1

Technical Memorandum

Date: March 30 , 2011

Subject: Summary of U.S. EPA Discussions with ExxonMobil Representatives to Discuss the
Polymers and Resins I Portion of the 2 0 10 RTR Proposal/Supplemental Proposal

From: Nick Parsons, EPA/OAR/OAQPS/SPPD/RCG

Th e purpose of this memorandum is to summarize a series of discussions between
representatives of the U.S. Environmental Protection Agency (EPA) and ExxonMobil. The topic

of these discussions was the proposed revisions to the National Emission Standards for Hazard

Air Pollutants (NESHAP) for Polymers and Resins I (40 CFR part 63, subpart U), specifically

for the Butyl Rubber and Ethylene Propylene Rubber P roduction source categories.

Participants

Nick Parsons, U.S. EPA
Penny Lassiter, U.S. EPA

Bob Morehouse, ExxonMobil

Dates of Discussions
February 25, 2011

March 17, 2011

M a r c h 2 2

, 2 0 1 1

March 23, 2011

March 28, 2011

Summary of Discussions
The purpose of these discussions was to discuss ExxonMobil’s comments on the October
21, 2010 proposal/supplemental proposal for severa l source categories, including the Butyl

Rubber (BR) and Ethylene Propylene Rubber ( E BR) Production source categories of the
Polymers and Resins I MACT (75 FR 65068).

ExxonMobil representatives presented their concerns with the proposed requirements for

the BR and EPR source categories. The key issue of concern for the company was their ability to
be in compliance with the MACT standard during periods of startup and shutdown.

Based on these discussions, ExxonMobil submitted additional technica l feasibility issues
and proposed alternative r e g u l a t o r y language during periods of startup and shutdown to be

considered

, d e p e n d i n g o n w h e t h e r E P A d e c i d e d t o s e t t h e s t a n d a r d a t t h e M A C T f l o o r o r2

b e y o n d

- t h e

- f

l o o r

. This information showed that it was not technically feasible for E x x o n M o b i l to
achieve 98% organic HAP control from a flare o r 9 8 % o r g a n i c H A P c o n t r o l a n d 9 9 % H C l

c o n t r o l f r o m a t h e r m a l oxidizer

/ s c r u b b e r due to low pressu re or low h eat content in the f r o n t

- e n d

process vent s d u r i n g t h e s e p e r i o d s

.

EPA agreed with ExxonMobil’s rationale that they could not comply with the MACT

standard for continuous front

- end process vents during periods of shutdown , and developed an

alternative standard f

o r continuous f

r o n t

- e n d p r o c e s s v e n t s i n t h e B R a n d E P R s o u r c e c a t e g o r i e s

d u r i n g periods of shutdown

.Appendix A

Supplemental S t a r t u p / S h u t d o w n Information ( 2 / 2 5 / 1 1 )Appendix B

Supplemental S t a r t u p / S h u t d o w n Information ( 3 / 1 7 / 1 1 )Recommended Procedures for Handling Group 1 Front

- end Process Vents From Butyl and Ethylene Propylene Rubber Source Categories

During Startup and Shutdown

Background:

For Butyl and Ethylene Propylene Rubber operations, the frequency of planned
startup s/shutdowns is a function of product demand and periodic maintenance or construction needs (e.g., a startup/shutdown may be needed to install the facilities required to comply with this proposal). Unplanned, but controlled, shutdowns and the subsequent st artups can also occur in anticipation of major weather events such as hurricanes. For the three ExxonMobil units impacted by this rule, we typically have one to three startups/shutdowns per year, with major turnarounds every 5

- 10 years. Most shutdowns do not involve the entire process unit, which means that only some vents would need to be routed away from the control devices. A shutdown may take 24 to 48 hours with process equipment clearing and depressuring occurring during the last part of the shutdow n. Startups typically take 12 hours. As pointed out in our comments on the proposal, adding a thermal oxidizer/scrubber for handling Group 1 continuous, halogenated front

- end process vents will introduce a significant additional maintenance concern

that may result in additional startup/shutdowns of the entire front

- end or in extending startup/shutdowns that occur primarily for other reasons. 1

At some point during the shutdown of Butyl Rubber and Ethylene Propylene Rubber source category units the propose d requirements for Group 1 continuous, halogenated front

- end
process vents to achieve at least a 98% organic HAP re duction and 99% HCl re duction cannot

be met because the minimum thermal oxidizer temperature cannot be maintained

. That situation persists u ntil some point in the startup sequence. On shutdown, where the equipment is to be gas

- freed, these instances occur after process fluid is no longer entering the equipment and the vent streams contain only the organic compounds and organic HAP s that were trapped in the process equipment being vented and the nitrogen being used to displace those organics

. As the nitrogen purging proceeds, the organic content of the vent streams rapidly diminishes. Typically, nitrogen purging is done by pressuring the equi pment with nitrogen and then rapidly depressuring to a low pressure. This approach is much more efficient that attempting to purge the equipment using a nitrogen flow

- through approach. On startup of equipment that has been

gas

- freed

, flow

- through or pres suring and depressuring using process gas must occur to displace the nitrogen in the equipment that was used to displace the air that entered when the equipment was opened . It may take several equipment volumes of nitrogen or process gas to complete the p urging cycles

.

1 ExxonMobil Comments to Docket ID EPA

- HQ

- OAR

- 2010

- 0600

- 0265.1, 12

- 6

- 2010, Page 20 “Thermal oxidizers and halogen scrubbers, on the other hand, due to more moving parts and the severity of service, require more maintenance and typically ar e not spared (a nd the cost of sparing was not included in the cost or cost

- effectiveness analyses). In this particular service, corrosion is expected to be a particular service factor issue.”Possible Approaches to and Considerations for Standards during Startup and Shutdown

There are two potential approaches to imposing standards on Group 1 continuous, halogenated

front

- end process vents during those portions of a start

- up an d shutdown when the normal organic HAP and halogen reduction requirements cannot be met. One possibility is to establish a lower organic HAP reduction requirement for such periods. The second, if the requirements of CAA section 112(h) are met, is to impo se a work practice requirement. We discuss the feasibility of these two approaches in detail below.

Lower Organic HAP Reduction Standard

Imposing an organic HAP reduction standard lower than the normal 98% reduction is a possible approach given that the scrubber system would still be capable of removing at least 99% of any HCl formed in the combustion process. (Because less organic halide is being converted to HCl by the thermal oxidizer during startup and shutdown, less than the normal mass of chlorine will be removed from the vent stream by the scrubber under these conditions.). However, there are two problems with this approach that make it impractical. First, the organic HAP reduction capability is constantly changing. Second, there is no way to d emonstrate compliance with the

lower reduction standard.

As nitrogen displaces organics in the process equipment being shut down, the thermal oxidizer temperature will fall 2 . At some point, the temperature will drop below the point that indicates 98% org anic HAP reduction (and 98% conversion of organic halide to hydrogen halide). As the vent stream continues to be diluted with nitrogen, the thermal oxidizer temperature will continue to fall as will the amount of organic HAP reduction. On startup, the te mperature in the thermal oxidizer will drop as nitrogen is displaced to the thermal oxidizer by organics entering the equipment and then, as the organic concentration in the vent increases, the temperature will increase until it is above the minimum temper ature required to achieve 98% organic HAP reduction (and 98% conversion of organic halide to HCl). It is these time periods during which the thermal oxidizer minimum firebox temperature cannot be maintained where an alternative standard is required. Sinc e the thermal oxidizer reduction capability is constantly changing during this time and varies with each startup/shutdown permutation, it is impossible to establish a single numerical standard for these situations.

If a percent organic HAP reduction requi rement were established for startup and shutdown periods when the normal standards cannot be met, performance tests would be needed to establish the reduction that corresponds to particular firebox temperatures, as the basis for continuously demonstrating compliance. Performance tests require at least three one

- hour test

runs 3 and stable operation for that time at the particular set of conditions being tested. But vent composition and flow are constantly and rapidly changing during startup and shutdown. Additionally, the entire period of concern is likely to be less than 3 hours for some startups and shutdowns and only somewhat longer for most. Finally, there are a large number of permutations of startup/shutdown situations. Thus, it is difficult, if no t impossible; to develop a sound correlation between firebox temperature, vent conditions and organic HAP reduction. Attempting to run performance tests at simulated startup and shutdown conditions is impractical, because the constantly changing condition s and the multitude of potential situations cannot be

simulated.

2 Temperature is the specified continuous compliance monitoring parameter for thermal oxidizers and is an indicator of the org anic

HAP reduction achieved.

3 It is likely that m ore than 3 hours of operation would be needed to measur e the very low levels o f organic HAP in the thermal

oxidizer outlet that would occur in these situations.Work Practice Standard

As this discussion demonstrates, it is technically and economically impractical to measure organic HAP reduction during startup and shutdown situations or to demonst rate compliance with an organic HAP reduction requirement, particularly in light of the insignificant amount of organic HAP and HCl emission potential during this time. Even if a mass emissions limit were established instead of a reduction requirement for such periods, it would be impossible to

measure emissions for the same reasons

- the period when the normal reduction requirements cannot be met is of very short duration, with constantly changing vent flows and emissions. In

summary, it is not technical ly feasible to complete stack testing

- in particular, to repeat the multiple required test runs

- during periods of startup and shutdown due to physical limitations

and the short duration of startup and shutdown periods. Therefore, establish ment of a sep arate work practice standard for periods of startup and shutdown is authorized by CAA section 112(h) and the approach we recommend

.

Work Practice Recommendation

A work practice requirement would provide an emission standard for startup and shutdown perio ds, while minimizing emissions during periods when the thermal oxidizer/scrubber system cannot achieve the specified emission reduction requirements and while facilitating the rapid and efficient removal of hydrocarbon from process equipment.

In order t o quickly and efficiently clear hydrocarbon from process equipment, the equipment is isolated from process fluids, drained of liquids, pressured with nitrogen and then depressured to a low pressure. Depressuring to higher pressures is ineffective, and flo w

- through approaches are slow and use inordinate amounts of nitrogen, extending downtimes and thermal oxidizer criteria pollutant emissions. For these operations, the pressure needed to get the Group 1 continuous, halogenated front

- end process vents into the thermal oxidizer/scrubber system is anticipated to be relatively high compared to the low pressures needed for optimal removal of the organics from the process equipment.

Because flare gas collection systems operate at low pressure, diverting the Grou p 1 continuous, halogenated process vents to the flare when they can no longer be handled in the thermal oxidizer or when it is necessary to allow efficient hydrocarbon clearing of the process equipment makes sense. Use of the flare is an allowed complian ce option for non

- halogenated streams and thus will allow compliance with the organic HAP reduction requirement for most of the startup/shutdown time period, while continued use of the thermal oxidizer system would not. It

is true some HCl emissions will result from diverting these vents from the thermal oxidizer/scrubber to the flare, but the amount of HCl will be small since the vents will contain only residual amounts of organic halide and this situation will only occur for short periods. This

small am ount of HCl emission is preferable to the release of organic halide from a thermal oxidizer/scrubber system operating at lower rates of reduction and the emissions associated with slow, inefficient removal of hydrocarbon from the process equipment.It is difficult to identify just what conditions would require relief from the normal requirements

prior to designing and testing the thermal oxidizer/scrubber system. Thus, we recommend the parameter values that would trigger diversion from the thermal oxidiz er to the flare and then from the flare to the atmosphere be established following equipment design and initial system testing and then communicated in the Notice of Compliance Status (NOCS).

At some point, the vent stream pressure will not allow routing these streams or Group 1
continuous, non

- halogenated front

- end process vents to the flare and they will have to be routed to the atmosphere. We believe being unable to send the vent to the flare due to low pressure or achieving 50 ppmv organic HAP content (the criterion for a vent being a Group 1 vent, as demonstrated through engineering analysis) is the appropriate point at which to allow routing Group 1 continuous front

- end vents from the flare to the atmosphere.

Proposed shutdown work practice procedur e: Keep Group 1 continuous, halogenated front

end process vents aligned to the thermal oxidizer/scrubber until equipment to be shutdown is isolated (i.e., no additional hydrocarbon or halogen is entering the equipment) and the minimum

thermal oxidizer fir ebox temperature can no longer be maintained. Then, either route the vent to the flare or demonstrate by engineering analysis that the vent contains < 5 0 ppmv organic HAP, in which case it may be routed to the atmosphere . Group 1 continuous, halogenated

f ront

- end process vents may be routed to the atmosphere when 1) the vent pressure is too low to go to the flare, or 2) the vent contains < 5 0 ppmv organic HAP as demonstrated by engineering analysis.

Proposed startup work practice procedure (from point wher e equipment is under
nitrogen pressure): Align the Group 1 continuous front

- end process vent to the flare and begin
displacing nitrogen to the flare with process gas. For Group 1 continuous, halogenated front

end process vents, route the vent to the ther mal oxidizer/scrubber when the vent composition is
acceptable for maintaining the required minimum firebox temperature , based on engineering

assessment.

Suggested Regulatory Language

§63.485(w) Startup and shutdown

(1) During periods of shutdown, when the requirements of §63.113(a) (2 ) for a Group 1
halogenated continuous front

- end process vent cannot be met, a Group 1 halogenated

continuous front

- end process vent is not subject to the requirements of §63.113(c) and may be
routed to a flare, if process f luid is not entering the process vessel that is the source of the vent.
The vent may be routed to the atmosphere when the vent characteristics no longer allow routing
it to the flare or the organic HAP concentration in the vent is <50 ppmv (as demonstrate d by
engineering analysis).

(2) During periods of startup , when the requirements of §63.113(a) (2 ) for a Group 1
halogenated continuous front

- end process vent cannot be met, a Group 1 halogenated

continuous front

- end process vent is not subject to the req uirements of §63.113(c) and may be
routed to a flare, until the stream characteristics allow the requirements of §63.485(a)(2) to be

met.(3) The owner/operator shall identify the parameter(s) and parameter values that indicate the

requirements of §63.113(a)(2) and (c) cannot be met for Group 1 halogenated continuous front

end process vents and report those parameters in the Notice of Compl iance Status required by
§63.506(e)(5)Appendix C

Supplemental S t a r t u p / S h u t d o w n Information ( 3 / 23 / 1 1 )Recommended Procedures for Handling Group 1 Front

- end Process Vents From Butyl and Ethylene Propylene Rubber Source Categories

During Startup and Shutdown

Background:

For Butyl and Ethylene Propylene Rubber operations, the frequency of planned

start ups/shutdowns is a function of product demand and periodic maintenance or construction needs (e.g., a startup/shutdown may be needed to install the facilities required to comply with this proposal). Unplanned, but controlled, shutdowns and the subsequent startups can also occur in anticipation of major weather events such as hurricanes. For the three ExxonMobil units impacted by this rule, we typically have one to three startups/shutdowns per year, with major turnarounds every 5

- 10 years. Most shutdowns do not involve the entire process unit, which means that only some vents would need to be routed away from the flare. A shutdown may take 24 to 48 hours with process equipment clearing and depressuring occurring during the last part of the shutdown. Star tups typically take 12 hours.

Recommended Approach for Standards during Startup and Shutdown of Vents Normally

Routed to the Flare.

At some point during the shutdown of Butyl Rubber and Ethylene Propylene Rubber source
category front

- end equipment for th e purpose of opening that equipment the proposed requirements for Group 1 continuous front

- end process vents to route the vent to a flare or to remove 98% of the organic HAP can no longer be met

. T hese instances occur during shutdown

after process fluid i s no longer entering the equipment and the vent streams contain only small

amounts of residual organic compounds and organic HAP s

. Typically, depressuring to the flare and nitrogen purging is used to displace the bulk of the hydrocarbon in the equipment. Since flare pressure is low, this quickly reduces the residual organic HAP to insignificant levels. The final step in removing any residual HAP and opening the equipment is to route the vent to the atmosphere.

It is technically and economically impracti cal to measure organic HAP reduction during this portion of the shutdown period or to demonstrate compliance with an organic HAP reduction or mass requirement, because the vent flow, pressure and HAP concentration is constantly changing and the HAP concent ration and vent pressure are quickly reduced to zero. I t is not technically feasible to complete stack testing

- in particular, to repeat the multiple required test

runs

- during these portions of s hutdown due to physical limitations , methodology limitati ons and

the short duration of the final purging steps. Therefore, establish ment of a separate work practice standard for these periods of startup and shutdown is authorized by CAA section 112(h).Work Practice Recommendation

A work practice requirement would provide an emission standard for these shutdown periods when the vent streams can no longer be routed to the flare and facilitate the rapid and efficient removal of hydrocarbon from process equipment. We believe being unable to send the vent to

the flare due to low pressure or low heating value or achieving 50 ppmv organic HAP content (the criterion for a vent being a Group 1 vent, as demonstrated through engineering analysis) is the appropriate point at which to allow routing Group 1 continuous fro nt

- end vents from the flare to the atmosphere.

Proposed shutdown work practice procedure: Keep Group 1 continuous front

- end process vents aligned to the flare until 1) the vent pressure or heating value is too low to go to the flare, or 2) the vent conta ins < 5 0 ppmv organic HAP as demonstrated by engineering analysis.

Suggested Regulatory Language

§63.485(w) Shutdown

(1) During periods of shutdown, a Group 1 continuous front

- end process vent may be routed to
the atmosphere when the vent characterist ics no longer allow routing it to the flare or the
organic HAP concentration in the vent is <50 ppmv (as demonstrated by engineering analysis).Appendix D

Supplemental S t a r t u p / S h u t d o w n Information ( 3 / 2 8 / 1 1 )