Hardness reduction and scale inhibition method for coal gasification black water

Abstract

The invention discloses a coal gasification black water hardness reduction and scale inhibition method, and belongs to the technical field of sewage hardness reduction, the coal gasification black water hardness reduction and scale inhibition method comprises the following steps: coal gasification black water is coarsely filtered by a 60-80 mesh filter screen to obtain coarsely filtered black water, the coarsely filtered black water enters a flash tank for flash evaporation and discharging to obtain flash evaporation black water, the flash evaporation black water enters a primary fine filter, and the primary fine filter enters a secondary fine filter; carrying out primary fine filtration by the primary fine filter to obtain fine filtrate I and sewage I, and feeding the fine filtrate I into a secondary fine filter; according to the method, the nanofiltration membrane is modified, and the nanofiltration mode is optimized, so that the selective removal rate of hard water ions in the black water is effectively increased, the hardness and turbidity of the hardness-reduced water are reduced, long-acting and stable operation of the black water softening and hardness reducing process can be maintained, the hardness reducing treatment efficiency of the black water is improved, and the hardness reducing treatment cost of the black water is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of sewage hardness reduction, and in particular to a method for reducing hardness and preventing scale of coal gasification black water. Background Art

[0002] The Shenning furnace pulverized coal gasification unit uses pulverized coal as raw material, oxygen and sub-high-pressure steam as gasifying agents, and produces crude synthesis gas with CO2 and H2 as effective ingredients. Under the high-temperature gasification reaction or quenching conditions of the gasifier, substances produced by side reactions dissolve in the water system to form black water. The black water in the water system is high-temperature and high-pressure circulating water. If its hardness is high, scaling will easily occur during operation. The scaling materials are easily adsorbed together and adhere to the pipe wall and will be deposited in the pipes and equipment, resulting in serious scaling of the pipes and equipment, affecting the service life of the pipes and equipment, and causing serious impact on the operation and maintenance of the gasification unit.

[0003] The hardness of traditional black water reaches 1500mg / L, and the black water needs to be softened and reduced in hardness. However, in the process of softening and reducing the hardness of water, flocculation and sedimentation are usually used to treat it. For this treatment method, for coal gasification black water with high hardness and high suspended matter, although the flocculant can remove suspended matter, it is powerless against the hardness ions dissolved in the water. Therefore, the effect of flocculation and sedimentation on reducing hardness is not ideal. Although nanofiltration membrane fine filtration can reduce the ion content in hard water, it is easy to form pollution blockage on the surface of the nanofiltration membrane during the nanofiltration process. The surface is only modified by fluorine-containing compounds. Although it can improve its surface anti-fouling performance, it also reduces its water flux at the same time, resulting in the efficiency of black water hardness reduction needs to be further improved. Summary of the invention

[0004] The object of the present invention is to provide a method for reducing the hardness and preventing scale of coal gasification black water, so as to solve the technical problem in the prior art that the effect and efficiency of black water softening and hardness reduction need to be further improved.

[0005] The purpose of the present invention can be achieved by the following technical solution: A method for reducing hardness and preventing scale of coal gasification black water, comprising the following steps:

[0006] S1. Coal gasification black water is coarsely filtered through a 60-80 mesh filter to obtain coarse filtered black water, and the coarse filtered black water enters a flash tank for flash evaporation, and the material is discharged to obtain flash evaporated black water;

[0007] S2, the flash black water enters the first-stage fine filter, and after the first-stage fine filtration by the first-stage fine filter, the fine filtrate 1 and the sewage 1 are obtained, the fine filtrate 1 enters the second-stage fine filter, and after the second-stage fine filtration by the second-stage fine filter, the fine filtrate 2 and the sewage 2 are obtained, the fine filtrate 2 enters the third-stage fine filter, and after the third-stage fine filtration by the third-stage fine filter, the hardness-reduced water and the sewage 3 are obtained, wherein the first-stage fine filter, the second-stage fine filter and the third-stage fine filter have the same structure and are all equipped with a plurality of nanofiltration membrane groups;

[0008] S3, sewage one, sewage two and sewage three enter the flocculation sedimentation tank, flocculant is added to the flocculation sedimentation tank, the sludge flocculates and settles in the flocculation sedimentation tank, and after overflow, the overflow liquid of the supernatant layer and the settled sludge are obtained. The settled sludge is dehydrated by filter pressing to obtain sludge and filter press water. The filter press water and overflow liquid enter the first-level fine filter for circulating fine filtration.

[0009] Furthermore, in step S2, the volume ratio of sewage 1 discharged from the first-stage fine filter to the total solution entering the first-stage fine filter is 1:9-10, the volume ratio of sewage 2 discharged from the second-stage fine filter to the fine filtrate 1 entering the second-stage fine filter is 1:18-20, and the volume ratio of sewage 3 discharged from the tertiary fine filter to the fine filtrate 2 entering the tertiary fine filter is 1:22-25.

[0010] Furthermore, in step S3, the concentration of the flocculant in the flocculation sedimentation tank is 3-8 mg / L, and the flocculant is composed of non-ionic polyacrylamide and polyferric sulfate in a weight ratio of 3:1.

[0011] Furthermore, the nanofiltration membrane group is processed by the following steps:

[0012] A1. Depositing a polypropylene-based spinning solution on the surface of a nanofiltration base membrane by electrospinning to form a polypropylene-based nanostructure on both sides of the nanofiltration base membrane, thereby preparing a crude nanofiltration membrane;

[0013] A2. Place the crude nanofiltration membrane in a cyclohexanehexayl chloride solution, keep it completely immersed for 60-80 seconds at room temperature, and post-treat it to obtain a nanofiltration membrane;

[0014] A3. Stack several nanofiltration membranes layer by layer, and then fix them on a frame with a supporting back plate to obtain a nanofiltration membrane group.

[0015] Furthermore, in step A1, the nanofiltration base membrane is a polyethersulfone ultrafiltration membrane, the polypropylene-based spinning solution is composed of polyacrylic acid, polyacrylamide and N,N-dimethylformamide in a ratio of 3-4g:2-3g:100mL, the electrospinning voltage is 18-20kV, the drum speed is 120-130r / min, the receiving distance is 30cm, the spinneret aperture is 0.5mm, the supply rate of the polypropylene-based spinning solution is 11-13μL / min, and the single-sided deposition time is 50-60min.

[0016] Furthermore, in step A2, the cyclohexanehexayl chloride solution is composed of cyclohexanehexayl chloride and tetrahydrofuran at a ratio of 1 g:30 mL, and the post-treatment includes: after the reaction is completed, taking the membrane out of the solution, rinsing it with n-hexane three times, placing it in a drying oven at a temperature of 60-70°C, and drying it to constant weight to obtain a nanofiltration membrane.

[0017] Furthermore, in step A3, the number of the nanofiltration membranes is 8-10, and the supporting back plate is a porous stainless steel mesh.

[0018] Furthermore, the preparation method of cyclohexanehexacarboxylic acid chloride is as follows: under nitrogen protection, 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, phosphorus pentachloride and xylene are mixed, the temperature of the reaction system is increased to 125-135° C., the reaction is kept warm for 6-8 hours, and post-processed to obtain cyclohexanehexacarboxylic acid chloride.

[0019] The synthetic reaction formula of cyclohexanehexaacyl chloride is:

[0020]

[0021] The synthetic reaction mechanism of cyclohexanehexaacyl chloride is:

[0022] During the reaction, under heating conditions, the chlorine atoms of phosphorus pentachloride react with the hydroxyl groups in cyclohexanehexacarboxylic acid to form a phosphorus oxychloride intermediate complex of carboxylic acid. Due to the strong chlorination ability of phosphorus pentachloride, the chlorine atoms replace the hydrogen atoms in the hydroxyl groups to form acyl chloride groups, thereby forming cyclohexanehexacarboxylic acid chloride with six acyl chloride groups. According to mass spectrometry analysis, the molecular weight of cyclohexanehexacarboxylic acid chloride is 458.8904, m / z: 457.8266 (100.0%), 459.8237 ( 79.9%),455.8296(52.1%),461.8207(34.1%),458.8300(13.0%),460.8270(10.4%),463.8178(8.2%),456.8329(6.8%),462.8241(4.4%),459.8308(1.2%),464.8211(1.1%),465.8148(1.0%).

[0023] Furthermore, the molar ratio of the 1,2,3,4,5,6-cyclohexanehexacarboxylic acid to phosphorus pentachloride is 1:8, the amount ratio of the 1,2,3,4,5,6-cyclohexanehexacarboxylic acid to xylene is 1g:10mL, and the post-treatment comprises: after the reaction is completed, the temperature of the reaction system is reduced to 5-10°C, cyclohexane is added to the reaction system, solid is precipitated, the reaction system is stirred for 40-60 minutes, and the filter is filtered, the filter cake is washed with cyclohexane at a temperature of 5-10°C for 3 times and then dried, the filter cake is transferred to a drying oven at a temperature of 50-60°C, and vacuum dried to constant weight to obtain cyclohexanehexayl chloride.

[0024] Furthermore, taking the first-stage fine filter as an example, the structure of the first-stage fine filter includes: a shell, several groups of nanofiltration membrane groups installed inside the shell, and a slag box fixed to the bottom of the shell, the bottom of the shell is provided with a sewage trough connected to the slag box and arranged corresponding to the several groups of nanofiltration membrane groups, an inlet pipe is installed on the top of one side of the shell, a water outlet pipe is installed on the other side of the shell, and a slag discharge pipe is installed on one side of the slag box.

[0025] Furthermore, a check plate corresponding to a plurality of sewage drains is installed at the bottom of the shell, the nanofiltration membrane group is inclined at 10-15 degrees toward the water inlet pipe, and a plurality of the nanofiltration membrane groups are arranged in parallel.

[0026] The present invention has the following beneficial effects:

[0027] 1. The method for reducing hardness and preventing scale of coal gasification black water of the present invention comprises the following steps: a spinning solution is composed of polyacrylic acid and polyacrylamide, a polypropylene-based nanostructure is modified on a polyethersulfone ultrafiltration membrane substrate in the form of electrospinning, cyclohexanehexayl chloride is used as a modifier, and the acyl chloride groups on the cyclohexanehexayl chloride molecules are used to react with the amino groups on the nanofiltration membrane crude product to undergo an amidation reaction, thereby promoting the deposition and cross-linking of the polypropylene-based nanostructure modified on the ultrafiltration membrane substrate on the membrane substrate, and the unreacted acyl chloride groups modified on the membrane are hydrolyzed into carboxylic acid groups after being soaked in deionized water to obtain a nanofiltration membrane. The carboxylic acid groups modified on the nanofiltration membrane improve the hydrophilicity of the nanofiltration membrane, which helps to reduce the attachment of pollutants such as organic matter and colloids on the membrane surface. In addition, the modification of the carboxyl groups introduces negative charges on the nanofiltration membrane, so that the surface charge of the nanofiltration membrane becomes more negatively charged, and cations in the water (such as hard water ions such as calcium ions and magnesium ions) are more easily adsorbed and retained by the surface of the nanofiltration membrane, thereby enhancing the selective retention capacity of the nanofiltration membrane.

[0028] 2. The method for reducing hardness and preventing scale of coal gasification black water of the present invention uniformly modifies amino and carboxyl groups on the ultrafiltration membrane substrate by the physical method of electrospinning, and then cross-links it with cyclohexanehexacarbonyl chloride to promote the cross-linking of the modified layer and the membrane substrate, thereby making it uniformly distributed on the membrane, thereby improving the uniform distribution of carboxyl groups on the surface of the nanofiltration membrane, and further improving its adsorption and retention performance for heavy metal ions. At the same time, the surface negative charge of the nanofiltration membrane modified with carboxyl groups increases, which produces relative repulsion to anions and neutral molecules in the water, reduces the adsorption and deposition of these pollutants on the membrane surface, and improves the anti-fouling performance of the nanofiltration membrane. Selecting stainless steel mesh as support can effectively improve the mechanical bearing strength of the nanofiltration module.

[0029] 3. The method for reducing hardness and preventing scale of coal gasification black water of the present invention preliminarily removes mechanical impurities and volatile gases in the black water through coarse filtration and flash evaporation, and then intercepts and filters the hard water ions in the black water in the form of three-stage fine filtration to reduce the content of hard water ions in the black water. In the fine filtration process, a sewage pipe is set in the fine filter, and a large amount of impurities are avoided from being deposited on the nanofiltration membrane group by optimizing the inclination angle of the nanofiltration membrane group and the sewage discharge flow rate. The sewage discharge amount is adjusted according to the impurity content in each stage of fine filtration, thereby reducing the sewage discharge amount. The sewage is then flocculated and settled by a flocculant to promote the sedimentation and separation of sludge impurities, reduce the content of precipitable impurities in the overflow liquid, and return it to the first-stage fine filtration to dilute the impurity concentration in the black water, thereby promoting the long-term and stable operation of the overall process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a flowchart of the black water hardness reduction process of the present invention;

[0032] Figure 2 It is a schematic diagram of the internal structure of the first-stage fine filter in the present invention.

[0033] In the figure: 100, shell; 101, nanofiltration membrane group; 102, water inlet pipe; 103, water outlet pipe; 104, sewage trough; 105, slag receiving box; 106, slag discharge pipe. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In this application, the polyethersulfone ultrafiltration membrane has a filtration accuracy of 0.22 μm, a thickness of 0.11-0.13 mm, a flux of 12000 L / H, and a longitudinal strength of 2 MPa;

[0036] In this application, the CAS number of nonionic polyacrylamide is 9003-05-8, and the implementation standard is GB17514-2008;

[0037] In the present application, the CAS number of polyferric sulfate is 35139-28-7, the content is 20%, and the implementation standard is GB15892-2009.

[0038] Example 1

[0039] See also Figure 2 The present embodiment provides a fine filter for reducing hardness and preventing scale of coal gasification black water, comprising: a shell 100 and a slag receiving box 105 fixedly connected to the bottom of the shell, a water inlet pipe 102 is installed on the top of one side of the shell 100, a water outlet pipe 103 is installed on the bottom of the other side of the shell, and several groups of nanofiltration membrane groups 101 are arranged in parallel inside the shell 100.

[0040] The black water enters the housing 100 of the fine filter through the water inlet pipe 102, and is finely filtered through a plurality of nanofiltration membrane groups 101 to intercept calcium, magnesium and other ions in the black water. The filtered black water is discharged from the water outlet pipe 103 and enters the next process.

[0041] A sewage trough 104 is provided at the bottom of the shell 100 and is connected to the slag receiving box 105 and is arranged corresponding to the plurality of nanofiltration membrane groups 101. A check plate is provided at the bottom of the sewage trough 104 to prevent water from flowing upward into the shell 100. A slag discharge pipe 106 is installed on one side of the slag receiving box.

[0042] When sewage enters the slag box 105 from the sewage trough 104, the sludge on the nanofiltration membrane group 101 enters the slag box 105 along with the black water. By controlling the amount of sewage discharged from the slag pipe 106, it is avoided that the sludge accumulates in large quantities on the nanofiltration membrane group 101 and causes the module to be blocked, thereby maintaining a good filtering effect of the fine filter.

[0043] The nanofiltration membrane group 101 is inclined toward the water inlet pipe, and the angle between the nanofiltration membrane group 101 and the vertical plane is 10-15°.

[0044] The inclined nanofiltration membrane group 101 is more conducive to the sludge gathering at the bottom of the shell 100, so that the sludge is more easily discharged into the slag box 105.

[0045] Example 2

[0046] This embodiment provides a method for preparing a nanofiltration membrane group for reducing hardness and preventing scale in coal gasification black water, comprising the following steps:

[0047] A1. Preparation of crude nanofiltration membrane

[0048] Polyacrylic acid, polyacrylamide and N,N-dimethylformamide were mixed in a ratio of 3 g:2 g:100 mL, stirred until the system was dissolved, and allowed to stand for degassing to obtain a polypropylene-based spinning solution;

[0049] The polyethersulfone ultrafiltration membrane was fixed on the receiving cylinder, and the distance between the polyethersulfone ultrafiltration membrane and the spinneret was set to 30 cm. The voltage of the electrospinning was set to 18 kV, the drum speed was set to 120 r / min, and the polypropylene-based spinning solution was ejected from the spinneret with a pore size of 0.5 mm at a supply rate of 11 μL / min. The membrane was deposited for 50 minutes, and the polyethersulfone ultrafiltration membrane was turned over. The electrospinning operation was repeated, and the other side of the polyethersulfone ultrafiltration membrane was used as the receiving side. Polypropylene-based nanostructures were formed on both sides of the nanofiltration base membrane to prepare a crude nanofiltration membrane.

[0050] A2. Preparation of cyclohexanehexaacyl chloride

[0051] Weigh: 34.8 g of 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, 166.6 g of phosphorus pentachloride and 348 mL of xylene, add into a three-necked flask protected by nitrogen and stir, raise the temperature of the three-necked flask to 125°C, keep warm for 6 hours, lower the temperature of the three-necked flask to 5°C, add 700 mL of cyclohexane into the three-necked flask, solid precipitates, keep warm and stir for 40 minutes, filter, wash the filter cake with cyclohexane at 5°C for 3 times and then dry, transfer the filter cake into a drying oven at 50°C, and vacuum dry to constant weight to obtain cyclohexanehexaoyl chloride.

[0052] A3. Preparation of nanofiltration membrane

[0053] Cyclohexanehexayl chloride and tetrahydrofuran were mixed evenly at a ratio of 1 g:30 mL to obtain a cyclohexanehexayl chloride solution;

[0054] The crude nanofiltration membrane was placed in a cyclohexanehexayl chloride solution and kept completely immersed for 60 seconds at room temperature. The membrane was taken out from the solution, rinsed with n-hexane three times, and then soaked in deionized water for 20 minutes. After being fished out and drained, it was placed in a drying oven at a temperature of 60°C and dried to constant weight to obtain a nanofiltration membrane.

[0055] A4. Preparation of nanofiltration membrane group

[0056] The nanofiltration membrane was cut into standard pieces of the same size, and then 8 nanofiltration membranes were stacked layer by layer and fixed on a frame supported by a porous stainless steel mesh to obtain a nanofiltration membrane group.

[0057] Example 3

[0058] This embodiment provides a method for preparing a nanofiltration membrane group for reducing hardness and preventing scale in coal gasification black water, comprising the following steps:

[0059] A1. Preparation of crude nanofiltration membrane

[0060] Polyacrylic acid, polyacrylamide and N,N-dimethylformamide were mixed in a ratio of 3.5 g:2.5 g:100 mL, stirred until the system was dissolved, and allowed to stand for degassing to obtain a polypropylene-based spinning solution;

[0061] The polyethersulfone ultrafiltration membrane was fixed on the receiving cylinder, and the distance between the polyethersulfone ultrafiltration membrane and the spinneret was set to 30 cm. The voltage of the electrospinning was set to 19 kV, the drum speed was set to 125 r / min, and the polypropylene-based spinning solution was ejected from the spinneret with a pore size of 0.5 mm at a supply rate of 12 μL / min. The membrane was deposited for 55 minutes, and the polyethersulfone ultrafiltration membrane was turned over. The electrospinning operation was repeated, and the other side of the polyethersulfone ultrafiltration membrane was used as the receiving side. Polypropylene-based nanostructures were formed on both sides of the nanofiltration base membrane to prepare a crude nanofiltration membrane.

[0062] A2. Preparation of cyclohexanehexaacyl chloride

[0063] Weigh: 34.8 g of 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, 166.6 g of phosphorus pentachloride and 348 mL of xylene, add into a three-necked flask protected by nitrogen and stir, raise the temperature of the three-necked flask to 130°C, keep warm for 7 hours, lower the temperature of the three-necked flask to 8°C, add 700 mL of cyclohexane into the three-necked flask, solid precipitates, keep warm and stir for 50 minutes, filter, wash the filter cake with cyclohexane at 8°C for 3 times and then dry, transfer the filter cake into a drying oven at 55°C, and vacuum dry to constant weight to obtain cyclohexanehexayl chloride.

[0064] A3. Preparation of nanofiltration membrane

[0065] Cyclohexanehexayl chloride and tetrahydrofuran were mixed evenly at a ratio of 1 g:30 mL to obtain a cyclohexanehexayl chloride solution;

[0066] The crude nanofiltration membrane was placed in a cyclohexanehexayl chloride solution and kept completely immersed for 70 seconds at room temperature. The membrane was taken out from the solution, rinsed with n-hexane three times, and then soaked in deionized water for 25 minutes. After being fished out and drained, it was placed in a drying oven at a temperature of 65°C and dried to constant weight to obtain a nanofiltration membrane.

[0067] A4. Preparation of nanofiltration membrane group

[0068] The nanofiltration membrane was cut into standard pieces of the same size, and then 9 nanofiltration membranes were stacked layer by layer and fixed on a frame supported by a porous stainless steel mesh to obtain a nanofiltration membrane group.

[0069] Example 4

[0070] This embodiment provides a method for preparing a nanofiltration membrane group for reducing hardness and preventing scale in coal gasification black water, comprising the following steps:

[0071] A1. Preparation of crude nanofiltration membrane

[0072] Mix polyacrylic acid, polyacrylamide and N,N-dimethylformamide in a ratio of 4 g:3 g:100 mL, stir until the system is dissolved, and stand for degassing to obtain a polypropylene-based spinning solution;

[0073] The polyethersulfone ultrafiltration membrane was fixed on the receiving cylinder, and the distance between the polyethersulfone ultrafiltration membrane and the spinneret was set to 30 cm. The voltage of the electrospinning was set to 20 kV, the drum speed was set to 130 r / min, and the polypropylene-based spinning solution was ejected from the spinneret with a pore size of 0.5 mm at a supply rate of 13 μL / min. The membrane was deposited for 60 minutes, and the polyethersulfone ultrafiltration membrane was turned over. The electrospinning operation was repeated, and the other side of the polyethersulfone ultrafiltration membrane was used as the receiving side. Polypropylene-based nanostructures were formed on both sides of the nanofiltration base membrane to prepare a crude nanofiltration membrane.

[0074] A2. Preparation of cyclohexanehexaacyl chloride

[0075] Weigh: 34.8 g of 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, 166.6 g of phosphorus pentachloride and 348 mL of xylene, add into a three-necked flask protected by nitrogen and stir, raise the temperature of the three-necked flask to 135°C, keep warm for 8 hours, lower the temperature of the three-necked flask to 10°C, add 700 mL of cyclohexane into the three-necked flask, solid precipitates, keep warm and stir for 60 minutes, filter, wash the filter cake with cyclohexane at 10°C for 3 times and then dry, transfer the filter cake into a drying oven at 60°C, and vacuum dry to constant weight to obtain cyclohexanehexayl chloride.

[0076] A3. Preparation of nanofiltration membrane

[0077] Cyclohexanehexayl chloride and tetrahydrofuran were mixed evenly at a ratio of 1 g:30 mL to obtain a cyclohexanehexayl chloride solution;

[0078] The crude nanofiltration membrane was placed in a cyclohexanehexayl chloride solution and kept completely immersed for 80 seconds at room temperature. The membrane was taken out from the solution, rinsed with n-hexane three times, and then soaked in deionized water for 30 minutes. After being fished out and drained, it was placed in a drying oven at 70°C and dried to constant weight to obtain a nanofiltration membrane.

[0079] A4. Preparation of nanofiltration membrane group

[0080] The nanofiltration membrane was cut into standard pieces of the same size, and then 10 nanofiltration membranes were stacked layer by layer and fixed on a frame supported by a porous stainless steel mesh to obtain a nanofiltration membrane group.

[0081] Example 5

[0082] This embodiment provides a method for reducing hardness and preventing scale in coal gasification black water, comprising the following steps:

[0083] S1. Black water pre-treatment

[0084] The coal gasification black water is coarsely filtered through a 60-mesh filter to obtain coarsely filtered black water;

[0085] The coarsely filtered black water is transported to the flash tank for flash evaporation, and harmful gases such as H2S, NH3, HCN, etc. dissolved in the black water are separated to obtain flash black water.

[0086] S2, fine filtration

[0087] The nanofiltration membrane group prepared in Example 2 was installed in the fine filter of Example 1 at an inclination angle of 13°, and three fine filters prepared in Example 1 were selected and connected in series through pipelines, and were named as a primary fine filter, a secondary fine filter and a tertiary fine filter in order from the direction of water flow;

[0088] The flash black water enters the primary fine filter, and the valve on the sewage pipe of the primary fine filter is adjusted so that the volume ratio of sewage 1 discharged from the primary fine filter to the total solution entering the primary fine filter is 1:9, and the primary fine filtration obtains fine filtrate 1 and sewage 1;

[0089] The fine filtrate 1 enters the secondary fine filter, and the valve on the sewage discharge pipe of the secondary fine filter is adjusted so that the volume ratio of sewage 2 discharged from the secondary fine filter to the fine filtrate 1 entering the secondary fine filter is 1:18, and the fine filtrate 2 and sewage 2 are obtained through the secondary fine filtration;

[0090] The refined filtrate 2 enters the tertiary refined filter, and the valve on the sewage pipe of the tertiary refined filter is adjusted so that the volume ratio of sewage 3 discharged from the tertiary refined filter and the refined filtrate 2 entering the tertiary refined filter is 1:22. After tertiary refined filtration in the tertiary refined filter, hardness-reduced water and sewage 3 are obtained.

[0091] S3, loop

[0092] The nonionic polyacrylamide and the polyferric sulfate are mixed uniformly in a weight ratio of 3:1 to obtain a flocculant;

[0093] Sewage 1, sewage 2 and sewage 3 in step S2 enter the flocculation sedimentation tank, and flocculant is added to the flocculation sedimentation tank according to the concentration of flocculant in the flocculation sedimentation tank of 3 mg / L. The sludge is flocculated and settled in the flocculation sedimentation tank. After overflow, the overflow liquid of the supernatant layer and the settled sludge are obtained. The settled sludge is dehydrated by filter pressing to obtain sludge and filter press water. The filter press water and overflow liquid enter the first-level fine filter for circulating fine filtration.

[0094] Example 6

[0095] This embodiment provides a method for reducing hardness and preventing scale in coal gasification black water, comprising the following steps:

[0096] S1. Black water pre-treatment

[0097] The coal gasification black water is coarsely filtered through a 70-mesh filter to obtain coarsely filtered black water;

[0098] The coarsely filtered black water is transported to the flash tank for flash evaporation, and harmful gases such as H2S, NH3, HCN, etc. dissolved in the black water are separated to obtain flash black water.

[0099] S2, fine filtration

[0100] The nanofiltration membrane group prepared in Example 3 was installed in the fine filter of Example 1 at an inclination angle of 13°. Three fine filters prepared in Example 1 were selected and connected in series through pipelines, and were named as a primary fine filter, a secondary fine filter and a tertiary fine filter in order from the direction of water flow;

[0101] The flash black water enters the primary fine filter, and the valve on the sewage pipe of the primary fine filter is adjusted so that the volume ratio of sewage 1 discharged from the primary fine filter to the total solution entering the primary fine filter is 1:9.5, and the primary fine filtration obtains fine filtrate 1 and sewage 1;

[0102] The fine filtrate 1 enters the secondary fine filter, and the valve on the sewage discharge pipe of the secondary fine filter is adjusted so that the volume ratio of sewage 2 discharged from the secondary fine filter to the fine filtrate 1 entering the secondary fine filter is 1:19, and the fine filtrate 2 and sewage 2 are obtained through the secondary fine filtration;

[0103] The refined filtrate 2 enters the tertiary refined filter, and the valve on the sewage pipe of the tertiary refined filter is adjusted so that the volume ratio of sewage 3 discharged from the tertiary refined filter to the refined filtrate 2 entering the tertiary refined filter is 1:23. After tertiary refined filtration in the tertiary refined filter, hardness-reduced water and sewage 3 are obtained.

[0104] S3, loop

[0105] The nonionic polyacrylamide and the polyferric sulfate are mixed uniformly in a weight ratio of 3:1 to obtain a flocculant;

[0106] Sewage 1, sewage 2 and sewage 3 in step S2 enter the flocculation sedimentation tank, and flocculant is added to the flocculation sedimentation tank according to the concentration of flocculant in the flocculation sedimentation tank of 5 mg / L. The sludge flocculates and settles in the flocculation sedimentation tank. After overflow, the overflow liquid of the supernatant layer and the settled sludge are obtained. The settled sludge is dehydrated by filter pressing to obtain sludge and filter press water. The filter press water and overflow liquid enter the first-level fine filter for circulating fine filtration.

[0107] Example 7

[0108] This embodiment provides a method for reducing hardness and preventing scale in coal gasification black water, comprising the following steps:

[0109] S1. Black water pre-treatment

[0110] The coal gasification black water is coarsely filtered through an 80-mesh filter to obtain coarsely filtered black water;

[0111] The coarsely filtered black water is transported to the flash tank for flash evaporation, and harmful gases such as H2S, NH3, HCN, etc. dissolved in the black water are separated to obtain flash black water.

[0112] S2, fine filtration

[0113] The nanofiltration membrane group prepared in Example 4 was installed in the fine filter of Example 1 at an inclination angle of 13°. Three fine filters prepared in Example 1 were selected and connected in series through pipelines, and were named as a primary fine filter, a secondary fine filter and a tertiary fine filter in order from the direction of water flow;

[0114] The flash black water enters the primary fine filter, and the valve on the sewage pipe of the primary fine filter is adjusted so that the volume ratio of sewage 1 discharged from the primary fine filter to the total solution entering the primary fine filter is 1:10, and the primary fine filtration obtains fine filtrate 1 and sewage 1;

[0115] The fine filtrate 1 enters the secondary fine filter, and the valve on the sewage discharge pipe of the secondary fine filter is adjusted so that the volume ratio of sewage 2 discharged from the secondary fine filter to the fine filtrate 1 entering the secondary fine filter is 1:20, and the fine filtrate 2 and sewage 2 are obtained through the secondary fine filtration;

[0116] The refined filtrate 2 enters the tertiary refined filter, and the valve on the sewage pipe of the tertiary refined filter is adjusted so that the volume ratio of sewage 3 discharged from the tertiary refined filter and the refined filtrate 2 entering the tertiary refined filter is 1:25. After tertiary refined filtration in the tertiary refined filter, hardness-reduced water and sewage 3 are obtained.

[0117] S3, loop

[0118] The nonionic polyacrylamide and the polyferric sulfate are mixed uniformly in a weight ratio of 3:1 to obtain a flocculant;

[0119] Sewage 1, sewage 2 and sewage 3 in step S2 enter the flocculation sedimentation tank, and flocculant is added to the flocculation sedimentation tank according to the concentration of flocculant in the flocculation sedimentation tank of 8 mg / L. The sludge flocculates and settles in the flocculation sedimentation tank. After overflow, the overflow liquid of the supernatant layer and the settled sludge are obtained. The settled sludge is dehydrated by filter pressing to obtain sludge and filter press water. The filter press water and overflow liquid enter the first-level fine filter for circulating fine filtration.

[0120] Comparative Example 1

[0121] The difference between this comparative example and Example 7 is that, when preparing the nanofiltration membrane group used, steps A2-A3 are omitted, and the nanofiltration membrane in step A4 is replaced by the crude nanofiltration membrane in Example 4.

[0122] Comparative Example 2

[0123] The difference between this comparative example and Example 7 is that, when preparing the nanofiltration membrane group used, steps A1 to A3 are omitted, and the polyethersulfone ultrafiltration membrane in Example 4 is used to replace the nanofiltration membrane in step A4.

[0124] Comparative Example 3

[0125] The difference between this comparative example and Example 7 is that the inclination angle of the nanofiltration membrane group in step S2 is 0°.

[0126] Comparative Example 4

[0127] The difference between this comparative example and Example 7 is that in step S3, the filter press water and overflow liquid do not enter the primary fine filter for circulating fine filtration.

[0128] Performance Testing:

[0129] The turbidity and total hardness of the hardness-reducing water prepared in Examples 5-7 and Comparative Examples 1-4 were measured with reference to the standard GB 5749-2022 "Sanitary Standard for Drinking Water";

[0130] Reference formula , the water attenuation rate of the hardness reducing water prepared by the coal gasification black water hardness reducing and scale inhibition in Examples 5-7 and Comparative Examples 1-4 before and after 100 hours of work was determined, wherein V0 is the sum of the outflow rates of the refined filtrate 1, refined filtrate 2 and the hardness reducing water after the black water hardness reducing and scale inhibition is stabilized (unit: L / min), and V1 is the sum of the outflow rates of the refined filtrate 1, refined filtrate 2 and the hardness reducing water 100 hours after the black water hardness reducing and scale inhibition is stabilized (unit: L / min). The specific test results are shown in Table 1 below.

[0131] Table 1-Performance test data of the sample

[0132]

[0133] Data Analysis:

[0134] A comparative analysis of the data in Table 1 above shows that the turbidity of the hardened water obtained by the black water hardness reduction of the present invention is reduced to 25NTU, the total hardness is reduced to 485mg / L, the effluent attenuation rate is reduced to 7.2%, and all performance parameters are better than those of the comparative example. The present invention not only effectively improves the selective removal rate of hard water ions in black water and reduces the hardness and turbidity of the hardened water by modifying the nanofiltration membrane and optimizing the nanofiltration method, but also after 100h of circulation, the effluent attenuation rate is only 7.2%, which can achieve long-term and stable operation, improve the black water hardness reduction treatment efficiency, and reduce the treatment cost of black water hardness reduction.

[0135] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for reducing hardness and preventing scale in coal gasification black water, characterized in that: The following steps are involved: S1. Coal gasification black water is coarsely filtered through a 60-80 mesh filter to obtain coarse filtered black water, and the coarse filtered black water enters a flash tank for flash evaporation, and the material is discharged to obtain flash evaporated black water; S2, the flash black water enters the first-stage fine filter, and after the first-stage fine filtration by the first-stage fine filter, the fine filtrate 1 and the sewage 1 are obtained, the fine filtrate 1 enters the second-stage fine filter, and after the second-stage fine filtration by the second-stage fine filter, the fine filtrate 2 and the sewage 2 are obtained, the fine filtrate 2 enters the third-stage fine filter, and after the third-stage fine filtration by the third-stage fine filter, the hardness-reduced water and the sewage 3 are obtained, wherein the first-stage fine filter, the second-stage fine filter and the third-stage fine filter have the same structure and are all equipped with a plurality of nanofiltration membrane groups; S3, sewage one, sewage two and sewage three enter the flocculation sedimentation tank, flocculant is added to the flocculation sedimentation tank, the sludge flocculates and settles in the flocculation sedimentation tank, and after overflow, the overflow liquid of the supernatant layer and the settled sludge are obtained. The settled sludge is dehydrated by filter pressing to obtain sludge and filter press water. The filter press water and overflow liquid enter the first-level fine filter for circulating fine filtration.

2. The method for reducing hardness and preventing scale of coal gasification black water according to claim 1, characterized in that: In step S2, the volume ratio of sewage 1 discharged from the first-stage fine filter to the total solution entering the first-stage fine filter is 1:9-10, the volume ratio of sewage 2 discharged from the second-stage fine filter to the fine filtrate 1 entering the second-stage fine filter is 1:18-20, and the volume ratio of sewage 3 discharged from the tertiary fine filter to the fine filtrate 2 entering the tertiary fine filter is 1:22-25.

3. The method for reducing hardness and preventing scale of coal gasification black water according to claim 1, characterized in that: In step S3, the concentration of the flocculant in the flocculation sedimentation tank is 3-8 mg / L, and the flocculant is composed of non-ionic polyacrylamide and polyferric sulfate in a weight ratio of 3:

1.

4. The method for reducing hardness and preventing scale of coal gasification black water according to claim 2, characterized in that: The nanofiltration membrane group is processed by the following steps: A1. Depositing a polypropylene-based spinning solution on the surface of a nanofiltration base membrane by electrospinning to form a polypropylene-based nanostructure on both sides of the nanofiltration base membrane, thereby preparing a crude nanofiltration membrane; A2. Place the crude nanofiltration membrane in a cyclohexanehexayl chloride solution, keep it completely immersed for 60-80 seconds at room temperature, and post-treat it to obtain a nanofiltration membrane; A3. Stack several nanofiltration membranes layer by layer, and then fix them on a frame with a supporting back plate to obtain a nanofiltration membrane group.

5. The method for reducing hardness and preventing scale of coal gasification black water according to claim 4, characterized in that: In step A1, the nanofiltration base membrane is a polyethersulfone ultrafiltration membrane, the polypropylene-based spinning solution is composed of polyacrylic acid, polyacrylamide and N,N-dimethylformamide in a ratio of 3-4g:2-3g:100mL, the electrospinning voltage is 18-20kV, the drum speed is 120-130r / min, the receiving distance is 30cm, the spinneret aperture is 0.5mm, the supply rate of the polypropylene-based spinning solution is 11-13μL / min, and the single-sided deposition time is 50-60min.

6. The method for reducing hardness and preventing scale of coal gasification black water according to claim 4, characterized in that: In step A2, the cyclohexanehexayl chloride solution is composed of cyclohexanehexayl chloride and tetrahydrofuran at a ratio of 1 g:30 mL, and the post-treatment includes: after the reaction is completed, taking the membrane out of the solution, rinsing it with n-hexane three times, placing it in a drying oven at a temperature of 60-70° C., and drying it to constant weight to obtain a nanofiltration membrane.

7. The method for reducing hardness and preventing scale of coal gasification black water according to claim 4, characterized in that: In step A3, the number of the nanofiltration membranes is 8-10, and the supporting back plate is a porous stainless steel mesh.

8. The method for reducing hardness and preventing scale of coal gasification black water according to claim 4, characterized in that: The preparation method of cyclohexanehexacarboxylic acid chloride is as follows: under nitrogen protection, 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, phosphorus pentachloride and xylene are mixed, the temperature of the reaction system is increased to 125-135° C., the reaction is kept warm for 6-8 hours, and post-processed to obtain cyclohexanehexacarboxylic acid chloride.

9. The method for reducing hardness and preventing scale of coal gasification black water according to claim 8, characterized in that: The molar ratio of the 1,2,3,4,5,6-cyclohexanehexacarboxylic acid to phosphorus pentachloride is 1:8, the dosage ratio of the 1,2,3,4,5,6-cyclohexanehexacarboxylic acid to xylene is 1g:10mL, and the post-treatment comprises: after the reaction is completed, the temperature of the reaction system is reduced to 5-10°C, cyclohexane is added to the reaction system, solid is precipitated, the reaction system is stirred for 40-60 minutes, and the filter is filtered, the filter cake is washed with cyclohexane at a temperature of 5-10°C for 3 times and then dried, the filter cake is transferred to a drying oven at a temperature of 50-60°C, and vacuum dried to constant weight to obtain cyclohexanehexayl chloride.

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