Document ID: EPA-HQ-OAR-2017-0664-0103
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2019-09-25T04:00Z

MEMORANDUM

To:		David Putney, U.S. Environmental Protection Agency (EPA), OAQPS

From:		Mike Laney and Beatrix Jackson, RTI International
		David Putney, US. EPA

Date:		July 23, 2019

Subject:	Draft Technology Review for the Taconite Iron Ore Processing Source Category
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Background
Requirements of Section 112(d)(6) of the CAA
      Section 112 of the CAA requires the EPA to establish technology-based standards for sources of hazardous air pollutants (HAP). These technology-based standards are often referred to as maximum achievable control technology (MACT) standards. Section 112 also contains provisions requiring the EPA to periodically revisit these standards. Specifically, paragraph 112(d)(6) states:

      (6) REVIEW AND REVISION.  -  The Administrator shall review and revise as necessary (taking into account developments in practices, processes, and control technologies), emissions standards promulgated under this section no less often than every 8 years.
Description of the Taconite Iron Ore Processing Source Category and Requirements of the Current NESHAP
      The current National Emission Standards for Hazardous Air Pollutants (NESHAP) for the Taconite Iron Ore Processing source category was promulgated on October 30, 2003 (68 FR 61868) as 40 CFR part 63, subpart RRRRR. This subpart applies to affected new and existing sources of HAP emissions at taconite iron ore processing plants that are (or are part of) a major source of HAP. A taconite iron ore processing plant is a major source of HAP if it emits or has the potential to emit any single HAP at a rate of 10 tons or more per year or any combination of HAP at a rate of 25 tons or more per year. Taconite iron ore processing is defined (40 CFR §63.9652) as the separation and concentration of iron ore from taconite, a low-grade iron ore, to produce taconite pellets.

      There are currently eight taconite iron ore processing plants that are subject to this subpart, one of which is currently idle. An affected source is defined in this subpart as each new or existing ore crushing and handling operation (OCH), ore dryer, pellet indurating furnace (PI), or finished pellet handling operation (PH). The rule also applies to certain fugitive dust emission sources. Each of these affected sources was described in the preamble for the initial taconite iron ore processing NESHAP proposal (refer to 67 FR 77564 through 77565 and 77567 through 77570). Those descriptions are summarized in Section 1.3, below, for convenience.

      This subpart includes numeric emission limits for particulate matter (PM) as a surrogate for metal HAP emissions from affected OCH, ore dryers, PI, and PH sources, and as a surrogate for acid gas emissions from affected PI sources. This subpart also includes work practice standards for PM as a surrogate for metal HAP emissions from affected fugitive dust emission sources and operation and maintenance requirements for emissions of formaldehyde and other HAP products of incomplete combustion from affected PI sources.
      
Current Practices for Affected Sources

Ore Crushing and Handling Operations
      
      Ore crushing and handling operations (OCH) begin "... where crude taconite iron ore is dumped into the primary crusher and ends where the unfired (green) pellets enter the indurating furnace." (67 FR 77569) OCH operations exclude the ore drying operations that occur at one plant (described below) and any operations wherein crushed ore is saturated with water for further processing (e.g., wet milling and magnetic separation), which suppresses HAP emissions. The OCH emission sources consist of operations to transport the raw ore and crush it down to about the size of coarse sand (i.e., a size suitable to separate the taconite, iron-bearing, material from the gangue, or waste material). Examples of OCH include ore crushers, ore screens, ore storage silos and bins, concentrate handling, and ore conveyors and transfer points. The control devices most commonly found in use to reduce PM emissions from affected OCH operations are wet scrubbers. However, rotoclones, multicyclones, electrostatic precipitators (ESP) and fabric filters are also utilized.
      
Ore Drying
      
      Ore drying using rotary-type, natural gas-fired ore dryers is conducted at one plant, the Tilden Mine plant in Michigan. The ore dryers, which are made necessary due to the more fine-grained ore processed in this plant, further dry the raw, crushed ore prior to the agglomerating operations (i.e., prior to formation of the "green" pellets). PM emissions from each ore dryer are reduced by a cyclone pre-cleaner in series with a wet scrubber.
      
Pellet Induration
      
      Pellet induration (PI) "... begins at the point where the grate feed conveyor discharges green pellets onto the furnace traveling grate and ends where the hardened pellets exit the finished pellet cooler." (67 FR 77569) PI refers to the pellet indurating furnaces, including the green pellet grate feeds and finished pellet discharges, which are used to indurate, or harden, the green pellets via oxidation from magnetite to hematite, at about 2,400 ℉. The indurating furnaces are one of two types: straight grate type or grate kiln type. These are typically natural gas-fired devices with another fuel (e.g., fuel oil, coal, coke and/or biomass) used as a backup fuel.
      
      In straight grate indurating furnaces, a continuous bed of unfired pellets is carried on a metal grate through different furnace temperature zones. In the drying zone, heated air is blown through the pellets. After they are dried, the pellets enter a preheat zone of the furnace where the temperature is gradually increased for the indurating stage. The pellets then enter the firing zone for induration where they are exposed to the highest temperature. The fired pellets then enter the post-firing zone, where the oxidation process is completed. Finally, the pellets are cooled using ambient air. Waste gases from the straight grate furnace are discharged primarily through two ducts: the hood exhaust, which handles the cooling and drying gases; and the windbox exhaust, which handles the preheat, firing, and after- firing gases. For a typical straight grate furnace, the two discharge ducts are combined into one common header before the flow is divided into several ducts to be exhausted to the atmosphere after control.
      
      The grate kiln indurating furnace system consists of a traveling grate, a rotary kiln, and an annular cooler. The grate kiln system is a newer generation of indurating furnaces and is widely used in the taconite industry. In a grate kiln system, a bed of unfired pellets is laid on a continuously moving, traveling grate, which conveys the pellets into a dryer/preheater. In the first half of the traveling grate, pellets are gradually dried by hot air. The second half of the traveling grate, the preheater, heats the pellets to a temperature of 2,000 ⁰F. The pellets are then discharged into the rotary kiln where, at a temperature of 2,300 to 2,400 ⁰F, the pellets are oxidized from magnetite (Fe3O4) into hematite (Fe2O3). The hardened pellets are then discharged to a large annular-shaped cooler where ambient air is used to partially cool the pellets. The heated air from this part of the cooler is used as preheated combustion air in the kiln. The partially cooled pellets enter a final cooling zone where additional ambient air further cools the pellets. Air exiting the final cooling zone is directed to the dryer section of the traveling grate. Combustion air from the rotary kiln is used to maintain the temperature in the preheat section of the traveling grate. Pellet cooler vent stacks are atmospheric vents in the cooler section of a grate kiln indurating furnace. Pellet cooler vent stacks exhaust cooling air that is not returned for heat recuperation. Straight grate furnaces do not have pellet cooler vent stacks.
      
      The rule establishes subcategories within the indurating furnace affected source to distinguish between the two types of furnace designs - grate kiln furnaces and straight grate furnaces. Physical and operational differences that affect emissions and the controllability of emissions distinguish the two types of furnaces.
      
      Grate kiln furnaces have production rates approximately 30 percent greater than those of straight grate furnaces. Grate kiln furnaces have two furnace sections, a continuous grate followed by a rotary kiln. Straight grate furnaces have only a continuous grate. In the grate kiln, the tumbling action in the kiln increases pellet breakage and the entrainment of particles in the air stream results in higher metal HAP emissions. Also, air flow through a grate kiln furnace is more than twice the air flow through a straight grate furnace.
      
      The rule also makes a distinction based on the ore type processed by grate kilns. Based on PM test data, grate kiln furnaces exhibit higher PM emissions when hematite ore is processed rather than magnetite ore. The finer grain of the hematite ore results in a higher breakage rate and higher emissions. Therefore, the emission standards make a distinction based on ore type processed within grate kilns.
      
      PM emissions from the PI affected sources are most commonly reduced by either wet scrubbers or wet walled electrostatic precipitators (WWESP). However, multicyclones are also used. The high moisture content of furnace exhaust precludes control via baghouses.
      
Pellet Handling Operations
      
      Pellet handling operations (PH) "... begins at the indurating furnace discharge and ends where the finished pellets are stockpiled." (67 FR 77569) The PH emission sources consist of operations to transport the finished pellets to stockpiles or storage bins. Examples of PH include pellet screens, conveyors, transfer points, storage silos and bins. The control devices most commonly found in use to reduce PM emissions from affected PH operations are wet scrubbers. However, rotoclones, multicyclones, electrostatic precipitators (ESP) and fabric filters are also utilized.

Fugitive Dust Emission Sources
      
      Fugitive dust emissions sources refers to the emission sources that are subject to the fugitive dust control requirements of the NESHAP (see 40 CFR 63.9591). All plants subject to the rule are required to prepare and implement a written fugitive dust emissions control plan. The plan must describe in detail the measures that will be put in place to control fugitive dust emissions from the following sources at a plant, as applicable: stockpiles, material transfer points, plant roadways, tailings basin, pellet loading areas and yard areas. Based on a review of current permits, dust control measures include the use of water, chemical dust suppressants and ground cover.
Developments in Practices, Processes, and Control Technologies

      For the purposes of this technology review, a "development" was considered to be:

 Any add-on control technology or other equipment that was not identified and considered during development of the original MACT standards;
 Any improvements in add-on control technology or other equipment (that were identified and considered during development of the original MACT standards) that could result in significant additional emissions reduction;
 Any work practice or operational procedure that was not identified or considered during development of the original MACT standards;
 Any process changes or pollution prevention alternatives that could be broadly applied to the industry and that were not identified or considered during development of the original MACT standards; and
 Any significant changes in the cost (including cost effectiveness) of applying add-on control technology or other equipment to affected sources (including controls the EPA considered during the development of the original MACT standards).

      We researched practices, processes and control technologies through a literature review with a view toward identifying "developments" as defined above. Developments in the industry were discussed with representatives from three taconite iron ore processing companies (i.e., U.S. Steel, ArcelorMittal, and Cliffs Natural Resources) during site visits to taconite processing plants in Minnesota. In addition, State permits were reviewed to assess control technologies at taconite iron ore processing plants. The review also included the following two Federal Register notices: Approval and Promulgation of Air Quality Implementation Plans, States of Minnesota and Michigan, Regional Haze State Implementation Plan (78 FR 59825, 2013) and Federal Implementation Plan for Regional Haze (78 FR 8705, 2013). The results of the review are presented in the following sections.
Ore Crushing and Handling (OCH)
      No developments in OCH control technologies were identified through the literature review or discussions with industry representatives. The taconite iron ore processing industry has implemented some OCH process modifications to improve production rates and improve efficiency but none to reduce emissions, as explained below.
      
      High-pressure grinding rolls (HPGR) were evaluated in a 2013 analysis as a possible improvement in ore crushing and handling operations. During OCH operations, magnetite or hematite ore is liberated from its silicate matrix. A 2013 cost analysis, prepared by the Australian Queensland Centre for Advanced Technology and presented at the PERUMIN 31[st] Mining Convention in Peru, (Jankovic et al., 2013) examined the operating cost associated with high capacity processing of a hard, fine grained silica rich magnetite ore with more efficient grinding technologies such as HPGR for fine crushing and stirred milling for fine grinding. HPGR has been in use since before 2001 at Empire Mine and resulted in a mill throughput increase of 20 percent. Vertimill(R) fine grinding technology at Hibbing Taconite Company facilitated processing of lower grade ores and increased the concentrate production. The study concluded that, for the ore type evaluated, the application of HPGR and stirred mill technology appear to reduce energy consumption by up to 25 percent compared with conventional processes with wet tumbling mills (Jankovic et al., 2013). Although described as more efficient, the analysis did not indicate that the technology reduced emissions over other OCH technologies nor is it considered a new technology as it was in use prior to the development of the original MACT standard.
      
Pellet Induration (PI)
Air Pollution Control Technology

      No developments in pellet induration furnace control technologies or processes were identified through the literature review or discussions with industry representatives. A technology to reduce SO2 emissions that potentially also could control PM emissions is described below.
      
      As part of a best available retrofit technology (BART) analysis by the state of Michigan, spray drying absorption (SDA) retrofitting was considered for its ability to reduce SO2 emissions and potentially eliminate the need for the existing venturi rod scrubbers used to control PM emissions from taconite indurating furnaces. It was suggested that, as a result, the technology could reduce water consumption, gas stream moisture content, and PM emissions due to the higher efficiency of the baghouse. However, EPA agreed with the state of Michigan that the technology was not cost effective and, therefore not BART (78 FR 8705, February 6, 2013). In addition, the 2006 MPCA BART analysis (MPCA, 2006a; MPCA, 2006b) found SDA to be not technically feasible under indurating furnace waste gas conditions due to the high moisture content of the lime slurry spray. This study did not include information on HAP reductions or cost-effectiveness.
      
In 2012, Environment Canada entered a voluntary Performance Agreement Concerning Air Pollutants from the Iron Ore Pellet Sector with Iron Ore Company of Canada and ArcelorMittal Mining Canada G.P. (EC, 2012) to reduce atmospheric emissions of SO2, PM2.5, and NOx from new and existing induration furnaces at iron ore pelletizing operations in Canada. ArcelorMittal's two induration furnaces are controlled by a multicyclone and then exhaust to a dry ESP. Exhaust gases from Iron Ore Canada's six induration furnaces are treated by multicyclones before being released to the stacks. No new technologies were identified as part of this 2012 performance agreement.
Process Technology
      
      The following process technologies illustrate efforts in the industry to reduce induration process footprints, improve furnace life, reduce fuel and power requirements, and reduce fugitive emissions, although none are intended to directly reduce HAP emissions. No developments in practices, processes, or control technologies that would reduce HAP emissions were identified during the review of literature and state permits or as a result of discussions with industry representatives.

      Circular Pelletizing Technology (CPT) - CPT is a circular version of a travelling-grate or straight grate kiln, intended mainly to reduce the plant footprint. The circular design allows the furnace hood to cover more than twice as many pallet cars compared to a straight-type induration furnace. Capacity is 0.6-3.0 million tons per year (Aichinger, et al., 2015). In addition to the reduced plant footprint, this technology offers flexibility on location (mine site, at steel works or direct reduction plants), fuel flexibility, fully automated operation, and lowest capital expenditure solution for blast furnace and Direct Reduction pellets (Siemens, 2013). Exhaust gases are controlled by ESPs or bag filter systems (Aichinger, et al., 2015). The first plant was contracted in 2011 and a second plant in 2013, both in India, however status updates were not available (Siemens, 2013). There are no plants in the U.S. that use this technology. No information on emissions from furnaces using this technology was identified.

      Grate-kiln system improvements  -  The Finnish Metso Corporation lists on-going developments in grate-kiln systems in a 2012 brochure, however, cost and HAP emissions reduction information are not provided (Metso, 2012). The company's list includes:
 The use of higher-grade alloys in the traveling grate for longer life.
 Floating seals in the traveling grate to reduce air leakage.
 Annular coolers made with water seals and fabricated steel pallets.
 Patented kiln seals to reduce air leakage.
 Finite element analysis on grate components to improve life, reduce fuel and power requirements.
 Heat and mass balance model studies to optimize a system for a particular iron ore
            concentrate or fuel.
       Mathematical models  -  Our research indicates that the most recent approaches (post-2010) of improving straight grate and grate kiln furnaces focus on mathematical models (Cameron, et al., 2015), rather than technology updates.

2.3	Pellet Handling (PH)
      Although not a development in practices, processes, or control technology that reduces HAP emissions, the following is an improvement in the pellet handling part of the taconite iron ore process.
      
      Natural Resources Research Institute (NRRI) Pellet Fines Removal System (FRS) was designed to remove taconite pellet fines and pellet chips using an endless conveyor belt in place of vibrating screens to lower overall costs associated with upkeep and capital input. The technology is available for a $30,000 conversion fee plus royalty fees (University of Minnesota, 2018). In a 2010 full scale study, improved wear parts allow the conveyor belt to be operated at feed rates of 300-350 tons per hour, 24 hours per day, without needing to replace chevron lifter bars on the belt surface for at least 3-month intervals. During test runs at one of the operating Minnesota taconite plants, older rubber chevron lifters were replaced with new abrasion resistant steel AR400 lifter plates bolted to the conveyor belt surface resulting in approximately 650,000 tons of potential pellet processing versus 25,000 tons with older rubber chevron lifters. Results showed greater than 90 percent removal of minus 1/4-inch fines from pellet feeds (NRRI, 2010). However, tests conducted at a Minnesota taconite operation in 2012 did not produce results sufficient to classify this technology as a replacement for vibrating screen technology used to produce pellet screening of at least 99.5 percent purity level at feed rates of 350 tph (NRRI, 2013 and NRRI, 2018). NRRI reports that the process results in a 98 percent purity level (NRRI, 2018). Information on whether the system reduces PM emissions, or the cost of the system was not provided.
2.4	Ore Drying
      The Tilden Mine plant is the only taconite plant that uses ore drying equipment due to the finer-grained ore processed at that plant. PM emissions from each ore dryer are controlled by a cyclone pre-cleaner in series with an impingement wet scrubber. Improvements to dryer technology and control technology were not identified. No development in practices, processes, or control technology were identified that would reduce HAP emissions from ore drying.

2.5	Fugitive Dust Emission Sources
      
      Fugitive dust emissions control plans are required at taconite plants to manage fugitive dust emissions from stockpiles, material transfer points, plant roadways, tailings basins, pellet loading areas, and yard areas. Based on a review of current permits, dust control measures include the use of water, chemical dust suppressants and ground cover and may include practices to address seasonal variations that impact dust generation. A 2009 study of suppression of airborne particulates in iron ore processing asserted that surfactants which provide the fastest wetting of iron ore, are not considered highly effective taconite dust suppressants. Instead, the use of a hygroscopic reagent which retained moisture reduced PM10 by as much as 85 percent (Copeland, et al, 2009). However, the use of surfactants is not a new technology or practice. No development in practices, processes, or control technology that would for reduce HAP emissions from fugitive dust sources were identified in the review of literature or state permits or from discussions with industry representatives.
      
 3.0	Summary

   This technology review investigated practices, processes and controls with a view toward identifying "developments" as defined in section 2.0 of this document. To summarize, to be considered a "development" it must be any of the following:

 Any add-on control technology or other equipment that was not identified and considered during development of the original MACT standards;
 Any improvements in add-on control technology or other equipment (that were identified and considered during development of the original MACT standards) that could result in significant additional emissions reduction;
 Any work practice or operational procedure that was not identified or considered during development of the original MACT standards;
 Any process changes or pollution prevention alternatives that could be broadly applied to the industry and that were not identified or considered during development of the original MACT standards; and
 Any significant changes in the cost (including cost effectiveness) of applying add-on control technology or other equipment to affected sources (including controls the EPA considered during the development of the original MACT standards).
   The current NESHAP regulates PM emissions as a surrogate for metal HAP emissions from fugitive dust emission sources, ore crushing and handling (OCH), pellet indurating (PI), pellet handling (PH), and ore drying. PM emissions are also regulated as a surrogate for acid gases from PI sources.

   The use of high pressure grinding rolls (HPGR) were reported to reduce energy consumption during OCH and have been in use in the industry prior to the development of the MACT standards for the taconite industry. No information was found on the ability of HPGR to reduce HAP emissions.

   For the control of metal HAP emissions from induration furnaces, cyclone separators (i.e., multiclones), wet scrubbers, and WWESPs were identified. These are not new technologies and were in use in the industry during development of the MACT standard. SDA has also been identified as a technology that can reduce SO2 emissions as well as PM emissions. However, it was not considered cost effective by the EPA (78 FR 8705, 2013).

   CPT and FRS were identified as pellet handling technologies that improve the efficiency of the process, but no information was found that these technologies would reduce HAP emissions.

   Process improvements in straight grate and grate kiln induration furnaces have been introduced over time that have increased plant capacity. These improvements have been introduced to increase plant capacity and are not recognized for any ability to reduce HAP emissions.

   In summary, no developments in practices, processes, or control technologies were identified that would reduce HAP emissions from crushing and handling (OCH), pellet indurating (PI), pellet handling (PH), ore drying, and/or fugitive dust emission sources have been identified.

4.0	REFERENCES

78 FR 8705. 2013. Approval and Promulgation of Air Quality Implementation Plans; States of Minnesota and Michigan; Regional Haze State Implementation Plan; Federal Implementation Plan for Regional Haze. Available at https://www.federalregister.gov/documents/2013/02/06/2013-01473/approval-and-promulgation-of-air-quality-implementation-plans-states-of-minnesota-and-michigan

Aichinger et al. 2015. Circular Pelletizing Technology  -  The World's Most Compact Pelletizing Plant. Technical contribution to the 45º Seminário de Redução de Minério de Ferro e Matérias-primas, to 16º Simpósio Brasileiro de Minério de Ferro and to 3º Simpósio Brasileiro de Aglomeração de Minério de Ferro, part of the ABM Week, August 17th-21st, 2015, Rio de Janeiro, RJ, Brazil.Available at https://abmproceedings.com.br/en/article/download-pdf/circular-pelletizing-technology-the-world-s-most-compact-pelletizing-plant

Cameron et al. 2015. Guidelines for Selecting Pellet Plant Technology. Available at https://businessdocbox.com/Metals/75815396-Guidelines-for-selecting-pellet-plant-technology-i-cameron-m-huerta-j-bolen-m-okrutny-k-o-leary.html

Copeland, C.R., T. Eisele, and S. Kawatra. 2009. Suppression of airborne particulates in iron ore processing facilities. International Journal of Mineral Processing 93(3):232-238. Available at https://www.researchgate.net/publication/229272795_Suppression_of_airborne_particulates_in_iron_ore_processing_facilities/citations

EC (Environment Canada). 2012. Performance Agreement Concerning Air Pollutants from the Iron Ore Pellet Sector. Available at https://www.canada.ca/en/environment-climate-change/services/environmental-performance-agreements/iron-ore-pellet-sector-overview/agreement.html

Jankovic et al. 2013. Eco-Efficient and Cost-Effective Process Design for Magnetite Iron Ore. Conference Paper. PERUMIN - 31st Mining Convention. Arequipa, Peru. Available at https://www.metso.com/showroom/mining/eco-efficient-and-cost-effective-process-design-for-magnetite-iron-ore/

Metso (Metso Corporation). 2012. Iron ore pelletizing. Grate-Kiln[TM] system. Available at https://www.metso.com/globalassets/saleshub/documents---episerver/great-kiln-system-brochure.pdf

MPCA (Minnesota Pollution Control Agency). 2006a. Northshore Mining Company Analysis of Best Available Retrofit Technology (BART). Available at https://www.pca.state.mn.us/sites/default/files/bart-facility-northshore.pdf

MPCA . 2006b. Hibbing Taconite Analysis of Best Available Retrofit Technology (BART). Available at https://www.pca.state.mn.us/sites/default/files/bart-facility-northshore.pdf

NRRI (Natural Resources Research Institute). 2010. 2010 Semi-Annual Report. July  -  December. https://www.nrri.umn.edu/sites/nrri.umn.edu/files/2010julyreport.pdf

NRRI (Natural Resources Research Institute). 2013. 2013 Semi-Annual Report. January  -  June. http://www.nrri.umn.edu/sites/nrri.umn.edu/files/2013janreport.pdf

NRRI (Natural Resources Research Institute). 2018. Mining Technology for Pellet Fine Removal. http://license.umn.edu/technologies/z03035_mining-technology-for-pellet-fine-removal

Siemens. 2013. Circular Pelletizing Technology. 18th Middle East Iron & Steel Conference 2014  -  Dubai, U.A.E. Available at http://www.metalbulletin.com/events/download.ashx/document/speaker/7205/a0ID000000X0jz6MAB/Presentation

University of Minnesota. 2018. Mining Technology for Pellet Fine Removal. Available at http://license.umn.edu/technologies/z03035_mining-technology-for-pellet-fine-removal