Energy-saving device and method utilizing double-tower flash evaporation in gasification system

Abstract

The invention relates to a double-tower flash evaporation energy-saving device and method in a gasification system. Comprising a gasification furnace connected with an outlet of a coal mill and an oxygen pipeline connected with the gasification furnace, a gas phase outlet of the gasification furnace is connected with a cyclone separator, a gas phase outlet of the cyclone separator is connected with a water scrubber, and a gas phase outlet of the water scrubber is connected with a subsequent conversion section. A liquid phase outlet of the gasification furnace, a liquid phase outlet of the cyclone separator and a liquid phase outlet of the water scrubber are respectively connected with a primary evaporation hot water tower, a liquid phase outlet of the primary evaporation hot water tower is connected with an inlet of a secondary evaporation hot water tower, and a liquid phase outlet of the secondary evaporation hot water tower is connected with an ash water gas-liquid separation circulating unit through a vacuum flash evaporator; the method has the advantages that the process design is reasonable, the heat energy utilization rate is increased, the use amount of circulating cooling water is reduced, the operation cost of a gasification system is reduced, the lower-layer slurry is recycled, so that the particle size distribution of the coal slurry is adjusted, the concentration of the coal slurry is increased, and the gasification efficiency is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of gasification systems, and in particular to a double-tower flash evaporation energy-saving device and method utilizing the gasification system. Background Art

[0002] In the prior art, the gasification system generates high-temperature and high-pressure black water through a gasifier. The high-temperature and high-pressure black water needs to undergo three-stage flash evaporation for solid-liquid separation. The ash water after solid-liquid separation can be used as washing water for a water scrubber, and the ash residue after solid-liquid separation is sold externally. In the aforementioned three-stage flash evaporation process, a large amount of circulating water is consumed to exchange heat for the high-temperature and high-pressure black water. At the same time, the ash water after solid-liquid separation needs steam to heat it to meet the requirements of the water scrubber. That is, the operation of the existing gasification system requires the consumption of a large amount of circulating water and steam, resulting in a waste of water resources and heat sources, and further increasing the operating costs of the enterprise. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a double-tower flash evaporation energy-saving device and method utilizing a gasification system to solve the defects in the prior art.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A double-tower flash evaporation energy-saving device in a gasification system comprises a gasifier connected to a coal mill outlet, and an oxygen pipeline connected to the gasifier, the gas phase outlet of the gasifier is connected to a cyclone separator, the gas phase outlet of the cyclone separator is connected to a water scrubber, the gas phase outlet of the water scrubber is connected to a subsequent conversion section, the liquid phase outlet of the gasifier, the liquid phase outlet of the cyclone separator and the liquid phase outlet of the water scrubber are respectively connected to a primary evaporation hot water tower, the liquid phase outlet of the primary evaporation hot water tower is connected to an inlet of a secondary evaporation hot water tower, the liquid phase outlet of the secondary evaporation hot water tower is connected to a gray water gas-liquid separation circulation unit through a vacuum flash evaporator; the upper hot water section inlet of the secondary evaporation hot water tower is connected to a raw water tank, the upper hot water section outlet of the secondary evaporation hot water tower is connected to the upper hot water section inlet of the primary evaporation hot water tower, and the upper hot water section outlet of the first evaporation hot water tower is connected to the circulating water inlet of the water scrubber.

[0006] The beneficial effects of the present invention are as follows: by setting a primary evaporation hot water tower, a secondary evaporation hot water tower and a vacuum flash evaporator, and utilizing the characteristics of the black water after flash evaporation to utilize its thermal energy, the consumption of water resources can be reduced under the premise of fully utilizing the thermal energy; specifically, the present invention utilizes the flash steam in the secondary evaporation hot water tower to preheat the circulating water, and further, the flash steam in the primary evaporation hot water tower is used to perform deep heat exchange on the preheated circulating water to increase its temperature entering the water washing tower, and finally achieves the characteristic of improving the water vapor ratio in the synthesis gas leaving the gasification boundary zone.

[0007] Preferably, the grey water gas-liquid separation circulation unit comprises at least a clarification tank, the raw water tank is connected to the upper hot water section inlet of the secondary evaporative hot water tower through a raw water pump and a first tee, and the supernatant outlet of the clarification tank is connected to the third end of the first tee.

[0008] Preferably, the supernatant outlet of the clarification tank is connected to a gray water tank, and the outlet of the gray water tank is connected to the third end of the first tee through a gray water pump.

[0009] Preferably, the bottom slurry outlet of the clarification tank is connected to the filter press through a slurry pump and a second tee, and the third end of the second tee is connected to the coal mill inlet.

[0010] Preferably, the gas phase outlet at the top of the vacuum flash evaporator is connected to the heat exchange channel of the desalted water preheater, the heat exchange channel outlet of the desalted water preheater is connected to the inlet of the clarification tank; the desalted water channel inlet of the desalted water preheater is connected to the desalted water pipeline, and the desalted water channel outlet of the desalted water preheater is connected to the deaerator.

[0011] Preferably, the top gas phase outlets of the first-stage evaporative hot water tower and the second-stage evaporative hot water tower are respectively connected to a flare device.

[0012] Preferably, a first water supply pump is provided between the upper hot water section outlet of the secondary evaporative hot water tower and the upper hot water section inlet of the primary evaporative hot water tower, and a second water supply pump is provided between the upper hot water section outlet of the primary evaporative hot water tower and the circulating water inlet of the water washing tower.

[0013] The present invention also provides a method for utilizing a double-tower flash evaporation energy-saving device in a gasification system, the method comprising the following steps:

[0014] Step 1: Oxygen from the oxygen pipeline and water-coal slurry from the coal mill enter the gasifier together and react under high temperature and high pressure. The gas phase generated by the reaction is quenched in the quenching chamber of the gasifier. The quenched gas phase enters the cyclone separator to remove part of the fine ash and liquid. The gas phase passing through the cyclone separator enters the water washing tower for washing. The washed gas phase enters the subsequent conversion section for subsequent reaction;

[0015] Step 2: The liquid phase in the gasifier, the liquid phase in the cyclone separator and the liquid phase in the water washing tower are black water, which enter the primary evaporation hot water tower together. The pressure in the primary evaporation hot water tower is 1.5 MPa (G). After flash evaporation, the black water rises to the hot water section through the central tube of the primary evaporation hot water tower, and mass transfer and heat exchange are performed on the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device through the gas phase outlet at the top of the primary evaporation hot water tower for combustion; when the liquid phase in the gasifier, the liquid phase in the cyclone separator and the liquid phase in the water washing tower enter the primary evaporation hot water tower, the temperature is 240-245° C. and the pressure is: 6.48 MPa (G);

[0016] Step 3: the liquid phase in the first evaporation hot water tower flashes and then enters the second evaporation hot water tower. The pressure in the second evaporation hot water tower is 0.2 MPa (G). The black water entering the second evaporation hot water tower rises to the hot water section through the central pipe of the second evaporation hot water tower (8) after flashing, and performs mass transfer and heat exchange with the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device through the gas phase outlet at the top of the second evaporation hot water tower and is burned;

[0017] Step 4: The black water flashed by the secondary evaporation hot water tower enters the vacuum flash evaporator for further flash evaporation. The pressure in the vacuum flash evaporator is 25Kpa (A). The gas phase flashed by the vacuum flash evaporator enters the heat exchange channel of the desalted water preheater to preheat the desalted water and then condense. The condensed condensate and the black water of the vacuum flash evaporator enter the clarification tank together;

[0018] The desalted water in the desalted water pipeline enters the desalted water channel of the desalted water preheater for heat exchange and is then sent to the deaerator for further deoxygenation before being used in the boiler or waste boiler;

[0019] Step 5: The black water in the clarifier tank settles naturally, and the supernatant overflows into the gray water tank. The gray water in the gray water tank is pumped into the upper hot water section of the secondary evaporative hot water tower as circulating water, and is heat-exchanged to 115-125°C through the flash steam in the secondary evaporative hot water tower;

[0020] Step 6: The circulating water after heat exchange in the upper hot water section of the secondary evaporative hot water tower enters the upper hot water section of the primary evaporative hot water tower through the first water supply pump, and is heat exchanged to 200-210° C. through the flash steam in the primary evaporative hot water tower; the circulating water heated by the upper hot water section of the primary evaporative hot water tower enters the water washing tower through the second water supply pump and the circulating water inlet of the water washing tower for use as washing water;

[0021] Step 7: After the black water in step 5 naturally settles, the lower middle part of the clarification tank is the lower slurry, which is pumped into the coal mill through a slurry pump to be mixed with the raw coal to reduce the particle size of the coal slurry.

[0022] Preferably, when the amount of circulating water in step 5 is small, the raw water pump is turned on to mix the raw water in the raw water tank with the gray water from the first tee and the gray water tank and use them together as circulating water.

[0023] Preferably, when there is too much slurry in step 7, the slurry pump transports the lower layer slurry to the filter press through the second tee for solid-liquid separation.

[0024] According to the above scheme, a double-tower flash evaporation energy-saving device and method using a gasification system is made. A first-level evaporation hot water tower and a second-level evaporation hot water tower are set to flash the black water according to the characteristics of high-temperature and high-pressure black water. The second-level evaporation hot water tower preheats the circulating washing water, and the first-level evaporation hot water tower heats the preheated circulating washing water, so that the temperature entering the washing tower is 200-210°C, which is higher than the temperature of the washing water entering the traditional washing tower (the traditional temperature is about 150°C); the above method can not only effectively utilize thermal energy, but also save a large amount of cooling water, and at the same time can also achieve the characteristic of improving the water vapor ratio in the synthesis gas leaving the gasification boundary zone. ; Furthermore, the present invention also utilizes the relatively clean flash gas in the vacuum flash evaporator to heat the desalted water to meet its need to enter the deaerator; the present invention utilizes the lower layer slurry that passes through the clarifier to flow back to the coal mill, and utilizes the high solid content, small particle size and coal content in the lower layer slurry to adjust the particle size distribution of the coal slurry to increase the coal slurry concentration and thus improve the gasification efficiency. It has the advantages of reasonable process design, improved thermal energy utilization, reduced use of circulating cooling water, reduced operating costs of the gasification system, and reuse of the lower layer slurry to adjust the particle size distribution of the coal slurry to increase the coal slurry concentration and thus improve the gasification efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of the present invention.

[0026] In the figure:

[0027] 1. Coal mill; 2. Gasifier; 3. Oxygen pipeline; 4. Cyclone separator; 5. Water scrubber; 6. Subsequent conversion section; 7. Primary evaporation hot water tower; 8. Secondary evaporation hot water tower; 9. Vacuum flash evaporator; 10. Raw water tank; 11. Circulating water inlet; 12. Clarifying tank; 13. Raw water pump; 14. First tee; 15. Ash water tank; 16. Ash water pump; 17. Slurry pump; 18. Second tee; 19. Filter press; 20. Desalted water preheater; 21. Desalted water pipeline; 22. Deaerator; 23. Flare device; 24. First feed water pump; 25. Second feed water pump. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] See also Figure 1The present invention is a double-tower flash evaporation energy-saving device and method in a gasification system. The device comprises a gasifier 2 connected to the outlet of a coal mill 1, and an oxygen pipeline 3 connected to the gasifier 2. The gas phase outlet of the gasifier 2 is connected to a cyclone separator 4, the gas phase outlet of the cyclone separator 4 is connected to a water scrubber 5, the gas phase outlet of the water scrubber 5 is connected to a subsequent conversion section 6, the liquid phase outlet of the gasifier 2, the liquid phase outlet of the cyclone separator 4 and the liquid phase outlet of the water scrubber 5 are respectively connected to a primary evaporation hot water tower 7, the liquid phase outlet of the primary evaporation hot water tower 7 is connected to an inlet of a secondary evaporation hot water tower 8, the liquid phase outlet of the secondary evaporation hot water tower 8 is connected to a ash-water gas-liquid separation circulation unit through a vacuum flash evaporator 9; the upper hot water section inlet of the secondary evaporation hot water tower 8 is connected to a raw water tank 10, the upper hot water section outlet of the secondary evaporation hot water tower 8 is connected to the upper hot water section inlet of the primary evaporation hot water tower 7, and the upper hot water section outlet of the primary evaporation hot water tower 7 is connected to the circulating water inlet 11 of the water scrubber 5. The present invention realizes effective utilization of the heat energy in the high-temperature and high-pressure black water by setting a primary evaporation hot water tower 7 and a secondary evaporation hot water tower 8, which saves the setting of the original flash evaporator and the corresponding cooler, and saves the use of circulating cooling water; thereby achieving the characteristics of full utilization of the heat of the flash evaporation system in the gasification system and zero consumption of circulating water.

[0030] Furthermore, the gray water gas-liquid separation circulation unit at least includes a clarification tank 12, the raw water tank 10 is connected to the upper hot water section inlet of the secondary evaporation hot water tower 8 through a raw water pump 13 and a first tee 14, and the supernatant outlet of the clarification tank 12 is connected to the third end of the first tee 14. The above arrangement enables the supernatant of the clarification tank 12 to be used as washing water for the water washing tower 5, and the above method can achieve effective utilization of water resources in the gasification system, and effective utilization of black water thermal energy in the gasification system by using water resources in the gasification system, thereby achieving the characteristics of recycling water resources and thermal energy of the gasification system itself, and achieving energy saving and consumption reduction; in actual use, the present invention preferentially selects to use the supernatant from the clarification tank 12, and when the supernatant is insufficient to meet the operation requirements of the water washing tower 5, it can be supplemented by the raw water in the raw water tank 10.

[0031] Furthermore, the supernatant liquid outlet of the clarifier tank 12 is connected to the gray water tank 15, and the outlet of the gray water tank 15 is connected to the third end of the first tee 14 through the gray water pump 16. The present invention can buffer and temporarily store the supernatant liquid from the clarifier tank 12 through the gray water tank 15 to ensure the long-term stable operation of the gasification system, and at the same time, the gray water pump 16 is used to pressurize the supernatant liquid to achieve the purpose of transporting it to the hot water section of the secondary evaporation hot water tower 8.

[0032] Furthermore, the bottom slurry outlet of the clarifier 12 is connected to the filter press 19 through the slurry pump 17 and the second tee 18, and the third end of the second tee 18 is connected to the inlet of the coal mill 1. The bottom slurry of the clarifier 12 described in the present invention is the lower layer slurry, which has the characteristics of high solid content, low particle size and coal content. The present invention applies it to the coal mill 1 according to the above characteristics, especially in the coal with high internal water content and high organic matter content, the coal slurry concentration is difficult to increase during the grinding and slurrying process. The coal consumption and oxygen consumption of gasification are greatly increased due to the inability to increase the coal slurry concentration. The present invention adjusts the particle size distribution of the coal slurry by mixing the above-mentioned high solid content coal slime partly back to the coal mill to achieve the characteristics of increasing the coal slurry concentration and then improving the gasification efficiency, thereby improving the economic benefits of the enterprise.

[0033] Furthermore, the gas phase outlet at the top of the vacuum flash evaporator 9 is connected to the heat exchange channel of the desalted water preheater 20, and the heat exchange channel outlet of the desalted water preheater 20 is connected to the inlet of the clarification tank 12; the desalted water channel inlet of the desalted water preheater 20 is connected to the desalted water pipeline 21, and the desalted water channel outlet of the desalted water preheater 20 is connected to the deaerator 22. According to the analysis, the flash gas produced in the vacuum flash evaporator 9 is relatively clean and has less impact on the scouring and corrosion of the equipment. The present invention applies the above-mentioned flash gas to the heating of desalted water through its characteristics, thereby realizing the recovery of heat energy and meeting the desalted water supply demand of the deaerator 22 without using circulating water.

[0034] Furthermore, the top gas phase outlets of the primary evaporation hot water tower 7 and the secondary evaporation hot water tower 8 are respectively connected to the flare device 23. In the present invention, the flare device 23 can be provided to simultaneously burn the non-condensable gas produced by the primary evaporation hot water tower 7 and the secondary evaporation hot water tower 8, so as to achieve the characteristics of reducing the equipment purchase cost and improving the equipment utilization rate under the premise of meeting the environmental protection requirements.

[0035] Furthermore, a first water supply pump 24 is provided between the upper hot water section outlet of the secondary evaporation hot water tower 8 and the upper hot water section inlet of the primary evaporation hot water tower 7 , and a second water supply pump 25 is provided between the upper hot water section outlet of the primary evaporation hot water tower 7 and the circulating water inlet 11 of the water washing tower 5 .

[0036] The present invention also provides a method for utilizing a double-tower flash evaporation energy-saving device in a gasification system, the method comprising the following steps:

[0037] Step 1: Oxygen from the oxygen pipeline 3 and the water-coal slurry from the coal mill 1 enter the gasifier 2 together, react under high temperature and high pressure, and the gas phase generated by the reaction is quenched in the quenching chamber of the gasifier 2. The quenched gas phase enters the cyclone separator 4 to remove part of the fine ash and liquid, and the gas phase passing through the cyclone separator 4 enters the water washing tower 5 for washing. The washed gas phase enters the subsequent conversion section 6 for subsequent reaction;

[0038] Step 2: The liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 are black water, which enter the primary evaporation hot water tower 7 together. The pressure in the primary evaporation hot water tower 7 is 1.5 MPa (G). After flash evaporation, the black water rises to the hot water section through the central tube of the primary evaporation hot water tower 7, and mass transfer and heat exchange are performed on the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the primary evaporation hot water tower 7 for combustion; When the liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 enter the primary evaporation hot water tower 7, the temperature is 240-245° C. and the pressure is: 6.48 MPa (G);

[0039] Step 3: The liquid phase in the primary evaporation hot water tower 7 flashes and enters the secondary evaporation hot water tower 8. The pressure in the secondary evaporation hot water tower 8 is 0.2 MPa (G). The black water entering the secondary evaporation hot water tower 8 rises to the hot water section through the central tube of the secondary evaporation hot water tower 8 after flashing, and performs mass transfer and heat exchange with the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the secondary evaporation hot water tower 8 and is burned;

[0040] Step 4: The black water flashed by the secondary evaporation hot water tower 8 enters the vacuum flash evaporator 9 for further flash evaporation. The pressure in the vacuum flash evaporator 9 is 25Kpa (A). The gas phase flashed by the vacuum flash evaporator 9 enters the heat exchange channel of the desalted water preheater 20 to preheat the desalted water and then condense. The condensed condensate and the black water of the vacuum flash evaporator 9 enter the clarification tank 12 together;

[0041] The desalted water in the desalted water pipeline 21 enters the desalted water channel of the desalted water preheater 20 for heat exchange and is then sent to the deaerator 22 for further deoxygenation before being used in the boiler or waste boiler;

[0042] Step 5: The black water in the clarification tank 12 settles naturally, and the supernatant overflows into the gray water tank 15. The gray water in the gray water tank 15 is sent to the upper hot water section of the secondary evaporative hot water tower 8 through the gray water pump 16 as circulating water, and is heat-exchanged to 115-125° C. through the flash steam in the secondary evaporative hot water tower 8;

[0043] Step 6: The circulating water after heat exchange in the upper hot water section of the secondary evaporation hot water tower 8 enters the upper hot water section of the primary evaporation hot water tower 8 through the first water supply pump 24, and is heat exchanged to 200-210° C. by the flash steam in the primary evaporation hot water tower 8; the circulating water heated by the upper hot water section of the primary evaporation hot water tower 8 enters the water washing tower 5 through the second water supply pump 25 and the circulating water inlet 11 of the water washing tower 5 for use as washing water;

[0044] Step 7: After the black water naturally settles in step 5, the lower middle part of the clarification tank 12 is the lower slurry, which is sent to the coal mill 1 through the slurry pump 17 to be mixed with the raw coal to reduce the particle size of the coal slurry.

[0045] Furthermore, when the amount of circulating water in step 5 is small, the raw water pump 13 is turned on to mix the raw water in the raw water tank 10 with the gray water from the gray water tank 15 through the first three-way valve 14 and the gray water from the gray water tank 15 and use them together as circulating water. In the present invention, gray water is preferably used as circulating water. When the amount of gray water is small and cannot meet the washing requirements in the water washing tower according to the actual working conditions, it can be supplemented with the raw water in the raw water tank 10 to maintain the normal operation of the gasification system.

[0046] Furthermore, when there is too much slurry in step 7, the slurry pump 17 conveys the lower slurry to the filter press 19 for solid-liquid separation through the second tee 18. The lower slurry in the present invention has the characteristics of high solid content, small particle size and coal content. By returning it to the coal mill, the particle size distribution of the coal slurry can be adjusted to increase the coal slurry concentration, thereby increasing the gasification efficiency, so as to achieve the characteristics of improving the emergency benefits of the enterprise; the lower slurry described in the present invention first meets the use of the coal mill. When there is still excess lower slurry after meeting the use of the coal mill, it can enter the filter press 19 for solid-liquid separation, and the gasified ash can be sold.

[0047] The present invention realizes the effective utilization of high-temperature and high-pressure black water thermal energy through a two-stage evaporation hot water tower, and cancels the original low-pressure flash evaporator gas-phase circulating water cooler and vacuum flash evaporator gas-phase circulating water cooler and other related settings, and concentrates the solid materials in the black water through the step-by-step flash evaporation of high-temperature and high-pressure black water, and the heat generated by the flash evaporation is used internally, which changes the previous circulating water condensation, not only greatly reduces the circulating water consumption of the gasification device, but also improves the temperature of the washing water of the gasification system water washing tower, and finally improves the water-vapor ratio of the synthesis gas out of the gasification boundary area, greatly increases the amount of by-product steam in the downstream conversion section, and in addition, by partially returning the high-solid content coal slime to the coal mill and adjusting the particle size distribution of the coal slurry, the coal slurry concentration is increased, thereby improving the gasification efficiency. In summary, it can bring huge benefits to the enterprise.

[0048] In order to explain the present invention in more detail, the present invention is further described in conjunction with embodiments. Specific embodiments are as follows:

[0049] Example 1

[0050] A double-tower flash evaporation energy-saving device in a gasification system comprises a gasifier 2 connected to the outlet of a coal mill 1, and an oxygen pipeline 3 connected to the gasifier 2, the gas phase outlet of the gasifier 2 is connected to a cyclone separator 4, the gas phase outlet of the cyclone separator 4 is connected to a water scrubber 5, the gas phase outlet of the water scrubber 5 is connected to a subsequent conversion section 6, the liquid phase outlet of the gasifier 2, the liquid phase outlet of the cyclone separator 4 and the liquid phase outlet of the water scrubber 5 are respectively connected to a primary evaporation hot water tower 7, the liquid phase outlet of the primary evaporation hot water tower 7 is connected to an inlet of a secondary evaporation hot water tower 8, the liquid phase outlet of the secondary evaporation hot water tower 8 is connected to a ash water gas-liquid separation circulation unit through a vacuum flash evaporator 9; the upper hot water section inlet of the secondary evaporation hot water tower 8 is connected to a raw water tank 10, the upper hot water section outlet of the secondary evaporation hot water tower 8 is connected to the upper hot water section inlet of the primary evaporation hot water tower 7, and the upper hot water section outlet of the primary evaporation hot water tower 7 is connected to the circulating water inlet 11 of the water scrubber 5. The ash water gas-liquid separation circulation unit at least comprises a clarifier 12, the raw water tank 10 is connected to the upper hot water section inlet of the secondary evaporation hot water tower 8 through a raw water pump 13 and a first tee 14, and the supernatant outlet of the clarifier 12 is connected to the third end of the first tee 14. The supernatant outlet of the clarifier 12 is connected to the ash water tank 15, and the outlet of the ash water tank 15 is connected to the third end of the first tee 14 through an ash water pump 16. The bottom slurry outlet of the clarifier 12 is connected to the filter press 19 through a slurry pump 17 and a second tee 18, and the third end of the second tee 18 is connected to the inlet of the coal mill 1. The gas phase outlet at the top of the vacuum flash evaporator 9 is connected to the heat exchange channel of the desalted water preheater 20, and the heat exchange channel outlet of the desalted water preheater 20 is connected to the inlet of the clarifier 12; the desalted water channel inlet of the desalted water preheater 20 is connected to the desalted water pipeline 21, and the desalted water channel outlet of the desalted water preheater 20 is connected to the deaerator 22. The top gas phase outlets of the primary evaporation hot water tower 7 and the secondary evaporation hot water tower 8 are respectively connected to the flare device 23. A first water supply pump 24 is provided between the upper hot water section outlet of the secondary evaporation hot water tower 8 and the upper hot water section inlet of the primary evaporation hot water tower 7, and a second water supply pump 25 is provided between the upper hot water section outlet of the primary evaporation hot water tower 7 and the circulating water inlet 11 of the water washing tower 5.

[0051] The present invention also provides a method for utilizing a double-tower flash evaporation energy-saving device in a gasification system, the method comprising the following steps:

[0052] Step 1: Oxygen from the oxygen pipeline 3 and the water-coal slurry from the coal mill 1 enter the gasifier 2 together, react under high temperature and high pressure, and the gas phase generated by the reaction is quenched in the quenching chamber of the gasifier 2. The quenched gas phase enters the cyclone separator 4 to remove part of the fine ash and liquid, and the gas phase passing through the cyclone separator 4 enters the water washing tower 5 for washing. The washed gas phase enters the subsequent conversion section 6 for subsequent reaction;

[0053] Step 2: The liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 are black water, which enter the primary evaporation hot water tower 7 together. The pressure in the primary evaporation hot water tower 7 is 1.5 MPa (G). After flash evaporation, the black water rises to the hot water section through the central tube of the primary evaporation hot water tower 7, and mass transfer and heat exchange are performed on the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the primary evaporation hot water tower 7 for combustion; when the liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 enter the primary evaporation hot water tower 7, the temperature is 240° C. and the pressure is: 6.48 MPa (G);

[0054] Step 3: The liquid phase in the primary evaporation hot water tower 7 flashes and enters the secondary evaporation hot water tower 8. The pressure in the secondary evaporation hot water tower 8 is 0.2 MPa (G). The black water entering the secondary evaporation hot water tower 8 rises to the hot water section through the central tube of the secondary evaporation hot water tower 8 after flashing, and performs mass transfer and heat exchange with the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the secondary evaporation hot water tower 8 and is burned;

[0055] Step 4: The black water flashed by the secondary evaporation hot water tower 8 enters the vacuum flash evaporator 9 for further flash evaporation. The pressure in the vacuum flash evaporator 9 is 25Kpa (A). The gas phase flashed by the vacuum flash evaporator 9 enters the heat exchange channel of the desalted water preheater 20 to preheat the desalted water and then condense. The condensed condensate and the black water of the vacuum flash evaporator 9 enter the clarification tank 12 together;

[0056] The desalted water in the desalted water pipeline 21 enters the desalted water channel of the desalted water preheater 20 for heat exchange and is then sent to the deaerator 22 for further deoxygenation before being used in the boiler or waste boiler;

[0057] Step 5: The black water in the clarification tank 12 settles naturally, and the supernatant overflows into the gray water tank 15. The gray water in the gray water tank 15 is sent to the upper hot water section of the secondary evaporative hot water tower 8 through the gray water pump 16 as circulating water, and is heat-exchanged to 115° C. through the flash steam in the secondary evaporative hot water tower 8;

[0058] Step 6: The circulating water after heat exchange in the upper hot water section of the secondary evaporation hot water tower 8 enters the upper hot water section of the primary evaporation hot water tower 8 through the first water supply pump 24, and is heat exchanged to 200° C. by the flash steam in the primary evaporation hot water tower 8; the circulating water heated by the upper hot water section of the primary evaporation hot water tower 8 enters the water washing tower 5 through the second water supply pump 25 and the circulating water inlet 11 of the water washing tower 5 for use as washing water;

[0059] Step 7: After the black water naturally settles in step 5, the lower middle part of the clarification tank 12 is the lower slurry, which is sent to the coal mill 1 through the slurry pump 17 to be mixed with the raw coal to reduce the particle size of the coal slurry.

[0060] Example 2

[0061] A double-tower flash evaporation energy-saving device using a gasification system, comprising a coal mill 1 and a double-tower flash evaporation energy-saving device and method, the device comprising a gasifier 2 connected to the outlet of the coal mill 1, and an oxygen pipeline 3 connected to the gasifier 2, the gas phase outlet of the gasifier 2 is connected to a cyclone separator 4, the gas phase outlet of the cyclone separator 4 is connected to a water scrubber 5, the gas phase outlet of the water scrubber 5 is connected to a subsequent conversion section 6, the liquid phase outlet of the gasifier 2, the liquid phase outlet of the cyclone separator 4 and the water scrubber 5 are connected to the subsequent conversion section 6, and the liquid phase outlet of the gasifier 2, the liquid phase outlet of the cyclone separator 4 and the water scrubber 5 are connected to the subsequent conversion section 6. The liquid phase outlet is connected to the first evaporation hot water tower 7, the liquid phase outlet of the first evaporation hot water tower 7 is connected to the inlet of the second evaporation hot water tower 8, and the liquid phase outlet of the second evaporation hot water tower 8 is connected to the gray water gas-liquid separation circulation unit through the vacuum flash evaporator 9; the upper hot water section inlet of the second evaporation hot water tower 8 is connected to the raw water tank 10, the upper hot water section outlet of the second evaporation hot water tower 8 is connected to the upper hot water section inlet of the first evaporation hot water tower 7, and the upper hot water section outlet of the first evaporation hot water tower 7 is connected to the circulating water inlet 11 of the washing tower 5. The gray water gas-liquid separation circulation unit at least includes a clarification tank 12, the raw water tank 10 is connected to the upper hot water section inlet of the second evaporation hot water tower 8 through a raw water pump 13 and a first tee 14, and the supernatant outlet of the clarification tank 12 is connected to the third end of the first tee 14. The supernatant outlet of the clarification tank 12 is connected to the gray water tank 15, and the outlet of the gray water tank 15 is connected to the third end of the first tee 14 through the gray water pump 16. The bottom slurry outlet of the clarifier 12 is connected to the filter press 19 through the slurry pump 17 and the second tee 18, and the third end of the second tee 18 is connected to the inlet of the coal mill 1. The gas phase outlet at the top of the vacuum flash evaporator 9 is connected to the heat exchange channel of the desalted water preheater 20, and the heat exchange channel outlet of the desalted water preheater 20 is connected to the inlet of the clarifier 12; the desalted water channel inlet of the desalted water preheater 20 is connected to the desalted water pipeline 21, and the desalted water channel outlet of the desalted water preheater 20 is connected to the deaerator 22. The top gas phase outlets of the first-stage evaporation hot water tower 7 and the second-stage evaporation hot water tower 8 are respectively connected to the flare device 23. A first water supply pump 24 is provided between the upper hot water section outlet of the second-stage evaporation hot water tower 8 and the upper hot water section inlet of the first-stage evaporation hot water tower 7, and a second water supply pump 25 is provided between the upper hot water section outlet of the first-stage evaporation hot water tower 7 and the circulating water inlet 11 of the water washing tower 5.

[0062] The present invention also provides a method for utilizing a double-tower flash evaporation energy-saving device in a gasification system, the method comprising the following steps:

[0063] Step 1: Oxygen from the oxygen pipeline 3 and the water-coal slurry from the coal mill 1 enter the gasifier 2 together, react under high temperature and high pressure, and the gas phase generated by the reaction is quenched in the quenching chamber of the gasifier 2. The quenched gas phase enters the cyclone separator 4 to remove part of the fine ash and liquid, and the gas phase passing through the cyclone separator 4 enters the water washing tower 5 for washing. The washed gas phase enters the subsequent conversion section 6 for subsequent reaction;

[0064] Step 2: The liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 are black water, which enter the primary evaporation hot water tower 7 together. The pressure in the primary evaporation hot water tower 7 is 1.5 MPa (G). After flash evaporation, the black water rises to the hot water section through the central tube of the primary evaporation hot water tower 7, and mass transfer and heat exchange are performed on the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the primary evaporation hot water tower 7 and is burned; when the liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 enter the primary evaporation hot water tower 7, the temperature is 245° C. and the pressure is: 6.48 MPa (G);

[0065] Step 3: The liquid phase in the primary evaporation hot water tower 7 flashes and enters the secondary evaporation hot water tower 8. The pressure in the secondary evaporation hot water tower 8 is 0.2 MPa (G). The black water entering the secondary evaporation hot water tower 8 rises to the hot water section through the central tube of the secondary evaporation hot water tower 8 after flashing, and performs mass transfer and heat exchange with the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the secondary evaporation hot water tower 8 and is burned;

[0066] Step 4: The black water flashed by the secondary evaporation hot water tower 8 enters the vacuum flash evaporator 9 for further flash evaporation. The pressure in the vacuum flash evaporator 9 is 25Kpa (A). The gas phase flashed by the vacuum flash evaporator 9 enters the heat exchange channel of the desalted water preheater 20 to preheat the desalted water and then condense. The condensed condensate and the black water of the vacuum flash evaporator 9 enter the clarification tank 12 together;

[0067] The desalted water in the desalted water pipeline 21 enters the desalted water channel of the desalted water preheater 20 for heat exchange and is then sent to the deaerator 22 for further deoxygenation before being used in the boiler or waste boiler;

[0068] Step 5: The black water in the clarification tank 12 settles naturally, and the supernatant overflows into the gray water tank 15. The gray water in the gray water tank 15 is sent to the upper hot water section of the secondary evaporative hot water tower 8 through the gray water pump 16 as circulating water, and is heat-exchanged to 125° C. through the flash steam in the secondary evaporative hot water tower 8;

[0069] Step 6: The circulating water after heat exchange in the upper hot water section of the secondary evaporation hot water tower 8 enters the upper hot water section of the primary evaporation hot water tower 8 through the first water supply pump 24, and is heat exchanged to 210° C. by the flash steam in the primary evaporation hot water tower 8; the circulating water heated by the upper hot water section of the primary evaporation hot water tower 8 enters the water washing tower 5 through the second water supply pump 25 and the circulating water inlet 11 of the water washing tower 5 for use as washing water;

[0070] Step 7: After the black water naturally settles in step 5, the lower middle part of the clarification tank 12 is the lower slurry, which is sent to the coal mill 1 through the slurry pump 17 to be mixed with the raw coal to reduce the particle size of the coal slurry. When the amount of circulating water in step 5 is small, the raw water pump 13 is turned on to mix the raw water in the raw water tank 10 with the gray water from the first three-way 14 and the gray water from the gray water tank 15 and use them together as circulating water.

[0071] Example 3

[0072] A double-tower flash evaporation energy-saving device using a gasification system, comprising a coal mill 1 and a double-tower flash evaporation energy-saving device and method, the device comprising a gasifier 2 connected to the outlet of the coal mill 1, and an oxygen pipeline 3 connected to the gasifier 2, the gas phase outlet of the gasifier 2 is connected to a cyclone separator 4, the gas phase outlet of the cyclone separator 4 is connected to a water scrubber 5, the gas phase outlet of the water scrubber 5 is connected to a subsequent conversion section 6, the liquid phase outlet of the gasifier 2, the liquid phase outlet of the cyclone separator 4 and the water scrubber 5 are connected to the subsequent conversion section 6, and the liquid phase outlet of the gasifier 2, the liquid phase outlet of the cyclone separator 4 and the water scrubber 5 are connected to the subsequent conversion section 6. The liquid phase outlet is connected to the first evaporation hot water tower 7, the liquid phase outlet of the first evaporation hot water tower 7 is connected to the inlet of the second evaporation hot water tower 8, and the liquid phase outlet of the second evaporation hot water tower 8 is connected to the gray water gas-liquid separation circulation unit through the vacuum flash evaporator 9; the upper hot water section inlet of the second evaporation hot water tower 8 is connected to the raw water tank 10, the upper hot water section outlet of the second evaporation hot water tower 8 is connected to the upper hot water section inlet of the first evaporation hot water tower 7, and the upper hot water section outlet of the first evaporation hot water tower 7 is connected to the circulating water inlet 11 of the washing tower 5. The gray water gas-liquid separation circulation unit at least includes a clarification tank 12, the raw water tank 10 is connected to the upper hot water section inlet of the second evaporation hot water tower 8 through a raw water pump 13 and a first tee 14, and the supernatant outlet of the clarification tank 12 is connected to the third end of the first tee 14. The supernatant outlet of the clarification tank 12 is connected to the gray water tank 15, and the outlet of the gray water tank 15 is connected to the third end of the first tee 14 through the gray water pump 16. The bottom slurry outlet of the clarifier 12 is connected to the filter press 19 through the slurry pump 17 and the second tee 18, and the third end of the second tee 18 is connected to the inlet of the coal mill 1. The gas phase outlet at the top of the vacuum flash evaporator 9 is connected to the heat exchange channel of the desalted water preheater 20, and the heat exchange channel outlet of the desalted water preheater 20 is connected to the inlet of the clarifier 12; the desalted water channel inlet of the desalted water preheater 20 is connected to the desalted water pipeline 21, and the desalted water channel outlet of the desalted water preheater 20 is connected to the deaerator 22. The top gas phase outlets of the first-stage evaporation hot water tower 7 and the second-stage evaporation hot water tower 8 are respectively connected to the flare device 23. A first water supply pump 24 is provided between the upper hot water section outlet of the second-stage evaporation hot water tower 8 and the upper hot water section inlet of the first-stage evaporation hot water tower 7, and a second water supply pump 25 is provided between the upper hot water section outlet of the first-stage evaporation hot water tower 7 and the circulating water inlet 11 of the water washing tower 5.

[0073] The present invention also provides a method for utilizing a double-tower flash evaporation energy-saving device in a gasification system, the method comprising the following steps:

[0074] Step 1: Oxygen from the oxygen pipeline 3 and the water-coal slurry from the coal mill 1 enter the gasifier 2 together, react under high temperature and high pressure, and the gas phase generated by the reaction is quenched in the quenching chamber of the gasifier 2. The quenched gas phase enters the cyclone separator 4 to remove part of the fine ash and liquid, and the gas phase passing through the cyclone separator 4 enters the water washing tower 5 for washing. The washed gas phase enters the subsequent conversion section 6 for subsequent reaction;

[0075] Step 2: The liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 are black water, which enter the primary evaporation hot water tower 7 together. The pressure in the primary evaporation hot water tower 7 is 1.5 MPa (G). After flash evaporation, the black water rises to the hot water section through the central tube of the primary evaporation hot water tower 7, and mass transfer and heat exchange are performed on the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the primary evaporation hot water tower 7 and is burned; when the liquid phase in the gasifier 2, the liquid phase in the cyclone separator 4 and the liquid phase in the water washing tower 5 enter the primary evaporation hot water tower 7, the temperature is 2403° C. and the pressure is: 6.48 MPa (G);

[0076] Step 3: The liquid phase in the primary evaporation hot water tower 7 flashes and enters the secondary evaporation hot water tower 8. The pressure in the secondary evaporation hot water tower 8 is 0.2 MPa (G). The black water entering the secondary evaporation hot water tower 8 rises to the hot water section through the central tube of the secondary evaporation hot water tower 8 after flashing, and performs mass transfer and heat exchange with the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device 23 through the gas phase outlet at the top of the secondary evaporation hot water tower 8 and is burned;

[0077] Step 4: The black water flashed by the secondary evaporation hot water tower 8 enters the vacuum flash evaporator 9 for further flash evaporation. The pressure in the vacuum flash evaporator 9 is 25Kpa (A). The gas phase flashed by the vacuum flash evaporator 9 enters the heat exchange channel of the desalted water preheater 20 to preheat the desalted water and then condense. The condensed condensate and the black water of the vacuum flash evaporator 9 enter the clarification tank 12 together;

[0078] The desalted water in the desalted water pipeline 21 enters the desalted water channel of the desalted water preheater 20 for heat exchange and is then sent to the deaerator 22 for further deoxygenation before being used in the boiler or waste boiler;

[0079] Step 5: The black water in the clarification tank 12 settles naturally, and the supernatant overflows into the gray water tank 15. The gray water in the gray water tank 15 is sent to the upper hot water section of the secondary evaporative hot water tower 8 through the gray water pump 16 as circulating water, and is heat-exchanged to 120° C. through the flash steam in the secondary evaporative hot water tower 8;

[0080] Step 6: The circulating water after heat exchange in the upper hot water section of the secondary evaporation hot water tower 8 enters the upper hot water section of the primary evaporation hot water tower 8 through the first water supply pump 24, and is heat exchanged to 205° C. by the flash steam in the primary evaporation hot water tower 8; the circulating water heated by the upper hot water section of the primary evaporation hot water tower 8 enters the water washing tower 5 through the second water supply pump 25 and the circulating water inlet 11 of the water washing tower 5 for use as washing water;

[0081] Step 7: The lower middle part of the clarification tank 12 after the natural sedimentation of the black water in step 5 is the lower slurry, which is sent to the coal mill 1 through the slurry pump 17 to be mixed with the raw coal to reduce the particle size of the coal slurry. When the amount of circulating water in step 5 is small, the raw water pump 13 is turned on to mix the raw water in the raw water tank 10 with the first tee 14 and the gray water from the gray water tank 15 and use them together as circulating water. When there is too much slurry in step 7, the slurry pump 17 transports the lower slurry to the filter press 19 through the second tee 18 for solid-liquid separation.

[0082] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A double-tower flash energy-saving device in a gasification system, comprising a gasifier (2) connected to an outlet of a coal mill (1), and an oxygen pipeline (3) connected to the gasifier (2), the gas phase outlet of the gasifier (2) connected to a cyclone separator (4), the gas phase outlet of the cyclone separator (4) connected to a water scrubber (5), the gas phase outlet of the water scrubber (5) connected to a subsequent conversion section (6), characterized in that: The liquid phase outlet of the gasifier (2), the liquid phase outlet of the cyclone separator (4) and the liquid phase outlet of the water washing tower (5) are respectively connected to the primary evaporation hot water tower (7), the liquid phase outlet of the primary evaporation hot water tower (7) is connected to the inlet of the secondary evaporation hot water tower (8), and the liquid phase outlet of the secondary evaporation hot water tower (8) is connected to the gray water gas-liquid separation circulation unit through the vacuum flash evaporator (9); The upper hot water section inlet of the secondary evaporation hot water tower (8) is connected to the raw water tank (10), the upper hot water section outlet of the secondary evaporation hot water tower (8) is connected to the upper hot water section inlet of the primary evaporation hot water tower (7), and the upper hot water section outlet of the primary evaporation hot water tower (7) is connected to the circulating water inlet (11) of the water washing tower (5).

2. The double-tower flash evaporation energy-saving device in a gasification system according to claim 1, characterized in that: The grey water gas-liquid separation circulation unit comprises at least a clarification tank (12); the raw water tank (10) is connected to the upper hot water section inlet of the secondary evaporation hot water tower (8) via a raw water pump (13) and a first tee (14); and the supernatant outlet of the clarification tank (12) is connected to the third end of the first tee (14).

3. The double-tower flash evaporation energy-saving device in a gasification system according to claim 2, characterized in that: The supernatant liquid outlet of the clarification tank (12) is connected to the gray water tank (15), and the outlet of the gray water tank (15) is connected to the third end of the first three-way (14) through the gray water pump (16).

4. The double-tower flash evaporation energy-saving device in a gasification system according to claim 2, characterized in that: The bottom slurry outlet of the clarification tank (12) is connected to the filter press (19) via a slurry pump (17) and a second tee (18), and the third end of the second tee (18) is connected to the inlet of the coal mill (1).

5. The double-tower flash evaporation energy-saving device in a gasification system according to claim 2, characterized in that: The gas phase outlet at the top of the vacuum flash evaporator (9) is connected to the heat exchange channel of the desalted water preheater (20), and the heat exchange channel outlet of the desalted water preheater (20) is connected to the inlet of the clarification tank (12); The desalted water channel inlet of the desalted water preheater (20) is connected to the desalted water pipeline (21), and the desalted water channel outlet of the desalted water preheater (20) is connected to the deaerator (22).

6. The double-tower flash evaporation energy-saving device in a gasification system according to claim 1, characterized in that: The top gas phase outlets of the first evaporation hot water tower (7) and the second evaporation hot water tower (8) are respectively connected to the flare device (23).

7. The double-tower flash evaporation energy-saving device in a gasification system according to claim 1, characterized in that: A first water supply pump (24) is provided between the upper hot water section outlet of the secondary evaporation hot water tower (8) and the upper hot water section inlet of the primary evaporation hot water tower (7), and a second water supply pump (25) is provided between the upper hot water section outlet of the primary evaporation hot water tower (7) and the circulating water inlet (11) of the water washing tower (5).

8. A method for utilizing a double-tower flash evaporation energy-saving device in a gasification system, characterized in that: The method comprises the following steps: Step 1: Oxygen from the oxygen pipeline (3) and water-coal slurry from the coal mill (1) enter the gasifier (2) together, react under high temperature and high pressure, and the gas phase generated by the reaction is quenched in the quenching chamber of the gasifier (2). The quenched gas phase enters the cyclone separator (4) to remove part of fine ash and liquid, and the gas phase passing through the cyclone separator (4) enters the water washing tower (5) for washing. The washed gas phase enters the subsequent conversion section (6) for subsequent reaction; Step 2: The liquid phase in the gasifier (2), the liquid phase in the cyclone separator (4) and the liquid phase in the water scrubber (5) are black water, which enter the primary evaporation hot water tower (7) together. The pressure in the primary evaporation hot water tower (7) is 1.5 MPa (G). After flash evaporation, the black water rises to the hot water section through the central tube of the primary evaporation hot water tower (7), and performs mass transfer and heat exchange with the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device (23) through the gas phase outlet at the top of the primary evaporation hot water tower (7) for combustion. When the liquid phase in the gasifier (2), the liquid phase in the cyclone separator (4) and the liquid phase in the water scrubber (5) enter the primary evaporation hot water tower (7), the temperature is 240-245° C. and the pressure is 6.48 MPa (G); Step 3: The liquid phase in the primary evaporation hot water tower (7) enters the secondary evaporation hot water tower (8) after flash evaporation. The pressure in the secondary evaporation hot water tower (8) is 0.2 MPa (G). The black water entering the secondary evaporation hot water tower (8) rises to the hot water section through the central tube of the secondary evaporation hot water tower (8) after flash evaporation, and performs mass transfer and heat exchange with the circulating water in the hot water section. The non-condensable gas after mass transfer and heat exchange enters the flare device (23) through the gas phase outlet at the top of the secondary evaporation hot water tower (8) and is burned; Step 4: The black water flashed by the secondary evaporation hot water tower (8) enters the vacuum flash evaporator (9) for further flash evaporation. The pressure in the vacuum flash evaporator (9) is 25 Kpa (A). The gas phase flashed by the vacuum flash evaporator (9) enters the heat exchange channel of the desalted water preheater (20) to preheat the desalted water and then condense. The condensed liquid and the black water of the vacuum flash evaporator (9) enter the clarification tank (12) together. The desalted water in the desalted water pipeline (21) enters the desalted water channel of the desalted water preheater (20) for heat exchange and is then sent to the deaerator (22) for further deoxygenation before being used in the boiler or waste boiler; Step 5: The black water in the clarification tank (12) settles naturally, and the supernatant overflows into the gray water tank (15). The gray water in the gray water tank (15) is sent to the upper hot water section of the secondary evaporative hot water tower (8) through the gray water pump (16) as circulating water, and is heat-exchanged to 115-125° C. through the flash steam in the secondary evaporative hot water tower (8); Step 6: the circulating water after heat exchange in the upper hot water section of the secondary evaporation hot water tower (8) enters the upper hot water section of the primary evaporation hot water tower (8) through the first water supply pump (24), and is heat exchanged to 200-210° C. by the flash steam in the primary evaporation hot water tower (8); the circulating water heated by the upper hot water section of the primary evaporation hot water tower (8) enters the water washing tower (5) through the second water supply pump (25) and the circulating water inlet (11) of the water washing tower (5) and is used as washing water; Step 7: After the black water in step 5 has naturally settled, the lower middle part of the clarification tank (12) is the lower slurry. The lower slurry is sent to the coal mill (1) through a slurry pump (17) to be mixed with the raw coal to reduce the particle size of the coal slurry.

9. A method for utilizing a double-tower flash evaporation energy-saving device in a gasification system according to claim 8, characterized in that: When the amount of circulating water in step 5 is small, the raw water pump (13) is turned on to mix the raw water in the raw water tank (10) with the gray water from the first three-way valve (14) and the gray water tank (15) and use them together as circulating water.

10. A method for utilizing a double-tower flash evaporation energy-saving device in a gasification system according to claim 9, characterized in that: When there is too much slurry in step 7, the slurry pump (17) transports the lower layer of slurry to the filter press (19) through the second tee (18) for solid-liquid separation.

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