CN111765717A - Process device and method for extracting ethane from natural gas - Google Patents

Process device and method for extracting ethane from natural gas Download PDF

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Publication number
CN111765717A
CN111765717A CN201910259407.9A CN201910259407A CN111765717A CN 111765717 A CN111765717 A CN 111765717A CN 201910259407 A CN201910259407 A CN 201910259407A CN 111765717 A CN111765717 A CN 111765717A
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China
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demethanizer
gas
ethane
natural gas
cold box
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王铁军
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Tianjin Branch Company China Petroleum Pipeline Engineering Co ltd
Tianjin Zhongyou Keyuan Petroleum Engineering Co ltd
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Tianjin Branch Company China Petroleum Pipeline Engineering Co ltd
Tianjin Zhongyou Keyuan Petroleum Engineering Co ltd
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Priority to CN201910259407.9A priority Critical patent/CN111765717A/en
Publication of CN111765717A publication Critical patent/CN111765717A/en
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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
    • 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
    • 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
    • F25J3/0238—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 2 carbon atoms or more
    • 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
    • F25J3/0242—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 3 carbon atoms or more
    • 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
    • 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
    • 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
    • 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
    • F25J2200/50—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column
    • 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
    • F25J2200/74—Refluxing the column with at least a part of the partially condensed overhead gas
    • 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
    • F25J2200/76—Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
    • 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
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
    • 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
    • F25J2215/62—Ethane or ethylene
    • 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
    • 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
    • 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)
  • 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 process device and a method for extracting ethane from natural gas, wherein the first step of the method is that the natural gas is precooled to-30 to-80 ℃ by a cold box and then enters a low-temperature separator to be divided into gas phase and liquid phase: secondly, the liquid phase enters a cold box for reheating and then flows back to the middle part of a demethanizer; the third step is that the gas phase is divided into two parts, and one part of the gas phase enters a cold box to be supercooled and liquefied to be used as reflux liquid at the top of the demethanizer; the fourth step is that the other part of the gas phase enters the expansion end of the compression expansion machine to be expanded and then flows back to the demethanizer, and meanwhile, the gas phase of the externally-conveyed dry gas enters the top of the demethanizer after being refluxed and reheated; and fifthly, feeding the bottom liquid of the demethanizer into a deethanizer for deethanizing, wherein the top gas of the deethanizer is a product gas, and the invention adopts unit refrigerant for refrigeration to produce ethane, effectively utilizes the balance of cold and heat of the device, improves the operating pressure and the operating temperature of the demethanizer, effectively solves the problem of low-temperature ice blockage of carbon dioxide, and ensures that the ethane recovery rate can reach more than 95 percent.

Description

Process device and method for extracting ethane from natural gas
Technical Field
The invention relates to the field of natural gas condensation separation, in particular to a method and a device for extracting ethane from natural gas.
Background
At present, in view of abundant hydrocarbon resources in most natural gases, the natural gases need to extract ethane, liquefied petroleum gas and light hydrocarbon resources before being exported, and meanwhile, the abundant ethane resources in the natural gases are used as the best raw materials for cracking ethylene, so that the market demand is large, the prospect is good, the crude oil consumption can be effectively saved, the oil is indirectly replaced by gas, and the natural gas ethane recovery process mainly comprises a low-temperature oil absorption method, a liquid-phase supercooling method and the like. The low-temperature oil absorption method needs a large amount of circulating solvent oil, the solvent oil has certain loss, the ethane yield is lower and is generally only 80 percent, the liquid-phase supercooling method only has liquid-phase reflux, the supercooling capacity is low, the ethane recovery rate is low, the energy consumption is high, the ethane recovery rate of a light hydrocarbon recovery device of most of the existing natural gas treatment plants is only 80 percent, the recovery depth is only to meet the dew point requirement of the hydrocarbon of the external gas transmission, and therefore most of hydrocarbon components are not recovered and utilized.
Disclosure of Invention
The invention aims to solve the main technical problem that the invention provides a method for extracting ethane from natural gas. The 'unit refrigerant refrigeration gas-filling gas-liquid supercooling process' is adopted, refrigeration loads with different temperature positions can be reasonably matched, the operating pressure and the operating temperature of the demethanizer are improved, the problem of low-temperature ice blockage of carbon dioxide is effectively solved, and the ethane recovery rate can reach more than 95 percent and C3The recovery rate can reach more than 99 percent.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a method for extracting ethane from natural gas comprises the steps that 3.0-8.0 MPa.g of pretreated dry natural gas enters a cold box of a liquid hydrocarbon recovery device, is precooled to-30-80 ℃ by the cold box and then enters a low-temperature separator to be divided into gas-liquid two phases: the liquid phase enters a cold box for cooling and then flows back to the middle part of the demethanizer; the gas phase is divided into two parts, and one part of the gas phase enters a cold box to be supercooled and liquefied to be used as reflux liquid at the top of the demethanizer; the other part of the gas phase enters the expansion end of a compression expansion machine and is expanded to 1.0 to 4.0MPa.g, and then enters the middle part of the demethanizer. The bottom liquid of the demethanizer enters a deethanizer for deethanization, and the top gas of the deethanizer is the product gas.
Aiming at the gas quality characteristic of high carbon dioxide content in the raw natural gas, a combined refrigeration process of 'unit refrigerant refrigeration gas-filling gas-liquid supercooling' is adopted, refrigeration loads of different temperature positions are reasonably matched, the operating pressure and the operating temperature of the demethanizer are improved, and the problem of low-temperature ice blockage of carbon dioxide is effectively solved.
Aiming at C in raw natural gas2+ low gas quality, use of "unit refrigerant refrigeration air-entrapping gas-liquid super-cooling reflux" C2+ recovery process, ethane recovery rate can reach 95% or more, C3The recovery rate can reach more than 99 percent.
The multi-flow plate-fin type cold box is selected, the minimum pinch temperature is close to 1-6 ℃, the logarithmic mean temperature difference is lower, the technology is mature and reliable, the heat exchange efficiency is high, and the load of a refrigeration system is reduced.
The introduced compression-expansion machine cooling technology with coaxial pressurization is adopted, the mechanical efficiency is high, the operation is stable and reliable, and the lean gas pressurization power is reduced.
The technology of leading out the side line of the demethanizer is adopted, the low-temperature cold quantity of the demethanizer material is fully utilized, the refrigeration load of the device is reduced, the energy utilization efficiency is high, and the energy-saving effect is obvious.
The unit refrigerant of the invention can adopt any one of four common refrigerant formulas of ethane, ethylene, propane or propylene.
The invention also provides a process unit for extracting ethane from natural gas, which comprises a cold box, a demethanizer bottom reboiler, a demethanizer top condenser, a compression expander, a low-temperature separator, a demethanizer and a deethanizer, wherein the cold box is sequentially connected with the low-temperature separator and the compression expander, the compression expander is connected with the cold box and the demethanizer, and a liquid phase outlet of the low-temperature separator is connected with the cold box.
The demethanizer may preferably be a packed column, a plate column or a combined column in which a packed column and a plate column are combined.
Wherein the liquid phase outlet of the cryogenic separator is preferably connected to the cold box via a throttle valve. The cold box is preferably connected to the demethanizer via a throttle valve.
In order to recover the cold energy and the energy of the product gas, a product gas outlet at the top of the demethanizer is sequentially connected with a cold box and a compression expansion machine.
The cold box provides a place for energy exchange of refrigerant and other logistics, and the cold box can be split into 2 cold boxes. The compression expansion machine is a main refrigeration device and provides cold energy for natural gas deep cooling, and the compression expansion machine is a partial expansion gas compressor and is used for pressurizing the natural gas, throttling and supercooling after condensation and serving as return liquid at the top of the demethanizer. The demethanizer serves as a mass transfer location for the extraction of ethane.
The invention has the beneficial effects that:
the invention relates to a process device and a method for extracting ethane from natural gas, wherein expansion gas is condensed after heat exchange through pressurization of a compression expansion machine, and then the stream is supercooled through throttling and depressurization to provide cold energy for deep deethanization, wherein the compression expansion machine is mature and reliable, compared with other refrigeration deethanization processes adopting unit refrigerants, the compression expansion machine has the advantages of lower requirement, less investment, short manufacturing period, one set of less refrigeration systems and simpler operation and maintenance, so that the total engineering investment of the process is greatly reduced, the ethane extraction effect is good, the ethane in the natural gas is removed as much as possible on the premise of ensuring the heat value of the gas of an external product, a high-quality raw material is provided for ethylene cracking, the consumption of crude oil is reduced, the raw material supply of the ethylene industry is ensured, the separation of liquid hydrocarbon of the external gas is effectively avoided, the national energy structure can be optimized, and the ethane is effectively extracted from the natural gas product, the process flow is simple, the investment is saved, the process flow is greatly simplified compared with the traditional process flow for extracting ethane in natural gas, ethane is extracted in a deethanizer by natural gas condensation throttling supercooling reflux, hydrocarbon resources in the natural gas are recovered, and the requirement of natural gas hydrocarbon dew point is met. And the unit refrigerant is adopted for refrigerating to produce ethane, so that the cold and heat balance of the device can be effectively utilized, the operating pressure and the operating temperature of the demethanizer are improved, the problem of low-temperature ice blockage of carbon dioxide is effectively solved, and the recovery rate of ethane can reach more than 95%.
Drawings
The invention is further illustrated by the following examples in conjunction with the accompanying drawings
FIG. 1 is a schematic diagram showing the structural connection of a process unit for extracting ethane from natural gas according to the present invention
FIG. 2 is a schematic flow diagram of a process for extracting ethane from natural gas in accordance with the present invention
In the figure:
1: and (3) a cold box 2: compression expansion machine
3: the low-temperature separator 4: first throttle valve
5: the second throttle valve 6: third throttle valve
7: the fourth throttle valve 8: fifth throttle valve
9: sixth throttle valve 10: demethanizer bottoms reboiler
11: demethanizer 12: deethanizer
13: deethanizer overhead condenser 14: deethanizing tower top reflux tank
15: deethanizer bottom reboiler 16: first port
17: second port 18: third port
19: fourth port 20: the fifth port
21: sixth port 22: the seventh port
23: deethanizer overhead reflux pump
Detailed Description
A process plant and method for extracting ethane from natural gas according to the present invention will now be described in further detail with reference to the accompanying drawings and detailed description:
as shown in fig. 1, the apparatus comprises a cold box 1, a compression expansion machine 2, a cryogenic separator 3, a demethanizer 11 and a deethanizer 12, wherein the cold box 1 is sequentially connected with the cryogenic separator 3, the compression expansion machine 2 and the demethanizer 11, and the compression expansion machine 2 is connected with the cold box 1 and the demethanizer 11.
As shown in fig. 2, in the first step S1 of the method, the natural gas is pre-cooled to-30 to-80 ℃ by the cold box 1, and then enters the low temperature separator 3 to be divided into two phases of gas and liquid; the second step S2 is that the liquid phase enters the cold box 1 for reheating and then flows back to enter the middle part of the demethanizer 11; step S3, dividing the gas phase into two parts, and allowing one part of the gas phase to enter the cold box 1 for supercooling liquefaction to be used as reflux liquid at the top of the demethanizer 11; the fourth step S4 is that the other part of the gas phase enters the expansion end of the compression expansion machine 2 to be expanded and then flows back to the demethanizer 11, and meanwhile, the gas phase of the externally transported dry gas enters the top of the demethanizer 11 after being refluxed and reheated; in the fifth step S5, the bottom liquid of the demethanizer 11 enters the deethanizer 12 to deethanize, and the top gas of the deethanizer 12 is the product gas.
Example 1
A method for extracting ethane from natural gas comprises the steps of precooling the natural gas to-30 to-80 ℃ through a cold box 1, and then separating the natural gas into a gas phase and a liquid phase in a low-temperature separator 3. The gas phase separated by the low temperature separator 3 is divided into two parts, wherein a small part of the gas phase, for example 20%, is cooled and liquefied by the cold box 1 and then is used as the top reflux liquid of the demethanizer 11, and the other part of the gas phase enters the expansion end of the compression expansion machine 2 and is expanded to 1.0 to 4.0MPa.g and then enters the middle part of the demethanizer 11. The natural gas is subjected to mass transfer and fractionation in the demethanizer 11, the liquid at the bottom of the demethanizer 11 enters the deethanizer 12 for deethanization, and the gas at the top of the deethanizer 12 is the product gas containing ethane.
In the method of the embodiment, after the natural gas is precooled by the cold box, a small part of gas phase separated by the low-temperature separator 3 is cooled and liquefied by the cold box, a liquid phase separated by the low-temperature separator 3 is cooled and liquefied by the cold box 1, and the gas expanded by the expansion end of the compression expansion machine 2 respectively enters the demethanizer 11 as reflux, so that most of ethane in the natural gas is removed, and the energy consumption of the device is effectively reduced.
Example 2
A process unit for extracting ethane from natural gas comprises a cold box 1, a compression expansion machine 2, a low-temperature separator 3, a demethanizer 11 and a deethanizer 12, wherein the low-temperature separator 3 is provided with two gas phase outlets, one of the gas phase outlets is connected with the compression expansion machine 2 and then connected with the demethanizer 11, the other gas phase outlet of the low-temperature separator 3 is directly connected with the cold box 1, the cold box 1 is connected with the demethanizer 11, a liquid phase outlet of the low-temperature separator 3 is connected with the cold box 1 through a third throttle valve 6, the cold box 1 is connected with the demethanizer 11, and according to optimization of a heat exchange network, the cold box 1 can be also split into two small cold boxes, one of the small cold boxes serves as a demethanizer reboiler 13 at the bottom of the demethanizer, and the fifth throttle valve 8 is used for controlling the space between the cold box 1.
In other embodiments, the liquid phase outlet of the cryogenic separator 3 may also be connected to the cold box 1 via a throttle valve, and the cold box 1 may also be connected to the demethanizer 11 via a throttle valve.
Example 3
A process unit for extracting ethane from natural gas comprises a cold box 1, a compression expansion machine 2, a low-temperature separator 3, a first throttling valve 4, a second throttling valve 5, a third throttling valve 6, a fourth throttling valve 7, a fifth throttling valve 8, a sixth throttling valve 9, a demethanizer bottom reboiler 10, a demethanizer 11, a deethanizer 12, a deethanizer top condenser 13, a deethanizer top reflux tank 14, a deethanizer bottom reboiler 15 and a deethanizer top reflux pump 23, as shown in figure 1. Wherein:
the high-pressure refrigerant refrigeration unit and the lean gas supercharging device are not shown in the figure, the raw gas at the third port 18 enters the cold box 1, then enters the low-temperature separator 3 through the cold box 1, the dry gas is input through the fifth port 20, the dry gas output is controlled by the first throttle valve 4, the dry gas output flows to the lean gas supercharging device, the compression expander 2 is a coaxial compression expander, the unit refrigerant is output through the second port 17, the backflow dry gas is input through the fifth port 20, the backflow dry gas comes from the lean gas compression device, the unit refrigerant returns to the cold box 1 from the high-pressure refrigerant refrigeration unit through the fourth port 19 and then is controlled by the fourth throttle valve 7, the final finished product ethane is output through the sixth port 21, and the deethanizer 12 is controlled by the sixth throttle valve 9 to discharge deethanizer bottom liquid from the seventh port 22.
The cold box 1 is connected with the low-temperature separator 3, the low-temperature separator 3 is provided with two gas phase outlets, one of the gas phase outlets is connected with the compression expansion machine 2, the compression expansion machine 2 is sequentially connected with the cold box 1 and the demethanizer 11, the other gas phase outlet of the low-temperature separator 3 is directly connected with the cold box 1, the cold box 1 is connected with the demethanizer 12, the liquid phase outlet of the low-temperature separator 3 is connected with the cold box 1, the cold box 1 is respectively connected with the demethanizer 11 through the first throttle valve 4 and the second throttle valve 5, and the gas outlet of the tower top product of the demethanizer 11 is sequentially connected with the cold box 1 and the compression expansion machine 2. The bottom liquid of the demethanizer 11 is connected with a cold box 1 and a deethanizer 12 in sequence.
The demethanizer 11 is preferably a packed column, a plate column or a combined column, which means a combination of a packed column and a plate column.
A strand of lean natural gas from the lean gas supercharging device is subcooled and liquefied by a cold box 1 and is used as reflux of the top of the demethanizer 11
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiment according to the technical spirit of the present invention still fall within the scope of the technical solution of the present invention.
In summary, the present invention fully meets the needs of industrial development in terms of structural design, practical use and cost effectiveness, and the disclosed structure has an unprecedented innovative structure, novelty, creativity and practicability, and meets the requirements of related new patent requirements, so that the application is drawn by law.

Claims (19)

1. A process for extracting ethane from natural gas, characterized by: the first step (S1) of the method is that natural gas is precooled to-30 to-80 ℃ by a cold box (1) and then enters a low-temperature separator (3) to be divided into gas and liquid phases: the second step (S2) is that the liquid phase enters the cold box (1) for reheating and then flows back to enter the middle part of the demethanizer (11); the third step (S3) is that the gas phase is divided into two parts, and one part of the gas phase enters the cold box (1) to be subcooled and liquefied to be used as the reflux liquid at the top of the demethanizer (11); the fourth step (S4) is that the other part of gas phase enters the expansion end of the compression expansion machine (2) to be expanded and then flows back to the demethanizer (11), and meanwhile, the gas phase of the externally-conveyed dry gas enters the top of the demethanizer (11) after being refluxed and reheated; and the fifth step (S5) is that the bottom liquid of the demethanizer (11) enters a deethanizer (12) for deethanization, and the top gas of the deethanizer (12) is the product gas.
2. The process for the extraction of ethane from natural gas according to claim 1, wherein the gas phase at the top of the deethanizer (12) is ethane and the process employs any one of total condensation and partial condensation.
3. The process for the extraction of ethane from natural gas according to claim 1, wherein the compressor-expander (2) is a coaxial compressor-expander.
4. A method for extracting ethane from natural gas according to claim 1 or 2, characterized in that the liquid phase separated by the cryogenic separator (3) is re-heated in the cold box (1) and fed to the demethanizer (11).
5. A process for the extraction of ethane from natural gas according to claim 1 or 2, characterized in that the liquid phase separated in the cryogenic separator (3) is fed directly to the demethanizer (11).
6. A method for extracting ethane from natural gas according to claim 1 or 2, characterized in that a lean natural gas stream from a lean gas pressurizing device is subcooled and liquefied by the cold box (1) and used as reflux of the top of the demethanizer (11).
7. A method for extracting ethane from natural gas according to claim 1 or 2, characterized in that the export dry gas is liquefied by supercooling through the cold box (1) and used as reflux for the top of the demethanizer (11).
8. The process for the extraction of ethane from natural gas according to claim 1 or 2, wherein a part of the gaseous phase separated in the cryogenic separator (3) is sent to the cold box (1) to be subcooled and liquefied as reflux liquid at the top of the demethanizer (11).
9. The process for the extraction of ethane from natural gas according to claim 8, wherein the other part of the gaseous phase separated in the cryogenic separator (3) is expanded at the expansion end of the compressor-expander (2) and used as reflux at the top of the demethanizer (11).
10. The process for the extraction of ethane from natural gas as claimed in claim 1 or 2, wherein the process alternatively employs gas-liquid subcooling, gas-gas subcooling, gas-liquid subcooling, gas subcooling and liquid subcooling.
11. The method for extracting ethane from natural gas according to claim 1 or 2, wherein the refrigeration loads of different temperature positions are matched, the operation pressure and the operation temperature of the demethanizer (11) are increased, and the carbon dioxide is prevented from being blocked by ice at low temperature.
12. The method for extracting ethane from natural gas as claimed in claim 1 or 2, wherein any one of ethane, ethylene, propane and propylene is used as the unit refrigerant of the method.
13. A process unit for extracting ethane from natural gas is characterized by comprising a cold box (1), a compression expansion machine (2), a low-temperature separator (3), a demethanizer (11) and a deethanizer (12), wherein the cold box (1) is sequentially connected with the low-temperature separator (3), the compression expansion machine (2) and the demethanizer (11), and the compression expansion machine (2) is connected with the cold box (1) and the demethanizer (11).
14. The process plant for the extraction of ethane from natural gas of claim 13 wherein the demethanizer (11) is one of a packed column, a tray column and a combined column.
15. A process plant for the extraction of ethane from natural gas according to claim 13 or 14, wherein: according to the optimization of a heat exchange network, one cold box (1) is split into two parts.
16. The plant for extracting ethane from natural gas according to claim 13 or 14, wherein any one of the feed gas, the gas from the high pressure refrigerant refrigeration unit, and the export dry gas from the lean gas booster is used as a heat source for the demethanizer bottom reboiler (10).
17. The plant for the extraction of ethane from natural gas according to claim 13 or 14, wherein any combination of the feed gas, the gas from the high pressure refrigerant refrigeration unit, and the export dry gas from the lean gas booster is used as a heat source for the demethanizer bottom reboiler (10).
18. The process unit for extracting ethane from natural gas as claimed in claim 13 or 14, wherein the demethanizer (11) is drawn out in a side line, the refrigeration load of the unit is reduced by utilizing the low-temperature cold energy of the demethanizer (11) material, and a side pump is adopted according to the installation condition, the medium condition, the side gasification rate and the position of a side extraction tray.
19. A process plant for the extraction of ethane from natural gas according to claim 13 or 14, wherein: and the positions of a plurality of feeding plates of the demethanizer (11) are optimized according to the heat exchange network and the effective energy, and the positions of the feeding plates are selected.
CN201910259407.9A 2019-04-02 2019-04-02 Process device and method for extracting ethane from natural gas Pending CN111765717A (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4695303A (en) * 1986-07-08 1987-09-22 Mcdermott International, Inc. Method for recovery of natural gas liquids
CN1254411A (en) * 1997-05-07 2000-05-24 埃尔科公司 Process for separating hydrocarbon gas constituents
CN1678412A (en) * 2002-08-27 2005-10-05 国际壳牌研究有限公司 Method of removing solid carbon dioxide
CN108507277A (en) * 2018-04-28 2018-09-07 中国石油工程建设有限公司 A kind of the cold comprehensive utilization device and method of natural gas ethane recovery

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4695303A (en) * 1986-07-08 1987-09-22 Mcdermott International, Inc. Method for recovery of natural gas liquids
CN1254411A (en) * 1997-05-07 2000-05-24 埃尔科公司 Process for separating hydrocarbon gas constituents
CN1678412A (en) * 2002-08-27 2005-10-05 国际壳牌研究有限公司 Method of removing solid carbon dioxide
CN108507277A (en) * 2018-04-28 2018-09-07 中国石油工程建设有限公司 A kind of the cold comprehensive utilization device and method of natural gas ethane recovery

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