FROM: Jeff Coburn, Leslie Pearce and Kevin Bradley

TO: Brian Cook, EPA/OAR/CCD

DATE: July 10, 2015

SUBJECT: Proposed Changes to Flare Pilot Gas Reporting Requiremen ts under the

Greenhouse Gas Reporting Program (GHGRP)

1. Purpose
The purpose of this memorandum is to provide recommendations to clarify the reporting requirements for greenhouse gas (GHG) emissions associat ed with flare pilot gas use under Subparts Q, X and Y.
2. Background
Flares are used in a variety of industries to dispose of was te gases generated at the facility either during normal operations or due to startup, shutdown, or malfu nction (SSM) events. Flares can emit significant quantities of carbon dioxide (CO 2 ) as a result of hydrocarbon combustion. They may also emit methane (CH 4 ), primarily as a result of methane in the waste gas that remains uncombusted, and small amounts of nitrous oxide (N 2 O) as a combustion byproduct. On October 30, 2009, the U.S. Environmental Protection Agency (E PA) promulgated mandatory greenhouse gas reporting requirements (74 FR 56260; 40 CFR part 98) f or a variety of GHG emission sources. Flares were specifically excluded fro m the General Stationary Fuel Combustion Sources source category (40 CFR part 98, subpart C); however, other industrial source categories could require reporting of GHG emission s from flares and could refer to the calculation methods in subpart C, if deemed appropriate. Th e following subparts (in 40 CFR part 98) require reporting of emissions, at least to some exten t, from flares: subparts Q, W, X, Y, HH, II, and TT. The EPA is proposing to amend the rule to a llow, but not require, facilities to exclude pilot gas from the flare gas GHG emissions calcu lations in Subparts Q, X, and Y. Purge/sweep gas would still be included in the flare GHG emis sions calculations. This change would not impact reporting of emissions from flares under other Subparts.
3. Flare Terminology and Operation
Flares can be used to dispose of gases that are consiste ntly generated and have relatively constant flow, but they are often used to dispose of gases that ar e generated due to transient operations, such as batch processes or SSM events. Consequently, f lares may often operate with little to no waste gas flow. To ensure oxygen does not enter into the flare stack or flare gas header system, some amount of gas is added to the flare header or to the b ase of the flare stack; this gas is often referred to as purge or sweep gas. To ensure the waste gases exiting the flare ignite once they do mix with ambient air, flares operate with pilot flam es at the perimeter of the flare tip. Large diameter flares may have numerous pilot flames at diff erent points around the perimeter of theTechnical Memorandum – Proposed Changes to Flare Pilot Gas Reporting Requirements July 10, 2015

2 flare tip. Many industries, such as refineries and petroch emical facilities are required to continuously operate the flare pilots, regardless of was te gas flow. Other industries may use flares with automated flare ignition systems, in these systems, a spark ignition source is fired (similar to an automatic lighting system for a gas grill ) to ignite the flare gas either at regular intervals or during times when a significant flare was te gas flow is detected.
To clarify the discussion of flares and flare emissio ns sources, we will use the following terminology to describe potential sources of flare GHG e missions.

• Flare waste gas. This is the excess gas generated at th e facility that needs disposal. This is the gas the flare was installed to treat/destroy.

• Purge/sweep gas. This is the gas that must be added to the flare header system or to the base of the flare in order to prevent oxygen ingress durin g periods of low waste gas flow.

• Pilot gas. This is the gas used to maintain a pilot fla me at the flare tip.
The amount of purge/sweep gas needed is dependent on the com plexity of the flare gas header system and the flare diameter and tip design. Flares ge nerally require at least 0.1 to 0.2 foot per second (ft/s) flow velocity at the tip to prevent oxygen ingress (Bai et al., 2014), but can be significantly higher for flares with complex header s ystems. For a 2 foot diameter flare, this translates to a minimum flow of 1,100 to 2,200 cubic feet pe r hour or 1 to 2 million British thermal units per hour (mmBtu/hr). The recommended minim um heat rate for industrial flare pilots is 0.045 mmBtu/hr (Bellovich et al., 2007), suggesting fla re pilots would not contribute significantly to emissions even during long periods of sta ndby (no direct waste gas flow).
4. Relative Impact of Excluding Flare Pilot Gas from GHG Rep orting Requirements
GHG emissions from flare pilots is expected to be smal l in most cases. In efforts to estimate the relative contribution of flare pilot gas to flare emis sions, we developed engineering estimates of flare emissions specifically for petroleum refineries as additional information is available for petroleum refinery flares through a detailed information c ollection request (ICR) of petroleum refineries conducted by the EPA (EPA, 2011).
Flare Pilot Gas Usage Estimates
As noted previously, the recommended minimum heat rate f or industrial flare pilots is approximately 0.045 mmBtu/hr (Bellovich et al., 2007). For cost ing purposes, the EPA recommends an average flare pilot use rate of 70 scf/hr (EPA, 2002), which is essentially 0.07 mmBtu/hr. The number of pilot burners required depends on flare size and, possibly, on flare gas composition and typical wind conditions. The EP A provides the following general guide for the number of pilot burners by flare size (EPA , 2002):

• 1 pilot for flare tip diameters of 1 to 10 inches

• 2 pilots for flare tip diameters of 12 to 24 inches

• 3 pilots for flare tip diameters of 30 to 60 inches

• 4 pilots for flare tip diameters greater than 60 inchesTechnical Memorandum – Proposed Changes to Flare Pilot Gas Reporting Requirements July 10, 2015

3 The GHGRP does not collect data on flare tip diameter, but this information was collected as part of the refinery ICR (EPA, 2011). We developed model fla res of 0.5, 1.5, 3.5, and 6 feet to correspond with the flare tip diameter ranges used to esti mate the number of pilots. We used the refinery ICR data to develop a proportionate number of fl ares for each size range. In the ICR database, there were numerous flares with flare diame ters well over 12 feet. In reviewing these data, we expect that several facilities reported their flare diameter in “inches” rather than in “feet”. Consequently, we divided the reported flare diamet er by 12 for all flares that reported a diameter of 9 feet or more to correct data that appeared to be reported in “inches” rather than in “feet.” We also evaluate the size distribution of fl ares that were reported to be “routine flow” flares and compared that to the size distribution of fl ares used only for startup, shutdown, or upsets. The size distribution was very similar, so we developed a single weighting factor for each model flare size: 10 percent very small, 36 percent small, 52 percent medium and 2 percent large for model flare diameters of 0.5, 1.5, 3.5 and 6 feet, res pectively.

The CO 2 emissions from flare pilot usage was estimated using an average heat rate of 0.07 mmBTU/hr per pilot times the number of pilots for a given model flare size times the number of flares of that size times the default flare CO 2 emissions factor of 60 kg/mmBtu.
Flare Purge Gas Usage Estimates

As described in the Section 3 of this memorandum, flares generally require at least 0.1 to 0.2 ft/s flow velocity at the tip to prevent oxygen ingress (Bai e t al., 2014). There are flare tip designs with internal gas seals or “molecular seals” (also known as density or labyrinth seals) that allow much lower flare tip velocities ranging from 0.001 to 0.04 ft/ s (EPA, 2002; John Zink, 1998). No information is available from the GHGRP regarding the pr evalence of use of molecular seals. A molecular seal system adds weight to the flare tip, re quiring more structural support for the flare stack (Coburn, 2013). The molecular seal and additional str uctural support can add significantly to the costs of the flare. Consequently, molecular sea l systems are most commonly used for larger flares that were originally expected to have a lim ited hours of waste gas flow (i.e., flares where the monetary savings in purge gas usage reductions exce eds the additional capital costs of the flare with a molecular seal).
The GHGRP does collect data on flare service type (gene ral facility flare, unit flare, emergency only flare or back-up flare). We expect that the larger flares with no routine gas flow (emergency only or back-up flares) would be the most like ly to use molecular seals to reduce fuel gas or natural gas consumption. We consider it very unlikely that a molecular seal would be used for a 6 inch (0.5 feet) diameter flare, but for all other model flare sizes, we assumed a purge flare tip velocity of 0.02 ft/s for emergency only and back-up flares. For all general facility and unit flares and for the very small emergency flares, we used a purge flare tip velocity of 0.15 ft/s. The CO 2 emissions from flare purge gas was estimated as the produc t of the cross-sectional area of the flare, the flare tip velocity, the number of f lares of that size, an assumed heat content of the gas (1,000 Btu/scf), and the default flare CO 2 emissions factor of 60 kg/mmBtu.
Refinery Flare CO 2 Emissions
The GHGRP data for the 2013 reporting year (RY2013) was queried to determine the number of flares and the corresponding CO 2 emissions. Table 1 provides a summary of the results as wellTechnical Memorandum – Proposed Changes to Flare Pilot Gas Reporting Requirements July 10, 2015

4 as a summary of the CO 2 emissions estimated for each of the model flares. The proportion of emissions from flare pilot gas was compared to the emi ssions estimated for flare purge gas and to the total flare emissions reported in Subpart Y. As see n in Table 1, for larger flares, CO 2 emissions for purge gas are significantly higher than fro m pilot gas. Overall, including flare pilot gas may increase the total flare emissions reported under Subpart Y by 1 to 2 percent.

Table 1. Summary of CO 2 Emission Estimates for Flares and Flare Pilot and Purge Gas

Model Flare a Flare Diameter (ft) Number of

Flares b CO 2

Emissions From Pilot Gas Usage (Mg/yr) CO 2

Emissions From Pilot Gas Usage (Mg/yr) Pilot Gas

CO 2 Ratio to Total Pilot and Purge Gas CO 2 (%) Very small, routine flare 0.5 38 1,398 2,118 40% Small, routine flare 1.5 136 10,007 68,212 13% Medium, routine flare 3.5 197 21,744 537,949 4% Large, routine flare 6 8 1,177 64,199 2% Very small, emergency flare 0.5 8 294 446 40% Small, emergency flare 1.5 30 2,208 2,006 52% Medium, emergency flare 3.5 44 4,857 16,020 23% Large, emergency flare 6 2 294 2,140 12%

Model Flare a CO 2 Emissions From Pilot Gas Usage (Mg/yr) CO 2

Emissions From Pilot Gas Usage (Mg/yr) Pilot Gas

CO 2 Ratio to Total Pilot and Purge Gas CO 2 (%) Total CO 2

Emissions Reported in RY2013 (Mg/yr) Pilot Gas

CO 2 Ratio to Total GHGRP CO 2 (%) All routine model flares 34,327 672,478 4.9% 2,639,7 10 1.3% All emergency model flares 7,653 20,612 27.1% 162,32 3 4.7% All model flares 41,980 693,091 5.7% 2,802,033 1.5%

a Routine flares are those designated as either gene ral facility flare or unit flare in the GHGRP; emer gency flares are those designated as either emergency only flare or back-up flare in the GHGRP.

b Number of flares reported in the GHGRP classified a s routine (379) or emergency (84) times the proport ion of flares of that size based on the data reported in t he refinery ICR (EPA, 2011).

5. References
Bai, Yong-Zhong, P. Wang, and J. Jiang. 2014. “Determinatio n of the minimum safe purge gas flow rate in flare systems with a velocity seal.” Chemistry & Technology of Fuels & Oils
, Vol. 49 Issue 6, p. 474. January.

Bellovich, J., J. Franklin and B. Schwartz. 2007. “Flare pilot system safety.” Process Safety Progress, Vol. 26, No. 1, p. 10-14. March. Available at http://www.johnzink.com/wpcontent/uploads/Flare-Pilot-Safety.pdf

.Technical Memorandum – Proposed Changes to Flare Pilot Gas Reporting Requirements July 10, 2015

5 Coburn, J. 2013. “Meeting Minutes for February 13, 2013, Meeti ng Between the U.S. EPA and Representatives from John Zink Hamworthy Combustion.” Mem orandum from Jeff Coburn, RTI International, to Andrew Bouchard and Brenda Shine, EP A/OAQPS/SPPD. Dated February 18, 2013. Docket ID No. EPA-HQ-OAR-2010-0682-0219.
EPA (U.S. Environmental Protection Agency). 2002. EPA Ai r Pollution Control Cost Manual. Sixth Edition. EPA/452/B-02-001. Office of Air Quality Planning a nd Standards, Research Triangle Park, North Carolina. Vol. 49 Issue 6, p. 474. Januar y.
EPA (U.S. Environmental Protection Agency). 2011. “Non-CB I compiled database of all Component 1 submittals” based on Refinery Information Colle ction Request (ICR) for Calendar Year 2010. Available at: http://www.epa.gov/ttn/atw/petref/petrefpg.html

. John Zink Company. 1998. “Purge Conservation Systems.” Bulle tin 5085B 2M298. Available
at http://www.johnzink.com/wp-content/uploads/flar_purge.pdf

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