Integrated compression and membrane separation process for removal of CO2 from raw natural gas
A single compressor is used to separately compress permeate from cascaded first and second gas separation membrane-based separation units and residue from a fourth gas separation membrane-based separation unit in order to avoid too high a CO2 partial pressure in the compressed permeate. After the permeates from the first and second stages are compressed, the compressed stream is fed to a third gas separation membrane-based separation unit.
1. A method of removing amounts of CO 2 from CO 2 /hydrocarbon mixtures, said method comprising the steps of:
feeding a feed stream, comprising CO 2 and hydrocarbons, to a first gas separation membrane-based separation unit comprising one or more banks of one or more membranes arranged in parallel or in series that are selective for CO 2 over methane to produce, in comparison to a CO 2 content of the feed stream, a first CO 2 -enriched permeate stream and a first CO 2 -deficient residue stream;
withdrawing the first CO 2 -deficient residue stream from the first gas separation membrane-based seperation unit as product natural gas;
compressing the first CO 2 -enriched permeate stream in one or more compressors of a multi-stage compression unit comprising a plurality of compressors arranged in series to produce a compressed stream of the first CO 2 -enriched permeate stream;
feeding the compressed stream of the first CO 2 -enriched permeate stream to a second gas separation membrane-based separation unit comprising one or more banks of one or more membranes arranged in parallel or in series that are selective for CO 2 over methane to produce, in comparison to the compressed stream of the first CO 2 -enriched permeate stream, a second CO 2 -enriched permeate stream and a second CO 2 -deficient residue stream;
compressing the second CO 2 -deficient residue stream in one or more compressors of the multi-stage compression unit to produce a compressed second residue stream, the one or more compressors used to compress the first CO 2 -enriched permeate stream being different from the one or more compressors used to compress the second CO 2 -deficient residue stream;
feeding the compressed second residue stream to a third gas separation membrane-based separation unit comprising one or banks of one or more membranes that are selective for CO 2 over methane to produce, in comparison to the second CO 2 -deficient residue stream, a third CO 2 -enriched permeate stream and a third CO 2 -deficient residue stream;
withdrawing the second and third CO 2 -enriched permeate streams as one or more streams of product CO 2 ; and
combining the third CO 2 -deficient residue stream with a stream of a mixture of CO 2 and hydrocarbons, to produce the feed stream, the mixture of CO 2 and hydrocarbons including methane.
2. The method of claim 1 , wherein the stream of a mixture of CO 2 and hydrocarbons is raw natural gas that has been partially treated.
3. The method of claim 1 , wherein a pressure of the stream of a mixture of CO 2 and hydrocarbons ranges from 30-100 bar.
4. The method of claim 1 , wherein the stream of a mixture of CO 2 and hydrocarbons comprises 30-80 mol % CO 2.
5. The method of claim 1 , wherein the product natural gas comprises at most 20 mol % CO 2.
6. The method of claim 1 , wherein the one or more compressors are driven with a single drive.