Petroleum gas (LPG) recovery from gas streams

A process for recovery of C3+ hydrocarbons from gas streams containing C1, C2 and C3+, the process comprising:

• compressing a feed gas containing C1, C2 and C3+ to a pressure of 15 bar;
• adjusting temperature of the compressed feed gas to a temperature of 30° C.;
• feeding the compressed feed gas to a first membrane module;
• retrieving a permeate stream comprising a first C3+-rich stream from the first membrane module, the first C3+-rich stream comprising a higher content of C3+ than the feed gas;
• retrieving a retentate stream comprising a first C1- and C2-rich stream from the first membrane module, the first C1- and C2-rich stream comprising a higher content of C1 and C2 than the feed gas;
• recycling a remaining amount of C3+ in the first C1- and C2-rich stream by enriching the C1- and C2-rich stream in a second membrane module, comprising:
• feeding the first C1- and C2-rich stream to the second membrane module;
• retrieving a retentate stream comprising a second C1- and C2-rich stream from the second membrane module, the second C1- and C2-rich stream comprising a higher content of C1 and C2 than the first C1- and C2-rich stream;
• extracting a second C3+-rich stream from the second membrane module, the second C3+-rich stream comprising a permeate stream from the second membrane module;
• and
• recycling the second C3+-rich stream to the first membrane module by mixing the second C3+-rich stream with the feed gas;
• compressing the first C3+-rich stream to a pressure of 15 bar;
• forming a two-phase stream by cooling the compressed first C3+-rich stream to a temperature of 30° C.;
• separating the two-phase stream to a liquid phase of the two-phase stream and a vapor phase of the two-phase stream in a separator unit at a constant temperature of 30° C., the liquid phase of the two-phase stream forming a separator-liquid C3+-rich stream comprising a higher content of C3+ than the first C3+-rich stream;
• removing volatile compounds from the separator-liquid C3+-rich stream, comprising:
• feeding the separator-liquid C3+-rich stream to a distillation column;
• performing a distillation process in the distillation column, comprising:
• withdrawing a liquid stream from a bottom of the distillation column;
• generating a vapor flow by heating the withdrawn liquid stream in a reboiler unit to a temperature in a range of 55° C. to 75° C. using the compressed feed gas as a thermal energy source, the vapor flow comprising the volatile compounds of the separator-liquid C3+-rich stream;
• and
• returning the generated vapor flow to the distillation column;
• and
• withdrawing a bottoms C3+-rich stream comprising a liquid flow from the reboiler unit, the liquid flow comprising non-volatile compounds of the separator-liquid C3+-rich stream with a higher content of C3+ than the separator-liquid C3f-rich stream;
• and
• recovering a C3+ content remaining in the vapor phase of the two-phase stream and a vapor outlet from a top of the distillation column, comprising:
• forming an overhead stream by mixing the vapor phase of the two-phase stream and the vapor outlet from the top of the distillation column;
• feeding the overhead stream to a third membrane module;
• and
• recycling a permeate stream from the third membrane module to the first membrane module by mixing the permeate stream from the third membrane module with the feed gas.