Method of processing natural gas
Patent Information
- Application Number
- CA3268459
- Authority / Receiving Office
- CA · CA
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-03-21
- Publication Date
- 2026-10-08
Abstract
Description
1 METHOD OF PROCESSING NATURAL GAS TECHNICAL FIELD
[0001] This relates to a method of processing natural gas, and in particular, using a pressure exchanger to compress and / or decompress. 5 BACKGROUND
[0002] Natural gas is commonly used as a source of energy, and as used as a feedstock to produce various products. Natural gas is transported and treated in various ways to separate different components, and to achieve different states of matter. Natural gas is commonly transported in pipeline networks, which are highly integrated to delivers 10 natural gas from production areas to consumers worldwide. This integrated network that delivers gas over long distances and country borders require the use of compression stations between about 75 and 150 km to overcome pressure friction losses. The flowrate of gas transported through these pipeline networks is variable due to a variable consumer and seasonal demand. The operation and reliability of these compressor stations help 15 ensure the delivery of natural gas from producers to consumers.
[0003] Natural gas may also be liquefied. Liquid natural gas (LNG) is natural gas that has been cooled to a cryogenic condition to condense methane, the natural gas main component. A temperature of around -160ºC is required to produce and keep natural gas in a liquid state at standard atmospheric pressure. These temperature and pressure 20 conditions are the generally accepted definition of LNG. Liquefaction reduces the volume by approximately 600 times, thus making it more economical to transport over great distances versus traditional pipelines. LNG is also produced in small scale liquefaction plants to meet peak demands, as well as to make natural gas available to regions where it is not economical or technically feasible to build pipelines. In addition, liquefaction often 25 produces natural gas liquids (NGLs) made up of hydrocarbons that are heavier than methane, and liquefy at higher temperatures than methane.2
[0004] Large LNG plants typically seek to minimize capital costs, with minimizing energy consumption as a second objective. These two objectives can also go together; thus an optimization of the efficiency of the plant may involve a reduction in the investment of the equipment. On the other hand, a higher efficiency can result in an 5 increase in LNG production, so the efficiency factor has a significant impact on the plant economics. In small to medium LNG plants, it is often not efficiency, but other factors such as simplicity, modularization, ease of maintenance, operation and installation that are given more weight when selecting a liquefaction technology. The direct consequence of these different selection criteria is that liquefaction technologies for small to medium 10 scale applications are not the same as the ones that are used in large LNG plants.
[0005] The two main types of liquefaction technologies are the mixed refrigerant technologies and expansion-based technologies. The mixed refrigerant technologies are “condensing type” processes, where the refrigerant used for the liquefaction makes use of its latent heat of vaporization to cool the natural gas. The expansion-based 15 technologies are processes where the refrigerant is always in gas phase and only makes use of its sensible heat to cool the natural gas. However, each of the processes operate based on the expansion of low boiling fluids, be it through expanders or JT valves, closed or open cycles, etc. where the difference between them is in the process efficiencies that result in lower capital and operating costs per unit of LNG produced. 20
[0006] The following mixed refrigerant technologies are examples of processes currently used in industry: PRICO (Poly Refrigerated Integrated Cycle Operation) is licensed by Black and Veatch and consists of a single cycle of mixed refrigerant (a mixture of methane, ethane, propane, butane, nitrogen and sometimes isopentane). The claimed advantages claimed include operating flexibility, modular design and reduced refrigerant 25 inventory. The AP-M (Air Products) is licensed by APCI, and consists of a single mixed refrigerant that is vaporized at two different levels of pressure. The dual pressure cycle is more efficient than the single pressure cycle, resulting in smaller heat exchangers and compressor. The LiMuM (Linde Multistage Mixed Refrigerant) is licensed by Linde and consists of a spiral wound heat exchanger and one 3-stage single mixed refrigeration 30 loop for the precooling, liquefaction and sub-cooling of the natural gas. This process3 allows for high-capacity throughput. PCMR (Pre-cooled Mixed Refrigerant) is licensed by Kryopak and consists of a pre-cooling stage (ammonia or propane cycle) followed by a single mixed refrigerant cycle, where the mixed refrigerant is a mixture of nitrogen, methane, ethane, propane and butanes. This process is used primarily in small plants. 5 OSMR (Optimized Single Mixed Refrigerant) is licensed by LNG Limited, the process is a single mixed refrigerant process complemented with a standard package ammonia absorption process. The utilization of an ammonia process improves the efficiency of the process and results in an increase in LNG output compared to traditional single mixed refrigerant processes. 10
[0007] In the above mixed refrigerant technologies, the main differences between them are the composition of the mixed refrigerant (although the refrigerants are the same ie; nitrogen, methane, ethane, etc…), the metallurgy of the heat exchangers, the orientation of the equipment, and the operations set points. Mixed refrigerant processes are generally improved upon by improving efficiency, and reducing capital and operating 15 costs.
[0008] The expansion-based technologies have various processes based on the use of nitrogen as a refrigerant to liquefy natural gas, i.e., the N2 expansion cycle. Some of these processes use a single cycle, others use a dual expansion cycle and in other cases a precooling cycle is added to improve efficiency. Several licensors, such as APCI, 20 Hamworthy, BHP Petroleum Pty, Mustang Engineering and Kanfa Oregon, offer the N2 expansion cycles processes but differ by proprietary process arrangement. In these processes, the cooling is provided by an external refrigeration plant using nitrogen expanders. The Niche LNG process is licensed by CB&I Lummus and consists of two cycles: one cycle uses methane as a refrigerant and the other uses nitrogen. The 25 methane provides cooling at moderate and warm levels while the nitrogen cycle provides refrigeration at the lowest temperature level. The OCX process is licensed by Mustang Engineering and is based on the use of the inlet gas as a refrigerant in an open refrigerant cycle with turbo-expanders. There are also variations, such as OCX-R, which adds a closed loop propane refrigerant to the OCX process, and OCX-Angle, which incorporates 30 LPG recovery.4 SUMMARY
[0009] According to an aspect, there is provided a method of producing LNG, where a pipeline gas stream is first pre-treated to remove impurities. The treated natural gas stream is mixed with a gas / liquid recycle stream and separated to generate two process 5 gaseous streams and a liquid stream. A treated gaseous stream is used to generate, electricity, cold thermal energy and liquid streams. The second gaseous stream is precooled and expanded to generate electricity and cold thermal energy to produce NGL’s and LNG. The method includes the steps of: pre-treating the gas stream in a pre-treater to remove the impurities; mixing the treated gas stream and a recycled gas / liquid stream 10 in a separator; separate the mixture in a separator into gas and a liquid streams; splitting the separated gas stream into two streams; wherein the first gas stream is expanded through a gas expander to generate electricity and cold thermal energy, and to separate the generated natural gas liquids and the expanded gas; the separated gas stream is routed into a recycle gas header and the natural gas liquid stream into a natural gas 15 liquids header; the second gas stream is pre-cooled by the cold thermal energy generated in the first stream, the generated natural gas liquids are separated and the separated gas stream is expanded through a gas expander to generate electricity and cold thermal energy, and the expanded gas stream is routed into a LNG gas separator. The separated pressurized liquid streams is routed through pressure exchangers to compress the 20 recycle gas stream and route the depressurized liquids stream to an LNG separator. The expanded gas streams are combined in a gas recycle common header. The generated natural gas liquids are combined in a common liquids header. A pressure exchanger is used in a LNG production plant. Generated and pressurized natural gas liquid streams is used as the motive liquid for gas compression in pressure exchangers. Separated lean 25 gas streams are expanded in gas expanders and separated in a gas / liquid separator into a recycle gas header as the recycle gas stream to pressure exchangers. The surplus natural gas liquids produced are exported into storage once steady state liquids flow to pressure exchangers is achieved.
[0010] According to other aspects, the impurities removed may be carbon dioxide and 30 water; the liquids may be natural gas liquids; the liquids provided as the motive force for5 the pressure exchanger may be generated from the natural feed gas stream or may be a closed loop; the recycled gaseous streams may be collected in a header from the separated gas generated in the gas expanders and pressure exchangers; the electrical energy required for the process may be generated by the expansion of the gaseous 5 streams in a gas expander; the cold thermal energy required for the process may be generated by the expansion of the gaseous streams in a gas expander and or pressure exchangers; electrical energy may be used to pump the liquid motive force for the pressure exchangers is generated by gas pressure recovery in gas expanders; no external sources of refrigeration or electrical energy may be employed to produce LNG; 10 the described process may be a zero GHG emissions process; the motive energy required for the compression of recycled gas stream in pressure exchangers may be supplied by natural gas liquids pumps; the refrigeration energy required to produce LNG from natural gas may be provided by combining heat exchangers, separators, pipeline pressure natural gas expansion and expansion of recycle gas streams pressured through 15 pressure exchangers; the electrical energy may be generated by the expansion of the pipeline natural gas feed pressure and recycle gas pressure generated by pressure exchangers;
[0011] According to an aspect, there is provided a method for compression of natural gas at a pipelines networks compression stage using one or more pressure exchangers, 20 a hydrocarbon liquids storage tank, and one or more hydrocarbon liquids pressure pumps; the method comprising the steps of: routing natural gas flowing through compressor stations to a pressure exchanger in lieu of a gas compressor; providing a pressurized hydrocarbons liquids stream to a pressure exchanger where it give up its pressure to a pipeline gas stream in a pressure exchanger; and providing a close loop 25 circulation system complete with a hydrocarbons liquids storage drum and circulation pressure pumps.
[0012] According to other aspects, the pressure exchanger motive force may be an hydrocarbons liquids stream; multiple pressure exchangers may be employed in parallel and or on standby; multiple pressure pumps may be employed in parallel and or on 30 standby; the proposed pressure exchange hydrocarbon liquids driven system may6 replace gas compressor systems at gas plants; the proposed pressure exchange hydrocarbon liquids driven system may replace gas compressor systems at oil refineries; the proposed pressure exchange hydrocarbon liquids driven system may replace gas compressor systems at petrochemical plants; the proposed pressure exchange in vapor 5 compression may be driven by water. The proposed pressure exchange hydrocarbon liquids driven system may replace any gas compressor system.
[0013] According to an aspect, there is provided a method that involves pre-treating the gas stream in a pre-treater to remove impurities, and mixing the pre-treated gas stream with a recycled compressed gas stream and passed into a first gas / liquid 10 separator. The separated liquid stream is routed to a liquids header. The separated gas stream is split into first and second gas streams. The first gas stream is routed to a gas expander that decreases the gas pressure to a controlled gas pressure. The expander may have a rotating shaft that is connected to an electrical generator to produce electricity. The pressure-reduced gas exits the expander as a cold stream mixture of gas 15 and condensates, which enters a second gas / liquid separator. The gaseous stream from the second gas / liquid separator is routed through a heat exchanger to give up its sensible cold thermal energy and routed to a gas recycle header. The separated liquid stream exits the second gas / liquid separator, is routed to a pump, pressurized and routed to a heat exchanger to give up its latent and sensible energy to the second gas stream. The 20 pre-cooled second gas stream is further cooled in a second heat exchanger and routed to a third gas / liquid separator. The separated liquid stream gives up its cold energy and is routed to a liquids header. The separated gaseous stream is further cooled in a third heat exchanger and routed to a fourth gas / liquid separator. The separated liquid stream exits the fourth gas / liquid separator, is mixed with a liquid stream from the third 25 liquid / separator, and is routed to the second heat exchanger to give up its latent and sensible cold energy. The gaseous stream from the fourth separator is routed through a fourth heat exchanger for further cooling before entering a fifth liquid gas separator. The separated liquid stream from the fifth liquid / gas separator is routed to a pressure exchanger, and the gas pressure is reduced to a controlled LNG liquids separator 30 pressure. The pressure-reduced liquid stream exits the pressure exchanger as a cold7 stream mixture of gas and LNG and enters the LNG liquids separator. The separated gaseous stream from the fifth liquid / gas separator is routed to a gas expander, and the gas pressure is decreased to a controlled LNG liquids separator pressure. This may be done to generate shaft power that is connected to an electrical generator to produce 5 electricity. The pressure-reduced gas exits the expander as a cold stream mixture of gas and LNG, and enters a LNG liquids separator. The separated LNG stream exits the LNG liquid separator and is routed to storage or transport, while the gaseous stream from the LNG separator first enters a heat exchanger for cold energy recovery and is then routed as a recycle gas stream for re-compression in pressure exchangers. 10
[0014] According to an aspect, there is provided a method of producing LNG from a pipeline natural gas feed stream. First, the gas is treated to remove impurities, such as carbon dioxide and water. Second, the mass flowrates and associated pressure drops of the two separated natural gas treated and recycle mixed streams are controlled to generate electricity and cold temperatures, which may be cryogenic. The electricity may 15 be used to power plant operations and the cryogenic temperatures may be used by the process equipment to condense and produce natural gas liquids (NGLs) and LNG. The condensed NGLs are pumped to a higher pressure and employed as the motive force to recycle the gaseous natural gas stream through pressure exchangers. The surplus NGLs generated are routed to storage. The produced LNG stream is routed to storage or 20 transport. A steady state may be reached in which a ratio of the recycled gas stream mixing with the treated natural gas feed stream by controlling the pressure and mass flow rates.
[0015] According to an aspect, there is provided a method of controlling the pressure of a natural gas stream, comprising: using a pressure exchanger, decreasing a pressure 25 of a high pressure natural gas stream while increasing a pressure of a low pressure natural gas stream.
[0016] According to an aspect, there is provided a method of compressing natural gas in a pipeline network using a compressor station comprising one or more pressure exchangers, a liquid pressure loop, and one or more liquid pumps, the method comprising8 the steps of: routing natural gas in a pipeline through a first path of the one or more pressure exchangers; pressurizing a liquid flow in the liquid pressure loop using the one or more liquid 5 pumps, and passing the pressurized liquid flow through the one or more pressure exchangers, such that the pressurized liquid flow pressurizes the natural gas in the pipeline via the one or more pressure exchangers.
[0017] According to other aspects, the liquid pressure loop may comprises two or more parallel flow paths, each flow path comprising a pressure exchanger, and wherein 10 the liquid flow is pressurized in two or more liquid pumps connected in parallel; the two or more parallel flow paths may be separately controllable; the liquid pressure loop may comprise a hydrocarbon-based liquid, or a water-based liquid.
[0018] According to an aspect, there is provided a method of producing liquid natural gas (LNG), comprises the steps of: 15 cooling and expanding an input stream to generate a stream of LNG, a stream of natural gas liquids (NGLs), and a recycle vapour stream, the stream of LNG, the stream of NGLs, and the recycle vapour stream being separated in a plurality of phase separators, and wherein: pressurizing NGLs obtained from the stream of NGLs in a liquid pressure loop, 20 the liquid pressure loop comprising: an NGL inlet connected to receive NGLs from the stream of NGLs; a liquid pump that pressurizes the NGLs in the liquid pressure loop; an NGL outlet that outputs excess NGLs from the liquid pressure loop; and a pressure exchanger that pressurizes the recycle vapour stream to 25 produce a pressurized recycle vapour stream; and combining the pressurized recycle vapour stream with the input stream.
[0019] According to other aspects, cooling and expanding the input stream may comprise using one or more heat exchangers and one or more or more upstream pressure reducer to condense the stream of NGLs from the input stream, separating the9 stream of NGLs from the input stream in one or more phase separators, using a downstream pressure reducer to generate the stream of LNG and a cold vapour stream, and separating the stream of LNG and the cold vapour stream in an LNG phase separator, the cold vapour stream comprising at least a portion of the recycle vapour 5 stream; the one or more upstream pressure reducer and the downstream pressure reducer may comprises at least one pressure exchanger; the NGL inlet may be connected to an NGL header that collects NGLs from one or more of the plurality of phase separators; the recycle vapour stream may be collected from one or more of the plurality of phase separators in a vapour header; the input stream may be pretreated to remove 10 impurities; one or more intermediate gas streams may be expanded in a gas expander that powers an electrical generator that generates electricity; the stream of LNG, the stream of natural gas liquids (NGLs), and the recycle vapour stream may be produced without external refrigeration; the stream of LNG, the stream of natural gas liquids (NGLs), and the recycle vapour stream may be produced without external electrical 15 energy.
[0020] Using this process, NGLs and LNG may be produced at zero or near zero GHG emissions. The process energy requirements, electricity and cold thermal energy may be provided by recovering the pipeline pressure energy through the use of gas expanders and the combination of using pressure exchangers in lieu of compressors. 20 The liquid stream used as the motive force for the pressure exchangers may be provided by recovered NGLs, which are components of the pipeline natural gas feed stream.
[0021] In other aspects, only pressure exchangers may be employed in lieu of gas expanders, and electrical requirements for liquid pumps may be provided by an external electrical source. In other aspects, a pressure exchanger may be employed in the natural 25 gas feed stream to booster the inlet pressure to the plant.
[0022] The process may be designed to operate without external power inputs, or external refrigeration systems and compressors. This may result in substantial savings in both capital and operating costs. The process may be developed with a view to produce NGLs and LNG at zero or near zero GHG emissions.10
[0023] Various process configurations may be employed to meet specific sites natural gas feed source stream conditions to meet desirable outcomes. In other aspects, the features described above may be combined together in any reasonable combination as will be recognized by those skilled in the art. 5 BRIEF DESCRIPTION OF THE DRAWINGS
[0024] These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: FIG. 1 is a schematic diagram of a process that produces electricity, NGLs, 10 and LNG. FIG. 2 is a schematic diagram of a process with one gas expander. FIG. 3 is a schematic diagram of a process that uses pressure exchangers in lieu of gas expanders, where any electrical requirements are supplied by an external electrical source. 15 FIG. 4 is a schematic diagram of a process that uses a pressure boost supplied by a pressure exchanger at the treated natural gas plant inlet feed stream. FIG. 5 is a schematic diagram of a facility designed with a single gas expander to generate electricity at the back end of the process. FIG. 6 is a schematic diagram of a closed loop hydrocarbon liquids circulating 20 stream that uses a pressure exchanger to pressurize a natural gas pipeline stream. FIG. 7 is a schematic diagram of a closed loop hydrocarbon liquids circulating stream that that uses multiple pressure exchanger to separately compress multiple stream from a natural gas pipeline stream. FIG. 8 is a schematic diagram of a pressure exchanger used to reduce the 25 pressure of a liquid hydrocarbon stream. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] There will now be described methods of processing natural gas using pressure11 exchangers. FIG. 1 through 5 are examples of processes that produce LNG, and which may be incorporated into an LNG facility, such as may be found at any suitable location where LNG is to be produced. In some examples, the method may be employed to produce Liquid Natural Gas (LNG) without external power sources, and thus a zero or 5 near zero GHG emissions LNG process. In other examples, the method may be used to more efficiently produce LNG while using external power sources. FIG. 6 and 7 are examples of processes that use pressure exchangers to pressurize natural gas in a pipeline network. FIG. 8 is an example of a process that uses a pressure exchanger to reduce the pressure of a liquid. 10
[0026] In the discussion below, it will be understood that the function of a single element may be performed by multiple elements, or a single element may perform multiple functions, based on available equipment.
[0027] Referring to FIG. 1, a pressurized pipeline natural gas stream 1 is pre-treated in a pretreatment unit 2 to remove the water and carbon dioxide components from the 15 natural gas stream to meet LNG product specifications. The pre-treated natural gas stream 3 is routed to liquid / gas separator 4. A re-compressed recycling stream 16 is also routed and mixed with pre-treated gas stream 3 in liquid / gas separator 4. The separated liquid fraction, exits separator 4 through line 54 to a liquids header 55. The separated gaseous stream 5 is split into stream 6 and stream 23. 20
[0028] The gaseous stream 6 is routed to gas expander 7 where the gas stream 6 is depressurized at a controlled pressure and exits gas expander 7 through stream 9 into a gas / liquid separator 10. The pressure drop across gas expander 7 generates shaft work which is recovered by a shaft connected electricity generator 8 to produce electricity, the electricity is routed through electrical line 69 to an electrical main distribution system 71. 25 Moreover, the pressure reduction and subsequent expansion of gaseous stream 6 across gas expander 7 results in a decrease in temperature of the depressurized gas stream 9 relative to stream 6. The resultant temperature decrease generated is dependent on the pressure difference across gas expander 7 and controlled at gas / liquid separator 10. The controlled, generated cold temperature of stream 9 may be used to control the liquid-gas12 separation ratio to meet process objectives. The separated liquid hydrocarbons fraction exits gas / liquid separator 10 through liquids stream 17 and routed to pump 18 where it is pressurized and routed through stream 19 to heat exchanger 20 to pre-cool stream 23 and exits heat exchanger 20 through stream 21 mixed with stream 46 into a liquids 5 header 55. The cold gaseous stream 11 is routed through heat exchanger 12 where it gives up its cold thermal energy to stream 28 and exits heat exchanger 12 through stream 13 into gaseous header 14, which recycles gas to separator 4 for further treatment.
[0029] The gaseous stream 23 is first pre-cooled in heat exchanger 20 and routed through stream 24 to heat exchanger 25 where it is further cooled by liquid stream 45 10 and exits through stream 26 into a gas / liquid separator 27. The condensed liquid fraction exits gas / liquid separator 27 through liquid stream 45, mixed with liquid stream 50 and mixed stream 46 is routed through heat exchanger 25 to pre-cool stream 24, exits heat exchanger 25 through stream 47 and is mixed with stream 21 into a mixed stream 22 that exits into liquids header 54. 15
[0030] The separated gaseous stream 28 is further cooled in heat exchanger 12 by gas stream 11 and exits through stream 29 into a gas / liquid separator 30. The condensed liquid fraction exits gas / liquid separator 30 through stream 48 and is pressurized bypump 49. The pressurized stream 50 is mixed with stream 45, and the mixed stream 46 gives up its cold energy to stream 24 through heat exchanger 25. 20
[0031] The separated gaseous stream 31 from gas / liquid separator 30 is further cooled in heat exchanger 32 by gaseous stream 41 and the colder stream 33 enters liquid / gas separator 34. The separated liquid fraction 51 is routed to pressure exchanger 43, where the liquid stream 51 is depressurized to a target pressure for LNG separator 39 and exits pressure exchanger 42 through stream 52 into LNG separator 39. The 25 pressure exchanger 43 recovers pressure from liquid stream 51 to boost pressure in gas stream 42 and the pressurized gas stream 44 enters gas recycle stream header 14 for further gas re-compression.
[0032] The separated gas stream 35 is routed to gas expander 36 where the gas13 stream 35 is depressurized to the target pressure for LNG separator 39 and exits gas expander 36 through stream 38 into LNG separator 39. The gas stream 35 pressure drop across gas expander 36 generates shaft work which is recovered by an attached electricity generator 37 to produce electricity, the electricity is routed through electrical 5 line 70 to an electrical distribution system 71.
[0033] At LNG separator 39, the liquid fraction stream 53 is sent to LNG storage. The gaseous fraction stream 40 is split into streams 41 and stream 57. Stream 41 is routed to heat exchanger 32 and the exiting stream 42 is compressed in pressure exchanger 43. The pressurized gas stream 44 is routed to recycle gas header 14. Gas stream 57 10 may be used as a nitrogen purge stream, controlled through valve 56, to prevent nitrogen build-up in the gas recycling stream.
[0034] The hydrocarbons liquids header 55 which consists primarily of NGLs, may be used to provide the liquids stream required for motive force of pressure exchanger 15. Once steady state process control is achieved, any surplus NGLs generated are exported 15 to storage or transport through stream 66, as controlled by pressure control valve 67, and routed through stream 68 to storage or transport.
[0035] A recycle loop 72 is used to pressurize recycling stream 16. Recycle loop 72 uses liquid pumps to pressurize the liquid in recycle loop 72 to achieve a desired pressure that is then used to pressurize recycling stream 16. In the depicted example, 20 hydrocarbons liquid stream 55 is mixed with make-up pressurized liquid stream 65, and the mixed liquids stream 58 is further pressurized by pump 59 to achieve the required motive force for pressure exchanger 15 through liquids stream 60. The depressurized stream 61 is returned to accumulator 62. Make-up liquids stream 63 is recycled through pressure pump 64 to generate a pressurized make up liquids stream 65. The excess 25 NGLs produced are routed to storage or transport through stream 66 via valve 67.
[0036] The recycle gas header stream 14 is routed to pressure exchanger 15 where gas pressure stream 16 is pressurized to liquids / gas separator 4 operating pressure, which may be the pipeline pressure in stream 1, thus completing the gas recycle and re14 compression circuit. The motive pressure for pressure exchanger 15 is provided by NGLs pressure pump 59 through liquids stream 60.
[0037] The method as described above is an example of how a pipeline gas stream supply may be processed into NGLs and LNG without the use of standard gas 5 compressors and external sources of refrigeration. The motive energy required for the process is provided by the natural gas pipeline feed pressure, which may be recovered to generate electricity and cold thermal energy. The electricity may be used to power processing equipment such as liquid pumps, including pumps 59 and 64 that provide pressure to pressurize recycle gas stream 16. The cold thermal energy may be used for 10 the condensation and liquefaction of natural gas liquids and the liquefaction of methane gas to produce LNG. As described, the process may be used as a zero or near zero GHG emissions method to produce LNG.
[0038] The process may also be employed without the use of external sources of energy for refrigeration compression systems and process operations. The flexibility of 15 the process allows various operating conditions to be met by controlling operating pressures and mass flowrates to produce the electricity and cold thermal energy required to produce NGLs and LNG from a natural gas feed stream, such as a pipeline. Pressure exchangers are used in the process as the motive force to recycle and compress low pressure, treated gas. When compared with static compressors such as liquid injector 20 compressors, pressure exchangers are more efficient and operate at lower motive flow pressures. Moreover, the process does not require the motive fluid to be mixed with the compressible gas, resulting in smaller lines and volumes.
[0039] Referring to FIG. 2, another example is shown in which gas expander / generator 36 shown in FIG. 1 has been replaced by pressure exchanger 236. 25 The use of pressure exchanger 236 lieu of gas expander / generator 36 provides an alternate mode of operation to FIG 1. As a result of this modification, gas expander / generator 36 is not connected to an electrical line 70 as it does not generate electricity. Instead, stream 235 is depressurized in pressure exchanger 235 to produce stream 238. Separated vapour stream 40 is separated into stream 57 and stream 24015 that is pressurized by pressure exchanger 236 to produce pressurized stream 241.
[0040] Referring to FIG. 3, another example is shown in which gas expanders 7 and 36 shown in FIG. 1 has been replaced by pressure exchangers 307 and 336. As discussed below, the electrical power requirements for this mode of operation may be 5 provided by an external electrical supply.
[0041] Referring to FIG. 3, a pressurized pipeline natural gas stream 301 first is pretreated in a unit 302 to remove the water and carbon dioxide components from the natural gas stream to meet LNG product specifications. The pre-treated natural gas stream 303 is routed to liquid / gas separator 304. A re-compressed recycling stream 316 is also 10 routed and mixed with pre-treated gas stream 303 in liquid / gas separator 304. The separated liquid fraction 353, exits separator 304 to a liquids header 354. The separated gaseous stream 305 is split into streams 306 and 323.
[0042] The gaseous stream 306 is routed to pressure exchanger 307 where the gas stream 306 is depressurized at a controlled pressure and exits the pressure exchanger 15 307 through stream 308 into a gas / liquid separator 309. The pressure exchanger 307 boosts the pressure of gas stream 313, the boosted pressure stream 314 is routed to pressure exchanger 315 for further compression. Moreover, the pressure reduction and subsequent expansion of gaseous stream 306 across pressure exchanger 307, results in a decrease in temperature of the depressurized gas stream 308. The resultant 20 temperature decrease is dependent on the pressure difference across pressure exchanger 307 and controlled at gas / liquid separator 309. The generated cold temperature of stream 308 may be controlled to produce a liquid gas separation ratio according to process specifications. The separated liquid hydrocarbons fraction exits gas / liquid separator 309 through liquids stream 317 and routed to pump 318 where it is 25 pressurized and routed through stream 319 to heat exchanger 320 to pre-cool stream 323 and exits heat exchanger 320 through stream 321, and is mixed with stream 346 into a liquids header 354. The cold gaseous stream 310 is routed through heat exchanger 311 where it gives up its cold thermal energy to stream 328 and exits heat exchanger 311 through stream 312 into gaseous header 313.16
[0043] The gaseous stream 323 is first pre-cooled in heat exchanger 320 and routed through stream 324 to heat exchanger 325 where it is further cooled by liquid stream 345 and exits through stream 326 into a gas / liquid separator 327. The condensed liquid fraction exits gas / liquid separator 327 through liquid stream 344, mixed with liquid stream 5 349 and route the mixed stream 345 through heat exchanger 325 to pre-cool stream 324, exiting heat exchanger 325 through stream 346 and mixed with stream 321, where the mixed stream 322 exits into liquids header 354.
[0044] The separated gaseous stream 328 is further cooled in heat exchanger 311 by gas stream 310 and exits through stream 329 into a gas / liquid separator 330. The 10 condensed liquid fraction exits gas / liquid separator 330 through stream 347 into pump 348, the pressurized stream 349 is mixed with stream 344, and the mixed stream 345 gives up its cold energy to stream 324 through heat exchanger 325.
[0045] The separated gaseous stream 331 from gas / liquid separator 330 is further cooled in heat exchanger 332 by gaseous stream 340 and the colder stream 333 enters 15 liquid / gas separator 334. The separated liquid fraction 350 is routed to pressure exchanger 342, where the liquid stream 350 is depressurized to the operating pressure of LNG separator 338 and exits pressure exchanger 342 through stream 351 into LNG separator 338. The pressure exchanger 342 recovers pressure from liquid stream 350 to boost the pressure of gas stream 341 and the pressurized gas stream 343 enters gas 20 recycle stream header 313 for further gas compression.
[0046] The separated gas stream 335 is routed to pressure exchanger 336, where the gas stream 335 is depressurized to match the pressure of LNG separator 338 and exits pressure exchanger 336 through stream 337 into LNG separator 338. The pressure exchanger 336 recovers the gas stream 335 pressure to boost gas stream 339 pressure 25 and the pressurized gas stream 340 enters heat exchanger 332 to further cool gas stream 331.
[0047] At LNG separator 338, the liquid fraction stream 352 is sent to LNG storage. The gaseous fraction stream 339 is routed to pressure exchanger 336, and the17 pressurized gas stream 340 gives up its cold energy at heat exchanger 332 and the exiting stream 341 is further compressed in pressure exchanger 342. The pressurized gas stream is routed to recycle gas header 313. Gas stream 356 may be used as a nitrogen purge stream controlled through valve 355 to prevent nitrogen build-up in the 5 gas recycling stream.
[0048] The hydrocarbons (NGLs) liquids header 354 provides the liquids stream required for motive force of pressure exchanger 315, once steady state process control is achieved the surplus NGLs generated are exported to storage or transport through stream 365, pressure control valve 366 and routed through stream 367 to storage or 10 transport.
[0049] The hydrocarbons liquid stream 354 is mixed with make-up pressurized liquid stream 364, the mixed liquids stream 357 is further pressurized by pump 358 to required motive force for pressure exchanger 315 through liquids stream 359. The depressurized stream 360 is returned to accumulator 361. Make-up liquids stream 362 is recycled 15 through pressure pump 363 to generate a pressurized make up liquids stream 364. The excess NGLs produced are routed to storage or transport through stream 365.
[0050] The recycle gas header stream 313 is routed to pressure exchanger 307 where recycle gas pressure stream 313 is pressurized by pressure exchanger 307. The pressurized recycle gas stream 314 is further pressurized by pressure exchanger 315 to 20 liquids / gas separator 304 operating pressure, thus completing the gas recycle and recompression circuit. The motive pressure for pressure exchanger 315 is provided by NGLs pressure pump 358 through liquids stream 359. Other pressure exchangers and / or liquid pumps may be used to add energy to the system and allow for more control options in producing LNG. 25
[0051] The method as described is an example of how a pipeline gas stream supply may be processed into NGLs and LNG without the use of standard gas compressors and external sources of refrigeration. The motive energy required for the process may be provided by the natural gas pipeline feed pressure, which is recovered in pressure heat18 exchangers to generate cold thermal energy and produce LNG. The use of pressurized natural gas liquids as the motive force in pressure exchangers to recycle low pressure treated gas completes the process.
[0052] The method may be employed without refrigeration compression systems and 5 process operations commonly used in general practice. The method may also provide flexibility to meet various operating conditions by controlling operating pressures and mass flowrates to produce the cold thermal energy required to produce NGLs and LNG. In addition, the use of pressure exchangers as the motive force to recycle and compress low pressure treated gas, which may be used as a more efficient alternative to static 10 compressors, such as liquid injector compressors, and that operate at lower motive flow pressures. Moreover, pressure exchangers do not require the motive fluid to be mixed with the compressible gas resulting in smaller lines and volumes.
[0053] Referring to FIG. 4, the depicted process is similar to the process shown in FIG. 3 with the addition of a pressure exchanger 464 to boost the pressure of pretreated 15 natural gas stream 303, such as a pipeline treated plant inlet gas stream.
[0054] A treated natural gas feed stream 303 is routed through pressure exchanger 464 to boost the pressure of the plant inlet gas stream to produce stream 403. The motive force for pressure exchanger 464 is provided by fluids gas stream 463 and the pressure supplied by natural gas liquids pump 358. Pressurized liquid stream 359 is separated into 20 stream 461 and stream 463. Stream 461 is depressurized in pressure exchanger 315 while pressurizing stream 316 to produce pressurized stream 314. Stream 463 is depressurized in pressure exchanger 464 to produce pressure reduced stream 465. The pressure reduced stream 465 exits pressure exchanger 464, is mixed with stream 462 and routed through line 466 to liquids accumulator 361. 25
[0055] The addition of pressure exchanger 464 to the treated gas plant inlet stream 303 allows for an alternate mode of operation at gas supply lower pipeline gas pressures.
[0056] Referring to FIG. 5, the depicted system does not separate a vapour phase 5 of the treated inlet stream 3 into separate streams 6 and 23 (as shown in FIG. 1), where19 stream 6 becomes a recycled gas stream and stream 23 is subject to further processing to produce LNG. Instead, the process in FIG. 5 processes the gas phase in a single stream to produce LNG.
[0057] A pressurized pipeline natural gas stream 501 first is pre-treated in a unit 502 5 to remove the water and carbon dioxide components from the natural gas stream to meet LNG product specifications. The pre-treated natural gas stream 503 is routed to liquid / gas separator 504. A re-compressed recycling stream 534 is also routed and mixed with pretreated gas stream 503 in liquid / gas separator 504. The separated liquid fraction 535 exits separator 504 to a liquids header 536. 10
[0058] The separated gaseous stream 505 is routed to heat exchanger 506, the precooled stream 507 is further cooled in heat exchanger 508, the colder stream 509 is routed to gas / liquid separator 510. The separated liquid hydrocarbons fraction exits gas / liquid separator 510 through liquids stream 515 and routed to pump 516 and routed through stream 517 to heat exchanger 506 to pre-cool stream 505 and exits heat 15 exchanger 506 through stream 518 into liquids header 536. The cold gaseous stream 511 is routed through heat exchanger 512 where is further cooled by stream 529 and exits heat exchanger 512 through stream 513 into gas / liquid separator 514.
[0059] The separated liquid fraction 519 is routed to pressure exchanger 520, where the liquid stream 519 is depressurized to the operating pressure of LNG separator 526 20 and exits pressure exchanger 520 through stream 521 into LNG separator 526. The pressure exchanger 520 recovers pressure from the liquid stream 519 to boost the pressure of gas stream 530.
[0060] The separated gas stream 522 is routed to gas expander 523 where the gas stream 522 is depressurized to the operating pressure of LNG separator 526 and exits 25 gas expander 523 through stream 525 into LNG separator 526. The gas stream 522 pressure drop across gas expander 523 may be used to generate shaft work, which is recovered by an attached electricity generator 524 to produce electricity.
[0061] At LNG separator 526, the liquid fraction stream 527 is sent to LNG storage.20 The gaseous fraction stream 528 is split into streams 529 and stream 548. The gas stream 529 is first routed heat exchanger 512, the heated stream 530 enters pressure exchanger 520, the pressurized gas stream 531 gives up its cold energy at heat exchanger 508 and the exiting stream 532 is further compressed in pressure exchanger 5 533. The pressurized recycle gas stream 534 is routed to inlet gas separator 504. Gas stream 548 may be used as a nitrogen purge stream controlled through valve 549 to prevent nitrogen build-up in the gas recycling stream.
[0062] The hydrocarbons (NGLs) liquids header 536 provides the liquids stream required for motive force of pressure exchanger 533. Once steady state process control 10 is achieved, surplus NGLs generated may be exported to storage or transport through stream 545, as controlled by pressure control valve 546, and routed through stream 547 to storage or transport.
[0063] The hydrocarbons liquid stream 536 is mixed with make-up pressurized liquid stream 544, the mixed liquids stream 537 is further pressurized by pump 538 to required 15 motive force for pressure exchanger 533 through liquids stream 539. The depressurized stream 540 is returned to accumulator 541. Make-up liquids stream 542 is recycled through pressure pump 543 to generate a pressurized make up liquids stream 544. The excess NGLs produced are routed to storage or transport through stream 547.
[0064] The various features shown in the processes FIG. 1 through 5 may be modified 20 and incorporated into the other processes. In particular, gas expanders and pressure exchangers may be used interchangeably to produce LNG.
[0065] The processes used herein avoids the need for mixed refrigerant compression cycles or gas compressors and the energy requirements associated with the standard operations practices. The process as described herein may be used to achieve relatively 25 lower capital and operating costs and may be employed in LNG plants of various sizes.
[0066] In addition to the use of pressure exchangers to produce LNG, the processes may be modified to produce other pressures and temperatures to separate different streams of hydrocarbons or to produce other hydrocarbon streams, such as compressed21 cold natural gas (CCNP), pressurized liquid natural gas (PLNG), or to recover NGLs from a pipeline, such as at pressure let down stations. Pressure exchangers may also be used in other natural gas applications, either as a compressor and / or as an expander. Referring to FIG. 6 and 7, a method for compressing natural gas in a pipeline network at 5 a compressor station is shown.. This method may be used to compress gas with pressure exchangers at compressor stations along natural-gas transmission and distribution pipelines rather than a more common type of gas compressor, thus enabling natural gas to be compressed using pressure exchangers driven in a closed loop by circulating pressurized liquids. 10
[0067] Referring to FIG. 6, in the proposed natural-gas compressor station in a naturalgas transmission pipeline, the lower pressure stream 601 enters pressure exchanger 602 where the pressure of stream 601 is boosted and exits pressure exchanger 602 through pipeline stream 603. The motive force for pressure exchanger 602 is provided by hydrocarbon liquids pressure stream 607 and gives its pressure to stream 601 through 15 pressure exchanger 602. The depressurized hydrocarbons liquids stream 608 exits pressure exchanger 602 and returns to hydrocarbons liquids storage drum 604. The pressure in hydrocarbons liquids storage drum 604 is maintained to prevent flashing of any of the hydrocarbons liquids composition. The hydrocarbons liquids circulation feed stream 605 enters pump 606, pressurizes the hydrocarbon liquids stream 607 to the 20 operating pressure for pressure exchanger 602 thus completing this closed loop hydrocarbon liquids pressurized system. The above describes the proposed natural gas compression to existing natural-gas transmission-pipeline compression stations. In addition to being more efficient relative to traditional gas compressors, pressure exchangers are able to handle mixed-phase fluids. This may be important, for example, 25 if liquids have condensed in a pipeline between compressor stations. The pressure exchange may be used to boost the pipeline pressure without separating liquids first, which is generally required to avoid damaging a gas compressor.
[0068] Referring to FIG. 7, another example is shown in which natural gas in a pipeline 701 is pressurized using pressure exchangers 703, 707, 710. Relative to FIG. 6, the 30 method in FIG. 7 includes parallel trains of pressure exchangers 703, 707, 710 and22 hydrocarbon liquids pumps 714, 724, which may be used to increase compression reliability at compressor stations, and / or to address variable gas flowrates through the seasons. Where liquid pumps 714, 724 are variable speed pressure pumps, the process may be used to provide for a fast response to pipeline pressure changes. 5
[0069] Referring to FIG. 7, a pipeline natural gas stream 701, is split into multiple streams, such as streams 702, 706 and 709. Stream 702 enters pressure exchanger 703 and exits as a compressed gas stream 704 and enters compressed pipeline transmission stream 705. Stream 706 enters pressure exchanger 707 and exits as a compressed gas stream 708 and enters compressed pipeline transmission stream 705. Stream 709 enters 10 pressure exchanger 710 and exits as a compressed gas stream 711 and enters compressed pipeline transmission stream 705.
[0070] The motive force for pressure exchangers 703, 707 and 710 is provided by hydrocarbon liquids pressure stream 715 and is split into streams; 716, 718 and 720. Pressurized hydrocarbons liquid stream 716 enters pressure exchanger 703 and gives 15 its pressure to stream 702 through pressure exchanger 703. The depressurized hydrocarbons liquids stream 717 exits pressure exchanger 703 and enters hydrocarbons liquids header 722 returning the hydrocarbons storage drum or accumulator 712. Pressurized hydrocarbons liquid stream 718 enters pressure exchanger 707 and gives its pressure to stream 706 through pressure exchanger 707. The depressurized 20 hydrocarbons liquids stream 719 exits pressure exchanger 707 and enters hydrocarbons liquids header 722 returning the hydrocarbons storage drum 712. Pressurized hydrocarbons liquid stream 720 enters pressure exchanger 710 and gives its pressure to stream 709 through pressure exchanger 710. The depressurized hydrocarbons liquids stream 721 exits pressure exchanger 710 and enters hydrocarbons liquids header 722 25 returning the hydrocarbons storage drum 712.
[0071] The pressure in hydrocarbons liquids storage drum 712 may be maintained to prevent flashing of any of the hydrocarbons liquids composition. The hydrocarbons liquids circulation feed streams 713 and 723 enters pumps 714 and 724 to pressurize hydrocarbon liquids stream 715 at pressure exchangers 703, 707 and 710 operations23 pressure, thus completing a close loop hydrocarbon liquids pressure system. The above describes a proposed natural gas compression to existing natural-gas transmissionpipeline compression stations. The additional gas pressure exchangers and pressure pumps to enhance gas compressor stations reliability as depicted is an example of 5 potential arrangements to increase reliability and not limited to other process configurations that employ pressure exchangers and liquids motive force for the pressure exchangers. The flow through each path may be controlled separately, such that the parallel paths may be employed when needed.
[0072] Referring to FIG. 8, another example of how a pressure exchanger may be 10 used in processing natural gas. In this example, a high pressure, inlet liquid stream 801 is depressurized in a pressure exchanger 802 to produce a low pressure fluid stream 803, where a portion of the fluid have flashed to a vapour. A separator 804 is used to separate a low pressure liquid stream 806 from a low pressure vapour stream 805. Low pressure vapour stream is pressurized in pressure exchanger 802 to produce a high 15 pressure vapour stream 806 to recover some of the energy in high pressure stream 801. Other examples may also be seen, for example, in FIG. 1, where a pressure exchanger 43 is used to pressurize stream 42 while depressurizing stream 51 in a different part of the process.
[0073] In this patent document, the word "comprising" is used in its non-limiting sense 20 to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements.
[0074] The scope of the following claims should not be limited by the preferred 25 embodiments set forth in the examples above and in the drawings, but should be given the broadest interpretation consistent with the description as a whole.
Claims
24 What is Claimed is:
1. A method of controlling the pressure of a natural gas stream, comprising: using a pressure exchanger, decreasing a pressure of a high pressure natural 5 gas stream while increasing a pressure of a low pressure natural gas stream.
2. A method of compressing natural gas in a pipeline network using a compressor station comprising one or more pressure exchangers, a liquid pressure loop, and one or more liquid pumps, the method comprising the steps of: routing natural gas in a pipeline through a first path of the one or more pressure 10 exchangers; pressurizing a liquid flow in the liquid pressure loop using the one or more liquid pumps, and passing the pressurized liquid flow through the one or more pressure exchangers, such that the pressurized liquid flow pressurizes the natural gas in the pipeline via the one or more pressure exchangers. 15 3. The method of claim 2, wherein the liquid pressure loop comprises two or more parallel flow paths, each flow path comprising a pressure exchanger, and wherein the liquid flow is pressurized in two or more liquid pumps connected in parallel.
4. The method of claim 3, wherein the two or more parallel flow paths are separately controllable. 20 5. The method of claim 2, wherein the liquid pressure loop comprises a hydrocarbon-based liquid, or a water-based liquid.
6. A method of producing liquid natural gas (LNG), comprises the steps of: cooling and expanding an input stream to generate a stream of LNG, a stream of natural gas liquids (NGLs), and a recycle vapour stream, the stream of LNG, the stream 25 of NGLs, and the recycle vapour stream being separated in a plurality of phase separators, and wherein: pressurizing NGLs obtained from the stream of NGLs in a liquid pressure loop, the liquid pressure loop comprising:25 an NGL inlet connected to receive NGLs from the stream of NGLs; a liquid pump that pressurizes the NGLs in the liquid pressure loop; an NGL outlet that outputs excess NGLs from the liquid pressure loop; and a pressure exchanger that pressurizes the recycle vapour stream to 5 produce a pressurized recycle vapour stream; and combining the pressurized recycle vapour stream with the input stream.
7. The method of claim 6, wherein cooling and expanding the input stream comprises: using one or more heat exchangers and one or more or more upstream 10 pressure reducer to condense the stream of NGLs from the input stream; and separating the stream of NGLs from the input stream in one or more phase separators; using a downstream pressure reducer to generate the stream of LNG and a cold vapour stream; and 15 separating the stream of LNG and the cold vapour stream in an LNG phase separator, the cold vapour stream comprising at least a portion of the recycle vapour stream.
8. The method of claim 7, wherein the one or more upstream pressure reducer and the downstream pressure reducer comprises at least one pressure exchanger. 20 9. The method of claim 7, wherein the NGL inlet is connected to an NGL header that collects NGLs from one or more of the plurality of phase separators.
10. The method of claim 7, wherein the recycle vapour stream is collected from one or more of the plurality of phase separators in a vapour header.
11. The method of claim 6, wherein the input stream is pretreated to remove 25 impurities.
12. The method of claim 6, wherein one or more intermediate gas streams are expanded in a gas expander that powers an electrical generator that generates electricity.26 13. The method of claim 6, wherein the stream of LNG, the stream of natural gas liquids (NGLs), and the recycle vapour stream are produced without external refrigeration.
14. The method of claim 6, wherein the stream of LNG, the stream of natural gas 5 liquids (NGLs), and the recycle vapour stream are produced without external electrical energy.