Cryogenic process for crude helium recovery from natural gas

A cryogenic process to produce crude helium from pretreated natural gas consisting of 80-98 mole % methane, 3-20 mole % methane plus hydrocarbon, 0.1-5.0 mole % nitrogen %, 0.01-0.5% mole % helium, 1-10 ppmv H2S, 5-50 ppmv water, wherein said process comprising the steps of:

• a) subjecting the pretreated natural gas (1) to a first cooler (E1) for its cooling in the temperature range of minus 85-minus 140° C.;
• b) subjecting a partially condensed gas (2) to a throttling device (TD) to reduce its pressure and generating cold and routing a stream (2A) from the (TD) to a first flash stage (FSI) or the partially condensed gas (2) direct routing to the first flash stage (FSI) for generating an uncondensed gas stream (3) and a liquid stream (4);
• c) subjecting the uncondensed gas stream (3) for its cooling in a second heat exchanger (E2), which uses a cold process liquid stream (7) and external cold utility (ER1) in the temperature range of minus 100-minus 150° C.;
• d) subjecting a second partially condensed gas stream (5) to a second flash stage (FSII), which has 2-6 trays below a feed entry location and use a helium free stripping stream (19) to generate in the second flash stage (FSII) a gas stream (6) and the cold process liquid stream (7);
• e) subjecting the gas stream (6) to a multi stream third heat exchanger (E3) for its heating;
• f) subjecting a heated gas stream (6A) along a high-pressure purge stream (15D) having a pressure in the range of 6-20 bars from a purification system (PS) to a gas compressor (K2) for increasing combined streams pressure in the range of 20-50 bars;
• g) subjecting a pressurized gas stream (8) emanating from the gas compressor (K2) to a water or air cooler (E6), subsequently cooling of a gas stream (9) emanating from the water or air cooler (E6) is fed to the multi stream third heat exchanger (E3) using either process cold streams or both process cold stream and external utility, cooling of a stream (10) in a fourth heat exchanger (E5) and then a stream (11) from the fourth heat exchanger (E5) is again routed to the multi-stream heat third exchanger (E3) for its cooling and producing a partially condensed stream (12) having a temperature in the range of minus 85-minus 140° C.;
• h) subjecting the partially condensed gas stream (12) emanating from the multi-stream third heat exchanger (E3) to a distillation column (DC) having multiple trays in its stripping and rectification sections and having the process stream and/or external utility coils cooler (E6) inside the distillation column (DC) overhead section to generate an in situ liquid for a rectification section;
• i) cooling a gas stream (13) emanating from the distillation column (DC) in a fifth heat exchanger (E4) for its partial condensation;
• j) subjecting a cooled gas stream (14) emanating from the fifth heat exchanger (E4) to a separating vessel (V1) for generating the crude helium (15) and the reflux liquid stream (16) used as a reflux stream in a top section of the distillation column (DC);
• k) recycling a low pressure purge stream (15C) having a pressure in the range of 1-10 bars from the purification system to a first pressure increasing device (K3) to produce an increased pressure stream (15E), which is further routed to a gas compressor (K2);
• l) Recycling a high pressure purge stream (15D) having pressure in the range of 8-20 bars from the purification system to the gas compressor (K2);
• m) splitting the distillation column (DC) bottom liquid stream (17) into two streams (18) and (20);
• n) subjecting the stream (18) to a throttling valve/expender (PV1) to generate a low-pressure stream (18A), which is routed to the multi stream third heat exchanger (E3) for its cold recovery;
• o) Subjecting the stream (20) to a throttling valve/expander (PV2) to generate a low-pressure stream (20A), which is routed to a fifth heat exchanger (E4) for its cold recovery;
• p) subjecting a stream (20B) either to a cold utility generation system or to the multi stream third heat exchanger (E3) for its cold recovery;
• q) subjecting a stream (7C), stream (18B), stream (20B) or (20B1) to a cold utility generation system (CUGS) for recovering their cold;
• r) subjecting a stream (20C) to a second pressure increasing device (K4) with or without a stream (7D);
• s) subjecting a stream (7E) from the second pressure increasing device (K4) to a second gas compressor (K1) for recycling the hydrocarbon stream for further processing and utilization;
• t) recycling third stream (18D), increased pressure stream (21), and second process stream (7D) to upstream process for further processing and utilization.