Page 1 of 5 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: Scrubber Dump Valves Memo

Summary: This document provides background on transmission scrubber dump valve emissions and why this source warrants m onitoring in the Final Rule.Page 2 of 5 Scrubber Dump Valves

EPA has elected to include transmission st orage tanks in Subpart W of the Greenhouse Gas Reporting Rule (GHGRP) as an emissi on source for reporting because there is information suggesting malfunctioning scrubbe r dump valves can vent a significant amount of gas through the compressor station condensate tanks. This document provides background on scrubber dump valve emissions and why this source warrants monitoring

in the Final Rule.

Scrubber dump valves, when stuck open, allo w the gas feed to a compressor to blow through a condensate tank and out the tank vent. Scrubber dump valves were not identified in the EPA/GRI 1996 Study, and ther efore, are not an emission source in the U.S. Inventory 1 . Natural Gas STAR 2 Partners have stated th at scrubber dump valves represent one of the larges t leaking components found at natural gas transmission stations. EPA believes that malfunctioning scru bber dump valves contribute significantly to transmission storage tank emissions simila r to how malfunctioning gas-liquid separator dump valves may contribute to onshore production tank emissions. EPA expects the

GHGRP will collect sufficient information a nd data on the significance of transmission compressor scrubber dump valve malfunctions to inform future policy at minimal additional burden to the petrol eum and natural gas industry.

I. The Scrubber Dump Valve Emission Source

Scrubber dump valves open periodically to reduce the accumulation of condensate liquids

in the scrubber. Scrubbers are located imme diately before compressors to remove any liquids in the natural gas that may harm the compressor. The natura l gas feed enters and contacts the cool metal wall or demister pad of the scrubber. The slightly cooled or filtered natural gas rises and exits the top of the scrubber while any liquids entrained in or condensed from the gas will drop out as condensate and accumulate at the bottom. When

the accumulated condensate reaches a set leve l, a level controller opens the scrubber dump valve to allow the condensate to flow under scrubber pressure typically to an atmospheric tank. When the condensate falls to a set low level, a properly functioning dump valve closes, as diagramed in Exhibit 1.

1 EPA. (2007) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006 . Online at <http://epa.gov/climatechange/emissions/downloads/08_CR.pdf>

2 http://www.epa.gov/gasstar/Page 3 of 5 Exhibit 1. Scrubber Diagram

Some instances have been reported of dump valves remaining open after the liquid level has fallen below the set point, allowing na tural gas from the scrubber to continuously flow through the dump valve ultimately passi ng through the storage tank’s atmospheric vent. This may occur because debris or an equipment malfunction prevents the scrubber dump valve from closing properly. An impr operly closed scrubber dump valve can be a significant source of methane emissions because , for an extended period, a portion of the natural gas compressor feed is esse ntially vented to the atmosphere.

Transmission scrubber dump valves are not included in the U. S. Inventory as an emission source. In the Technical Support Do cument (TSD) (EPA-HQ-OAR-2009-0923) the source selection analysis decision tree was not necessarily ideal for scrubber dump valves

because it is known to be underestimated in cu rrent inventories. Therefore, the decision

tree was overridden and this source was included in the reporting rule.. EPA’s knowledge of scrubber dump valves consists of presentations by Natural Gas STAR

Partners.

II. Evidence that Scrubber Dump Valves are a Significant Emission Source

Natural Gas STAR Partners have experien ced leaking scrubber dump valves as an

emission source. One Natural Gas STAR Part ner who inspected and quantified emissions from transmission stations using an IR camera and high volume sampler stated that scrubber dump valves leaking through conde nsate tanks were their largest source of emissions, exceeding emissions from reciprocating compressor rod packing andPage 4 of 5 blowdown valves. 3 In addition, Heath Consultant s Inc. conducted a transmission compressor station measurement study that showed emissions from scrubber dump valves contributing more than 90 pe rcent of the total emissions. 4 Exhibit 2 shows this result.

Exhibit 2. Natural Gas STAR Transmis sions Compressor Station Emissions

Webcast

For transmission scrubber dump valves, as the emission point is distant from the malfunctioning valve, the gas is not detectible by sound, sight or smell (unless sour production gas) and remote, unmanned faciliti es may experience such undetected gas blow-through for long periods of time. Dump valves on scrubbers open when the liquid

level in the vessel is above a set level and close when the liquid level in the vessel is below a set level, but still c overing the drain nozzle. If th e dump valve malfunctions and remains open, the gas entering the vessel will partially exit through the dump valve. And since scrubber dump valves t ypically allow liquid to pass to a storage tank, bypassed gas will also pass to the storage tank and ultimately through the tank vent, into the atmosphere.

Based on this evidence, EPA chose to requi re natural gas transmission reporters to inspect for malfunctioning scrubber dump valves and quantify emissions from transmission storage tanks for which ups tream scrubber dump valves have been

determined to malfunction.

3 EPA. Methane Savings from Compressors . Compressors Technology Transf er Webcast. Presentation. 18

Jan. 2006. Slide 36

4 EPA. Methane Savings from Compressors . Compressors Technology Transf er Webcast. Presentation. 18

Jan. 2006. Slide 39 Dump Valves $14,651,510 Rod Packing $1,034,090 Standardized Components

$207,170 Unit Valves

$445,320

Pressure Relief

Valves $62,980 Blow Down

Valves $223,582

Heath Consultants Inc. 2005 321 Leak Sources

1.6 Bcf $10/McfPage 5 of 5 III. Reporting Scrubber Dump Valve Emissions in Subpart W

Subpart W requires onshore natural gas tran smission reporters to annually view their storage tank vents with an optical leak imag ing camera during the annual leak inspection. Only when emissions are viewed continuously for 5 minutes or through-valve leakage is detected, the reporter is require d to directly measure the tank’ s emissions with a meter or each dump valve’s through-valve leakage with an acoustic detection device which has correlation factors for through-va lve leakage. Alternativel y, operators can inspect the dump valves individually for leakage using an acoustic leak detection device.

Summary

In summary, EPA included scrubber dump valv es via transmission storage tanks in the

Final Rule because Natural Gas STAR Partners have demonstrated them to be a significant emission source in onshore natura l gas transmission. EPA incorporated reporting scrubber dump valve emissions in subpart W while keeping the additional burden to reporters at a minimum. Given th e highly uncertain, yet significant emissions from scrubber dump valves, EPA expects to gather sufficient information on the significance of this source’s emi ssions to inform future policy.