Black water waste heat recovery method and application

Abstract

The invention provides a black water waste heat recovery method and application, and belongs to the technical field of chemical engineering, the method is as follows: a black water pipeline from a gasification furnace is sequentially flashed through a high-pressure flash tank, a low-pressure flash tank and a vacuum flash tank and finally reaches a precipitation tank; a process pipeline is additionally arranged on the upstream of a black water pipeline adjusting valve at the bottom of a high-pressure flash tank, the process pipeline is connected to a shell pass of a high-pressure carbon dioxide heat exchanger in parallel and exchanges heat with a tube pass of the high-pressure carbon dioxide heat exchanger, the temperature is increased after heat exchange, and the process pipeline is sent to all users for use; after black water discharged from the high-pressure flash tank is subjected to heat exchange through the high-pressure CO2 heat exchanger, the temperature is reduced, the flow to the low-pressure flash tank is controlled by adjusting a downstream black water flow adjusting valve, the thermal load of the low-pressure flash tank is indirectly reduced, the flow to the vacuum flash tank is controlled by the low-pressure flash tank through a downstream black water adjusting valve, and the thermal load of the vacuum flash tank is reduced. And the vacuum pump of the vacuum flash is reduced or stopped according to the vacuum flash pressure condition, so that energy is saved. High-flash black water waste heat replaces low-pressure steam, and the true flash load is indirectly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, in particular to a method for recovering waste heat from black water and its application. Background Art

[0002] In general, the present invention addresses the deficiencies in the prior art and provides a rationally designed and efficient method for recovering waste heat from black water.

[0003] The black water from the gasifier exits at a temperature of 202°C and 4.1 MPa before entering a high-pressure flash tank for flash evaporation at a pressure of 0.5 MPa and a temperature of 155°C. The black water at the bottom of the tank is then sent to a low-pressure flash tank for flash evaporation at a temperature of 133°C and 0.2 MPa. Flash gas from the top of the low-pressure flash tank is sent to a deaerator for use as gray water, converted into low-temperature condensate, and used to replenish deionized water for system deoxygenation. The black water after low-pressure flash evaporation then enters a vacuum flash tank for further flash evaporation at a temperature of 92°C and -0.02 MPa. After condensation in a vacuum flash condenser, the flash gas enters a vacuum flash separator. The separated water flows by gravity to a settling tank, and non-condensable gases are discharged to the atmosphere by a vacuum pump. True flash pressure is affected by low flash pressure and black water temperature. During normal production, this pressure is adjusted by a vacuum pump. Large pressure fluctuations require additional vacuum pumps to control the pressure, increasing power consumption and making operation uneconomical. Summary of the Invention

[0004] The technical task of the present invention is to solve the deficiencies of the prior art and provide a black water waste heat recovery method and application.

[0005] The technical solution of the present invention is implemented in the following manner: a method for recovering waste heat from black water of the present invention is: The black water pipeline from the gasifier passes through the high-pressure flash tank, low-pressure flash tank, and vacuum flash tank for flash evaporation in sequence and finally reaches the sedimentation tank; A process pipeline is added upstream of the black water pipe regulating valve at the bottom of the high-pressure flash tank. The process pipeline is connected in parallel to the shell side of the high-pressure carbon dioxide heat exchanger to exchange heat with the tube side of the high-pressure carbon dioxide heat exchanger. After heat exchange, the temperature is raised and the water is delivered to various users. Specifically: The downstream branch of the process pipeline is connected to the black water inlet pipeline of the high-pressure CO2 heat exchanger, and the black water inlet pipeline of the high-pressure CO2 heat exchanger is connected to the shell side of the high-pressure CO2 heat exchanger. After heat exchange, the black water pipelines of the shell side are connected to the downstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank; The high-pressure CO2 tank is divided into a CO2 inlet pipeline connected to the high-pressure CO2 heat exchanger. The CO2 inlet pipeline runs through the pipe side of the high-pressure CO2 heat exchanger, entering from the bottom and exiting from the top. The CO2 outlet pipelines of the pipe side converge and connect to the CO2 pipelines to each user. The low-pressure steam downstream branch is connected to the low-pressure steam inlet pipeline of the high-pressure CO2 heat exchanger, and the low-pressure steam inlet pipeline is connected to the shell side of the high-pressure CO2 heat exchanger. A condensate output pipeline is configured at the bottom of the shell side; The downstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank is connected to the low-pressure flash tank, the black water pipeline at the bottom of the low-pressure flash tank is connected to the vacuum flash tank, and the black water pipeline at the bottom of the vacuum flash tank is connected to the sedimentation tank; The temperature of the black water from the high-pressure flash tank is reduced after heat exchange in the high-pressure CO2 heat exchanger. The flow to the low-pressure flash tank is controlled by adjusting the downstream black water flow regulating valve, thereby indirectly reducing the heat load of the low-pressure flash tank. The flow to the vacuum flash tank is controlled by the downstream black water regulating valve of the low-pressure flash tank, thereby reducing the heat load of the vacuum flash tank. The vacuum pump of the vacuum flash is reduced or disabled according to the vacuum flash pressure to achieve energy saving.

[0006] The black water inlet pipeline of the high-pressure CO2 heat exchanger, the shell side of the high-pressure CO2 heat exchanger, and the black water pipeline of the shell side constitute the black water waste heat release route; as well as, The CO2 inlet pipeline, the pipe side of the high-pressure CO2 heat exchanger, and the CO2 outlet pipeline at the outlet side constitute the temperature increase route of the high-pressure CO2; The waste heat of black water is used to heat high-pressure CO2; The low-pressure steam inlet pipeline, the shell side of the high-pressure CO2 heat exchanger, and the condensate output pipeline constitute the heat supply route; The above configuration is set up in two sets, that is, each pipeline and high-pressure CO2 heat exchanger is configured with two parallel sets, one in operation and one in standby, which can be switched over at any time.

[0007] The process pipeline is equipped with temperature monitors, pressure monitors, flow monitors, temperature regulating valves and black water shut-off valves.

[0008] Manual valves and backwash are installed on each inlet and outlet pipe of the high-pressure CO2 heat exchanger for online cleaning of the cut-out system; Each outlet pipe of the high-pressure CO2 heat exchanger is equipped with flow, temperature and pressure gauges. The outlet temperature is automatically interlocked with the black water pipeline regulating valve to automatically adjust the inlet flow according to the temperature to keep the carbon dioxide temperature at the heat exchanger outlet stable.

[0009] The high-pressure CO2 heat exchanger is equipped with a pressure gauge and a drain on the shell side. When the black water side pressure exceeds the standard, the black water shut-off valve is interlocked and closed to prevent high pressure from flowing into low pressure. The black water inlet and outlet pipes of the high-pressure flash tank are equipped with manual valves and drains. When the pressure difference before and after the heat exchanger is high, the spare heat exchanger is switched off and the system is cut out for online cleaning and then put into standby use.

[0010] The structure of the black water waste heat recovery device of the present invention is as described above.

[0011] The black water waste heat recovery method is applied to the waste heat recovery process downstream of the gasifier.

[0012] The black water waste heat recovery device is used in the waste heat recovery process downstream of the gasifier.

[0013] Working principle of the present invention: The black water from the gasifier quenching chamber, coal ash separator and the bottom of the water washing tower is depressurized and sent to the high-pressure flash tank for flash evaporation. After flash evaporation, the top flash gas enters the flash gas scrubber, and after countercurrent heat exchange with the deoxygenated water from the deoxygenated water pump under the action of the tower plate, enters the flash gas cooler for condensation, and then enters the high-pressure flash separator. The separated condensate can be sent to the ash water tank or sedimentation tank. The flash gas from the top of the high-pressure flash separator is pressure-regulated and sent to the flare device for complete combustion and then discharged during start-up, shutdown or accident. The ash water discharged from the bottom of the flash gas scrubber is pressurized by the high-pressure ash water pump and sent to the water washing tower and slag lock hopper for pressurization for indirect use.

[0014] The black water at the bottom of the high-pressure flash tank is sent to the low-pressure flash tank for flash evaporation. The flash gas at the top of the low-pressure flash tank is sent to the deaerator for use as gray water, conversion of low-temperature condensate, and desalination of the system's supplementary desalted water for deoxygenation. The black water after low-pressure flash evaporation then enters the vacuum flash tank for further flash evaporation. The flash gas is condensed in the vacuum flash condenser and then enters the vacuum flash separator. The separated water flows by gravity to the sedimentation tank, and the non-condensable gas is discharged to the atmosphere by a vacuum pump. The liquid and solid mixture at the bottom of the vacuum flash tank flows by gravity into the sedimentation tank. Water pumped from the slag pool is sent to the vacuum flash tank for treatment.

[0015] High-pressure CO2 is primarily used for pulverized coal pressurization and delivery systems, flame detector purging and protection, gasifier annular space purging and protection, and fuel gas pipeline purging for startup burners and pulverized coal burner pulverized coal pipeline purging. During normal production, CO2 is pressurized to 6.5 MPa and 93°C by the CO2 unit. One route enters the pulverized coal pressurization CO2 buffer tank for pulverized coal pressurization, and another route enters the pulverized coal delivery CO2 buffer tank. Low-pressure steam (2 tons / hour) is used to heat the CO2 heat exchanger to 105°C, where it is used as the pulverized coal delivery medium before being delivered to the gasifier burners and various protective gases.

[0016] The beneficial effects of the present invention compared with the prior art are: The present invention provides a blackwater waste heat recovery method and application. This utilizes the waste heat from the bottom blackwater of a high-flash reactor to heat pulverized coal for transporting high-pressure carbon dioxide gas. This waste heat replaces the low-pressure steam in the high-pressure carbon dioxide heat exchanger. This simultaneously lowers the temperature of the high-flash reactor blackwater to remove the low-flash reactor, reducing the amount of heat required to remove the true flash reactor. This allows the vacuum pump to be deactivated, allowing the true flash reactor pressure to be controlled, thereby achieving energy savings and consumption reductions. The waste heat from the high-flash reactor blackwater replaces low-pressure steam, indirectly reducing the true flash reactor load and deactivating the vacuum pump.

[0017] The present invention adds a high-flash bottom black water to the high-pressure carbon dioxide heat exchanger heating pipeline. The black water exchanges heat with the high-pressure carbon dioxide to replace the low-pressure steam. The black water after heat exchange goes to the low-flash tank, and the low-flash black water goes to the true flash tank, which indirectly reduces the low-flash and true flash loads. After the vacuum pump is deactivated, the true flash pressure can be controlled, thereby achieving the purpose of reducing costs and increasing efficiency.

[0018] The present invention can achieve: 1. Recycling of waste heat from black water can save 2 tons of steam per hour.

[0019] 2. Two high-pressure carbon dioxide heat exchangers are set up in parallel to achieve online cleaning and ensure long-term operation.

[0020] 3. After the true flash heat load is reduced, the vacuum pump is stopped and the power saving effect is obvious.

[0021] 4. High investment cost efficiency, obvious energy saving effect and reduced production costs.

[0022] 5. Interlocking is set, with high safety factor, simple structure, easy operation and convenient maintenance.

[0023] This invention aims to be safe, energy-efficient, and environmentally friendly. It uses waste heat from black water to replace low-pressure steam while meeting the outlet temperature of the high-pressure CO2 heat exchanger, saving energy. It also reduces the flash heat load, disables the vacuum pump, saves electricity, and lowers production costs.

[0024] The black water waste heat recovery method and application of the present invention have reasonable design, simple structure, safety and reliability, convenient use and easy maintenance, and have great promotion and utilization value. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] The symbols in the accompanying drawings represent: 1. Black water pipeline from gasifier, 2. High-pressure flash tank, 3. Low-pressure flash tank, 4. Vacuum flash tank, 5. Sedimentation tank, 6. Black water pipeline regulating valve, 7. Process pipeline, 8. High-pressure carbon dioxide heat exchanger, 9. Shell side of high pressure carbon dioxide heat exchanger, 10. The tube side of the high-pressure carbon dioxide heat exchanger, 11. Black water inlet pipeline of high-pressure CO2 heat exchanger, 12. Black water pipeline in the shell process, 13. High-pressure CO2 tank, 14. CO2 inlet pipeline of high-pressure CO2 heat exchanger, 15. CO2 outlet pipeline of the outlet pipe, 16. CO2 goes to each user pipeline, 17. Low-pressure steam, 18. Low-pressure steam inlet pipeline of high-pressure CO2 heat exchanger, 19. Condensate output pipeline, 20. Black water shut-off valve. DETAILED DESCRIPTION

[0027] The following is a detailed description of a black water waste heat recovery method and application of the present invention in conjunction with the accompanying drawings.

[0028] As shown in the accompanying drawings, the present invention provides a method and application for recovering waste heat from black water, including a high-pressure flash tank (hereinafter referred to as high flash), a low-pressure flash tank (hereinafter referred to as low flash), and a vacuum flash tank (hereinafter referred to as true flash).

[0029] Specific implementation: The present invention is carried out while ensuring safe and stable operation of the system, and can realize online cleaning of the heat exchanger. Two heat exchangers are arranged in parallel, one is in operation and the other is in standby, and can be switched back at any time.

[0030] A DN200 pipeline was added before the regulating valve on the high-flash bottom black water pipeline (pressure 0.5MPa, temperature 155°C) and connected to the shell-side of the high-pressure CO2 heat exchanger. This pipeline exchanges heat with the high-pressure CO2 on the pipe side (pressure 5.1MPa, temperature 93°C). After heat exchange, the temperature is raised to 105°C before delivery to various users. A DN200 manual valve was added to the high-flash bottom black water pipeline. Before the DN200 manual valve, the pipeline is connected to the heat exchanger inlet pipeline, which is equipped with temperature, pressure, flow, electric valves, and a shut-off valve. The DN200 outlet pipeline of the heat exchanger is connected after the new manual valve and before the regulating valve on the high-flash bottom black water pipeline. The regulating valve controls the flow of the black water to the low-flash tank after heat exchange. Manual valves and drains are installed on both the black water inlet and outlet pipelines. Pressure, temperature, flow, and differential pressure gauges are also installed on the pipeline. The inlet and outlet pipes of the carbon dioxide heat exchanger are equipped with manual valves and backflow drains to facilitate online cleaning of the cut-out system. The outlet pipe of the carbon dioxide heat exchanger is equipped with flow, temperature, and pressure gauges. The outlet temperature and the black water regulating valve are automatically adjusted. The inlet flow is automatically adjusted according to the temperature to keep the carbon dioxide temperature at the outlet of the heat exchanger stable. The temperature of the black water after heat exchange is reduced from 155 degrees to 130 degrees, and the flow to the low flash tank is controlled by the black water regulating valve. The shell side of the heat exchanger is equipped with a pressure gauge and a drain. When the pressure on the black water side exceeds the standard, the black water shut-off valve is interlocked and closed to prevent high pressure from flowing into low pressure. The inlet and outlet pipes of the high flash black water are equipped with manual valves and drains. When the pressure difference before and after the heat exchanger is high, the standby heat exchanger is backflowed and the system is cut out for online cleaning and then put into standby.

[0031] After heat exchange, the temperature of high-flash black water is reduced to about 130 degrees. By adjusting the black water flow regulating valve to control the flow to the low-flash tank, the low-flash heat load (temperature 108 degrees) is indirectly reduced. The low-flash flow is controlled by the black water regulating valve to control the flow to the true flash tank, reducing the true flash heat load (temperature 68 degrees). According to the true flash pressure, the vacuum pump (75KW.H) is reduced or stopped to achieve energy saving.

[0032] The present invention: 1. Add a new black water to heat exchanger pipeline, and set the electric regulating valve and heat exchanger outlet temperature to automatically control to achieve automatic temperature control.

[0033] 2. The newly added black water pipeline inlet and outlet pipelines are equipped with a pressure differential gauge, and a spare heat exchanger is cut back to achieve online cleaning.

[0034] 3. When the shell pressure of the heat exchanger exceeds the standard, the black water inlet pipeline cut-off valve will be interlocked and closed to ensure safety.

[0035] 4. The present invention has low investment cost, obvious energy-saving effect and high safety factor.

Claims

1. A method for recovering waste heat from black water, characterized in that The method is: The black water pipeline from the gasifier passes through the high-pressure flash tank, low-pressure flash tank, and vacuum flash tank for flash evaporation in sequence and finally reaches the sedimentation tank; Add a process pipeline upstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank. The process pipeline is connected in parallel to the shell side of the high-pressure carbon dioxide heat exchanger to exchange heat with the tube side of the high-pressure carbon dioxide heat exchanger. After heat exchange, the temperature is raised and the water is delivered to various users. Specifically: The downstream branch of the process pipeline is connected to the black water inlet pipeline of the high-pressure CO2 heat exchanger, and the black water inlet pipeline of the high-pressure CO2 heat exchanger is connected to the shell side of the high-pressure CO2 heat exchanger. After heat exchange, the black water pipelines of the shell side are connected to the downstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank; The high-pressure CO2 tank is divided into a CO2 inlet pipeline connected to the high-pressure CO2 heat exchanger. The CO2 inlet pipeline runs through the pipe side of the high-pressure CO2 heat exchanger, entering from the bottom and exiting from the top. The CO2 outlet pipelines of the pipe side converge and connect to the CO2 pipelines to each user. The low-pressure steam downstream branch is connected to the low-pressure steam inlet pipeline of the high-pressure CO2 heat exchanger, and the low-pressure steam inlet pipeline is connected to the shell side of the high-pressure CO2 heat exchanger. A condensate output pipeline is configured at the bottom of the shell side; The downstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank is connected to the low-pressure flash tank, the black water pipeline at the bottom of the low-pressure flash tank is connected to the vacuum flash tank, and the black water pipeline at the bottom of the vacuum flash tank is connected to the sedimentation tank; The temperature of the black water from the high-pressure flash tank is reduced after heat exchange in the high-pressure CO2 heat exchanger. The flow to the low-pressure flash tank is controlled by adjusting the downstream black water flow regulating valve, thereby indirectly reducing the heat load of the low-pressure flash tank. The flow to the vacuum flash tank is controlled by the downstream black water regulating valve of the low-pressure flash tank, thereby reducing the heat load of the vacuum flash tank. The vacuum pump of the vacuum flash is reduced or disabled according to the vacuum flash pressure to achieve energy saving.

2. The method for recovering waste heat from black water according to claim 1, wherein: The black water inlet pipeline of the high-pressure CO2 heat exchanger, the shell side of the high-pressure CO2 heat exchanger, and the black water pipeline of the shell side constitute the black water waste heat release route; as well as, The CO2 inlet pipeline, the pipe side of the high-pressure CO2 heat exchanger, and the CO2 outlet pipeline at the outlet side constitute the temperature increase route of the high-pressure CO2; The waste heat of black water is used to heat high-pressure CO2; The low-pressure steam inlet pipeline, the shell side of the high-pressure CO2 heat exchanger, and the condensate output pipeline constitute the heat supply route; The above configuration is set up in two sets, that is, each pipeline and high-pressure CO2 heat exchanger is configured with two parallel sets, one in operation and one in standby, which can be switched over at any time.

3. The method for recovering waste heat from black water according to claim 1, wherein: The process pipeline is equipped with temperature monitors, pressure monitors, flow monitors, temperature regulating valves and black water shut-off valves.

4. The method for recovering waste heat from black water according to claim 3, wherein: Manual valves and backwash are installed on each inlet and outlet pipe of the high-pressure CO2 heat exchanger for online cleaning of the cut-out system; Each outlet pipe of the high-pressure CO2 heat exchanger is equipped with flow, temperature and pressure gauges. The outlet temperature is automatically interlocked with the black water pipeline regulating valve to automatically adjust the inlet flow according to the temperature to keep the carbon dioxide temperature at the heat exchanger outlet stable.

5. The method for recovering waste heat from black water according to claim 4, characterized in that: The high-pressure CO2 heat exchanger is equipped with a pressure gauge and a drain on the shell side. When the black water side pressure exceeds the standard, the black water shut-off valve is interlocked and closed to prevent high pressure from flowing into low pressure. The black water inlet and outlet pipes of the high-pressure flash tank are equipped with manual valves and drains. When the pressure difference before and after the heat exchanger is high, the spare heat exchanger is switched off and the system is cut out for online cleaning and then put into standby use.

6. A black water waste heat recovery device, characterized in that The structure of the device is: The black water pipeline from the gasifier passes through the high-pressure flash tank, low-pressure flash tank, and vacuum flash tank for flash evaporation in sequence and finally reaches the sedimentation tank; Add a process pipeline upstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank. The process pipeline is connected in parallel to the shell side of the high-pressure carbon dioxide heat exchanger to exchange heat with the tube side of the high-pressure carbon dioxide heat exchanger. After heat exchange, the temperature is raised and the water is delivered to various users. Specifically: The downstream branch of the process pipeline is connected to the black water inlet pipeline of the high-pressure CO2 heat exchanger, and the black water inlet pipeline of the high-pressure CO2 heat exchanger is connected to the shell side of the high-pressure CO2 heat exchanger. After heat exchange, the black water pipelines of the shell side are connected to the downstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank; The high-pressure CO2 tank is divided into a CO2 inlet pipeline connected to the high-pressure CO2 heat exchanger. The CO2 inlet pipeline runs through the pipe side of the high-pressure CO2 heat exchanger, entering from the bottom and exiting from the top. The CO2 outlet pipelines of the pipe side converge and connect to the CO2 pipelines to each user. The low-pressure steam downstream branch is connected to the low-pressure steam inlet pipeline of the high-pressure CO2 heat exchanger, and the low-pressure steam inlet pipeline is connected to the shell side of the high-pressure CO2 heat exchanger. A condensate output pipeline is configured at the bottom of the shell side; The downstream of the black water pipeline regulating valve at the bottom of the high-pressure flash tank is connected to the low-pressure flash tank, the black water pipeline at the bottom of the low-pressure flash tank is connected to the vacuum flash tank, and the black water pipeline at the bottom of the vacuum flash tank is connected to the sedimentation tank; The temperature of the black water from the high-pressure flash tank is reduced after heat exchange in the high-pressure CO2 heat exchanger. The flow to the low-pressure flash tank is controlled by adjusting the downstream black water flow regulating valve, thereby indirectly reducing the heat load of the low-pressure flash tank. The flow to the vacuum flash tank is controlled by the downstream black water regulating valve of the low-pressure flash tank, thereby reducing the heat load of the vacuum flash tank. The vacuum pump of the vacuum flash is reduced or disabled according to the vacuum flash pressure.

7. Application of the black water waste heat recovery method according to claims 1 to 5 in a waste heat recovery process downstream of a gasifier.

8. Application of the black water waste heat recovery device as claimed in claim 6 in a waste heat recovery process downstream of a gasifier.

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