Page 1 of 4 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

OFFICE OF
AIR AND RADIATION

Petroleum and Natural Gas Systems (Subpart W) of the Greenhouse Gas Reporting Rule Docket: EPA-HQ-OAR-2009-0923

Title: Equipment Threshold for Small Combustion Units

Summary: This memorandum describes the analysis that was conducted to set an equipment

threshold on small external combustion units.Page 2 of 4 

### Equipment Threshold for Small Combustion Units

In the final rule, EPA has set an equipment thre shold on sources with a ra ted heat capacity equal

to or less than 5 million British thermal units per hour (MMBtu/hr) on external combustion devices, below which only activity da ta is required to be reporte d. This equipment threshold was developed in response to several comments th at suggested small combustion devices with minimal fuel use should not be required to repo rt emissions using rigo rous and/or burdensome quantification methods. This memorandum describe s the analysis that was conducted to set an equipment threshold on small external combusti on units. This threshold does not apply to internal combustion engines or turbines.

Comments Commenters from onshore production and natural gas distribution have described the burden on owners and operators who must comply with the metering requirements under the Tier 3 methodology in subpart C of the Greenhouse Gas Reporting Rule, for minor combustion units including heat tracers, glycol de hydrator reboilers, separator heater s, crude oil he ater-treaters, and small tank heaters. Commenters suggested that these small combustion devices typically have an average heat rating of approximately 0.3 MMBtu/hr. In addition, EPA has proposed amendments to subpart C that w ould ease the Tier 3 requirements for combustion units less than

30 MMBtu/hr.

Expert Opinion EPA consulted experts to gather opinions on the distribution of equipmen t heat ratings in the onshore petroleum and natural gas production segment. Opinion was that a 5 MMBtu/hr equipment threshold would exclude 50% of ex ternal combustion devices, while a 10 MMBtu/hr equipment threshold would exclude nearly all external combustion units . Additionally, most

heater-treaters consume less than 5 MMBtu/hr and glycol dehydrator rebo ilers typically consume

0.4 MMBtu/hr.

Quantitative Analysis of Floor Options The objective in determining the equipment threshol d is to not require all of the small emission sources listed by the commenters as minor combustion devices. To test the thresholds suggested by experts and commenters, calculations were performed on glycol dehydrator reboilers, which

commenters listed as a small external combustion unit. The suggested equipment thresholds for

the external combustion devices were converted to dehydrator throughputs. Hence, the number of dehydrator reboilers excluded was determined.

Methodology

In the Natural Gas STAR Lessons Learned docum entation titled “Replacing Glycol Dehydrators with Desiccant Dehydrators 1 ,” partners are able to quantify th e fuel gas used by a glycol reboiler unit using Equation 1.

Mcf cf Hv yr days R Qr W F FGR / 1000 . 365

⋅ ⋅ ⋅ ⋅ ⋅

= Equation 1

1 http://www.epa.gov/gasstar/documents/ll_desde.pdfPage 3 of 4 where,

FGR = Fuel gas for reboiler (Mcf/yr)

F

= Gas flow rate (MMcf/d)

W

= Inlet minus outlet water content (lb/MMcf) Qr = Heat duty of reboiler (Btu/gal TEG) 2

Hv = Heating value of natural gas (Btu/scf) 3

R = Glycol-to-water ratio (gal TEG/lb water) 4

This equation can be rearra nged as shown in Equation 2.

hour/day R Qr W F
hour/day days/year Mcf cf Hv FGR Rate Heat 24 24 365 / 1000

⋅ ⋅ ⋅

=

⋅ ⋅ ⋅

= Equation 2

where Heat Rate is the combustion heat delivered by the fuel gas used in the reboiler each hour. Equation 2 can be further manipul ated to estimate the throughput of a glycol dehydrator with knowledge of the heat rate.

R Qr W hour/day Rate Heat F

⋅ ⋅ ⋅

= 24 Equation 3

Equation 3 was used to estimate the natural ga s throughput of a glycol dehydrator unit that requires a reboiler with a heat rate of 0.3 MMBtu/hr, 5 MMBtu/hr, and 10 MMBtu/hr. The percentage of dehydrators excluded was estimated using the calculated size of glycol dehydrators from the memo “Equipment Threshold for Dehydrators.”

The definition for external combustion is as follows:

External combustion means fired combustion in wh ich the flame and products of combustion are separated from contact with the process fluid to which the energy is delivered. Process fluids may be air, hot water, or hydrocarbons. External combustion equipment may include fired heaters, indus trial boilers, and commercial and domestic

combustion units.

The definition for internal combustion is as follows:

Internal combustion means the combustion of a fuel that occurs with an oxidizer (usually air) in a combustion chamber. In an intern al combustion engine the expansion of the high-temperature and –pressure gases produced by combustion applies direct force to a component of the engine, such as pistons, tu rbine blades, or a nozzle. This force moves the component over a distance, generating usef ul mechanical energy. Internal combustion

2 Based on calculation in Engineering Data Book, Volume II , 11th edition, Gas Processors Supply Association, 1998, Section 20-Dehydration.

3 Energy Information Administration (EIA), Monthly Engineering Review, Table A4.

4 From EPA's Lessons Learned: Optimize Glycol Circulation and Install Flash Tank Separators in Glycol Dehydrators.Page 4 of 4 equipment may include gasoline and diesel industrial engines, natural gas-fired reciprocating engines, and gas turbines.

Result

A reboiler with a 0.3 MMBtu/hr heat rate is asso ciated with glycol dehy drator with a throughput of 152.52 MMcf/day. This throughput is larger than approximately 99% of all glycol dehydrators in the onshore petroleum and natural gas pr oduction segment, based on the distribution of dehydrator sizes estimated in the memo “Equi pment Threshold for Dehydrators.” A 5.0 or 10.0

MMBtu/hr heat rate is associated with glycol dehydrators having throughputs of 2,542 MMcf/day and 5,084 MMcf/day, respectively. Both th ese heat rates do not include all onshore production glycol dehydrators. In addition, base d on comments from the natural gas distribution segment, this threshold would also not in clude small combustion units in distribution.

Table 1: Estimated throughput of glycol dehydrators and percentage of dehydrators below each threshold.

Heat Rate (MMBtu/hr) Throughput (MMcf/day) Percentage of Dehydrators Below

Threshold

0.3 152.52 99%

5.0 2,541.94 100%

10.0 5,083.88 100%

Conclusion An equipment threshold of 0.3 MMBtu/hr will not in clude 99% of all glycol dehydrators but will likely not eliminate from reporting all heater-treat ers as per expert opini on. EPA is aware that there are large external combustion equipment in some onshore production operations, , such as large steam boilers used for secondary recovery which can range from under 10 MMBtu/hr up to 40 MMBtu/hr, and in distribution internal comb ustion, such as compressors. EPA does not want to not include such equipment. As a result, the equipment threshold on external combustion devices was set at a rated heat capacity equal to or less than 5 MMBtu/hr.