CN108955085B - Small skid-mounted coal bed gas liquefaction system and method - Google Patents
Small skid-mounted coal bed gas liquefaction system and method Download PDFInfo
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- 239000003245 coal Substances 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 title claims abstract description 26
- 239000012071 phase Substances 0.000 claims abstract description 56
- 239000002994 raw material Substances 0.000 claims abstract description 40
- 239000007788 liquid Substances 0.000 claims abstract description 38
- 239000012530 fluid Substances 0.000 claims abstract description 32
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 28
- 238000000746 purification Methods 0.000 claims abstract description 20
- 239000007791 liquid phase Substances 0.000 claims abstract description 16
- 238000001816 cooling Methods 0.000 claims abstract description 14
- 230000007246 mechanism Effects 0.000 claims abstract description 13
- 238000002156 mixing Methods 0.000 claims abstract description 3
- 239000012535 impurity Substances 0.000 claims description 7
- 239000000203 mixture Substances 0.000 claims description 4
- 238000004781 supercooling Methods 0.000 claims description 4
- 230000009467 reduction Effects 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 99
- 230000008569 process Effects 0.000 description 17
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 238000007906 compression Methods 0.000 description 4
- 230000006835 compression Effects 0.000 description 4
- 238000005265 energy consumption Methods 0.000 description 3
- 238000000605 extraction Methods 0.000 description 3
- 239000001294 propane Substances 0.000 description 3
- 238000010992 reflux Methods 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 238000005057 refrigeration Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0201—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using only internal refrigeration means, i.e. without external refrigeration
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0203—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle
- F25J1/0205—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle as a dual level SCR refrigeration cascade
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
- F25J1/0022—Hydrocarbons, e.g. natural gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
- F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
- F25J1/0035—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
- F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
- F25J1/004—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by flash gas recovery
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/30—Compression of the feed stream
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Abstract
The invention provides a small skid-mounted coal bed methane liquefaction system and a method, wherein the system comprises: the system comprises a raw material gas purification mechanism, a first-stage compressor cooler, a second-stage compressor cooler, a first-stage heat exchanger, a first-stage turboexpander, a second-stage heat exchanger, a gas-liquid separator, a third-stage heat exchanger, a second-stage turboexpander, a throttling valve and a product storage tank; the raw material gas passes through a raw material gas purification mechanism, a primary compressor cooler, a secondary compressor and a secondary compressor cooler to be purified, compressed and cooled; then, heat exchange and cooling are carried out through a primary heat exchanger, and adiabatic expansion is carried out through a primary turbine expander; conveying to a secondary heat exchanger to reduce the temperature of the expanded fluid, and conveying to a gas-liquid separator to separate a liquid phase from a gas phase; the gas phase enters a secondary turbine expander for two-phase expansion, and the liquid phase enters a throttling valve after being cooled in a tertiary heat exchanger; and mixing the throttled two-phase fluid with the expanded two-phase fluid.
Description
Technical Field
The invention relates to the technical field of mechanical equipment, in particular to a small skid-mounted coal bed gas liquefaction system and method.
Background
The coal bed gas is a gas rich in methane, is widely applied to the fields of chemical industry and fuel, and the application of the coal bed gas requires that the content of the methane in the coal bed gas product is liquefied to be more than 90%. In Xinjiang, inner Mongolia and other places in China, the coal bed gas reserves are rich, a large number of small coal bed gas fields with low reserves exist, and because the small gas fields are different from the traditional large coal bed gas fields, the small gas fields are wide in distribution range, small in raw material gas flow, large in raw material gas pressure fluctuation and low in concentration, and the methane content is lower than 30% under certain conditions, the gas fields are difficult to liquefy by using the traditional large coal bed gas field liquefying process, and therefore the small skid-mounted coal bed gas liquefying system becomes an effective method for solving the problem.
Because large-scale coal bed gas field is because its coal bed gas reserves are big, and flow and pressure fluctuation are less, therefore the flow mode that large-scale coal bed gas liquefaction adopted usually includes: a cascade liquefaction process, a mixed refrigerant liquefaction process and a liquefaction process with a turboexpander. The process of the turboexpander is divided into three cycles of propane precooling, turborefrigeration and raw material gas liquefaction, the raw material gas is firstly precooled by using propane and then cooled by heat exchange with low-temperature nitrogen of the nitrogen expansion cycle, and enters a gas-liquid separator after throttling to complete a main liquefaction process, the liquefaction rate of the process can reach 90%, and the unit energy consumption is low. For a small coal bed gas liquefaction system, due to the skid-mounted requirement, the arrangement space of flow equipment is limited, the equipment is required to be simplified as far as possible, and due to the existence of precooling circulation and refrigeration circulation, the coal bed gas liquefaction flow of a large gas field cannot be suitable for the small skid-mounted liquefaction system.
Disclosure of Invention
Aiming at the problems in the prior art, the technical problem to be solved by the embodiment of the invention is to provide a small skid-mounted coal bed methane liquefaction system and method, and at least partially solve the problems in the prior art.
In order to solve the above problem, an embodiment of the present invention provides a small skid-mounted coal bed methane liquefaction system, including: the system comprises a raw material gas purification mechanism 1, a primary compressor 2, a primary compressor cooler 3, a secondary compressor 4, a secondary compressor cooler 5, a primary heat exchanger 6, a primary turboexpander 7, a secondary heat exchanger 8, a gas-liquid separator 9, a tertiary heat exchanger 10, a secondary turboexpander 11, a throttle valve 12 and a product storage tank 13;
the feed gas purification mechanism 1, the first-stage compressor 2, the first-stage compressor cooler 3, the second-stage compressor 4 and the second-stage compressor cooler 5 are sequentially connected in series, so that the feed gas is purified by the feed gas purification mechanism 1 to filter impurities; then the compressed air passes through a first-stage compressor 2, a first-stage compressor cooler 3, a second-stage compressor 4 and a second-stage compressor cooler 5 to be compressed and cooled;
wherein the secondary compressor cooler 5 is sequentially connected with a primary heat exchanger 6, a primary turboexpander 7, a secondary heat exchanger 8 and a gas-liquid separator 9; purified, compressed and cooled raw gas delivered by a secondary compressor cooler 5 is subjected to heat exchange and temperature reduction through a primary heat exchanger 6, and then is subjected to adiabatic expansion through a primary turboexpander 7; then the gas is conveyed to a secondary heat exchanger 8 to reduce the temperature of the expanded fluid so that the feed gas enters a two-phase state, and then the gas is conveyed to a gas-liquid separator 9 to separate the liquid phase and the gas phase in the gas-liquid separator;
the gas-liquid separator 9 is respectively connected with the tertiary heat exchanger 10 and the secondary turboexpander 11 so as to enable the separated gas phase to enter the secondary turboexpander 11 for two-phase expansion, and the liquid phase enters the throttling valve 12 for throttling after being further cooled in the tertiary heat exchanger 10;
wherein, the two-stage turbo expander 11 and the throttle valve 12 are connected with the product storage tank 13 to mix the throttled two-phase fluid and the expanded two-phase fluid and then convey the mixture to the product storage tank 13.
Wherein, the gas emptying channel of the product storage tank 13 is connected with the third-stage heat exchanger 10, the second-stage heat exchanger 8 and the first-stage heat exchanger 6 so as to release cold energy through the heat exchangers in sequence when the product storage tank empties gas.
Wherein, the pressure ratio and the flow rate of the second stage turbine expansion machine 11 are determined according to the fluid ratio of the gas phase and the liquid phase separated in the gas-liquid separator 9 and the working condition of the first stage turbine expansion machine 7.
Wherein, the liquid supercooling degree and the flow rate at the front end of the throttle valve 12 are determined according to the system working condition;
the first-stage turbo expander is also connected with the second-stage compressor, and the second-stage turbo expander is also connected with the first-stage compressor.
Meanwhile, the embodiment of the invention also provides a coal bed gas liquefaction method by using the small skid-mounted coal bed gas liquefaction system, which comprises the following steps:
purifying the raw material gas by a raw material gas purification mechanism to filter impurities; then the compressed air passes through a first-stage compressor, a first-stage compressor cooler, a second-stage compressor and a second-stage compressor cooler to be compressed and cooled; then, the purified, compressed and cooled raw material gas is subjected to heat exchange and cooling through a primary heat exchanger, and then is subjected to adiabatic expansion through a primary turboexpander, and the primary turboexpander also transfers adiabatic expansion energy to a secondary compressor; the first-stage compressor operates under the drive of two-phase expansion energy from the second-stage turbo expander, and the second-stage compressor operates under the drive of adiabatic expansion energy from the first-stage turbo expander;
delivering the gas to a secondary heat exchanger to reduce the temperature of the expanded fluid so that the feed gas enters a two-phase state, and delivering the gas to a gas-liquid separator to separate a liquid phase and a gas phase in the gas-liquid separator; then the separated gas phase enters a secondary turbine expander for two-phase expansion, and the liquid phase enters a throttling valve for throttling after being further cooled in a tertiary heat exchanger; the two-stage turbo expander also transfers the two-phase expansion energy to the first-stage compressor;
and mixing the throttled two-phase fluid and the expanded two-phase fluid and conveying the mixture to a product storage tank.
The technical scheme of the invention has the following beneficial effects: the technical scheme provides a small skid-mounted coal bed gas liquefaction system and a method, the small skid-mounted coal bed gas liquefaction system can be skid-mounted and moved, and is suitable for wide flow and pressure ranges of a gas field; removing feed gas impurities other than methane and nitrogen using a purification system; the temperature of the split-flow part of the raw gas is reduced and regenerated by a turbine expander; the two-phase turbo expander is used for replacing a throttling valve in the liquefaction process, so that the liquefaction rate of the process is effectively improved, and the energy consumption of the system is reduced. The novel small skid-mounted low-concentration coal bed gas liquefaction process has the characteristics of simple process structure, skid-mounted movement, wide raw material gas pressure application range, high liquefaction rate, low unit energy consumption and high liquefaction speed.
Drawings
FIG. 1 is a schematic structural diagram of an embodiment of the present invention;
description of reference numerals:
1. a raw material gas purification mechanism;
2. a first stage compressor;
3. a first stage compressor cooler;
4. a secondary compressor;
5. a secondary compressor cooler;
6. a primary heat exchanger;
7. a first stage turboexpander;
8. a secondary heat exchanger;
9. a gas-liquid separator;
10. a tertiary heat exchanger;
11. a secondary turboexpander;
12. a throttle valve;
13. and (5) a product storage tank.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
Specifically, as shown in fig. 1, an embodiment of the present invention provides a small skid-mounted coal bed methane liquefaction system, including:
wherein the raw material gas is purified by a raw material gas purification mechanism 1 to filter impurities; and then passed through a primary compressor 2, a primary compressor cooler 3, a secondary compressor 4, a secondary compressor cooler 5 for compression and cooling. Then the purified, compressed and cooled raw material gas is conveyed to a first-stage heat exchanger 6 for heat exchange and temperature reduction, and then is subjected to adiabatic expansion through a first-stage turbo expander 7; then, the gas is sent to a secondary heat exchanger 8 to reduce the temperature of the expanded fluid so that the raw gas enters a two-phase state, and the gas is sent to a gas-liquid separator 9 to separate the liquid phase and the gas phase in the gas-liquid separator; the separated gas phase enters a secondary turbine expander 11 for two-phase expansion, and the liquid phase is further cooled in a tertiary heat exchanger 10 and then enters a throttle valve 12 for throttling; then the throttled two-phase fluid and the expanded two-phase fluid are mixed and then delivered to the product storage tank 13. When the product is output, the product in the product storage tank 13 is sequentially output after the cold energy is released by the three-stage heat exchanger 10, the two-stage heat exchanger 8 and the first-stage heat exchanger 6, and the product storage tank 13 is emptied; the first-stage turbo expander is also connected with the second-stage compressor, and the second-stage turbo expander is also connected with the first-stage compressor.
Wherein, the raw material gas after purification, compression and cooling of raw material gas purification mechanism 1, primary compressor 2, primary compressor cooler 3, secondary compressor 4, secondary compressor cooler 5, pressure matches with the pressure that turbine output work can reach, and can cool the raw material gas to near normal temperature. And then the raw material gas passes through a primary heat exchanger 6, a primary turboexpander 7, a secondary heat exchanger 8 and a gas-liquid separator 9 in sequence, and the expansion ratio can be changed between 2 and 7 according to the difference between the gas flow and the pressure of the raw material gas of the system.
In the embodiment of the invention, two stages of turboexpanders are adopted, namely: a first stage turbo expander 7 and a second stage turbo expander 11. The refrigerating capacity of the two-stage turbo expander and the throttle valve 12 can meet the requirements of refrigerating capacity and temperature required by each link of liquefied coal bed gas extraction. The pressure ratio and flow rate of the second turboexpander 11 may be determined according to the flow ratio of the gas-liquid phase separated in the gas-liquid separator 9 and the operating condition of the first turboexpander 7. Meanwhile, the degree of supercooling and the flow rate of the liquid at the front end of the throttle valve 12 may be determined according to the system operating conditions.
From the above description, the embodiment of the present invention provides a novel small skid-mounted coal bed methane liquefaction process using a low-temperature two-phase turboexpander, including:
1) a purification process: the raw gas enters a purification system after reaching the standard through methane concentration detection, the raw gas of the system is a mixture of methane and nitrogen, and impurities such as ethane, propane, heavy hydrocarbon and the like are removed in the purification system;
2) a compressor cooling process; the process utilizes the pressure of the coal bed gas, and the power consumption of the compression system is provided by the output power of the turboexpander. Compressing the purified feed gas by a two-stage compressor, and cooling to ambient temperature by a cooling system;
3) two-phase expansion liquefaction process: the compressed and cooled raw material gas is firstly cooled to a certain temperature through a primary heat exchanger, and enters a primary turbine expander for expansion and cooling, and the compressed and cooled raw material gas can be subjected to superheated single-phase expansion or two-phase expansion according to working condition requirements in the primary turbine expander; the expanded fluid enters a secondary heat exchanger for continuous cooling, part of gas in the cooled fluid is liquefied and enters a two-phase state, and the fluid is divided into two branches of liquid and gas after passing through a gas-liquid separator; the gas part enters a secondary turbine expander for two-phase expansion, the liquid part is cooled by a heat exchanger and then throttled, and the expanded fluid and the throttled fluid are mixed and then enter a storage tank; the gas part in the storage tank enters a three-stage heat exchanger for reflux cooling and emptying, and the liquid part is a liquefied product;
further: the temperature of the raw material gas purified by the purification system is close to the local air temperature, and the purified coal bed raw material gas only contains methane and nitrogen;
further: after purification, the raw material gas is compressed by a raw material gas two-stage compressor, the pressure of the raw material gas entering the system is determined according to the self pressure of the extracted raw material gas and the compression energy provided by the turbine output function in the system, and the raw material gas is cooled to be close to the local air temperature after being discharged from the compressor;
further: the two-phase expansion liquefaction process comprises the following steps:
a1, cooling the compressed and cooled raw material gas to a certain temperature through a first-stage heat exchanger, entering a first-stage turbo expander for expansion and cooling, wherein the compressed and cooled raw material gas can be subjected to superheated single-phase expansion or two-phase expansion according to the working condition requirement in the first-stage turbo expander; the first stage turboexpander also transfers adiabatic expansion energy to the second stage compressor;
a2, the expanded fluid enters a secondary heat exchanger to be continuously cooled, part of gas in the cooled fluid is liquefied and enters a two-phase state, and the fluid is divided into two branches of liquid and gas after passing through a gas-liquid separator;
a3, the gas part enters a secondary turbine expander for two-phase expansion, the liquid part is cooled by a tertiary heat exchanger and then throttled, and the expanded fluid and the throttled fluid are mixed and then enter a storage tank; the two-stage turbo expander also transfers the two-phase expansion energy to the first-stage compressor;
a4, feeding the gas part into a storage tank into a three-stage heat exchanger for reflux cooling and emptying, wherein the liquid part is a liquefied product;
further: the pressure of the purified, compressed and cooled raw material gas is matched with the pressure which can be achieved by the turbine output power, the raw material gas which is close to the normal temperature enters a liquefaction process, sequentially passes through a primary heat exchanger, a primary turbo expander, a secondary heat exchanger, a gas-liquid separator and a secondary turbo expander, and the expansion ratio can be changed between 2 and 7 according to the difference between the gas flow and the pressure of the system raw material gas;
further: the working condition of the first-stage turbo expander can be switched between single-phase overheat expansion and two-phase expansion according to the working condition requirement of the system;
further: two stages of turboexpanders in this example: the refrigerating capacity of the first-stage turbo expander, the second-stage turbo expander and the throttle valve can meet the requirements on refrigerating capacity and temperature in each link of liquefied coal bed gas extraction, and the pressure ratio and the flow rate of the second-stage turbine are determined according to the gas-liquid phase fluid ratio in the gas-liquid separator and the working condition of the first-stage turbine;
further: two stages of turboexpanders in this example: the refrigerating capacities of the first-stage turbo expander, the second-stage turbo expander and the throttle valve can meet the requirements on refrigerating capacity and temperature in each link of liquefied coal bed gas extraction, and the supercooling degree and the flow of liquid in front of the throttle valve are determined according to the working condition of the system.
In the present invention, the first stage turboexpander also transfers adiabatic expansion energy to the second stage compressor; the primary compressor operates under two-phase expansion energy from the secondary turboexpander and the secondary compressor operates under adiabatic expansion energy from the primary turboexpander.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (4)
1. The utility model provides a small-size sled dress formula coal bed gas liquefaction system which characterized in that includes: the system comprises a raw material gas purification mechanism, a first-stage compressor cooler, a second-stage compressor cooler, a first-stage heat exchanger, a first-stage turboexpander, a second-stage heat exchanger, a gas-liquid separator, a third-stage heat exchanger, a second-stage turboexpander, a throttling valve and a product storage tank;
the feed gas purification mechanism, the primary compressor cooler, the secondary compressor and the secondary compressor cooler are sequentially connected in series, so that the feed gas is purified by the feed gas purification mechanism to filter impurities; then the compressed air passes through a first-stage compressor, a first-stage compressor cooler, a second-stage compressor and a second-stage compressor cooler to be compressed and cooled;
the secondary compressor cooler is sequentially connected with the primary heat exchanger, the primary turboexpander, the secondary heat exchanger and the gas-liquid separator; the purified, compressed and cooled raw material gas delivered by the secondary compressor cooler is subjected to heat exchange and temperature reduction through a primary heat exchanger, and then is subjected to adiabatic expansion through a primary turboexpander; then the gas is conveyed to a secondary heat exchanger to reduce the temperature of the expanded fluid so that the feed gas enters a two-phase state, and then the gas is conveyed to a gas-liquid separator to separate a liquid phase and a gas phase in the gas-liquid separator;
the gas-liquid separator is respectively connected with the third-stage heat exchanger and the second-stage turbo expander so as to enable the separated gas phase to enter the second-stage turbo expander for two-phase expansion, and the liquid phase enters the throttle valve for throttling after being further cooled in the third-stage heat exchanger;
wherein the two-stage turbo expander and the throttle valve are connected with the product storage tank so as to mix the throttled two-phase fluid and the expanded two-phase fluid and convey the mixed fluid to the product storage tank; the gas emptying channel of the product storage tank is connected with the third-stage heat exchanger, the second-stage heat exchanger and the first-stage heat exchanger so as to release cold energy through the heat exchangers in sequence when the product storage tank empties gas;
the first-stage turbo expander is also connected with the second-stage compressor, and the second-stage turbo expander is also connected with the first-stage compressor.
2. The small skid-mounted coal bed methane liquefaction system according to claim 1, wherein the pressure ratio and the flow rate of the secondary turboexpander are determined according to the fluid ratio of the gas-liquid phase separated from the gas-liquid separator and the working condition of the primary turboexpander.
3. The small skid-mounted coal bed methane liquefaction system of claim 1, wherein the liquid supercooling degree and the flow rate of the front end of the throttle valve are determined according to the system working condition.
4. A coal bed gas liquefaction method using the small skid-mounted coal bed gas liquefaction system according to any one of claims 1 to 3, comprising the following steps:
purifying the raw material gas by a raw material gas purification mechanism to filter impurities; then the compressed air passes through a first-stage compressor, a first-stage compressor cooler, a second-stage compressor and a second-stage compressor cooler to be compressed and cooled; then, the purified, compressed and cooled raw material gas is subjected to heat exchange and cooling through a primary heat exchanger, and then is subjected to adiabatic expansion through a primary turboexpander, and the primary turboexpander also transfers adiabatic expansion energy to a secondary compressor; the first-stage compressor operates under the drive of two-phase expansion energy from the second-stage turbo expander, and the second-stage compressor operates under the drive of adiabatic expansion energy from the first-stage turbo expander;
delivering the gas to a secondary heat exchanger to reduce the temperature of the expanded fluid so that the feed gas enters a two-phase state, and delivering the gas to a gas-liquid separator to separate a liquid phase and a gas phase in the gas-liquid separator; then the separated gas phase enters a secondary turbine expander for two-phase expansion, and the liquid phase enters a throttling valve for throttling after being further cooled in a tertiary heat exchanger; the two-stage turbo expander also transfers the two-phase expansion energy to the first-stage compressor;
mixing the throttled two-phase fluid and the expanded two-phase fluid and then conveying the mixture to a product storage tank; the gas emptying channel of the product storage tank is connected with the third-stage heat exchanger, the second-stage heat exchanger and the first-stage heat exchanger so as to release cold energy through the heat exchangers in sequence when the product storage tank empties gas.
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