CN113154798B - Multi-target separation process for comprehensively utilizing liquefied tail gas of helium-rich natural gas - Google Patents

Multi-target separation process for comprehensively utilizing liquefied tail gas of helium-rich natural gas Download PDF

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CN113154798B
CN113154798B CN202110505989.1A CN202110505989A CN113154798B CN 113154798 B CN113154798 B CN 113154798B CN 202110505989 A CN202110505989 A CN 202110505989A CN 113154798 B CN113154798 B CN 113154798B
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helium
gas
natural gas
tail gas
liquefied
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CN113154798A (en
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阮雪华
王佳铭
贺高红
李宇鹏
肖武
姜晓滨
代岩
焉晓明
郑文姬
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Dalian University of Technology
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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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    • F25J3/0605—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the feed stream
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    • F25J3/0635—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of CnHm with 1 carbon atom or more
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    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/0685—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of noble gases
    • F25J3/069—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of noble gases of helium
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    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/20—Processes or apparatus using other separation and/or other processing means using solidification of components
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    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
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    • F25J2205/50—Processes or apparatus using other separation and/or other processing means using absorption, i.e. with selective solvents or lean oil, heavier CnHm and including generally a regeneration step for the solvent or lean oil
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    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/80—Processes or apparatus using other separation and/or other processing means using membrane, i.e. including a permeation step
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    • 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
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Abstract

The invention provides a multi-target separation process for comprehensively utilizing liquefied tail gas of helium-rich natural gas, belonging to the field of petrochemical industry. The helium-containing tail gas from the natural gas liquefaction device is prepared by firstly taking light hydrocarbon by-products of the liquefaction device as a solvent, performing cryogenic absorption and separation on methane to produce liquefied natural gas, then sequentially passing the absorption tail gas through catalytic oxidation, multistage membrane separation and cryogenic dehydration units to obtain crude helium gas, filling and conveying the crude helium gas to a high-purity helium gas device. Through the zero-clearance matching and the synergistic interaction of various technologies, helium and methane can be separated out with high efficiency and high yield, and the comprehensive utilization of the liquefied tail gas of natural gas is realized. By adopting the multi-target separation process, for the natural gas liquefied tail gas with the helium concentration of 4.60 vol%, the methane yield exceeds 98.5%, the helium yield reaches 93.5%, the purity reaches 97.0 vol%, and the unit consumption of separation of liquefied tail gas in each standard is not more than 0.51 ℃.

Description

Multi-target separation process for comprehensively utilizing liquefied tail gas of helium-rich natural gas
Technical Field
The invention relates to a multi-target separation process for realizing comprehensive utilization of helium-rich natural gas liquefied tail gas by multi-technology coupling, belonging to the field of petrochemical industry.
Background
Natural gas is a mixture of light hydrocarbon components and non-hydrocarbon gases naturally accumulated in a crust layer, and is a high-quality fuel and a chemical raw material. The commercial natural gas has strict requirements on combustion heat value, and according to the Chinese national standard GB17820-2017 revised and released in 2012, the heat value index of one type of natural gas is 36MJ/Nm3The carbon dioxide content is not more than 2.0 vol%. The common non-hydrocarbon gases in natural gas are mainly nitrogen, carbon dioxide, hydrogen sulfide, hydrogen and helium, most of which are non-combustible components. To ensureTo verify the calorific value index of commercial natural gas, specialized separation units are required to remove these non-hydrocarbon gases.
TABLE 1 byproduct of natural gas liquefaction plant in certain area of China for liquefying tail gas rich in helium
Figure BDA0003058422620000011
The natural gas liquefaction process liquefies methane and condensable hydrocarbon components through pressurization and temperature reduction, so that the methane and the condensable hydrocarbon components are separated from non-condensable gases such as nitrogen and the like, and the process is a key production process for improving the heat value of commercial natural gas. In addition, the liquefaction process converts natural gas from a gaseous state to a liquid state, with a volume reduction of 600 times, which is advantageous for transport and storage. Along with the liquefaction of hydrocarbon components such as methane, ethane, propane and the like at low temperature, ultralow boiling point gases such as hydrogen, helium, nitrogen and the like are enriched in non-condensable gas to form natural gas liquefied tail gas. For helium-containing natural gas, after the natural gas is treated by a natural gas purification unit (for removing carbon dioxide, hydrogen sulfide and moisture) and a liquefaction unit (for ethane, propane, butane, pentane, heavy hydrocarbon and most of methane), the helium content in the liquefied tail gas can be concentrated by 30-50 times. Taking a natural gas liquefaction device containing helium in a certain place in China as an example, according to actual operation data, the helium content of the feed gas is about 0.14 vol%, and the helium content can be increased to about 4.60 vol% by cryogenic liquefaction at-150 ℃ and under the condition of 0.30MPaG, which is far higher than the standard of common helium-rich natural gas. The composition of the helium-rich natural gas liquefaction tail gas by-produced by the above natural gas liquefaction plant is given in table 1. According to the actual flow rate of the liquefied tail gas of the natural gas liquefaction device, the total amount of helium in the tail gas exceeds 38000 standard squares/year, and the total amount of methane exceeds 584000 standard squares/year. According to the concentration and the yield of the helium, the high-purity helium is produced by taking the liquefied tail gas of the helium-rich natural gas as a raw material, so that the recovery value is very high; in addition, the low-temperature refrigeration unit based on the liquefaction device is significant in recovering methane in the liquefied tail gas, so that the yield of the liquefied natural gas is increased.
How to separate helium from methane with high efficiency and high yield is a key problem of comprehensively utilizing the helium-rich natural gas liquefied tail gas. Common gas separation techniques include cryocondensation, absorption, membrane separation, and pressure swing adsorption. Due to the particularity of the composition of the helium-rich natural gas liquefied tail gas, it is difficult to effectively separate helium and methane from the liquefied tail gas by a single separation technology. The liquefied tail gas of the helium-rich natural gas is the non-condensable gas of cryogenic separation, so the low-temperature condensation technology is difficult to meet the separation requirement; absorption is a gas separation technology with selective dissolution of a solvent, but the solubility of nitrogen and hydrogen in various absorbents is very low, so that the requirements of helium concentration and purification are difficult to meet; the membrane separation is a separation technology based on the difference of permeation rates, and does not depend on the phase balance of a separation system, but the permeation properties of hydrogen and helium are very close, the permeation properties of nitrogen and methane are very close, and the separation requirement of the natural gas liquefied tail gas is difficult to meet only by the membrane separation; pressure swing adsorption is a separation technology based on porous material surface selective adsorption, and most of adsorbents have low nitrogen/methane selectivity and are difficult to meet the separation requirement of the liquefied tail gas of the natural gas.
Aiming at the problem that the common gas separation technology cannot meet the requirement of comprehensive utilization of the liquefied tail gas of the helium-rich natural gas, the invention provides a multi-target separation process integrating a cryogenic absorption unit, a catalytic oxidation unit, a multi-stage membrane separation unit and a cryogenic liquefaction dehydration unit. Through the zero-gap matching and the synergistic interaction of various separation technologies, the multi-technology integrated separation process can realize the comprehensive utilization of the liquefied tail gas of the helium-rich natural gas with high efficiency and high yield, and produce the liquefied natural gas and the crude helium with lower energy consumption.
Disclosure of Invention
The invention aims to provide a multi-target separation process for coproducing liquefied natural gas and crude helium gas by using helium-rich natural gas liquefied tail gas as a raw material. According to the process, through a multi-technology integration process of cryogenic absorption, catalytic oxidation, multi-stage membrane separation and cryogenic liquefaction dehydration, methane in the helium-rich natural gas liquefaction tail gas is separated and sent to a natural gas liquefaction device to produce liquefied natural gas, low-concentration helium gas (>2.0 vol%) is concentrated to produce crude helium gas (>97.0 vol%), and the crude helium gas is filled at high pressure and sent to a high-purity helium gas device. Through the zero-gap matching and the synergistic interaction of various separation technologies, the recovery rates of helium and methane are obviously improved, and the separation energy consumption is reduced. The specific technical scheme for realizing helium concentration and methane separation in the invention is as follows:
the helium-rich natural gas liquefaction tail gas S1 as a byproduct of the natural gas liquefaction device firstly enters a cold box 1, the cold energy in the tail gas is recovered and then enters a first compressor 2, the tail gas is pressurized and then enters a first cooler 3, the tail gas is cooled to normal temperature and then called pressurized helium-rich natural gas liquefaction tail gas S2, and the pressurized helium-rich natural gas liquefaction tail gas S2 enters an absorption tower 4 from the bottom of the tower; a byproduct light hydrocarbon S3 of a natural gas liquefaction device firstly enters a cold box 1, enters a second cooler 5 after precooling, realizes deep freezing by evaporative refrigeration of liquefied natural gas, is called low-temperature frozen light hydrocarbon S4, and enters an absorption tower 4 from the top of the tower; the low-temperature frozen light hydrocarbon S4 and the pressurized helium-rich natural gas liquefaction tail gas S2 are in countercurrent contact in an absorption tower 4, and are extracted from the bottom of the tower after absorbing most of methane, so that the methane-rich light hydrocarbon S5 is obtained and sent to a natural gas liquefaction device; the pressurized liquefied tail gas S2 of the helium-rich natural gas is extracted from the top of the absorption tower 4 after most of methane is removed, called liquefied tail gas S6 after demethanization, then enters a cold box 1 to recover cold energy, then enters a catalytic oxidation dehydrogenation reactor 6 to convert hydrogen into water, then enters a third cooler 7, is cooled to normal temperature, enters a gas-liquid separation tank 8 to separate condensed water, and then is extracted from the top of the tank to obtain a membrane separation raw material S7 which is sent to a multistage membrane separation unit 9; in a multi-stage membrane separation unit, nitrogen and methane are intercepted on the retentate side of a membrane to obtain nitrogen-rich tail gas S8, helium and water are preferentially permeated and enriched on the low-pressure permeation side of the membrane, then the nitrogen-rich tail gas enters a cryogenic liquefaction dehydration unit, two groups of heat exchangers are respectively in a freeze dehydration state and a heating and unfreezing state, gaseous water in crude helium is frozen and separated, an obtained gas-phase product is called dehydrated crude helium S10, and the dehydrated crude helium S10 is filled at high pressure and sent to a high-purity helium device.
The invention has the beneficial effects that: the method is characterized in that the tail gas of the liquefaction of the helium-rich natural gas is comprehensively utilized by a multi-target separation process of coupling and integrating cryogenic absorption, catalytic oxidation, multi-stage membrane separation and cryogenic liquefaction and dehydration, methane is separated firstly and is sent to a natural gas liquefaction device, and then crude helium (F, H, L, H, L, H>97.0vol％)，High-pressure filling and sending to a high-purity helium device. The invention can separate helium and methane with high efficiency and high yield by the zero-clearance matching and the synergistic interaction of various separation technologies, thereby realizing the comprehensive utilization of the liquefied tail gas of natural gas. By adopting the multi-target separation process, for the natural gas liquefied tail gas with helium concentration of 4.60 vol% and methane concentration of 70.67 vol%, simulation results show that the methane recovery rate exceeds 98.5%, the content of non-combustible components meets the index of commercial natural gas, and meanwhile, the helium recovery rate can reach more than 93.5%, and the purity can reach more than 97.0 vol%. According to the simulation results, the unit consumption (electricity) of separation is not more than 0.51kWh/Nm3And liquefying the tail gas by using the helium-rich natural gas.
Drawings
FIG. 1 is a flow diagram of the principle of a multi-technology integrated separation process for the comprehensive utilization of a helium-rich natural gas liquefied tail gas.
Description of symbols and numbering in the figures: 1, cooling the box; 2a first compressor; 3 a first cooler; 4, an absorption tower; 5 a second cooler; 6, a catalytic oxidation dehydrogenation reactor; 7 a third cooler; 8, a gas-liquid separation tank; 9 a multistage membrane separation unit; 10 a second compressor; 11 a fourth cooler; 12a first cryogenic liquefaction dehydration unit; 12b a second cryogenic liquefaction dehydration unit; s1 helium-rich natural gas liquefaction tail gas; s2, liquefying the tail gas of the pressurized helium-rich natural gas; s3 natural gas liquefaction equipment by-product light hydrocarbon; s4 light hydrocarbons frozen at low temperature; s5 a methane-rich light hydrocarbon; s6 demethanized liquefied tail gas; s7 membrane separation raw material; s8 nitrogen-rich tail gas; s9 crude helium; s10 dehydrates the crude helium gas.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
Example 1
Example 1 for a helium-rich natural gas liquefaction tail gas by-produced from a natural gas liquefaction plant, the tail gas composition is shown in table 1, and the average value of the tail gas flow is 100Nm3The invention relates to a multi-technology integrated process comprising cryogenic absorption, catalytic oxidation, multi-stage membrane separation, cryogenic liquefaction dehydration and other separation units, the principle flow structure is shown as figure 1, methane and helium in tail gas are comprehensively utilized, and the separated methane is sent to the skyAnd filling the crude helium obtained by the gas liquefaction device into a high-purity helium device.
The helium-rich natural gas liquefied tail gas S1 as a byproduct of the natural gas liquefaction device firstly enters a cold box 1, enters a first compressor 2 after cold energy in the tail gas is recovered (the temperature is increased from-150 ℃ to 25 ℃), enters a first cooler 3 after pressurization (the temperature is increased from 0.20MPaG to 1.80MPaG), is called as pressurized helium-rich natural gas liquefied tail gas S2 after being cooled to normal temperature, and enters an absorption tower 4 from the bottom of the tower; a byproduct light hydrocarbon S3 of a natural gas liquefaction device firstly enters a cold box 1, enters a second cooler 5 after precooling, realizes deep freezing (-150 ℃) through evaporative refrigeration of liquefied natural gas, is called low-temperature frozen light hydrocarbon S4, and enters an absorption tower 4 from the top of the tower; the low-temperature frozen light hydrocarbon S4 and the pressurized helium-rich natural gas liquefaction tail gas S2 are in countercurrent contact in an absorption tower 4, and are extracted from the bottom of the tower after absorbing most of methane, so that the methane-rich light hydrocarbon (S5, the methane concentration is 30.58 mol%) is sent to a natural gas liquefaction device; the pressurized liquefied tail gas S2 of the helium-rich natural gas is extracted from the top of the absorption tower 4 after most of methane is removed, called liquefied tail gas after demethanization (S6, the methane concentration is 2.72 vol%), then enters a cold box 1 to recover cold energy (the temperature is raised from minus 142 ℃ to 25 ℃), then enters a catalytic oxidation dehydrogenation reactor 6 to convert hydrogen into water, then enters a third cooler 7 to be cooled to normal temperature, then enters a gas-liquid separation tank 8 to separate condensed water, and a membrane separation raw material S7 is extracted from the top of the tank and sent to a multistage membrane separation unit 9; in a multi-stage membrane separation unit, nitrogen and methane are trapped on a retentate side, nitrogen-rich tail gas is obtained (S8, the nitrogen concentration is 95.78 vol%, the helium concentration is 0.84 vol%), helium and water are preferentially permeated, helium and water are enriched on a low-pressure permeate side of a membrane, then the nitrogen-rich tail gas enters a second compressor 10, after pressurization (10.0MPaG), the nitrogen-rich tail gas enters a fourth cooler 11, after being cooled to the normal temperature, the nitrogen-rich tail gas is called crude helium (S9, the helium concentration is 97.11 vol%), then the nitrogen-rich tail gas enters a cryogenic liquefaction dehydration unit, gaseous water in the crude helium is frozen and separated, an obtained gas phase product is called dehydrated crude helium (S10, the content of residual water is lower than 10ppmv), and the gas product is filled at high pressure and sent to a high-purity helium device.
In this embodiment, the first compressor, the second compressor and the membrane separation unit are internalThe total power consumption of the circulating compressor is about 11kW, the low-temperature cold energy consumed by the second cooler (5) is reduced to 40kW, and the purification unit power consumption (electricity) is about 0.51kWh/Nm in combination with the average flow rate of the liquefied tail gas of the helium-rich natural gas3And (4) air intake. According to the process simulation results given in table 2, the methane recovery rate reached 98.9% and the helium recovery rate reached 93.7%. The annual production of 150 ten thousand yuan for methane recovery, 430 ten thousand yuan for crude helium production, 50 ten thousand yuan for operating costs, 80 ten thousand yuan for equipment depreciation, and 450 ten thousand yuan for economic benefits per year are expected at the prices of liquefied natural gas and helium (considering the cost of further purification) of 2020. In conclusion, the comprehensive utilization process of the helium-rich natural gas liquefied tail gas described in the invention can increase the yield of the liquefied natural gas and realize reasonable utilization of helium resources through multi-technology coupling integration of cryogenic absorption, catalytic oxidation, multi-stage membrane separation and cryogenic liquefaction dehydration, and has remarkable economic benefits.
Table 2 summary of the composition and operating parameters of the key materials in example 1.
Figure BDA0003058422620000041

Claims (1)

1. A multi-target separation process for comprehensively utilizing liquefied tail gas of helium-rich natural gas is characterized by comprising the following steps of:
the method comprises the following steps that (1) helium-rich natural gas liquefied tail gas (S1) which is a byproduct of a natural gas liquefaction device firstly enters a cold box (1), enters a first compressor (2) after cold energy is recovered, enters a first cooler (3) after pressurization, is called as pressurized helium-rich natural gas liquefied tail gas (S2) after being cooled to normal temperature, and enters an absorption tower (4) from the bottom of the tower; a byproduct light hydrocarbon (S3) of a natural gas liquefaction device firstly enters a cold box (1), precools the byproduct light hydrocarbon and then enters a second cooler (5), the byproduct light hydrocarbon is called low-temperature frozen light hydrocarbon (S4) after deep freezing, and the low-temperature frozen light hydrocarbon enters an absorption tower (4) from the top of the tower; the low-temperature frozen light hydrocarbon (S4) and the pressurized helium-rich natural gas liquefied tail gas (S2) are in countercurrent contact in an absorption tower (4), and are extracted from the bottom of the tower after absorbing most of methane, so that the methane-rich light hydrocarbon (S5) is sent to a natural gas liquefaction device; removing most of methane from the pressurized liquefied tail gas (S2) of the helium-rich natural gas in an absorption tower (4), extracting the liquefied tail gas from the top of the tower, namely the liquefied tail gas (S6) after demethanization, then entering a cold box (1) for recovering cold energy, then entering a catalytic oxidation dehydrogenation reactor (6), converting hydrogen into water, then entering a third cooler (7), cooling to normal temperature, then entering a gas-liquid separation tank (8) for separating condensed water, extracting a membrane separation raw material (S7) from the top of the tank, and sending the membrane separation raw material to a multistage membrane separation unit (9); obtaining nitrogen-rich tail gas (S8) on the retentate side of a multistage membrane separation unit (9), enriching helium on the permeate side, then entering a second compressor (10), pressurizing, entering a fourth cooler (11), cooling to normal temperature, then calling crude helium (S9), then entering a deep cooling liquefaction dehydration unit, wherein two groups of heat exchangers are respectively in a freeze dehydration state and a heating and unfreezing state, freezing gaseous water in the crude helium and realizing separation, obtaining a gas phase product called dehydrated crude helium (S10), and filling under high pressure and sending the gas phase product to a high-purity helium device.
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