Matthew Todd

1220 L Street NW Washington, DC 20005

- 4070
USA Telephone: 202

- 682

- 8319 Email: toddm@api.org www.api.org

August 2 8

, 2012

M s

. Brenda Shine

US EPA Office of Air Quality Planning and Standards Mail Drop E143

- 01 Research Triangle Park, NC 27711 shine.brenda@epa.gov

Re: Potential Delayed Coker Emission Controls

Dear Brenda :

The American Petroleum Inst itute (“API”) ha s been working with EPA on the Refinery Sector Rulemaking since the beginning of th at effort

. We appreciate the dialogue we have been able to

have about emissions from delayed coker s and their control. I n particular, we appreciate the

rec ent sharing of your impressions from your June visit to three delayed cok ing units (DCUs)

. We believe those impressions reflect a reasonable understanding of the complex , inter

- related issues associated with managing DCU operations and their emissions, th e individuality of each

installation

, and the criticality of coker throughput to meeting refined product market demand

.

Introduction

Coke drum vent pressure at the time the drum vent is routed to the atmosphere is a readily

measurable parameter that has been established as the key parameter reflective of coke drum

vent emissions

. A p ressure criterion is already used in RMACT 1

, NSPS Ja, s tate regulations,

and facility permits as the basis for allowing releas e of the coke drum vent to the atmosphere.

The refore, establishing a revised RMACT 1 pressure criterion as a work practice for l imiting

coke dr um emissions to the atmosphere represents the best , most consistent way to further manage coke drum emiss i ons in the Refinery Sector R ulemaking

.

In order to help inform your decision on what the most justifiable pressure criterion would be

,

r efinery coker experts have evaluated the potential emission reductions and costs for achieving

various pressure levels. They conclude that the available data show s that there is little difference

in c oke drum emissions at vent pressure thresholds between 5 psig and 2 psig and that there can be significant costs associated with meeting a 2 psig criterion versus meeting a 5 psig criterion

. Thus, while the available emissio ns and cost data are sparse and of varying quality, they do notPage 2

support establishing a work practice standard for existing DCUs that is any more stringent than that recently adopted for modified and reconstructed DCUs in NSPS Ja (i.e., 5 psi g ).

Emissions and risk

The pressure at which coke drums are vent ed to the atmosphere varies from unit to unit and facility to facility based upon a number of criteria , including type of coke produced, equipment design, and fractionator, flare, or fuel gas system backpr essure. Some drums can be vented at pressures as low as 2 psig and others approach 15 psig before being vented

. As we discuss in Attachment 1, the a vailable data do not demonstrate a significant emissions difference for an atmospheric release criterion b elow 5 p sig. This is consistent with the estimates EPA developed in the NSPS Ja rulemaking where the Agency estimated an insignificant incremental VOC

reduction of only 1.31 lb/event for 2 psig versus 5 psig 1

.

For this rulemaking, the impact of coke drum emissions on risk are being assessed by using HAP

emission estimates collected in Part 2 of the recent Refinery Information Collection Request (ICR). As we also discuss in Attachment 1, the e mission factors that were required to be used

for these HAP est imates were based on a single data set (the HOVENSA data) . The additional data recently collected in Part 4 of the ICR indicate that th ose emission factors and thus the

calculated HAP emissions and risk are significantly overstated and actual HAP emission s and risk from coke drums may be as much as several orders of magnitude lower than were used by EPA in the risk modeling for this rulemaking.

In summary, our review of the available data indicates that ( 1)

, there is likely only a small VOC

and HAP emissi on reduction potential associated with setting a coke drum release to the atmosphere criterion below 5 psig and ( 2)

, the HAP emissions and thus risk increment attributed

to coke drum emissions in the current rulemaking effort is likely significantly overst ated because

the HAP emission factors used in the ICR significantly overstate the actual emissions

.

Equipment considerations and costs of pressure reduction

The quenching of a coke drum full of hot coke involves adding water from the bottom of the

drum . The water cools the coke by means of a phase change from liquid to vapor. The steam

vapor formed in this process passes across the remaining hot coke and out the top of the coke drum. During the quenching operation, the coke drum vapors are routed to the DCU

“ blowdown ” section where the steam and most hydrocarbons are cooled, condensed, and separated into a water phase and a hydrocarbon phase.

The blowdown section of the plant typically uses fin fan coolers (air coole d heat exchangers ) for removing heat from the coke drum vapor. Under fin fan cooler conditions, a portion of the hydrocarbon leaving the coke drum cannot be fully condensed. These non

- condensable hydrocarbon molecules were originally routed to a flare system . Over time, flare gas reco very has been added to many DCUs to compress these gases and deliver them to a refinery fuel gas

1 Docket Item EPA

- HQ

- OAR

- 2007

- 0011

- 0226.1 , Delayed Coker Cost Effectiven e ss Spreadsheet. EPA calculated, based on an assumed 20 hour cycle time and no outages, a model coke d rum would have 438 such events per year, resulting in an annual

estimated emission of 0.29 Tons of VOC.Page 3

system rather than to a flare

. On some cokers

, non

- condensable hydrocarbon molecules from the

blowdown section are routed to the coker main fractionator overh ead system for recovery during at least part of the coke drum quench cycle rather than to a flare or flare gas recovery system

.

Once the water level in the coke drum is above the level of coke in the drum, the generation of steam is reduced significantly. At that point, the pressure on the drum is a function of:

1) t he pressure drop between the coke drum and the blowdown system caused by the remaining flow of vapor ; and

2) the operating pressure of the blowdown system.

Due to physical layout constraints, DCUs vary greatly in the configuration, length

, and diameter of the piping between the coke drum s and blowdown section. S ome blowdown sections are

closer to the drum s in some DCUs than are others. In DCU s with multiple drums, the blowdown

section is fart her away from some drums than from other drums. As a result, the pressure on a well

- quenched drum will be different from unit to unit and drum to drum.

L owering the back

- p ressure on a quenched coke drum below th e p ressure set by the DCU design

without in creasing cycle time require s significant changes in the mechanical hardware in the

DCU

. Generally

, this involves lowering the blowdown section operating pressure and/or reducing the pressure drop between the coke drum and the blowdown section (by upsizing long runs of large diameter pipe, adding eductors and/or compressors, and/or adding blowdown section cooling)

. Attachment 2 discusses the types of changes that might be required in more

detail

. Of course, the specific changes that will be needed will be different fr o m unit to unit and

drum to drum

. In addition to the typical problems associated with installing new facilities in an existing, congested unit without impacting production, a s the pressure is lowered in the blowdown section, there is increase d risk of creat ing a negative pressure somewhere in the

system

, and safeguards must be incorporated in to the design to prevent such an occurrence

.

Little data is available on the cost of reducing coke drum vent pressure from 5 psig to 2 psig

because the se changes are often done as part of larger projects and cannot easily be separated and

because each situation is different

. For some DCUs our member s report that there is no investment associated with meeting a 2 psig limit because they already are achie ving that level or because of their DCU’s design. Other members indicate that significant investments will be

needed.

One of our member s reports that the c ost to lower the coke drum outlet release pressure from 5 psig to 2 psig for one DCU was $3.7 milli on for steam eductors and additional blowdown fin fan

coolers. For this particular DCU, no investment in compression was required. Another member reports an investment of approximately $1.5 million for adding eductors to achieve 2 psig. On

the other han d, two members identified seven DCUs where an incremental investment of $5

- 8 million per DCU will be needed to meet a 2 psig criterion versus meeting a 5 psig criterion. This is consistent with the $6 million incremental investment EPA used in evaluating the 2 psig criterion versus a 5 psig criterion in the NSPS Ja rulemaking.

Even with these investments

, a lower vent pressure criterion may cause coke drum operating cycles to be longer, as it may take longer to reach the target vent pressure. Longer cycl e timesPage 4

can result in lower coker throughput and

, thus

, large refinery product production debits. These large lost opportunity costs have not been quantified in evaluating the cost effectiveness of DCU

vent limitations.

Conclusion

In summary, the increm ental investment cost for meeting a 2 psig vent criterion versus a 5 psig criterion likely ranges from no capital investment to at least $8 million dollars. E ven assuming a high emission reduction potential of 3 t ons of VOC 2 , where investment is needed, a nnualized

investment costs 3 alone will easily exceed $100,000 per ton of VOC reduced and the cost per ton will be much higher than that for those DCUs where more than $ 3.2 million investment is needed and when annual costs and lost production debits are in cluded. Costs per ton of HAP reduced will be even higher than the costs per ton of VOC

.

We believe that using coke drum pressure as the compliance factor is the correct approach and

that a release to the atmosphere criterion of no less than 5 psig is the appropriate target metric, based on the high costs associated with an industry

- wide standard of 2 psig as well as the small

emissions reduction benefit that would be expected with that lower threshold

.

Again, we appreciate the dialogue that we c ontinue t o have with you on this and other refinery

sector issues. Please let me know if you would like to discuss our analysis further.

Sincerely,

/s/

Matt hew Todd

cc Ms. Penny Lassiter

, US EPA

2 Five times what EPA calcu lated for a 2 coke drum DCU in the NSPS Ja rulemaking.

3 Based on 7% interest for 20 years (CRF = 0.094392926)Attachment 1

Coke Drum Emissions and Risk

Available stack test data do not demonstrate significant additional emissions reduction with a reduction in the coke drum atmospheric release criterion from 5 psig to 2 psig.

For example, if one considers the VOC and benzene vent data from the recent Re finery ICR

data 4 set as a function of pressure, it appears that

, within the scatter of the data, there is little potential reduction per drum opening.

4 The data set s include ExxonMobil, HOVENSA, Houston Refining, Marathon and Husky. Both the Houston Refining and the Husky data assume a nominal vent pressure of 5 psig as presented. HOVENSA data are indicated in red.Page 6

T he data from the HOVENSA report appears to be an outlier when compared to more recent
DCU vent tests with respect to both the magnitude of reported gaseous emissions and the length of the vent time (>2 hours) 5

. It is our understanding that the mass of PAH constituents emitted per coke drum venting used to estimate emissions under the ICR protocol ( and which are the risk drivers motivating changing the coke drum depressurization work practice ) were derived exclusively from the HOVENSA data set. For instance, as shown in the table below, e xamining

2

- methylnaphthalene, one can see that the 2.913 lb/ drum venting reported in the HOVENSA study contrasts significantly ( by more than 2 orders of magnitude in one case on a lb/ drum venting basis ) from the other available data

. Similarly, other hydrocarbons w ere significantly

lower in the new Part 4 ICR data sets when compared to the HOVENSA data set

. Th is comparison strongly suggest s that the HAP emissions and risk s calculated from emission

estimates based on the ICR Protocol are significantly overstated.

M easured Emission Rates for Four Hydrocarbons (Note: Methane and Ethan e are not VOCs or HAPs)

HOVENSA ExxonMobil Houston Refining Husky Marathon

2

- methylnaphthalene

(lb/ drum venting ) 2.913 0.256 0.0132167 0.727

-

Methane (lb/ drum venting ) 795.6 75.3 5.3 321 263

E thane (lb/ drum venting ) 168.6 21.4 0.77 54.9 67.2

B enzene (lb/ drum venting ) 11 0.341 0.012 1.9 0.76

5 The reasons for these differences are unknown, but the HOVENSA tests were among the first using a new protocol and the individual test runs showed significant differences, which su ggests possible operating or sampling problems.Page 7

Attachment 2

Coke Drum Vent Pressure Reduction Considerations

Once the drum is quenched, lowering the coke drum pressure below th e minimu m pressure set by the system design requires significant changes in the mechanical hardware in the unit. The required changes typical ly fall into two categories

– lowering the blowdown section operating pressure and reducing the pressure drop between the coke drum outlet and the blowdown section. The types of changes often needed are described as follows.

1. Lower the blowdown section operating pressure.

a. In most plants, the DCU blowdown section is designed to float on the relief (e.g.,
flare) header. Dep ending on the specific equipment configuration, installing
larger pipe between the blowdown system and the relief system (perhaps all the
way to the flare) may decrease pressure drop somewhat and allow the blowdown
operating system pressure to be reduced s omewhat . However, installing larger
diameter pipe can be very expensive where space is restricted by existing
equipment and/or the distance to the relief device (i.e., flare) is significant

. Also,
piping changes can only reduce blowdown system backpressure to the operating
pressure of the relief system or the relief system compressor suction, which may

not be much different than current ly achieved.

b. For some DCUs, a dditional fin fan coolers may be required in the blowdown

section to better condense coker ve nt steam and hydrocarbon to reduce the flow of
vapor out of the blowdown section to the relief system.

c. Where pressure drop is not the issue, a ddition of eductors and condensers in the
relief system to forcibly move material out of the blowdown section and into the
relief system may be required to lower the blowdown section pressure. Coke

drums and b lowdown systems are not typically designed to handle a vacuum, so
safeguards must be included to prevent the blowdown section pressure from
dropping too low.

d. Finally, compression may be needed to lower the blowdown section pressure
enough to meet the release criterion or to allow routing the vapors to higher
pressure dispositions such as fuel gas.

2. Lower the pressure drop between the coke drum and blowdown sect ion of the plant.

If, after getting the blowdown section operating pressure as low as possible, the coke drum
pressure is still too high, one or more of the following may be necessary to achieve a lower
coke drum outlet pressure.Page 8

a. Increase the diameter of some or all of the piping from the coke drum to the

blowdown section.

b. Addition of educators and condensers at the coke drum to forcibly move material

out of the drum and then into the blowdown section

.