Zero-discharge treatment method for coal gasification wastewater

Abstract

The invention discloses a zero-discharge treatment method for coal gasification wastewater, and belongs to the technical field of coal gasification wastewater treatment. The technical scheme is as follows: coal gasification wastewater enters a reaction area of a 1 # reaction sedimentation tank, sodium carbonate is added, pH is controlled, wastewater after precipitation reaction enters a sedimentation area for standing and sedimentation, and upper-layer effluent enters a 2 # reaction sedimentation tank; adding sodium hydroxide to control pH, adding magnesium chloride and disodium hydrogen phosphate, allowing the wastewater after precipitation reaction to enter a precipitation zone for standing precipitation, and allowing upper-layer effluent to enter a neutralization tank; and adding an acid solution to carry out acid-base neutralization reaction, and adding sodium hypochlorite after the solution is neutral. According to the method, main pollutants such as COD (Chemical Oxygen Demand) and ammonia nitrogen in the coal gasification wastewater can be efficiently removed, meanwhile, the alkalinity and the salt content of the wastewater can be greatly reduced, efficient and long-term operation of ion exchange resin is ensured, and zero emission of the coal gasification wastewater is realized.

Description

Technical Field

[0001] The invention relates to the technical field of zero-treatment of coal gasification wastewater, and in particular to a zero-discharge treatment method for coal gasification wastewater. Background Art

[0002] Through different process, coal can be converted into various chemical raw materials. At present, many coal chemical technologies have been successfully applied, such as coal-to-methanol, coal-to-olefins, coal-to-ethylene glycol, coal-to-natural gas, coal-to-hydrogen, etc. These technologies can solve the contradiction between poor oil and gas energy. The above coal chemical technologies all require coal gasification. The commonly used coal gasification technology is water-coal slurry pressurized gasification technology, that is, coal, water, additives, alkali, limestone, etc. are mixed in a certain proportion, and a water-coal slurry containing about 60% coal is formed through a coal mill. The water-coal slurry and oxygen react at high temperature and high pressure in the gasifier to generate crude synthesis gas, and then refined synthesis gas is produced through sulfur-resistant conversion, low-temperature methanol cleaning and other processes. Coal gasification high brine mainly refers to the reverse osmosis concentrated water of the reuse system, etc. The salt in the water is concentrated to 10000-50000 mg / L or even higher through the reverse osmosis membrane. Along with the salt, other pollutants in the wastewater are also enriched. The typical concentrated brine COD value is 500-2000 mg / L. The choice of method for treating high-salt wastewater must be based on the premise of satisfying the treatment effect, controlling the operating costs and expenses within a reasonable range, and efficiently combining different treatment methods to achieve the goal of meeting the treatment standards for high-salt wastewater.

[0003] A gas joint workshop currently has 3 gasifiers, 2 in operation and 1 in standby, using water-coal slurry gasification technology. A large amount of calcium and magnesium ions contained in the raw coal are enriched in the ash water. The ash water temperature is generally 50-60℃, the alkalinity is 400-600mg / L, and the hardness is 800-1200mg / L. The high hardness causes serious scaling of the pipes and equipment in the ash water system, and the scaling in the pipes is difficult to remove. The workshop uses filtration + resin adsorption technology to remove hardness and turbidity from the ash water. After the ash water hardness removal device is put into use, the hardness of the produced water can be reduced to ≤100mg / L, and the external discharge volume can be reduced by 35t / h. In this device, after the gray water is flocculated and filtered in the pretreatment unit, it is adsorbed and treated by the cation exchange resin in the adsorption unit for reuse. In the process of regenerating the cation exchange resin, wastewater with high calcium, high ammonia nitrogen, high COD and high alkalinity will be produced intermittently. The calcium ion concentration is as high as 38000mg / L, the ammonia nitrogen content is as high as 1200mg / L, the COD is about 400mg / L, the alkalinity is about 450mg / L, and the water volume is about 40-50 t / d. There is currently no more suitable treatment method for this wastewater. At present, it is usually mixed and diluted and sent to the downstream sewage treatment plant. If not treated in time, the combined effect of high alkalinity and high calcium hardness will not only cause the ion exchange resin to compact, greatly reducing the efficiency of the gray water hardness removal device, but also the transportation process of this wastewater is prone to aggravate the scaling of the pipeline, causing the pipeline and equipment to be blocked. At present, the SBR treatment process is mostly used for coal gasification process wastewater. The effluent can generally meet the discharge requirements. However, there are problems such as high salt content and high concentration of calcium and magnesium ions in the effluent, which makes it difficult to recycle and corrode subsequent deep treatment equipment. In addition, it is difficult to meet the discharge standards, and it is basically difficult to implement wastewater reuse.

[0004] The alkali precipitation method is to add strong alkaline substances into the water, and use the principle of solubility product to make the calcium and magnesium in the water form a mixed precipitate of calcium carbonate, calcium hydroxide, magnesium hydroxide, and magnesium carbonate, thereby reducing the calcium hardness, total hardness and alkalinity in the water. The main reactions are as follows: HCO3 - +OH - →H2O+CO3 2- CO3 2- +Ca 2+ →CaCO3↓ CO3 2- +Mg 2+ →MgCO3↓ 2OH - +Mg 2+ →Mg(OH)2↓ 2OH - +Ca 2+ →Ca(OH)2↓ Alkali precipitation method can be divided into lime precipitation method, liquid alkali precipitation method, lime soda ash method, and liquid alkali soda ash method. Lime precipitation method and liquid alkali precipitation method are used to soften water with high alkalinity, high calcium hardness and low total hardness; lime soda ash method and liquid alkali soda ash method are used to soften water with high calcium hardness, high total hardness and low alkalinity. The chemical reagents used are mainly lime, soda ash (sodium carbonate) and liquid alkali (sodium hydroxide).

[0005] There are many methods for treating ammonia nitrogen wastewater, mainly including: air stripping, resin exchange, breakpoint chlorination, membrane filtration, chemical precipitation and biological methods. Chemical precipitation is a method of adding a certain chemical agent to the water to react with certain soluble pollutants in the sewage to form insoluble salts and precipitate, thereby reducing the concentration of soluble pollutants in the water. Magnesium ammonium phosphate precipitation method, referred to as MAP method, is a method of removing high-concentration ammonia nitrogen in wastewater by chemical precipitation. Its basic principle is to add NH4 + Adding Mg to wastewater 2+ and HPO3 4- , and NH4 + The insoluble double salt MgNH4PO4·6H2O (MAP) crystals are generated, and then MAP is separated from the wastewater by gravity precipitation. The reaction formula can be expressed as: HPO4 3- +Mg 2+ +NH 4+ +H2O→MgNH4PO4·6H2O↓+H + The biggest feature of this method is that it can recover ammonia nitrogen and generate MAP compound fertilizer; and the precipitation reaction is not limited by temperature and toxins in the water. If the phosphate content in the sewage is very high, only magnesium salt needs to be added, and a small amount of phosphate or no phosphate can play a role in nitrogen and phosphorus removal.

[0006] Chinese invention patent CN102070277A discloses a coal gasification wastewater treatment process, which includes the following steps: adsorption treatment in a primary adsorption tank, sedimentation treatment in a first sedimentation tank, biochemical treatment in a first biochemical unit, adsorption treatment in a secondary adsorption tank, sedimentation treatment in a second sedimentation tank, biochemical treatment in a second biochemical unit, and filtration and discharge, which solves the coal chemical wastewater treatment process in the prior art. However, the adsorption capacity of activated coke is limited, which not only causes a high frequency of backwashing, but also produces a large amount of waste coke as a new secondary pollutant. At the same time, it also causes the high operating cost of the production process and the defects of unstable operation, which cannot meet the current environmental protection requirements.

[0007] Chinese invention patent CN115583764A provides a method for treating coal gasification wastewater, which includes: stripping process, acidification process, extraction process, flotation process, separation process, hydrolysis acidification, biochemical process and sludge acidification process. The acidification process of this patent can use the adsorption performance of residual sludge to adsorb pollutants in the wastewater in the residual sludge part while adjusting the pH of the wastewater, thereby improving the removal of pollutants and the extraction efficiency of the extraction process; the extraction process adopts multi-stage reverse extraction, so that the extractant is fully mixed with phenolic substances in the wastewater and fully contacts with the sludge in the wastewater, thereby improving the extraction efficiency; while reducing the energy consumption of wastewater treatment, it solves the foam problem when the wastewater enters the biochemical process and the problems of high COD and ammonia nitrogen in the effluent. However, this method does not effectively remove other pollutants in the wastewater, especially the problem of high salt content in the wastewater. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a zero-emission treatment method for coal gasification wastewater, which can not only efficiently remove major pollutants such as COD and ammonia nitrogen in the coal gasification wastewater, but also greatly reduce the alkalinity and salt content of the wastewater, ensure the efficient and long-term operation of the ion exchange resin, and achieve zero emission of coal gasification wastewater.

[0009] The technical solution of the present invention is: The zero-discharge treatment method for coal gasification wastewater comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of the 1# reaction sedimentation tank, and under stirring conditions, sodium carbonate is added and the pH is controlled to be alkaline; the wastewater after the precipitation reaction is completed enters the sedimentation zone of the 1# reaction sedimentation tank, where it is allowed to settle and the sediment is recycled, and the upper effluent enters the 2# reaction sedimentation tank; S2 The upper effluent from the sedimentation zone of the 1# reaction sedimentation tank enters the reaction zone of the 2# reaction sedimentation tank. Under stirring conditions, sodium hydroxide is added to control the pH to be alkaline, and magnesium chloride and disodium hydrogen phosphate are added. The wastewater after the precipitation reaction is completed enters the sedimentation zone of the 2# reaction sedimentation tank, and is allowed to settle in the sedimentation zone. The precipitate is recycled and the upper effluent enters the neutralization tank; The upper effluent from the sedimentation area of ​​S3 2# reaction sedimentation tank enters the neutralization tank, where acid is added for acid-base neutralization reaction. After reaching neutrality, sodium hypochlorite is added to remove COD.

[0010] Preferably, in step S1, the pH value of the reaction zone of the 1# reaction sedimentation tank is controlled to be 8.5-9.5, the stirring speed is 80-120r / m, and the residence time is 30-60min; the residence time of the wastewater after the precipitation reaction is completed in the sedimentation zone of the 1# reaction sedimentation tank is 50-100min.

[0011] Preferably, in step S2, a sodium hydroxide solution with a volume fraction of 30% is added to control the pH of the reaction zone of the 2# reaction sedimentation tank to 9-10, the stirring speed is 80-120r / m, and the residence time is 30-60min; the residence time of the wastewater after the precipitation reaction is completed in the sedimentation zone of the 2# reaction sedimentation tank is 60-120min.

[0012] Preferably, in step S2, the molar ratio of magnesium, phosphorus and nitrogen in the wastewater is 1.1-1.5:1-1.4:1.

[0013] Preferably, in step S3, hydrochloric acid is added to the neutralization tank to control the pH to 6-8.

[0014] Preferably, in step S3, sodium hypochlorite is added to remove COD and ammonia nitrogen that is not completely reacted in step S2, and the molar ratio of available chlorine to nitrogen is controlled to be 1.5-1.8:1, that is, when the mass ratio of chlorine to nitrogen is 7.6-9.2:1, the ammonia nitrogen concentration can be reduced to below 5 mg / L.

[0015] Preferably, in step S3, the effluent after COD removal is used as the analytical solution of the ion exchange resin.

[0016] Preferably, before using the effluent as an analytical solution to analyze the ion exchange resin, the ion exchange resin is firstly washed with hydrochloric acid.

[0017] Preferably, the concentration of hydrochloric acid is 1-5 mol / L.

[0018] Preferably, the waste acid after pickling the ion exchange resin is added to the neutralization tank as the acid solution in step S3.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The coal gasification wastewater treatment method of the present invention is suitable for the treatment of high-ammonia nitrogen petrochemical wastewater, which is difficult to treat, has high pollutant concentration, large fluctuations, and strict emission index requirements. The entire process of the present invention follows the principle of gradual progress. The state of the end of the previous process reaction can become the reaction condition of the subsequent process. There is no need to adjust the process conditions such as pH multiple times and significantly, which saves the use of acid, alkali and other agents to a certain extent and improves economic benefits.

[0020] 2. The salt content of wastewater will no longer increase during the treatment process of the agent of the present invention, and the oxidant not consumed in the oxidation process has a bactericidal effect, and does not increase the burden of subsequent desalination. As the number of cycles increases, the accumulation of ammonia nitrogen, COD, etc. in the process system can be avoided by adjusting the dosage of the agent, further ensuring the operating efficiency of the reuse process system. The entire process system has a simple structure, stable operation, and good treatment effect. There is no wastewater discharge during the whole process, and the sediment can be recycled and reused, which can achieve a zero-discharge effect, improve the utilization rate of water resources, and improve the economy of wastewater operation costs.

[0021] 3. The present invention introduces a pickling step before the ion exchange resin is analyzed to prevent the occurrence of caking and ensure the efficient and long-term operation of the ion exchange resin. The waste acid after pickling enters the neutralization tank of the subsequent process for acid-base neutralization reaction, ensuring the effective use of resources and avoiding waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 It is a structural schematic diagram of the zero-discharge treatment device for coal gasification wastewater of the present invention.

[0024] In the figure, 1, 1# reaction sedimentation tank; 2, 2# reaction sedimentation tank; 3, neutralization tank; 4, ion exchange resin; 5, waste acid tank. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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 should fall within the scope of protection of the present invention.

[0026] like Figure 1As shown, the zero-discharge treatment method for coal gasification wastewater of the present invention is carried out by using a zero-discharge treatment device for coal gasification wastewater, including a 1# reaction sedimentation tank 1, a 2# reaction sedimentation tank 2 and a neutralization tank 3 connected in sequence, wherein the 1# reaction sedimentation tank 1, the 2# reaction sedimentation tank 2 and the neutralization tank 3 are respectively provided with a reagent dosing mechanism, and the wastewater enters the 1# reaction sedimentation tank 1, the 2# reaction sedimentation tank 2 and the neutralization tank 3 in sequence for treatment; wherein the effluent from the neutralization tank 3 enters the ion exchange resin 4 as an analytical liquid to be analyzed, and before the analysis, hydrochloric acid is added to the ion exchange resin 4 to be pickled for pickling, and the waste acid after pickling enters the waste acid tank 5 as an acid solution to be added to the neutralization tank 3.

[0027] Example 1 The coal gasification wastewater in this embodiment has an ammonia nitrogen concentration of 812.2 mg / L, a COD of 1340 mg / L, a calcium hardness of 18369.6 mg / L, and a total hardness of 19651.2 mg / L.

[0028] The zero-discharge treatment method for coal gasification wastewater in this embodiment comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 100r / m and the pH is controlled to 8.5, and the residence time is 30min; the wastewater after the precipitation reaction is completed enters the sedimentation zone of 1# reaction sedimentation tank 1, and is left to settle for 50min in the sedimentation zone. The sediment is recycled, and the calcium hardness of the upper layer of water is 268.2mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of 1# reaction sedimentation tank 1 enters the reaction zone of 2# reaction sedimentation tank 2. At a stirring speed of 100r / m, sodium hydroxide is added to control the pH to 9, and magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.2:1:1 (molar ratio). The residence time is 40min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of 2# reaction sedimentation tank 2, and is allowed to settle in the sedimentation zone for 60min. The precipitate is recycled. The ammonia nitrogen in the upper effluent is 51.5mg / L, and it enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 6.8, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.8:1 (molar ratio); the final effluent water quality COD is 57.6 mg / L, ammonia nitrogen is 3.8 mg / L, and calcium hardness is 268.2 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4, and before analytical, the ion exchange resin 4 is first pickled with 1 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0029] Example 2 The coal gasification wastewater in this embodiment has: ammonia nitrogen concentration of 927.8 mg / L, COD of 540.8 mg / L, calcium hardness of 35884.8 mg / L, and total hardness of 38020.8 mg / L.

[0030] The zero-discharge treatment method for coal gasification wastewater in this embodiment comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 100r / m and the pH is controlled to 9, with a retention time of 40min; after the precipitation reaction, the wastewater enters the sedimentation zone of 1# reaction sedimentation tank 1, and is allowed to settle in the sedimentation zone for 60min. The sediment is recycled, and the calcium hardness of the upper effluent is 174.6mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of the 1# reaction sedimentation tank 1 enters the reaction zone of the 2# reaction sedimentation tank 2. At a stirring speed of 100r / m, sodium hydroxide is added to control the pH to 9.5. Magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.5:1.4:1 (molar ratio). The residence time is 50min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of the 2# reaction sedimentation tank 2. It is allowed to settle in the sedimentation zone for 100min. The precipitate is recycled. The ammonia nitrogen content of the upper effluent is 31.3mg / L and enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 7.3, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.8:1 (molar ratio); the final effluent COD is 35.2 mg / L, ammonia nitrogen is 3.3 mg / L, and calcium hardness is 174.6 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 2 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0031] Example 3 The coal gasification wastewater in this embodiment has: ammonia nitrogen concentration of 763.4 mg / L, COD of 566.3 mg / L, calcium hardness of 35884.8 mg / L, and total hardness of 38020.8 mg / L.

[0032] The zero-discharge treatment method for coal gasification wastewater in this embodiment comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 120r / m and the pH is controlled to 9, and the residence time is 40min; the wastewater after the precipitation reaction is completed enters the sedimentation zone of 1# reaction sedimentation tank 1, and is left to settle for 80min in the sedimentation zone. The sediment is recycled, and the calcium hardness of the upper effluent is 255.7mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of 1# reaction sedimentation tank 1 enters the reaction zone of 2# reaction sedimentation tank 2. At a stirring speed of 120r / m, sodium hydroxide is added to control the pH to 9.3. Magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.1:1:1 (molar ratio). The residence time is 30min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of 2# reaction sedimentation tank 2. It is allowed to settle in the sedimentation zone for 80min. The precipitate is recycled. The ammonia nitrogen in the upper effluent is 69.1mg / L and enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 7, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.5:1 (molar ratio); the final effluent COD is 39.2 mg / L, ammonia nitrogen is 9.60 mg / L, and calcium hardness is 255.7 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 5 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0033] Example 4 The coal gasification wastewater in this embodiment has: ammonia nitrogen concentration of 1155.0 mg / L, COD of 385.0 mg / L, calcium hardness of 36632.4 mg / L, and total hardness of 38341.2 mg / L.

[0034] The zero-discharge treatment method for coal gasification wastewater in this embodiment comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 100r / m and the pH is controlled to 9.5, and the residence time is 50min; the wastewater after the precipitation reaction is completed enters the sedimentation zone of 1# reaction sedimentation tank 1, and is left to settle for 80min in the sedimentation zone. The sediment is recycled, and the calcium hardness of the upper effluent is 83.9mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of 1# reaction sedimentation tank 1 enters the reaction zone of 2# reaction sedimentation tank 2. At a stirring speed of 100r / m, sodium hydroxide is added to control the pH to 9.5. Magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.1:1:1 (molar ratio). The residence time is 60min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of 2# reaction sedimentation tank 2. It is allowed to settle in the sedimentation zone for 120min. The precipitate is recycled. The ammonia nitrogen in the upper effluent is 76.5mg / L and enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 8, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.6:1 (molar ratio); the final effluent COD is 66.7 mg / L, ammonia nitrogen is 7.30 mg / L, and calcium hardness is 83.9 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 4 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0035] Example 5 The coal gasification wastewater in this embodiment has an ammonia nitrogen concentration of 698.4 mg / L, a COD of 338.3 mg / L, a calcium hardness of 16874.4 mg / L, and a total hardness of 17767.6 mg / L.

[0036] The zero-discharge treatment method for coal gasification wastewater in this embodiment comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 80r / m and the pH is controlled to 9.5, with a retention time of 60min; after the precipitation reaction, the wastewater enters the sedimentation zone of 1# reaction sedimentation tank 1, and is allowed to settle in the sedimentation zone for 100min. The sediment is recycled, and the calcium hardness of the upper effluent is 67.3mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of 1# reaction sedimentation tank 1 enters the reaction zone of 2# reaction sedimentation tank 2. At a stirring speed of 80r / m, sodium hydroxide is added to control the pH to 10, and magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.3:1.3:1 (molar ratio). The residence time is 30min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of 2# reaction sedimentation tank 2, and is allowed to settle in the sedimentation zone for 100min. The precipitate is recycled. The ammonia nitrogen content of the upper effluent is 58.6mg / L, and it enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 6, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.5:1 (molar ratio); the final effluent COD is 68.3 mg / L, ammonia nitrogen is 8.60 mg / L, and calcium hardness is 67.3 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 4 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0037] Comparative Example 1 The coal gasification wastewater of Comparative Example 1: the ammonia nitrogen concentration is 812.2 mg / L, the COD is 1340 mg / L, the calcium hardness is 18369.6 mg / L, and the total hardness is 19651.2 mg / L.

[0038] The zero-discharge treatment method for coal gasification wastewater of Comparative Example 1 comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 100r / m and the pH is controlled to 8, and the residence time is 30min; the wastewater after the precipitation reaction is completed enters the sedimentation zone of 1# reaction sedimentation tank 1, and is allowed to settle in the sedimentation zone for 50min. The sediment is recycled, and the calcium hardness of the upper effluent is 2061.2mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of the 1# reaction sedimentation tank 1 enters the reaction zone of the 2# reaction sedimentation tank 2. At a stirring speed of 100r / m, sodium hydroxide is added to control the pH to 9, and magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.2:1:1 (molar ratio). The residence time is 40min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of the 2# reaction sedimentation tank 2, and is allowed to settle in the sedimentation zone for 60min. The precipitate is recycled. The ammonia nitrogen in the upper effluent is 232.4mg / L, and it enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 6.8, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.8:1 (molar ratio); the final effluent water quality COD is 357.6 mg / L, ammonia nitrogen is 183.8 mg / L, and calcium hardness is 1277.3 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 1 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0039] Comparative Example 2 The coal gasification wastewater of Comparative Example 2: the ammonia nitrogen concentration is 927.8 mg / L, the COD is 540.8 mg / L, the calcium hardness is 35884.8 mg / L, and the total hardness is 38020.8 mg / L.

[0040] The zero-discharge treatment method for coal gasification wastewater of Comparative Example 2 comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 100r / m and the pH is controlled to 9, with a retention time of 40min; after the precipitation reaction, the wastewater enters the sedimentation zone of 1# reaction sedimentation tank 1, and is allowed to settle in the sedimentation zone for 60min. The sediment is recycled, and the calcium hardness of the upper effluent is 161.6mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of 1# reaction sedimentation tank 1 enters the reaction zone of 2# reaction sedimentation tank 2. At a stirring speed of 100r / m, sodium hydroxide is added to control the pH to 11, and magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.5:1.4:1 (molar ratio). The residence time is 50min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of 2# reaction sedimentation tank 2, and is allowed to settle in the sedimentation zone for 100min. The precipitate is recycled. The ammonia nitrogen content of the upper effluent is 517.4mg / L, and it enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 7.3, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.8:1 (molar ratio); the final effluent COD is 92.9 mg / L, ammonia nitrogen is 285.5 mg / L, and calcium hardness is 161.6 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 2 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0041] Comparative Example 3 The coal gasification wastewater of Comparative Example 3: the ammonia nitrogen concentration is 763.4 mg / L, the COD is 566.3 mg / L, the calcium hardness is 35884.8 mg / L, and the total hardness is 38020.8 mg / L.

[0042] The zero-discharge treatment method for coal gasification wastewater of Comparative Example 4 comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 120r / m and the pH is controlled to 9, and the residence time is 40min; the wastewater after the precipitation reaction is completed enters the sedimentation zone of 1# reaction sedimentation tank 1, and is left to settle for 80min in the sedimentation zone. The sediment is recycled, and the calcium hardness of the upper effluent is 251.0mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of the 1# reaction sedimentation tank 1 enters the reaction zone of the 2# reaction sedimentation tank 2. At a stirring speed of 120r / m, sodium hydroxide is added to control the pH to 9.3. Magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1:0.9:1 (molar ratio). The residence time is 30min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of the 2# reaction sedimentation tank 2. It is allowed to settle in the sedimentation zone for 80min. The precipitate is recycled. The ammonia nitrogen in the upper effluent is 121.7mg / L and enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 7, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.5:1 (molar ratio); the final effluent COD is 350.4 mg / L, ammonia nitrogen is 99.3 mg / L, and calcium hardness is 251 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 5 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0043] Comparative Example 4 The coal gasification wastewater of Comparative Example 4: the ammonia nitrogen concentration is 1155.0 mg / L, the COD is 385.0 mg / L, the calcium hardness is 36632.4 mg / L, and the total hardness is 38341.2 mg / L.

[0044] The zero-discharge treatment method for coal gasification wastewater of Comparative Example 4 comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 100r / m and the pH is controlled to 9.5, and the residence time is 50min; the wastewater after the precipitation reaction is completed enters the sedimentation zone of 1# reaction sedimentation tank 1, and is allowed to settle in the sedimentation zone for 80min. The sediment is recycled, and the calcium hardness of the upper effluent is 80.4mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of 1# reaction sedimentation tank 1 enters the reaction zone of 2# reaction sedimentation tank 2. At a stirring speed of 100r / m, sodium hydroxide is added to control the pH to 9.5. Magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.1:1:1 (molar ratio). The residence time is 60min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of 2# reaction sedimentation tank 2. It is allowed to settle in the sedimentation zone for 120min. The precipitate is recycled. The ammonia nitrogen in the upper effluent is 73.2mg / L and enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 8, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.4:1 (molar ratio); the final effluent COD is 150.4 mg / L, ammonia nitrogen is 34.8 mg / L, and calcium hardness is 80.4 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4. Before analytical treatment, the ion exchange resin 4 is first pickled with 4 mol / L hydrochloric acid, and the waste acid after pickling is added to the neutralization tank 3 as acid solution.

[0045] Comparative Example 5 The coal gasification wastewater of Comparative Example 5: the ammonia nitrogen concentration is 698.4 mg / L, the COD is 338.3 mg / L, the calcium hardness is 16874.4 mg / L, and the total hardness is 17767.6 mg / L.

[0046] The zero-discharge treatment method for coal gasification wastewater of Comparative Example 5 comprises the following steps: S1 coal gasification wastewater first enters the reaction zone of 1# reaction sedimentation tank 1, and sodium carbonate is added at a stirring speed of 80r / m and the pH is controlled to 9.5, with a retention time of 60min; after the precipitation reaction, the wastewater enters the sedimentation zone of 1# reaction sedimentation tank 1, and is allowed to settle in the sedimentation zone for 100min. The sediment is recycled, and the calcium hardness of the upper effluent is 67.3mg / L, and enters 2# reaction sedimentation tank 2; S2 The upper effluent from the sedimentation zone of 1# reaction sedimentation tank 1 enters the reaction zone of 2# reaction sedimentation tank 2. At a stirring speed of 80r / m, sodium hydroxide is added to control the pH to 10, and magnesium chloride and disodium hydrogen phosphate are added. The addition ratio of magnesium chloride and disodium hydrogen phosphate is Mg:P:N=1.3:1.3:1 (molar ratio). The residence time is 30min. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of 2# reaction sedimentation tank 2, and is allowed to settle in the sedimentation zone for 100min. The precipitate is recycled. The ammonia nitrogen content of the upper effluent is 58.6mg / L, and it enters the neutralization tank 3. The upper effluent from the sedimentation zone of S3 2# reaction sedimentation tank 2 enters the neutralization tank 3, and the waste acid in the waste acid tank in the hydrochloric acid step (1) is added to carry out acid-base neutralization reaction. After pH = 6, sodium hypochlorite is added to remove COD. The dosing ratio of effective chlorine and nitrogen is Cl:N = 1.5:1 (molar ratio); the final effluent COD is 68.3 mg / L, ammonia nitrogen is 8.60 mg / L, and calcium hardness is 67.3 mg / L. The effluent can be used as the analytical solution of ion exchange resin 4; and before analysis, the ion exchange resin 4 is not acid-washed with hydrochloric acid.

[0047] In the case of directly analyzing without acid washing the ion exchange resin 4, since the alkalinity of the inlet water of the gray water hardness removal device is 300-1000 mg / L, on the one hand, the combined effect of high alkalinity and high calcium hardness will cause the ion exchange resin 4 to harden, greatly reducing the operating efficiency of the gray water hardness removal device. After a period of continuous operation, the calcium hardness in the water produced by the gray water hardness removal device gradually increases. In order to achieve the water production reuse index, the cleaning and replacement times of the ion exchange resin 4 are increased accordingly. On the other hand, the wastewater transportation process is prone to aggravate pipeline scaling, causing pipeline and equipment blockage, and may even cause equipment corrosion damage, resulting in greatly increased economic costs. In the present invention, the waste acid after acid washing is not only added to the neutralization tank 3 as an acid solution to adjust the pH, but can also be added to the gray water hardness removal device inlet tank and the analytical solution storage tank to reduce the alkalinity, prevent the ion exchange resin 4 from hardening, scaling of the pipeline, and equipment blockage, which has certain economic benefits.

[0048] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, and all of these shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A zero-discharge treatment method for coal gasification wastewater, characterized in that: The following steps are involved: S1 coal gasification wastewater first enters the reaction zone of the 1# reaction sedimentation tank (1), and under stirring conditions, sodium carbonate is added and the pH is controlled to be alkaline; after the precipitation reaction is completed, the wastewater enters the sedimentation zone of the 1# reaction sedimentation tank (1), and is allowed to settle in the sedimentation zone, and the upper layer of water enters the 2# reaction sedimentation tank (2); S2 The upper effluent from the sedimentation zone of the 1# reaction sedimentation tank (1) enters the reaction zone of the 2# reaction sedimentation tank (2). Under stirring conditions, the pH is controlled to be alkaline, and magnesium chloride and disodium hydrogen phosphate are added. After the precipitation reaction is completed, the wastewater enters the sedimentation zone of the 2# reaction sedimentation tank (2), and is allowed to settle in the sedimentation zone. The upper effluent enters the neutralization tank (3); The upper effluent from the sedimentation area of ​​S3 2# reaction sedimentation tank (2) enters the neutralization tank (3), where acid is added for acid-base neutralization reaction. After reaching neutrality, sodium hypochlorite is added to remove COD.

2. The method for zero-discharge treatment of coal gasification wastewater according to claim 1, characterized in that: In step S1, the pH value of the reaction zone of the No. 1 reaction sedimentation tank (1) is controlled to be 8.5-9.5, the stirring speed is 80-120 r / m, and the residence time is 30-60 min; the residence time of the wastewater after the precipitation reaction is completed in the sedimentation zone of the No. 1 reaction sedimentation tank (1) is 50-100 min.

3. The zero-discharge treatment method for coal gasification wastewater according to claim 1, characterized in that: In step S2, sodium hydroxide solution is added to control the pH of the reaction zone of the 2# reaction sedimentation tank (2) to 9-10, the stirring speed is 80-120 r / m, and the residence time is 30-60 min; the residence time of the wastewater after the precipitation reaction is completed in the sedimentation zone of the 2# reaction sedimentation tank (2) is 60-120 min.

4. The method for zero-discharge treatment of coal gasification wastewater according to claim 1, characterized in that: In step S2, the molar ratio of magnesium, phosphorus and nitrogen in the wastewater is 1.1-1.5:1-1.4:

1.

5. The method for zero-discharge treatment of coal gasification wastewater according to claim 1, characterized in that: In step S3, hydrochloric acid is added to the neutralization tank (3) to control the pH to 6-8.

6. The method for zero-discharge treatment of coal gasification wastewater according to claim 1, characterized in that: In step S3, when sodium hypochlorite is added, the molar ratio of chlorine to nitrogen in the wastewater is controlled to be 1.5-1.8:

1.

7. The method for zero-discharge treatment of coal gasification wastewater according to claim 1, characterized in that: In step S3, the effluent after COD removal is used as the analysis liquid of the ion exchange resin (4).

8. The method for zero-discharge treatment of coal gasification wastewater according to claim 7, characterized in that: Before using the effluent as an analytical solution to analyze the ion exchange resin (4), the ion exchange resin (4) is firstly washed with hydrochloric acid.

9. The method for zero-discharge treatment of coal gasification wastewater according to claim 8, characterized in that: The concentration of the hydrochloric acid is 1-5 mol / L.

10. The method for zero-discharge treatment of coal gasification wastewater according to claim 8, characterized in that: The waste acid after pickling the ion exchange resin (4) is added to the neutralization tank (3) as the acid solution in step S3.

Images