CN105254463A - Method for extracting methane from mixed gas containing methane, hydrogen and nitrogen - Google Patents
Method for extracting methane from mixed gas containing methane, hydrogen and nitrogen Download PDFInfo
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- CN105254463A CN105254463A CN201510696863.1A CN201510696863A CN105254463A CN 105254463 A CN105254463 A CN 105254463A CN 201510696863 A CN201510696863 A CN 201510696863A CN 105254463 A CN105254463 A CN 105254463A
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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
- F25J3/0228—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
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/04—Processes or apparatus using separation by rectification in a dual pressure main column system
- F25J2200/06—Processes or apparatus using separation by rectification in a dual pressure main column system in a classical double column flow-sheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure 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
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
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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
- 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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- 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
- F25J2240/00—Processes or apparatus involving steps for expanding of process streams
- F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
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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
- F25J2270/00—Refrigeration techniques used
- F25J2270/12—External refrigeration with liquid vaporising loop
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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
- F25J2270/00—Refrigeration techniques used
- F25J2270/66—Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
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- Engineering & Computer Science (AREA)
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- 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 method for extracting methane from mixed gas containing the methane, hydrogen and nitrogen. The method comprises the steps that feed gas is divided into two steams, namely, an air stream A and an air stream B, and the air stream A enters a high-pressure tower to be rectified and separated after being cooled through a main heat exchanger; the air stream B is pumped out from the heat exchanger after being cooled for a certain stage through the main heat exchanger, the pumped-out air stream B is directly fed into a low-pressure tower to be rectified after being depressurized, refrigerated and cooled through an expansion machine, and a liquid methane product is obtained at the tower bottom. Or after the feed gas enters the main heat exchanger and is cooled to a certain stage, the feed gas is divided into the two streams, namely, the air stream A and the air stream B, wherein the air stream A continuously enters the main heat exchanger and is cooled, then the cooled air stream A enters the high-pressure tower to be rectified and separated, the air stream B is directly fed into the low-pressure tower to be rectified after being depressurized, refrigerated and cooled through the expansion machine, and the liquid methane product is obtained at the tower bottom. By means of the method for extracting the methane from the mixed gas containing the methane, the hydrogen and the nitrogen, non-pressurized liquified natural gas with the purity being 98 percent or above can be directly obtained, the product does not need to be liquified again, energy consumption can be greatly reduced, the recovery rate of the methane can reach up to 99.5 percent, the recovery rate of the nitrogen can reach up to 99 percent, and the rewarmed nitrogen can be used as industrial nitrogen.
Description
Technical field
The present invention relates to a kind of method extracting methane from the gas mixture containing methane, hydrogen, nitrogen.
Background technology
Coal-seam gas, synthetic ammonia periodic off-gases, coal upgrading pyrolysis tail gas etc. are the gas mixture containing elements such as methane, hydrogen, nitrogen, and its main component comprises: CO
2, H
2, CH
4, CO, H
2o, N
2and other hydro carbons and sulfide.
(mainly CH in current gas mixture
4, H
2and N
2) methane separation technology has membrane separation process, pressure swing adsorption process.Though membrane separation technique is simple to operate, energy consumption is low, investment cost is comparatively large, and separating effect is poor, though pressure swing adsorption process is convenient and swift, because the absorption property of methane and nitrogen is close, causes the rate of recovery of gas product lower, and is difficult to separation of C H
4and N
2, and low temperature fractionation technology can directly isolate highly purified methane and nitrogen.
Summary of the invention
Goal of the invention: object of the present invention is exactly existingly extract the deficiency existed in the method for methane from the gas mixture containing methane, hydrogen, nitrogen for above-mentioned, provides the new deep cooling high-low pressure tower rectification process that effectively can extract methane.
Technical scheme: the invention provides a kind of method extracting methane from the gas mixture containing methane, hydrogen, nitrogen:
Unstripped gas is divided into two strands of air-flows, main air (air-flow A), secondary air flow (air-flow B): air-flow A enters high-pressure tower after entering main heat exchanger cooling and carries out rectifying separation; Air-flow B extracts out, directly sends into lower pressure column rectifying, obtain product liquid methane at the bottom of tower after decompressor step-down refrigeration cool-down after entering main heat exchanger cooling certain phase in the middle part of interchanger.
Or, unstripped gas enters after main heat exchanger is cooled to certain phase, be divided into two strands of air-flows, main air (air-flow A) and secondary air flow (air-flow B): air-flow A continues to enter high-pressure tower after main heat exchanger cooling and carries out rectifying separation, air-flow B directly sends into lower pressure column rectifying after decompressor step-down refrigeration cool-down, obtains product liquid methane at the bottom of tower.
The methane-rich liquid of lower pressure column tower reactor of the present invention enters condenser/evaporator, evaporation section as the upflowing vapor of lower pressure column, non-evaporation section from condenser/evaporator side draw, through supercooler cross cold after, obtain product liquify natural gas.The product obtained is the normal pressure liquify natural gas of purity more than 98%, and product is without the need to liquefying again, and greatly can reduce energy consumption, methane recovery is up to 99.5%.
The rich nitrogen that lower pressure column tower top of the present invention obtains with from high-pressure tower for uncooled rich nitrogen is together after re-heat, draw as product nitrogen gas.Concrete, the nitrogen that lower pressure column tower top obtains purity more than 99.5% can be used as industrial nitrogen use after re-heat.From high-pressure tower, drawing liquid nitrogen (high purity 99.8%) continuation cooling deutomerite flows to lower pressure column, as the phegma of lower pressure column.
In process of the present invention other part cold can by azeotrope compression cycle freeze provide or nitrogen expansion mechanism cold circulate provide.
In the present invention, operational condition is: lower pressure column pressure is that (more than (gauge pressure), high-pressure tower pressure is more than 0.4MPa (gauge pressure) to 0.01MPa.Because pressure is higher, stricter to equipment requirements, the present invention is under the prerequisite not affecting separating effect and extraction yield, extract after partial raw gas expands and directly enter lower pressure column, make full use of the rectifying potentiality of lower pressure column, and greatly can reduce the load of high-pressure tower, thus alleviate the manufacture difficulty of high-pressure tower.
Of the present inventionly can be realized by following two concrete technical schemes:
Scheme one:
By coal upgrading pyrolysis tail gas through desulfurization and decarburization, dewater, after taking off heavy hydrocarbon and trace impurity, enter methanation unit, the tail gas obtained is as unstripped gas.
Unstripped gas is divided into air-flow A, air-flow B two strands.
Wherein air-flow A enters main heat exchanger E1, through heat exchange, after unstripped gas partial liquefaction, enters the bottom of high-pressure tower T1, carries out preliminary rectifying separation.Wherein be rich in the volatile components of nitrogen along tower height upwards, gaseous stream stock (i.e. air-flow G) is drawn at high-pressure tower T1 tower top, enter in condenser/evaporator E4, carry out partial condensation, condensed liquid stream (i.e. air-flow C) through a supercooler E2 cross cold after decompression enter in the middle part of lower pressure column and continue rectifying.
Another gang of air-flow B wherein enters main heat exchanger E1, incoming stock decompressor EXP1 after cooling, after step-down cooling, with high-pressure tower tower bottoms and air-flow E, all enter in the middle part of lower pressure column T2, using high-pressure tower T1 overhead condensation liquid air-flow (i.e. air-flow C) as trim the top of column liquid, carry out the rectifying of lower pressure column T2, the methane-rich liquid of lower pressure column tower reactor enters condenser/evaporator E4 side, the rich nitrogen of the high pressure tower top that the vaporizer E4 opposite side that is condensed is heated to part evaporation, evaporation section is as the upflowing vapor of lower pressure column, non-evaporation section draws air-flow (i.e. air-flow H) from condenser/evaporator E4 side, through supercooler cross cold after as product liquify natural gas.
Scheme two:
By coal upgrading pyrolysis tail gas through desulfurization and decarburization, dewater, after taking off heavy hydrocarbon and trace impurity, enter methanation unit, the tail gas obtained is as unstripped gas.
Unstripped gas enters after main heat exchanger is cooled to certain phase, is divided into main air and secondary air flow.
Main air continues to enter high-pressure tower after main heat exchanger cooling and carries out rectifying separation, and secondary air flow directly sends into rectifying in the middle part of lower pressure column after decompressor step-down refrigeration cool-down, obtains product methane at the bottom of tower.
Described main air enters main heat exchanger (E1), and through heat exchange, unstripped gas is lowered the temperature or after partial liquefaction, entered the bottom of high-pressure tower (T1), carry out preliminary rectifying separation; Wherein be rich in the volatile components of nitrogen along tower height upwards, gaseous stream stock is drawn at high-pressure tower (T1) tower top, enter in condenser/evaporator (E4), carry out partial condensation, the decompression after a supercooler (E2) is excessively cold of condensed liquid stream enters in the middle part of lower pressure column and continues rectifying.
The incoming stock decompressor of described secondary air flow (EXP1), after step-down cooling, with high-pressure tower tower bottoms, all enter lower pressure column (T2) middle part, using high-pressure tower (T1) overhead condensation liquid air-flow as trim the top of column liquid, carry out the rectifying of lower pressure column (T2), the methane-rich liquid of lower pressure column tower reactor enters condenser/evaporator (E4) side, the rich nitrogen of the high pressure tower top that vaporizer (E4) opposite side that is condensed is heated to part evaporation, evaporation section is as the upflowing vapor of lower pressure column, non-evaporation section draws air-flow from condenser/evaporator (E4) side, through supercooler cross cold after as product liquify natural gas.
Beneficial effect: 1, the present invention directly can obtain the normal pressure liquify natural gas that purity is more than 98%, and product is without the need to liquefying again, and greatly can reduce energy consumption, methane recovery is up to 99.5%.Can obtain purity be more than 99% nitrogen, rate of recovery of nitrogen up to 99%, the nitrogen after re-heat can be used as industrial nitrogen use.
2, the present invention utilizes the rich nitrogen of the low temperature of lower pressure column tower top to cross cold low tower bottom product liquid methane, for product provides enough condensate depression, crosses the thick methane of cold anticyclone tower bottom simultaneously, to reduce the temperature that liquid enters lower pressure column, improves reflux ratio, improve rectifying ability.
3, the present invention, under the prerequisite not affecting separating effect and extraction yield, extracts after partial raw gas expands and directly enters lower pressure column, take full advantage of the rectifying potentiality of lower pressure column, greatly reduce the load of high-pressure tower, thus alleviate the manufacture difficulty of high-pressure tower.
Accompanying drawing explanation
Fig. 1 is the schematic flow sheet of the embodiment of the present invention 1;
Fig. 2 is the schematic flow sheet of the embodiment of the present invention 2.
Embodiment:
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described further,
Embodiment 1
As shown in Figure 1, in FIG, the equipment represented by each mark is as follows: P1-unstripped gas decompressor pressurized end; P2-azeotrope recycle compressor; E1-main heat exchanger; E2-supercooler; E3-azeotrope water cooler; E4-condenser/evaporator; EXP1-raw material expander end; T1-high-pressure tower; T2-lower pressure column; FL-gas-liquid separator.
Air-flow represented by each mark is as follows: the unstripped gas of the laggard high-pressure tower of air-flow A-precooling; The unstripped gas of the laggard lower pressure column of air-flow B-compression-expansion; Air-flow C-excessively cold enter the high pressure nitrogen overhead phlegma of lower pressure column; Air-flow D-enters thick methane at the bottom of the high-pressure tower tower of lower pressure column; Air-flow E-is used for the low pressure nitrogen overhead of re-heat; The gaseous stream stock that air-flow F-high-pressure tower tower top is drawn; Air-flow G-bottom product LNG.
Coal upgrading pyrolysis tail gas handled in the present embodiment, main component comprises: CO
2, H
2, CH
4, CO, H
2o, N
2and other hydro carbons and sulfide.
By this gas through desulfurization and decarburization, dewater, after taking off heavy hydrocarbon and trace impurity, enter methanation unit, the tail gas obtained is as unstripped gas, and unstripped gas tolerance is 25000Nm
3/ h, pressure is about 20bar, unstripped gas is divided into air-flow A, air-flow B two strands.Wherein 15000Nm
3/ h directly enters lower pressure column rectifying, residue 10000Nm for compressing after precooling is expanded
3/ h is through the laggard high-pressure tower rectifying of deep cooling.
Wherein air-flow A enters main heat exchanger E1, through heat exchange, after unstripped gas partial liquefaction, enters the bottom of high-pressure tower T1, carries out preliminary rectifying separation.Wherein be rich in the volatile components of nitrogen along tower height upwards, gaseous stream stock is drawn at high-pressure tower T1 tower top, i.e. air-flow F, enter in condenser/evaporator E4, carry out partial condensation, condensed liquid stream C through a supercooler E2 cross cold after decompression enter in the middle part of lower pressure column and continue rectifying, lower pressure column T2 nitrogen overhead air-flow E enters main heat exchanger E1, for process provides supplementary low temperature cold.
Another gang of air-flow B wherein through unstripped gas decompressor pressurized end P1 supercharging laggard enter main heat exchanger E1, cooling after incoming stock decompressor EXP1, step-down cooling after, with high-pressure tower tower bottoms, i.e. air-flow D, all enters in the middle part of lower pressure column T2, with high-pressure tower T1 overhead condensation liquid air-flow C (57500Nm
3/ h) as trim the top of column liquid, carry out the rectifying of lower pressure column T2, the methane-rich liquid of lower pressure column tower reactor enters condenser/evaporator E4 side, the rich nitrogen of the high pressure tower top that the vaporizer E4 opposite side that is condensed is heated to part evaporation, evaporation section is as the upflowing vapor of lower pressure column, non-evaporation section draws air-flow G from condenser/evaporator E4 side, through supercooler cross cold after as product liquify natural gas.
Embodiment 1 Raw gas and each step gas standard, as shown in table 1 below:
Table 1
| Gas after methanation | Unstripped gas after dehydration | The rich nitrogen of low pressure tower top | Product LNG | |
| Flow (Nm 3/h) | 300000 | 250000 | 206000 | 45630 |
| Temperature (DEG C) | 20 | 20 | -193 | -180 |
| Pressure (barA) | ～20 | ～20 | ～1.3 | ～1.4 |
| Composition (mol%) | ||||
| CH 4 | 14.57 | 17.72 | 9ppm | 98 |
| H 2 | 0.429 | 0.522 | 0.64 | 0 |
| N 2 | 67.18 | 81.75 | 99.36 | 2 |
| H 2O | 17.82 | 0 | 0 | 0 |
| CO | 31ppm | 38ppm | 41ppm | 22ppm |
Embodiment 2
As shown in Figure 2, in fig. 2, the equipment represented by each mark is as follows: P1-unstripped gas decompressor pressurized end; P2-azeotrope recycle compressor; E1-main heat exchanger; E2-supercooler; E3-azeotrope water cooler; E4-condenser/evaporator; EXP1-raw material expander end; T1-high-pressure tower; T2-lower pressure column; FL-gas-liquid separator.
Air-flow represented by each mark is as follows: the unstripped gas of the laggard high-pressure tower of air-flow A-precooling; Air-flow B-expands the unstripped gas of laggard lower pressure column; Air-flow C-excessively cold enter the high pressure nitrogen overhead phlegma of lower pressure column; Air-flow D-enters thick methane at the bottom of the high-pressure tower tower of lower pressure column; Air-flow E-is used for the low pressure nitrogen overhead of re-heat; The gaseous stream stock that air-flow F-high-pressure tower tower top is drawn; Air-flow G-bottom product LNG.
Gas handled in the present embodiment, main component comprises: CO
2, H
2, CH
4, CO, H
2o, N
2and other hydro carbons and sulfide.Unstripped gas enters after in the middle part of main heat exchanger, be divided into two strands, air-flow A and air-flow B, air-flow A continues to enter bottom high-pressure tower T1 after main heat exchanger E1 lowers the temperature, carry out preliminary rectifying separation, wherein be rich in the volatile components of nitrogen along tower height upwards, gaseous stream stock is drawn at high-pressure tower T1 tower top, i.e. air-flow F, enter in condenser/evaporator E4, carry out partial condensation, condensed liquid stream C through a supercooler E2 cross cold after decompression enter in the middle part of lower pressure column and continue rectifying, lower pressure column T2 nitrogen overhead air-flow E enters main heat exchanger E1, for process provides supplementary low temperature cold.
Air-flow B directly sends into lower pressure column T2 rectifying after decompressor EXP1 step-down refrigeration cool-down, with high-pressure tower tower bottoms, i.e. air-flow D, all enter in the middle part of lower pressure column T2, using high-pressure tower T1 overhead condensation liquid air-flow C as trim the top of column liquid, carry out the rectifying of lower pressure column T2, the methane-rich liquid of lower pressure column tower reactor enters condenser/evaporator E4 side, the rich nitrogen of the high pressure tower top that the vaporizer E4 opposite side that is condensed is heated to part evaporation, evaporation section is as the upflowing vapor of lower pressure column, non-evaporation section draws air-flow G from condenser/evaporator E4 side, through supercooler cross cold after as product liquify natural gas.
Embodiment 2 Raw gas and each step gas standard, as shown in table 2 below:
Table 2
| Gas after methanation | Unstripped gas after dehydration | The rich nitrogen of low pressure tower top | Product LNG | |
| Flow (Nm 3/h) | 300000 | 250000 | 206600 | 45600 |
| Temperature (DEG C) | 20 | 20 | -193 | -162 |
| Pressure (barA) | ～20 | ～20 | ～1.3 | ～1.4 |
| Composition (mol%) | ||||
| CH 4 | 14.57 | 17.72 | 9ppm | 98 |
| H 2 | 0.429 | 0.522 | 0.64 | 0 |
| N 2 | 67.18 | 81.75 | 99.36 | 2 |
| H 2O | 17.82 | 0 | 0 | 0 |
| CO | 31ppm | 38ppm | 40ppm | 28ppm |
Claims (10)
1. from the gas mixture containing methane, hydrogen, nitrogen, extract a method for methane, it is characterized in that, unstripped gas is divided into two strands of air-flows, after main air enters main heat exchanger cooling, send into high-pressure tower and carry out rectifying separation; Secondary air flow is extracted out, is directly sent into rectifying in the middle part of lower pressure column, obtain product methane at the bottom of tower after expander refrigeration decrease temperature and pressure after entering main heat exchanger cooling certain phase in the middle part of interchanger.
2. method according to claim 1, is characterized in that: described main air enters main heat exchanger (E1), and through heat exchange, unstripped gas is lowered the temperature or after partial liquefaction, entered the bottom of high-pressure tower (T1), carry out preliminary rectifying separation; Wherein be rich in the volatile components of nitrogen along tower height upwards, gaseous stream stock is drawn at high-pressure tower (T1) tower top, enter in condenser/evaporator (E4), carry out partial condensation, the decompression after a supercooler (E2) is excessively cold of condensed liquid stream enters in the middle part of lower pressure column and continues rectifying.
3. method according to claim 1, it is characterized in that: described air-flow B enters the rear incoming stock decompressor (EXP1) of main heat exchanger (E1) cooling, after step-down cooling, with high-pressure tower tower bottoms, all enter lower pressure column (T2) middle part, using high-pressure tower (T1) overhead condensation liquid air-flow as trim the top of column liquid, carry out the rectifying of lower pressure column (T2), the methane-rich liquid of lower pressure column tower reactor enters condenser/evaporator (E4) side, the rich nitrogen of the high pressure tower top that vaporizer (E4) opposite side that is condensed is heated to part evaporation, evaporation section is as the upflowing vapor of lower pressure column, non-evaporation section draws air-flow from condenser/evaporator (E4) side, through supercooler cross cold after as product liquify natural gas.
4. method according to claim 3, it is characterized in that in process that other part cold can be freezed by azeotrope compression cycle provide or nitrogen expansion mechanism cold circulates and provides.
5. method according to claim 1, it is characterized in that lower pressure column pressure is more than 0.01MPa, high-pressure tower pressure is more than 0.4MPa.
6. one kind is extracted the method for methane from the gas mixture containing methane, hydrogen, nitrogen, it is characterized in that, after unstripped gas enters main heat exchanger cooling, be divided into main air and secondary air flow: main air continues to enter high-pressure tower after main heat exchanger cooling and carries out rectifying separation, secondary air flow directly sends into rectifying in the middle part of lower pressure column after decompressor step-down refrigeration cool-down, obtains product methane at the bottom of tower.
7. method according to claim 6, is characterized in that: described main air enters main heat exchanger (E1), and through heat exchange, unstripped gas is lowered the temperature or after partial liquefaction, entered the bottom of high-pressure tower (T1), carry out preliminary rectifying separation; Wherein be rich in the volatile components of nitrogen along tower height upwards, gaseous stream stock is drawn at high-pressure tower (T1) tower top, enter in condenser/evaporator (E4), carry out partial condensation, the decompression after a supercooler (E2) is excessively cold of condensed liquid stream enters in the middle part of lower pressure column and continues rectifying.
8. method according to claim 6, it is characterized in that: the incoming stock decompressor of described secondary air flow (EXP1), after step-down cooling, with high-pressure tower tower bottoms, all enter lower pressure column (T2) middle part, using high-pressure tower (T1) overhead condensation liquid air-flow as trim the top of column liquid, carry out the rectifying of lower pressure column (T2), the methane-rich liquid of lower pressure column tower reactor enters condenser/evaporator (E4) side, the rich nitrogen of the high pressure tower top that vaporizer (E4) opposite side that is condensed is heated to part evaporation, evaporation section is as the upflowing vapor of lower pressure column, non-evaporation section draws air-flow from condenser/evaporator (E4) side, through supercooler cross cold after as product liquify natural gas.
9. method according to claim 6, it is characterized in that in process that other part cold can be freezed by azeotrope compression cycle provide or nitrogen expansion mechanism cold circulates and provides.
10. method according to claim 6, it is characterized in that lower pressure column pressure is more than 0.01MPa, high-pressure tower pressure is more than 0.4MPa.
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