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US-12623905-B2 - Cryogenic process for crude helium recovery from natural gas

US12623905B2US 12623905 B2US12623905 B2US 12623905B2US-12623905-B2

Abstract

The present invention relates to a cryogenic process to produce crude helium from pretreated natural gas. The pretreated natural gas is processed in two flash stages using the helium free process stream as a stripping agent, and a distillation column with the identified operating conditions and process scheme to ensure 100% helium recovery with reduced capital and operating cost for producing the crude helium. The integration of the cryogenic process with the already known purification system to produce pure helium is demonstrated to ensure high helium recovery in a hybrid process.

Inventors

  • Sunil Kumar
  • Bharat S. Mendhe
  • Nammi Ramya
  • Avinash S. Mhetre
  • Ojasvi SHARMA
  • Swapnil Diveker
  • Soumen Dasgupta
  • Manoj Srivastava
  • Anjan Ray
  • Aarti Arya
  • Prasenjit Ghosh

Assignees

  • COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
  • ONGC ENERGY CENTRE TRUST (OECT)

Dates

Publication Date
20260512
Application Date
20230605
Priority Date
20220606

Claims (10)

  1. 1 . 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 (E 1 ) 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 ( 2 A) 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 (E 2 ), which uses a cold process liquid stream ( 7 ) and external cold utility (ER 1 ) 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 (E 3 ) for its heating; f) subjecting a heated gas stream ( 6 A) along a high-pressure purge stream ( 15 D) having a pressure in the range of 6-20 bars from a purification system (PS) to a gas compressor (K 2 ) for increasing combined streams pressure in the range of 20-50 bars; g) subjecting a pressurized gas stream ( 8 ) emanating from the gas compressor (K 2 ) to a water or air cooler (E 6 ), subsequently cooling of a gas stream ( 9 ) emanating from the water or air cooler (E 6 ) is fed to the multi stream third heat exchanger (E 3 ) using either process cold streams or both process cold stream and external utility, cooling of a stream ( 10 ) in a fourth heat exchanger (E 5 ) and then a stream ( 11 ) from the fourth heat exchanger (E 5 ) is again routed to the multi-stream heat third exchanger (E 3 ) 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 (E 3 ) 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 (E 6 ) 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 (E 4 ) for its partial condensation; j) subjecting a cooled gas stream ( 14 ) emanating from the fifth heat exchanger (E 4 ) to a separating vessel (V 1 ) 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 ( 15 C) having a pressure in the range of 1-10 bars from the purification system to a first pressure increasing device (K 3 ) to produce an increased pressure stream ( 15 E), which is further routed to a gas compressor (K 2 ); l) Recycling a high pressure purge stream ( 15 D) having pressure in the range of 8-20 bars from the purification system to the gas compressor (K 2 ); 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 (PV 1 ) to generate a low-pressure stream ( 18 A), which is routed to the multi stream third heat exchanger (E 3 ) for its cold recovery; o) Subjecting the stream ( 20 ) to a throttling valve/expander (PV 2 ) to generate a low-pressure stream ( 20 A), which is routed to a fifth heat exchanger (E 4 ) for its cold recovery; p) subjecting a stream ( 20 B) either to a cold utility generation system or to the multi stream third heat exchanger (E 3 ) for its cold recovery; q) subjecting a stream ( 7 C), stream ( 18 B), stream ( 20 B) or ( 20 B 1 ) to a cold utility generation system (CUGS) for recovering their cold; r) subjecting a stream ( 20 C) to a second pressure increasing device (K 4 ) with or without a stream ( 7 D); s) subjecting a stream ( 7 E) from the second pressure increasing device (K 4 ) to a second gas compressor (K 1 ) for recycling the hydrocarbon stream for further processing and utilization; t) recycling third stream ( 18 D), increased pressure stream ( 21 ), and second process stream ( 7 D) to upstream process for further processing and utilization.
  2. 2 . The process as claimed in claim 1 , wherein the methane plus hydrocarbon is selected from ethane, propane, butane, isobutene, pentane, iso-pentane and hexane in any proportion.
  3. 3 . The process as claimed in claim 1 , wherein the distillation column (DC) is operating, preferably in the pressure range of 20-50 bars and most preferably in the temperature range of 20-40 bars.
  4. 4 . The process as claimed in claim 1 , wherein in another embodiment of the present invention, the throttling device (TD) is represented by throttling valve or expansion valve or similar device and the first pressure increasing device (K 3 ) is represented by a compressor or ejector using compressing process stream ( 6 A), wherein the first pressure increasing device (K 3 ) may be single-stage or multistage with inter stage cooling.
  5. 5 . The process as claimed in claim 1 , wherein the second pressure increasing device (K 4 ) is represented by a compressor for compressing the stream ( 20 C) or ejector using compressing process stream ( 7 D).
  6. 6 . The process as claimed in claim 1 , wherein the crude helium stream ( 15 ) after its cold recovery in the cold utility generation system (CUGS) is subjected to a known purification system (PS) for producing the pure helium stream ( 15 B).
  7. 7 . The process as claimed in claim 6 , wherein the purification system (PS) is either membranes or pressure swing adsorption or vacuum swing adsorption or a combination of thereof.
  8. 8 . The process as claimed in claim 1 , wherein the gas stream ( 13 ) from the top of distillation column (DC) is cooled in the fifth heat exchanger (E 4 ) using either process cold streams ( 20 A) and external refrigeration stream (ER 2 ) in the temperature range of minus 150-minus 185° C. or process cold streams ( 20 A) in the temperature range of minus 140-minus 165° C.
  9. 9 . The process as claimed in claim 1 , wherein stream ( 20 B) is subjected to the multi stream third heat exchanger (E 3 ) for its cold recovery prior to its routing to the (CUGS).
  10. 10 . The process as claimed in claim 1 , wherein external cold utility stream (ER 1 A) ( FIG. 2 ) from the (CUGS) is used in the multi stream third heat exchanger (E 3 ) to reduce stream ( 12 ) temperature in the range of minus 85-minus 120° C.

Description

FIELD OF THE INVENTION The present invention relates to a cryogenic process for crude helium recovery from natural gas. More particularly, the present invention relates to the processing scheme of a cryogenic process for natural gas to produce the crude helium with 100% helium recovery and to enhance helium recovery by minimizing the helium loss in a hybrid process consisting of the cryogenic process of the present invention and a known purification system, with reduced helium production capital and operating costs. BACKGROUND OF THE INVENTION Helium is a unique gas with a wide range of important medical, scientific and industrial applications based on helium's extremely low boiling temperature, inert and non-flammable nature and small molecular size. Most of the helium is produced from Natural Gas (NG). With the increasing world's demand for helium, the value of NG fields, even with very small helium content, is likely to rise significantly if the helium can be recovered efficiently. The vol % of helium present in the natural petroleum gases in India is very low (˜0.05 vol %) than that of the USA, Poland, and Russia (3.00-7.00 vol %), which are treated as global suppliers of helium (Chaudhuri et al., 2010). Despite low helium content, the large volume availability of NG makes it the most potential and practical source for helium production in (Nisith K. Das, R. K. Bhandari, 2020). The major components in the natural gases are nitrogen and methane, higher hydrocarbons, carbon dioxide, moisture, along with helium. Most of the process for helium recovery from natural gas includes NG pretreatment step for impurities (water vapour, CO2, water, H2S, higher hydrocarbon, etc) removal followed by helium up-gradation step through nitrogen and hydrocarbon rejection and subsequent purification step to produce the pure helium. Most of the potential reported processes for helium up-gradation step to produce crude helium are either standalone cryogenic or a combination of cryogenic and PSA or cryogenic and membrane or membrane and PSA or their combinations. PSA is the most frequently used process for the purification of crude helium from NG to produce helium with a purity of more than 99.0% helium. The literature on helium production from natural gas revealed that cryogenic processes are one of the most processes used to produce crude helium from natural gas. PSA is suggested as the most widely used process for purifying crude helium to produce pure helium. Various cryogenic processes for producing crude helium from natural gas have been reported [Indian Patent No. IN237264, International patent Publication No. WO2013/015907A, United State patent No. U.S. Pat. No. 10,215,488B2, International patent Publication No WO2010/060533A1, International patent Publication No WO2016/130243A1. International patent Publication No. WO1988/008948A1, U.S. Pat. No. 3,653,220A, China State patent No. CN113735080A. United State patent No. U.S. Pat. No. 4,701,201A, United State patent No. U.S. Pat. No. 4,701,200A, China State patent No. CN113670002, United State patent No. U.S. Pat. No. 5,017,204]. The brief of processes reported in prior arts is described below. Reference may be made to Indian patent IN237264, wherein the natural gas comprising of helium (0.043%), methane (95.4%) and nitrogen (2.1%) and available at 58.6 bars and 22° C. is cooled in a heat exchanger using external cold utility and fed to a two-phase separator to generate vapour stream and a liquid stream disclosed. The vapour stream is further cooled and processed to generate the crude helium and liquid streams, further processed to generate the LNG and methane-rich gas for the generation of syngas. The helium recovery in crude helium in the examples of the proposed process is around 87-88%. The produced crude helium contains 46.8-63.35% helium, 29.9-45.8% nitrogen and 6.72-7.8% methane. Reference may be made to patent Application Publication No. WO2013/015907A1, wherein the compressed natural gas stream is passed through a cold box to condense liquids and the purification section to remove the impurities disclosed. The cooled gas comprising of methane (69.8%), nitrogen (28.1%) and helium (2.16%), and available at a temperature of −101.9° C. and pressure of ˜40 bars, is routed to a cryogenic stripper column. A raw helium product is removed from the top of the cryogenic stripper column, and the liquid product stream from the bottom. The liquid product stream may include a low BTU natural gas, which may be used to generate electrical power by its burning. The produced crude helium contains helium of 21.96-48.4%, methane of 2.2-28.9%, nitrogen of 49.1-49.4%. Reference may be made to US patent No. U.S. Pat. No. 10,215,488B2, wherein helium can be recovered from nitrogen-rich natural gas at high pressure with low helium loss by cryogenic distillation of the natural gas after pretreatment of the gas to remove incompatible impurities and then recovery of natural gas liquid (NGL)