Selexol stream compression

C02 can be separated from the shifted syngas stream in a Selexol type of absorber. Multistage flash drums can be used to extract C02 from absorbed solvents at various pressure levels typically ranging from atmospheric pressure to 400 psi. The C02 product stream is usually compressed to high pressure (llObar) for geologic storage or enhanced oil recovery. 

The amine unit is based on a 30% DEA solution. The feed gas is compressed to 285 psia and pretreated to remove heavy hydrocarbons. After passing through the DEA absorber, the sweet offgas is compressed to 650 psia and sent to the existing gas plant. The sour CO2 stream from the DEA stripper, at 20 psig, is compressed to 450 psia and sent to a Selexol sweetening process designed to reduce the H2S content of the CO2 product gas to less than 100 ppm. 

In the TEA bulk removal process, a TEA solution is used to remove the H2S and CO2 from the feed. The CO2 and H2S are then removed from the TEA solution by flashing it to about 20 psia. The TEA absorber overhead stream, containing about 20% CO2 and some H2S, is sent to a DEA unit for final clean up. The acid gas streams from the DEA unit and the TEA flash lower are compressed to 450 psia and sent to a Selexol unit for H2S removal. 

The membrane unit was designed to produce a permeate with a maximum of 5% hydrocarbons and a residue stream containing 20% CO2. The residue stream is sent to a DEA unit for cleanup. The acid gas from the DEA unit and the sour permeate streams are compressed and sent to a Selexol unit for H2S removal. To develop a range of costs, two cases were considered. The low cost case assumed a short membrane module life and a high permeation rate. The high cost case assumed a long module life with a lower permeation rate. 

---