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Federal Register / Vol. 86, No. 39 / Tuesday, March 2, 2021 / Rules and Regulations
between the NOX line and production line in the figure. From 2007 through 2009, before the installation of low NOX
burners, these lines are relatively close together. In 2010, the year when the low NOX burner was installed on Line 7, production rose dramatically while annual NOX emissions did not. Visually, there is a significant divergence between the NOX and production lines in the figure, indicating an increase in production without a commensurate increase in emissions. Correspondingly, after the low NOX burner was installed on Line 6 in 2011, the figure shows production increased between 2010 and 2011 while emissions decreased. Low NOX burners were installed on Lines 5
and 4 in December 2015 and December 2016, respectively. Similarly, the figure shows NOX emissions between 2015
and 2017 did not increase at the same rate as production.
Using the available CEMS data for the 20122017 time period, EPA further evaluated the differences between various NOX emission values pre and post-installation of low NOX burners on Lines 4 and 5.13 Data for both lines showed a decrease in the average lbs NOX/MMBtu, high 720-hour average lbs NOX/MMBtu, and 99th percentile lbs NOX/MMBtu. Even the average lbs NOX/
hour, which does not account for variations in production levels, decreased. U.S. Steel did not provide CEMS data for Lines 6 and 7 for the period prior to the installation of low NOX burners, so a similar comparison cannot be made for these lines.
Finally, the commenter asserts that the data suggest that U. S. Steel failed to optimize operation of the low NOX
burners from 2014 through 2017. As discussed in detail in responses to comments 9 and 14 in this document, after installation of the low NOX burner on each line, U.S. Steel optimized burner operation for NOX reduction while maintaining pellet quality. In addition, Minntac has remained subject to the limits in the 2013 FIP.
Comment 9: EPA did not explain how U.S. Steel arrived at its conclusion that the low NOX burners at each of the lines were optimized and functioning at their best. In prior regional haze actions, when the level of control has been uncertain at the time of EPAs final action, EPA requires a control technology demonstration, with explicit requirements for optimization of the control technology system. EPAs 2014
final FIP requirements for Arizona plants included a control technology 13 See Emission reduction estimates and Lines 3, 4, and 5 Data-L4_7 NOX CEMS Data files combined for docket, included in the docket.

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demonstration project for the emission control system at each plant, which entailed the collection of data and preparation of an optimization protocol that would be used to determine if a higher control efficiency would be achievable. There is no evidence that EPA required and oversaw implementation of a control technology project. Moreover, the BART Guidelines require the consideration of improvements to the low NOX burner controls 40 CFR part 51, appendix Y, at IV. D. Step 1 9.
Response: U.S. Steel has documented optimization studies at Lines 4, 5, 6, and 7 in final testing reports for each line.
Final testing reports for Lines 6 and 7
and preliminary data for Lines 4 and 5
are included in the docket. In addition, U.S. Steel submitted final testing reports for Lines 4 and 5, titled Final Report Line 4 Burner 092917. This document has also been added to the docket. In each report, U.S. Steel describes challenges encountered over the course of installing, operating, and testing each low NOX burner, and discusses how certain design and operational changes were found to optimize operation of each lines low NOX burners. As explained in the reports, U.S. Steel evaluated operation of each low NOX
burner to ensure each burner can operate in a manner that reduces NOX
emissions while making pellets that meet quality specifications. Each burner was evaluated according to hourly CEMS data and during expected operating scenarios, including while burning natural gas, solid fuels, and a combination of natural gas and solid fuels. Over the course of the testing, U.S. Steel identified several problems occurring at various stages of low NOX
burner operation and prescribed specific design and operational changes to improve operation in each scenario.
U.S. Steel states that each of the proposed solutions and design changesincluding adding blowers, increasing combustion air fan speed and capacity, adding rings to combustion air annuli, and adjusting and monitoring atomizing air and gas splitswere implemented in consultation with the burner manufacturer to optimize low NOX burner operation and NOX
reduction. In each case, U.S. Steel determined optimization of the low NOX burners involves achieving stoichiometric ratios of air to fuel at levels that create a tight flame shape in order to minimize NOX while ensuring proper process operation. U.S. Steel continues to monitor CEMS data and burner parameters to ensure the burners are operating effectively.

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As explained in response to Comments 1 and 3, at the time EPA
established limits in the 2013 FIP, low NOX burners had only been in operation on Lines 6 and 7 since April 2011 and May 2010, respectively, and there were limited CEMS data available upon which to base a limit. However, since EPA promulgated the initial BART
limits for Minntac in the 2013 FIP, U.S.
Steel has continued to operate low NOX
burners on Lines 6 and 7 and has installed low NOX burners on Lines 4
and 5.14 There are significantly more data available from which to determine whether the 2013 FIP emission limits are actually achievable through the utilization of low NOX burners at Minntac. In addition, and as noted above, U.S. Steel has submitted final testing reports for Lines 4 through 7 that detail U.S. Steels optimization efforts for each of these low NOX burners. In contrast to the scenario cited by commenter where the control technology had not yet been installed and only minimal data were available regarding performance of the control technology at issue, EPA is basing the revised limit for Minntac on actual CEMS data. U.S. Steel has also provided information concerning its low NOX
burner optimization efforts for Minntac Lines 4 through 7 and has provided post-optimization emissions data for Lines 4 through 7.
In the Arizona 2014 Regional Haze FIP 79 FR 52420 cited by the commenter, EPA stated the following with regard to Selective Non-Catalytic Reduction SNCR at lime kilns: While this type of control technology demonstration is not typically required as part of a regional haze plan, we consider it to be appropriate here, given the minimal data available about the performance of SNCR at lime kilns. 79
FR 52440. With regard to SNCR at cement kilns, we explained, While this type of control technology demonstration is not typically required as part of a regional haze plan, we consider it to be appropriate here, given the significant variability in control efficiencies achievable with SNCR at cement kilns. 79 FR 52456; 79 FR
52462. The control technologies required for lime kilns and cement kilns in the 2014 Arizona FIP had not yet been installed at the time the Arizona FIP was promulgated. This is a different scenario than the situation we are addressing with regard to Minntac.
Commenter cites to the BART
Guidelines at 40 CFR part 51, appendix 14 U.S. Steel installed low NO burners on Lines X
4 and 5 on December 15, 2016, and December 20, 2015, respectively.

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