number of 

problems, and suggests further that low-stoich LNB options may 

provide more effective control. 

A mass emission rate comparison between high-stoich and 

low-stoich LNB options was presented by Metso, during a July 28, 

2014 meeting between EPA and Cliffs and summarized in a 

subsequent August 8, 2014 letter to EPA. Metso’s analysis 

compared the amount of NOX that would be generated when a furnace 

is retrofitted with a high-stoich LNB and low-stoich staged 

combustion LNB options. This analysis demonstrated that 

although the lbs NOX/MMBtu may be lower from a high-stoich 

burner, the high-stoich LNB will require more fuel (and BTUs) 

and result in higher NOX emissions. The additional primary air 

required for high-stoich LNB requires 60% more fuel to sustain 

temperature in the simulation performed for UTAC Line 2. The 

low-stoich LNB option does not require more fuel or primary 

combustion air. At the same lb/MMBtu NOX rate, the high-stoich 

LNB produces more NOX emissions on a mass basis. 

One of the mitigation options for the high-stoich LNB 

technology is to reduce the amount of primary air to see if 

there is a point where NOX is reduced without pellet quality 

concerns. To properly evaluate this option, the mass amount of 
NOX emitted by the high-stoich LNB with primary air reduced must 

be compared with the mass amount of NOX emitted by the 

low-stoich option. Metso’s analysis demonstrates that a lower 

stoich LNB retrofit technology such as the low-stoich staged 

combustion for the Cliffs grate kiln furnaces will reduce more 

NOX than the high-stoich LNB with the excess air reduced to 

mitigate pellet quality issues. 

More specifically, Metso analyzed the effect of reducing 

the stoichiometric air from 110-115% to 50-55% (“mitigated highstoich”) to determine if this would produce less NOX than the 

low-stoich LNB option that requires no increase in primary air. 

Operating at 50-55% stoichiometric air is expected to reduce NOX

by 33% from baseline NOX emissions based on the Minntac graph 

provided during the July 28 meeting. Metso’s simulation 

demonstrated that 50-55% stoichiometric air would require 20-40% 

more heat input than the low-stoich staged-combustion 

alternative. The vendor for the low-stoich staged combustion 

LNB predicts NOX reductions up to 50%. Metso’s simulation for 

UTAC Line 2 indicates that the low-stoich LNB option will 

generate 60-90% less NOX mass emissions to the atmosphere. 

2. Tilden - NOX

The Metso September 14, 2012 and January 13, 2015 technical 

analyses for applying LNB technology to the Tilden Line 1 grate 

kiln provide modeling simulations that compare current 
operations versus operations using high-stoich LNBs. Current 

operating conditions at Tilden 1 were simulated using existing 

air flow studies, operating parameters, feed mineralogy, etc. 

This baseline model was then modified to simulate LNB operating 

conditions. The current (at the time) operating parameters and 

anticipated high-stoich LNB operating conditions were then 

compared. 

 The high-stoich LNB technology, upon which the FIP limits 

were established, were based upon increasing the amount of air 

from a range between 3 and 75 percent of stoichiometric to a 

range between 75 and 125 percent of stoichiometric, directly 

injected through the burner (unheated primary combustion air). 

The FIP limits were based upon high-stoich LNBs operating with 

air flow at 100 percent of stoichiometric through the primary 

burner. Primary combustion air is measured as a percentage of 

the air that supplies oxygen to burn the fuel introduced with 

the burner. As indicated earlier, the air is considered 100% 

stoichiometric air when the air supplies a chemically balanced 

quantity of combustion that does not result in any excess 

oxygen. 

 When the primary combustion air is less than 100 percent of 

stoichiometric, the remaining secondary combustion 

stoichiometric air is supplied from the primary zone of the 

cooler and is in the range of 1700°F to 2200°F. Furnaces 
requiring a greater primary combustion air stoichiometric rate 

will require increased fuel to compensate for reducing the 

heated secondary combustion air. Tilden operates with primary 

combustion air at 15.5 percent of stoichiometric, and Metso 

estimated that primary combustion air at 100 to 110 percent of 

the stoichiometric rate is required to meet the 2013 Taconite 

FIP limits. Metso performed simulations 1 through 3 using 

natural gas, maintaining peak pellet temperature and maintaining 

final product temperature. The total air supplied to the cooler 

was adjusted as needed to maintain final product temperature 

across all three simulations. These simulations were intended 

to isolate the effects of various process parameters when 

applying high-stoich LNB technology to Tilden 1. All 

simulations were based on then current operating conditions. 

Simulation 1 represented current operating conditions on natural 

gas with 15.5 percent of stoichiometric primary combustion air. 

 Simulation 2 conditions were chosen to simulate a 110 

percent of stoichiometric primary combustion air rate 

representing LNB technology operating parameters with recoup 

temperatures less than 1500°F so as not to degrade pellet 

quality. Simulation 3 was the same except with 100 percent 

stoichiometric primary combustion air. Simulations 1, 2 and 3 

were created in 2012. Some of the results of these simulations 

are: 
- Fuel usage rate is expected to increase 25 to 35 percent. 

- Up Draft Drying (UDD) and Down Draft Drying (DDD) 

exhaust gas volumes increase 10 to 20 percent due to higher 

temperatures and air flow rates through the grate. The fans 

that move the UDD and DDD will require more electricity and may 

not have sufficient capacity. 

- Process dust generation from altered heating and cooling 

rates may change the dust loading to UDD and DDD exhaust gas 

cleaning equipment and may increase particulate emissions. 

- High-stoich LNB burner technology alters the flame 

temperature profile which may adversely affect pellet quality. 

 The Metso document dated January 2015 provides a 

comparative analysis of simulations 8 through 11 in which 

current operating data are applied to the COEN high-stoich LNB 

design conditions required for NOX reduction (in COEN’s Final 

Report for Tilden Line 1). All engineering simulations were 

developed by holding several of the key process parameters 

constant. The process parameters held constant were pellet 

production rate, greenball moisture, bentonite, and flux rate. 

The total air supplied to the cooler was adjusted as needed to 

maintain final product temperature across all simulations. 

Maintaining these parameters ensures that fuel changes are not 

due to altered processing requirements. 
 Two comparison sets were analyzed including one set for 

comparing baseline gas with COEN high-stoich LNB gas (simulation 

8 compared to 9) and another set comparing baseline coal with 

COEN high-stoich LNB coal operation (simulation 10 compared to 

11). The high-stoich LNB COEN simulations were compared to the 

baseline simulation for several key process parameters. The 

comparison values, when stated below, are stated first for the 

gas comparison and then the coal comparison. These comparisons 

reveal a number of significant operational and environmental 

impacts as a result of COEN high-stoich LNB installation, some 

of which are listed below: 

- Fuel rate is expected to increase 28% and 21% when 

incorporating LNB. The increase in unheated primary combustion 

air to the burner will require an increase in fuel to replace 

the heat not used from heated secondary combustion air. 

- A more aggressive pellet heat up rate when using the 

high-stoich LNB simulations may require blending outside air to 

reduce process temperatures in order to cause a heat up rate 

closer to the base case. This additional outside air will 

increase fuel rate further. 

- The DDD exhaust gas volumes increased by 20% and 14% due 

to higher temperatures and increased air flow rates through the 

grate. The fans that move the DDD exhaust will see an increase 

in kilowatt usage by the percent of additional volume along with 
additional pressure requirements due to larger pressure losses 

in handling the extra volume. Existing fan capacity may 

therefore be required to handle increased volume and pressure 

requirements. 

- The split of cooling air between primary and secondary 

cooling will change drastically. Although the same amount of 

total process cooling air to cool the product is required for 

LNB technology, the split of cooling air between the zones in 

the cooler will change thereby altering the cooling down cycle 

of the pellets, which may affect pellet quality and dust 

generation. Secondary cooling air will increase while primary 

cooling air is decreased to accommodate high-stoich LNB 

technology requirements of high burner primary air. The 

secondary cooling air fan may not be able to handle the 

increased flow requirements. 

- The change of the split between primary and secondary 

cooling will require rezoning of the cooler air. This is 

because of the resulting imbalance of pressure between primary 

and secondary cooling along with the high secondary cooling air 

velocity. When rezoning the cooler the location of the gas offtakes such as parallel flow duct, recoup duct, and the cooler 

stack will have to be relocated. 

- The volume of secondary cooling air exiting the cooler 

vent stack is projected to increase between 415% and 360%. This 
may adversely affect the process, pellet quality, and cause an 

increase in dust loading. 

- Dust emissions from UDD and DDD exhaust gas are expected 

to increase. This will be attributable to altered heat up rate 

and lower gas cleaning equipment efficiency due to an increase 

in gas volume through the gas cleaning equipment. 

- High-stoich LNB burner technology alters the flame 

temperature profile and may affect pellet quality. 

- The computational fluid dynamic (CFD) modeling shows that 

the high-stoich LNBs will cause a much greater exhaust gas and 

grate chain heat loss resulting in increased fuel requirements. 

3. Mass Emission Rate Comparison Between High-Stoich and LowStoich LNB Options 

 A mass emission rate comparison between high-stoich and 

low-stoich LNB options was presented by Metso, during a July 28, 

2014 meeting between EPA and Cliffs and summarized in a 

subsequent August 8, 2014 letter to EPA. Metso’s analysis 

compared the amount of NOX that would be generated when a furnace 

is retrofitted with a high-stoich LNB and low-stoich staged 

combustion LNB options. This analysis demonstrated that 

although the lbs NOX/MMBtu may be lower from a high-stoich 

burner, the high-stoich LNB will require more fuel (and BTUs) 

and result in higher NOX emissions. The additional primary air 

required for high-stoich LNB requires 60% more fuel to sustain 
temperature in the simulation performed for UTAC Line 2. The 

low-stoich LNB option does not require more fuel or primary 

combustion air. At the same lb/MMBtu NOX rate, the high-stoich 

LNB produces more NOX emissions on a mass basis. 

One of the mitigation options for the high-stoich LNB 

technology is to reduce the amount of primary air to see if 

there is a point where NOX is reduced without pellet quality 

concerns. To properly evaluate this option, the mass amount of 

NOX emitted by the high-stoich LNB with primary air reduced must 

be compared with the mass amount of NOX emitted by the 

low-stoich option. Metso’s analysis demonstrates that a lower 

stoich LNB retrofit technology such as the low-stoich staged 

combustion for the Cliffs grate kiln furnaces will reduce more 

NOX than the high-stoich LNB with the excess air reduced to 

mitigate pellet quality issues. 

More specifically, Metso analyzed the effect of reducing 

the stoichiometric air from 110-115% to 50-55% (“mitigated highstoich”) to determine if this would produce less NOX than the 

low-stoich LNB option that requires no increase in primary air. 

Operating at 50-55% stoichiometric air is expected to reduce NOX

by 33% from baseline NOX emissions based on the Minntac graph 

provided during the July 28 meeting. Metso’s simulation 

demonstrated that 50-55% stoichiometric air would require 20-40% 

more heat input than the low-stoich staged-combustion 
alternative. The vendor for the low-stoich staged combustion 

LNB predicts NOX reductions up to 50%. Metso’s simulation for 

UTAC Line 2 indicates that the low-stoich LNB option will 

generate 60-90% less NOX mass emissions to the atmosphere. This 

analysis also applies to Tilden.