CN109405413B - Oxygen-containing coal bed gas cryogenic rectification system and method avoiding explosion limit - Google Patents
Oxygen-containing coal bed gas cryogenic rectification system and method avoiding explosion limit Download PDFInfo
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- CN109405413B CN109405413B CN201811370337.6A CN201811370337A CN109405413B CN 109405413 B CN109405413 B CN 109405413B CN 201811370337 A CN201811370337 A CN 201811370337A CN 109405413 B CN109405413 B CN 109405413B
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- 239000007789 gas Substances 0.000 title claims abstract description 55
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 31
- 239000001301 oxygen Substances 0.000 title claims abstract description 31
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 31
- 239000003245 coal Substances 0.000 title claims abstract description 27
- 238000004880 explosion Methods 0.000 title claims abstract description 17
- 238000000034 method Methods 0.000 title claims abstract description 10
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 356
- 239000007788 liquid Substances 0.000 claims abstract description 71
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 56
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 28
- 238000012546 transfer Methods 0.000 claims abstract description 8
- 238000010992 reflux Methods 0.000 claims abstract description 5
- 230000001105 regulatory effect Effects 0.000 claims description 36
- 238000004891 communication Methods 0.000 claims description 12
- 238000001514 detection method Methods 0.000 claims description 12
- 230000000630 rising effect Effects 0.000 claims description 11
- 238000005507 spraying Methods 0.000 claims description 3
- 239000003949 liquefied natural gas Substances 0.000 description 7
- 238000013461 design Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
Classifications
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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
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
- F25J3/0209—Natural gas or substitute 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
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
- F25J3/0223—H2/CO mixtures, i.e. synthesis gas; Water gas or shifted synthesis 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
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
- F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
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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
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
- F25J3/0257—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of nitrogen
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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
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0295—Start-up or control of the process; Details of the apparatus used, e.g. sieve plates, packings
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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
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
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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
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/40—Features relating to the provision of boil-up in the bottom of a column
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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
- F25J2205/00—Processes or apparatus using other separation and/or other processing means
- F25J2205/30—Processes or apparatus using other separation and/or other processing means using a washing, e.g. "scrubbing" or bubble column for purification purposes
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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
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/40—Air or oxygen enriched air, i.e. generally less than 30mol% of O2
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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
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/04—Recovery of liquid products
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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
- F25J2280/00—Control of the process or apparatus
- F25J2280/02—Control in general, load changes, different modes ("runs"), measurements
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Separation By Low-Temperature Treatments (AREA)
Abstract
The invention discloses a cryogenic rectification system and a cryogenic rectification method for oxygen-containing coal bed gas avoiding explosion limit. Oxygen-containing coal bed gas enters from the middle part of the rectifying tower, the gas part is upwards used as stripping of the rectifying section, mass transfer and heat transfer exchange are carried out on the tower plates and liquid, liquid nitrogen is sprayed from the top of the rectifying tower and used as reflux liquid of the rectifying tower, and the methane content of a gas phase space between the first tower plate and the top of the tower body and the methane content of a gas phase space between the second tower plate and the first tower plate are monitored in real time through an online methane content detector, so that the methane content of the gas phase space between the first tower plate and the top of the tower body is always kept to be less than 5%, and the methane content of the gas phase space between the second tower plate and the first tower plate is more than 15% or less than 5%, thereby realizing avoidance of explosion limit.
Description
Technical Field
The invention relates to a coalbed methane treatment technology, in particular to an oxygen-containing coalbed methane cryogenic rectification system and method avoiding explosion limit.
Background
The low-concentration coal bed gas not only contains 20% -50% of methane, but also contains a large amount of air containing nitrogen and oxygen, is a harmful factor in coal mine production, not only pollutes the air, but also causes explosion when the content of the coal bed gas in the air is 5% -16%, and causes safety accidents.
The method of the low-temperature rectifying tower is adopted to separate out the non-condensable gases such as oxygen, nitrogen and the like in the oxygen-containing coal bed gas, and the bottom of the rectifying tower is used for preparing liquefied natural gas, and the non-condensable gases such as oxygen, nitrogen and the like are discharged from the top of the rectifying tower. The volume fraction of methane in the stripping component from bottom to top in the rectifying tower is reduced from 98% to 2%, the risk of crossing the explosion limit is 5% -15%, and the safety of the rectifying tower is seriously reduced, so that it is necessary to design an oxygen-containing coalbed methane cryogenic rectifying system avoiding the explosion limit.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a low-temperature rectification system which has reasonable structural design and can treat oxygen-containing coal bed gas without explosion limit, and specific method steps are provided.
The invention solves the problems by adopting the following technical scheme: an oxygen-containing coalbed methane cryogenic rectification system avoiding explosion limits, comprising a rectification column, characterized in that: the system also comprises a reboiler, a coalbed methane input pipeline, a liquid nitrogen input pipeline, a circulating methane pipeline, an exhaust pipeline and a liquid methane output pipeline; the rectifying tower is a plate-type tower and comprises a tower body and a tower seat cavity which is positioned at the bottom of the tower body and is used for collecting liquid, a plurality of tower plates are arranged in the tower body from top to bottom, and overflow pipes are arranged at the ends of the tower plates; the tower body is provided with a first online methane content detector for detecting the methane content of a gas phase space between the first tower plate and the top of the tower body, a second online methane content detector for detecting the methane content of the gas phase space between the second tower plate and the first tower plate, and a third online methane content detector for detecting the methane content at the bottom of the tower body; the reboiler is arranged in the tower seat cavity; the circulating methane pipeline penetrates through the tower seat cavity and is connected with the reboiler, and is used for providing a heat source for the reboiler; the tower seat cavity is provided with a liquid level detector for detecting the liquid level in the tower seat cavity; one end of the liquid methane output pipeline is connected with the bottom of the tower seat cavity, the other end of the liquid methane output pipeline is connected with an external LNG storage tank, a liquid level regulating valve is arranged on the liquid methane output pipeline, and the liquid level detector is in communication connection with the liquid level regulating valve; one end of the coalbed methane input pipeline is led to the middle part of the tower body, one end of the liquid nitrogen input pipeline is led to the upper part of the tower body, and the top of the tower body is connected with the exhaust pipeline; the device is characterized in that a fourth online methane content detector is arranged on the coalbed methane input pipeline, a fifth online methane content detector is arranged on the exhaust pipeline, a first flow regulating valve is arranged on the liquid nitrogen input pipeline, and the fourth online methane content detector and the fifth online methane content detector are all in communication connection with the first flow regulating valve.
Preferably, the exhaust pipeline is further provided with a pressure detector and a pressure control valve, and the pressure detector is in communication connection with the pressure control valve.
Preferably, the circulating methane pipeline comprises a circulating methane input pipeline for sending circulating methane into the reboiler, a circulating methane output pipeline for outputting the circulating methane from the reboiler, and an adjusting bypass for connecting the circulating methane input pipeline and the circulating methane output pipeline, wherein a second flow adjusting valve is arranged on the adjusting bypass, a sixth online methane content detector is arranged on the circulating methane input pipeline, and the sixth online methane content detector and the third online methane content detector are both in communication connection with the second flow adjusting valve.
In order to solve the technical problems, the invention also provides another technical scheme: a method for cryogenic rectification of oxygen-containing coal bed gas that avoids explosion limitations, comprising the steps of:
step one: spraying liquid nitrogen into the upper part of the tower body through a liquid nitrogen input pipeline to serve as reflux liquid of the rectifying tower, conveying the oxygen-containing coal bed gas controlled in a certain low temperature state into the middle part of the tower body through the coal bed gas input pipeline, enabling the oxygen-containing coal bed gas phase part to flow upwards, carrying out mass transfer and heat transfer exchange contact with the liquid nitrogen on the tower plate, and enabling methane in the rising gas to flow downwards until the methane enters the tower seat cavity for collection; non-condensable gases such as nitrogen, oxygen and the like in the rising gas are enriched, and continuously flow upwards to enter an exhaust pipeline, the fourth online methane content detector detects the methane content in the oxygen-containing coal bed gas, and the fifth online methane content detector detects the methane content in the exhaust pipeline;
step two: methane is introduced into the reboiler through a circulating methane input pipeline to be used as a heat source of the reboiler, so that the reboiler generates upward steam stripping;
step three: the opening degree of the first flow regulating valve is regulated according to the detection values of the fourth online methane content detector and the fifth online methane content detector, so that the methane content detected by the first online methane content detector is controlled to be always less than 5%, and the methane content detected by the second online methane content detector is controlled to be more than 15% or less than 5%; according to the detection values of the sixth online methane content detector and the third online methane content detector, a second flow regulating valve is regulated, the flow of circulating methane entering the reboiler is controlled, and the bottom temperature of the rectifying tower and the rising stripping amount are further controlled; according to the detection value of the pressure detector, the opening degree of the pressure control valve is regulated, so that the operation pressure of the rectifying tower is controlled; the opening of the liquid level regulating valve is regulated according to the detection value of the liquid level detector, so that liquid methane collected in the tower cavity is timely output to the external LNG storage tank.
Compared with the prior art, the invention has the following advantages and effects:
1. the whole rectification system has perfect functions, can realize the treatment of the oxygen-containing coal bed gas avoiding explosion limit, and monitors the methane content of the gas phase space between the first column plate and the top of the tower body and the methane content of the gas phase space between the second column plate and the first column plate in real time by arranging an online methane content detector, so as to ensure that the methane content of the gas phase space between the first column plate and the top of the tower body is always kept less than 5 percent and the methane content of the gas phase space between the second column plate and the first column plate is more than 15 percent or less than 5 percent, thereby realizing the avoidance of explosion limit;
2. the circulating methane is used as a heat source of a reboiler at the bottom of the rectifying tower, the methane quantity entering the reboiler is controlled by adjusting a bypass, and the rising stripping quantity is further controlled, so that the methane concentration in the liquefied natural gas at the bottom of the rectifying tower is controlled;
3. liquid nitrogen is sprayed from the top of the rectifying tower and is used as reflux liquid of the rectifying tower, methane in rising gas is condensed and gasified into gas, the condensate continuously flows downwards, the concentration of methane in the condensate is continuously improved, and liquid coming out from the bottom of the rectifying tower is high-concentration methane and is led out and stored as liquefied natural gas products.
Drawings
Fig. 1 is a schematic structural view of an embodiment of the present invention.
Reference numerals illustrate: coalbed methane input pipeline 1, liquid methane output pipeline 2, exhaust pipeline 3, liquid nitrogen input pipeline 4, circulating methane input pipeline 5, regulating bypass 7, circulating methane output pipeline 8, rectifying tower 11, tower body 12, tower plate 13, overflow pipe 14, tower seat cavity 15, reboiler 16, first online methane content detector 37, second online methane content detector 38, third online methane content detector 35, fourth online methane content detector 34, fifth online methane content detector 32, sixth online methane content detector 36, liquid level detector 31, pressure detector 33, liquid level regulating valve 51, pressure control valve 53, first flow regulating valve 52, and second flow regulating valve 54.
Detailed Description
The present invention will be described in further detail by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and not limited to the following examples.
Examples
See fig. 1.
The embodiment is an oxygen-containing coalbed methane cryogenic rectification system avoiding explosion limit, which comprises a rectification tower 11, a reboiler 16, a coalbed methane input pipeline 1, a liquid nitrogen input pipeline 4, a circulating methane pipeline, an exhaust pipeline 3 and a liquid methane output pipeline 2.
In this embodiment, the rectifying tower 11 is a plate tower, and includes a tower body 12 and a tower seat cavity 15 located at the bottom of the tower body 12 and used for collecting liquid, a plurality of tower plates 13 are disposed in the tower body 12 from top to bottom, the uppermost is a first tower plate, other tower plates are sequentially ordered from top to bottom, and an overflow pipe 14 is installed at the end of the tower plate 13. The column 12 is provided with a first online methane content detector 37 for detecting the methane content of the gas phase space between the first tray and the top of the column, a second online methane content detector 38 for detecting the methane content of the gas phase space between the second tray and the first tray, and a third online methane content detector 35 for detecting the methane content of the bottom of the column.
In this embodiment, reboiler 16 is installed in tower base cavity 15; the recycle methane line is connected to reboiler 16 through column foot cavity 15 for providing a heat source to reboiler 16. The tower base cavity 15 is provided with a liquid level detector 31 for detecting the liquid level in the tower base cavity 15. One end of the liquid methane output pipeline 2 is connected with the bottom of the tower base cavity 15, the other end of the liquid methane output pipeline 2 is connected with an external LNG storage tank, a liquid level regulating valve 51 is arranged on the liquid methane output pipeline 2, and the liquid level detector 31 is in communication connection with the liquid level regulating valve 51.
In this embodiment, one end of the coalbed methane input pipeline 1 is led to the middle part of the tower body 12, one end of the liquid nitrogen input pipeline 4 is led to the upper part of the tower body 12, and the top of the tower body 12 is connected with the exhaust pipeline 3. The coalbed methane input pipeline 1 is provided with a fourth online methane content detector 34, the exhaust pipeline 3 is provided with a fifth online methane content detector 32, a pressure detector 33 and a pressure control valve 53, the liquid nitrogen input pipeline 4 is provided with a first flow regulating valve 52, the fourth online methane content detector 34 and the fifth online methane content detector 32 are all in communication connection with the first flow regulating valve 52, and the pressure detector 33 is in communication connection with the pressure control valve 53.
In this embodiment, the circulating methane pipeline includes a circulating methane input pipeline 5 for sending circulating methane into the reboiler 16, a circulating methane output pipeline 8 for outputting circulating methane from the reboiler 16, and an adjusting bypass 7 for connecting the circulating methane input pipeline 5 and the circulating methane output pipeline 8, a second flow rate adjusting valve 54 is provided on the adjusting bypass 7, a sixth online methane content detector 36 is provided on the circulating methane input pipeline 5, and the sixth online methane content detector 36 and the third online methane content detector 35 are both in communication connection with the second flow rate adjusting valve 54.
In this embodiment, the oxygen-containing coalbed methane cryogenic rectification method avoiding the explosion limit comprises the following steps:
step one: spraying liquid nitrogen into the upper part of a tower body 12 through a liquid nitrogen input pipeline 4 to serve as reflux liquid of a rectifying tower 11, conveying oxygen-containing coal bed gas controlled in a certain low-temperature state into the middle part of the tower body 12 through a coal bed gas input pipeline 1, enabling a gas phase part of the oxygen-containing coal bed gas to flow upwards, carrying out mass transfer and heat transfer exchange contact with the liquid nitrogen on a tower plate 13, and enabling methane in the rising gas to flow downwards until the methane enters a tower seat cavity 15 for collection; non-condensable gases such as nitrogen, oxygen and the like in the rising gas are enriched, and continue to flow upwards into the exhaust pipeline 3, the fourth online methane content detector 34 detects the methane content in the oxygen-containing coal bed gas, and the fifth online methane content detector 32 detects the methane content in the exhaust pipeline 3;
step two: methane is introduced into the reboiler 16 through the circulating methane input pipeline 5 and is used as a heat source of the reboiler 16, so that the reboiler 16 generates upward steam stripping;
step three: the opening degree of the first flow regulating valve 52 is regulated according to the detection values of the fourth online methane content detector 34 and the fifth online methane content detector 32, so that the methane content detected by the first online methane content detector 37 is controlled to be always less than 5%, and the methane content detected by the second online methane content detector 38 is controlled to be more than 15% or less than 5%; the second flow regulating valve 54 is regulated according to the detection values of the sixth online methane content detector 36 and the third online methane content detector 35, so as to control the flow of the circulating methane entering the reboiler 16 and further control the bottom temperature of the rectifying tower 11 and the rising stripping amount; according to the detection value of the pressure detector 33, the opening degree of the pressure control valve 53 is adjusted, thereby controlling the operating pressure of the rectifying column 11; the opening of the liquid level regulating valve 51 is regulated by the detection value of the liquid level detector 31, so that the liquid methane collected in the tower base cavity 15 is timely output to the external LNG storage tank.
Although the present invention has been described with reference to the above embodiments, it should be understood that the invention is not limited to the embodiments described above, but is capable of modification and variation without departing from the spirit and scope of the present invention.
Claims (1)
1. A method for performing cryogenic rectification on oxygen-containing coal bed gas by using an oxygen-containing coal bed gas cryogenic rectification system avoiding explosion limit, wherein the oxygen-containing coal bed gas cryogenic rectification system avoiding explosion limit comprises a rectification tower (11), a reboiler (16), a coal bed gas input pipeline (1), a liquid nitrogen input pipeline (4), a circulating methane pipeline, an exhaust pipeline (3) and a liquid methane output pipeline (2); the rectifying tower (11) is a plate-type tower and comprises a tower body (12) and a tower seat cavity (15) which is positioned at the bottom of the tower body (12) and is used for collecting liquid, a plurality of tower plates (13) are arranged in the tower body (12) from top to bottom, and overflow pipes (14) are arranged at the ends of the tower plates (13); a first online methane content detector (37) for detecting the methane content of the gas phase space between the first tower plate and the top of the tower body, a second online methane content detector (38) for detecting the methane content of the gas phase space between the second tower plate and the first tower plate, and a third online methane content detector (35) for detecting the methane content of the bottom of the tower body are arranged on the tower body (12); the reboiler (16) is arranged in the tower seat cavity (15); the circulating methane pipeline passes through the tower seat cavity (15) and is connected with the reboiler (16) and is used for providing a heat source for the reboiler (16); a liquid level detector (31) for detecting the liquid level in the tower seat cavity (15) is arranged on the tower seat cavity (15); one end of the liquid methane output pipeline (2) is connected with the bottom of the tower seat cavity (15), the other end of the liquid methane output pipeline is connected with an external LNG storage tank, a liquid level regulating valve (51) is arranged on the liquid methane output pipeline (2), and the liquid level detector (31) is in communication connection with the liquid level regulating valve (51); one end of the coalbed methane input pipeline (1) is communicated with the middle of the tower body (12), one end of the liquid nitrogen input pipeline (4) is communicated with the upper part of the tower body (12), and the top of the tower body (12) is connected with the exhaust pipeline (3); the coalbed methane input pipeline (1) is provided with a fourth online methane content detector (34), the exhaust pipeline (3) is provided with a fifth online methane content detector (32), the liquid nitrogen input pipeline (4) is provided with a first flow regulating valve (52), and the fourth online methane content detector (34) and the fifth online methane content detector (32) are all in communication connection with the first flow regulating valve (52); the exhaust pipeline (3) is also provided with a pressure detector (33) and a pressure control valve (53), and the pressure detector (33) is in communication connection with the pressure control valve (53); the circulating methane pipeline comprises a circulating methane input pipeline (5) for conveying circulating methane into a reboiler (16), a circulating methane output pipeline (8) for outputting the circulating methane from the reboiler (16) and an adjusting bypass (7) for connecting the circulating methane input pipeline (5) and the circulating methane output pipeline (8), wherein a second flow adjusting valve (54) is arranged on the adjusting bypass (7), a sixth online methane content detector (36) is arranged on the circulating methane input pipeline (5), and the sixth online methane content detector (36) and the third online methane content detector (35) are all in communication connection with the second flow adjusting valve (54), and the circulating methane pipeline is characterized in that: the method comprises the following steps:
step one: spraying liquid nitrogen into the upper part of a tower body (12) through a liquid nitrogen input pipeline (4), and taking the liquid nitrogen as reflux liquid of a rectifying tower (11), conveying oxygen-containing coal bed gas controlled in a certain low temperature state into the middle part of the tower body (12) through a coal bed gas input pipeline (1), enabling the oxygen-containing coal bed gas phase part to flow upwards, carrying out mass transfer and heat transfer exchange contact with the liquid nitrogen on a tower plate (13), and enabling methane in the rising gas to flow downwards until the methane enters a tower seat cavity (15) for collection; non-condensable gases such as nitrogen, oxygen and the like in the rising gas are enriched, and continuously flow upwards to enter an exhaust pipeline (3), the fourth online methane content detector (34) detects the methane content in the oxygen-containing coal bed gas, and the fifth online methane content detector (32) detects the methane content in the exhaust pipeline (3);
step two: methane is introduced into the reboiler (16) through a circulating methane input pipeline (5) and is used as a heat source of the reboiler (16), so that the reboiler (16) generates upward steam stripping;
step three: the opening degree of a first flow regulating valve (52) is regulated according to the detection values of a fourth online methane content detector (34) and a fifth online methane content detector (32), so that the methane content detected by a first online methane content detector (37) is controlled to be always kept smaller than 5%, and the methane content detected by a second online methane content detector (38) is controlled to be larger than 15% or smaller than 5%; according to the detection values of the sixth online methane content detector (36) and the third online methane content detector (35), a second flow regulating valve (54) is regulated, the flow of circulating methane entering the reboiler (16) is controlled, and the bottom temperature of the rectifying tower (11) and the rising stripping amount are further controlled; according to the detection value of the pressure detector (33), the opening degree of the pressure control valve (53) is regulated, so that the operating pressure of the rectifying tower (11) is controlled; the opening degree of the liquid level regulating valve (51) is regulated according to the detection value of the liquid level detector (31), so that liquid methane collected in the tower cavity (15) is timely output to an external LNG storage tank.
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