CN112742172B - Energy gas purification method - Google Patents
Energy gas purification method Download PDFInfo
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- CN112742172B CN112742172B CN201911049275.3A CN201911049275A CN112742172B CN 112742172 B CN112742172 B CN 112742172B CN 201911049275 A CN201911049275 A CN 201911049275A CN 112742172 B CN112742172 B CN 112742172B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
- B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
- B01D53/047—Pressure swing adsorption
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2256/00—Main component in the product gas stream after treatment
- B01D2256/24—Hydrocarbons
- B01D2256/245—Methane
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/10—Single element gases other than halogens
- B01D2257/102—Nitrogen
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/50—Carbon oxides
- B01D2257/504—Carbon dioxide
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2259/00—Type of treatment
- B01D2259/40—Further details for adsorption processes and devices
- B01D2259/414—Further details for adsorption processes and devices using different types of adsorbents
- B01D2259/4141—Further details for adsorption processes and devices using different types of adsorbents within a single bed
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02C20/00—Capture or disposal of greenhouse gases
- Y02C20/40—Capture or disposal of greenhouse gases of CO2
Abstract
The invention discloses a method for purifying energy gas containing nitrogen and carbon dioxide. By adopting the sectional type pressure swing adsorption tower, a novel process and an innovative control method, the energy gas mainly comprising methane, concentrated nitrogen and carbon dioxide can be obtained in one adsorption tower, and the recovery rate and concentration of at least two products can be ensured.
Description
Technical Field
The invention relates to the field of energy gas purification, in particular to a process method for removing nitrogen and carbon dioxide in energy gas by adopting a pressure swing adsorption method.
Background
For some unconventional energy gas, such as associated gas generated by oil displacement of nitrogen and oil displacement of carbon dioxide in oil fields, and energy gas generated by gas production of biomass, which often contains a certain amount of nitrogen and carbon dioxide, qualified natural gas mainly containing methane is required to be obtained from the energy gas, at present, the carbon dioxide is usually removed by adopting a solvent absorption method or a membrane separation method, and the nitrogen is removed by adopting methods such as cryogenic separation, membrane separation, pressure swing adsorption separation and the like.
One of the core technologies for pressure swing adsorption for natural gas denitrification is the selectivity of the adsorbent. Patent CN102962036 a reviews adsorbents such as molecular sieves, activated carbon, carbon molecular sieves, etc. that can be used for methane/nitrogen separation, and discloses a method for preparing a metal organic framework adsorbent with higher methane adsorption selectivity. Patent CN108329962A discloses a natural gas denitrification method combining temperature swing adsorption and two-stage pressure swing adsorption. Patent CN85103557a discloses a process flow for replacing nitrogen in a bed with product methane to increase the concentration of methane in desorbed gas. Patent CN104403710a discloses a method for recovering carbon dioxide in associated gas by using a membrane separation method. The patent CN204079928U adopts a method of low-temperature fractionation and membrane separation to separate associated gas. The patent CN101760270A adopts a method of combining membrane separation and pressure swing adsorption to remove and recover carbon dioxide in natural gas.
It is known from the prior patents that, for removing nitrogen and carbon dioxide in energy gas, the carbon dioxide is generally removed by a membrane separation method or a solvent absorption method, and the nitrogen is removed by a cryogenic fractionation method, a membrane separation method or a pressure swing adsorption method, and for the energy gas containing oil carbon dioxide and nitrogen at the same time, the above-mentioned method combination process is also generally adopted. The traditional process has the defects of complex flow, high investment, large occupied area, high energy consumption and the like in the process of simultaneously removing nitrogen and carbon dioxide, purifying (concentrating) and recovering methane, and if a solvent absorption method needs a large amount of solvent for circulation and regeneration, the pressure drop in the membrane separation process is large, and a middle adsorption force product cannot be obtained by conventional pressure swing adsorption.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for simultaneously removing nitrogen and carbon dioxide in energy gas (natural gas mainly containing methane). The invention can adopt a sectional pressure swing adsorption tower and a novel process, and can obtain three products of nitrogen, natural gas (mainly methane) and carbon dioxide meeting production requirements in one adsorption tower by matching with an innovative control method.
The invention relates to an energy gas purification method, which comprises the following steps:
providing n (n is an integer and is more than or equal to 3) sectional type adsorption towers, and dividing each adsorption tower into an upper section, a middle section and a lower section along the flowing direction from a raw material gas to a product gas (from the tower bottom to the tower top); according to different adsorption forces of the same adsorbent on nitrogen, methane and carbon dioxide (generally, nitrogen < methane < carbon dioxide), the upper section is a light component section which is difficult to adsorb and has high component concentration, and a light component product, namely concentrated nitrogen, is discharged from the top of the upper section; the middle section is a section with high component concentration and the adsorption force is in the middle, and a natural gas product with the main component of methane is discharged from the top of the middle section; the lower section is a recombination section with the most easily adsorbed component with high concentration, and the lower section discharges a heavy component product, namely carbon dioxide gas, from the bottom; two control valves are arranged among the three sections of the upper section, the middle section and the lower section, and a methane concentration detector is arranged behind the control valves of the upper section and the middle section and is used for detecting the concentration of the control component at the outlet;
in each of the segmental adsorption towers, the following steps are cyclically performed in sequence:
(1) Adsorption: a step of adsorption with basic constant pressure under high pressure, a step of adsorbing each component in the feed gas by an adsorbent in an adsorption tower, and obtaining a purified (concentrated) light component product at the tower top according to different adsorption forces and adsorption capacities of the adsorbent to different components;
(2) Pressure equalizing and reducing: after the adsorption step is finished, reducing the pressure of the adsorption tower, continuously discharging light component product gas from the tower top, and using the light component product gas for the other desorption to finish the pressure boosting process of the adsorption tower;
(3) Reverse amplification: a step of depressurizing the adsorption tower against the feeding direction, which aims to reduce the pressure of the adsorption tower to be close to normal pressure, so that the impurity components can be effectively desorbed from the adsorbent, desorption gas generated by reverse desorption is discharged from the bottom of the tower as heavy components, and two control valves between the upper section and the middle section and between the middle section and the lower section are in an open state in the step;
(4) Vacuumizing: a step of evacuating the adsorption column in a direction opposite to the direction of feeding, for the purpose of further recovering the dead space in the adsorption column and the heavy component adsorbed in the adsorbent, thereby improving the concentration and recovery rate of the heavy component; in the invention, the vacuumizing is carried out in two steps, wherein in the first step, a control valve between an upper section and a middle section is closed, the control valve between the middle section and a lower section is kept open, the vacuumizing desorption is started until the vacuum degree reaches 50-200 mm Hg, and at the moment, carbon dioxide adsorbed on the adsorbent at the bottom in the adsorption tower at the middle section is desorbed and enters the adsorption tower at the lower section; closing a control valve between the middle section and the lower section, and continuously vacuumizing to ensure that the vacuum degree of the lower section of the adsorption tower is not less than 700 mm Hg and the carbon dioxide in the lower section of the adsorption tower is fully desorbed;
(5) Voltage equalizing +: after the reverse desorption is finished, closing a desorption gas discharge valve, and then opening a control valve between the middle section and the lower section, wherein the pressure of the adsorption bed in the middle section is higher than that of the lower section, so that the two sections can perform a pressure equalization process, and simultaneously, heavy components in the adsorption bed in the middle section are released into the lower section in a pressure equalizing process; after the pressure equalization of the middle section and the lower section is finished, opening a control valve between the upper section and the middle section to finish the pressure equalization of the upper section adsorption bed and the middle and lower sections adsorption beds, and simultaneously, further regenerating the upper section adsorption bed;
(6) Pressure equalization and rise: the adsorption tower which finishes desorption receives the light component product gas from the pressure equalizing and reducing adsorption tower, and the pressure of the adsorption tower is boosted against the feeding direction, and the step is coupled with the pressure equalizing and reducing step; the pressure energy can be recovered and the yield of light component products can be improved in the pressure equalizing process;
(7) Final charging: a step of raising the pressure of the adsorption column to the adsorption pressure against the direction of the feed with the light component, the purpose of which is to avoid pressure fluctuation when the adsorption column is switched to the adsorption step.
In the invention, the sectional pressure swing adsorption tower is divided into an upper section, a middle section and a lower section, and a control valve is arranged between each two sections.
The flowing direction of the raw gas to the product gas in the adsorption tower generally means that the raw gas enters from the bottom of the tower, passes through an adsorbent bed layer, and heavy components in the raw gas are adsorbed in an adsorbent porous structure and are left in the adsorbent bed layer, so that light components are purified (concentrated) and finally discharged from the top end of the adsorption tower. For natural gas containing nitrogen and carbon dioxide, carbon dioxide is a heavy component, methane is a middle adsorptive component, and nitrogen is a light component. For typical molecular sieve, activated carbon, silica gel and other adsorbents, the adsorption force of the three gases on the adsorbents is carbon dioxide > methane > nitrogen in turn.
The segmentation of the adsorption tower means that in order to remove carbon dioxide and nitrogen in natural gas and simultaneously obtain concentrated natural gas mainly containing methane and concentrated nitrogen and carbon dioxide, the three products are obtained in one adsorption tower, concentrated nitrogen is obtained from the top of the tower, concentrated natural gas is obtained in the middle of the tower, and concentrated carbon dioxide is obtained from the bottom of the tower according to the difference of adsorption force of the three gases on an adsorbent.
The concentrated natural gas refers to natural gas from which carbon dioxide and nitrogen are removed and mainly comprises methane, the concentrated natural gas is obtained from the middle of the adsorption tower, and the concentrated natural gas is obtained by leading out a product pipeline from the position of a control valve between the upper section and the middle section of the adsorption tower.
A methane concentration detection point is arranged behind the control valve between the upper section and the middle section, and the concentration range of control components at the detection point can be set according to the composition of the raw material gas and the quality requirement of the product gas.
The adsorption tower is divided into three sections, according to the typical volume concentration of raw material gas, the methane is 50% -65%, the nitrogen is 10% -20%, the carbon dioxide is 10% -20%, and the typical proportions of the adsorption tower sections are 15% -25% of the upper section, 45% -55% of the middle section and 15% -25% of the lower section. When the content of methane in the feed gas exceeds 65%, the ratio of the middle section of the adsorption tower is increased; when nitrogen in the feed gas is the main impurity, the lower segment ratio is reduced; when carbon dioxide in the raw material gas is a main impurity, the lower section proportion needs to be properly increased, and the upper section proportion needs to be reduced.
The methane concentration detection point is used for detecting the concentration of methane in the adsorption tower when the methane concentration detection point leaves the top of the middle section of the adsorption tower, the concentration of the methane at the position is determined according to the requirement on the methane concentration in nitrogen discharged from the top of the tower, and the typical methane content is that when the methane content in the nitrogen discharged from the top of the tower is required to be not more than 3%, the detected methane content behind the control valve is not more than 90%, and when the methane content in the nitrogen discharged from the top of the tower is required to be not more than 1%, the detected methane content at the middle control valve is not more than 85%.
The function of the methane concentration detection point of the control valve position is also an important basis for determining the section position of the adsorption tower.
The control valve arranged between the two sections participates in the sequential control process of pressure swing adsorption, and the specific participation stage is that after the reverse discharge is finished, the vacuumizing step is divided into two steps, and the two valves are controlled to be closed in sequence; after the step sequence of vacuumizing, the pressure equalizing and step sequence controls the two valves to be opened in sequence.
When the vacuum pumping desorption is adopted, the typical vacuum degree in the first step is not higher than 200 mm Hg, and the typical vacuum degree in the second step is not lower than 700 mm Hg. Under high vacuum degree, the desorption of the lower section can be ensured as completely as possible, thereby improving the utilization rate of the adsorbent bed. In addition, because the upper section and the middle section of the adsorption tower are isolated step by step, the nitrogen at the upper section and the gas with higher methane content at the middle section cannot enter the desorption gas, thereby ensuring the concentration of carbon dioxide in the desorption gas at the bottom of the tower.
After the pressure equalizing and pressure equalizing processes between the reverse desorption, the vacuum-pumping desorption and the adsorption tower segmented adsorption beds are completed, the adsorption tower is controlled by the time sequence to complete the subsequent pressure equalizing, pressure rising and final filling processes to prepare for the next adsorption.
Further, the carbon dioxide product gas can be used as a purge gas to replace the methane gas in the lower section of the adsorption tower, which means that when the methane recovery rate needs to be improved and the carbon dioxide concentration and recovery rate are improved at the same time (typically, the methane recovery rate is required to be greater than 90% and the carbon dioxide concentration is required to be greater than 95%), after the adsorption step is completed and before the pressure equalization step starts, the carbon dioxide product gas is used as the purge gas and enters the lower section of the adsorption tower from the bottom of the adsorption tower to replace the methane in the lower section and the middle section of the adsorption bed of the adsorption tower, so that the methane recovery rate is improved, and the concentration of the obtained carbon dioxide in the desorption process is improved.
In the process of replacing methane by carbon dioxide, the control valve between the upper section and the middle section of the adsorption tower is closed, and the control valve between the middle section and the lower section is opened.
The adsorbent bed filled in the upper, middle and lower sections of the adsorption tower typically comprises the upper section filled with activated carbon and molecular sieve, the middle section filled with silica gel and activated carbon, and the lower section filled with silica gel and activated carbon.
The activated carbon filled in the upper section is used for adsorbing methane, and the molecular sieve is used for adsorbing low-concentration methane and is mainly used for ensuring that the methane does not penetrate through a bed layer.
The silica gel filled in the middle section is used for adsorbing a small amount of carbon dioxide which penetrates through the bed layer from the lower section and enters the middle section, the activated carbon is used for adsorbing methane, and in the section, the filling amount of the activated carbon exceeds 75 percent.
The lower section is filled with silica gel mainly used for adsorbing carbon dioxide, the activated carbon is used for controlling the speed and the amount of carbon dioxide penetrating through a bed layer, and in the section, the filling amount of the silica gel exceeds 75 percent.
The methane/nitrogen separation coefficient of the activated carbon selected in the lower section and the middle section is 2.5-3.5 from the economical point of view. The partial pressure of methane in the bed layer of the section is high, the mass transfer driving force is large, and the device investment can be reduced by adopting the activated carbon with relatively small separation coefficient.
The upper section adopts active carbon, the methane/nitrogen separation coefficient is more than 3.5, and the methane adsorption performance is good under low partial pressure. Because the gas in the adsorption tower section mainly comprises methane and nitrogen, a molecular sieve can be replaced by metal organic framework materials above the activated carbon, cu-MOF, MIL, zn-MOF and the like can be typically selected, the separation coefficient of the metal organic framework materials to the methane/nitrogen is required to be more than 6, and high adsorption capacity is still provided under low partial pressure of the methane, namely when the volume concentration of the methane is lower than 5%, so that the packing amount of the light upper section adsorbent can be effectively reduced, and the content of the methane in the nitrogen product at the top of the tower is effectively ensured not to exceed the standard.
The filling scheme of the adsorbents with different sections of the upper section, the middle section and the lower section is determined according to the change rule of the concentration of the gas component in different sections in the adsorption tower and the adsorption force, selectivity and low partial pressure adsorption performance of different adsorbents on the gas component, so that the adsorption quantity and the desorption performance of the gas component adsorbed in each section are ensured to be considered, and simultaneously, the aim of obtaining three products in three sections of one adsorption tower can be achieved by combining an innovative control method.
Compared with the prior art, the energy gas purification method provided by the invention has the following advantages:
1. the design of an upper section, a middle section and a lower section of the adsorption tower is carried out, meanwhile, an adsorbent filling scheme is designed according to the quality requirement of each section of product, and the design of a specific component concentration control detection method in a specific section is combined with the process of vacuum pumping step-by-step desorption and pressure equalization, so that the aim of simultaneously obtaining three products of nitrogen, methane and carbon dioxide in one adsorption tower is fulfilled.
2. The method can design different section proportions according to the contents of nitrogen and carbon dioxide in the raw material gas, and simultaneously adopts different adsorbent beds in different sections to realize the maximum utilization rate of the adsorbent bed.
3. Through the sectional design of the adsorption tower, the upper section and the middle section are isolated in the vacuumizing desorption stage, heavy component (carbon dioxide) product gas meeting the requirements can be obtained under higher vacuum degree, and the recovery rate of the device and the desorption effect of a bed layer are ensured.
4. Through the segmentation design to the adsorption tower, keep apart the upper segment in the adsorption phase, can adopt carbon dioxide replacement hypomere adsorption tower on the absorbent adsorbed methane to can improve the yield of methane, further improve yield and concentration when carbon dioxide is as heavy ends product simultaneously.
Drawings
FIG. 1 is a schematic flow diagram of a novel four-column pressure swing adsorption apparatus employing a segmented column of the present invention.
Detailed Description
The energy gas purification technology of the present invention will be described in detail with reference to the following examples. It is to be understood that the matter herein set forth is for the purpose of illustration and description only and is not intended to be limiting.
Comparative example 1
The four-tower pressure swing adsorption adopts a pressure swing adsorption process of one-tower adsorption and twice pressure equalization, and the conventional realization process flow is shown in table 1.
TABLE 1 TIME-SEQUENCE TABLE FOR IMPLEMENTING TECHNOLOGY FLOW OF FOUR-TOWER PRESSURE-CHANGE ADSORPTION
Example 1
The feed gas is exemplified by the typical nitrogen-containing, carbon dioxide-containing natural gas volume concentration composition, methane: 53%, ethane: 2%, nitrogen, 25%, CO 2 ：20%。
Referring to FIG. 1, a flow diagram of a novel four-column pressure swing adsorption apparatus using a segmented column according to the present invention is shown. 1. 2, 3 and 4 are respectively four adsorption towers, 11, 21, 31 and 41 are respectively first sections of the four adsorption towers, 12, 22, 32 and 42 are respectively second sections of the four adsorption towers, and 13, 23, 33 and 43 are respectively third sections of the four adsorption towers; as shown in fig. 1, from left to right, there are material gas valves V1, V3, V5, V7, desorption gas valves (i.e. heavy component product gas valves) V2, V4, V6, V8; product gas valves (namely light component product gas valves) V9, V11, V13 and V15, pressure equalizing valves V10, V12, V14 and V16 and purging gas exchange valves V17, V18, V19 and V20.5 is a feed gas line, 6 is a stripping gas line (heavy component product gas line), 7 is a product gas line (light component product gas line), 8 is an intermediate product gas line (in the present invention, natural gas which is purified and mainly contains methane), and 9 is a purge replacement gas line (in this example, carbon dioxide).
As shown in fig. 1, from left to right, the first stage 11, the second stage 12 and the third stage 13 constitute adsorption columns 1, 21, 22 and 23 via valves K11 and K12 and adsorption columns 2 via valves K21 and K22, 31, 32 and 33 constitute adsorption columns 3 via valves K31 and K32, and 41, 42 and 43 constitute adsorption column 4 via valves K41 and K42.
Table 2 is a timing chart of a novel four-column pressure swing adsorption process flow using the segmented column of the present invention.
TABLE 2
TABLE 2 continuation
In table 1, the process principle of each step is (1) adsorption: adsorbing each component in the feed gas by an adsorbent in an adsorption tower under high pressure, and obtaining a purified (concentrated) light component product at the tower top according to different adsorption forces and adsorption amounts of the adsorbent to different components; (2) pressure equalizing: the two adsorption towers with different pressures are subjected to pressure equalization, wherein the adsorption tower with reduced pressure is subjected to pressure equalization, the adsorption tower with increased pressure is subjected to pressure equalization, and the purpose of pressure equalization is to recover light components in dead spaces in the adsorbers and fully utilize pressure energy, so that the recovery rate of light component products is improved; (3) placing in sequence: the step of reducing the pressure of the adsorption tower along the feeding direction is called sequential placing, and the purpose is to utilize light components in the dead space of the adsorption tower to flush the other adsorption tower in the flushing step, wherein the sequential placing corresponds to the flushing step; (4) reverse amplification: the step of reducing the pressure of the adsorption tower against the feeding direction, which aims to reduce the pressure of the adsorption tower to be close to the normal pressure, so that the heavy component can be effectively desorbed from the adsorbent, and desorption gas generated by reverse release is discharged from the bottom of the tower as the heavy component; (5) flushing: and a step of purging the adsorption column with the light component against the feed direction. The method aims to further reduce the partial pressure of impurity components in a bed layer of an adsorption tower by utilizing light components, so that the impurity components are thoroughly desorbed from an adsorbent, and flushing gas is discharged from the bottom of the tower; (6) final charging: a step of raising the pressure of the adsorption column to the adsorption pressure against the feed direction with the light component, the purpose of which is to avoid pressure fluctuations when the adsorber is switched to the adsorption step.
The energy gas purification technology is different from the conventional process flow in that the adsorption towers 1, 2, 3 and 4 in equipment are respectively composed of three sections through the segmented middle control valves, and the specific process sequence is shown in table 2. In table 2, the difference from the conventional pressure swing adsorption step is that only one product is produced from the top of the column, and in the adsorption step of the present invention, two product gases are produced simultaneously, namely, a product gas with nitrogen produced from the top of the column as a main component, and a natural gas product with methane as a main component at the top of the middle section of the adsorption column, and meanwhile, the adsorption step of the present invention includes a displacement step, when the adsorption column is in the displacement step, the raw material gas is switched to another adsorption column, the control valve between the upper section and the middle section of the adsorption column is closed, and carbon dioxide is used as a purging displacement gas to enter the adsorption column from the pipeline 9 through the displacement gas valve.
Furthermore, the steps of normal pressure swing adsorption sequential release and flushing are eliminated, so that the recovery rate of the nitrogen of the light component product can be improved; further, a vacuumizing pressure-equalizing step is added after the reverse desorption, in the invention, vacuumizing is completed in two steps, after the reverse desorption is completed, the control valve between the upper section and the middle section of the adsorption tower is firstly closed, the vacuumizing step is started, when the vacuum degree reaches 50-200 mm Hg, preferably 100 mm Hg, the control valve between the middle section and the lower section of the adsorption tower is closed, and the vacuum is further vacuumized until the vacuum degree is not less than 600-700 mm Hg, the pressure equalization in the vacuumizing pressure-equalizing step refers to that after the vacuumizing step is completed, the control valve between the upper section and the middle section of the adsorption tower is firstly opened, the pressure equalization between the upper section and the middle section is completed, meanwhile, the heavy component adsorbed in the upper section is desorbed to the middle section, and then the control valve between the middle section and the lower section is opened, the pressure equalization between the upper section and the middle section is completed, meanwhile, the heavy component in the middle section is desorbed to the adsorbent bed, and in the lower section, the process, the heavy component in the upper section and the middle section of the adsorption tower can be fully regenerated. Then, the pressure equalization ascending step sequence is carried out, and the final filling process adopts light component product gas nitrogen.
In table 2, taking the adsorption column 1 as an example, the process principle of each step is as follows: (1) adsorption: a step of adsorption with basic constant pressure under high pressure, a step of adsorbing each component in the feed gas by an adsorbent in an adsorption tower, and obtaining a purified (concentrated) light component product at the tower top according to different adsorption forces and adsorption capacities of the adsorbent to different components; (2) pressure equalizing: and (4) carrying out pressure equalization on the two adsorption towers with different pressures. Wherein, the adsorption tower with reduced pressure is in pressure equalizing and the adsorption tower with increased pressure is in pressure equalizing and pressure equalizing, which aims at recovering the light component in the dead space of the absorber and fully utilizing the pressure energy to improve the recovery rate of the light component product; (3) reverse amplification: a step of depressurizing the adsorption tower against the feeding direction, which aims to reduce the pressure of the adsorption tower to be close to normal pressure, so that the impurity components can be effectively desorbed from the adsorbent, desorption gas generated by reverse desorption is discharged from the bottom of the tower as heavy components, and two control valves between the upper section and the middle section and between the middle section and the lower section are in an open state in the step; and (4) vacuumizing: a step of evacuating the adsorption column in a direction opposite to the direction of feeding, for the purpose of further recovering the dead space in the adsorption column and the heavy component adsorbed in the adsorbent, thereby improving the concentration and recovery rate of the heavy component; in the invention, the vacuumizing is carried out in two steps, wherein in the first step, a control valve between an upper section and a middle section is closed, the control valve between the middle section and a lower section is kept open, the vacuumizing desorption is started until the vacuum degree reaches 50-200 mm Hg, preferably 100 mm Hg, and then the carbon dioxide adsorbed on the adsorbent at the bottom in the middle adsorption tower is desorbed and enters the lower section adsorption tower; and step two, closing the control valve between the middle section and the lower section, and continuously vacuumizing to ensure that the vacuum degree of the lower section of the adsorption tower is not less than 600-700 mm Hg, so as to ensure that the carbon dioxide in the lower section of the adsorption tower is fully desorbed. (5) voltage equalizing +: after the reverse desorption is finished, closing a desorption gas discharge valve, and then opening a control valve between the middle section and the lower section, wherein the pressure of the adsorption bed in the middle section is higher than that of the lower section, so that the two sections can perform a pressure equalization process, and simultaneously, heavy components in the adsorption bed in the middle section are released into the lower section in a pressure equalizing process; after the pressure equalization of the middle section and the lower section is finished, the control valve between the upper section and the middle section is opened, the pressure equalization of the upper section adsorption bed and the middle and lower sections adsorption beds is finished, and meanwhile, the upper section adsorption bed is further regenerated. (6) final charging: a step of raising the pressure of the adsorption column to the adsorption pressure against the direction of feed with the light component, the purpose of which is to avoid pressure fluctuations when the adsorption column is switched to the adsorption step.
The ratio of the three sections to the adsorption tower is determined by the raw material gas composition, and the typical ratio of the three sections of the adsorption tower is as follows: 20%, middle section: 50%, upper stage: 30 percent.
In the aspect of filling the adsorbent, the difference from the traditional filling method is that the three-section pressure swing adsorption tower is used for recombining and filling alumina, silica gel and activated carbon by sections, filling the silica gel and the activated carbon in the middle section, and filling the activated carbon, the molecular sieve and the metal organic framework material in the light section.
In terms of process, taking the adsorption tower 1 as an example, the control valve V1 is opened under high pressure (0.5 MPa-7.0 MPa), the raw material gas 5 enters the tower 1 to start adsorption, and heavy components in the raw material gas comprise: methane, ethane, and,CO 2 The adsorbed gas stays in the bed layer filled with the adsorbent, the light component gas mainly containing nitrogen is discharged from the top of the tower through a pipeline 7, the adsorption capacity of the adsorbent to carbon dioxide is strongest, the concentration of nitrogen in the light component section is highest, the concentration of methane in the middle section is highest, the concentration of carbon dioxide in the recombination section is highest along with the progress of the adsorption step, meanwhile, when a methane content monitoring instrument J1 arranged behind K12 monitors that the methane content reaches a set value, for example, 90%, a valve (K12 can be a three-way valve) leading to a natural gas pipeline 8 at K12 is opened to obtain a natural gas product gas mainly containing methane, when the adsorption step is carried out to 80%, the raw gas is switched to another adsorption tower, a control valve between the upper section and the middle section of the adsorption tower is closed, the carbon dioxide gas is introduced through a pipeline 9, enters the adsorption tower through a gas exchange valve V17, the methane adsorbed by the lower section enters the middle section, the natural gas is obtained from the top of the middle section of the adsorption tower, and the replacement accounts for 20% of the adsorption step.
After the adsorption step sequence of the adsorption tower 1 is completed and before the pressure equalizing step is carried out, the control valves between the upper section and the middle section and between the middle section and the lower section of the adsorption tower are opened, the air exchange valves are closed at the same time, and then the pressure equalizing step sequence is started.
After the adsorption tower 1 finishes the pressure equalizing step sequence, the adsorption tower enters a reverse-releasing step sequence, control valves between the upper section and the middle section and between the middle section and the lower section of the adsorption tower are opened in the process, and reverse-releasing desorption gas enters a desorption gas pipeline 6 through a desorption gas valve V2.
And (3) starting a vacuumizing pressure equalizing + step sequence of the adsorption tower 1, firstly closing a control valve K12 between the upper section and the middle section of the adsorption tower, and closing a control valve K11 between the middle section and the lower section of the adsorption tower when the vacuum degree reaches 100 mm Hg until the vacuum degree is not less than 700 mm Hg. After the vacuum-pumping desorption is finished, the valve K12 is opened firstly, the pressure equalization between the upper section 13 and the middle section 12 of the adsorption tower is finished, and then the valve K11 is opened, and the pressure equalization between the three sections 11, 12 and 13 of the adsorption tower is finished.
The adsorption column 1 then begins a pressure equalization up step and finally ends with the light component product gas nitrogen. Ready for the next adsorption process.
A typical material balance for the purification of nitrogen-containing, carbon dioxide-containing natural gas using the present invention is shown in table 3.
TABLE 3 materials balance table (volume concentration composition)
Claims (11)
1. An energy gas purification method, comprising the following steps:
providing n sectional adsorption towers, wherein n is an integer greater than or equal to 3; dividing each adsorption tower into an upper section, a middle section and a lower section along the flowing direction of the raw gas to the product gas; according to different adsorption forces of the same adsorbent on nitrogen, methane and carbon dioxide, the upper section is a light component section which is difficult to adsorb and has high component concentration, and the upper section discharges light component product nitrogen from the top; the middle section is a section with high component concentration and the adsorption force is in the middle, and a natural gas product with the main component of methane is discharged from the top of the middle section; the lower section is a recombination section which is most easy to absorb and has high component concentration, and the lower section discharges carbon dioxide gas as a heavy component product from the bottom; two control valves are arranged among the three sections of the upper section, the middle section and the lower section, and a methane concentration detector is arranged behind the control valves of the upper section and the middle section and used for detecting the concentration of the control component at the outlet;
in each of the segmental adsorption towers, the following steps are cyclically performed in sequence:
(1) Adsorption: an adsorption step at substantially constant pressure at elevated pressure to obtain a purified light fraction product at the top of the column;
(2) Pressure equalizing and reducing: after the adsorption step is finished, reducing the pressure of the adsorption tower, continuously discharging light component product gas from the tower top, and using the light component product gas for the other desorption to finish the pressure boosting process of the adsorption tower;
(3) Reverse amplification: the step of reducing the pressure of the adsorption tower against the feeding direction, reducing the pressure of the adsorption tower to be close to the normal pressure, effectively desorbing impurity components from an adsorbent, discharging desorption gas generated by reverse release as a heavy component from the bottom of the tower, and opening two control valves between the upper section and the middle section and between the middle section and the lower section in the step;
(4) Vacuumizing: vacuumizing the adsorption tower along the direction opposite to the feeding direction, further recovering dead spaces in the adsorption tower and heavy components absorbed in the adsorbent, and improving the concentration and the recovery rate of the heavy components; the vacuum pumping is carried out in two steps: the first step, closing the control valve between the upper section and the middle section, keeping the control valve between the middle section and the lower section open, starting to pump vacuum for desorption, and desorbing carbon dioxide adsorbed on the adsorbent at the bottom in the adsorption tower at the middle section to obtain desorption and enter the adsorption tower at the lower section; secondly, closing a control valve between the middle section and the lower section, and continuously vacuumizing to ensure that carbon dioxide in the lower section of the adsorption tower is fully desorbed;
(5) Voltage equalizing +: after the reverse desorption is finished, closing a desorption gas discharge valve, then opening a control valve between the middle section and the lower section, carrying out pressure equalization on the middle section adsorption bed and the lower section adsorption bed, and simultaneously releasing heavy components in the middle section adsorption bed into the lower section in a pressure equalizing process; after the pressure equalization of the middle section and the lower section is finished, opening a control valve between the upper section and the middle section to finish the pressure equalization of the upper section adsorption bed and the middle and lower section adsorption beds, and simultaneously further regenerating the upper section adsorption bed;
(6) Pressure equalization and rise: the adsorption tower which finishes desorption receives the light component product gas from the pressure equalizing and reducing adsorption tower, and the pressure of the adsorption tower is boosted against the feeding direction, and the step is coupled with the pressure equalizing and reducing step;
(7) Final charging: and a step of raising the pressure of the adsorption column against the direction of the feed with the light component to the adsorption pressure.
2. The purification method according to claim 1, wherein when the volume concentration of the feed gas is: 50-65% of methane, 10-20% of nitrogen and 10-20% of carbon dioxide, wherein the proportions of the sections of the adsorption tower are as follows: 15-25% of the upper section, 45-55% of the middle section and 15-25% of the lower section.
3. The purification method according to claim 2, wherein when the content of methane in the feed gas exceeds 65%, the ratio of the middle section of the adsorption tower is increased; when nitrogen in the feed gas is the main impurity, the lower segment ratio is reduced; when carbon dioxide in the raw material gas is a main impurity, the ratio of the lower section needs to be increased, and the ratio of the upper section needs to be reduced.
4. The purification method according to claim 1, wherein the methane concentration detection point is used for detecting the concentration of methane in the adsorption tower when the methane concentration detection point leaves the top of the middle section of the adsorption tower, and when the methane content in the nitrogen discharged from the top of the adsorption tower is required to be not more than 3%, the detected methane content after the control valve is not more than 90%; when the methane content in the nitrogen discharged from the top of the tower is required to be not more than 1%, the methane content detected at the intermediate control valve is not more than 85%.
5. The purification method according to claim 1, wherein when the methane recovery rate is required to be increased and the carbon dioxide concentration and recovery rate are increased, after the adsorption step is completed and before the pressure equalization step is started, the product gas carbon dioxide is used as a purge gas and enters the lower section of the adsorption tower from the bottom of the adsorption tower to replace the methane in the lower section and the middle section of the adsorption tower, thereby increasing the methane recovery rate and increasing the concentration of the carbon dioxide obtained in the desorption process.
6. The purification method according to claim 1, wherein in the process of replacing methane with carbon dioxide, the control valve between the upper section and the middle section of the adsorption tower is closed, and the control valve between the middle section and the lower section is opened.
7. The purification method according to claim 1, wherein the adsorption tower is filled with activated carbon and molecular sieve at an upper section, silica gel and activated carbon at a middle section, and silica gel and activated carbon at a lower section.
8. The purification method according to claim 1, wherein the upper-stage packed activated carbon is used for adsorbing methane, and the molecular sieve is used for adsorbing methane with a low concentration; the silica gel filled in the middle section is used for adsorbing a small amount of carbon dioxide which penetrates through the bed layer from the lower section and enters the middle section, the activated carbon is used for adsorbing methane, and in the section, the filling amount of the activated carbon exceeds 75 percent; the lower section is filled with silica gel mainly used for adsorbing carbon dioxide, the activated carbon is used for controlling the speed and the amount of carbon dioxide penetrating through a bed layer, and the filling amount of the silica gel in the section is more than 75v%.
9. The purification method according to claim 1, wherein the activated carbon is selected for the lower section and the middle section to have a methane/nitrogen separation factor of 2.5-3.5.
10. The purification process according to claim 1, wherein the activated carbon used in the upper stage has a methane/nitrogen separation coefficient of greater than 3.5.
11. The purification method according to claim 1, wherein in the upper section, the molecular sieve is replaced by a metal-organic framework material above the activated carbon, and the metal-organic framework material is selected from at least one of Cu-MOF, MIL and Zn-MOF; the metal organic framework material has a methane/nitrogen separation coefficient greater than 6.
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