CN101480560B - Method for processing Claus tail gases by membrane separation - Google Patents

Abstract

A method for treating Claus tail gas by membrane separation. After pretreatment, the Claus tail gas enters membrane separation at a pressure of 1.0-2.5MPa, preferably 1.5-2.0MPa, and a temperature of 40-80°C, preferably 50-60°C. The device separates the retentate gas containing high concentration of nitrogen and the permeate gas enriched with SO ₂ and H ₂ S. Part of the permeate gas is returned to the Claus unit to recover sulfur, and the other part is returned to the membrane separator for further recovery of nitrogen. Compared with the low-temperature Claus process sulfur recovery, the present invention has the advantages of low equipment investment cost, simple operation, low energy consumption and common nitrogen by-product.

Description

A method for treating Claus tail gas by membrane separation

technical field

The invention belongs to the refining and utilization of Claus tail gas, more specifically, a method for separating Claus tail gas in a membrane separator, producing sulfur-free common nitrogen, and recycling the sulfur-containing gas.

Background technique

Except for a small amount of SO ₂ , H ₂ S and a small amount of O ₂ , the tail gas discharged from the Claus device is mostly nitrogen, and the mass fraction of nitrogen is 90% by weight, or even more than 95% by weight. Nitrogen in Claus tail gas is suitable for producing common nitrogen for industrial use, but its acid gases SO ₂ and H ₂ S are discharged into the atmosphere, which not only causes serious harm to the environment, but also is a great waste of sulfur resources.

At present, the tail gas treatment process of Claus sulfur recovery unit can be roughly divided into three categories: low-temperature Claus method, reduction absorption method and catalytic oxidation method according to its principle, and there are common defects such as complex device, difficult operation and large investment. At present, the most widely used is the low-temperature Claus method, which involves making the H ₂ S and SO ₂ in the tail gas continue to undergo low-temperature liquid phase at a temperature slightly higher than the melting point of sulfur in an organic solvent added with a special catalyst. Claus reaction, or at a temperature lower than the sulfur dew point, a low-temperature solid-phase Claus reaction occurs on a solid catalyst, as described in patent CN1031194A. The low-temperature Claus method cannot reduce the content of COS and CS ₂ in the tail gas, and the sulfur recovery rate is low, about 98.5% to 99.5%.

With the development of membrane technology, the removal of acid gas SO ₂ and H ₂ S in industrial tail gas has also been devoted to the membrane method that integrates separation and absorption to absorb and treat sulfur-containing tail gas in recent years to remove SO ₂ and H ₂ S. Membrane tail gas desulfurization, especially membrane flue gas desulfurization, has the advantages of less investment, simple operation and low energy consumption. Membrane tail gas desulfurization mainly adopts hollow fiber tubular membrane separator at present, wherein the hollow fiber membrane is a selective gas permeable membrane, such as CN1199718C, CN1234448C, CN1235669C all disclose cellulose hollow fiber gas separation membrane and its preparation. SO ₂ and CO ₂ in the tail gas can selectively enter the alkaline solution (Na ₂ SO ₃ or NaOH) through the membrane pores, and react with it to form NaHSO ₃ , NaHCO ₃ , while N ₂ , O ₂ and other substances in the flue gas The gas stays in the gas phase, so as to realize flue gas desulfurization and CO ₂ removal. The process flow of hollow fiber membrane flue gas removal of acid gas is as follows: the flue gas enters the hollow fiber membrane separator after dust removal and heat exchange, the flue gas is discharged through the chimney after the removal of SO ₂ and CO ₂ , and the absorption liquid enters the absorption liquid regeneration device Regenerate and recover sulfur or _CO2 . At present, hollow fiber membrane flue gas desulfurization and _CO2 removal are considered to be a flue gas treatment technology with great potential for commercial application, especially flue gas desulfurization technology with higher economic benefits.

In order to improve desulfurization efficiency, membrane desulfurization is often combined with other gas separation methods, as CN1140318C announces the method for separating/recovering gas in the combination of separation membrane unit and PSA unit, and CN1047632A utilizes water-soluble polymer chelate and membrane of polyvalent metal A method for removing nitrogen oxides and sulfur oxides from gas streams with a separation device, CN1919423A sulfur dioxide-air battery and its application in desulfurization technology, CN1297337C a device and method for removing sulfur dioxide in gas by combining ultrasonic waves and hollow fiber impregnated liquid membranes.

Compared with existing Claus tail gas desulfurization technology and membrane absorption desulfurization, equipment investment costs are high, operation is complicated, and energy consumption is high; however, membrane absorption desulfurization absorbing liquid is easily polluted and regeneration is difficult, and membrane pores are easily blocked and desulfurization rate is low (desulfurization rate of about 60 to 90%), thus hindering the industrial application of membrane tail gas desulfurization, to be further developed Claus tail gas sulfur recovery technology.

Contents of the invention

The purpose of the present invention is to provide a kind of method that adopts membrane separation to process Claus tail gas on the basis of prior art, and then returns to Claus plant to continue Claus reaction reclaiming sulfur and then to concentrate the harmful gas in Claus tail gas Production of common nitrogen for industrial use.

The purpose of the present invention is achieved by the following scheme: after the Claus tail gas is pretreated, it enters the membrane separation under the conditions of pressure 1.0～2.5MPa, preferably 1.5～2.0MPa, temperature 40～80°C, preferably 50～60°C device to separate the retentate gas containing high concentration of nitrogen and the permeate gas enriched with SO ₂ and H ₂ S, wherein part of the permeate gas is returned to the Claus unit to recover sulfur, and the other part is returned to the membrane separator for further recovery of nitrogen, said The Claus tail gas contains more than 85% by weight of nitrogen, less than 1% by weight of O ₂ content and the total amount of SO ₂ and H ₂ S is not higher than 6% by weight, and the pretreatment includes dust removal, dehydration and drying , the solid particle content of pretreated flue gas≤0.01mg/Nm ³ , H ₂ O≤1ppm.

The method provided by the present invention is applicable to any Claus tail gas with a nitrogen content higher than 85% by weight and an _O2 content lower than 1% by weight, especially suitable for nitrogen content higher than 90% by weight and an _O2 content lower than 0.5 % by weight of Claus exhaust. Other components in the Claus tail gas include SO ₂ , H ₂ S, COS, S, CO ₂ , H ₂ O, etc., wherein the total amount of SO ₂ and H ₂ S is preferably not higher than 6% by weight, and the content of COS and S Preferably not higher than 1% by weight. The composition of all gases is 100%.

The pretreatment of Claus tail gas includes dehydration and dust removal, pressurization and heat exchange. The pretreated Claus tail gas is also called membrane gas, its fine dust content is ≤0.01mg/Nm ³ , and H ₂ O is ≤1ppm.

Dehydration and dust removal include all dust removal methods that remove all solid particles with a diameter greater than 0.01 μm and oil mist, water mist and aerosols entrained in the gas, such as inertial dust removal, wet dust removal, electrostatic dust removal, filter dust removal, single Cylinder cyclone dust removal method and multi-tube cyclone dust removal method, centrifugal force separation, gravity sedimentation, baffle separation, wire mesh separation, ultrafiltration separation, packing separation, etc. Centrifugal force separation and filter type dust removal method are preferred. Dust content ≤ 0.01mg/Nm ³ , the residual oil content is required to be less than 0.01 mg/m ³ , and the gas entering the membrane must contain traces of water vapor or no water vapor, and H ₂ O in the gas entering the membrane is required to be ≤ 1ppm.

The membrane gas can be pressurized to 1.0-2.5MPa, preferably 1.5-2.0MPa, by means of pressurization, including any suitable pneumatic booster pump or gas booster for sulfur and nitrogen-containing gases.

The temperature of the membrane gas can be reduced to 40-80°C, preferably 50-60°C by means of heat exchange. The flue gas heat exchange means include various hybrid, heat storage or partition heat exchangers, preferably partition heat exchange The intermediate wall heat exchanger can be a special type heat exchanger composed of jacket type, tube type, plate type or various special-shaped heat transfer surfaces. The flow modes of the hot and cold fluids in the heat exchanger include forward flow, countercurrent flow, cross flow, mixed flow, preferably countercurrent flow.

The membrane separator includes any gas membrane separator composed of one or more flat-plate, roll-type or hollow-fiber membrane modules suitable for gas separation. Wherein the membrane material includes one or a composite of polymer materials, inorganic materials, and metal materials, preferably a polymer membrane, more preferably a composite polymer membrane. The polymer membrane is selected from polydimethylsiloxane (PDMS), polysulfone (PSF), polyaramid, cellulose acetate (CA), ethyl cellulose (EA), polycarbonate (PC), polyamide One or more of imide, polyphenylene ether, silicone rubber film, preferably polysulfone (PSF), polyimide film, methyl silicone rubber film or its modified film and several polymer materials Composite film. Membrane separators can be used in one-stage, two-stage or multi-stage processes.

The retentate gas requires a nitrogen concentration higher than 99.5% by weight, and a SO ₂ and H ₂ S concentration lower than 0.5% by weight. Its non-membrane conventional Claus tail gas desulfurization method includes any alkali liquid absorption, amine liquid absorption, and molecular sieve, activated carbon and metal oxide solid adsorption desulfurization, etc. to remove trace H ₂ S and SO ₂ methods, preferably loaded metal oxide adsorption desulfurization method.

The permeate gas is divided into two parts, one part is directly sent to the SO ₂ and H ₂ S reactor in the Claus process to recover sulfur after heat exchange, and the Claus sulfur recovery reaction temperature is 200-370 °C; the other part is desulfurized (The desulfurization method is the same as the nitrogen desulfurization method above) or pressurize without desulfurization, and then enter the membrane separator or secondary membrane separator to further recover the nitrogen in it. The pressurization method is the same as the feed gas pressurization method. The weight ratio between the permeate gas sent to the Claus unit and the permeate gas returned to the membrane separator is 0.5-8.5, preferably 2.5-5.5.

Compared with the prior art, the present invention has the following characteristics:

1. As a tail gas sulfur recovery process, compared with the low-temperature Claus process sulfur recovery, the present invention has the advantages of low equipment investment cost, simple operation and low energy consumption.

2. The present invention has the advantages of good selectivity for Claus tail gas treatment, high separation efficiency and no secondary pollution.

3. As a nitrogen production process, compared with air pressure swing adsorption nitrogen production, the membrane system occupies a small area and has a long service life; the equipment investment cost is low, the operation is simple, and the operation cost is low.

4. Compared with the pressure swing adsorption method, the present invention has the advantages of no moving parts, less pretreatment parts, fast start-up, no need for cooling water and low energy consumption.

Description of drawings

Figure 1 is a schematic diagram of a composite hollow fiber membrane separator for separating flue gas and recovering nitrogen.

Fig. 2 is a structural schematic diagram of a composite hollow fiber membrane separator.

Detailed ways

The method provided by the present invention will be further described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

Figure 1 is a schematic diagram of composite hollow fiber membrane separator for separating Claus tail gas and recovering nitrogen. The normal-temperature tail gas from the Claus process passes through the gas centrifuge 1 to initially remove the solid particles and water carried in the tail gas, and then enters the high-pressure storage tank 3 after being pressurized by the gas booster 2 to 1.0-2.5 MPa; passes through the activated carbon filter 4 After further dehydration and dust removal, the temperature of the Claus tail gas reaches 40-80°C after exchanging heat through the tube-and-tube countercurrent heat exchanger 5, and then passes through the precision filter 6 to remove all solid particles with a diameter greater than 0.01 μm to obtain water-free and micro The dust entering the membrane enters the composite hollow fiber membrane separator 7 suitable for acid gas separation under the conditions of pressure 1.5-2.5MPa and temperature 40-80°C, and separates retentate gas containing high concentration nitrogen and concentrated SO _2. Permeate gas of H ₂ S. Wherein the permeate gas is drawn from the permeate gas outlet through the pipeline 14 and is divided into two parts, one part is returned to the Claus device to recover sulfur through the pipeline 15, and the other part is successively passed through the pipeline 16, the gas booster 17, the pipeline 18 activated carbon filter 4, and replaced by the activated carbon filter 4. After heat exchange by the heat exchanger 5 and deep filtration by the precision filter 6, enter the membrane separator again to further recover nitrogen; the nitrogen content in the retentate gas is higher than 99.5% by weight, and it is further absorbed or adsorbed and removed by the desulfurization device 8 at room temperature to 200°C Trace amount of SO ₂ produces higher purity nitrogen.

Fig. 2 is a structural schematic diagram of a composite hollow fiber membrane separator. The composite hollow fiber membrane separator has a housing 10, and a membrane module 11 is arranged in the housing, and a Claus tail gas inlet 9 is arranged in parallel with the membrane module 11 at one end of the housing 10, and is parallel with the membrane module 11 at one end of the housing 10 A retentate gas outlet 12 is provided, and a permeate gas outlet 13 is provided on the upper side of the shell. The Claus tail gas flows inside the composite hollow fiber membrane module, the slow nitrogen gas goes through the tube side of the membrane module and is discharged through the nitrogen outlet, and the fast gas such as SO ₂ and H ₂ S permeates through the membrane module and is discharged through the permeate gas outlet.

The following examples will further illustrate the method provided by the present invention, but the present invention is not limited thereto.

The composition of the feed gas used in the examples is listed in Table 1. The hollow fiber membranes and membrane modules used are Mode I#PA3030-P1-3A-00 separators produced by Permea Co., Ltd. The parameters of the hollow fiber membrane modules used in the embodiments of the present invention are shown in Table 1 respectively.

Embodiment 1-4

Examples 1 to 4 illustrate: adopt the method provided by the present invention to investigate the results of processing different raw materials under different process conditions with different membrane separators.

The Claus tail gases A~C listed in Table 2 are used as raw materials respectively, and the SO ₃ content is all lower than 10ppm. After pretreatment, membrane separation and adsorption. The specific test steps are as follows: the Claus tail gas enters the high-pressure storage tank after preliminary centrifugal separation and pressurization, and then is filtered through an activated carbon filter for dehydration and dust removal, and after heat exchange and fine filtration, the dust content is ≤0.01mg/Nm ³ , H ₂ O ≤ 1ppm, enter different membrane separators such as polysulfone membrane, polyimide membrane and methyl silicone rubber, and separate the nitrogen-rich retentate gas and sulfur-containing permeate gas. The retentate gas is adsorbed by different adsorbents such as 10% by weight sodium hydroxide aqueous solution, 40% N-methyldiethanolamine solution, and commercially available zinc oxide, iron oxide desulfurizer, etc., and further removes trace sulfur to obtain high-concentration nitrogen; According to a certain proportion, the gas is sent to the Claus sulfur recovery reactor as the residual gas through heat exchange. The alumina-based commercial Claus reaction catalyst LS-981 produced by Shandong Qilu Keli Chemical Research Institute Co., Ltd. is used at 200-370 Under the condition of ℃, the reaction recovers sulfur; the other part of the permeate gas is pressurized as reflux gas and returns to the membrane separator to continue nitrogen production. The test conditions, test results and nitrogen composition are listed in Table 3.

It can be seen from Table 3 that the Claus tail gas with different compositions is treated by membrane processor at different flow rates of 500-1000Nm ³ /h, and the retentate gas is treated by desulfurization technology, and the nitrogen yield is above 60.9% by weight. Its purity is above 99.5%; the permeate gas sent to the Claus device is subjected to Claus sulfur recovery reaction at different temperatures, and the recovery rate of SO ₂ is above 97.1%, and the recovery rate of H ₂ S is above 95.3%. .

Table 1. Membrane module parameters

Table 2. Composition of Claus Tail Gas Raw Materials

Raw gas number A B C N ₂ , wt% 86.6 90.9 96.2 SO ₂ , wt% 2.7 1.5 0.38 H ₂ S, wt% 4.8 2.8 0.9 CO ₂ , wt% 4 2.5 0.47 _H2O , weight % 0.7 0.9 0.2 O ₂ , wt% 0.2 0.5 0.9 COS, weight % 0.8 0.4 0.1 S, weight % 0.2 0.5 0.85 Total, % by weight 100.00 100.00 100.00

Table 3. Test conditions and results

Remarks (1): H ₂ S was added appropriately during the experiment, so that the molar flow rate ratio of H ₂ S and SO ₂ was close to 2:1 during the reaction.

Claims (10)

1. a method that adopts film separating treatment Claus tail gases is characterized in that Claus tail gases after preliminary treatment, enters membrane separator under the condition of 40～80 ℃ of pressure 1.0～2.5MPa, temperature, isolates to contain oozing residual air and having concentrated SO of nitrogen ₂, H ₂The infiltration gas of S wherein permeates gas and partly returns Cross unit recovery sulphur, and another part returns membrane separator and further reclaims wherein nitrogen, and described Claus tail gases comprises the O that is higher than the above nitrogen of 85 weight %, is lower than 1 weight % ₂Content and SO ₂, H ₂The total amount of S is not higher than 6 weight %, and described preliminary treatment comprises dedusting, dehydration and drying, pretreated flue gas solid content≤0.01mg/Nm ³, H ₂O≤1ppm.

2. according to the method for claim 1, it is characterized in that described Claus tail gases comprises the O that is higher than the above nitrogen of 90 weight %, is lower than 0.5 weight % ₂The SO that content is following with being lower than 2 weight % ₂, be lower than the following H of 4 weight % ₂S.

3. according to the method for claim 1, it is characterized in that the condition that film separates is: 50～60 ℃ of pressure 1.5～2.0MPa, temperature.

4. according to the method for claim 1, it is characterized in that described membrane separator is made of one or more flat, rollings or doughnut formula membrane module, wherein membrane material comprises the compound of one or more materials in macromolecular material, inorganic material, the metal material.

5. according to the method for claim 4, it is characterized in that described macromolecular material is selected from one or more in dimethyl silicone polymer, polysulfones, Nomex, cellulose acetate, ethyl cellulose, Merlon, polyimides, polyphenylene oxide, the silicone rubber membrane.

6. according to the method for claim 1 or 5, it is characterized in that described membrane separator adopts one-level flow process, two-stage process or multistage flow process.

7. according to the method for claim 1, it is characterized in that describedly oozing that nitrogen gas concn is higher than 99.5 weight %, SO in the residual air ₂With H ₂The total amount of S concentration is lower than 0.5 weight %.

8. according to the method for claim 1, the weight ratio between the infiltration gas that it is characterized in that sending into the infiltration gas of Cross unit and returning membrane separator is 0.5～8.5.

9. according to the method for claim 8, the weight ratio between the infiltration gas that it is characterized in that sending into the infiltration gas of Cross unit and returning membrane separator is 2.5～5.5.

10. according to the method for claim 1, it is characterized in that described Cross unit reaction temperature is 200～370 ℃, H in the course of reaction ₂S and SO ₂The molar flow rate ratio near 2: 1.

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