FROM: Jeff Coburn, RTI International

TO: Brenda Shine, EPA/OAQPS/SPPD

FOR: Docket ID No. EPA-HQ-OAR-2010-0682

DATE: July 2, 2012

SUBJECT: Technology Review for Catalytic Reform ing Units at Petroleum Refineries

1. Purpose

This memorandum documents the technology review of emission controls for catalytic reforming units (CRU) at petr oleum refineries.

2. Background

Section 112 of the Clean Air Act (CAA) establishe s a two-stage regulatory process to address emissions of hazardous air pollutants (HAP) from stationary sources. In the first stage,

section 112 of the CAA directs the U.S. Envir onmental Protection Agency (EPA) to develop technology-based standards to control all major and some area sources emitting HAP. On July 16, 1992 (57 FR 31576), the EPA published a lis t of major and area s ource categories for

which national emissions standards for haza rdous air pollutants (N ESHAP) are to be promulgated. Petroleum refineries were listed under two source categories. Standards for the first source category, 40 CFR part 63, subpart CC (commonly referred to as Refinery MACT 1), were promulgated on August 18, 1995 (60 FR 43244) . Those standards, however, did not address three process unit vents associated with catalytic cracking units, catalytic reforming units, and sulfur recovery units, which we re covered under the second source category. Standards for the second source category, 40 CF R part 63, subpart UUU (commonly referred to as Refinery MACT 2), were promulgated on April 11, 2002 (67 FR 17762). The EPA is then required to review these technology-based standa rds and to revise them “as necessary (taking into account developments in practices, processe s and control technologies)” no less frequently than every 8 years, under CAA section 112(d)(6). To support this review, the EPA conducted a detailed Information Collection Request (ICR) in April 2011 to gather 201 0 process and control system information from all known petroleum refineries in the United States (EPA, 2011) (referred to as “Refinery ICR” in this memorandum; see: http://www.epa.gov/ttn/atw/petref/petrefpg.html and https://refineryicr.rti.org/ for more detailed information). As part of the ICR, selected facili ties were requested to test specific units at their facility. Twelve facilities we re requested to test the CRU catalyst regeneration vent(s); 10 sources completed the requested tests and two un its did not complete the test because the unit was either not operating or no regeneration cycl e was being performed during the year. This

memorandum documents the results of the I CR and technology review for CRU catalyst regeneration.Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

2 3. Catalytic Reforming Unit Process Descri ption, Emission Points, and Controls

A CRU is designed to reform ( i.e. , change the chemical structure of) naphtha into higher octane aromatics. This is accomplished by passing naph tha through a reactor co ntaining a catalyst at elevated pressure and temperature to promote dehydrogenation, isomerization, and hydrogenolysis reactions. The reforming reactio n is endothermic, meaning the reaction causes the temperature of the system to decrease during processing. Cons equently, the CRU is typically designed using reactors in series, with heat supp lied to the process fluid between each reactor. The reforming process uses a platinum or bimetal ( e.g. , platinum and rhenium) catalyst material. Halides (chlorine and fluorine) promote the activ ity of the platinum-alu mina catalyst and are stripped from the surface of the catalyst as hyd rogen chloride (HCl) or hydrogen fluoride (HF) during the reforming reactions, thus reducing catalyst activity.

Dehydrogenation reactions are favored by low pre ssure and high temperature; however, coke (carbon) is also formed at low pressure which te nds to deactivate the catalyst and reduce yields. Coke formation can be reduced by operating under high hydrogen pressure; other important variables in dehydrogenation activit y include temperature, space ve locity, recycle gas rate, and particle size of the catalyst us ed. The desired product quality (octane number) may be obtained by balancing the system pressure, temperature, space velocity, and recycle gas rate even as catalyst activity decreases. When yields can no longer be obtained, the catalyst must be regenerated.

Based on the Refinery ICR (EPA, 2011), we have detailed information on 151 CRU in the United States (although not all were operating in 2010). There are th ree types of CRU classified by differences in how the units are designed and operated to effect reforming catalyst regeneration. Semi-regenerative reforming is ch aracterized by shutdown of the reforming unit at specified intervals, or at the operator’s convenience, for in s itu catalyst regeneration. Semiregenerative systems were the most common type of CRU approximately 15 years ago, representing approximately half the reform ing capacity (EPA, 1998), but now represent only 30 percent of CRU nationwide capacity (EPA , 2011). Semi-regenerative CRU typically regenerate catalyst once every 8 to 18 months, with the regeneration cycle lasting approximately 2 weeks. Cyclic regeneration reforming is ch aracterized by continuous or continual reforming operation with periodic (but freque nt) regeneration of catalyst in situ by isolating one of the reactors in the series, regenera ting the catalyst, then returning the reactor to the reforming operation. The regeneration of th e catalyst in a single reactor may occur numerous times per year ( e.g. , once a month), and the regeneration of each r eactor may take 3 to 5 days to complete. Approximately 30 percent of the nationwide CR U capacity is provided by cyclic CRU (EPA, 2011). Continuous regeneration reforming units u tilize moving catalyst bed reactors situated vertically (which is why they ar e often referred to as platforming units). Catalyst flows down the

series of reactors. At the bottom of the last reactor, cat alyst is continually isolated and sent to a special regenerator. After regeneration, the rege nerated catalyst is contin ually fed to the first (top) reactor. Thus, continuous regeneration reforming units are char acterized by continuous reforming operation along with continuous regeneration operation. Continuous reforming capacity has grown over the past 15 years a nd currently accounts for 40 percent of the nationwide CRU capacity (EPA, 1998; EPA, 2011).Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

3 The catalytic reforming reaction is performed in a closed reactor system; there are no emissions associated with the processing portion of the CRU. There ar e a series of emission points associated with the CRU catalyst regenerator. Re gardless of the type of CRU used, there are a series of steps conducted to effect catalyst regeneration. These step s are: (1) initial depressurization/purge; (2) coke burn-off; (3) catalyst rejuvenation; and (4) reduction/final purge. A brief description of the processing step and emission points are provided in the following subsections. Table 1 summarizes the I CR responses regarding the emission controls for the various cycles of the CRU regeneration process (EPA, 2011).

Table 1. Summary of Controls Used for CRU Regeneration Cycles

Regeneration Cycle/ Type of CRU Regenerator Number of CRU indicating control as:No control, vent toatmosphereFuel gas system, flare,process heaterRecycle to processOther VOC control (e.g.,carbon canister)aCaustic Injection, sprayadsorptionPacked or tray towerwet/caustic scrubberChlorsorbTMDry chloride adsorptionbedOther HCl control or workpracticeNo vent, not specified ornot operating

Depressurization

Continuous 37 1 1 1 1 3

Cyclic 37 1 1

Semi-regenerative 2 63 3

Coke Burn-off

Continuous 8 25 10 1

Cyclic 1 1 18 11 6 1 1

Semi-regenerative 1 1 57 2 2 2 3

Rejuvenation

Continuous 3 12 5 16 6 2

Cyclic 8 3 16 6 4 2

Semi-regenerative 23 6 30 2 2 5

Reduction

Continuous 1 15 16 1 2 3 1 5

Cyclic 3 22 2 6 1 3 2

Semi-regenerative 10 36 5 2 1 14

a VOC = volatile organic compounds.Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

4 3.1 Initial Depressurization/Purge Cycle

In the first step of the regene ration cycle, any resi dual hydrocarbons in the reactor and/or on the catalyst particles are purged from the system us ing nitrogen and/or a va cuum. In a continuous CRU, a small quantity of catalyst is isolated in a lock hopper and the purging is conducted on this lock hopper container. For cyclic and semi-r egenerative systems, the en tire reactor (or series of reactors) is (are) isolated from processing and purged. The initial purge gas is typically conducted with hydrogen, methane, or nitrogen and ve nted to the refinery’s fuel gas system. The system is typically repressurized with nitr ogen and purged several times to ensure no hydrocarbons remain in the system. Subsequent purge gas is commonly vented to the flare header system or process heater. During the fi nal purge, when the nitrogen content of the purge gas is high and the hydrocarbon cont ent is near zero the final pur ge gas may be vented to the atmosphere. Also, when the pressure within the regenerator falls below the pressure needed to exhaust to the flare header, typi cally about 5 pounds per square in ch gauge (psig), purge gas may be vented to the atmosphere.

Air pollution control devi ces potentially applicable to this CRU purge vent stream include combustion devices such as a flare or vapor inci nerator and carbon adsorption systems. Flares and vapor incinerators employ heat and oxyge n to oxidize (combust) organic chemicals, converting them to carbon dioxide and water vapor. Although destruction efficiencies of vapor incinerators may be slightly high er than flare systems, flare systems typically achieve destruction efficiencies of 98 percent or higher and they are more suitable for the intermittent flows typical of the CRU purge vent. Carbon adsorption may also be used to remove organic chemicals from gas streams by selective adsorption onto the surface of activated carbon. Carbon adsorption systems are expected to have collection effici encies of 95 to 98 percent, but have reduced

efficiencies at low inlet con centrations. Carbon adsorption systems are not commonly used for controlling organic emissions from any CRU catalyst regeneration vent, although a carbon adsorber was noted for one depressurization/purge cycle control.

Two facilities tested their depressurization/purge cycle vent. The data from these tests are

summarized in Tables 2 and 3. It was confirme d that the cyclic CRU tests were conducted during the purging of different reactors, with each test spanning the entire purge venting period (about 115 minutes) for a single reactor. This ty pe of operation may explain why the different runs have variable pollutant con centrations (rather than sequentially lower concentrations). For the semi-regenerative CRU, the purge occurs for all reactors at the same time and each of the

different runs were conducted dur ing sequential purges of the enti re reactor system. That is, after the initial depressurization, the reactors are re-pressurized with nitrogen and depressured again for several cycles. The test data for the semi-regenerative system indicate, as expected, that the emissions during the subsequent depressu rization purge events are less than the previous

purge event.

The current Refinery MACT 2 requirements during the depressurization/purge cycle are to vent the emissions to the refinery’s fuel gas system, flare, or control device that achieves either a 98 percent reduction in total organic compound (TOC ) emissions or an outlet TOC concentration of 20 parts per million by volume (ppmv), dry basis, as hexane, corrected to 3 percent oxygen. The emission limits do not apply once the system pressure drops below 5 psig. The emissionTechnical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

5 limits are based on the historical control efficiency of a thermal incinerator. As indicated by the summary of ICR responses in Tabl e 1, nearly all refineries cont rol the primary depressurization and purge gases to some combustion source, whether via the fuel gas system, a flare, or directly to a process heater.

Table 2. Summary of Volatile Hydrocarbon Emissions Test Data for CRU Regeneration Purge Vents

Pollutant CRU 6 (Cyclic) Concentration (ppmv) a CRU 7 (Semi-regenerative) Concentration (ppmv) a

Run 1 Run 2 Run 3 Run 1a Run 1b Run 2 Run 3

Organic HAP

Benzene 206.2 4,342 151.5 0.79 0.06 0.03 0.03

Chlorobenzene BDL 1.73 3.63 0.05 0.008 0.002 0.004

Cumene 2.3 9.09 11.58

1,2-Dibromoethane 16.2 224.9 46.3 BDL BDL BDL BDL

Ethylbenzene 45.2 374 241.9 0.57 0.10 0.06 0.05

Hexane 41.8 570.4 49.6 0.49 0.01 0.003 0.003

Methyl isobutyl ketone 1.87 41.7 20.6 BDL BDL BDL BDL

Nitrobenzene 7.6 13 6.7 BDL BDL 0.0004

Toluene 260.1 4,779 297.2 1.69 0.22 0.12 0.12

Xylenes 650.5 4,939 1,124.5 1.95 0.47 0.33 0.33

Formaldehyde 0.13 0.12 0.13 0.92 1.10 1.65

Acetaldehyde BDL BDL BDL 36.9 13.1 32.8

Total Hydrocarbons

Methane 270 12,332 192 3.5 BDL BDL

Ethane 41.1 6,453 73.1 BDL BDL BDL

NM TOC as hexane
corrected to 3% O 2 b 686 9,695 793 6.4 0.38 0.38

a BDL = below detection limit, indicates that all runs were below detection limit.

b NM TOC as hexane corrected to 3% O 2 = non-methane total organic compounds concentration as hexane, corrected to 3 percent oxygen.Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

6 Table 3. Summary of Semi-Volatile Hydrocarbon Emissions Test Data for CRU Regeneration Purge Vents

Pollutant CRU 6 (Cyclic) Concentration ( μ g/dscm) CRU 7 (Semi-regenerative) Concentration ( μ g/dscm)

Run 1 Run 2 Run 3 Run 1 Run 2 Run 3

Semi-volatile Organic HAP

Acenaphthene 152.5 5,620 26.5 0.42 0.17 0.26

Acenaphthylene 32.3 34.4 19.2 <0.12 <0.17 <0.13

Analine <24.7 <35.4 <19.7 <1.39 <1.67 <1.30

Anthracene 1,354 13,608 1,563 <0.07 <0.13 <0.10

Benzidine <812 <1,163 <648 <5.55 <6.69 <5.22

Benzo[a]anthracene 791 5,967 603 <0.11 <0.13 <0.10

Benzo[b]fluoranthrene 1,396 25,614 978 <0.11 <0.13 <0.10

Benzo[k]fluoranthrene 328 1,571 171 <0.14 <0.17 <0.13

Benzo[g,h,i]perylene 506 2,713 385 <0.11 <0.13 <0.10

Benzo[a]pyrene 389 2,428 351 <0.14 <0.17 <0.13

Biphenyl 9,418 94,824 4,536 0.83 <0.47 0.91

Chrysene 504 5,427 476 <0.11 <0.13 <0.10

Fluoranthene 10,373 61,601 9,822 <0.11 <0.13 <0.10

Fluorene 12,610 124,529 10,140 1.15 0.67 1.00

2-Methylnaphthalene 34,887 429,506 15,227 39.6 19.2 38.7

Naphthalene 72,082 562,818 43,261 87.4 43.0 88.6

Phenanthrene 20,667 104,230 19,451 1.10 0.80 1.36

Pyrene 6,305 21,901 4,655 <0.14 <0.17 <0.13

a μ g/dscm = micrograms per dry standard cubic meter.

The concentrations of both the volatile and semi- volatile HAP from the purge vent of the cyclic CRU (CRU 6) are much greater than expected. Rather than repressurizing the reactor several times with nitrogen before venting to the atmos phere, this unit does an in itial depressurization to the fuel gas system and a low pressure line until th e reactor pressure is less than 5 psig and then opens the vent to the atmosphere and purges the r eactor with nitrogen to the atmosphere. Thus, any organics left in the reactor after the initia l depressurization are esse ntially evacuated to the atmosphere during this purge event. The CRU creates cyclic and aromatic hydrocarbons from straight chain hydrocarbons (commonly referred to as alkanes). Consequently, a significant portion of the hydrocarbon emissions are HAP. Fr om Table 2, one can see that the sum of the organic HAP concentrations actu ally exceeds the total hydrocarbon concentration (as hexane). The mass emission rates reported for the total hydrocarbons for Runs 1, 2, and 3 were 14.9, 134, and 15 pounds per hour (lb/hr). The sum of the mass emission rates reported for the organic HAP for Runs 1, 2, and 3 were 26.7, 244, and 39 lb/hr. This is due, in part, because the flame ionization detector (FID) response for aromatic hydrocarbons is less than for alkanes with the same number of carbon atoms. In any event, this comparison verifies that a significant portion of the CRU processing stream and purge vent’s non-methane hydrocarbon emissions are HAP.Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

7 There is significant variation in the quantity of emissions between the different runs. This is expected to be normal variation in the amount of hydrocarbons remaining in the reactor at the start of the purging process. It may be different for different reactors in the series, and it is expected to be related, to some degree, to the pressure of the vessel when the reactor is first vented to the atmosphere. Based on the operation of CRU 6, the purge vent cycle lasts just under 2 hours and approximately 100 regeneration cycles are performed each year. The annual emissions for this unit, based on the average em issions from the three source test runs, are presented in Table 4. For comparison, the annual emissions were also estimated for the semiregenerative CRU (CRU 7). CRU 7 purge venting runs spanned approximately 20 hours. From this, it was estimated that the purge vent emi ssions occur for approximately 30 hours per year.

The Emission Estimation Protocol for Petroleum Refineries (RTI, 2011) provides some organic emission factors for CRU, but these were develope d primarily from data for the coke burn-off cycle; emissions during purging were expected to be minimal. The volatile organic HAP emissions from CRU 6 are approximately 100 times greater than expected and the semi-volatile

HAP emissions are 3 to 4 orders of magnitude greater than exp ected, compared to the emission factors for these HAP as provide d in the Protocol document. On the other hand, the organic emissions from CRU 7’s purge vent appears to be minimal and coul d easily be considered to be

included within the Protocol’s defau lt emission factors for the CRU vent.

Table 4. Annual Organic HAP Emissions from Purge Vents

Pollutant CRU 6 (Cyclic)

Estimated Annual Emissions (tpy) a CRU 7 (Semi-regenerative)

Estimated Annual Emissions (tpy) a

Benzene 2.11 2.3E-05

1,2-Dibromoethane 0.32 1.1E-07

Ethylbenzene 0.42 2.7E-05

Hexane 0.33 1.4E-05

Toluene 2.83 6.5E-05

Xylenes 4.23 1.1E-04

2-Methylnaphthalene 0.067 1.0E-06

Naphthalene 0.096 2.4E-06

a tpy = tons per year.

Based on our review of the ICR responses and test data, there are considerable differences in the depressurization and purgi ng practices of different refineries th at lead to substantial differences in the emissions. The original Refinery MA CT 2 requirements were developed with the understanding that the general pr actice was to perform an initial depressurization of the reactor vessel and then subsequent “purging operations ” were accomplished by repressurizing the vessel with nitrogen and then depressurizing/purging the vessel and repeating that process several times. At the time, the practice of actively purgi ng the reactor vessel continuously to atmosphere was not considered and such practice appears to undermine the intent of the rule’s provision to allow atmospheric venting while the reactor vessel pressure is less than 5 psig. Considering theseTechnical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

8 apparent changes in practices , it is recommended that the requirements for CRU catalyst regeneration depressurization/pur ge vent emission controls be revised to prevent the active purging of the CRU vessel to atmosphere unless the (non-methane) TOC concentration is at or below 20 ppmv (dry basis as hexane) as per the or iginal intent of the Refinery MACT 2 organic

HAP emission limits for CRU.

3.2 Coke Burn-off and Rejuvenation Cycles

Once the catalyst is hydrocarbon free, the coke burn-off cycle can begin. For continuous reformers, the isolated catalyst in the lock hoppe r is transferred to the special regenerator, the

first section of which is used for coke burn-off. For cyclic and semi-regenerative CRU, the coke burn-off is conducted in situ within the reactors, which must first be heat ed using recirculating nitrogen stream to a temperature suitable for coke -burn-off. During coke burn-off, air is slowly introduced to the CRU reactor (or first secti on of the regenerator) to begin the combustion process, with the coke serving to fuel the com bustion process. The flue gas from the CRU coke combustion is predominately recirculated, with small amounts of fresh air continuously added to

the recirculated air to control the coke burn-off rate. Excess flue gas from the coke combustion is vented to the atmosphere from a small pipe ve nt as necessary to maintain the desired pressure within the system.

The combustion process naturally produces some wate r. The water tends to leach chloride atoms from the catalyst, which reduces the catalyst’s performance. Conseque ntly, a chloride source (usually a chlorinated organic such as perchloroeth ene or trichloroethene) is used to replace the chloride atoms stripped by the water. The chlo ride addition may occur simultaneously while the coke burn cycle is under way or only duri ng the subsequent rejuvenation cycle.

Once all the coke is burned-off the catalyst, th e rejuvenation cycle is conducted. This step consists of increasing the oxygen co ntent of the system and adding a chloriding agent. Together this helps to redistribute the noble metal on the catalyst. This pro cess is sometimes referred to as the oxidation step, the chlorina tion step, or the oxy-chlorina tion step based on the two key components of this “rejuvenation” process. In a cyclic or semi-regenerative CRU, the rejuvenation emissions are typically released thro ugh the same vent and controlled in the same manner as the coke burn-off emissions, only at a la ter point in time. There may be no discernible change in vent flow rates as the coke burn-o ff cycle shifts to the rejuvenation cycle; the characteristic change noting the onset of the re juvenation cycle is the increase in the oxygen content of the vent gas. 1 In a continuous CRU regenerator, the rejuvenation process occurs in the second section of the regenerator, separated from the first and third sectio n of the regenerator by a series of baffles. Gas from the rejuvenati on section is primarily recirculated via the chlorination loop, but a portion of the gas from th e rejuvenation section will slip into the coke burn-off section of the regenerator and be emitted with the coke burn-off gases.

1 The control options provided in the Refinery ICR (EPA, 2011) regarding rejuvenation cycle specified organic control options ( i.e. , sending gases to a flare or process heater) rather than HCl control options. It is expected that some respondents indicated or ganic controls primarily because these were the control options provided. Even so, most refineries indicated they used “other” cont rols, and then specified a type of HCl control.Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

9 The primary HAP emitted during the coke burn cycle and rejuvenation cycle are HCl and chlorine. Caustic injection, caustic scrubbing, an d wet scrubbing are all applicable air pollution control techniques for removing HC l and chlorine from the CRU coke burn-off flue gas. Wet scrubbers use a liquid, usually water, to effect re moval of the desired pollutant. For vapor phase pollutants, scrubbing typically removes the polluta nt by absorption into the liquid phase. Since HCl and chlorine are readily soluble in water, wet scrubbing or abso rption (with or without caustic addition) can achieve high removal efficiencies. The control efficiency is based on the

number of “theoretical c ontact stages” within the wet scrubber; the use of caustic additives in the water tends to increase the control efficiency. A single stage contactor, such as a spray chamber or in-line spray injection system, typically ach ieves approximately 90 to 95 percent control efficiency. A packed bed wet scrubber system is expected to achieve removal efficiencies of 97 percent or more.

The current Refinery MACT 2 requirements dur ing the coke burn-off cycle and rejuvenation cycles are 92 percent removal of HCl or an outle t concentration of 30 ppmv dry basis, corrected to 3 percent oxygen for semi-regenerative CRU a nd 97 percent removal of HCl or an outlet concentration of 10 ppmv dry basis, corrected to 3 percent oxygen for cyclic and continuous CRU. After promulgation of the Refinery MACT 2 rule in 2002, a new dry scrubbing system was identified. This dry scr ubbing technique for continuous CRU, referred to as the ChlorsorbTM System, used spent catalyst from the lock hopper after the depressurization/purge cycle as a dry

sorbent to remove HCl released during the coke burn-off cycle. Use of other dry sorbents, such as alumina, was also identified as a potential means to achieve the required level of emissions control. These control systems are expected to achieve similar levels of control as the wet scrubber systems that formed the basis of the Refinery MACT 2 requirements. The Refinery MACT 2 rule was amended on February 9, 2005 (70 FR 6930) to include appropriate operating limits and monitoring requirements when these c ontrol systems are used. According to the Refinery ICR responses (see Tabl e 1), most (121 of 151) CRU employ some sort of wet, caustic

scrubber to control the coke burn- off vent. There are 19 units that use either ChlorsorbTM System or fixed-bed dry sorbent system s for the coke burn-off vent.

As footnoted previously, the cont rol options provided in the Refi nery ICR regarding rejuvenation cycle were organic control-relate d rather than HCl control-relate d, so we expect that the higher fraction of uncontrolled or organi c control options specified in th e ICR responses are most likely

related to the different contro l options provided for the rejuve nation cycle compared to the control options provided for the coke burn-off cycl e. Even with the misleading control options provided for the rejuvenation cycle, most respondents indicated th ey used “other” controls for HCl and wrote in the type of HCl control. We note that responses for 34 CRU indicated the rejuvenation cycle gas stream was vented to th e atmosphere. The facilities reporting for these CRU may have indicated this becau se the specifically listed cont rols were not applicable, but it may also suggest some additional misunderstanding of what is meant by the term “rejuvenation cycle.” It appears that clarif ication may be needed, such as clearly defining the “rejuvenation cycle” term within Refinery MACT 2 rule, to ensure the rejuvenation cycle vent is properly controlled (similar to th e coke burn-off vent).Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

10 Tables 5, 6 and 7 provide a summary of the emi ssions data collected du ring the coke burn-off cycle. The emission rates were normalized by the CRU throughput to provide a comparison of the measured emissions with those anticipated ba sed on the default emission factors presented in

Emission Estimation Protocol for Petroleum Refineries (RTI, 2011).Technical Memorandum – TechnologyReview for Catalytic ReformingUnits at Petroleum RefineriesJuly 2, 201211Table 5. Summary of Volatile Organic and Acid Gas Emissions Test Data for CRU Regeneration Coke Burn-Off VentPollutantEmission Rate (lb/1,000 bbl)aContinuous CRUCyclic CRUSemi-regen. CRUCRU 1CRU 2CRU 5CRU 10CRU 3CRU 4CRU 6CRU 8bCRU 7CRU 9DefaultcVolatile Organic HAPBenzene 7.5E-3 <0.18 2.8E-4 <3E-6 0.689 2.9E-3 8.4E-3 2.7E-6 5.9E-4 <3E-54.0E-3Chlorobenzene 9.1E-5 <2E-5 <5E-6 7.2E-5 <3E-6 <7E-5 <1E-5 6.8E-7 <1E-5Cumene 1.4E-4 2.0E-5 <6E-6 1.9E-4 <3E-6 1.3E-3 <2E-5<8E-7Ethylbenzene 6.7E-3 2.2E-4 <2E-4 5.8E-3 4.1E-5 1.5E-2 6.6E-5 4.1E-4 7.6E-6Hexane <7E-4 0.22 <3E-4 <2E-6 <7E-4 <2E-34.8E-4 2.2E-5 1.0E-4 <2E-5Methyl isobutylketone<5.6E-5 <2E-5 <4E-6 4.4E-5 <3E-6 4.9E-4 <2E-5 <9E-6 <6E-6Nitrobenzene 2.0E-3 1.2E-4 <2E-5 4.7E-4 <1E-5 5.2E-3 <4E-7 4.9E-6 <2E-6Nitropropane 2.1E-4 <0.11 5.6E-5 <1E-5 5.0E-5 5.2E-5 <5E-4 <6E-4<6E-6Toluene 6.1E-2 3.2E-3 <5E-6 0.499 8.0E-3 1.8E-2 4.6E-4 1.6E-3 <9E-59.6E-3Xylenes 7.5E-2 1.7E-3 8.1E-4 4.7E-2 2.8E-4 0.11 3.8E-4 1.9E-3 7.8E-57.0E-3Inorganic HAPHCl 4.0E-2<2E-2 3.8E-5 7.2E-5 1.4E-4 <8E-61.7E-3 2.0E-5 8.0E-5 <3E-60.13dChlorine 2.7E-4 <8E-3 <9E-7 1.1E-4<2E-5 <8E-5 8.5E-3 9.2E-6 <7E-6 <2E-56.9E-3dalb/1,000 bbl = pounds per 1,000 barrels.bAverage emission factor across coke burn-off and rejuvenation “oxychlorination” cycle, except HCl and chlorine, which were only measured during coke burn-off.cDefault emission factor fromEmission Estimation Protocol for Petroleum Refineries(RTI, 2011).dDefault emission factor adjusted for control efficiency of a multiple-stage wet scrubber (RTI, 2011).Technical Memorandum – TechnologyReview for Catalytic ReformingUnits at Petroleum RefineriesJuly 2, 201212Table 6. Summary of Semi-Volatile Hydrocarbon Emissions Test Data for CRU Regeneration Purge VentsPollutantCoke Burn-off/Rejuvenation EmissionsCRU 6 (Cyclic)CRU 8 (Cyclic)CRU 10 (Continuous)DefaultaDetectblb/1,000 bblcDetectblb/1,000 bblcDetectblb/1,000 bblclb/1,000 bblcAcenaphthene4.0E-063.1E-08BDL9.2E-084.3E-08Acenaphthylene1.4E-068.8E-09BDL1.6E-073.0E-08Anthracene3.1E-053.6E-07BDL6.2E-079.1E-08Benzo[a]anthracene 4.2E-07 9.5E-09 BDL 8.0E-099.0E-10Benzo[b]fluoranthrene 9.7E-07 2.6E-08 BDL 1.2E-081.5E-09Benzo[g,h,i]perylene 3.0E-07 9.0E-09 BDL 1.3E-084.0E-09Benzo[a]pyrene BDL2.9E-07 5.6E-09BDL2.9E-09Benzo[e]pyrene3.9E-072.1E-08BDL1.4E-082.9E-09Biphenyl1.6E-04DLL2.1E-071.7E-06Cresols3.7E-05BDL3.9E-07Chrysene3.8E-071.9E-084.3E-08Fluoranthene7.1E-061.0E-079.7E-071.0E-07Fluorene1.8E-041.6E-062.3E-062.0E-072-Methylnaphthalene 1.8E-04 4.3E-05 9.3E-061.3E-06Naphthalene2.2E-041.7E-062.1E-053.5E-05Perylene BDL2.9E-07DLL7.7E-101.4E-08Phenanthrene3.8E-045.8E-073.9E-066.1E-07Pyrene3.1E-063.7E-081.5E-071.5E-08aDefault emission factor fromEmission Estimation Protocol for Petroleum Refineries(RTI, 2011).bDetect codes are as follows: BDL = below detection limit, indicates that all runs were below detection limit; DLL = detectionlimit limited, at least 1 run was abovedetection limit and at least one run was below detection limit.clb/1,000 bbl = pounds per 1,000 barrels.Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

13 Table 7. Summary of Dioxin Emissions Test Data for CRU Regeneration Coke Burn-Off

Vent

Facility Dioxin TEQ a
Emission Rate (lb/1,000 bbl)

CRU 1 - Continuous 1.6E-11

CRU 2 - Continuous 6.4E-10

CRU 5 - Continuous 2.0E-10

CRU 10 - Continuous 1.6E-08

CRU 3 - Cyclic 1.5E-11

CRU 4 - Cyclic 6.9E-12

CRU 6 - Cyclic 8.5E-11

CRU 8 - Cyclic 8.6E-13

CRU 7 - Semi-regenerative 3.1E-11

CRU 9 - Semi-regenerative 4.3E-14

Default a 5.7E-09

a Dioxin TEQ = dioxin toxicity equivalence emission factors calculated using the 2005 World Health Organization consensus toxicity equivalence factors (EPA, 2010).

a Default emission factor from Emission Estimation Protocol for Petroleum Refineries (RTI, 2011).

The test reports generally did not provide adeq uate information to determine actual throughput and venting durations for the year, so the unit ca pacities were used and the annual venting times were estimated based on the type of regenerator. Continuous CRU were es timated to have coke burn-off venting 8,760 hours per year; cyclic CRU we re estimated to have coke burn-off venting 2,000 hours per year; and semi-regenerative CRU were estimated to have coke burn-off venting 120 hours per year. The hourly emissions measured during the source test were converted to

annual emissions based on these default venti ng times, and then the annual throughput was estimated based on the unit’s capacity and assu ming operation 365 days per year. While using these default assumptions increases the uncertainty of the emission factors, the uncertainty introduced is not expected to be that significan t compared to the overall variability in process operations and uncertainty in the defa ult emission factors in general.

The volatile organic HAP emissions factors estimated from the sour ce tests (see Table 5) show a significant amount of variation, but generally agree reasonably well with the expected emissions based on the default emission factors presented in the Emission Estimation Protocol for Petroleum Refineries (RTI, 2011). The acid ga s (inorganic HAP) emissions measured for the coke burn-off cycle are all at or below the pr ojected emissions for a well-controlled coke burnoff vent. One CRU exhibited semi-volatile emis sions that were much higher than expected

based on the default emission factor s; this is the same CRU with high volatile emissions from its purging operations, and the elevat ed emissions may be caused by inadequate purging of the unit prior to initiating coke burn-off, but this is high ly speculative. The other CRU that tested theirTechnical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

14 semi-volatile emissions during the coke burn- off/rejuvenation cycle had emissions very comparable to the default emission factors (see Table 6).

The dioxin/furan tests were of particular inte rest because the coke burn-off and rejuvenation cycles (which are combustion processes) occur wh ile there is a source of chlorides (either from the catalyst or from the addition of a chloridi ng agent). All but one of the measured dioxin toxicity equivalence (TEQ) emissi on factors were below the defau lt emission factor presented in

the Emission Estimation Protocol for Petroleum Refineries (RTI, 2011), and the one test resulting in a greater emission fa ctor was only a factor of 2 highe r than the default, which in terms of an emission factor is very reasonable ag reement. Thus, it appears that the default dioxin TEQ emission factor provided in the Pr otocol is sufficiently conservative.

Based on the ICR responses and source test resu lts (and with understand ing of the confusion regarding the rejuvenation control option re sponses), there appear s to have been no developments in practices, processes, and contro l technologies associated with the CRU catalyst regeneration coke burn-off and rejuvenation vent emission contro ls since the Refinery MACT 2 rule was amended in July 2005.

3.3 Reduction/Final Purge Cycle

Once the catalyst is rejuvenated, the catalyst mu st be purged to remove any oxygen and create a reducing atmosphere to convert the noble metal to its catalytically active fo rm prior to returning to naphtha processing. In cyclic and semi-regenera tive units, the system is typically purged with nitrogen to remove any oxygen and residual chlo riding agent from the system, and then purged with hydrogen to reduce the catalyst from the metallic ox ide formed during the coke burn-off and rejuvenation cycle back to its active (eleme ntal) metal state prior to bringing the unit back on-line. In a continuous reforming unit, the cat alyst from the chlorination/rejuvenation section then moves past another series of baffles into the drying section. In this section, hot air is used to strip any chloride agent remaining on the catalyst and dry the catalyst. The drying air flows by a set of baffles to the rejuvena tion section and serves to pr ovide make-up air for the oxychlorination (rejuvenation) reaction. After the drying secti on, the catalyst is returned to the CRU reactor by another series of small hoppers. These hoppers serv e the function of the final purge cycle (to remove oxygen and create a reducing atmosphere) of th e semi-regenerative or cyclic

systems.

The reduction/final purge cycle ve nt gases from may contain low levels of the chloriding agent (trichloroethene or perchloroeth ene) and/or residual HCl or ch lorine. Safety considerations ( i.e. , the presence of oxygen) generall y restrict the venting of th e initial reduction/final purge cycle vent gases to the fuel gas system or th e flare header system. The purge gases may be directly vented to a combustion device ( e.g. , process heater, or incine rator), however, the final purge gas is expected to cont ain some chlorine-containing pollu tants, and the combustion of these gases provides the potential for the forma tion of chlorinated dioxins and furans. The current Refinery MACT 2 has no specific emissi on limitations for the final purge vent. The purge gas is expected to cont ain limited, if any, HAP, and requi ring combustion control may be environmentally counter-productive. Based on the ICR responses, there is no venting associated with the reduction/final purge cycle or that the gases or vented back to the process for 44 CRUTechnical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries July 2, 2012

15 (see Table 1). Seventy-three CRU had responses i ndicating the vent gases we re sent to the fuel gas system, flare, or process heater. If these ga ses do contain trace amounts of chlorides, there is a potentially detrimental impact associated with additional combustion control of this gas stream. Based on the ICR responses, it appears that thes e combustion controls are used primarily when purging with hydrogen (after an ini tial purge or “drying section” fo r continuous reformers). This hydrogen purge gas stream is not expected to c ontain appreciable amounts of chloride (chorides are expected to be removed predominately with the initial nitrogen purge or “drying” phase). Responses for other CRU indicate that 19 CRU use so me type of HCl control and 14 vent to the atmosphere. There is likely some confusion regard ing the final purge cycle vent controls, as the nitrogen purge may be routed differently from the hydrogen purge and, as with the rejuvenation controls, only organic control op tions were provided for the reduc tion purge, with no delineation if multiple types of purges are used. Based on the ICR data, there appears to have been no developments in practices, processes, and cont rol technologies for reduc ing the emission from the CRU catalyst regeneration fina l purge (reduction) vent. Furt hermore, if the TOC or HCl control limits were specified for these purge gases, it is expected that these gases would contain less than 20 ppmv TOC or 10 ppmv HCl, so they would comply with the depressurization purge

and/or coke burn-off emission limits w ithout the need for additional control.

4. References

EPA (U.S. Environmental Protection Agency). 1998. Petroleum refineries—Background information for proposed standards, catalytic cracking (fluid and othe r) units, catalytic reforming units, and sulfur recovery units . Washington, DC: U.S. Government Printing

Office. EPA-453/R-98-003.

EPA (U.S. Environmental Protection Agency). 2010. Recommended Toxicity Equivalence Factors (TEFs) for Human Health Risk Assessm ents of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and Dioxin-Like Compounds . Office of the Science Adviso r, Risk Assessment Forum.

December 2010. EPA/100/R-10/005.

EPA (U.S. Environmental Protection Agency). 2011. Petroleum Refinery Database, based on Refinery Information Collection Request (I CR) for Calendar Year 2010. September 2011.

Docket Item Nos. EPA- HQ-OAR-2010-0682-0061 through 0069.

RTI (RTI International). 2011. Emission Estimation Protocol for Petroleum Refineries

. Version 2.1.1, Final ICR Version Corrected. Pr epared for U.S. Environmental Protection Agency, Office of Air Quality Planning and St andards, Research Triangle Park, NC. May 2011. Docket Item No. EPA-HQ-OAR-2010- 0682-0060. Most current version also

available at http://www.epa.gov/ttn/chief/efpac/protocol/

.