Coal chemical gasification ash water isothermal low-pressure environment-friendly low-carbon type deamination method

Abstract

The application discloses a coal chemical gasification ash water isothermal low-pressure environment-friendly low-carbon type deamination method, and mainly comprises the following steps: after the impurity removal of gasification ammonia-containing ash water, the ash water is mixed with flash condensate saturated with carbon dioxide in a raw material water mixing tank, and then enters an ash water deamination tower as raw material water; low flash gas purification utilizes generated secondary steam, and low flash gas incondensable gas, flash condensate stripping acid gas, carbon dioxide and the like enter the ash water deamination tower as deamination medium, and ammonia gas in the ash water is stripped; the tower is not heated and not warmed, the pressure in the tower is maintained according to the saturated steam pressure under the temperature of the raw material water entering the tower; the removed ammonia gas forms low-temperature ammonia water, and enters an original shift stripping tower and an ammonia recovery system of an enterprise for recycling. Finally, the problems of scaling and plugging in the ash water deamination and conveying processes are completely solved, the purification utilization of low flash gas is realized, water vapor consumption is completely replaced, the consumption of circulating water for low flash gas condensation is reduced, the ash water reaches the standard for environmental protection, carbon emission is indirectly reduced, and the isothermal, low-pressure, environment-friendly and low-carbon ammonia-containing ash water treatment target is achieved. The application has no steam consumption, low process investment and operation cost, and good economic benefits, and the investment recovery period is 3-5 years.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment in chemical industries such as coal chemical, petrochemical, and new energy chemical. Specifically, it relates to an isothermal low-pressure environmentally friendly low-carbon ammonia removal method for gasification ash water, and a method for recovering and utilizing the removed ammonia. Background Technology

[0002] High-temperature, high-pressure washing water generated during coal gasification and coal gas washing and purification processes in coal chemical, petrochemical, and new energy chemical enterprises is called gasification black water. This black water passes sequentially through a high-pressure flash tank, a medium-pressure flash tank, a low-pressure flash tank, and a vacuum flash tank, where high-flash gas, medium-flash gas, low-flash gas, and true flash gas are flashed out, respectively. After entering the black water clarification tank of the slag water system, solid-liquid separation is performed. The solid phase is filtered by a filter press, and the filter cake is transported off-site for reuse. The filtrate is returned to the clarification tank for further solid-liquid separation. The supernatant of the liquid phase overflows into the ash water tank of the original slag water system, becoming gasification ammonia-containing ash water. After being pumped by a low-pressure ash water pump, a portion is returned to the evaporation hot water tower or deaerator of the slag water system for reuse in the gasification system. The remaining approximately 40%-60% (by mass) is cooled by an ash water cooler and discharged to the downstream wastewater biological treatment system for further treatment to meet discharge standards or for reuse. Because the wastewater biological treatment system has strict requirements on the ammonia nitrogen content and temperature of the ash water, the ash water must be purified by ammonia removal and cooled before being discharged into the biological treatment system. Furthermore, since the ash water originates from the supernatant after multi-stage flash evaporation and sedimentation of gasified black water, the scaling factors such as calcium and magnesium in it are saturated at a certain temperature and have already crystallized. This makes it difficult to fully separate and settle in the clarification tank, resulting in a small amount of crystalline particles remaining in the ash water entering the ash water tank. During the ash water transportation and reuse or cooling and discharge process, these particles are highly likely to adhere to the pipe walls and heat exchangers. Scale buildup in heaters and other components affects heat exchange efficiency and easily clogs pipes, requiring companies to expend significant manpower, financial resources, and materials annually for cleaning and restoration. Furthermore, despite multi-stage flash evaporation, the ash water still contains a certain amount of ammonia nitrogen. Depending on the gasification pressure, raw coal quality, and treatment process, the ammonia nitrogen level in the ash water remains between 400-1200 mg / L, failing to meet the ammonia nitrogen standard (200-300 mg / L) for direct entry into the biological treatment system. Therefore, ammonia removal treatment is necessary. Companies typically use steam stripping to remove ammonia from the ash water. Currently, a tower temperature of 105-140℃ and a tower pressure of 125-351 kPa are generally used for steam stripping. Since the temperature of ash water is generally between 65-85°C, as it enters the tower and is heated to 105-139°C, the calcium and magnesium ions in the ash water will further crystallize and precipitate due to the reduced solubility. In addition, there are already incompletely settled and separated crystalline particles in the ash water, which will quickly form scale on the trays, downcomers, and tower walls, clogging the trays and pipelines. Under normal circumstances, the stripping tower can hardly continue to operate after 10-15 days, and cannot achieve the designed ammonia removal effect. Even with improved processes, such as first removing impurities and purifying the ash water before stripping, the operating time is unlikely to exceed one month. This situation has plagued the industry for many years and has become an environmental and technological bottleneck in the enterprise's slag and wastewater treatment process.Previously, when environmental regulations were less stringent, this ammonia-containing ash water could be discharged with minimal effort or mixed with other clean production water before being discharged. However, under the current increasingly severe environmental regulations and the higher requirements of refined large-scale production, enterprises face serious environmental risks and technological challenges. In addition, the heavy cleanup tasks have affected the normal production process. Furthermore, the ammonia removal from ash water requires a large amount of steam resources, resulting in serious energy waste and indirectly increasing carbon emissions.

[0003] In coal chemical enterprises, a portion of the low-flash gas (temperature 115-152℃, absolute pressure 169Kpa-502Kpa) enters the gasification deaerator to heat the ash water. The unused portion is cooled by circulating cooling water and discharged into the ash water tank, becoming part of the gasification ash water. This wastes the heat energy of the low-flash gas and increases circulating water consumption. Some enterprises use the low-flash gas for stripping ammonia removal or heating cold materials, but due to the high impurity content, heat exchange efficiency is affected, making full utilization difficult.

[0004] Therefore, chemical enterprises in industries such as coal chemical, petrochemical, and new energy chemical urgently need a method that can remove and recover ammonia from ammonia-containing ash water during gasification, solve the scaling problem in internal components such as trays of the ash water deammoniation tower and in ash water conveying pipelines and equipment, reduce water vapor consumption in ash water deammoniation, and simultaneously meet the environmental protection requirements of downstream biochemical treatment systems while recovering ammonia, utilizing low-flash gas, and systematically solving the scaling problem in ash water. This would achieve comprehensive resource utilization and environmentally friendly, low-carbon production, with relatively moderate investment and, as far as possible, positive operating returns. Only in this way can the environmental and technological bottlenecks of the aforementioned industries and enterprises be solved, promoting their long-term healthy development. Summary of the Invention

[0005] The purpose of this invention is to provide an isothermal, low-pressure, environmentally friendly, and low-carbon ammonia removal method for coal chemical gasification ash water. This method solves problems such as scaling in tower internals, ash water conveying pipelines, and equipment during the ammonia removal process, fully meeting the ammonia nitrogen requirements for further biochemical treatment in enterprises. Ammonia is recovered and recycled into the enterprise's shift stripping tower or purification unit ammonia recovery system. Simultaneously, low-flash gas is purified and utilized, completely replacing all water vapor consumption in the ash water ammonia removal process, achieving the treatment goals of isothermal, low-pressure, environmental protection, and low carbon emissions. Furthermore, it realizes waste heat recovery and comprehensive resource utilization, turning waste into treasure, ultimately improving production quality, enhancing socio-economic benefits and environmental and low-carbon effects, and increasing enterprise productivity.

[0006] To achieve the above objectives, the present invention adopts the following solution: an isothermal low-pressure environmentally friendly low-carbon ammonia removal method for coal chemical gasification ash water, comprising the following steps:

[0007] A. The low-pressure ash water pump (1) of the slag water system introduces the gasified ammonia-containing ash water and adds sodium carbonate alkaline solution through the dosing system to adjust the pH value to between 8 and 11. The temperature is 60-90℃. The ash water enters the lower part of the closed ash water impurity remover (2) of the ash water removal system and flows from bottom to top. The automatic scraper (3) rotates at a uniform speed. Its blades scrape off the impurities and slurry deposited on the wall of the impurity remover and the bottom sedimentation inclined plate (4). After the slurry flows down, it is pumped into the original clarification tank of the slag water system along with the bottom ash water through the impurity removal slurry pump (5). It is separated into solid and liquid in the clarification tank together with the gasified black water. The solid phase enters the original filter press for filtration. The filter cake is transported out for use. The filtrate is returned to the clarification tank for solid-liquid separation again. The supernatant of the liquid phase overflows into the ash water tank of the original slag water system and becomes gasified ammonia-containing ash water. Then, through the low-pressure ash water pump (1), part of it is returned to the gasification for reuse, and the rest enters the ash water removal system.

[0008] The supernatant at the top of the closed ash water separator (2) is introduced into the raw water mixing tank (7) via the ash water transfer pump (6).

[0009] B. Flash condensate feed pump (8) pumps flash condensate (either low flash condensate, true flash condensate, or any mixture thereof) into the upper part of flash condensate stripping tower (9), and after distribution, it flows from top to bottom; at the same time, the carbon dioxide (of which carbon dioxide accounts for 96%-99.5%, carbon monoxide accounts for 3%-0.3%, hydrogen accounts for 0.5%-0.1%, nitrogen accounts for 0.5%-0.1%, by mass ratio) of the original purification unit of the enterprise, with an absolute pressure of 300-400Kpa and a temperature of room temperature, is partially fed into the flash condensate stripping tower (9). 0.1%-5% (by mass) of the flash condensate feed is introduced into the bottom of the flash condensate stripping tower (9) to strip the flash condensate from bottom to top. The stripped non-condensable gas (ammonia 2%-10%, carbon dioxide 95%-89.64%, carbon monoxide 2.2%-0.2%, hydrogen 0.4%-0.08%, nitrogen 0.4%-0.08% by mass) is introduced into the lower acid gas inlet of the ash water deammoniation tower (13); another part of the carbon dioxide is directly introduced into the bottom of the ash water deammoniation tower (13).

[0010] The flash condensate stripping tower (9) maintains an absolute pressure of 101-232 kPa. No heat source is used for heating; instead, carbon dioxide is used for pressure maintenance. After the flash condensate reaches the bottom of the stripping tower (9), the temperature is 40-90℃. A portion (5%-30% by mass) is pumped by the cleaning water pump (10) into the ash water deammoniation tower (13) and the flash condensate preheater (17) as cleaning water (intermittently, 50% each by mass). The remainder is pumped by the flash condensate discharge pump (11) into the raw material water mixing tank (7) to mix with the ash water in the tank as deammoniation raw material water.

[0011] C. A portion of the low-flash gas discharged from the original low-pressure flash tank (5%-20% by mass of the feed water of the ash water deammoniation tower (13)) is introduced into the lower part of the low-flash gas purification tower (15) and flows from bottom to top. The purified water from the bottom of the original shift stripping tower (which can be replaced by demineralized water) is introduced into the upper part of the low-flash gas purification tower (15) by the original purified water booster pump at 10%-20% by mass of the low-flash gas entering the low-flash gas purification tower (15). After distribution, it flows from top to bottom. The flow of the low-flash gas in the tower is used to wash and purify it. The purified condensate flows out of the tower bottom and is pumped into the clarification tank of the raw slag water system by the low-flash gas purified condensate pump (16). The purified low-flash gas is discharged from the tower and introduced into the shell side of the reboiler (17). It is heated and introduced into the boiler water in the tube side of the reboiler via the evaporator (18) and pumped into the reboiler tube side by the circulating pump (19). The condensed low-flash gas mixture is discharged from the bottom of the reboiler and flows into the low-flash condensate separator (20) by gravity. At the same time, the original low-pressure flash gas... The remaining low-flash gas discharged from the steam tank first enters the flash condensate preheater (21), preheats the low-flash condensate separator (20), and is then pumped into the flash condensate preheater (21) by the low-flash condensate booster pump (22). After entering the low-flash gas water cooler (23), it is further condensed and cooled by circulating water, and then enters the low-flash condensate separator (20). Together with the low-flash condensate mixture discharged from the reboiler (17), the gas and liquid phases are separated, and the liquid phase low-flash condensate is self-separated. The liquid is discharged from the bottom of the device (20). Part of it is pumped into the flash condensate preheater (21) by the low flash condensate booster pump (22). After being preheated, it is discharged to the outlet of the low-pressure ash water pump (1) of the raw slag water system to the gasification reuse pipeline and returned to the gasification system (deaerator or evaporation hot water tower) for reuse. The other part flows into the inlet pipeline of the flash condensate feed pump (8) by gravity. The non-condensable gas separated by the low flash condensate separator (20) is introduced into the flash vapor inlet in the middle of the ash water deammoniation tower (13).

[0012] The boiler water heated in the reboiler (17) tubes returns to the evaporator (18), where it flashes to generate secondary steam, which is then directly fed into the bottom of the ash water deammoniation tower (13). At the bottom of the evaporator (18), 2%-10% of the boiler water entering the evaporator is discharged as the remaining boiler water. This water is then pumped back to the outlet pipe of the low flash gas purification tower condensate via the boiler water discharge pump (31), and together with the condensate, pumped back to the original clarification tank of the slag water system via the low flash gas purification condensate pump.

[0013] D. The raw water is drawn from the raw water mixing tank (7) and pumped into the upper part of the stripping section of the ash water deammoniation tower (13) by the raw water pump (12), flowing from top to bottom;

[0014] The secondary steam generated by flash evaporation in the evaporator (18) introduced into the bottom of the deammoniation tower (13), together with the low flash non-condensable gas discharged from the low flash condensate separator (20) introduced into the flash steam inlet of the deammoniation tower (13), the acid gas discharged from the flash condensate stripping tower (9) introduced into the acid gas inlet, and the carbon dioxide directly introduced into the bottom of the tower, strip and purify the raw water from bottom to top.

[0015] Water ring vacuum pumps (27) and (29) are installed to extract non-condensable gas from the ammonia removal tower (13) and maintain an absolute pressure of 20-100 kPa at the top of the ammonia removal tower (13) (the specific pressure is determined according to the saturated vapor pressure corresponding to the feed water temperature, and the feed water temperature is not increased in the tower). Ammonia-containing vapor is discharged from the top of the ammonia removal tower (13), enters the ammonia water condenser (24) for condensation, and then enters the ammonia liquid separator (25) for gas-liquid separation. After the liquid phase is pressurized by the dilute ammonia water pump (26), a portion (30%-95%) of it is separated. The mass ratio) refluxes the ammonia stripping tower (13) to the distillation section, and the rest is introduced into the original shift stripping tower or the original purification device ammonia recovery system to recover ammonia water. The gas phase separated by the ammonia liquid separator (25) enters the vacuum pump (27) and then enters the demineralized water scrubber (28). After being scrubbed with demineralized water, it is introduced into the vacuum pump (29), and the gas phase is extracted and then enters the demineralized water scrubber (30). The gas phase is introduced into the original acid gas flare, and after combustion, it meets the emission standards. The liquid phases of the scrubbers (28) and (30) are both refluxed to the bottom of the ammonia liquid separator (25).

[0016] When the raw water reaches the bottom of the deammoniation tower (13), the ammonia content in it meets the ammonia nitrogen requirements for further treatment in the biochemical treatment system, and becomes purified ash water. It is introduced into the inlet pipe of the raw ash water cooler of the slag water system by the purified ash water pump (14), and after cooling, it is discharged into the biochemical treatment system for further treatment.

[0017] The main features of this invention are as follows: First, the low-flash gas is thoroughly purified, and its heat is used to produce low-temperature, low-pressure secondary steam to replace steam as the main deammoniation medium and the sole heat source for the ash water deammoniation tower. Second, the deammoniation temperature of the ash water deammoniation tower is maintained between 60-90℃, meaning that the raw water, composed of ash water and flash condensate, enters the ash water deammoniation tower without heating or temperature rise, thus solving the scaling problem caused by calcium and magnesium ion crystallization during ash water heating. Third, the flash condensate stripping tower is used to adjust the flash condensate into a weakly acidic solution after absorbing carbon dioxide. After mixing with the purified ammonia-containing ash water in the material buffer tank, the remaining calcium and magnesium impurities in the ammonia-containing ash water are redissolved and absorbed into the solution, further reducing scaling during the ash water deammoniation process. Fourth, in the ammonia-containing ash water deammoniation tower, the low-flash gas utilizes the generated secondary steam, the low-flash gas non-condensable gas introduced at the flash steam inlet, and the acid gas introduced at the acid gas inlet and discharged from the flash condensate stripping tower. The method employs several techniques: First, it utilizes carbon dioxide, introduced directly from the bottom of the stripping tower along with the reactive gas, as a heat source and stripping medium for the ammonia removal tower. This maintains the slightly acidic nature of the raw water within the tower without raising the temperature, further dissolving residual trace amounts of calcium and magnesium ions, as well as any calcium and magnesium ions that might precipitate due to slight temperature fluctuations. This effectively solves the problem of scaling and clogging within the tower. Second, it features a special design for the ash water stripping tower, incorporating a self-cleaning system. The flash condensate, saturated with carbon dioxide, is used to periodically and automatically clean the tower trays, preventing undissolved calcium and magnesium ions from clogging the trays and affecting the ammonia removal efficiency. Third, this method seamlessly integrates with existing wastewater systems, fully utilizing existing clarifiers, filter presses, booster pumps, low-flash gas water coolers, ash water coolers, and other equipment and pipelines. This reduces project investment and operating costs. After the project is operational, it will not only solve a series of existing problems and achieve significant environmental, low-carbon, and social benefits, but also generate economic benefits. This method can also be applied to the comprehensive treatment and utilization of similar wastewater in industries such as coal chemical, petrochemical, and new energy chemical industries. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the experimental apparatus in an embodiment of the present invention. Detailed Implementation

[0019] A method for isothermal low-pressure environmentally friendly low-carbon ammonia removal from coal chemical gasification ash water includes the following steps:

[0020] A. The low-pressure ash water pump (1) of the slag water system introduces the gasified ammonia-containing ash water and adds alkaline solutions such as sodium carbonate through the dosing system to adjust the pH value to between 8 and 11. The temperature is 60-90℃. The ash water enters the lower part of the closed ash water impurity remover (2) of the ash water removal system and flows from bottom to top. The automatic scraper (3) rotates at a uniform speed. Its blades scrape off the impurities and slurry deposited on the wall of the impurity remover and the bottom sedimentation inclined plate (4). After the slurry flows down, it is pumped into the original clarification tank of the slag water system along with the bottom ash water through the impurity removal slurry pump (5). It is separated into solid and liquid in the clarification tank together with the gasified black water. The solid phase enters the original filter press for filtration. The filter cake is transported out for use. The filtrate is returned to the clarification tank for solid-liquid separation again. The supernatant of the liquid phase overflows into the ash water tank of the original slag water system and becomes gasified ammonia-containing ash water. Then, through the low-pressure ash water pump (1), part of it is returned to the gasification for reuse, and the rest enters the ash water removal system.

[0021] The supernatant at the top of the closed ash water separator (2) is introduced into the raw water mixing tank (7) via the ash water transfer pump (6).

[0022] B. Flash condensate feed pump (8) pumps flash condensate (either low flash condensate, true flash condensate, or any mixture thereof) into the upper part of the flash condensate stripping tower (9), and after distribution, it flows from top to bottom; at the same time, the carbon dioxide (carbon dioxide accounts for 96%-99.5%, carbon monoxide accounts for 3%-0.3%, hydrogen accounts for 0.5%-0.1%, nitrogen accounts for 0.5%-0.1%, mass ratio) of the original purification unit of the enterprise, with an absolute pressure of 300-400Kpa and a temperature of room temperature, is partially fed into the flash condensate stripping tower (9). 0.1%-5% (by mass) of the flash condensate feed is introduced into the bottom of the flash condensate stripping tower (9) to strip the flash condensate from bottom to top. The stripped non-condensable gas (ammonia 2%-10%, carbon dioxide 95%-89.64%, carbon monoxide 2.2%-0.2%, hydrogen 0.4%-0.08%, nitrogen 0.4%-0.08% by mass) is introduced into the lower acid gas inlet of the ash water deammoniation tower (13); another part of the carbon dioxide is directly introduced into the bottom of the ash water deammoniation tower (13).

[0023] The flash condensate stripping tower (9) maintains an absolute pressure of 101-232 kPa. No heat source is used for heating; instead, carbon dioxide is used for pressure maintenance. After the flash condensate reaches the bottom of the stripping tower (9), the temperature is 40-90℃. A portion (5%-30% by mass) is pumped by the cleaning water pump (10) into the ash water deammoniation tower (13) and the flash condensate preheater (17) as cleaning water (intermittently, 50% each by mass). The remainder is pumped by the flash condensate discharge pump (11) into the raw material water mixing tank (7) to mix with the ash water in the tank as deammoniation raw material water.

[0024] C. A portion of the low-flash gas discharged from the original low-pressure flash tank (5%-20% by mass of the feed water of the ash water deammoniation tower (13)) is introduced into the lower part of the low-flash gas purification tower (15) and flows from bottom to top. The purified water from the bottom of the original shift stripping tower (which can be replaced by demineralized water) is introduced into the upper part of the low-flash gas purification tower (15) by the original purified water booster pump at 10%-20% by mass of the low-flash gas entering the low-flash gas purification tower (15). After distribution, it flows from top to bottom. The flow of the low-flash gas in the tower is used to wash and purify it. The purified condensate flows out of the tower bottom and is pumped into the clarification tank of the raw slag water system by the low-flash gas purified condensate pump (16). The purified low-flash gas is discharged from the tower and introduced into the shell side of the reboiler (17). It is heated and introduced into the boiler water in the tube side of the reboiler via the evaporator (18) and pumped into the reboiler tube side by the circulating pump (19). The condensed low-flash gas mixture is discharged from the bottom of the reboiler and flows into the low-flash condensate separator (20) by gravity. At the same time, the original low-pressure flash gas... The remaining low-flash gas discharged from the steam tank first enters the flash condensate preheater (21), preheats the low-flash condensate separator (20), and is then pumped into the flash condensate preheater (21) by the low-flash condensate booster pump (22). After entering the low-flash gas water cooler (23), it is further condensed and cooled by circulating water, and then enters the low-flash condensate separator (20). Together with the low-flash condensate mixture discharged from the reboiler (17), the gas and liquid phases are separated, and the liquid phase low-flash condensate is self-separated. The liquid is discharged from the bottom of the device (20). Part of it is pumped into the flash condensate preheater (21) by the low flash condensate booster pump (22). After being preheated, it is discharged to the outlet of the low-pressure ash water pump (1) of the raw slag water system to the gasification reuse pipeline and returned to the gasification system (deaerator or evaporation hot water tower) for reuse. The other part flows into the inlet pipeline of the flash condensate feed pump (8) by gravity. The non-condensable gas separated by the low flash condensate separator (20) is introduced into the flash vapor inlet in the middle of the ash water deammoniation tower (13).

[0025] The boiler water heated in the reboiler (17) tubes returns to the evaporator (18), where it flashes to generate secondary steam, which is then directly fed into the bottom of the ash water deammoniation tower (13). At the bottom of the evaporator (18), 2%-10% of the boiler water entering the evaporator is discharged as the remaining boiler water. This water is then pumped back to the outlet pipe of the low flash gas purification tower condensate via the boiler water discharge pump (31), and together with the condensate, pumped back to the original clarification tank of the slag water system via the low flash gas purification condensate pump.

[0026] D. The raw water is drawn from the raw water mixing tank (7) and pumped into the upper part of the stripping section of the ash water deammoniation tower (13) by the raw water pump (12), flowing from top to bottom;

[0027] The secondary steam generated by flash evaporation in the evaporator (18) introduced into the bottom of the deammoniation tower (13), together with the low flash non-condensable gas discharged from the low flash condensate separator (20) introduced into the flash steam inlet of the deammoniation tower (13), the acid gas discharged from the flash condensate stripping tower (9) introduced into the acid gas inlet, and the carbon dioxide directly introduced into the bottom of the tower, strip and purify the raw water from bottom to top.

[0028] Water ring vacuum pumps (27) and (29) are installed to extract non-condensable gas from the ammonia removal tower (13) and maintain an absolute pressure of 20-100 kPa at the top of the ammonia removal tower (13) (the specific pressure is determined according to the saturated vapor pressure corresponding to the feed water temperature, and the feed water temperature is not increased in the tower). Ammonia-containing vapor is discharged from the top of the ammonia removal tower (13), enters the ammonia water condenser (24) for condensation, and then enters the ammonia liquid separator (25) for gas-liquid separation. After the liquid phase is pressurized by the dilute ammonia water pump (26), a portion (30%-95%) of it is separated. The mass ratio) refluxes the ammonia stripping tower (13) to the distillation section, and the rest is introduced into the original shift stripping tower or the original purification device ammonia recovery system to recover ammonia water. The gas phase separated by the ammonia liquid separator (25) enters the vacuum pump (27) and then enters the demineralized water scrubber (28). After being scrubbed with demineralized water, it is introduced into the vacuum pump (29), and the gas phase is extracted and then enters the demineralized water scrubber (30). The gas phase is introduced into the original acid gas flare, and after combustion, it meets the emission standards. The liquid phases of the scrubbers (28) and (30) are both refluxed to the bottom of the ammonia liquid separator (25).

[0029] When the raw water reaches the bottom of the deammoniation tower (13), the ammonia content in it meets the ammonia nitrogen requirements for further treatment in the biochemical treatment system, and becomes purified ash water. It is introduced into the inlet pipe of the raw ash water cooler of the slag water system by the purified ash water pump (14), and after cooling, it is discharged into the biochemical treatment system for further treatment.

[0030] The main equipment of this invention includes:

[0031] 1. Isothermal low-pressure ammonia removal and ammonia recovery system: It consists of an ammonia removal tower for ash water (13), a raw water mixing tank (7), a raw water pump (12), a purified ash water pump (14), an ammonia water condenser (24), an ammonia liquid separator (25), a dilute ammonia water pump (26), a vacuum pump (27) (29), a demineralized water scrubber (28) (30) and other equipment;

[0032] As shown in the attached diagram of the instruction manual: the raw water is pumped into the upper part of the stripping section of the ash water deammoniation tower (13) by the raw water pump (12); the stripping medium is discharged from the top of the flash condensate stripping tower (9) and introduced into the upper middle part of the stripping section of the ash water deammoniation tower (13), discharged from the top of the low flash condensate separator (20) and introduced into the middle part of the stripping section of the ash water deammoniation tower (13), discharged from the top of the evaporator (18) and introduced into the bottom of the ash water deammoniation tower (13), and introduced into the lower part of the secondary steam inlet of the bottom of the ash water deammoniation tower (13) by the carbon dioxide feed pipe of the original purification unit; the purified ash water formed by stripping in the bottom of the tower is introduced into the ash water inlet pipe of the original ash water cooler by the purified ash water pump (14); the ash water deammoniation tower (13) The ammonia-containing vapor discharged from the top is introduced into the ammonia water condenser (24) through a pipeline, and after condensation, it enters the ammonia liquid separator (25); the liquid phase discharged from the ammonia liquid separator (25) is pumped back to the upper part of the rectification section of the ash water deammoniation tower (13) and the original shift stripping tower or ammonia recovery system via the dilute ammonia water pump (26); the gas phase discharged from the ammonia liquid separator (25) is introduced into the demineralized water scrubber (28) via the vacuum pump (27); the gas phase from the demineralized water scrubber (28) is introduced into the demineralized water scrubber (30) via the vacuum pump (29); the gas phase from the demineralized water scrubber (30) is introduced into the original acid gas flare; the liquid phases from the demineralized water scrubber (28) and (30) are both introduced into the ammonia liquid separator (25).

[0033] 2. Low flash gas purification and utilization system: It consists of a low flash gas purification tower (15), a low flash gas purification condensate pump (16), an evaporator (17), an evaporator (18), a circulating pump (19), a low flash condensate separator (20), a flash condensate preheater (21), a low flash condensate booster pump (22), a low flash gas water cooler (23), and a boiler water discharge pump (31). The connections between the equipment are shown in the attached diagram in the instruction manual.

[0034] 3. Gasification ash water impurity removal system: It consists of a low-pressure ash water pump (1), ash water impurity remover (2), scraper (3), sedimentation inclined plate (4), impurity removal slurry pump (5), ash water conveying pump (6), etc. The connections between the equipment are shown in the attached diagram of the instruction manual.

[0035] 4. Flash condensate stripping system: It consists of a flash condensate feed pump (8), a flash condensate stripping tower (9), a cleaning water pump (10), a flash condensate discharge pump (11), and other equipment. The connections between the equipment are shown in the attached diagram in the instruction manual.

[0036] 5. Electrical and instrumentation control system: It consists of electrical system, DCS control system, control valves, control instruments, etc.

[0037] In this invention, all the heat and media required for ammonia removal, except for carbon dioxide, are supplied internally by the system, completely replacing external live steam. The discharged carbon dioxide and other non-condensable gases are burned in the original flare system and discharged in compliance with standards. Impurities in the ash water are treated by solid-liquid separation in the original clarification tank. The system itself has no material enrichment problem.

Claims

1. A coal chemical gasification ash water isothermal low pressure environment-friendly low carbon type deamination method, characterized in that: The method comprises the following steps: A. The low-pressure ash water pump (1) of the slag water system is introduced, and sodium carbonate alkaline solution is added through the dosing system to adjust the pH value of the gasification ammonia-containing ash water to 8-11, the temperature is 60-90℃, and the gasification ammonia-containing ash water is introduced into the lower part of the closed ash water removal device (2) of the ash water removal system and flows from bottom to top. The automatic scraper (3) rotates at a uniform speed, and the blades scrape off the impurity slurry deposited on the device wall and the bottom deposition inclined plate (4). After the slurry flows downward, it is pumped into the original clarifier of the slag water system together with the bottom ash water through the slurry pump (5), and is separated from the gasification black water in the clarifier. The solid phase is pressed and filtered in the original pressure filter, and the filter cake is transported out for use. The filtrate returns to the clarifier for re-solid-liquid separation; The supernatant of the liquid phase overflows into the ash water tank of the original slag water system to become gasification ammonia-containing ash water, which is then pumped by the low-pressure ash water pump (1), part of which is returned to the gasification for reuse, and the rest is introduced into the ash water removal system. The supernatant in the upper part of the closed ash water removal device (2) is introduced into the raw water mixing tank (7) through the ash water conveying pump (6); B. The flash condensate feeding pump (8) pumps the flash condensate into the upper part of the flash condensate stripping tower (9) and flows from top to bottom after liquid distribution. Meanwhile, the carbon dioxide from the original purification device of the enterprise, with an absolute pressure of 300-400Kpa and a temperature of room temperature, is introduced into the tower bottom of the flash condensate stripping tower (9) at 0.1%-5% of the mass of the flash condensate feeding of the flash condensate stripping tower (9), and flows from bottom to top to strip the flash condensate. The non-condensable gas stripped out is introduced into the lower part of the acid gas inlet of the ash water deamination tower (13). The rest of the carbon dioxide is directly introduced into the tower bottom of the ash water deamination tower (13); The absolute pressure in the flash condensate stripping tower (9) is maintained at 101-232Kpa, and no heat source is used for heating, but carbon dioxide is used for pressure maintenance. After the flash condensate reaches the bottom of the stripping tower (9), the temperature is 40-90℃, and 5%-30% of the mass of the flash condensate is pumped into the ash water deamination tower (13) and the flash condensate preheater (17) by the cleaning water pump (10) at 50% each, as cleaning water. The rest is pumped into the raw water mixing tank (7) by the flash condensate discharging pump (11) and mixed with the ash water in the tank as deamination raw water. C. The low flash gas discharged from the original low pressure flash tank is introduced into the lower part of the low flash gas purification tower (15) at 5-20% of the feed water mass of the original ash water deamination tower (13), and flows from bottom to top. The original shift stripping tower purifying water is introduced into the upper part of the low flash gas purification tower (15) at 10-20% of the low flash gas mass of the low flash gas purification tower (15) through the original purifying water booster pump, and flows from top to bottom after liquid distribution. The low flash gas in the tower is washed and purified. The purified condensate flows out from the tower bottom and is pumped into the original sludge water system clarifier through the low flash gas condensate pump (16). The purified low flash gas is discharged from the tower and introduced into the shell side of the reboiler (17) for heating. The low flash gas mixture condensed is introduced into the low flash condensate separator (20) from the lower part of the reboiler by gravity. At the same time, the remaining low flash gas discharged from the original low pressure flash tank is first introduced into the flash condensate preheater (21) to preheat the low flash condensate separator (20) and then into the low flash gas water cooler (23) for further condensation and cooling. The low flash gas is then introduced into the low flash condensate separator (20) again and separated from the low flash condensate mixture discharged from the reboiler (17). The liquid phase low flash condensate is discharged from the bottom of the low flash condensate separator (20) and part of it is pumped into the flash condensate preheater (21) through the low flash condensate booster pump (22) and then discharged to the outlet of the low pressure ash water pump (1) of the original sludge water system to the gasification recycling pipeline and returned to the deaerating tank or evaporation hot water tank of the gasification system. The other part of the low flash condensate flows into the flash condensate feed pump (8) inlet pipeline by gravity. The gaseous phase separated from the low flash condensate separator (20) is introduced into the middle flash gas inlet of the ash water deamination tower (13); The boiler water heated in the tube side of the reboiler (17) is returned to the evaporator (18) and the flash produces secondary steam which is directly introduced into the tower bottom of the ash water deamination tower (13). The remaining boiler water is discharged from the bottom of the evaporator (18) at 2-10% of the boiler water mass introduced into the evaporator and pumped back to the low flash gas purification tower condensate outlet pipeline through the boiler water discharge pump (31) and the low flash gas condensate pump to the original clarifier of the sludge water system; D. The feed water is introduced from the feed water mixing tank (7) and pumped into the upper part of the ash water deamination tower (13) through the feed water pump (12) and flows from top to bottom; The secondary steam produced by the flash in the evaporator (18) introduced into the tower bottom of the ash water deamination tower (13) is combined with the low flash gas non-condensable gas discharged from the low flash condensate separator (20) introduced into the low flash gas inlet of the ash water deamination tower (13), the acid gas discharged from the flash condensate stripping tower (9) introduced into the acid gas inlet, and the carbon dioxide directly introduced into the tower bottom to strip and purify the feed water from bottom to top. Water ring vacuum pumps (27), (29) are arranged to extract non-condensable gas in the grey water ammonia removal tower (13), maintain the absolute pressure of 20-100 KPa at the top of the ammonia removal tower (13), and discharge the ammonia-containing steam from the top of the ammonia removal tower (13) into the ammonia water condenser (24) for condensation, then into the ammonia liquid separator (25) for gas-liquid separation, and the liquid phase is pressurized by the dilute ammonia water pump (26) and then returned to the rectification section of the grey water ammonia removal tower (13) at 30%-95% of the liquid phase mass, and the rest is introduced into the original shift stripper or the original purification device ammonia recovery system to recover ammonia water, the gas phase separated in the ammonia liquid separator (25) is introduced into the vacuum pump (27), then into the desalted water scrubber (28), and then introduced into the vacuum pump (29) after being washed by desalted water, and the gas phase is extracted and then introduced into the desalted water scrubber (30), and the gas phase is introduced into the original acid gas flare, and is discharged after being combusted to meet the standard, and the liquid phases in the scrubbers (28), (30) are returned to the bottom of the ammonia liquid separator (25); The raw material water reaches the tower kettle of the ammonia removal tower (13), and the ammonia content therein meets the ammonia nitrogen requirement for entering the biochemical treatment system for deep treatment, and becomes purified grey water, which is introduced into the original grey water cooler inlet pipeline of the sludge water system by the purified grey water pump (14), discharged after being cooled, and deep treated in the original biochemical treatment system.

2. The coal chemical gasification grey water isothermal low pressure environment-friendly low-carbon type deamination method according to claim 1, characterized in that The flash condensate includes one of low flash condensate and true flash condensate, or any mixture thereof.

3. The coal chemical gasification grey water isothermal low pressure environment-friendly low-carbon type deamination method according to claim 1, characterized in that The carbon dioxide in the original purification device of the enterprise, in terms of mass ratio, contains 96%-99.5% of carbon dioxide, 3%-0.3% of carbon monoxide, 0.5%-0.1% of hydrogen, and 0.5%-0.1% of nitrogen.

4. The coal chemical gasification grey water isothermal low pressure environment-friendly low-carbon type deamination method according to claim 1, characterized in that The non-condensable gas stripped out, in terms of mass ratio, contains 2%-10% of ammonia, 95%-89.64% of carbon dioxide, 2.2%-0.2% of carbon monoxide, 0.4%-0.08% of hydrogen, and 0.4%-0.08% of nitrogen.

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