FROM: Jeff Coburn and Shelly J ohnson, RTI International

TO: Brenda Shine, EPA/OAQPS/SPPD

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

DATE: September 20, 2013

SUBJECT: MACT Analysis for Delayed Coking Unit Decoking Operations

1. Purpose

This memorandum discusses the procedure used to determine the maximum achievable control technology (MACT) standards for delayed coking unit (DCU) decoking operations.

2. Background Information on DCU Operations

The DCU uses thermal cracking to upgrade heav y feedstocks and to produce petroleum coke. Unlike most other refinery operations that ar e continuous, the DCU opera tes in a semi-batch system. Most DCU consist of a large process he ater, two or more coking drums, and a single product distillation column. The DCU feed is act ually fed to the unit’ s distillation column.

Bottoms from the distillation column are heated to near cracking temperatures and the resulting heavy oil is fed to one of the coking drums. As the cracking reactions occu r, coke is produced in the drum and begins to fill the drum with sponge -like solid coke material. During this process, the DCU is a closed system, with the produced gas streams piped to the unit’s distillation for product recovery.

When the first coke drum becomes filled with coke , the feed is diverted to the second coke drum and processing continues via the second coke drum. The full coke drum, which is no longer receiving oil feed, is taken through a number of steps, collectively referred to as decoking operations, to remove the coke from the drum and prepare the drum fo r subsequent oil feed processing. The decoking steps include: pur ging, cooling/quenching, venting, draining, deheading, and coke-cutting. A description of th ese steps and the potential emissions from these activities are provided in the next several paragraphs. Once the coke is removed, the vessel is resealed ( i.e. , the drain valve is closed and the “head” is re-attached), pressure tested (typically using steam), purged to remove oxygen, then slowly heated to processing temperatures so it can go back on-line. When the second coke drum become s filled with coke, feed is diverted back to

the first coke drum and the second drum is then decoked. In this manner, the DCU allows for continuous processing of oil even though the indi vidual coke drums operate in cyclical batch

fashion.

The first step in decoking operations is to purge the coke drum with steam. This serves to cool the coke bed and to flush oil or reaction products from the coke bed. The steam purge is initially sent to the product distillation column and then diverted to the unit’s blowdown system. TheTechnical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

2 blowdown system serves to condense the steam and other liquids entrained in the steam. Nearly all DCU operate a ”closed blowdown” system, su ch that uncondensed gases from the blowdown system are either sent to the pr oduct distillation column, the facil ity’s light gas plant, recovered as fuel gas, or combusted in a flare. In an open blowdown system, these uncondensed gases would be vented directly to atmosphere. The DCU vent discharge to the blowdown system is specifically defined in Refinery MACT 1 (40 CF R part 63, subpart CC) as the “delayed coker

vent.”

The next step in the decoking process is coolin g/quenching the coke drum and its contents via the addition of water, commonly re ferred to as quench water, at the bottom of the coke drum. The water added to the vessel quickly turns to steam due to the high temperature of the coke bed. The water/steam helps to further cool the coke bed and “quench” any residual coking reactions that may still occur within the hot coke bed. As with the steam purge, steam off-gas from the cooling/quenching cycle is recovered in the unit’ s blowdown system and this vent discharge is specifically defined in Refinery MACT 1 as the “delayed coker vent.” After several hours, the coke drum is sufficiently cooled so that water remains in the drum and the water level can be raised to entirely cover the c oke bed. Although water covers the coke bed, the upper portion of the coke bed may still be well above 212 degrees Fa hrenheit (°F) and steam will continue to be generated. In fact, since the coke drum vessel pre ssure is greater than at mospheric pressure, the equilibrium boiling point of water in the vessel is greater than 212 °F. Therefore, the water at the top of the coke drum is typically well above 212 °F (superheated water). As the coke drum and

its contents continue to cool from the evaporative cooling eff ect of the steam generation, the steam generation rate and the pressu re within the vessel will decrease.

Owners or operators of DCU may use different indicators or set points to determine when the system has cooled sufficiently to move to the venting step; however, one of the most common indicators monitored is the pre ssure of the coke drum vessel (o r steam vent line just above the coke drum, where steam exits the coke drum en r oute to the closed blowdown system). When the vessel has cooled sufficiently ( e.g. , when the coke drum vessel pr essure reaches the desired set point), valves are opened to allow the steam genera ted in the coke drum to vent directly to the atmosphere rather than the closed blowdown system . This vent is commonly referred to as the “coker steam vent.” This is typically the firs t direct atmospheric emission release during the decoking operations when an enclosed blowdown sy stem is used. While this vent gas contains predominately steam, methane and ethane, a vari ety of hazardous air pollutants (HAP) are also emitted with this steam. These HAP include light aromatics ( e.g. , benzene, toluene, and xylene) and light polycyclic organic matter (predominatel y naphthalene and 2-methyl naphthalene). HAP

emissions from the DCU have been found to be a function of the quantity of steam generated (Coburn, 2013).

In general, the next step in the decoking pro cess is draining the water from the coke drum by opening a large valve at the botto m of the coke drum. The drain water typically falls from the coke drum onto a slanted concrete pad that dire cts the water to the coke pit area (where water and coke are collected and separated). Some DCU owners or operators in itiate draining at the same time they initiate venting; other owners or operators may allow the vessel to vent for 20 or more minutes prior to initiati ng draining. While draining immedi ately may reduce the amount ofTechnical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

3 steam exiting the unit via the stack, it is not expect ed to alter the overall emissions from the unit. During the venting and draining process, the pressu re of the system falls to atmospheric. Steam will be generated until the evaporative cooling ef fect of that steam generation cools the coker quench water to 212 °F. If draini ng is initiated immediately, some of the superheated water may drain from the DCU before being cooled. A portion of that drained water will then flash to steam during the draining process as that superheated water contacts th e open atmosphere. Therefore, draining quickly is not expected to alter the total am ount of steam generated from the unit nor

alter the overall emissions from the unit. It wi ll, however, alter the re lative proportion of the

emissions that are released via the ve nt versus the quench water drain area.

The next step in the decoking process is “deheadi ng” the coke drum. At the top of the coke drum is a large 3- to 5-foot diam eter opening, which is sealed wi th a gasketed lid during normal operations. When the steam generation rate from the coke drum has sufficiently subsided, this gasketed lid is removed to allow access for a wate r drill that will be used to remove coke from the drum. The process of removing this lid is refe rred to as “deheading” th e coke drum. Different DCU owners or operators may use different criter ia for when to dehead the coke drum. If the coke drum is deheaded soon after venting is in itiated, some steam and associated HAP emissions may be released from this opening. As with drai ning, it is anticipated that the total volume of steam generated will be a function of the temper ature/pressure of the co ke drum. Deheading the coke drum prior to the coke drum contents reach ing 212 °F will generally m ean that some of the

steam will be released from the coke drum head opening. However, this will not alter the total amount of steam generated; it merely alters the location of the release (steam vent versus coke drum head opening). The HAP emissions from the deheading process are expected to be proportional to the amount of steam released in th e same manner as the emissions from the steam

vent.

The final step of the decoking process is coke-cu tting. A high-pressure water jet is used to drill

or cut the coke out of the vessel. The drilling water and coke slu rry exits the coke drum via the drain opening and collects in the coke pit. Ge nerally, the coke drum and its contents are sufficiently cooled so that this process is not expected to yield significant HAP emissions. However, if the other decoking steps are perfor med too quickly, hot spots may exist within the coke bed and HAP emissions may occur as water contacts these hot spot s and additional steam

and emissions are released.

Once the coke is cut out of the dr um, the drum is closed and prepared to go back on-line. This process includes pressurizing with steam to ensure there are no leaks ( i.e. , that the head is properly attached and sealed and th e drain valve is fully closed). The vessel is then purged to remove any oxygen and heated by diverting the produced gas from the processing coke drum through the empty drum prior to se nding it to the unit’s distillation column. A coke drum cycle is typically 28 to 36 hours from start of feed to star t of feed. Delays in th e decoking operations may impact process feed rates. That is, if the decoking and drum pr eparation steps take too long, the

feed rate to the other coke unit must be reduced to prevent overfilling one coke drum prior to being able to switch to the other coke drum. This issue is less critical for DCU that operate with three or four drums per distilla tion column, but a consistent incr ease in the decoking times across all drums may still limit the capacity of the DCU at some petroleum refineries.Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

4 3. Background Information of Regulatory Standards for DCU Decoking Operations

Refinery MACT 1 includes delayed coker vent s as an example within the definition of “miscellaneous process vent” (40 CFR part 63, subpart CC). However, Refinery MACT 1 goes

on to exclude from the definition of miscellane ous process vent “Coking unit vents associated with coke drum depressuring at or below a c oke drum outlet pressure of 15 pounds per square inch gauge [psig], deheading, draining, or dec oking (coke cutting) or pressure testing after decoking” (see 40 CFR 63.641). Refine ry MACT 1 defines a “delayed coker vent as “a vent that is typically intermittent in nature, and usua lly occurs only during the initiation of the depressuring cycle of the decoking operation when vapor from the coke drums cannot be sent to the fractionator column for produc t recovery, but instead is rout ed to the atmosphere through a closed blowdown system or directly to the atmosphere in an open blowdown system. The emissions from the decoking phases of delaye d coker operations, which include coke drum deheading, draining, or decoking (c oke cutting), are not considered to be delayed coker vents” (see 40 CFR 63.641 of subpart CC). The steam vent fr om depressurization is never mentioned in the definition of “delayed coker vent,” which fo cuses exclusively on the vent from the blowdown system. The steam vent is the place where HAP em issions would be vented to the atmosphere once they cease to be routed through the bl owdown system. Thus, the steam vent is not considered a delayed coker vent, and it is excl uded from being considered a miscellaneous process vent if it depressures at 15 psig or below. In other words, there is no applicable standard for atmospheric releases of delayed c oker HAP emissions through the steam vent.

We reviewed the background information from th e development of Refinery MACT 1. Given the statements in the background information document for the August 1995 final Refinery MACT 1 rule (EPA, 1995), the 15 psig pres sure limit for the direct venting of the DCU to the atmosphere

was not established as a MACT fl oor control level, but rather was established to accommodate all DCU at whatever pressure they typically sw itched from venting to the blowdown system to venting directly to the atmosphere. In addition, the U.S. Environmental Protection Agency (EPA)

conducted a detailed information collection request (ICR) of the petroleum refining industry in 2011 (EPA, 2011). The Refinery MACT 1 background information, along with data from the 2011 Refinery ICR, refinery enforcement settleme nts and other information indicates that all refineries depressurize the coke drum below 15 psig, which indicates that all direct atmospheric releases (which occur through th e steam vent) from the DCU d ecoking operations are excluded from the regulation. This exclusion, along with th e additional exclusions for deheading, draining, coke cutting, and pressure testi ng after decoking indicates that there is not an applicable MACT

standard for HAP emissions from the DCU.

4. Evaluation of MACT Emission Li mitations for DCU Decoking Operations

Based on our review of the existing requirements in Refinery MACT 1, it is evident that HAP emissions occur during DCU decoking operations a nd that these emissions are not subject to MACT emission limitations. Therefore, we evaluate d these emission sources in order to identify appropriate MACT emission limitations for the DCU decoking operations.

We first evaluated traditional controls for organi c HAP from process vents, such as the use of incinerators, flares, carbon adso rbers, or condensers. These control systems are generallyTechnical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

5 ineffective or not applicable gi ven the high moisture content of the DCU steam vent. In order to control these vapors, the vent w ould have to be processed in a blowdown system where the water

can be condensed and recovered and then the drie r gas stream can then be controlled. If the vent stream is diverted to the unit’s blowdown system , then this vent disc harge clearly meets the definition of a delayed coker vent and the uncon densed gas stream would require control under Refinery MACT 1 as a miscellaneous process vent. Thus, the longer the DCU coke drum is vented to the closed blowdown system, the more the DCU depressuring emissions can be controlled. Thus, establishing a lo wer pressure set point at which a DCU owner or operator can switch from venting to an enclosed blowdown system to venting to the atmosphere was identified as the primary c ontrol technique for reducing emissions from delayed coking operations.

As described in the impact estimates for DC U, organic HAP emissions from the decoking operations are a function of steam generation. Essent ially, there is a fixed quantity of steam that will be generated as the coke drum and its contents cool to 212 °F (the boiling point of water at atmospheric pressure). As the c oke bed cools, steam generation rates fall and the coke drum vessel pressure falls. Thus, the coke drum vessel pr essure is an indicator of the average coke bed temperature. A lower coke drum vessel pressure set point will require th e DCU to vent to the closed blowdown system longer, where the organi c HAP can be recovered or controlled, and will allow the coke drum contents to cool further prio r to atmospheric venting. This will result in less steam generation and fewer HAP emissions during the venting, draining and deheading process.

Refinery NSPS Ja (40 CFR part 60, subpart Ja) es tablishes a pressure limit of 5 psig prior to allowing the coke drum to be vented to the at mosphere. Based on a review of permit limits and consent decrees, we found that coke drum vesse l pressure limits have been established (and achieved) as low as 2 psig. There are 75 operati ng DCU according to the Refinery ICR responses (EPA 2011), so the sixth percentile is repr esented by the fifth-best performing DCU.

We researched permits, consent decrees, Refine ry ICR responses, and other rules addressing DCU depressurizing limits. Out of the 75 DCU, we identified at least 27 DCU that either currently operate or are required to operate by venting to the atmosphe re only after the coke drum vessel pressure has reached 2 psig or less. Table 1 summarizes these results. Many of the refinery owners or operators claimed thei r DCU operation data as confidential business information (CBI). Therefore, we only specifical ly identify a facility due to permit or consent decree requirements. For these facilities, we onl y indicate whether thei r response to the ICR question regarding typical DCU vesse l pressure when first venting to the atmosphere when they

did not claim this information as CBI. For a ll other facilities, we blinded the facility identification. Eight DCU were identified that had a consent decree, permit, or local rule requiring these units to not depr essure directly to the atmos phere until the DCU coke drum vessel pressure is 2 psig or less. While the Hove nsa plant is not operating, the limit and consent decree will remain in place for the unit if opera tion begins again. The South Coast Air Quality Management District (SCAQMD) Rule 1114 th at was adopted May 3, 2013 requires units to reduce the DCU vessel pressure to less than 2 ps ig prior to venting to the atmosphere. The SCAQMD rule is effective November 1, 2013, but includes provisions for owners or operators unable to comply with the 2 psig limit by N ovember 1, 2013, to temporarily comply with aTechnical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

6 higher venting pressure limit for a certain time period prior to requiring all DCU to meet the 2 psig venting pressure limit. Units 7 and 8 indi cated in their Refinery ICR response that they typically vent at pressures below 2 psig. As such, these two units will be required by rule to vent at vessel pressures below 2 psig effective November 1, 2013. Theref ore, we counted these units as having existing limits of 2 psig or less. DCU 9-11 indicated operating at the proposed conditions, but these units are on ly required by the Bay Area Air Quality Management District (BAAQMD) 8-10-301 standards to vent at a maximu m pressure of 4.6 psig. The remaining units, 12-27, indicated operating venting le vels at or below 2 psig. Ho wever, we could not identify anystate or local requirements or permit conditions limiting the venting pressure for these units.Technical Memorandum – MACT Analysis forDelayed Coking Unit Decoking OperationsSeptember 20, 20137Table 1. DCU Meeting the 2 psig Depressurizing LimitNo.CompanyCityStateUnitOperatingat orbelow 2psig limitin 2010aTypeofLimitbLimitDate ofPermit orConsentDecreeRegulatoryAgencyReference/Notes1 BP Whiting IN NewCokerCD Shall not commence CokeDrum Venting until theCoke Drum OverheadPressure is 2.0 psig or less9/28/12 ConsentDecree,2012b2 Marathon Detroit MI Coker P Shall not vent the activecoke drum to theatmosphere until the end ofthe coking cycle, when thedrum pressure is 2 psig orless1/11/12 MDEQ,20123-4 Marathon Garyville LA Unit 5Coker,Unit 205CokerYes P Shall relieve the CokerDrum Vents at a pressureequal to or less than 2 psigduring atmospheric venting8/29/13 LDEQ,20135 ConocoPhillips Co.,WRB Refining, LPWoodRiverIL Coker 2 CD Coke Drum OH PressureLimit of 2 psig for theCoker 2 Coke Drums2/28/12 ConsentDecree,2012a.6 Hovensa St. Croix USVI DelayedCokerUnitCD Shall comply with adepressurization level of 2psig for the Coker SteamVents1/26/11 ConsentDecree,2011Plant isshut down7-8 "7-8" "7-8" CA "7-8" Yes RA Shall depressurize eachcoke drum to less than two(2) pounds per squareinch, gauge (psig) prior toventing it to atmosphereSouth CoastAir QualityManagementDistrictSCAQMD,2013Technical Memorandum – MACT Analysis forDelayed Coking Unit Decoking OperationsSeptember 20, 20138No.CompanyCityStateUnitOperatingat orbelow 2psig limitin 2010aTypeofLimitbLimitDate ofPermit orConsentDecreeRegulatoryAgencyReference/Notes9-11 "9-11" "9-11" CA "9-11" Yes RA Shall be vented through aknock-out pot and thenabated in one of thefollowing ways, to as low avessel pressure aspossible, but at least untilpressure is reduced to lessthan 1000 mm Hg (4.6psig)cBay Area AirQualityManagementDistrictBAAQMD,200412-27"12-27" "12-27" varies "12-27" Yes NoneaAs reported in response to the Refinery ICR. This information was often claimed as CBI.b“Type of Limit” indicates what regulates the limit: CD= consent decree; “P” = Permit; “RA” = Regulatory Agency.cmmHg = millimeters of mercury.Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

9 While we identified eight DCU with permit requi rements or consent decrees specifying a coke drum venting pressure limit of 2 psig, we di d not identify any permit or consent decree requirements more stringent than 2 psig. Refinery owners and operators were asked to provide the “typical coke drum pressure just prior to venting” for eac h DCU in their responses to the Refinery ICR, and the responses indicate that fo ur DCU operate such that the typical venting pressure is 1 psig or less. However, this “typic al coke drum pressure” does not represent a not-tobe-exceeded pressure limit, but ra ther is indicative of a vessel th at is operated to meet a not-tobe-exceeded pressure limit of 2 psig. We do not have information to indicate whether these facilities can always depressurize at 1 psig or less, whereas in order to be in compliance with their permit limits, the best-performing sources must be able to depressurize at 2 psig or less at all times. Therefore, the MACT fl oor for DCU decoking operations is to depressure at 2 psig or less prior to venting to the atmosphe re for both new and existing sources.

We then considered control options beyond the floor level of 2 psig to determine if additional

emission reductions could be co st-effectively achieved. We cons idered a control option that allowed atmospheric venting only after the DCU ve ssel pressure reached 1 psig or less, since some facilities reported in the ICR depressurizing to that level pr ior to venting. There are several technical difficulties associated with establishing a pressure limit at this lower level. First, the lowest pressure at any point in a closed blowdown system is ge nerally designed to be no lower than 0.5 psig in order to prevent air ingress into the un it in the event a valve, flange, or other component leaks. Air ingress into the DCU or bl owdown system has the potential to create an explosive atmosphere. Consequently, for safe ty reasons, the DCU compressor system would operate with an inlet pressure of no less than 0.5 psig. Second , there are several valves and significant piping (for cooling and condensing st eam) between the DCU drum and the recovery compressor. There is an inherent pressure drop wh en a fluid flows through a pipe or valve. Two

valves are used for all DCU lines to make sure that the unit is either blocked off from the processing fluids or blocked in so there ar e no product losses out the steam line during processing. Considering the need for two valves and piping needed in the cooling system, DCU designed for a minimal pressure loss will genera lly still have a 0.5 to 1 psig pressure drop between the DCU drum and the recovery compresso r inlet. Finally, in order to meet a 1 psig pressure limit at all times, the DCU closed vent system would need to be designed to achieve a vessel pressure of approximately 0.5 psig. Given the above considerations, we do not consider it technically feasible to ro utinely achieve a vessel pressure of 0.5 psig in order to comply with a never-to-be-exceeded drum vessel pressure of 1 psig. As noted previously, facilities that “typically” achieve vessel pressures of about 1 or less are expected to do so in order to meet a

never-to-be-exceeded drum vessel pressure limit of 2 psig and no DCU is currently required to meet a drum vessel pressure limit of le ss than 2 psig for all venting events.

We also evaluated additional work practice st andards regarding draining, deheading, and coke cutting. As stated previously, the decoking emissions can be released from a variety of locations, and the 2 psig or less limit for depressurizing the coke drum will effectively reduce the emissions from all of these emission points. Although atypi cal, the owner or operato r of a DCU may start draining water prior to opening the steam vent. Ow ners or operators may adopt this practice as a means to reduce pressure in the coke drum prior to venting the drum to atmosphere in order to achieve the venting pressure limit. Initiating wa ter draining prior to reach ing 2 psig would resultTechnical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

10 in draining water that is hotte r than it would be had the drum been sufficiently cooled ( i.e. , the pressure limit achieved) prior to draining the vessel, effectively diverting HAP emissions to the water drain area rather than capturing these HAP in the enclosed blowdown system, where they can be either recovered or controlled. Therefore, we recommend that the 2 psig limit apply to all potential release points in the deco king operations, in cluding draining.

We also considered whether there were means to connect the bottom of the coke drum to a large

diameter “hose” so that the drained water and/or the coke cutting slurry could be discharged from the DCU and enter the coke pit in a s ubmerged fill manner. This enclosed transfer, submerged fill requirement would reduce the em issions released during these processes. However, we could identify no commercially ava ilable equipment to conne ct the coke drum to the coke pit. There may also be technical issu es associated with pl ugging of the drain hose during the coke cutting process. While submer ged filling has been used to reduce emissions during a variety of transfer operations, we conclude that this is not a vi able option for DCU at

this time.

We could not identify any other emission reduction options that c ould lower the emissions from the DCU decoking operations. Since we could not identify a technically feasible control option beyond the MACT floor, we recommend that the MACT floor pressure limit of 2 psig is MACT for both new and existing sources.

5. Justification for Work Practice St andards for DCU Decoking Operations

We believe that work practice standards are appropriate for the emissions associated with the DCU decoking operations. While the emissions fr om the DCU steam vent are released via a conveyance designed and constructed to emit or capture such pollutant, we believe that CAA section 112(h)(2)(B) applies in that it is not feasible to prescribe or enforce an emission standard for the DCU steam vent because the application of measurement methodology for this source is not practicable due to technol ogical and economic limitations. The DCU steam vent typically contains 99-percent water, wh ich interferes with common sample collection and analysis techniques. Also, the flow rate fr om this vent is not constant; rather, it decreases during the venting process as the pressure in the DCU coke drum approaches atmospheric pressure. Finally, the venting time can be very short, particularly for units complying with the proposed standards. Together, these factors make it extremely difficult to measure th e emissions from the DCU steam vent. As part of the ICR, the EPA requested stac k testing of eight DCU. After discussions with stack testing experts within the agency and with outside contract ors used by industry to perform the tests, the EPA concluded that sources with venting times less than 20 minutes would not be able to perform an emissions test that would yield valid results. Therefore, only two of the eight facilities actually performed the tests. We antic ipate all units complying with the proposed

standards for DCU steam vents woul d vent for less than 20 minutes.

Second, due to the interplay of the emission points associated with the decoking operations, it is possible to alter the amount of emissions released via the st eam vent (conveyance) depending when the subsequent decoking steps are conduc ted. If draining and deheading are initiated quickly after venting, this will reduce the emi ssions discharged from the vent (although as explained above, it does not reduce the emissions from the collective set of decoking operationsTechnical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

11 release points). Therefore, if the EPA regulates only the steam vent, owners or operators of DCU

could divert the emissions from the steam vent to the drain or other releas e points. Thus, it is not feasible or effective for the EPA to enforce an emission standard only on the steam vent ( i.e.

, only releases from the conveyed emissions) beca use the timing of draining and deheading can alter the portion of the decoki ng emissions that are released from the actual steam vent.

Third, the emissions from the draining, dehead ing and coke cutting steps cannot be emitted through a conveyance designed and constructed to emit or capture such pollutant. For example, the coke drum head must be removed to provide an accessible opening in the drum so the coke cutting equipment can be lowered into the drum . This opening cannot be sealed during cokecutting because the drilling shaf t will occupy the opening and the shaft must be free to be lowered or raised during the coke-cutting proce ss. We believe that the 2 psig work practice standard prior to venting, draining or any other decoking step will effectively limit the emissions from all phases of the decoking process, includi ng these release points that cannot be emitted through a conveyance and thereby meet the criteria for a work practice standard under CAA section 112(h)(2)(A).

Consequently, due to the unique nature of the DCU decoking operation emissions, the difficulties associated with monitoring the DCU steam vent, and the inability to construct a conveyance to capture emissions from all decoki ng operation release points, we believe it is appropriate for the EPA to develop work practice standards to limit the emissions associated with DCU decoking operations.

6. Evaluation of Cost and Environmental Im pacts of MACT Emission Limitations for Delayed Coking Units

DCU that cannot currently meet the 2 psig pressure limit would be expected to install a device (compressor or steam ejector system) to lower th e DCU vessel pressure. In the Refinery NSPS Ja impact analysis, facilities not ab le to meet the pressure thresh old were assumed to purchase and install a larger compressor to lower the blowdown system pressure (Coburn and Richardson, 2008). Other approaches to lo wering blowdown system (and coke drum) pressure exist. Specifically, steam ejectors have been identified as a method to help existing units depressurize more fully in order to achieve a set vessel pre ssure or drum bed temperature. Upgrading the closed vent system to reduce pressure losses or to increase steam condensing capacity may also allow the DCU to depressure more quickly while the emissions are still vented to the closed blowdown system.

For existing sources, we assumed all DCU that reported a “typical drum pressure prior to venting” of more than 2 psig would install and operate a steam ejector system to reduce the coke drum pressure to 2 psig prior to venting to at mosphere or draining. The operating costs of the steam ejector system are offset, to some extent , by the additional recovered vapors. Vapors from the additional gases routed to the blowdow n system contain high levels of methane (approximately 70 percent by volume on a dry basis) based on DCU steam vent test data. If these vapors are directed to the closed blowdown system rather than to the atmosphere, generally the dry gas can be recovered in the refinery fuel ga s system or light-ends gas plant. This recovered methane is expected to off-set natural gas purchases for the fuel gas system.Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations September 20, 2013

12 We anticipate that new DCU sources can be bui lt with a closed blowdown system designed to achieve a 2 psig vessel pressure with no significant increase in ca pital or operating costs of the new DCU. There may be a slight increase in capital costs for the low pressu re valve design or for larger diameter piping; however, these design improvements generally lower the operating costs of the DCU. For example, designi ng the system to vent at a lowe r pressure results in additional vapor recovery, which is expected to off-set any additional capital costs associated with the low pressure design closed blowdown system.

The costs of complying with the 2 psig coke dr um threshold prior to venting or draining are summarized in Table 2. The costs are appr oximately $1,000 per ton of volatile organic compounds (VOC) reduced and approximately $5,000 per ton of organic HAP reduced when considering VOC and methane recovery credits. Additional detail regarding the cost and environmental impact estimates are provided elsewhere (Coburn, 2013).

Table 2. Nationwide Emissions Reduction and Cost Impacts of Control Option for Existing Delayed Coking Units at Petroleum Refineries

Control Option Capital
Cost (million $) Annualized
Costs

Without Recovery

Credits (million

$/yr) Emissions Reduction, VOC (tpy) a Emissions Reduction, HAP (tpy) a Cost Effectiveness

($/ton HAP) Total
Annualized
Costs with
VOC Recovery

Credit (million

$/yr) Overall Cost

Effectiveness with
VOC Recovery Credit ($/ton HAP)

2 psig 52 10.2 4,250 850 12,000 3.98 4,700

a tpy = tons per year.

7. References

BAAQMD (Bay Area Air Quality Management Di strict). 2004. Process Vessel Depressurizing, Regulation 8, Rule 10-3 01. Last Amended 1/21/04. http://hank.baaqmd.gov/ds t/regulations/rg0810.pdf . [Accessed 9/16/2013].

Coburn, J. 2013. Impact Estimates for Delayed Coking Units . Memorandum to Brenda Shine, U.S. EPA, from Jeff Coburn, RTI In ternational. Revised September 12, 2013.

Coburn, J. and C. Richardson. 2008. Final Impacts Analysis for De layed Coker Depressurization

Emissions . Memorandum from Jeff Coburn and Carrie Richardson, RTI International, to Bob Lucas, EPA/SPPD. April 28, 2008. Docket Item No. EPA-HQ-OAR-2007-0011-0226.

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