A process for preparing agricultural potassium sulfate, desulfurized sodium bicarbonate and agricultural ammonium chloride
The process of producing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride has solved the environmentally unfriendly problem of solid waste treatment in coal mines and coal chemical industries, realized the resource utilization of solid waste, reduced energy consumption and environmental pollution, and produced high-value-added agricultural products.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA YIHUI HIGH-TECH DEVELOPMENT CO LTD
- Filing Date
- 2026-03-30
- Publication Date
- 2026-06-16
AI Technical Summary
Existing technologies for treating solid wastes such as mine water and concentrated brine residues generated during coal mining and coal chemical production are not environmentally friendly, occupy land, and easily pollute the environment. There is a lack of integrated energy-saving and environmentally friendly treatment processes.
The process of producing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride is adopted. Through salt separation, nanofiltration membrane separation, multi-effect evaporation and MVR heat pump technology, combined with a two-stage reaction process, the resource utilization of solid waste is realized, reducing energy consumption and by-product output.
It enables the high-value utilization of solid waste, reduces production energy consumption, reduces land occupation and environmental pollution, and produces high-quality agricultural products, resulting in significant social and economic benefits.
Smart Images
Figure CN122212178A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of coal chemical industry and coal mine solid waste treatment technology, specifically a process for producing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride. Background Technology
[0002] In the process of coal mining and coal chemical processing, the mine water and concentrated brine produced need to be desalinated. The resulting solid waste, such as miscellaneous salt residue, is currently mainly disposed of by landfill. This method is not only environmentally unfriendly and occupies a large amount of land, but also, if isolation measures are not in place, it can easily pollute the land and groundwater resources.
[0003] While existing technologies exist for treating concentrated brine and salts, there is no precedent in China for seamlessly integrating soda ash chemical engineering, inorganic salt chemical engineering, and environmental engineering units to form an energy-saving, environmentally friendly, and zero-emission production process system. This invention aims to address the shortcomings of existing solid waste treatment technologies and achieve high-value utilization of mixed salts and high-concentration brine. Summary of the Invention
[0004] The purpose of this invention is to provide a process for producing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride, so as to solve the problems mentioned in the background art.
[0005] To achieve the above objectives, the present invention provides the following technical solution: a process for producing agricultural potassium sulfate, desulfurizing sodium bicarbonate, and agricultural ammonium chloride, comprising the following steps:
[0006] Step 1: Raw material processing
[0007] The raw materials are mine water and concentrated brine produced during coal mining and coal chemical production, which are processed to remove miscellaneous salts, various types of salts, and concentrated brine and mother liquor produced during membrane filtration and evaporation, thus realizing the resource utilization of solid waste. The auxiliary materials in the raw materials are liquid ammonia and CO2. The liquid ammonia is purchased raw material, transported by cryogenic tank trucks and unloaded into liquid ammonia storage tanks. It is then vaporized into ammonia gas by a vaporizer and sent into the production system by an ammonia compressor. The CO2 is obtained from the exhaust gas from coal chemical production or purchased liquid CO2 gas, which is pressurized by a CO2 compressor and sent into the production system to realize CO2 emission reduction and recycling.
[0008] Step Two: Brine Preparation and Refining
[0009] The above-mentioned raw materials are processed through a brine-making process, in which the solid raw materials are dissolved to form a brine solution. The brine solution is then refined (purified) by using methods such as precipitation and filtration to remove suspended impurities, heavy metal ions and other harmful components from the brine solution, resulting in a pure brine solution that provides qualified raw materials for subsequent processes.
[0010] Step 3: Membrane separation and concentration
[0011] A two-stage nanofiltration process is used to treat the pure brine solution. By utilizing the selective permeability of the nanofiltration membrane, the monovalent salt (such as NaCl) and divalent salt (such as Na2SO4) are efficiently separated. The separated monovalent salt solution and divalent salt solution are then initially concentrated by passing them through an ultrafiltration membrane to increase the concentration of solutes in the solution and reduce the energy consumption of subsequent evaporation and concentration processes, resulting in concentrated monovalent brine and concentrated divalent brine.
[0012] Step 4: Evaporation and Concentration
[0013] The separated and concentrated monovalent and divalent brine are sent to the evaporation system for concentration. The evaporation system adopts a process flow of four-effect, five-body, two-stage co-current flow + MVR heat pump. By utilizing the energy-saving characteristics of multi-effect evaporation and the waste heat recovery function of MVR heat pump, the evaporation efficiency is greatly improved. This process eliminates the need for the traditional fiberglass cooling tower system and makes full use of the waste heat generated in the evaporation process, thereby achieving a significant reduction in production energy consumption.
[0014] Step 5: Flash distillation purification of heptahydrate nitrate
[0015] Sodium sulfate was purified using a Na₂SO₄·7H₂O flash evaporation process. Specifically, the divalent salt system was evaporated and crystallized through the first and second effects of the evaporation system. Since the divalent salt system contained a small amount of monovalent salt, the drastic changes in the solubility of sodium sulfate and sodium chloride at different temperatures were utilized. When sodium sulfate reached a saturated solution in the second effect, the solution was pumped out and sent to the flash evaporator. The flash evaporator maintained a low pressure and temperature, allowing sodium sulfate to rapidly crystallize into sodium sulfate heptahydrate (Na₂SO₄·7H₂O). After separation and dehydration by centrifuge, high-purity sodium sulfate was obtained. The molar ratio of divalent salt to monovalent salt was strictly controlled at 1:1 to ensure the purification effect.
[0016] Step Six: Preparation of Agricultural Potassium Sulfate
[0017] This process includes four sub-steps: a first-stage reaction to produce potassium sulfate, a second-stage reaction to produce potassium sulfate, washing, filtering, and dehydration of potassium sulfate, and drying of potassium sulfate. The core process utilizes a two-stage reaction using a supersaturated sodium sulfate solution, which improves reaction efficiency and virtually eliminates byproducts. The specific process is as follows:
[0018] The sodium sulfate heptahydrate obtained in step five is fed directly into a potassium sulfate reactor via a belt conveyor without drying. An appropriate amount of water is added to the reactor to prepare a saturated sodium sulfate solution. Simultaneously, excess potassium chloride solid is added, and the mixture is stirred at room temperature to produce potassium sodium sulfate double salt (Na₂SO₄). K2SO4 6H2O);
[0019] The saturated potassium sulfate solution was taken out from the first stage reactor and sent to the second stage reactor. Potassium chloride solid was added again and stirred thoroughly to produce potassium sulfate and sodium chloride. Under the process condition of excess potassium chloride, potassium sulfate was fully crystallized and precipitated.
[0020] The potassium sulfate crystal slurry after the reaction is taken out and dehydrated and washed using a belt filter to remove impurities and mother liquor adhering to the crystal surface; then it is dehydrated a second time using a centrifuge to reduce the water content of the crystals.
[0021] The dehydrated potassium sulfate crystals are sent to a drying oven for drying. After drying, the product is screened and sent to the packaging process. The packaged product is then stored in the warehouse to obtain the finished agricultural potassium sulfate product.
[0022] Step 7: Preparation of desulfurized sodium bicarbonate and agricultural ammonium chloride
[0023] Based on the principles of alkali chemical engineering, desulfurizing sodium bicarbonate (NaHCO3) and agricultural ammonium chloride (NH4Cl) are prepared using a monovalent brine system. The specific process is as follows:
[0024] The monovalent brine system obtained in step four is pumped into the third and fourth effects of the evaporation system for evaporation. The saturated brine is taken out in the fourth effect and separated and dehydrated by centrifuge. The obtained sodium chloride crystals are dehydrated again and sent to the saturated brine preparation process. An appropriate amount of water is added to make a saturated sodium chloride solution.
[0025] A saturated sodium chloride solution is pumped into an ammonia absorption tower, where it is fully contacted and mixed with the ammonia gas obtained after the liquid ammonia is vaporized, thus preparing a saturated ammonia brine in the ammonia absorption tower.
[0026] Saturated ammonia brine is fed into a carbonization reactor and reacted with pressurized CO2 to produce a slurry containing sodium bicarbonate and ammonium chloride.
[0027] The slurry after carbonization reaction is filtered and washed using a belt filter. The resulting filter cake is wet sodium bicarbonate, which is then sent to an airflow drying tube for drying. The dried desulfurized sodium bicarbonate is then screened, packaged, and stored in the warehouse.
[0028] The mother liquor filtered by the belt filter is sent to a cold salting-out tank for cold precipitation and salting-out treatment, so that the ammonium chloride in the mother liquor can be fully crystallized out. The precipitated ammonium chloride crystals are washed and filtered by the belt filter and dehydrated twice by the centrifuge. They are then sent to a new type of energy-saving dry ammonium chloride furnace for drying, which solves the technical problems of ammonium chloride being prone to clumping and sticking to the wall during drying. The dried agricultural ammonium chloride product is sent to the silo by the pneumatic conveyor, and then packaged and stored.
[0029] Compared with the prior art, the beneficial effects of the present invention are:
[0030] The production process of this invention has extremely low energy consumption. The evaporation adopts a four-effect five-body + MVR evaporation process, which utilizes the energy-saving characteristics of multi-effect evaporation and the MVR heat pump to improve efficiency, eliminating the need for a fiberglass cooling tower system and making full use of waste heat.
[0031] This invention addresses the tendency of ammonium chloride to clump and stick to the walls during drying by employing a novel energy-saving ammonium drying furnace, which offers significant energy savings and a long operating cycle.
[0032] This invention employs a two-stage reaction process to produce potassium sulfate from a supersaturated sodium sulfate solution, which improves reaction efficiency, virtually eliminates byproduct production, reduces CO2 emissions, decreases solid waste emissions, saves a significant amount of land, and provides a demonstration project for the resource utilization of concentrated brine containing complex components.
[0033] The agricultural potassium sulfate produced by this invention is a high-quality binary potassium fertilizer, the desulfurization sodium bicarbonate is the main catalyst for dry desulfurization, and the agricultural ammonium chloride is a basic fertilizer, realizing the social and economic benefits of resource utilization and high-value utilization of solid waste and hazardous waste. Attached Figure Description
[0034] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation
[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0036] Please see Figure 1 This invention provides a process for producing agricultural potassium sulfate, desulfurizing sodium bicarbonate, and agricultural ammonium chloride, comprising the following steps:
[0037] Step 1, Raw Material Processing: Prepare concentrated brine and mother liquor as raw materials, as well as liquid ammonia and CO2; the raw materials are the mixed salts (hazardous waste) produced by the separation treatment of mine water and concentrated brine generated in the coal mine and coal chemical production process, the various salts separated, and the concentrated brine and mother liquor produced by membrane filtration and evaporation processes; liquid ammonia is purchased externally, transported by cryogenic tank trucks and unloaded into liquid ammonia storage tanks, vaporized into ammonia gas by a vaporizer, and then sent into the system by a compressor for use as a production raw material; CO2 is obtained from the external exhaust gas of the coal chemical plant or purchased liquid CO2 gas, which is sent into the system by a CO2 compressor for use by the carbonization unit;
[0038] Step 2, Brine Preparation and Refining: The raw materials are processed through a brine preparation process, followed by a refining (purification) process to remove impurities;
[0039] Step 3, Membrane separation and concentration: The monovalent and divalent salts are first separated using a two-stage nanofiltration process, and then the initial concentration is performed using an ultrafiltration membrane;
[0040] Step 4, Evaporation and Concentration: The monovalent and divalent brine after separation and concentration are fed into the evaporation system for concentration. The evaporation and concentration adopts a process flow of four-effect five-body two-stage co-current + MVR heat pump. The four effects in the process flow of four-effect five-body two-stage co-current + MVR heat pump are four evaporation units in series: effect I, effect II, effect III, and effect IV. The four effects are the basis for the cascade utilization of waste heat.
[0041] The five-body evaporation system consists of five independent equipment bodies, namely four evaporation bodies and one MVR heat pump body. The MVR heat pump serves as an auxiliary heat source, compressing and heating the low-temperature secondary steam in the system and sending it back to the first effect as heating steam to further recover low-grade waste heat and maximize energy saving.
[0042] The two-stage co-current process divides the four-effect system into two stages. The first stage process, consisting of effects I and II, treats the divalent salt system; the second stage process, consisting of effects III and IV, treats the monovalent salt system. The salt solution flows sequentially through the corresponding effect body, ensuring independent concentration and crystallization of monovalent and divalent salts while also enabling the co-current utilization of steam waste heat in the four effect bodies.
[0043] Step 5, Flash evaporation purification of heptahydrate nitrate: During the evaporation and crystallization process, Na2SO4 is used... Sodium sulfate is purified by flash evaporation process using 7H2O. The divalent salt system is evaporated and crystallized in the first and second effects. Since the divalent salt system contains monovalent salt, the drastic change in the solubility of sodium sulfate and sodium chloride at different temperatures is utilized. The sodium sulfate solution in the second effect is pumped out and sent to the flash evaporator to form sodium sulfate heptahydrate crystals. The crystals are separated and dehydrated by centrifuge to obtain high-purity sodium sulfate. The molar ratio of divalent salt to monovalent salt is 1:1.
[0044] Step Six: Preparation of Agricultural Potassium Sulfate: This includes a first-stage reaction to produce potassium sulfate, a second-stage reaction to produce potassium sulfate, washing, filtering, and dehydrating the potassium sulfate, and drying the potassium sulfate. The produced heptahydrate potassium sulfate is directly fed into the potassium sulfate reactor via a belt conveyor without drying. In the first-stage reactor, a saturated sodium sulfate solution is prepared, and an excess of solid potassium chloride is added to react at room temperature to form a double salt of potassium sulfate. After the saturated potassium sulfate solution is removed, it enters the second-stage reactor to react fully with potassium chloride to produce potassium sulfate and sodium chloride. In the case of excess potassium chloride, potassium sulfate crystallizes. After removal, it is dehydrated and washed using a belt filter, then dehydrated a second time using a centrifuge, and then sent to a drying oven for drying. The dried product is then sent to the packaging process for packaging and warehousing.
[0045] Step 7: Preparation of desulfurized sodium bicarbonate and agricultural ammonium chloride: The monovalent brine system is pumped into the third and fourth effects of evaporation. The saturated brine slurry is taken out from the fourth effect and separated and dehydrated by centrifuge. The obtained sodium chloride is dehydrated by centrifuge and sent to the saturated brine preparation process. The saturated brine is pumped into the ammonia absorption tower. Ammonia gas comes from the liquid ammonia vaporizer. Saturated ammonia brine is prepared in the ammonia absorption tower. The saturated ammonia brine reacts with carbon dioxide in the carbonization tower to produce sodium bicarbonate and ammonium chloride. The slurry after the reaction is completed is filtered and washed by a belt filter. The filtered mother liquor is sent to the cold salting-out tank for cold precipitation and salting-out. The filter cake filtered by the belt filter is sodium bicarbonate. It is sent to the airflow drying tube for drying and then packaged and stored. The crystals obtained from cold precipitation and salting-out are ammonium chloride. After washing and filtering by a belt filter, it is sent to the centrifuge for secondary dehydration and then sent to the dry ammonium furnace for drying. After drying, the product is sent to the silo for packaging and storage by an airflow conveyor.
[0046] In summary:
[0047] This invention features extremely low energy consumption in its production process. Evaporation employs a four-effect, five-body + MVR evaporation process, utilizing the energy-saving characteristics of multi-effect evaporation and improving efficiency with an MVR heat pump. It eliminates the need for a fiberglass cooling tower system, fully utilizing waste heat. Addressing the tendency of ammonium chloride to clump and stick to walls during drying, a new type of energy-efficient dry ammonium furnace is used, resulting in significant energy savings and a long equipment operating cycle. The invention also employs a two-stage reaction process to produce potassium sulfate from a supersaturated sodium sulfate solution, improving reaction efficiency and virtually eliminating byproduct production.
[0048] Specifically:
[0049] 1. This invention uses solid waste such as miscellaneous salts and concentrated brine produced by coal mines and coal chemical industry as the main raw materials to prepare high-value-added agricultural potassium sulfate, desulfurized sodium bicarbonate and agricultural ammonium chloride, realizing the resource utilization of solid waste and hazardous waste, avoiding the land occupation and environmental pollution problems caused by landfill disposal, and providing a demonstration for the resource utilization of concentrated brine with complex components.
[0050] 2. Extremely low production energy consumption: The evaporation and concentration adopts a four-effect, five-body, two-stage co-current + MVR heat pump process, which utilizes the energy-saving characteristics of multi-effect evaporation and the waste heat recovery function of MVR heat pump, eliminating the need for a fiberglass cooling tower system and making full use of waste heat; the ammonium chloride drying adopts a new type of energy-saving dry ammonium furnace, which has significant energy-saving effect and long equipment operation cycle.
[0051] 3. High reaction efficiency and no by-products: The process technology of preparing potassium sulfate by two-stage reaction of preparing supersaturated sodium sulfate solution is adopted. By reacting in stages and controlling the condition of excess potassium chloride, the reaction efficiency of potassium sulfate preparation is greatly improved, and by-products are basically eliminated, thereby improving product purity and raw material utilization.
[0052] 4. Emission reduction and environmental protection with significant social benefits: CO2 is produced by external exhaust gas from coal chemical industry or by purchasing liquid CO2, achieving CO2 emission reduction and recycling; the production process has no solid waste or wastewater discharge, meeting environmental protection requirements; among the products prepared, agricultural potassium sulfate is a high-quality binary potassium fertilizer, desulfurized sodium bicarbonate is the main catalyst for dry desulfurization, and agricultural ammonium chloride is a basic fertilizer. The products have a wide range of applications and have significant economic and social benefits.
[0053] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A process for producing agricultural-grade potassium sulfate, desulfurized sodium bicarbonate, and agricultural-grade ammonium chloride, characterized in that: Includes the following steps: Step 1: Raw material processing, wherein the raw materials include concentrated brine and mother liquor, liquid ammonia and CO2; Step 2: Brine preparation and refining. The raw materials are processed through a brine preparation process, followed by a refining process to remove impurities, resulting in a pure brine solution. Step 3: Membrane separation and concentration. A two-stage nanofiltration process is used to separate the monovalent and divalent salts in the pure brine solution. Then, an ultrafiltration membrane is used to initially concentrate the separated salt solution to obtain monovalent concentrated brine and divalent concentrated brine. Step 4: Evaporation and concentration. The monovalent and divalent concentrated brine are fed into an evaporation system for concentration. The evaporation system adopts a process flow of four-effect five-body two-stage co-current + MVR heat pump. Step 5: Flash evaporation purification of sodium sulfate heptahydrate. During the evaporation and crystallization process, sodium sulfate is purified using the Na2SO4・7H2O flash evaporation process. Step Six: Preparation of agricultural potassium sulfate, which includes a first-stage reaction to produce potassium sulfate, a second-stage reaction to produce potassium sulfate, and potassium sulfate treatment; Step 7: Preparation of desulfurized sodium bicarbonate and agricultural ammonium chloride.
2. The process for preparing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride according to claim 1, characterized in that: The concentrated brine and mother liquor are the mixed salts, various salts separated from mine water and concentrated brine produced during coal mining and coal chemical production processes, as well as the concentrated brine and mother liquor produced during membrane filtration and evaporation processes. The liquid ammonia is vaporized by a vaporizer and then sent into the system by a compressor; The CO2 is fed into the system via a CO2 compressor.
3. The process for preparing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride according to claim 1, characterized in that: The process flow of the four-effect five-body two-stage co-current + MVR heat pump consists of four evaporation units connected in series: effect I, effect II, effect III, and effect IV. These four effects form the basis for the cascade utilization of waste heat. The five-body evaporation system includes five independent equipment bodies, namely four evaporation bodies and one MVR heat pump body. The MVR heat pump serves as an auxiliary heat source, compressing and heating the low-temperature secondary steam in the system and sending it back to the first effect as heating steam to further recover low-grade waste heat and maximize energy saving. The two-stage co-current process divides the four-effect system into two stages. The first stage, consisting of effects I and II, processes the divalent salt system; the second stage, consisting of effects III and IV, processes the monovalent salt system. The salt solution flows sequentially through the corresponding effect body, ensuring both the independent concentration and crystallization of monovalent and divalent salts and enabling the co-current utilization of waste heat from steam within the four effect bodies.
4. The process for preparing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride according to claim 2, characterized in that: Step five includes the following steps: The divalent salt system was evaporated and crystallized using the first and second effects. Since the divalent salt system contains monovalent salts, the drastic changes in the solubility of sodium sulfate and sodium chloride at different temperatures were utilized. The sodium sulfate solution in the second effect was pumped out and sent to the flash evaporator, where the sodium sulfate formed heptahydrate nitrate crystals. The crystals were then separated and dehydrated by centrifuge to obtain high-purity sodium sulfate.
5. The process for preparing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride according to claim 4, characterized in that: The molar ratio of the divalent salt to the monovalent salt is 1:
1.
6. The process for preparing agricultural potassium sulfate, desulfurizing sodium bicarbonate, and agricultural ammonium chloride according to claim 4, characterized in that: Step six includes the following steps: Potassium sulfate preparation by a single-stage reaction: The produced sodium sulfate heptahydrate is fed directly into a potassium sulfate reactor via a belt conveyor without drying. In the single-stage reactor, a saturated sodium sulfate solution is prepared, and an excess of potassium chloride solid is added to react at room temperature to generate a double salt of potassium sulfate. Water is then added to prepare a saturated potassium sulfate solution. Two-stage reaction to produce potassium sulfate: A saturated solution of potassium sulfate is introduced into a two-stage reactor and reacts fully with potassium chloride to produce potassium sulfate and sodium chloride. In the case of excess potassium chloride, potassium sulfate crystallizes. Potassium sulfate treatment: After the potassium sulfate is removed, it is dehydrated and washed using a belt filter, then dehydrated a second time using a centrifuge, and then sent to a drying oven for drying. The dried product is then sent to the packaging process and packaged for storage.
7. The process for preparing agricultural potassium sulfate, desulfurized sodium bicarbonate, and agricultural ammonium chloride according to claim 6, characterized in that: Step seven includes the following steps: The monovalent concentrated brine was pumped into the third and fourth effects for evaporation. The saturated brine was taken out in the fourth effect and separated and dehydrated by centrifuge. The sodium chloride obtained was used to prepare saturated brine. Saturated brine is pumped into an ammonia absorption tower, where ammonia gas is obtained from a liquid ammonia vaporizer. Saturated ammonia brine is prepared in the ammonia absorption tower. Saturated ammonia brine reacts with carbon dioxide in a carbonization tower to produce sodium bicarbonate and ammonium chloride. The slurry after the reaction is completed is filtered and washed by a belt filter. The filtered mother liquor is sent to a cold salting-out tank for cold precipitation and salting out. The filter cake, or baking soda, produced by the belt filter is sent into an airflow drying tube for drying, and then packaged and stored. The crystals formed by cold precipitation and salt precipitation are ammonium chloride. After being washed and filtered by a belt filter, the product is sent to a centrifuge for secondary dehydration, and then sent to a dry ammonium furnace for drying. After drying, the product is sent to a silo for packaging and storage by a pneumatic conveyor.