Method and system for removing H2S and CO2 in medium-high pressure gas

Abstract

The invention discloses a method and a system for removing H2S and CO2 in medium-high pressure gas. The removal method comprises the following steps: firstly, treating a medium-high pressure gas raw material by using a desulfurization absorbent to remove most H2S and a small part of CO2, then carrying out gas-liquid separation, then carrying out fine desulfurization to continuously remove H2S, and finally, carrying out membrane separation treatment to separate out CO2, thereby completing the purification of the medium-high pressure gas. The method comprises the following steps: firstly, removing most H2S and a small part of CO2 in gas by using an absorbent with high selectivity to H2S, carrying out gas-liquid separation and filtration on the gas from which H2S is removed, feeding the gas into a fine desulfurization tower to further remove residual H2S in the gas, feeding purified gas leaving from the fine desulfurization tower into a membrane separation device, and separating CO2 from the gas; the whole separation process is simple, the separation efficiency is high, and the cost is controllable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of gas separation and purification, and particularly relates to a method and system for removing H2S and CO2 from medium-high pressure gas. BACKGROUND

[0002] Some industrial gases contain H2S and CO2, which need to be removed before use or entering the next process. For example, natural gas extracted from gas fields, coal gasification process coal gas generally contains CO2, H2S and other acid gases, which need to be separated and removed to reach the use standard before further application. The common H2S and CO2 removal technologies at present include pressure swing / temperature swing adsorption method, chemical absorption method, physical and chemical absorption method, etc. Patent documents CN102585952A, CN105498720A, CN101653688B, etc. all provide methods for removing H2S and CO2 from mixed gas. However, these technologies using solid adsorbents all have problems of high energy consumption, large amount of waste liquid and waste residue in the treatment process, etc., which increase the purification cost.

[0003] Compared with conventional CO2 removal technologies, membrane separation technology has the advantages of simple process, low energy consumption, environmental friendliness and easy coupling with other technologies. However, due to the close molecular dynamics diameter of H2S and methane molecules, the effect of membrane separation method on the removal of H2S in natural gas is poor. In addition, organic membranes are prone to carbon brittleness under high CO2 concentration and high olefin concentration, which greatly affects the separation performance and stability of the membranes.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method and system for removing H2S and CO2 from medium-high pressure gas. First, an absorbent with high selectivity for H2S is used to remove most of the H2S and a small amount of CO2 in the gas. After the removal of H2S, the gas is subjected to gas-liquid separation and filtration, and then enters a fine desulfurization tower for further removal of the remaining H2S in the gas. The purified gas leaving the fine desulfurization tower enters a membrane separation device to separate CO2 from the gas. The whole separation process is simple, efficient and cost controllable.

[0006] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0007] In the first aspect, the present application provides a method for removing H2S and CO2 from medium-high pressure gas, which comprises the following steps: first, using a desulfurization absorbent to treat medium-high pressure gas raw material to remove most of the H2S and a small amount of CO2, then performing fine desulfurization after gas-liquid separation to continue removing H2S, and finally separating CO2 by membrane separation treatment, i.e. completing the purification of medium-high pressure gas.

[0008] As a preferred technical solution of the present application, the removal method specifically comprises the following steps: feeding the high-pressure gas to be purified into the lower part of the absorption tower, contacting with the desulfurization absorbent from the upper part of the absorption tower to remove most of the H2S and a small amount of CO2; then, feeding the preliminarily purified gas into the fine desulfurization tower;

[0009] The rich liquid absorbing H2S and CO2 is sent into the flash unit after leaving the absorption tower, and the liquid obtained by flash is sent into the regeneration tower after heat exchange with the lean liquid from the bottom of the regeneration tower to be desorbed; the lean liquid from the bottom of the regeneration tower is returned to the upper part of the absorption tower after heat exchange to be cyclically absorbed;

[0010] The gas treated by the fine desulfurization tower is filtered and dried, and then is fed into the membrane separation device to separate CO2 to obtain the purified high-pressure gas.

[0011] As a preferred technical solution of the present application, the desulfurization absorbent comprises the following components in 100% by mass: 20-35% of steric amine, 1-5% of active amine, 40-50% of organic solvent, 0.5-1% of auxiliary agent, and the rest of water. The steric amine comprises the following components or mixture of the two: 2-amino-2-methyl-1-propanol, L-aminopropanol, 2-(2-aminoethoxy)ethanol, t-butylaminoethoxy ethanol, etc.; the active amine is di-amine or tri-amine, comprising the following components: ethylenediamine, butanediamine, diethylenetriamine, etc.

[0012] As a preferred technical solution of the present application, the fine desulfurization tower is filled with activated carbon desulfurization agent.

[0013] As a preferred technical solution of the present application, the number of the fine desulfurization towers is 2, which are arranged in series or in parallel.

[0014] As a preferred technical solution of the present application, inorganic membrane is used in the membrane separation device.

[0015] As a preferred technical solution of the present application, the inorganic membrane is zeolite molecular sieve membrane.

[0016] As a preferred technical solution of the present application, the pressure of the high-pressure gas raw material is not less than 2 MPa.

[0017] In the second aspect, the present application provides a system for implementing the above removal method, comprising an absorption tower and a regeneration tower, the lower part of the absorption tower is communicated with a flash unit through a pipeline, the flash unit is communicated with the middle part of the regeneration tower through a pipeline via a lean-rich liquid heat exchanger; the bottom of the regeneration tower is communicated with the upper part of the absorption tower through a pipeline via a lean-rich liquid heat exchanger;

[0018] The top of the absorption tower is communicated with a fine desulfurization tower through a pipeline, and the fine desulfurization tower is communicated with a membrane separation device through a pipeline.

[0019] As a preferred technical scheme of the present application, the flash pressure of the flash unit is 0.4-0.9 MPa.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] (1) The present application provides a method for removing H2S and CO2 from a middle-high pressure gas, which adopts the coupling technology of absorption method and membrane separation method to realize the selective and efficient removal of H2S and the effective separation of CO2 from the mixed gas. The selective absorbent for H2S is used to remove most of the H2S in the gas, and then secondary desulfurization is performed to further remove the residual H2S in the gas, and finally the membrane separation unit is used for the separation of CO2. Compared with the current chemical absorption method for simultaneously removing H2S and CO2, the cost is greatly reduced, and the environmental pollution in the gas purification process is also reduced.

[0022] (2) The method for removing H2S and CO2 from a middle-high pressure gas provided by the present application can realize the efficient removal of H2S. The desulfurization absorbent used contains 20-35% of mixed steric amines and 1-5% of active amines, which can realize the high selective absorption of H2S, and also has the characteristics of not easy to degrade, small corrosion, low foaming tendency, high regeneration efficiency, etc. It needs to be particularly emphasized that the type of the desulfurization absorbent provided by the present application is obtained through repeated optimization, comparison and screening by the applicant, and very good desulfurization effect can be achieved.

[0023] (3) The method for removing H2S and CO2 from a middle-high pressure gas provided by the present application can realize the efficient separation of CO2. The gas after removal of H2S enters the membrane separation device, and the inorganic membrane assembly with fast CO2 permeation rate and high CO2 selectivity is used, which can separate faster and lose less CH4 compared with the organic polymer membrane assembly, and the performance of the membrane assembly is less affected by the water content in the gas. For example, under the conditions of 0.3 MPa and 30% CO2 content in the raw gas, the permeation rate of CO2 is 2600 GPU, and the CO2 / CH4 selectivity can reach more than 70.

[0024] (4) The method for removing H2S and CO2 from a middle-high pressure gas provided by the present application can reduce the purification cost of the mixed gas and reduce the generation of waste liquid. For the gas with high carbon-sulfur ratio, the absorbent with high selectivity for H2S is used to realize the deep removal of H2S under the conditions of high gas-liquid ratio and low absorbent circulation amount. Compared with the process of simultaneously removing H2S and CO2 in natural gas by using absorption method, the load and scale of the absorption and regeneration device are much smaller, and the generation of waste liquid is greatly reduced.

[0025] (5) The application provides a method for removing H2S and CO2 from medium-high pressure gas, which fully utilizes the pressure of raw gas, is beneficial to the absorption of H2S in the absorption stage, can reduce the carrying amount of hydrocarbons in the rich liquid and improve the H2S purity of the regenerated gas by performing flash evaporation before the regeneration of the rich liquid. The flash evaporation process can improve the flash evaporation effect by reducing the flash evaporation pressure and prolonging the flash evaporation time, and the process conditions can be adjusted according to the purity requirement of the regenerated gas.

[0026] (6) The removal system provided by the application has a simple process and is easy to realize industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The figure is a flowchart of the removal system provided by the application.

[0028] Figure 2 The desulfurization effects of Example 1 and Comparative Example 2 are compared.

[0029] 1, an absorption tower; 2, a regeneration tower; 3, a flash evaporation unit; 4, a fine desulfurization tower; and 5, a membrane separation device. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0031] Meanwhile, it should be noted that, in the examples, the specific conditions not mentioned are carried out according to the conventional conditions or the conditions recommended by the manufacturers. The reagents or instruments not mentioned by the manufacturers are conventional products that can be purchased in the market.

[0032] In the application, a method for removing H2S and CO2 from medium-high pressure gas is provided, which comprises the following steps: first, using a desulfurization absorbent to treat the medium-high pressure gas raw material to remove most of the H2S and a small amount of CO2, then performing fine desulfurization after gas-liquid separation to continue removing H2S, and finally separating out CO2 through membrane separation treatment, so as to complete the purification of the medium-high pressure gas.

[0033] More specifically, the steps of the removal method are as follows: the medium-high pressure gas to be purified is sent to the lower part of the absorption tower, contacts with the desulfurization absorbent from the upper part of the absorption tower, and removes most of the H2S and a small amount of CO2; then, the gas after preliminary purification is sent to the fine desulfurization tower;

[0034] The rich liquid absorbing H2S and CO2 is sent into a flash unit after leaving the absorption tower, the liquid obtained by flash is heat-exchanged with the lean liquid from the bottom of the regeneration tower and then enters the regeneration tower for desorption; the lean liquid from the bottom of the regeneration tower is heat-exchanged and then returned to the upper part of the absorption tower for circulation absorption.

[0035] The gas treated by the fine desulfurization tower is filtered and dried and then enters the membrane separation device, and the purified medium-high pressure gas is obtained after the CO2 is separated.

[0036] In the technical scheme, first, the absorbent with high selectivity to H2S is used to remove most of H2S and a small amount of CO2 in the gas, the gas after removal of H2S is separated by gas-liquid separation and filtration and then enters the fine desulfurization tower to further remove the remaining H2S in the gas, the purified gas leaving the fine desulfurization tower enters the membrane separation device, the CO2 is separated from the gas, and the permeated gas leaving the membrane separation device is the purified gas. The removal process has much lower cost than the chemical absorption method commonly used to remove H2S and CO2 at the same time. The removal method of H2S and CO2 is suitable for purification of gas with pressure ≥ 2 MPa and is suitable for purification of gas with low H2S content and high carbon-sulfur ratio.

[0037] In some embodiments, the desulfurization absorbent is selected from an absorbent with high selectivity to H2S, while being able to remove a small amount of organic sulfur that can be contained in the gas; more specifically, the desulfurization absorbent comprises, by mass, 20-35% of a steric amine, 1-5% of an active amine, 40-50% of an organic solvent, 0.5-1% of an additive, and the balance of water. The steric amine comprises the following components or a mixture of the two: 2-amino-2-methyl-1-propanol, L-aminopropanol, 2-(2-aminoethoxy)ethanol, t-butylaminoethoxy ethanol, etc.; the active amine is a di-amine or tri-amine, comprising the following components: ethylenediamine, butylenediamine, diethylenetriamine, etc. Common steric amines include 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, diisopropanolamine, etc. The hydrogen atoms on the amino group are replaced by groups with a Taft steric hindrance constant greater than 1.74, which significantly improves the selectivity of the steric amine to H2S. The reaction of the steric amine with H2S is a gas film-controlled instantaneous reaction, with a fast absorption rate, and the dissociation constant (pKa) of the steric amine is generally greater than 10, which increases the equilibrium constant of the reaction of the steric amine with H2S, and the absorption capacity is large. The reaction of the steric amine with CO2 cannot form stable carbamate, and finally generates bicarbonate, with a reaction rate much lower than that of the reaction with H2S, so when the mixed gas contains both H2S and CO2, the steric amine preferentially absorbs H2S, forming a high selectivity to H2S. The tertiary amine molecule has a hydroxyl group, and the nitrogen atom in the molecule has an unpaired electron, so that the aqueous solution is alkaline, and can react reversibly with H2S. This reversible reaction is a process of only hydrogen ion transfer, so the tertiary amine solution reacts instantaneously with H2S, and the reaction rate is mainly controlled by diffusion mass transfer. Due to the lack of free hydrogen ions, it cannot directly react with CO2, and needs to first hydrolyze CO2 to generate H + , and then combine with H + to form R2NH + CH3. The general hydrolysis reaction rate is slow, thereby reducing the overall reaction rate, so the tertiary amine solution also has high selectivity to H2S. The addition of a polyamine as an active agent in the desulfurization absorbent can improve the H2S absorption capacity and speed up the absorption process. In the above desulfurization absorbent, the organic solvent can be a common type, and the additive can be a corrosion inhibitor, etc. The type of corrosion inhibitor can be selected from common substances on the market to achieve the corresponding function.

[0038] In some embodiments, the fine desulfurization tower is filled with an activated carbon desulfurization agent, which can be a common product on the market, which is a very mature industrialized product.

[0039] In some embodiments, the number of fine desulfurization towers is 2, which are arranged in series or parallel. It can be understood that the number of fine desulfurization towers can be flexibly selected according to process needs, and a single tower can be operated, or two towers can be operated.

[0040] In some embodiments, the membrane separation device employs an inorganic membrane; more preferably, the inorganic membrane employs a zeolite molecular sieve membrane. The membrane has a CO2 permeation rate of ≥ 2500 GPU (i.e. 8.375 x 10 -7 mol / (m 2 .s.pa) at low pressure, a CO2 / CH4 selectivity of ≥ 35; a CO2 permeation rate of 650 GPU (i.e. 2.18 x 10 -7 mol / (m 2 .s.pa) at high pressure (2 MPa), a CO2 / CH4 selectivity of ≥ 20. The molecular sieve membrane crystal has a pore size of 0.38 nm, a special pore size, a high shape-selective separation selectivity, and a permeation capacity and selectivity much higher than that of an organic membrane, and has the characteristics of high mechanical strength and high chemical stability. The application of the molecular sieve membrane to the separation of CO2 in a gas can greatly improve the separation selectivity of CO2, and the permeation flux of CO2 is much higher than that of an inorganic membrane. Different structures of the molecular sieve membrane have different separation performances for CO2 and different hydrothermal stabilities. Among them, the T-type, Y-type and SAPO-34 molecular sieve membranes have strong hydrophilicity, and the presence of water greatly reduces the gas permeation flux. The high silicon content in the zeolite molecular sieve greatly improves the hydrophobicity, and the influence of water on the permeation flux and selectivity of the membrane is greatly reduced. The application of the inorganic molecular sieve membrane to the separation of CO2 in a gas can greatly improve the separation efficiency and reduce the purification cost of the gas, and the purification process does not produce waste liquid and waste residue, which is an environmentally friendly process technology.

[0041] In some embodiments, the pressure of the medium-high pressure gas raw material is not less than 2 MPa.

[0042] In addition, the present application also provides a removal system, comprising an absorption tower 1, a regeneration tower 2, the lower part of the absorption tower 1 is communicated with a flash unit 3 through a pipeline, the flash unit 3 is communicated with the middle part of the regeneration tower 2 through a pipeline via a lean-rich liquid heat exchanger; the bottom of the regeneration tower 2 is communicated with the upper part of the absorption tower 1 through a pipeline via a lean-rich liquid heat exchanger;

[0043] The top of the absorption tower 1 is communicated with a fine desulfurization tower 4 through a pipeline, and the fine desulfurization tower 4 is communicated with a membrane separation device 5 through a pipeline.

[0044] In the above technical solution, it can be understood that the membrane separation device 5 can be composed of one or more membrane separation units, which can be flexibly selected according to actual needs.

[0045] In some embodiments, the flash pressure of the flash unit 3 is 0.4-0.9 MPa.

[0046] Further referring to Figure 1 , the entire removal method of the present application is described in detail:

[0047] The gas to be purified first enters the lower part of the absorption tower 1 and is in countercurrent contact with the desulfurization absorbent from the upper part of the absorption tower 1 to remove most of the H2S and a small amount of CO2 in the gas, and the rich liquid for absorbing H2S flows out from the bottom of the absorption tower 1; the gas after the primary desulfurization enters the secondary desulfurization unit (i.e. the fine desulfurization tower 4, which is schematically shown as a two-tower process in parallel in the figure), which is filled with special activated carbon desulfurization agent, and the two desulfurization towers are operated in parallel by controlling the valves arranged thereon to further remove the remaining H2S in the gas;

[0048] The rich liquid after absorbing H2S exits from the bottom of the absorption tower 1 and enters the flash unit 3, from which part of the gas such as H2S and CO2 is flashed, and the flashed gas is separated from the liquid and then sent to the subsequent H2S treatment unit (not shown in the figure); the liquid after the flashing is heated with the lean liquid from the bottom of the regeneration tower 2 and then enters the regeneration tower 2 for desorption, and the H2S-rich gas desorbed from the rich liquid at a high temperature is condensed at the top of the tower and then sent to the H2S treatment unit (not shown in the figure); the lean liquid after the regeneration flows out from the bottom of the regeneration tower 2, is heated with the rich liquid after the flashing, and then returns to the upper part of the absorption tower 1 for cyclic absorption;

[0049] The gas after leaving the fine desulfurization tower 4 is filtered and preliminarily dried and then enters the membrane separation device to separate CO2 from the gas, the permeate gas rich in CO2 enters the membrane separation device 5 for further separation, and the purified gas exits the device.

[0050] The method and system for removing H2S and CO2 from a medium-high pressure gas are further described below in combination with specific embodiments.

[0051] Embodiment 1

[0052] A method for removing H2S and CO2 from a medium-high pressure gas, comprising the following steps:

[0053] The gas to be purified is natural gas produced by gas field exploitation, which contains about 1000 mg / m 3 of H2S and about 20 vol% of CO2, and the gas enters the lower part of the absorption tower 1 and is in countercurrent contact with the desulfurization absorbent (the composition of the absorbent is: L-aminopropanol 20 wt%, t-butyl amine ethoxy ethanol 10 wt%, diethylene triamine 4 wt%, corrosion inhibitor 0.3 wt%, organic solvent 60 wt%, and the rest is water); the CO2 content in the gas exiting from the top of the absorption tower 1 is 18.6 vol%, and the H2S content is 120 mg / m 3 , which is condensed at the top and then enters the fine desulfurization tower 2 to further remove H2S in the gas; the H2S content in the gas after leaving the secondary desulfurization unit is 18 mg / m 3, into the membrane separation device 5, the membrane assembly is a zeolite molecular sieve membrane, the pressure difference between the two sides of the membrane assembly is 1.25 MPa, the CO2 content in the retentate gas leaving the membrane assembly is 2.6%, the CH4 content is 97.4%, which is the product gas entering the conveying pipeline; the CO2 content in the permeate gas is 52%, which enters the secondary membrane separation device for further separation; the rich liquid flowing out from the bottom of the absorption tower 1 first enters the flash evaporation unit 3, the flash evaporation pressure is 0.55 MPa, the gas flashed out is subjected to H2S treatment in the gas-liquid separation unit, and the liquid after flash evaporation and the lean liquid from the bottom of the regeneration tower 2 are heat-exchanged and then enter the middle and upper part of the regeneration tower 2, and the lean liquid after regeneration returns to the absorption tower 1 for recycling.

[0054] Comparative Example 1

[0055] The gas to be purified is the same as that in Example 1, and the gas enters the absorption tower 1 and is countercurrently contacted with the absorbent. The difference is that, in Comparative Example 1, the absorbent composition is: 2-amino-2-methyl-1-propanol 30 wt%, MDEA 5 wt%, corrosion inhibitor 0.5 wt%, organic solvent 60 wt%, and the rest is water. The H2S content of the gas leaving the top of the absorption tower is 214 mg / m 3 , the CO2 content is 17.5 v%, which is condensed at the top of the tower and then enters the fine desulfurization tower, and the remaining steps are similar to those in Example 1.

[0056] The desulfurization performance of the absorbent in Example 1 is compared with that in the comparative example, as shown in Table 1. Figure 2 It can be seen that the acid gas load and H2S / CO2 selectivity of the desulfurizer in Example 1 are both better than those in the comparative example.

[0057] The above examples illustrate the technical concept of the present application, but the present application is not limited to the above examples, i.e. it does not mean that the present application must rely on the above examples to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of individual raw materials of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for removing H2S and CO2 from a medium-high pressure gas, characterized in that, The method comprises the following steps: firstly, treating the medium-high pressure gas raw material with a desulfurization absorbent to remove most of H2S and a small amount of CO2; then, after gas-liquid separation, performing fine desulfurization to further remove H2S; and finally, separating CO2 through membrane separation treatment, thereby completing the purification of the medium-high pressure gas.

2. A method for removing H2S and CO2 from a medium-high pressure gas according to claim 1, characterized in that, The method comprises the following steps: sending the medium-high pressure gas to be purified into the lower part of an absorption tower, contacting the desulfurization absorbent from the upper part of the absorption tower to remove most of H2S and a small amount of CO2; then, sending the preliminarily purified gas into a fine desulfurization tower; The rich liquid for absorbing H2S and CO2 is sent into a flash unit after leaving the absorption tower, and the liquid obtained through flash is sent into a regeneration tower after heat exchange with the lean liquid from the bottom of the regeneration tower to perform desorption; the lean liquid from the bottom of the regeneration tower is returned to the upper part of the absorption tower after heat exchange to perform cyclic absorption; The gas treated by the fine desulfurization tower is sent into a membrane separation device after filtration and drying treatment, and the medium-high pressure gas is obtained after separation of CO2.

3. A method for removing H2S and CO2 from a medium-high pressure gas according to claim 2, characterized in that, The desulfurization absorbent comprises the following components in 100% by mass: a steric amine 20-35%, an active amine 1-5%, an organic solvent 40-50%, an additive 0.5-1%, and the rest is water.

4. The method for removing H2S and CO2 in a medium-high pressure gas according to claim 2, characterized in that, The fine desulfurization tower is filled with an activated carbon desulfurization agent.

5. The method for removing H2S and CO2 in a medium-high pressure gas according to claim 2, characterized in that, The number of the fine desulfurization tower is 2, which are arranged in series or parallel.

6. The method for removing H2S and CO2 in a medium-high pressure gas according to claim 2, characterized in that, The membrane separation device adopts an inorganic membrane.

7. A method for removing H2S and CO2 from a medium-high pressure gas according to claim 6, characterized in that, The inorganic membrane is a zeolite molecular sieve membrane.

8. The method for removing H2S and CO2 in a medium-high pressure gas according to claim 1, characterized in that, The pressure of the medium-high pressure gas raw material is not less than 2 MPa.

9. A system for carrying out the removal process according to any one of claims 1 to 8, characterized in that The method comprises an absorption tower and a regeneration tower, the lower part of the absorption tower is communicated with a flash unit through a pipeline, the flash unit is communicated with the middle part of the regeneration tower through a lean-rich liquid heat exchanger and a pipeline, the bottom of the regeneration tower is communicated with the upper part of the absorption tower through a lean-rich liquid heat exchanger and a pipeline. The top of the absorption tower is communicated with a fine desulfurization tower through a pipeline, and the fine desulfurization tower is communicated with a membrane separation device through a pipeline.

10. The system of claim 9, wherein, The flash pressure of the flash unit is 0.4-0.9 MPa.

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