Question

A natural gas processing plant uses a flare to control acid gas (gas containing high H2S) releases. A release event for an acid gas stream to the flare contained 0.15 % ( dry volume) H2S at flowrate of 1,000 dscfm (gas industry standard is 60F at 14.7 psia). Flare destruction efficiency is 98% (ie 98% of H2S is oxidised into SO2). The release lasted 8 hours. What are the total emission rates of SO2 and H2S for the event?

Answer 1

Release of H2S to flare = Total gas rate * H2S mole fraction in gas

= 1000*0.15/100 = 1.5 dscfm

Release of H2S from flare = H2S to flare* (1- flare destruction efficienncy/100)

= 1.5*(1-98/100) = 0.03 dscfm

not for 8 hours or 8*60 = 480 minutes, H2S released/emissioned = 0.03*480 = 14.4 dscf

Now for SO2:

since 98% of H2S to flare is converted to SO2

so SO2 rate from flare = H2S rate to flare*98/100 = 1.5*98/100 = 1.47 dscfm

now in 8 hours time = 8*60 =480 minutes, total SO2 emissioned = 1.47*480= 705.6 dscf