1 MEMORANDUM

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

From: David Green and MattHakos, RTI International

Date: September 3, 2015

Subject: Final Technology Review for the Pr imary Aluminum Production Source Category

1.0 BACKGROUND

1.1 Requirements of Section 112(d)(6) of the CAA Section 112 of the CAA requires th e EPA to establish technology-ba sed standards for sources of hazardous air pollutants (HAP). These technology-bas ed standards are often referred to as maximum achievable control technology (MACT), standards. S ection 112 also contains provisions requiring the EPA to periodically revisit these standards. Specificall y, paragraph 112(d)(6) states: (6) REVIEW AND REVISION. – The Administrato r shall review, and revise as necessary (taking into account developments in practices, processes, and control technologies), emissions standards promulgated under this sec tion no less often than every 8 years.

1.2 Description of the Primary Aluminum Produc tion Source Category and Requirements of the Current NESHAP

The current National Emissions Standards for Hazardous Air Pollutants (NESHAP) for Primary Aluminum Reduction Plants was promulgated on October 7, 1997 (62 FR 52407) as 40 CFR part 63, subpart LL (subpart LL). The rule was am ended at 69 FR 18803, April 9, 2004; 70 FR 66284, November 2, 2005; and 71 FR 20458, April 20, 2006. Subpa rt LL applies to affected sources of HAP emissions at primary aluminum reduction plants. A pr imary aluminum reduction plant is defined as any facility manufacturing aluminum by electrolytic reduction. This el ectrolytic reduction process takes place in reduction cells, or pots, th at are electrically connected in se ries to form potlines. Typically, a potline will be comprised of 100 or more reduction cells. There are currently 11 faci lities that are subject to subpart LL, two of which are presently idle. One of these subject facilities does not manufacture aluminum but does produce prebaked anodes for use at primary aluminum reduction pl ants that utilize the prebake pr ocess and contains an affected source. Affected sources include new pitch storag e tanks and new and existing paste production plants, anode bake furnaces and potlines. The current subpart LL includes emission limits for total fluoride (TF), as a surrogate for hydrogen fluoride (HF), from new and existing potlines and anode bake furnaces and for polycyclic organic matter (POM) from new and existing Soderberg potlines and anode bake furnaces. The current NESHAP also includes work practice requirements to limit POM emissions from new pitch storage tanks and new a nd existing paste production plants.2 Control devices currently in use to reduce emissi ons from affected sources subject to subpart LL include dry alumina scrubbers (w ith baghouses) or wet scrubbers to control TF and POM emissions from potlines, dry alumina scrubbers (with baghouses ) to control TF and POM emissions from anode bake furnaces, dry coke scrubbers (with baghouses) to control POM emissions from paste production plants and carbon adsorbers and condensers to c ontrol POM emissions from pitch storage tanks. One facility also operates wet scrubbers to control secondary emissions from potlines. 1.3 Additional Requirements of Amended NESHAP

The final NESHAP amendments include emissi on limits for carbonyl sulfide (COS) and POM from new and existing potlines; for particulate matte r (PM, as a surrogate for non-mercury (Hg) metal HAP) from new and existing potlines, anode bake fu rnaces and paste production plants; for Hg from new and existing anode bake furnaces; and for nick el, arsenic and polychlor inated biphenyls (PCBs) from new and existing Soderberg potlines; equipmen t standards to limit POM emissions from existing pitch storage tanks; and work pract ice standards for potlines, anode bake furnaces and paste production plants during periods of startup and normal operation.

1.4 Current Practices

1.4.1 Potrooms At the time of the initial promulgation of subpart LL two main primary aluminum reduction processes (i.e., the Soderberg and prebake processes) were in use in the primary aluminum production source category and several different pot configurations were in use for each of these processes (i.e., three for Soderberg processes and four for prebake pr ocesses, for a total of seven pot configurations). The differences in achievable emission rates for each of the seven different pot configurations were recognized during development of subpart LL and diffe rent emission limits were promulgated for each pot configuration. With the closure of approximately one half of the plants in the industry since promulgation of subpart LL, two Sode rberg pot configurations were no longer in use at the time of the proposal (and the last Soderberg plant is now permanently shut down). The amended rule includes standards for only five of the original seven pot c onfigurations. No improved pot configurations have been developed in the U.S. or in other parts of the world since promulgation of subpart LL. The Soderberg process is an older, less effi cient, higher emitting process in which the anode paste mixture is baked in place in the reduction cells to produce anodes. The prebake process is a newer, lower emitting process in which the anode paste mixtur e is baked in a separate anode bake furnace to produce anodes. The difference in the TF emissions between the different pot configurations is due almost entirely to the capture efficiency achievable w ith the different pot confi gurations. The same types of control devices are used and control efficiencies of the captured emissions are similar. The different variants of pot configurations in the prebake and the Soderberg pro cesses have different TF emission limits, reflecting their different capture efficiencies. The current subpart LL rule includes more stringent TF limits for new potlines (without regard to pot c onfiguration, or process type) recognizing that the best controlled processes are those prebake pr ocesses with the best capture efficiency.3 The difference in POM emissions between the diff erent Soderberg pot configurations are mainly due to differences in capture efficiency achievable between the different pot configurations whereas the difference in POM emissions between Soderberg pr ocesses and prebake processes are due both to differences in capture efficiency achievable between the different pot configurations and because POM emissions resulting from baking anodes in the pots (a s in the case of Soderber g processes) are higher than those resulting from baking anodes in bake fu rnaces (as in the case of prebake processes). These higher POM emissions from the Soderberg processes re flect both the lower capture efficiencies of the Soderberg cell configurations and that prebaked anode production POM emissions are more efficiently captured and controlled from anode bake furnaces. The different pot configurations of the Soderberg process had different POM emission limits for existing potlines in the initially promulgated subpart LL rule, reflecting their different cap ture efficiencies, and more stri ngent POM limits for new Soderberg potlines, without regard to pot configuration, recognizi ng that the best controlled processes are those pot configurations with the best capture efficiency. Emissions of POM, TF and PM from potlines consist of emissions from stacks of the potline control device (typically a dry alumina scrubber followed by a baghouse), referred to as primary emissions, and emissions from roof vents which ex tend over the length (typi cally, about 1,000 feet) of the potroom, referred to as secondary emissions. Th e secondary emission stream is much higher in volumetric air flow than the primary emission stream . The secondary emission stream is controlled by wet scrubbers at one facility and is uncontrolled at each of the remaining 9 f acilities that are equipped with potlines. COS emissions, which were not initially regula ted under subpart LL, are produced as the anodes are consumed in the reduction ce lls and the carbon, sulf ur (found as an impurity in the anodes) and alumina react. Approximately 5 to 10 percent of the su lfur present in the anodes is emitted as COS, with the balance being convertedto sulfur dioxide (SO 2 ). No add-on control devices are currently in use by the primary aluminum reduction indu stry to control COS emissions. Th eoretically, COS emissions from primary aluminum reduction facilities can be decreased by using coke with a lower sulfur content for anode preparation. However, petroleum coke is the source of anode grade coke used in the primary aluminum industry and the availabili ty of low sulfur content petroleum coke is limited and insufficient to meet the current needs of the primary aluminum industry. PM emissions, which were not regulated under the initially promulgated subpart LL, consist of condensed emissions of HAP metals, metal oxides and fluoride salts volati lized from the pots, as well as suspended alumina. Capture systems and control devi ces presently in place at all potlines to control emissions of TF and POM are also effective for control of PM emissions. As with TF and POM, secondary emissions of PM make up the majority of potline PM emissions and are minimized by effective capture of emissions in the hooding and r outing them through the primary emissions control device.4 1.4.2 Anode Bake Furnaces Most prebake facilities, as we ll as one facility that does not produce aluminum but produces prebaked anodes for use off-site, are equipped with, and operate, anode bake furnaces. Anode bake furnaces emit POM which is released when the anode paste (consisting of a mixture of about 78 percent petroleum coke and about 22 percent pitch) is ba ked to produce anodes and TF, which results from recycling of the butt ends of previous ly used anodes (which have been exposed to fluoride in the pots) in the anode paste. Anode bake furnaces also emit PM which results from condensed organics volatilized from the green anodes, fluoride salts and dust associ ated with the placement and removal of packing coke (used as an insulator). These PM emissions are known to contain non-Hg HAP metals. Anode bake furnaces also emit Hg, which is present in the anode paste at low concentrations. This Hg is volatilized and driven off during the baking process. POM and TF emissions from all anode bake furnaces are controlled by dry alumina scrubbers followed by baghouses . These controls are also effective for control of PM emissions and provide some control of Hg emissions.

1.4.3 Paste Production Plants Most prebake and Soderberg facilities are equi pped with, and operate, paste production plants. Paste production plants emit POM which is released during the mixing of heated pitch with coke to produce anode paste. Emissions at all paste producti on plants are controlled wi th dry coke scrubbers followed by baghouses. Paste producti on plants also emit PM generated from the mixing of petroleum coke and pitch, as well as condensed pitch vapo rs. These PM emissions are known to contain HAP metals. The systems used to control POM emissions fr om the paste production plants are also effective for control of PM emissions from these sources. 1.4.4 Pitch Storage Tanks Most prebake and Soderberg facilities are equipp ed with, and operate, pitch storage tanks. Pitch storage tanks emit POM from the displacement of POM laden gases during filling and from working losses that result from temperature ch anges. Most of the existing pitch storage tanks at these facilities are uncontrolled. However, three f acilities do have control devices fo r pitch storage tank emissions. The most effective control devices are condensers and activated carbon adsorb ers. The final rule amendments include MACT equipment standards (p romulgated under section 112(d)(2) and (3) of the CAA) that will require that all pitch storage tanks to be controlled such that inlet POM emissions are reduced by a minimum of 95%.

2.0 DEVELOPMENTS IN PRACTICES, PR OCESSES AND CONTROL TECHNOLOGIES For the purposes of this technology review, a “d evelopment” was considered to be a (n):

 Add-on control technology that was not identified dur ing the development of the current NESHAP for this source category;

 Improvement to an existing add-on control technology that could result in significant additional HAP emissions reductions;5  Work practice or operational procedure that was not identified duri ng development of the current NESHAP for this source category; or

 Applicable process change or pollution preven tion alternative that was not identified and considered during the development of the cu rrent NESHAP for this source category. We investigated developments in practices, processes and control t echnologies through a literature review and discussions with industry representatives, and incl uded questions in an information request that was sent to the comp anies subject to subpart LL in 2011. 2.1 Potline, Anode Bake Furnace and Paste Production Plant Startup Procedures The MACT control technology typically used for potlines and anode bake furnaces is a dry alumina scrubber followed by a baghouse. The MACT control technology typi cally used for paste production plants is a dry coke sc rubber followed by a baghouse. Faci lities further decrease emissions from these sources by implementation of certain pract ices during periods of startup. For example, for anode bake furnaces and paste produ ction plants these practices incl ude the development of startup schedules and operation of the associated control systems within normal parametric limits prior to startup. Some examples of practices used during startup of potlines in clude the development of startup schedules, minimizing the time that hooding is removed during anode changes, reducing cell temperatures to as low as practicable, and resealing pot crusts that have been broken as often and as soon as practicable. These startup work practices are require d by the final rule. 2.2 Work Practices to Limit Emissions During Normal Operations Work practices that have been developed to improve the performance and efficiency of potlines are also effective at limiting HAP emissions. The final rule specifies the following work practices which are applicable to periods of normal potline operations: (1) Ensure the potline scrubbers and exha ust fans are operational at all times. (2) Ensure that the primary capture and control system is operating at all times. (3) Hood covers should be replaced as soon as possible after each potroom operation. (4) Inspect potlines daily and a) identify unstable pots as soon as practicable but in no case more than 12 hours from the time the pot became unstabl e, b) reduce cell temperatures to as low as practicable, and c) reseal pot cr usts that have been broken as often and as soon as practicable. (5) Ensure that hood covers fit properly and are in good condition. (6) If the exhaust system is e quipped with an adjustable damper system, the hood exhaust rate for individual pots must be increased whenever hood covers are removed from a pot, provided that the exhaust system will not be overloaded by placing too many pots on high exhaust. (7) Dust entrainment must be minimized duri ng material handling operations and sweeping of the working aisles.6 (8) Only tapping crucibles with functional aspira tor air return systems (for returning gases under the collection hooding) can be used, unless the re gulatory authority approv es alternative tapping crucibles. In addition, the final rule require s either twice daily visual emi ssions observation, the use of bag leak detection systems, or the ope ration of a particulate matter cont inuous emissions monitoring system on the exhausts from all control devices.

2.3 Substitution of Coal-Based Coke in Anodes We investigated the feasibility of substituting metallurgical coke (also known as coal-based coke) for the petroleum coke used by all facilities in the production of anodes. Metallurgical coke contains lower sulfur and would t hus lead to lower emissions of CO S. In addition, metallurgical coke has a lower content of some HAP metals, particularly nickel. Testing concl uded that unprocessed coke produced from coal does not have properties suitab le for the production of carbon anodes. Coal-based coke has a high ash content and this leads to unacceptable properties, including poor electrical conductivity, high carbon consumption and unacceptable aluminum purity. 1 Coal or coal-based coke could be processed (f or example by solvent extraction) to remove the impurities at a considerable cost. However, anodes produced with 100 percent processed coal-based coke have similar drawbacks, such as brittleness and hi gh carbon consumption. 2 The EPA concluded that it is not approp riate to require substitution of metallurgical coke for petroleum coke as a means of decreasing COS emissions due mainly to increase d ash content and mechanical weakness in anodes produced from metallurgical coke. While it may be technically feasible to produ ce acceptable anodes by blending petroleum based coke and processed coal-based coke, the need to blend with petroleum coke to produce usable or acceptable anodes defeats the initia l benefits of removing the impurities. Furthermore, suitable processed coal-based coke is not commercially availa ble today. Therefore, the EP A concluded that it is not appropriate to require such use of coal-b ased coke or the blending of these cokes. 2.4 Improved Potroom Capture Efficiency A process has been developed 3 to improve capture of emissions from prebake pots by detecting the drop in temperature in the air space above the pot crust, but within the hooding, associated with the temporary hooding removal for anode changes and using a control system to alte r the air flow on a potby-pot basis. When hoods are open, pr essurized air is supplied to the inside of the hood and increased suction is supplied through a second duct to direct emissions to the dr y alumina scrubber. As described, this system should improve capture efficiency and decrease secondary emissions. However, the EPA is not promulgating emission standards based on th e installation of this process because: 1) It is not currently in us e in any primary aluminum pr oduction facility in the U.S.; 2) It is not known to be suitable for retrofit to existing potlines;7 3) No data are available regarding the actua l emissions of TF and POM from a potroom equipped with this system; 4) No information is available about the cost of retrofit or th e incremental costs associated with implementing this system in a new plant; and 5) While the patent descripti on is publically available, deta ils necessary for successful implementation are proprietary.

3.0 CONCLUSIONS Other than the startup procedures and work pract ices for potlines, anode bake furnaces and paste production plants, this review did not identify any other developments in practices, processes or control technologies that have been implemented in this source category since prom ulgation of the current NESHAP that indicate any additional amendments to NESHAP would be appr opriate under the Section 112(d)(6) technology review. At the tim e that subpart LL was developed, the potline configurations in use differed considerably in their potential HAP emission rates, theref ore seven separate subcategories of potlines were established, each with different MACT floors. As the primary aluminum production industry has contracted from 23 facilit ies to 11 facilities (9 of which ar e presently operating) in the time since promulgation of the initial NESHAP, some of the higher emitting potline subcategories have ceased operation. The new MACT standards that EPA has promulgated are consistent with emissions from the lower emitting potline subcategories. Although no new developments in practices, proc esses or control technologies have been implemented in this source category since promulga tion of the current NES HAP (again, other than startup procedures and work practices), existing technologies could be adapted to achieve lower emissions. As an example, POM, PM and TF captu re can be improved by increasing the flow through the dry alumina scrubber. However, such an incr ease in flow would require a redesign of the scrubber/baghouse system and the data needed to estim ate the associated reducti on in emissions are not available. Overall POM, PM and TF emissions could also be reduced by retrofit of a control device to treat the high volume, low concentration secondary em issions from the potroom roof vents. However, it is not known whether the current buildings could accommodate such control devices (e.g., it is not known whether the necessary space is available or whether the building st ructure could support the additional weight). Therefore, the EPA has not promulgated any amendments to the NESHAP based on these control measures.

1 Wells, C. Personal communication to David Putney, May 30, 2014.

2 Hamaguchi, M., et al. Prebaked Anode from Coal - Utilization of Coal Extract as a Coke Feedstock. Light Metals. 2010. p. 923-928.

3 Girault, G, and P. Cantin. Patent PCT/IB2007/001612 (US200090159434 A1). System and Process for Collecting Effluents from an Electrolytic Cell. 2009.