BORSIG propylene and nitrogen recovery

After separating the condensate, the remaining purge gas is fed into the membrane system while the permeate side of the membrane separation stage is fed back to compressor’s suction side. By means of the resulting pressure difference and the hydrocarbon selective membrane material, the purge gas stream is separated into the purified nitrogen stream and the recycled propylene-rich permeate stream. A small part of the separated stream is sent to the flare to prevent accumulation of lighter components. In some cases a hydrogen-selective membrane stage is used in order to meet the requirements of the highly purified nitrogen. In principal this stage is installed downstream of the hydrocarbon-selective membrane stage.