System and method for heating desalted water by using waste heat of black water gasification process

Abstract

The invention discloses a system and method for heating desalted water by using waste heat of a black water gasification process, and belongs to the technical field of coal chemical industry energy conservation, and the system is additionally provided with a black water heat exchanger, a desalted water heat exchanger, a boiler water buffer tank and a circulating pump on an original net pipe. According to the method, a closed circulation loop with boiler water as an intermediate heating medium is constructed, high-temperature black water from a gasification furnace is subjected to indirect heat exchange with the boiler water in a black water heat exchanger, and waste heat is recycled; the heated boiler water is buffered and pumped and then indirectly exchanges heat with desalted water to be heated in the desalted water heat exchanger, so that the desalted water is heated to the required temperature and then fed into a boiler deaerator. According to the invention, direct replacement of desalted water heating steam by black water waste heat is safely and reliably realized, meanwhile, the black water cooling load is reduced, and remarkable energy-saving and consumption-reducing effects and economic benefits are achieved; clean boiler water is adopted as an intermediate heating medium, so that the risks of blockage, corrosion and cross contamination possibly caused by direct heat exchange are avoided.

Description

Technical Field

[0001] This invention relates to the field of energy-saving technology in coal chemical industry, and in particular to a system and method for heating demineralized water using waste heat from the gasification black water process. Background Technology

[0002] In the coal chemical industry, coal gasification units are the core production units. During operation, gasifiers generate large amounts of high-temperature black water, typically exceeding 200°C, carrying significant waste heat. The current mainstream treatment process involves directly cooling some of this high-temperature black water using gasification quench water before sending it to a high-pressure flash tank and subsequent slag and water treatment system. While this process meets safety requirements, it means a large amount of high-quality thermal energy is wasted without utilization, resulting in serious energy waste.

[0003] On the other hand, to ensure the safe and efficient operation of the boiler, the boiler feedwater (demineralized water) needs to be heated to about 150°C to remove dissolved oxygen before entering the boiler deaerator. Currently, low-pressure steam of about 0.5MPa is commonly used for direct heating. This method consumes a large amount of high-grade steam, resulting in high plant operating costs. Moreover, from the perspective of energy cascade utilization, heating low-temperature working fluid with high-quality steam is not economical.

[0004] While there have been attempts in the industry to recover waste heat from black water, such as for generating low-pressure steam or preheating other media, the characteristics of gasified black water, including high pressure, easy scaling, and the presence of solid particles and corrosive components, coupled with the extremely stringent requirements for water purity and pressure stability in boiler feedwater systems, make it difficult to directly, safely, and efficiently exchange heat between these two working fluids due to their vastly different physicochemical properties and incompatible operating conditions.

[0005] Therefore, a method is proposed to solve the above problems by directly using the waste heat of black water to replace precious steam for heating desalinated water. Summary of the Invention

[0006] The purpose of this invention is to provide a system and method for heating demineralized water using waste heat from the gasification black water process, which can safely, reliably and efficiently recover waste heat from black water and directly replace the steam used to heat demineralized water, thereby achieving significant energy saving and consumption reduction.

[0007] To achieve the above objectives, the present invention provides a system for heating demineralized water using waste heat from a blackwater gasification process, comprising: The black water heat exchanger has a black water channel used to connect the black water outlet of the gasifier to the high-pressure flash tank. The demineralized water heat exchanger has a demineralized water channel used to connect the demineralized water source to the boiler deaerator. A boiler water buffer tank, the inlet of which is connected to the outlet of the boiler water channel of the black water heat exchanger via a pipeline; A circulating pump, the inlet of which is connected to the outlet of the boiler water buffer tank, and the outlet of which is connected to the inlet of the boiler water channel of the demineralized water heat exchanger; The outlet of the boiler water channel of the demineralized water heat exchanger is connected back to the inlet of the boiler water channel of the black water heat exchanger, thus forming a boiler water circulation pipeline.

[0008] Preferably, the black water heat exchanger is a shell-and-tube heat exchanger, with the black water channel being the tube side and the boiler water channel being the shell side.

[0009] Preferably, the demineralized water heat exchanger is a shell-and-tube heat exchanger, with the demineralized water channel being the tube side and the boiler water channel being the shell side.

[0010] Preferably, the inlet pipe of the boiler water buffer tank is equipped with a liquid level regulating valve to stabilize the system pressure and flow rate.

[0011] Preferably, an online conductivity meter is installed on the demineralized water outlet pipe of the demineralized water heat exchanger to monitor whether the heat exchanger is leaking in real time.

[0012] The present invention also provides a method for heating desalinated water using waste heat from the gasification black water process using the above-described system, comprising the following steps: S1. Construct a closed-loop circulation circuit with boiler water as the intermediate medium; the circuit flows sequentially through the boiler water side of the black water heat exchanger, the boiler water buffer tank, the circulation pump, and the boiler water side of the demineralized water heat exchanger. S2. The high-temperature black water from the gasifier is indirectly heated with the boiler water in the closed-loop circulation in the black water heat exchanger. The black water is discharged after the temperature is reduced. S3. The boiler water, after being heated by heat exchange, enters a boiler water buffer tank and is then transported to the demineralized water heat exchanger via a circulating pump. S4. In the demineralized water heat exchanger, the boiler water and the demineralized water to be heated exchange heat indirectly, transferring heat to the demineralized water. The heated demineralized water is then sent to the boiler deaerator. S5. The boiler water that has released heat in the demineralized water heat exchanger is returned to the black water heat exchanger for reheating, thus completing the cycle.

[0013] Preferably, the pressure of the boiler water is 2.4~2.6MPa.

[0014] Preferably, in step S3, online water quality monitoring is performed at the desalinated water outlet of the desalinated water heat exchanger; a water quality monitoring instrument is installed on the desalinated water outlet pipe of the desalinated water heat exchanger to monitor in real time changes in the desalinated water quality caused by potential leaks in the heat exchanger.

[0015] Preferably, by adjusting the inlet or outlet of the boiler water buffer tank, the internal liquid level is kept stable, thereby ensuring stable pressure and flow in the closed-loop circulation circuit.

[0016] Therefore, the system and method for heating desalinated water using waste heat from the gasification black water process of the present invention have the following beneficial effects: (1) Direct energy saving and significant benefits: The high-temperature waste heat of the originally abandoned gasified black water was successfully recovered and directly used to replace 0.5MPa steam to heat the desalinated water, which greatly reduced the consumption of high-quality steam and directly saved production costs.

[0017] (2) System synergy, dual benefits: While recovering waste heat, the amount of chilled water required for black water cooling is reduced, realizing the integrated solution of upstream waste heat recovery and downstream heat demand, and the system energy efficiency is significantly improved.

[0018] (3) Safe and reliable, stable operation: Boiler water matching the boiler pressure level is used as the intermediate heat medium. Through indirect heat exchange, the two working fluids with different qualities and pressures, black water and demineralized water, are effectively isolated, avoiding the risks of blockage, corrosion and pollution that may be caused by direct heat exchange; buffer tanks and liquid level control are set up to ensure the stability of pressure and flow of the circulation system.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of an embodiment of the present invention; Figure label: 1. Gasifier; 2. Black water heat exchanger; 3. High-pressure flash tank; 4. Boiler water buffer tank; 5. Liquid level regulating valve; 6. Circulating pump; 7. Demineralized water heat exchanger; 8. Online conductivity meter; 9. Boiler deaerator; 10. Demineralized water source; 11. Boiler water piping network. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0023] Example This embodiment provides a system for heating demineralized water using waste heat from a black water gasification process, such as... Figure 1 As shown, the system mainly adds the following equipment to the original process: black water heat exchanger 2, demineralized water heat exchanger 7, boiler water buffer tank 4, circulating pump 6, and corresponding connecting pipes and monitoring instruments. The connection relationships of the components in this system are as follows: Black water heat exchanger 2 is a shell-and-tube heat exchanger. Its tube-side inlet is connected to the black water outlet of gasifier 1 via a pipe; its tube-side outlet is connected to the inlet of the existing high-pressure flash tank 3 via a pipe. Its shell-side inlet and shell-side outlet are used to connect to the boiler water circulation loop. In this embodiment, black water flows through the tube side, while 2.5MPa boiler water from the boiler water system flows through the shell side.

[0024] The demineralized water heat exchanger 7 is a shell-and-tube heat exchanger. Its tube-side inlet is connected to the demineralized water source 10 (i.e., the combined demineralized water pipeline from the low-pressure heater, slag cooler, and transfer station) via a pipeline; its tube-side outlet is connected to the inlet of the boiler deaerator 9 via a pipeline, and an online conductivity meter 8 is installed on this outlet pipeline to continuously monitor the conductivity of the heated demineralized water, thereby monitoring for any water pollution risks caused by leaks in the heat exchanger. Its shell-side inlet and outlet are connected to the boiler water circulation loop. In this embodiment, the 1.2 MPa demineralized water flows through the tube side, and the boiler water flows through the shell side.

[0025] Boiler water circulation loop: The inlet of the boiler water buffer tank 4 is connected to the shell-side outlet of the black water heat exchanger 2 via a pipeline, and a liquid level regulating valve 5 is installed on the inlet pipeline to automatically control and maintain the stability of the liquid level in the tank.

[0026] The outlet of boiler water buffer tank 4 is connected to the inlet of circulating pump 6 via a pipeline. The outlet of circulating pump 6 is connected to the shell-side inlet of demineralized water heat exchanger 7 via a pipeline. The shell-side outlet of demineralized water heat exchanger 7 is connected back to the shell-side inlet of black water heat exchanger 2 via a pipeline, thus forming a complete closed-loop forced circulation loop for boiler water. An online conductivity meter 8 is installed on the demineralized water outlet pipeline of demineralized water heat exchanger 7.

[0027] Using the above system, taking a certain factory area as an example, the waste heat from the gasification black water process is used to heat the demineralized water, which mainly includes the following steps: S1. Construct a closed-loop circulation system with boiler water as the intermediate medium: Draw a branch line from the 2.5MPa boiler water pipeline network 11 in the plant area to inject water into the boiler water circulation loop and vent air. Start the circulation pump 6 to establish the flow of boiler water in the circulation loop.

[0028] S2. High-temperature black water from gasifier 1 undergoes indirect heat exchange with boiler water in a closed-loop circulation circuit in black water heat exchanger 2. The black water is discharged after its temperature decreases. Specifically, high-temperature black water from the bottom of gasifier 1, with a temperature of approximately 210℃, a pressure of approximately 4.0MPa, and a flow rate of approximately 180t / h, enters the tube side of black water heat exchanger 2. As the black water flows within the tube side, it transfers its heat through the tube walls to the boiler water flowing in the shell side. After heat exchange with the boiler water in the shell side, the temperature drops to approximately 178℃. The cooled black water is then discharged from the tube side outlet and returned to the high-pressure flash tank 3. This process recovers the sensible heat of the black water, reducing the consumption of quench water in subsequent processes.

[0029] S3. The boiler water, after being heated by heat exchange, enters the boiler water buffer tank 4, and is then transported to the demineralized water heat exchanger 7 by the circulating pump 6. Specifically, the boiler water heated to 145°C in the shell side of the black water heat exchanger 2 flows through the 2.5MPa boiler water buffer tank 4 (whose liquid level is automatically controlled by the liquid level regulating valve 5) for buffering and pressure stabilization, and is then transported to the shell side of the demineralized water heat exchanger 7 by the circulating pump 6.

[0030] S4. In the demineralized water heat exchanger 7, boiler water and the demineralized water to be heated exchange heat indirectly, transferring heat to the demineralized water in the tube side. During this process, demineralized water at approximately 115°C, 1.2 MPa, and a flow rate of approximately 225 m³ / h, drawn from the low-pressure heater, slag cooler, and shift converter, is introduced into the tube side of the demineralized water heat exchanger 7. As the demineralized water flows in the tube side, it absorbs heat from the high-temperature boiler water flowing in the shell side, thus being heated to 142~145°C. After the heated demineralized water passes the quality test by the online conductivity meter 8, it enters the boiler deaerator 9.

[0031] S5. The boiler water that has released heat and whose temperature has dropped to 120°C in the demineralized water heat exchanger 7 returns to the shell-side inlet of the black water heat exchanger 2 through the pipeline, and is reheated by the high-temperature black water, thus completing the cycle.

[0032] By implementing this embodiment, the temperature of the demineralized water entering the boiler deaerator 9 has been significantly increased from 115°C, fully meeting the process requirements for the inlet water temperature. This allows for the complete cessation or significant reduction of the supply of 0.5MPa steam originally used to heat the demineralized water, achieving the core objective of using waste heat to replace high-quality steam, resulting in significant energy savings and consumption reduction. At the same time, the system design avoids the risks of blockage, corrosion, and cross-contamination that may result from direct heat exchange.

[0033] Therefore, the present invention provides a system and method for heating demineralized water using waste heat from the gasification black water process. This system directly replaces the 0.5MPa steam used for heating demineralized water by utilizing the high-temperature waste heat from the originally discarded black water, reducing the consumption of high-quality steam and lowering production costs. The present invention cleverly couples the upstream "waste heat emission" problem with the downstream "heat demand" problem, reducing the amount of quench water required for cooling the original black water while recovering the waste heat from the black water. This achieves an integrated solution for upstream waste heat recovery and downstream heat demand, resulting in a significant improvement in system energy efficiency.

[0034] It uses boiler water matching the boiler pressure rating as the intermediate heat medium, and through a two-stage indirect heat exchange method, it effectively isolates black water and demineralized water, two working fluids of different qualities and pressures, avoiding the risks of blockage, corrosion, and pollution that may arise from direct heat exchange. The installation of buffer tanks and level control ensures stable pressure and flow in the circulation system. This technical solution can be achieved mainly by adding heat exchangers, buffer tanks, and pump sets to the existing plant pipeline network, requiring minimal modification work, having a short investment payback period, and being easily promoted in existing coal chemical plants.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A system for heating desalinated water using waste heat from a blackwater gasification process, characterized in that, include: The black water heat exchanger has a black water channel used to connect the black water outlet of the gasifier to the high-pressure flash tank. The demineralized water heat exchanger has a demineralized water channel used to connect the demineralized water source to the boiler deaerator. A boiler water buffer tank, the inlet of which is connected to the outlet of the boiler water channel of the black water heat exchanger via a pipeline; A circulating pump, the inlet of which is connected to the outlet of the boiler water buffer tank, and the outlet of which is connected to the inlet of the boiler water channel of the demineralized water heat exchanger; The outlet of the boiler water channel of the demineralized water heat exchanger is connected back to the inlet of the boiler water channel of the black water heat exchanger, thus forming a boiler water circulation pipeline.

2. The system according to claim 1, characterized in that: The black water heat exchanger is a shell-and-tube heat exchanger, with the black water channel on the tube side and the boiler water channel on the shell side.

3. The system according to claim 1, characterized in that: The demineralized water heat exchanger is a shell-and-tube heat exchanger, with the demineralized water channel on the tube side and the boiler water channel on the shell side.

4. The system according to claim 1, characterized in that: The boiler water buffer tank is equipped with a liquid level regulating valve on its inlet pipe.

5. The system according to claim 1, characterized in that: An online conductivity meter is installed on the demineralized water outlet pipe of the demineralized water heat exchanger.

6. A method for heating desalinated water using waste heat from a blackwater gasification process, employing the system as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Construct a closed-loop circulation circuit with boiler water as the intermediate medium; the circuit flows sequentially through the boiler water channel of the black water heat exchanger, the boiler water buffer tank, the circulation pump, and the boiler water channel of the demineralized water heat exchanger. S2. The high-temperature black water from the gasifier is indirectly heated with the boiler water in the boiler water channel in the black water heat exchanger. S3. The boiler water, after being heated by heat exchange, enters the boiler water buffer tank and is then transported to the demineralized water heat exchanger via a circulating pump. S4. In the demineralized water heat exchanger, the boiler water and the demineralized water to be heated exchange heat indirectly, and the heated demineralized water is sent to the boiler deaerator. S5. Boiler water that has released heat in the demineralized water heat exchanger is returned to the black water heat exchanger for reheating.

7. The method according to claim 6, characterized in that: The pressure of the boiler water is 2.4~2.6MPa.

8. The method according to claim 6, characterized in that: In step S3, online water quality monitoring is performed at the desalination outlet of the desalination heat exchanger.

9. The method according to claim 6, characterized in that: The internal liquid level of the boiler water buffer tank is maintained by adjusting the inlet or outlet of the liquid.

Images