Two-stage chemical softening method for coal gasification wastewater

Abstract

The invention provides a two-stage chemical softening method for coal gasification wastewater. The method comprises the following steps: S1, carrying out sulfonation modification pretreatment on waste fine coal gasification slag generated by coal gasification to prepare induced crystallization seed crystals; s2, adding the induced crystallization seed crystal into a first-stage chemical crystallization granulation fluidized bed, introducing the coal gasification wastewater into the fluidized bed, and adding a first-stage softening agent to remove calcium hardness in the coal gasification wastewater; s3, the effluent of the first-stage fluidized bed enters a second-stage chemical crystallization granulation fluidized bed, and a second-stage softening agent is added to remove the residual calcium hardness in the wastewater; s4, discharging the primary and secondary chemical granulation fluidized bed crystal particles out of the fluidized bed after the particles grow maturely; optionally, S5, mixing the crystallized particles with ceramsite to serve as filler of a low-load denitrification filter tank, and providing a carbon source in a slow release manner. According to the method, efficient induced crystallization seed crystals can be prepared by modifying the waste coal gasification fine slag, and efficient softening and hardness removal of the coal gasification wastewater are realized by combining oxalate in the nitrobenzene washing wastewater as a softening agent.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a two-stage chemical softening method for coal gasification wastewater. Background Technology

[0002] Wastewater from coal gasification units using the Texaco process is characterized by high hardness, high COD, and high ammonia nitrogen. While treated using biological processes such as SBR or A / O, the high hardness of the wastewater can cause scaling in transport pipelines, scaling and clogging of aeration discs in the biological treatment tanks, calcification of activated sludge, and blockage of reverse osmosis membranes for wastewater reuse. Chemical hardening is a commonly used technology for removing hardness from coal gasification wastewater. It typically involves adding NaOH-Na2CO3 and coagulants to precipitate and soften the wastewater. However, this method suffers from drawbacks in practical applications, including high consumption of acid-base adjusting agents, high salt ion concentrations, large sludge production, and high costs.

[0003] Crystallization granulation softening technology involves introducing wastewater into a fluidized bed device, adding sodium hydroxide to adjust the pH of the wastewater to alkaline, and adding sodium carbonate to promote the precipitation of calcium carbonate crystals. The resulting calcium carbonate crystals, induced by seed crystals within the fluidized bed, gradually grow into calcium carbonate particles with a diameter of 1–3 mm, effectively reducing water hardness and sludge production. However, in general engineering practice, chemical crystallization granulation softening requires the initial addition of caustic soda or other agents to adjust the environment to alkaline for softening. After the reaction, sulfuric acid or hydrochloric acid is used to restore the pH to neutral before transporting the wastewater to the biological treatment unit. This process requires the addition of large amounts of reagents. Furthermore, the presence of calcium salts within the fluidized bed results in a low crystallization rate on the surface of the induced crystal seed crystals, and some calcium salts precipitate but fail to crystallize on the seed crystal surface, leading to problems such as excessive suspended solids (SS) and hardness in the softening tower's permeate.

[0004] In summary, the treatment of high-hardness wastewater, such as that from coal gasification, still faces challenges such as slow growth of calcium salts on induced crystal seed crystals leading to low hardness removal efficiency, and the need to add large amounts of chemical precipitating agents for softening and hardness removal, which urgently need to be addressed. Summary of the Invention

[0005] To address the aforementioned problems, one objective of this invention is to provide a two-stage chemical softening treatment method for coal gasification wastewater. This method can prepare highly efficient induced crystallization seed crystals by modifying waste coal gasification fine slag, and combine it with oxalate in nitrobenzene washing wastewater as a softening agent to achieve efficient softening and hardening removal of coal gasification wastewater.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A method for two-stage chemical softening of coal gasification wastewater, the method comprising the following steps:

[0008] S1: Sulfonation modification pretreatment is performed on the waste coal gasification fine residue generated from coal gasification to obtain induced crystallization seed crystals;

[0009] S2: Induced crystallization seed crystals are added to a primary chemical crystallization granulation fluidized bed, coal gasification wastewater is introduced into the fluidized bed, and primary softening agent is added to remove calcium hardness from the coal gasification wastewater.

[0010] S3: The effluent from the primary fluidized bed enters the secondary chemical crystallization granulation fluidized bed, where secondary softening agents are added to remove the remaining calcium hardness in the wastewater;

[0011] S4: After the primary and secondary chemical granulation fluidized bed crystallization particles have grown and matured, they are discharged from the fluidized bed;

[0012] Optionally, S5: Crystallized particles are mixed with ceramsite and used as packing material in low-load denitrification filter beds to provide a slow-release carbon source.

[0013] The inventors discovered that sulfonation modification of fine coal gasification slag forms induced crystallization seed crystals. Grafting sulfonic acid groups onto the surface of the fine coal gasification slag can attract calcium ions in the wastewater, promoting the crystallization and precipitation of calcium ions on the surface of the induced crystallization seed crystals. At the same time, oxalate in the nitrobenzene washing wastewater reacts with calcium ions in the wastewater to form calcium oxalate, which continuously crystallizes and grows on the surface of the induced crystallization seed crystals, thereby achieving the removal of calcium hardness from coal gasification wastewater.

[0014] In one embodiment of the present invention, the sulfonation modification of the coal gasification fine slag in S1 is modified by a mercaptosilane coupling agent; preferably, the mercaptosilane coupling agent is a C3-C12 alkoxysilane containing mercapto groups, preferably one or more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethylsilane; preferably, the mass ratio of the mercaptosilane coupling agent to the coal gasification fine slag is 1:10-25.

[0015] In one embodiment of the present invention, in step S1, the modified sulfonated coal gasification fine slag is centrifuged and dried to obtain induced crystallization seed crystals.

[0016] For example, anhydrous ethanol can be added to the coal gasification fine slag at a mass ratio of 1:20, and the mixture can be stirred to obtain dispersed coal gasification fine slag; the dispersed coal gasification fine slag can be contacted with 3-mercaptopropyltrimethoxysilane coupling agent at a mass ratio of 1:15, and modified at 60°C for 2 hours. After the reaction, the mixture is washed and filtered with acetone and dried at 80°C for 12 hours to obtain coal gasification fine slag with surface thiol modification; the coal gasification fine slag with surface thiol modification can be placed in a reaction vessel, and 1% hydrogen peroxide can be added and stirred at room temperature for 24 hours to obtain coal gasification fine slag with surface sulfonation modification.

[0017] In one embodiment of the present invention, the calcium hardness of the coal gasification wastewater in S2 is 1000-1500 mg / L, and the calcium ion concentration is 400-600 mg / L.

[0018] In one embodiment of the present invention, the primary softening agent in S2 is nitrobenzene washing wastewater, preferably taken from the crude nitrobenzene acid washing unit in the nitrobenzene production process; preferably, the mixing mass ratio of the primary softening agent and the coal gasification wastewater is 1:0.5 to 0.7.

[0019] In one embodiment of the present invention, the secondary softening agent in S3 is oxalate, preferably sodium oxalate and / or potassium oxalate; preferably, the secondary softening agent is prepared as a solution with a concentration of 5-20 wt% when used; preferably, the dosage of the secondary softening agent is determined according to the hardness of the wastewater effluent from the primary softening process, based on Ca... 2+ The C2CO4 molar ratio is 1:0.8 to 1.2; preferably, the wastewater retention time is 0.3 to 0.5 hours.

[0020] In one embodiment of the present invention, in S4, the crystallized particles grow to a certain particle size of 1-10 mm, preferably 2-4 mm, and the growth cycle is 20-40 days.

[0021] In one embodiment of the present invention, the crystalline particles and ceramsite in S5 are mixed at a mass ratio of 1:50 to 200 as packing material for a low-load denitrification filter; preferably, the ceramsite particle size is 1-10 mm, more preferably 2-4 mm.

[0022] Another objective of this invention is to provide an application of a two-stage chemical softening method for coal gasification wastewater.

[0023] An application of a two-stage chemical softening method for coal gasification wastewater, wherein the method is the one described above, and the method is used for the chemical crystallization removal of calcium hardness in coal gasification wastewater.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The present invention uses modified waste coal gasification fine slag as seed crystals for induction crystallization. The induced crystallization rate of calcium oxalate is improved by sulfonation modification, while realizing the in-plant reuse of coal gasification fine slag and the resource utilization of coal gasification fine slag.

[0026] (2) The present invention uses oxalate in nitrobenzene washing wastewater as a softening agent. Compared with the existing NaOH-Na2CO3 combined softening technology, the present invention does not require pH adjustment, which reduces the amount of softening agent added and achieves comprehensive utilization of oxalate in wastewater.

[0027] (3) The mature crystalline calcium oxalate particles produced by this invention serve as a carbon source for denitrification filters, effectively reducing the hardness of the effluent while decreasing the production of chemically softened sludge. Attached Figure Description

[0028] Figure 1A schematic diagram of a two-stage chemical softening process for coal gasification wastewater;

[0029] Figure 2 The diagram shows the equipment used for two-stage chemical softening, where 101 is a gasification wastewater storage tank, 102 is a primary crystallization granulation fluidized bed, 103 is a secondary crystallization granulation fluidized bed, 104 is a product water collection tank, 105 is an oxalate-containing wastewater storage tank, 106 is a softening agent storage tank, 107 is an inducing crystal dosing device, and 108 is a mature crystal collection tank. Detailed Implementation

[0030] The following specific embodiments further illustrate the technical solution and effects of the present invention. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Simple modifications to the present invention based on its concept are all within the scope of protection claimed by the present invention.

[0031] Sources of raw materials and equipment:

[0032] Sodium oxalate, potassium oxalate, ethanol, and acetone were sourced from Beijing Inokai Co., Ltd., with a purity of AR. Hydrogen peroxide was sourced from Shanghai Aladdin Biochemical Technology Co., Ltd., with a concentration of 30-31%. The silane coupling agent was sourced from Nanjing Nengde New Material Technology Co., Ltd.

[0033] The coal gasification slag is taken from the gasification unit of Wanhua Chemical's Fujian Industrial Park, and the nitrobenzene washing wastewater is taken from the nitrobenzene unit of Wanhua Chemical's Fujian Industrial Park.

[0034] Example 1

[0035] Wastewater from the outlet of the black water settling tank of the coal gasification unit at Wanhua Chemical (Fujian) Co., Ltd. was collected, with a wastewater treatment capacity of 0.5 tons.

[0036] m 3 / h, the calcium ion content of the wastewater is 450mg / L, and the calcium hardness is 1125mg / L.

[0037] This embodiment uses Figure 2 The two-stage softening system shown treats the coal gasification wastewater. For example... Figure 2 As shown, the system consists of a gasification wastewater storage tank (101), a primary crystallization granulation fluidized bed (102), a secondary crystallization granulation fluidized bed (103), a product water collection tank (104), an oxalate-containing wastewater storage tank (105), a softening agent storage tank (106), an induced crystal dosing device (107), and a mature crystal collection tank (108).

[0038] Among them, the outlet of the gasification wastewater storage tank 101 is connected in sequence to the primary crystallization granulation fluidized bed 102, the secondary crystallization granulation fluidized bed 103, and the product water collection tank 104; the wastewater outlet of the oxalate-containing wastewater storage tank 105 is connected to the inlet of the primary crystallization granulation fluidized bed tower 102; the wastewater outlet of the softening agent storage tank 106 is connected to the inlet of the secondary crystallization granulation fluidized bed tower 103; and the induced crystal dosing device 107 is connected to the crystal dosing port in the middle of the primary crystallization granulation fluidized bed 102 and the secondary crystallization granulation fluidized bed 103, respectively.

[0039] In the 101-primary crystallization granulation fluidized bed reactor, seed crystals are added from the crystal inlet to 5% of the reactor height, with a seed crystal loading height of 10 cm. A perforated plate is used for water distribution at the bottom of the reactor, and the circulating pump for the crystallization granulation fluidized bed is set to an upward flow velocity of 50 m / h.

[0040] Induced crystals were prepared using the following method:

[0041] The coal gasification slag was crushed and screened to obtain coal gasification slag with a particle size range of 0.1-0.2 mm. Anhydrous ethanol was added to the coal gasification slag at a mass ratio of 1:20, and the stirring speed was 60 rpm / min to obtain dispersed coal gasification slag. 3-Mercaptopropyltrimethoxysilane was added to the dispersed coal gasification slag at a mass ratio of 1:10 to mercaptosilane coupling agent, and the surface was modified with mercaptosilane at 60 °C for 2 h. Then it was dried at 80 °C for 12 h to obtain mercapto-modified coal gasification slag. The surface-modified coal gasification slag was placed in a reaction vessel, and 1% hydrogen peroxide was added. The mixture was stirred at room temperature for 24 h at a stirring speed of 100 rpm / min to obtain surface-sulfonated coal gasification slag. The modified sulfonated coal gasification slag was centrifuged and dried at 80 °C for 24 h to obtain the induced crystal seed crystals.

[0042] The wastewater from nitrobenzene washing (a primary softening agent) was mixed with coal gasification wastewater at a mass ratio of 1:0.5 using a peristaltic pump from the bottom of a crystallization granulation fluidized bed to form calcium oxalate crystals. The residence time of the wastewater in the fluidized bed was 30 minutes. The effluent from the primary fluidized bed then entered the secondary fluidized bed for treatment. The calcium ion concentration in the primary product was 103 ppm, with a calcium ion removal rate of 77.1%.

[0043] The secondary softening agent sodium oxalate and the primary effluent calcium hardness are calculated according to Ca... 2+ The C2CO4 molar ratio was 1:0.8, and sodium oxalate with a concentration of 20wt% was continuously added from the bottom of the crystallization granulation fluidized bed using a peristaltic pump. The residence time of the wastewater in the fluidized bed was 20 minutes. The calcium ion concentration in the permeate of the secondary crystallization granulation fluidized bed was 12 ppm, and the calcium ion removal rate was 97.3%.

[0044] After 20 days of operation of the two-stage chemical softening system, the average particle size of calcium oxalate particles in the first-stage chemical crystallization granulation fluidized bed reached 3 mm. Calcium oxalate particles were mixed with 3 mm ceramsite from a low-load biological filter at a mass ratio of 1:50 to form the reactor bed of the low-load biological filter. The effluent from the aerated biological filter was used as the influent. After 20 days of operation, the total nitrogen (TN) of the effluent remained <10 ppm. After using calcium oxalate crystallized particles as slow-release filter media, the amount of methanol added as an additional carbon source to the filter was reduced by 5.1%.

[0045] Example 2

[0046] The process flow used in this embodiment is consistent with that in Embodiment 1, with adjustments only made to the preparation method of the induced crystallization seed crystals, the wastewater source, and the operating parameters. Wastewater from the outlet of the black water settling tank of the coal gasification unit at Wanhua Chemical (Ningbo) Co., Ltd. was used, with a treatment capacity of 0.5 m³ / h, a calcium ion content of 423 mg / L, and a calcium hardness of 1057 mg / L. Induced crystallization seed crystals were added to the primary crystallization granulation fluidized bed from the crystal inlet to 5% of the reactor height, with a seed crystal loading height of 10 cm. A perforated plate was used for water distribution at the bottom of the reactor, and the upward flow velocity of the crystallization granulation fluidized bed circulation pump was set to 60 m / h.

[0047] Induced crystals were prepared using the following method:

[0048] The coal gasification slag was crushed and screened to obtain coal gasification slag with a particle size range of 0.1-0.2 mm. Anhydrous ethanol was added to the coal gasification slag at a mass ratio of 1:25, and the stirring speed was 60 rpm / min to obtain dispersed coal gasification slag. 3-Mercaptopropyltriethoxysilane was added to the dispersed coal gasification slag at a mass ratio of 1:15 of mercaptosilane coupling agent to coal gasification slag. The surface mercaptomodification treatment was carried out at 60°C for 2 h, followed by drying at 80°C for 12 h to obtain mercaptomodified coal gasification slag. The surface mercaptomodified coal gasification slag was placed in a reaction vessel, and 1% hydrogen peroxide was added. The reaction was carried out at room temperature and stirred at a stirring speed of 100 rpm / min for 24 h to obtain surface sulfonated coal gasification slag. The modified sulfonated coal gasification slag was centrifuged and dried at 80°C for 24 h to obtain the induced crystal seed crystals.

[0049] The wastewater from nitrobenzene washing (a primary softening agent) was mixed with coal gasification wastewater at a mass ratio of 1:0.6 using a peristaltic pump from the bottom of a crystallization granulation fluidized bed to form calcium oxalate crystals. The residence time of the wastewater in the fluidized bed was 30 minutes. The effluent from the primary fluidized bed then entered the secondary fluidized bed for treatment. The calcium ion concentration in the primary product was 86 ppm, with a calcium ion removal rate of 79.7%.

[0050] The secondary softening agent potassium oxalate and the primary effluent calcium hardness are calculated according to Ca...2+ The C2CO4 molar ratio was 1:1, and potassium oxalate with a concentration of 5wt% was continuously added from the bottom of the crystallization granulation fluidized bed using a peristaltic pump. The residence time of the wastewater in the fluidized bed was 25 min. The calcium ion concentration in the permeate of the secondary crystallization granulation fluidized bed was 15 ppm, and the calcium ion removal rate was 96.4%.

[0051] After 20 days of operation of the two-stage chemical softening system, the average particle size of calcium oxalate particles in the first-stage chemical crystallization granulation fluidized bed reached 3 mm. Calcium oxalate particles were mixed with 3 mm ceramsite from a low-load biological filter at a mass ratio of 1:100 to form the reactor bed of the low-load biological filter. The effluent from the aerated biological filter was used as the influent. After 20 days of operation, the total nitrogen (TN) of the effluent remained below 10 ppm. After using calcium oxalate crystallized particles as slow-release filter media, the amount of methanol added as an additional carbon source to the filter was reduced by 4.5%.

[0052] Example 3

[0053] The process flow used in this embodiment is consistent with that in Embodiment 1, with adjustments only made to the preparation method of the induced crystallization seed crystals, the wastewater source, and the operating parameters. Wastewater from the outlet of the black water settling tank of the coal gasification unit at Wanhua Chemical (Yantai) Co., Ltd. was used, with a treatment capacity of 0.5 m³ / h, a calcium ion content of 510 mg / L, and a calcium hardness of 1275 mg / L. Induced crystallization seed crystals were added to the primary crystallization granulation fluidized bed through the crystal addition port to 5% of the reactor height, with a seed crystal loading height of 10 cm. A perforated plate was used for water distribution at the bottom of the reactor, and the circulating pump of the crystallization granulation fluidized bed was set to an upward flow velocity of 75 m / h.

[0054] Induced crystals were prepared using the following method:

[0055] The coal gasification slag was crushed and screened to obtain coal gasification slag with a particle size range of 0.1-0.2 mm. Anhydrous ethanol was added to the coal gasification slag at a mass ratio of 1:30, and the stirring speed was 60 rpm / min to obtain dispersed coal gasification slag. 3-Mercaptopropylmethyldimethylsilane was added to the dispersed coal gasification slag at a mass ratio of 1:25 to mercaptosilane coupling agent. The surface was treated with mercaptosilane at 60 °C for 2 h, and then dried at 80 °C for 12 h to obtain mercaptosilane-modified coal gasification slag. The surface mercaptosilane-modified coal gasification slag was placed in a reaction vessel, and 1% hydrogen peroxide was added. The mixture was stirred at room temperature for 24 h at a stirring speed of 100 rpm / min to obtain surface sulfonated coal gasification slag. The modified sulfonated coal gasification slag was centrifuged and dried at 80 °C for 24 h to obtain the induced crystal seed crystals.

[0056] The wastewater from nitrobenzene washing (a primary softening agent) was mixed with coal gasification wastewater at a mass ratio of 1:0.7 using a peristaltic pump from the bottom of a crystallization granulation fluidized bed to form calcium oxalate crystals. The residence time of the wastewater in the fluidized bed was 30 minutes. The effluent from the primary fluidized bed then entered the secondary fluidized bed for treatment. The calcium ion concentration in the primary product was 150 ppm, with a calcium ion removal rate of 70.5%.

[0057] The secondary softening agent sodium oxalate and the primary effluent calcium hardness are calculated according to Ca... 2+ The C2CO4 molar ratio was 1:1.2, and sodium oxalate with a concentration of 10wt% was continuously added from the bottom of the crystallization granulation fluidized bed using a peristaltic pump. The residence time of the wastewater in the fluidized bed was 30 min. The calcium ion concentration in the permeate of the secondary crystallization granulation fluidized bed was 9.5 ppm, and the calcium ion removal rate was 98.1%.

[0058] After 20 days of operation of the two-stage chemical softening system, the average particle size of calcium oxalate particles in the first-stage chemical crystallization granulation fluidized bed reached 3 mm. Calcium oxalate particles were mixed with 4 mm ceramsite from a low-load biological filter at a mass ratio of 1:150 to form the reactor bed of the low-load biological filter. The effluent from the aerated biological filter was used as the influent. After 20 days of operation, the total nitrogen (TN) of the effluent remained <10 ppm. After using calcium oxalate crystallized particles as slow-release filter media, the amount of methanol added as an additional carbon source to the filter decreased by 2.3%.

[0059] Comparative Example 1

[0060] Compared with Example 1, the process flow and operating parameters used in this comparative example are the same as those in Example 1. The only difference is that the coal gasification fine slag is used directly as seed crystals for inducing crystallization without modification treatment.

[0061] The wastewater from nitrobenzene washing (a primary softening agent) was mixed with coal gasification wastewater at a mass ratio of 1:0.5 using a peristaltic pump from the bottom of a crystallization granulation fluidized bed to form calcium oxalate crystals. The residence time of the wastewater in the fluidized bed was 30 minutes. The effluent from the primary fluidized bed then entered the secondary fluidized bed for treatment. The calcium ion concentration in the primary product was 213 ppm, with a calcium ion removal rate of 52.7%.

[0062] The secondary softening agent sodium oxalate and the primary effluent calcium hardness are calculated according to Ca... 2+ The C2CO4 molar ratio was 1:0.8, and sodium oxalate with a concentration of 20% was continuously added from the bottom of the crystallization granulation fluidized bed using a peristaltic pump. The residence time of the wastewater in the fluidized bed was 25 minutes. The calcium ion concentration in the product water of the secondary crystallization granulation fluidized bed was 95 ppm, and the calcium ion removal rate was 78.9%.

[0063] After 20 days of operation of the two-stage chemical softening system, the average particle size of calcium oxalate particles in the first-stage chemical crystallization granulation fluidized bed reached 2.5 mm. Calcium oxalate particles were mixed with 3 mm ceramsite from a low-load biological filter at a mass ratio of 1:50 to form the reactor bed of the low-load biological filter. The effluent from the aerated biological filter was used as the influent. After 20 days of operation, the total nitrogen (TN) of the effluent remained <10 ppm. After using calcium oxalate crystallized particles as slow-release filter media, the amount of methanol added as an additional carbon source in the filter was reduced by 2.1%.

[0064] Comparative Example 2

[0065] Compared with Example 1, the induced crystallization seed modification steps used in this comparative example are the same as those in Example 1. The only difference is that nitrobenzene wastewater was not added during the first-stage softening process in the process flow.

[0066] The addition of nitrobenzene washing wastewater as a primary softening agent was stopped. The residence time of the coal gasification wastewater in the primary softening fluidized bed was 30 minutes. The effluent from the primary fluidized bed entered the secondary fluidized bed treatment. The calcium ion concentration in the primary product water was 450 ppm, with a calcium ion removal rate of 0%.

[0067] The secondary softening agent sodium oxalate and the primary effluent calcium hardness are calculated according to Ca... 2+ The C2CO4 molar ratio was 1:0.8. Sodium oxalate with a concentration of 20% was continuously added from the bottom of the crystallization granulation fluidized bed using a peristaltic pump. The residence time of the wastewater in the fluidized bed was 25 minutes. The calcium ion content of the product water from the secondary crystallization granulation fluidized bed was 117 ppm, and the calcium ion removal rate was 74%.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for two-stage chemical softening of coal gasification wastewater, characterized in that, The method includes the following steps: S1: Sulfonation modification pretreatment is performed on the waste coal gasification fine residue generated from coal gasification to obtain induced crystallization seed crystals; S2: Induced crystallization seed crystals are added to a primary chemical crystallization granulation fluidized bed, coal gasification wastewater is introduced into the fluidized bed, and primary softening agent is added to remove calcium hardness from the coal gasification wastewater. S3: The effluent from the primary fluidized bed enters the secondary chemical crystallization granulation fluidized bed, where secondary softening agents are added to remove the remaining calcium hardness in the wastewater; S4: After the primary and secondary chemical granulation fluidized bed crystallization particles have grown and matured, they are discharged from the fluidized bed; Optionally, S5: Crystallized particles are mixed with ceramsite and used as packing material in low-load denitrification filter beds to provide a slow-release carbon source.

2. The method according to claim 1, characterized in that, The sulfonation modification of fine coal gasification residue in S1 is replaced by modification with mercaptosilane coupling agent; Preferably, the mercaptosilane coupling agent is a C3-C12 alkoxysilane containing a mercapto group, and more preferably one or more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethylsilane; Preferably, the mass ratio of the mercaptosilane coupling agent to the coal gasification fine slag is 1:10-25; And / or, in S1, the modified sulfonated coal gasification fine slag is centrifuged and dried to obtain induced crystallization seed crystals.

3. The method according to claim 1, characterized in that, The calcium hardness of the coal gasification wastewater described in S2 is 1000-1500 mg / L, and the calcium ion concentration is 400-600 mg / L; And / or, the primary softening agent mentioned in S2 is nitrobenzene washing wastewater, preferably taken from the crude nitrobenzene acid washing unit in the nitrobenzene production process; Preferably, the mixing mass ratio of the primary softening agent to the coal gasification wastewater is 1:0.5 to 0.

7.

4. The method according to claim 1, characterized in that, The secondary softening agent described in S3 is oxalate, preferably sodium oxalate and / or potassium oxalate; Preferably, the secondary softening agent is prepared as a solution with a concentration of 5-20 wt% when used; Preferably, the dosage of the secondary softening agent is determined based on the hardness of the wastewater effluent from the primary softening process, according to Ca... 2+ The C2CO4 molar ratio is 1:0.8 to 1.2 when added. Preferably, the wastewater retention time is 0.3 to 0.5 hours.

5. The method according to claim 1, characterized in that, In S4, the crystallized particles grow to maturity when the particle size reaches a certain range of 1-10 mm, preferably 2-4 mm, and the growth cycle is 20-40 days.

6. The method according to claim 1, characterized in that, In S5, crystalline particles and ceramsite are mixed at a mass ratio of 1:50-200 as packing material for low-load denitrification filter beds. Preferably, the particle size of the ceramsite is 1-10 mm, more preferably 2-4 mm.

7. An application of a two-stage chemical softening method for coal gasification wastewater, wherein the method is the method according to any one of claims 1-6, and the method is used for the chemical crystallization removal of calcium hardness in coal gasification wastewater.

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