**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 provide d significant additional information in their petitions f or reconsideration and supplemental submittals that EPA finds suffic ient to warrant proposing revised BART limits. The following disc ussion details the new information upon which EPA is relying to justify its proposal to rev ise the BART emission limits and compliance schedules for these facilities. **1. United Taconite - NO**  **X** 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 NO X 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 NO X 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 NO X /MMBtu may be lower from a high-stoich burner, the high-stoich LNB will require more fuel (and BTUs) and result in higher NO X 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 NO Xrate, the high-stoich LNB produces more NO X 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 NO X is reduced without pellet quality concerns. To properly evaluate this option, the mass amount ofNO X emitted by the high-stoich LNB with primary air reduced must be compared with the mass amount of NO X 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

NO X than the high-stoich LNB with the excess air reduced to mitigate pellet quality issues. More specifically, Metso analyzed the effect of reducingthe stoichiometric air from 110-115% to 50-55% (“mitigated highstoich”) to determine if this would produce less NO X than the low-stoich LNB option that requires no increase in primary air. Operating at 50-55% stoichiometric air is expected to reduce NO X by 33% from baseline NO X 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 NO X reductions up to 50%. Metso’s simulation for UTAC Line 2 indicates that the low-stoich LNB option will generate 60-90% less NO X mass emissions to the atmosphere. **2. Tilden - NO X**  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 currentoperations 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. Furnacesrequiring 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 NO X 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 withadditional 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 airvelocity. 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%. Thismay 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 Low Stoich 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 NO X 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 NO X /MMBtu may be lower from a high-stoich burner, the high-stoich LNB will require more fuel (and BTUs) and result in higher NO X emissions. The additional primary air required for high-stoich LNB requires 60% more fuel to sustaintemperature 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 NO Xrate, the high-stoich LNB produces more NO X 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 NO X is reduced without pellet quality concerns. To properly evaluate this option, the mass amount of

NO X emitted by the high-stoich LNB with primary air reduced must be compared with the mass amount of NO X 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

NO X than the high-stoich LNB with the excess air reduced to mitigate pellet quality issues. More specifically, Metso analyzed the effect of reducingthe stoichiometric air from 110-115% to 50-55% (“mitigated highstoich”) to determine if this would produce less NO X than the low-stoich LNB option that requires no increase in primary air. Operating at 50-55% stoichiometric air is expected to reduce NO X by 33% from baseline NO X 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-combustionalternative. The vendor for the low-stoich staged combustion LNB predicts NO X reductions up to 50%. Metso’s simulation for UTAC Line 2 indicates that the low-stoich LNB option will generate 60-90% less NO X mass emissions to the atmosphere. This analysis also applies to Tilden.