Coal gasification industrial waste salt recycling method

Abstract

The invention belongs to the technical field of waste reutilization, and discloses a coal gasification industrial waste salt reutilization method. The method comprises the following steps that sodium sulfate waste salt is dissolved in water and then stands still, supernate is taken, and the mass fraction of sodium sulfate in the supernate is 29%-30.5%; reacting the supernate with ammonium bisulfate to obtain a solid-liquid mixture; filtering the solid-liquid mixture to obtain solid sodium bicarbonate and mother liquor; mixing the solid sodium bicarbonate with water, performing centrifugal washing to obtain a first product, and drying the first product to obtain a sodium bicarbonate product; adjusting the pH value of the mother liquor to 3-6 to obtain an acidified solution, ammonia gas and carbon dioxide gas, and carrying out evaporation concentration, cooling crystallization and solid-liquid separation on the acidified solution to obtain an ammonium sulfate product. According to the method, high-purity sodium bicarbonate and ammonium sulfate can be prepared from the sodium sulfate waste salt, and reutilization of the coal gasification industrial waste salt is achieved. The product prepared by the method disclosed by the invention is high in purity, low in treatment equipment cost and high in environmental tolerance.

Description

Technical Field

[0001] The invention relates to the technical field of waste material recycling, and in particular to a method for recycling waste salt from coal gasification industry. Background Art

[0002] In recent years, coal chemical industry has become an important part of my country's energy and chemical industry. At the same time, the accompanying environmental problems are becoming increasingly serious, especially water resources and water environment problems have become an important factor affecting the development of coal chemical industry. The waste brine of coal gasification enterprises mainly comes from gas washing wastewater, circulating water system drainage, chemical water station drainage, etc. in the production process. After evaporation and crystallization, the precipitated solid waste salt mainly contains cationic Ca 2+ Mg 2+ and Na + , anion Cl - 、SO4 2- and CO3 2- At present, waste salt treatment generally relies on third-party companies for rigid landfill treatment, which is expensive. Landfilling waste salt not only occupies land but also wastes waste salt resources. Therefore, there is great potential in finding economical and low-cost waste salt treatment methods.

[0003] The existing waste salt treatment technologies mainly include chemical treatment, high temperature treatment, membrane treatment, etc. The invention of patent CN110642270A discloses a method for chemical treatment of waste salt, which removes organic impurities in waste salt by chemical and adsorption to obtain sodium chloride products, but chemical treatment requires the addition of new substances into the waste salt, and secondary solid waste is generated during the treatment of waste salt, and the practicality of the process is relatively small; the invention of patent CN207222538U discloses a high temperature treatment method, which uses high temperature pyrolysis to remove organic matter from industrial waste salt slag, but the energy consumption is high, the equipment is prone to corrosion, and the maintenance cost is high; membrane treatment uses the selectivity of the membrane to achieve the separation, purification, and concentration of different components, and has high requirements on the performance of the membrane. The membrane needs to be treated for long-term use, and the membrane cost is expensive. Summary of the invention

[0004] In order to solve the problems in the background technology, the present invention provides a method for recycling waste salt from coal gasification industry, which can obtain sodium bicarbonate and ammonium sulfate products.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A method for recycling waste salt from coal gasification industry comprises the following steps: Dissolve the sodium sulfate waste salt in water and let it stand until the mass fraction of sodium sulfate in the solution is controlled to be 29-30.5%, then take the supernatant; reacting the supernatant with ammonium bisulfate to obtain a solid-liquid mixture; The solid-liquid mixture is filtered to obtain solid sodium bicarbonate and mother liquor; Mixing solid sodium bicarbonate with water and washing by centrifugation to obtain a first product, and drying the first product to obtain a sodium bicarbonate product; The pH of the mother liquor is adjusted to 3-6 to obtain an acidified solution, ammonia gas and carbon dioxide gas, the gas is recovered, and the acidified solution is evaporated and concentrated, cooled and crystallized, and solid-liquid separation is performed to obtain an ammonium sulfate product.

[0006] Preferably, during the process of dissolving the sodium sulfate waste salt in water, the system temperature is 50-55°C.

[0007] Preferably, the temperature during the reaction of the supernatant and ammonium bisulfate is 35-38° C., and the reaction time is 1.5-2 h.

[0008] Preferably, the molar ratio of sodium sulfate to ammonium bicarbonate during the reaction of the supernatant with ammonium bisulfate is 1:(1.05-1.1).

[0009] Preferably, solid sodium bicarbonate is mixed with water in a mass ratio of 1:(0.55-0.60) and then centrifuged for washing.

[0010] Preferably, the purity of the sodium bicarbonate product is 98.5-99.5%.

[0011] Preferably, the pH of the mother liquor is adjusted to 3-6 with sulfuric acid.

[0012] Preferably, the temperature for evaporation and concentration of the acidified solution is 130° C., and the evaporation amount is 30-40% of the mass of the acidified solution.

[0013] Preferably, the temperature of the cooling crystallization is 55-60°C.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The invention can utilize sodium sulfate waste salt to prepare high-purity sodium bicarbonate and ammonium sulfate, thereby realizing the reuse of coal gasification industrial waste salt. The product prepared by the method of the invention has high purity, low processing equipment cost and high environmental tolerance. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments.It should be understood that these descriptions are exemplary only, and are not intended to limit the scope of the present invention.In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.Unspecified conditions in the embodiments are carried out according to the conditions of normal conditions or manufacturer recommendations.Reagents used or instruments that do not specify manufacturers are conventional products that can be purchased and obtained commercially.

[0016] The embodiment provided by the present invention is a method for recycling waste salt from coal gasification industry, comprising the following steps: Dissolve the sodium sulfate waste salt in water and let it stand until the mass fraction of sodium sulfate in the solution is controlled to be 29-30.5%, then take the supernatant; reacting the supernatant with ammonium bisulfate to obtain a solid-liquid mixture; The solid-liquid mixture is filtered to obtain solid sodium bicarbonate and mother liquor; Mixing solid sodium bicarbonate with water and washing by centrifugation to obtain a first product, and drying the first product to obtain a sodium bicarbonate product; The pH of the mother liquor is adjusted to 3-6 to obtain an acidified solution, ammonia gas and carbon dioxide gas, the gas is recovered, and the acidified solution is evaporated and concentrated, cooled and crystallized, and solid-liquid separation is performed to obtain an ammonium sulfate product.

[0017] It can be understood that when sodium sulfate waste salt is dissolved in water, the amount of the two is determined according to the mass fraction of sodium sulfate in the dissolved solution. As long as the mass fraction of sodium sulfate in the solution is 29-30.5%, this concentration is the best reaction ratio and the most sodium bicarbonate is produced.

[0018] It should be noted that the water generated during the centrifugal washing process after the solid sodium bicarbonate is mixed with water can be recovered and reused as a sodium sulfate waste salt raw material.

[0019] In some preferred embodiments, the temperature during the reaction of the supernatant with ammonium bisulfate is 35-38° C., and the reaction time is 1.5-2 h. Under these reaction conditions, the ammonium bicarbonate can be prevented from being decomposed into ammonia and carbon dioxide, and the reaction temperature can be kept in the optimal temperature range, and the sodium ion conversion rate can be improved; the molar ratio of sodium sulfate to ammonium bicarbonate during the reaction is preferably 1: (1.05-1.1); the specific reactions that occur are as follows: .

[0020] The solid sodium bicarbonate is washed and dried to obtain a sodium bicarbonate product. The purity of the sodium bicarbonate product obtained in the embodiment of the present invention is 98.5-99.5%.

[0021] In some preferred embodiments, sulfuric acid is used to adjust the pH of the mother liquor to 3-6, that is, the mother liquor is acidified to obtain an acidified solution, and the acidified solution is evaporated and concentrated, cooled and crystallized, and solid-liquid separated to obtain the ammonium sulfate product. In the solid-liquid separation process, an uncrystallized mother liquor is obtained, and this part of the mother liquor can be recycled as a sodium sulfate waste salt raw material for reuse.

[0022] In some preferred embodiments, the temperature for evaporation and concentration of the acidified solution is 130°C, the evaporation amount is 30-40% of the mass of the acidified solution, and the temperature for cooling and crystallization is 55-60°C.

[0023] In order to make the technical solution of the present invention clearer, the method for recycling waste salt from coal gasification industry is described in detail through multiple embodiments. The mass percentage of sodium sulfate in the waste salt used in the following embodiments is 91%.

[0024] Example 1 (1) Pretreatment: Mix 7 kg of solid waste salt and 15 kg of fresh water, stir and dissolve at 55 °C, stir for 30 min and then let stand for 30 min to obtain the supernatant; (2) Double decomposition reaction: The supernatant and ammonium bicarbonate are mixed and reacted, and ammonium bicarbonate is added according to the molar ratio of sodium sulfate to ammonium bicarbonate = 1:1.3, the reaction temperature is 35°C, the reaction time is 2h, and a solid-liquid mixture is obtained; (3) Filtration and washing: Separate the sodium bicarbonate solid and mother liquor in the solid-liquid mixture. According to the water content of the sodium bicarbonate paste, the mass ratio of sodium bicarbonate to washing water is 1:0.8, and centrifugal washing is performed twice to obtain sodium bicarbonate and washing water with a lower water content, and the washing water is recycled; (4) Drying: Drying the sodium bicarbonate with a low water content to obtain a sodium bicarbonate product; (5) Acidification: adding sulfuric acid to the mother liquor obtained in step 3 for acidification treatment, adjusting the pH value to 3, obtaining an acidified solution, ammonia gas and carbon dioxide gas, and recovering the gas; (6) Evaporation and crystallization: The acidified solution is evaporated and crystallized, the evaporation temperature is set at 130°C, and when the evaporation amount evaporates to 30% of the acidified solution, the heating is automatically stopped to obtain an evaporated crystallization solution; (7) Cooling crystallization: The evaporated crystallization solution is cooled to 60°C, and a large amount of ammonium sulfate crystals are precipitated. The temperature is maintained until ammonium sulfate crystals are precipitated to the maximum extent, thereby obtaining a solid-liquid mixture; (8) Solid-liquid separation: The solid-liquid mixture is separated into solid and liquid to finally obtain ammonium sulfate product. The remaining mother liquor can be recycled.

[0025] The mass fraction of sodium bicarbonate obtained by the above process is 98.5%, which meets the GBT1606-2008 industrial sodium bicarbonate Class III standard; the mass fraction of ammonium sulfate prepared is 98.6%, which meets the GBT535-2020 fertilizer grade ammonium sulfate Class II standard.

[0026] Example 2 (1) Pretreatment: 7 kg of solid waste salt and 15 kg of fresh water were introduced into a sedimentation tank and stirred to dissolve at 55 °C. The mass fraction of sodium sulfate in the mixed solution was found to be in the range of 29 to 30.5%. The mixture was stirred for 30 min and then allowed to stand for 30 min to obtain a supernatant. (2) Double decomposition reaction: The supernatant liquid and ammonium bicarbonate are mixed for reaction, the molar ratio of sodium sulfate to ammonium bicarbonate is 1:1.1, the reaction temperature is controlled at 35°C, the reaction time is 2h, and a solid-liquid mixture is obtained; (3) Filtration and washing: The sodium bicarbonate paste and the mother liquor in the solid-liquid mixture are filtered and separated. According to the water content of the sodium bicarbonate paste, the mass ratio of sodium bicarbonate to washing water is controlled to 1:0.6. Washing is performed twice to obtain sodium bicarbonate and washing water with a low water content. The washing water is recycled; (4) Drying: Drying the sodium bicarbonate with a low water content to obtain sodium bicarbonate; (5) Acidification: adding sulfuric acid to the mother liquor obtained in step 3 for acidification treatment, adjusting the pH value to 3, obtaining an acidified solution, ammonia gas and carbon dioxide gas, and recovering the gas; (6) Evaporation and crystallization: The acidified solution is evaporated and crystallized, and the evaporation temperature is set at 130°C. When the evaporation amount evaporates to 30% of the acidified solution, the heating is stopped to obtain an evaporated crystallization solution; (7) Cooling crystallization: Cool the evaporation crystallization solution, and set the cooling temperature to 60°C. When the solution temperature reaches the preset cooling temperature, a large amount of ammonium sulfate crystals are precipitated. Maintain the temperature for 15 minutes to precipitate ammonium sulfate crystals to the maximum extent, thereby obtaining a solid-liquid mixture. (8) Solid-liquid separation: The solid-liquid mixture is separated into solid and liquid to finally obtain ammonium sulfate product, and the remaining mother liquor is passed into the sedimentation tank for recycling.

[0027] The mass fraction of sodium bicarbonate prepared by the above process is 99.8%, which meets the Class I standard of industrial sodium bicarbonate of GBT1606-2008; the mass fraction of ammonium sulfate prepared is 99.2%, which meets the Class I standard of fertilizer-grade ammonium sulfate of GBT535-2020.

[0028] Example 3 (1) Pretreatment: 6.5 kg of solid waste salt and 15 kg of fresh water were mixed and stirred at 55 °C to dissolve. The mass fraction of sodium sulfate in the mixed solution was detected to be 28.3%. Solid waste salt was added and the mass fraction of sodium sulfate solution was adjusted to a range of 29 to 30.5%. The mixture was stirred for 30 min and then allowed to stand for 30 min to obtain a supernatant. (2) Double decomposition reaction: The supernatant liquid and ammonium bicarbonate are mixed for reaction, the molar ratio of sodium sulfate to ammonium bicarbonate is 1:1.05, the reaction temperature is controlled at 35°C, the reaction time is 2h, and a solid-liquid mixture is obtained; (3) Filtration and washing: The sodium bicarbonate solid and the mother liquor in the solid-liquid mixture are filtered and separated, and the mass ratio of sodium bicarbonate to washing water is 1:0.55. Washing is performed twice to obtain sodium bicarbonate and washing water with a low water content, and the washing water is recycled; (4) Drying: Drying the sodium bicarbonate with a low water content to obtain sodium bicarbonate; (5) Acidification: adding sulfuric acid to the mother liquor obtained in step 3 for acidification treatment, adjusting the pH value to 6, obtaining an acidified solution, ammonia gas and carbon dioxide gas, and recovering the gas; (6) Evaporation and crystallization: The acidified solution is evaporated and crystallized, and the evaporation temperature is set at 130°C. When the evaporation amount reaches 40% of the acidified solution, the heating is automatically stopped to obtain an evaporated crystallization solution; (7) Cooling crystallization: The evaporated crystallization solution is cooled and crystallized, and the cooling temperature is set at 60°C. When the solution temperature reaches the preset cooling temperature, a large amount of ammonium sulfate crystals are precipitated. The temperature is maintained for 10 minutes to precipitate ammonium sulfate crystals to the maximum extent, thereby obtaining a solid-liquid mixture.

[0029] The mass fraction of sodium bicarbonate prepared by the above process is 98.6%, which meets the national standard, and the mass fraction of ammonium sulfate prepared is 98.5%, which meets the fertilizer grade standard.

[0030] Example 4 (1) Pretreatment: 7 kg of solid waste salt and 15 kg of fresh water were mixed and stirred at 55 °C to dissolve. The mass fraction of sodium sulfate was 30.1%, which was within the preset range. After stirring for 30 min, the mixture was allowed to stand for 30 min to obtain a supernatant. (2) Double decomposition reaction: The supernatant liquid and ammonium bicarbonate are mixed for reaction, the molar ratio of sodium sulfate to ammonium bicarbonate is 1:1.10, the reaction temperature is controlled at 35°C, the reaction time is 2h, and a solid-liquid mixture is obtained; (3) Filtration and washing: Separate the sodium bicarbonate solid and mother liquor in the solid-liquid mixture. The mass ratio of sodium bicarbonate to washing water is 1:0.60. Wash twice to obtain sodium bicarbonate and washing water with a low water content. The washing water is recycled; (4) Drying: Drying the sodium bicarbonate with a low water content to obtain sodium bicarbonate; (5) Acidification: Sulfuric acid is added to the mother liquor obtained in step 3 for acidification, and the pH value is adjusted to 4. Ammonia and carbon dioxide are passed through a pipeline to a recovery tank for recovery; (6) Evaporation and crystallization: The acidified solution is evaporated and crystallized, and the evaporation temperature is set at 130°C. When the evaporation amount evaporates to 35% of the acidified solution, the heating is automatically stopped to obtain an evaporated crystallization solution; (7) Cooling crystallization: The evaporated crystallization solution is cooled and crystallized, and the cooling temperature is set at 60°C. When the solution temperature reaches the preset cooling temperature, a large amount of ammonium sulfate crystals are precipitated. The temperature is maintained for 15 minutes to precipitate ammonium sulfate crystals to the maximum extent, thereby obtaining a solid-liquid mixture.

[0031] The mass fraction of sodium bicarbonate prepared by the above process is 99.3%, which meets the national standard, and the mass fraction of ammonium sulfate prepared is 96.8%, which meets the fertilizer grade standard.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling waste salt from coal gasification industry, characterized in that: The following steps are involved: Dissolve the sodium sulfate waste salt in water, control the mass fraction of sodium sulfate in the solution to 29-30.5%, let it stand, and take the supernatant; reacting the supernatant with ammonium bisulfate to obtain a solid-liquid mixture; The solid-liquid mixture is filtered to obtain solid sodium bicarbonate and mother liquor; Mixing solid sodium bicarbonate with water and washing by centrifugation to obtain a first product, and drying the first product to obtain a sodium bicarbonate product; The pH of the mother liquor is adjusted to 3-6 to obtain an acidified solution, ammonia gas and carbon dioxide gas, the gas is recovered, and the acidified solution is evaporated and concentrated, cooled and crystallized, and solid-liquid separation is performed to obtain an ammonium sulfate product.

2. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: During the process of dissolving the sodium sulfate waste salt in water, the system temperature is 50-55°C.

3. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: The temperature during the reaction of the supernatant and ammonium bisulfate is 35-38° C., and the reaction time is 1.5-2 h.

4. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: During the reaction of the supernatant with ammonium bisulfate, the molar ratio of sodium sulfate to ammonium bicarbonate is 1:(1.05-1.1).

5. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: Solid sodium bicarbonate and water are mixed in a mass ratio of 1:(0.55-0.60) and then centrifuged and washed.

6. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: The purity of the sodium bicarbonate product is 98.5-99.5%.

7. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: The pH of the mother liquor was adjusted to 3-6 with sulfuric acid.

8. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: The temperature for evaporation and concentration of the acidified solution is 130°C, and the evaporation amount is 30-40% of the mass of the acidified solution.

9. The method for recycling waste salt from coal gasification industry according to claim 1, characterized in that: The temperature of the cooling crystallization is 55-60°C.