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 Reforming Units at Petroleum Refineries 

1. Purpose 

This memorandum documents the technology review of emission controls for catalytic reforming 

units (CRU) at petroleum refineries. 

2. Background 

Section 112 of the Clean Air Act (CAA) establishes 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. Environmental 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 list of major and area source categories for 

which national emissions standards for hazardous air pollutants (NESHAP) 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 were covered under the second source category. 

Standards for the second source category, 40 CFR 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 standards and to revise them “as necessary (taking 

into account developments in practices, processes 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 2010 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 facilities were requested to test specific units at their 

facility. Twelve facilities were requested to test the CRU catalyst regeneration vent(s); 

10 sources completed the requested tests and two units did not complete the test because the unit 

was either not operating or no regeneration cycle was being performed during the year. This 

memorandum documents the results of the ICR 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 Description, 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 naphtha through a reactor containing a catalyst at 

elevated pressure and temperature to promote dehydrogenation, isomerization, and 

hydrogenolysis reactions. The reforming reaction is endothermic, meaning the reaction causes 

the temperature of the system to decrease during processing. Consequently, the CRU is typically 

designed using reactors in series, with heat supplied 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 activity of the platinum-alumina catalyst and are 

stripped from the surface of the catalyst as hydrogen chloride (HCl) or hydrogen fluoride (HF) 

during the reforming reactions, thus reducing catalyst activity. 

Dehydrogenation reactions are favored by low pressure and high temperature; however, coke 

(carbon) is also formed at low pressure which tends to deactivate the catalyst and reduce yields. 

Coke formation can be reduced by operating under high hydrogen pressure; other important 

variables in dehydrogenation activity include temperature, space velocity, recycle gas rate, and 

particle size of the catalyst used. 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 three types of CRU classified 

by differences in how the units are designed and operated to effect reforming catalyst 

regeneration. Semi-regenerative reforming is characterized by shutdown of the reforming unit at 

specified intervals, or at the operator’s convenience, for in situ catalyst regeneration. Semiregenerative systems were the most common type of CRU approximately 15 years ago, 

representing approximately half the reforming 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 characterized by continuous or continual reforming 

operation with periodic (but frequent) regeneration of catalyst in situ by isolating one of the 

reactors in the series, regenerating the catalyst, then returning the reactor to the reforming 

operation. The regeneration of the catalyst in a single reactor may occur numerous times per 

year (e.g., once a month), and the regeneration of each reactor may take 3 to 5 days to complete. 

Approximately 30 percent of the nationwide CRU capacity is provided by cyclic CRU (EPA, 

2011). Continuous regeneration reforming units utilize moving catalyst bed reactors situated 

vertically (which is why they are often referred to as platforming units). Catalyst flows down the 

series of reactors. At the bottom of the last reactor, catalyst is continually isolated and sent to a 

special regenerator. After regeneration, the regenerated catalyst is continually fed to the first 

(top) reactor. Thus, continuous regeneration reforming units are characterized by continuous 

reforming operation along with continuous regeneration operation. Continuous reforming 

capacity has grown over the past 15 years and 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 are a series of emission points 

associated with the CRU catalyst regenerator. Regardless of the type of CRU used, there are a 

series of steps conducted to effect catalyst regeneration. These steps 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 ICR 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 to 

atmosphere 

Fuel gas system, flare, 

process heater 

Recycle to process 

Other VOC control (e.g., 

carbon canister)a

Caustic Injection, spray 

adsorption 

Packed or tray tower 

wet/caustic scrubber 

ChlorsorbTM 

Dry chloride adsorption 

bed 

Other HCl control or work 

practice 

No vent, not specified or 

not 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 regeneration cycle, any residual hydrocarbons in the reactor and/or on the 

catalyst particles are purged from the system using nitrogen and/or a vacuum. 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-regenerative systems, the entire 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 vented to the refinery’s fuel gas system. The 

system is typically repressurized with nitrogen 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 final purge, when the nitrogen content of the purge 

gas is high and the hydrocarbon content is near zero the final purge 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, typically about 5 pounds per square inch gauge (psig), purge gas may 

be vented to the atmosphere. 

Air pollution control devices potentially applicable to this CRU purge vent stream include 

combustion devices such as a flare or vapor incinerator and carbon adsorption systems. Flares 

and vapor incinerators employ heat and oxygen to oxidize (combust) organic chemicals, 

converting them to carbon dioxide and water vapor. Although destruction efficiencies of vapor 

incinerators may be slightly higher 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 efficiencies of 95 to 98 percent, but have reduced 

efficiencies at low inlet concentrations. 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 confirmed 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 type of operation may explain why the different 

runs have variable pollutant concentrations (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 during sequential purges of the entire 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 depressurization 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 emission 
Technical 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 Table 1, nearly all refineries control 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% O2

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% O2 = 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 (μg/dscm) 

CRU 7 (Semi-regenerative) 

Concentration (μg/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 μg/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 atmosphere, this unit does an initial depressurization to 

the fuel gas system and a low pressure line until the reactor pressure is less than 5 psig and then 

opens the vent to the atmosphere and purges the reactor with nitrogen to the atmosphere. Thus, 

any organics left in the reactor after the initial depressurization are essentially 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. From Table 2, one can see that the sum of the 

organic HAP concentrations actually 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 emissions 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 emissions 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 developed 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 expected, compared to the emission 

factors for these HAP as provided in the Protocol document. On the other hand, the organic 

emissions from CRU 7’s purge vent appears to be minimal and could easily be considered to be 

included within the Protocol’s default 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 purging practices of different refineries that lead to substantial differences 

in the emissions. The original Refinery MACT 2 requirements were developed with the 

understanding that the general practice 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 purging 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 these 
Technical 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/purge 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 original 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 hopper 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 heated 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 section of the regenerator) to begin the combustion 

process, with the coke serving to fuel the combustion 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 vent as necessary to maintain the desired pressure 

within the system. 

The combustion process naturally produces some water. The water tends to leach chloride atoms 

from the catalyst, which reduces the catalyst’s performance. Consequently, a chloride source 

(usually a chlorinated organic such as perchloroethene or trichloroethene) is used to replace the 

chloride atoms stripped by the water. The chloride addition may occur simultaneously while the 

coke burn cycle is under way or only during the subsequent rejuvenation cycle. 

Once all the coke is burned-off the catalyst, the rejuvenation cycle is conducted. This step 

consists of increasing the oxygen content of the system and adding a chloriding agent. Together 

this helps to redistribute the noble metal on the catalyst. This process is sometimes referred to as 

the oxidation step, the chlorination step, or the oxy-chlorination step based on the two key 

components of this “rejuvenation” process. In a cyclic or semi-regenerative CRU, the 

rejuvenation emissions are typically released through the same vent and controlled in the same 

manner as the coke burn-off emissions, only at a later point in time. There may be no discernible 

change in vent flow rates as the coke burn-off cycle shifts to the rejuvenation cycle; the 

characteristic change noting the onset of the rejuvenation 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 section of the regenerator by 

a series of baffles. Gas from the rejuvenation section is primarily recirculated via the 

chlorination loop, but a portion of the gas from the 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 organic controls primarily because these were the control options provided. Even so, 

most refineries indicated they used “other” controls, 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, and wet scrubbing are all applicable air pollution 

control techniques for removing HCl and chlorine from the CRU coke burn-off flue gas. Wet 

scrubbers use a liquid, usually water, to effect removal of the desired pollutant. For vapor phase 

pollutants, scrubbing typically removes the pollutant by absorption into the liquid phase. Since 

HCl and chlorine are readily soluble in water, wet scrubbing or absorption (with or without 

caustic addition) can achieve high removal efficiencies. The control efficiency is based on the 

number of “theoretical contact 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 achieves 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 during the coke burn-off cycle and rejuvenation 

cycles are 92 percent removal of HCl or an outlet concentration of 30 ppmv dry basis, corrected 

to 3 percent oxygen for semi-regenerative CRU and 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 scrubbing 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 control systems are used. According to the 

Refinery ICR responses (see Table 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 systems for the coke burn-off vent. 

As footnoted previously, the control options provided in the Refinery ICR regarding rejuvenation 

cycle were organic control-related rather than HCl control-related, so we expect that the higher 

fraction of uncontrolled or organic control options specified in the ICR responses are most likely 

related to the different control options provided for the rejuvenation cycle compared to the 

control options provided for the coke burn-off cycle. Even with the misleading control options 

provided for the rejuvenation cycle, most respondents indicated they 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 the atmosphere. The facilities reporting for these 

CRU may have indicated this because the specifically listed controls were not applicable, but it 

may also suggest some additional misunderstanding of what is meant by the term “rejuvenation 

cycle.” It appears that clarification 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 the 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 emissions data collected during 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 based on the default emission factors presented in 

Emission Estimation Protocol for Petroleum Refineries (RTI, 2011). 
Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries 

July 2, 2012 

11 

Table 5. Summary of Volatile Organic and Acid Gas Emissions Test Data for CRU Regeneration Cok

Pollutant 

Emission Rate (lb/1,000 bbl)a

Continuous CRU Cyclic CRU Semi-re

CRU 1 CRU 2 CRU 5 CRU 10 CRU 3 CRU 4 CRU 6 CRU 8b CRU 7 

Volatile Organic HAP Benzene 7.5E-3 <0.18 2.8E-4 <3E-6 0.689 2.9E-3 8.4E-3 2.7E-6 5.9E-4 Chlorobenzene 9.1E-5 <2E-5 <5E-6 7.2E-5 <3E-6 <7E-5 <1E-5 6.8E-7 Cumene 1.4E-4 2.0E-5 <6E-6 1.9E-4 <3E-6 1.3E-3 <2E-5 Ethylbenzene 6.7E-3 2.2E-4 <2E-4 5.8E-3 4.1E-5 1.5E-2 6.6E-5 4.1E-4 Hexane <7E-4 0.22 <3E-4 <2E-6 <7E-4 <2E-3 4.8E-4 2.2E-5 1.0E-4 Methyl isobutyl ketone <5.6E-5 <2E-5 <4E-6 4.4E-5 <3E-6 4.9E-4 <2E-5 <9E-6 Nitrobenzene 2.0E-3 1.2E-4 <2E-5 4.7E-4 <1E-5 5.2E-3 <4E-7 4.9E-6 Nitropropane 2.1E-4 <0.11 5.6E-5 <1E-5 5.0E-5 5.2E-5 <5E-4 <6E-4 Toluene 6.1E-2 3.2E-3 <5E-6 0.499 8.0E-3 1.8E-2 4.6E-4 1.6E-3 Xylenes 7.5E-2 1.7E-3 8.1E-4 4.7E-2 2.8E-4 0.11 3.8E-4 1.9E-3 Inorganic HAP HCl 4.0E-2 <2E-2 3.8E-5 7.2E-5 1.4E-4 <8E-6 1.7E-3 2.0E-5 8.0E-5 Chlorine 2.7E-4 <8E-3 <9E-7 1.1E-4 <2E-5 <8E-5 8.5E-3 9.2E-6 <7E-6 a lb/1,000 bbl = pounds per 1,000 barrels. b Average emission factor across coke burn-off and rejuvenation “oxychlorination” cycle, except HCl and chlorine, which were only measc Default emission factor from Emission Estimation Protocol for Petroleum Refineries (RTI, 2011). d Default emission factor adjusted for control efficiency of a multiple-stage wet scrubber (RTI, 2011). 
Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries 

July 2, 2012 

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Table 6. Summary of Semi-Volatile Hydrocarbon Emissions Test Data for CRU Regeneration P

Pollutant 

Coke Burn-off/Rejuvenation Emissions 

CRU 6 (Cyclic) CRU 8 (Cyclic) CRU 10 (Continuous) 

Detectb lb/1,000 bblc Detectb lb/1,000 bblc Detectb lb/1,000 bblc 

Acenaphthene 4.0E-06 3.1E-08 BDL 9.2E-08 Acenaphthylene 1.4E-06 8.8E-09 BDL 1.6E-07 Anthracene 3.1E-05 3.6E-07 BDL 6.2E-07 Benzo[a]anthracene 4.2E-07 9.5E-09 BDL 8.0E-09 Benzo[b]fluoranthrene 9.7E-07 2.6E-08 BDL 1.2E-08 Benzo[g,h,i]perylene 3.0E-07 9.0E-09 BDL 1.3E-08 Benzo[a]pyrene BDL 2.9E-07 5.6E-09 BDL 2.9E-09 Benzo[e]pyrene 3.9E-07 2.1E-08 BDL 1.4E-08 Biphenyl 1.6E-04 DLL 2.1E-07 1.7E-06 Cresols 3.7E-05 BDL 3.9E-07 Chrysene 3.8E-07 1.9E-08 4.3E-08 Fluoranthene 7.1E-06 1.0E-07 9.7E-07 Fluorene 1.8E-04 1.6E-06 2.3E-06 2-Methylnaphthalene 1.8E-04 4.3E-05 9.3E-06 Naphthalene 2.2E-04 1.7E-06 2.1E-05 Perylene BDL 2.9E-07 DLL 7.7E-10 1.4E-08 Phenanthrene 3.8E-04 5.8E-07 3.9E-06 Pyrene 3.1E-06 3.7E-08 1.5E-07 a Default emission factor from Emission Estimation Protocol for Petroleum Refineries (RTI, 2011). b Detect codes are as follows: BDL = below detection limit, indicates that all runs were below detection limit; DLL = detection limit limited

detection limit and at least one run was below detection limit. 

c lb/1,000 bbl = pounds per 1,000 barrels. 
Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries 

July 2, 2012 

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

Vent 

Facility 

Dioxin TEQa

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 

Defaulta 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 adequate information to determine actual throughput 

and venting durations for the year, so the unit capacities were used and the annual venting times 

were estimated based on the type of regenerator. Continuous CRU were estimated to have coke 

burn-off venting 8,760 hours per year; cyclic CRU were 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 venting times, and then the annual throughput was 

estimated based on the unit’s capacity and assuming 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 significant compared to the overall variability in process 

operations and uncertainty in the default emission factors in general. 

The volatile organic HAP emissions factors estimated from the source 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 gas (inorganic HAP) emissions measured for the 

coke burn-off cycle are all at or below the projected emissions for a well-controlled coke burnoff vent. One CRU exhibited semi-volatile emissions that were much higher than expected 

based on the default emission factors; this is the same CRU with high volatile emissions from its 

purging operations, and the elevated emissions may be caused by inadequate purging of the unit 

prior to initiating coke burn-off, but this is highly speculative. The other CRU that tested their 
Technical 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 interest because the coke burn-off and rejuvenation 

cycles (which are combustion processes) occur while there is a source of chlorides (either from 

the catalyst or from the addition of a chloriding agent). All but one of the measured dioxin 

toxicity equivalence (TEQ) emission factors were below the default emission factor presented in 

the Emission Estimation Protocol for Petroleum Refineries (RTI, 2011), and the one test 

resulting in a greater emission factor was only a factor of 2 higher than the default, which in 

terms of an emission factor is very reasonable agreement. Thus, it appears that the default dioxin 

TEQ emission factor provided in the Protocol is sufficiently conservative. 

Based on the ICR responses and source test results (and with understanding of the confusion 

regarding the rejuvenation control option responses), there appears to have been no 

developments in practices, processes, and control technologies associated with the CRU catalyst 

regeneration coke burn-off and rejuvenation vent emission controls since the Refinery MACT 2 

rule was amended in July 2005. 

3.3 Reduction/Final Purge Cycle 

Once the catalyst is rejuvenated, the catalyst must be purged to remove any oxygen and create a 

reducing atmosphere to convert the noble metal to its catalytically active form prior to returning 

to naphtha processing. In cyclic and semi-regenerative units, the system is typically purged with 

nitrogen to remove any oxygen and residual chloriding agent from the system, and then purged 

with hydrogen to reduce the catalyst from the metallic oxide formed during the coke burn-off 

and rejuvenation cycle back to its active (elemental) metal state prior to bringing the unit back 

on-line. In a continuous reforming unit, the catalyst 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 rejuvenation section and serves to provide make-up air for the oxychlorination (rejuvenation) reaction. After the drying section, the catalyst is returned to the CRU 

reactor by another series of small hoppers. These hoppers serve the function of the final purge 

cycle (to remove oxygen and create a reducing atmosphere) of the semi-regenerative or cyclic 

systems. 

The reduction/final purge cycle vent gases from may contain low levels of the chloriding agent 

(trichloroethene or perchloroethene) and/or residual HCl or chlorine. Safety considerations 

(i.e., the presence of oxygen) generally restrict the venting of the initial reduction/final purge 

cycle vent gases to the fuel gas system or the flare header system. The purge gases may be 

directly vented to a combustion device (e.g., process heater, or incinerator), however, the final 

purge gas is expected to contain some chlorine-containing pollutants, and the combustion of 

these gases provides the potential for the formation of chlorinated dioxins and furans. The 

current Refinery MACT 2 has no specific emission limitations for the final purge vent. The 

purge gas is expected to contain limited, if any, HAP, and requiring 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 CRU 
Technical Memorandum – Technology Review for Catalytic Reforming Units at Petroleum Refineries 

July 2, 2012 

15 

(see Table 1). Seventy-three CRU had responses indicating the vent gases were sent to the fuel 

gas system, flare, or process heater. If these gases 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 these combustion controls are used primarily when 

purging with hydrogen (after an initial purge or “drying section” for continuous reformers). This 

hydrogen purge gas stream is not expected to contain 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 some type of HCl control and 14 vent to the 

atmosphere. There is likely some confusion regarding 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 options were provided for the reduction 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 control technologies for reducing the emission from 

the CRU catalyst regeneration final purge (reduction) vent. Furthermore, 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 without 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 other) 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 Assessments of 2,3,7,8-Tetrachlorodibenzo-p-dioxin 

and Dioxin-Like Compounds. Office of the Science Advisor, 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 (ICR) 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. Prepared for U.S. Environmental Protection 

Agency, Office of Air Quality Planning and Standards, 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/.