Q487. How should an onshore natural gas processing facility report emissions from a membrane plant where CO₂ is removed from sweet gas and vented?

A487. Note that per 40 CFR 98.6, sour natural gas is natural gas containing concentrations of hydrogen sulfide and/or carbon dioxide that exceed the concentrations specified for commercially saleable natural gas. Therefore, if a membrane unit is used to remove CO₂ from natural gas that meets this definition of sour natural gas, then emissions must be calculated and reported as specified in 40 CFR 98.232(d)(5) and 40 CFR 98.233(d), as this process and its associated vented emissions meet the definitions of acid gas removal unit and acid gas removal vent emissions in 40 CFR 98.238, respectively.  Please see EPA-HQ-OAR-2009-0923-1298-18 in the Response To Comments (pages 1719 - 1720) https://www.regulations.gov/document?D=EPA-HQ-OAR-2009-0923-3608 for further details on the definitions of sweet and sour gas.

If the hydrogen sulfide and carbon dioxide concentrations both meet the specifications for commercially saleable natural gas prior to the membrane, the CO₂ emissions removed by the membrane plant are not reported under subpart W.