A low-pressure black water flash heat recovery system for coal gasification

Abstract

The present invention provides a low-pressure black water flash heat recovery system for coal gasification, which includes a low-pressure flash vessel. The top of the low-pressure flash vessel is connected to a deoxidation tank, a shift stripping column, a low-pressure flash condenser, and a steam jet vacuum pump. The bottom of the low-pressure flash vessel is connected to a vacuum flash vessel. The low-pressure flash condenser is connected to a low-pressure flash separator. The top of the vacuum flash vessel is connected to a vacuum flash condenser. The vacuum flash condenser is connected to a vacuum flash separator. The top of the vacuum flash separator is respectively connected to a steam jet vacuum pump and a water ring vacuum pump. Both the steam jet vacuum pump and the water ring vacuum pump are connected to a vacuum pump separator. The bottoms of the low-pressure flash separator, the vacuum flash separator, and the vacuum pump separator are all connected to an ash water tank. The present invention makes full use of the flash steam treated by the low-pressure flash system, reduces heat loss, improves the heat recovery efficiency, and reduces the production operation cost.

Description

Technical Field

[0001] The present invention relates to a low-pressure black water flashing heat recovery system for coal gasification, belonging to the technical field of low-pressure flashing of water coal slurry gasification process. Background Art

[0002] The gasification device of the entrained flow gasification process mainly includes three parts: a coal slurry preparation system, a gasification system, a primary purification system for syngas, and a slag water treatment system. The water coal slurry is pressurized by a high-pressure coal slurry pump and sent to the gasification furnace for reaction to produce raw syngas. The raw syngas is preliminarily washed in the quench chamber of the gasification furnace, and then enters a mixer, a cyclone separator, and a water wash tower for fine washing. The syngas with saturated water vapor after washing has a dust content of <1 mg / Nm 3 ; after the gasification system and the syngas washing system wash the syngas, a large amount of high-temperature black water will go to the slag water treatment system. The high-temperature black water passes through the slag water treatment system, removes acidic gases, and recovers heat. The high-temperature black water is flashed and cooled step by step under reduced pressure; the solid ash slag in the black water is settled and separated, and the ash water after separating the solid ash slag is treated and then returned to the system for reuse at 70-80 °C. Generally, the black water flashing of the slag water system in a typical water coal slurry gasification process adopts two-stage or three-stage flashing according to the pressure of the gasification system, namely a high-pressure flashing system, a low-pressure flashing system, and a vacuum flashing system.

[0003] The flashing steam of the existing low-pressure flashing system is mainly cooled and exchanged heat by a heat exchange condenser using circulating water. The non-condensable gas after heat exchange is discharged, and the condensate is recycled; the utilization rate of the flashing steam is not high, which is not beneficial to environmental protection and causes waste of resources. The present invention provides a low-pressure black water flashing steam heat recovery system for coal gasification, in which the flashing steam treated by the low-pressure flash evaporator is fully utilized, heat loss is reduced, heat recovery efficiency is improved, and production operation costs are saved. Summary of the Invention

[0004] In order to solve the above technical problems, a low-pressure black water flashing heat recovery system for coal gasification is proposed, and the technical solution is as follows.

[0005] A low-pressure black water flash heat recovery system for coal gasification, comprising a low-pressure flash tank. The top of the low-pressure flash tank is connected to a deoxidation tank, a shift stripping column, a low-pressure flash condenser, and a steam jet vacuum pump respectively through connecting pipelines. The bottom of the low-pressure flash tank is connected to a vacuum flash tank through a connecting pipeline. The low-pressure flash condenser is connected to a low-pressure flash separator through a connecting pipeline. The top of the vacuum flash tank is connected to a vacuum flash condenser through a connecting pipeline. The vacuum flash condenser is connected to a vacuum flash separator through a connecting pipeline. The top of the vacuum flash separator is connected to the steam jet vacuum pump and a water ring vacuum pump respectively through connecting pipelines. Both the steam jet vacuum pump and the water ring vacuum pump are connected to a vacuum pump separator. The bottoms of the low-pressure flash separator, the vacuum flash separator, and the vacuum pump separator are all connected to a ash water tank through connecting pipelines. The top of the low-pressure flash separator is connected to an acid gas flare pipeline. The top of the vacuum pump separator is connected to the outside through a connecting pipeline. The bottom of the vacuum flash tank is connected to a clarification tank through a connecting pipeline.

[0006] Preferably, the top of the vacuum flash separator is connected to the steam jet vacuum pump through a connecting pipeline provided with a first vacuum pressure regulating valve and a first manual regulating valve. The first manual regulating valve is located in the downstream pipe section of the first vacuum pressure regulating valve. The upstream pipe section of the first vacuum pressure regulating valve is connected to a connecting pipeline provided with a second vacuum pressure regulating valve. The water ring vacuum pump is connected to the pipe section between the first vacuum pressure regulating valve and the first manual regulating valve through a connecting pipeline.

[0007] Preferably, a liquid level regulating valve is provided on the connecting pipeline between the low-pressure flash tank and the vacuum flash tank.

[0008] Preferably, the low-pressure flash tank is connected to an evaporation hot water tower through a connecting pipeline.

[0009] Preferably, the deoxidation tank is connected to a low-pressure steam pipeline and a desalinated water pipeline.

[0010] The present invention makes full use of the flash steam treated by the low-pressure flash system, reduces heat loss, improves heat recovery efficiency and saves production operation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic structural diagram of a low-pressure black water flash heat recovery system for coal gasification according to the present invention.

[0012] In the figure: 1. Low-pressure flash evaporator; 2. Deoxidation tank; 3. Low-pressure flash condenser; 4. Steam jet vacuum pump; 5. Vacuum flash evaporator; 6. Low-pressure flash separator; 7. Vacuum flash condenser; 8. Vacuum flash separator; 9. Liquid ring vacuum pump; 10. Vacuum pump separator; 11. First vacuum pressure regulating valve; 12. First manual regulating valve; 13. Second vacuum pressure regulating valve; 14. Liquid level regulating valve; 15. Low-pressure steam pipeline; 16. Desalted water pipeline; 17. Second manual regulating valve. Detailed implementation mode

[0013] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0014] As Figure 1 shown, a low-pressure black water flash heat recovery system for coal gasification includes a low-pressure flash evaporator 1, and the low-pressure flash evaporator 1 is connected to an evaporation hot water tower through a connecting pipeline. The top of the low-pressure flash evaporator 1 is respectively connected to a deoxidation tank 2, a shift stripping tower, a low-pressure flash condenser 3, and a steam jet vacuum pump 4 through connecting pipelines, and the deoxidation tank 2 is connected to a low-pressure steam pipeline 15 and a desalted water pipeline 16. The bottom of the low-pressure flash evaporator 1 is connected to a vacuum flash evaporator 5 through a connecting pipeline, and a liquid level regulating valve 14 is provided on the connecting pipeline between the low-pressure flash evaporator 1 and the vacuum flash evaporator 5. The low-pressure flash condenser 3 is connected to a low-pressure flash separator 6 through a connecting pipeline, the top of the vacuum flash evaporator 5 is connected to a vacuum flash condenser 7 through a connecting pipeline, the vacuum flash condenser 7 is connected to a vacuum flash separator 8 through a connecting pipeline, the top of the vacuum flash separator 8 is respectively connected to the steam jet vacuum pump 4 and a liquid ring vacuum pump 9 through connecting pipelines, and both the steam jet vacuum pump 4 and the liquid ring vacuum pump 9 are connected to a vacuum pump separator 10. The bottoms of the low-pressure flash separator 6, the vacuum flash separator 8, and the vacuum pump separator 10 are all connected to a gray water tank through connecting pipelines, the top of the low-pressure flash separator 6 is connected to an acid gas flare through a connecting pipeline, the top of the vacuum pump separator 10 is connected to the outside through a connecting pipeline, and the bottom of the vacuum flash evaporator 5 is connected to a clarification tank through a connecting pipeline.

[0015] The top of the vacuum flash separator is connected to the steam jet vacuum pump through a connecting pipeline provided with a first vacuum pressure regulating valve and a first manual regulating valve. The first manual regulating valve is located in the downstream pipe section of the first vacuum pressure regulating valve. The upstream pipe section of the first vacuum pressure regulating valve is connected to a connecting pipeline provided with a second vacuum pressure regulating valve. The water ring vacuum pump is connected to the pipe section between the first vacuum pressure regulating valve and the first manual regulating valve through a connecting pipeline.

[0016] The specific working process of the present invention is as follows:

[0017] The black water from the gasification and syngas preliminary purification system is sent to the evaporation chamber of the evaporation hot water tower after being adjusted, controlled and depressurized. The black water preliminarily concentrated at the bottom of the evaporation hot water tower is sent to the low-pressure flash evaporator 1 through the liquid level regulating valve for control.

[0018] The black water entering the low-pressure flash evaporator 1 flashes under reduced pressure. The flash steam after flashing is recycled in four ways:

[0019] The first way: The flash steam of the low-pressure flash evaporator 1 mainly goes to the shift stripping tower to replace the low-pressure steam for use.

[0020] The second way: The flash steam of the low-pressure flash evaporator 1 goes to the deoxidizing tank 2. Before the gasification unit system is started up, the temperature of the deoxidizing tank 2 should be about 101°C and the pressure should be 0.015 MPa. Under these conditions, low-pressure steam and demineralized water are introduced into the deoxidizing tank through the low-pressure steam pipeline 15 and the demineralized water pipeline 16. The low-pressure steam is used to heat the demineralized water, and the demineralized water deoxygenated is pumped to the high-pressure flash system through a pump; after the system is started up normally and the flash steam of the low-pressure flash evaporator 1 is normal, that is, the pressure is 0.15 - 0.2 MPa, the flash steam is controlled by the second manual regulating valve 17 to flow to the deoxidizing tank 2 to replace the low-pressure steam for use.

[0021] The third way: A small amount of low-pressure flash steam goes to the steam jet vacuum pump 4. In the early stage of the start-up of the gasification unit system, the black water flash system is unstable. In order to maintain the normal operation of the vacuum flash separator 5, maintain the temperature at 70 - 80°C and the pressure at -0.056 MPa, the water ring vacuum pump 9 is used to draw negative pressure in the early stage of operation. At this time, the first vacuum pressure regulating valve 11 is opened, and the operation of the water ring vacuum pump 9 makes the vacuum flash separator 5, the vacuum flash condenser 7 and the vacuum flash separator 8 all maintain negative pressure. The second vacuum pressure regulating valve 13 is used to cooperate to control the pressure of the vacuum flash separator 5 to be maintained at -0.056 MPa; when the flash steam of the low-pressure flash evaporator 1 is normal, the low-pressure flash steam is connected through the first manual regulating valve 12 to start the steam jet vacuum pump 4, stop the water ring vacuum pump 9, and at the same time close the second vacuum pressure regulating valve 13. The coordinated adjustment of the first vacuum pressure regulating valve 11 and the second vacuum pressure regulating valve 13 can be realized through the PLC controller.

[0022] The black water at the bottom of the low-pressure flash evaporator 1 is sent into the vacuum flash evaporator 5 through the liquid level regulating valve 14. Due to the operation of the steam jet vacuum pump 4, the black water entering the vacuum flash evaporator 5 flashes under negative pressure. The flashed gas is cooled by heat exchange in the vacuum flash condenser 7, and the condensate enters the ash water tank after entering the vacuum flash separator 8. The gas phase forms a negative pressure in the vacuum flash evaporator 5 through the action of the steam jet vacuum pump 4. The condensate of the steam jet vacuum pump 4 enters the vacuum pump separator 10 and then enters the ash water tank. The trace non-condensable gas is discharged at a safe height. The black water at the bottom of the vacuum flash evaporator 5 is mixed with the flocculant in the static mixer and then enters the clarifying tank for solid-liquid separation. The clarified ash water in the clarifying tank overflows to the ash water tank and is pumped to the system for reuse.

[0023] The fourth path: When each device in the flash evaporation system does not require steam during the start-up and shutdown of the gasification device system or when a slight adjustment of the operating pressure of the low-pressure flash evaporator 1 is required, the low-pressure flash steam is controlled to enter the low-pressure flash condenser 3 for heat exchange and cooling through the pressure regulating valve. The condensate enters the low-pressure flash separator 6 and then enters the ash water tank, and a small amount of non-condensable gas goes to the acid gas flare.

[0024] Considering whether the flashed steam volume described above can meet the requirements of the four-way gas supply, generally, the gasification device has multiple series, which is sufficient for the demand of the four-way flashed steam, ensuring the full utilization of the low-pressure flash steam. The present invention realizes the heat recovery and effective utilization of the steam after step-by-step pressure reduction flashing in the low-pressure flash evaporation system. Generally, the flashed steam is mainly cooled and heat-exchanged by using circulating water through a heat exchanger, and the non-condensable gas after heat exchange is vented. The utilization rate of the flashed steam is not high, which is not beneficial to environmental protection and causes waste of resources. The flashed steam treated by the low-pressure flash evaporation system can be fully utilized, reducing heat loss, improving the heat recovery efficiency and saving the production operation cost.

[0025] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-pressure black water flash heat recovery system for coal gasification, characterized in that: It includes a low-pressure flash evaporator. The top of the low-pressure flash evaporator is respectively connected to a deoxidation tank, a conversion stripping column, a low-pressure flash condenser and a steam jet vacuum pump through connecting pipelines. The bottom of the low-pressure flash evaporator is connected to a vacuum flash evaporator through a connecting pipeline. The low-pressure flash condenser is connected to a low-pressure flash separator through a connecting pipeline. The top of the vacuum flash evaporator is connected to a vacuum flash condenser through a connecting pipeline. The vacuum flash condenser is connected to a vacuum flash separator through a connecting pipeline. The top of the vacuum flash separator is respectively connected to a steam jet vacuum pump and a water-ring vacuum pump through connecting pipelines. Both the steam jet vacuum pump and the water-ring vacuum pump are connected to a vacuum pump separator; the bottoms of the low-pressure flash separator, the vacuum flash separator and the vacuum pump separator are all connected to an ash water tank through connecting pipelines. The top of the low-pressure flash separator is connected to an acid gas flare through a connecting pipeline; the top of the vacuum pump separator is connected to the outside through a connecting pipeline. The bottom of the vacuum flash evaporator is connected to a clarification tank through a connecting pipeline; The top of the vacuum flash separator is connected to the steam jet vacuum pump through a connecting pipeline provided with a first vacuum pressure regulating valve and a first manual regulating valve. The first manual regulating valve is located in the downstream pipe section of the first vacuum pressure regulating valve. The upstream pipe section of the first vacuum pressure regulating valve is connected to a connecting pipeline provided with a second vacuum pressure regulating valve. The water-ring vacuum pump is connected to the pipe section between the first vacuum pressure regulating valve and the first manual regulating valve through a connecting pipeline; A liquid level regulating valve is provided on the connecting pipeline between the low-pressure flash evaporator and the vacuum flash evaporator.

2. The low-pressure black water flash heat recovery system for coal gasification according to claim 1, wherein: The low-pressure flash evaporator is connected to an evaporation hot water tower through a connecting pipeline.

3. The low-pressure black water flash heat recovery system for coal gasification according to claim 1, wherein: The deoxidation tank is connected to a low-pressure steam pipeline and a desalinated water pipeline.

Images