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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, t he 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

hurricane s . For the three ExxonMobil units i mpacted 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

. Th e final step in removing any residual HAP and opening the equipment is to route the vent to the atmosphere.

I t is technically and economically impracti cal to measure organic HAP re duction during

th is 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)

.

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Work Practice Recommendation

A work practice requirement would provide an emission standard for the se shutdown periods when the vent streams can no longer be routed to the flare and facilitat e 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

5 0 ppmv organic HAP cont ent (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 c ontinuous 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 ) S hutdown

(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)

.