Waste heat utilization system

Abstract

The utility model relates to a waste heat utilization system which comprises a boiler, a steam turbine, an air preheater, a fan heater unit, a low-temperature economizer, a first pipeline and a second pipeline. A flue gas outlet of the boiler is sequentially communicated with the air preheater and the low-temperature economizer through a flue gas pipeline; the fan heater unit is communicated with the air preheater; a first branch and a second branch are arranged at the outlet end of the first pipeline, the first branch is communicated with a low-temperature economizer and a first valve, the first valve is located on the downstream side of the low-temperature economizer, the second branch is communicated with a fan heater unit, the second pipeline is communicated between the low-temperature economizer and the fan heater unit, and the second pipeline is provided with a second valve; and the inlet end of the first pipeline, the outlet end of the first branch and the outlet end of the second branch are respectively communicated with a low-pressure heater system of the steam turbine. According to the waste heat utilization system, the inlet air temperature of the air preheater can be guaranteed while boiler flue gas waste heat is recycled, the conditions of cold end corrosion and blockage are relieved, and the stability of the system is guaranteed.

Description

Technical Field

[0001] The present application relates to the technical field of waste heat utilization, and in particular to a waste heat utilization system. Background Art

[0002] In the actual operation of large-scale coal-fired boilers, due to various reasons such as dust and slagging on the heated surface, changes in the composition of the coal used (such as increased moisture and ash content), improper operation by operators, etc., the boiler exhaust temperature is 10℃-20℃ higher than the design value, and the waste heat loss of boiler exhaust accounts for more than 75% of the heat loss of coal-fired units.

[0003] Recycling waste heat from boiler flue gas not only improves the thermal economy of the unit but also reduces coal consumption. Coal-fired boilers account for a large proportion of the nation's total, and waste heat from flue gas has enormous potential for utilization and energy conservation.

[0004] At present, the common practice for recovering and utilizing waste heat from boiler flue gas is to use the flue gas as the heat source for the air preheater, and to install a heat exchanger at a suitable position in the flue gas pipeline after the air preheater and before the desulfurization tower to heat condensate, boiler supply air or low-temperature return water from the urban heating network, thereby recovering part of the heat and achieving energy-saving, efficiency-enhancing and water-saving effects.

[0005] In order to reduce the corrosion of the cold end of the air preheater, power station boilers are generally equipped with a heater unit to increase the air temperature at the air preheater inlet. However, when the external ambient temperature is relatively low, the air temperature at the air preheater inlet may be low, leading to corrosion and blockage of the cold end, which in turn affects the boiler air supply and causes poor system stability.

[0006] How to recycle and utilize the waste heat from boiler flue gas while ensuring the inlet air temperature of the air preheater, reducing corrosion and blockage at the cold end, and ensuring system stability is a technical problem that technical personnel in this field urgently need to solve. Utility Model Content

[0007] The purpose of this application is to provide a waste heat utilization system that can recover and utilize the waste heat of boiler flue gas while ensuring the inlet air temperature of the air preheater, reducing corrosion and blockage at the cold end, and ensuring system stability.

[0008] In order to solve the above technical problems, the present application provides a waste heat utilization system, including a boiler, a steam turbine, an air preheater, a heater unit, a low-temperature economizer, a first pipeline and a second pipeline; the flue gas outlet of the boiler is connected to the air preheater and the low-temperature economizer in sequence through the flue gas pipeline; the heater unit is connected to the air preheater; the outlet end of the first pipeline is provided with a first branch and a second branch, the first branch is connected to the low-temperature economizer and the first valve component, the first valve component is located on the downstream side of the low-temperature economizer, the second branch is connected to the heater unit, the second pipeline is connected between the low-temperature economizer and the heater unit, and the second pipeline is provided with a second valve component; the inlet end of the first pipeline, the outlet end of the first branch and the outlet end of the second branch are respectively connected to the low-pressure heater system of the steam turbine.

[0009] When the first valve component is in the open state and the second valve component is in the closed state, the low-temperature economizer and the heating unit are in parallel mode; when the first valve component is in the closed state and the second valve component is in the open state, the low-temperature economizer and the heating unit are in series mode; when the first valve component and the second valve component are both in the open state, the low-temperature economizer and the heating unit are in a mixed mode.

[0010] By adjusting the first valve and the second valve, the water inlet temperature of the heater can be guaranteed, so that the primary air and the secondary air can ensure the inlet air temperature of the air preheater after heat exchange through the heater, thereby reducing the corrosion of the cold end of the air preheater.

[0011] Optionally, the inlet end of the first pipeline is connected to the condensate outlet end of the 7# low-pressure heater of the low-pressure heater system of the steam turbine, and the outlet end of the second branch is connected to the inlet end of the 8# low-pressure heater of the low-pressure heater system.

[0012] Optionally, the outlet end of the first branch is connected to the inlet end of the 6# low-pressure heater of the low-pressure heater system.

[0013] Optionally, the low-pressure heater system further includes a medium pipeline connected between the 6# low-pressure heater and the 7# low-pressure heater; the waste heat utilization system further includes a three-way structure, the three-way structure is connected to the medium pipeline and is connected to the inlet end of the first pipeline;

[0014] The first pipeline and the medium pipeline are respectively provided with an isolation door and an adjustment door on the side facing the #low-pressure heater.

[0015] Optionally, a first thermometer, a first flow meter and a pressure gauge are further provided on the inlet side of the first pipeline.

[0016] Optionally, a third pipeline is also included, one end of the third pipeline is connected to the first pipeline, and the other end of the third pipeline is connected to the outlet of the heater unit. The third pipeline is provided with a regulating valve, and the first pipeline is also provided with a second thermometer. The connection point between the third pipeline and the first pipeline is located on the upstream side of the second thermometer.

[0017] Optionally, a third thermometer and a second flow meter are further provided on the outlet side of the heater unit.

[0018] Optionally, the heater unit is a steel-aluminum fin heat exchanger.

[0019] Optionally, the low-temperature economizer is a flue gas molten salt heat exchanger.

[0020] Optionally, the heater unit is further provided with a pressure differential transmitter, and the pressure differential transmitter is used to detect the pressure difference between the air inlet and the air outlet of the heater unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural diagram of the waste heat utilization system provided in an embodiment of the present application.

[0022] Attachment Figure 1 In the figure, the reference numerals are described as follows:

[0023] 1 air preheater;

[0024] 2 heating units;

[0025] 3 Low temperature economizer;

[0026] 4 first pipeline, 41 first branch, 411 first valve, 412 third flowmeter, 413 fourth thermometer, 42 second branch, 421 third thermometer, 422 second flowmeter, 423 pressurizing pump, 424 third valve, 43 first thermometer, 44 second thermometer, 45 first flowmeter, 46 pressure gauge;

[0027] 5 second pipeline, 51 second valve member;

[0028] 6 third pipeline, 61 regulating valve, 62 on-off valve;

[0029] 71 6# low-pressure heater, 72 7# low-pressure heater, 73 8# low-pressure heater, 74 medium pipeline;

[0030] 8 isolation doors;

[0031] 9. Adjust the door;

[0032] 10. Flue gas pipeline. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solution of the present application, the present application is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] An embodiment of the present application provides a waste heat utilization system, which includes a boiler, a steam turbine, an air preheater 1, a warm air unit 2, a low-temperature economizer 3, a first pipeline 4 and a second pipeline 5.

[0035] Specifically, such as Figure 1 As shown, the flue gas outlet of the boiler is connected to the air preheater 1 and the low-temperature economizer 3 in sequence through the flue gas pipeline 10. That is to say, the flue gas generated by the boiler is discharged from the flue gas outlet. When passing through the air preheater 1 through the flue gas pipeline 10, it can exchange heat with the air in the air preheater 1, so that the air is heated. The flue gas after heat exchange is then passed into the low-temperature economizer 3 to exchange heat with the medium in the low-temperature economizer 3. The flue gas after heat exchange is then passed into the chimney for discharge. The waste heat of the boiler flue gas can be fully recovered and utilized through the air preheater 1 and the low-temperature economizer 3, thereby improving economic efficiency.

[0036] It is not difficult to understand that the boiler flue gas needs to be purified before being discharged. How to purify it is an existing technology well known to those skilled in the art. To save space, it will not be described here.

[0037] The heating unit 2 is connected to the air preheater 1 , and can heat the primary air and secondary air entering the air preheater 1 , thereby increasing the inlet air temperature of the air preheater 1 and reducing cold end corrosion of the air preheater 1 .

[0038] The inlet end of the first pipeline 4 is connected to the low-pressure heating system of the steam turbine, and is used to lead out the medium in the low-pressure heating system. Part of the medium will follow the first pipeline 4, and part of the medium will pass through the first branch 41 into the low-temperature economizer 3 and exchange heat with the flue gas. The temperature of the medium increases after the heat exchange, and part of the medium will pass through the second pipeline 5 into the heating unit for heat exchange with the primary air and secondary air to increase the inlet air temperature of the air preheater 1.

[0039] The second pipeline 5 is connected between the outlet end of the low-temperature economizer 3 and the inlet end of the heater unit 2. That is to say, after the medium passes through the low-temperature economizer 3 and is heated by heat exchange with the flue gas, it can also be passed into the heater unit 2 along the second pipeline 5 to heat the primary air and secondary air, thereby increasing the inlet air temperature of the air preheater 1.

[0040] like Figure 1 As shown, the first branch 41 is provided with a first valve component 411, which is arranged on the downstream side of the low-temperature economizer 3. The first valve component 411 can control the on-off of the first branch 41, and the second pipeline 5 is provided with a second valve component 51, which can control the on-off of the second pipeline 5.

[0041] When the first valve component 411 is in the open state and the second valve component 51 is in the closed state, the low-temperature economizer 3 and the heating unit 2 are in parallel mode. When the first valve component 411 is in the closed state and the second valve component 51 is in the open state, the low-temperature economizer 3 and the heating unit 2 are in series mode. When the first valve component 411 and the second valve component 51 are both in the open state, the low-temperature economizer 3 and the heating unit 2 are in a mixed mode.

[0042] By adjusting the first valve 411 and the second valve 51, the water inlet temperature of the heater unit 2 can be ensured, so that the primary air and the secondary air can ensure the inlet air temperature of the air preheater 1 after heat exchange through the heater unit 2, thereby reducing the cold end corrosion of the air preheater 1.

[0043] The inlet of the first pipeline 4 communicates with a suitable location in the low-pressure heating system. The medium drawn from this location exchanges heat with the primary and secondary air as it passes through the heater unit 2, ensuring that the inlet air temperature of the air preheater 1 meets the requirements for mitigating cold-end corrosion. Under normal operating conditions, the first valve 411 is open, the second valve 51 is closed, and the low-temperature economizer 3 and heater unit 2 are in parallel operation. After the medium passes through the low-temperature economizer 3, its temperature is raised by heat exchange with the flue gas, and then it returns to the low-pressure heater system along the first branch 41.

[0044] However, due to factors such as changes in ambient temperature, the medium introduced into the heater unit 2 may be heated by the primary air and secondary air, resulting in the inlet air temperature of the air preheater 1 being unable to meet the requirements for reducing cold-end corrosion. At this time, the second valve 51 can be opened, and the medium passing through the low-temperature economizer 3, after the temperature is increased by heat exchange with the flue gas, part of it returns to the low-pressure heater system along the first branch 41, and part of it enters the heater unit 2 along the second pipeline 5, participating in the heat exchange of the primary air and secondary air, thereby increasing the inlet air temperature of the air preheater 1 and reducing the cold-end corrosion of the air preheater 1.

[0045] In both the series mode and the mixed mode, the air passing through the heater unit 2 can be heated by the medium heated by the low-temperature economizer 3. It is not difficult to understand that in the series mode, the medium heated by the low-temperature economizer 3 is completely passed into the heater unit 2, which has a better effect on increasing the inlet air temperature of the air preheater 1.

[0046] That is to say, in the waste heat utilization system provided by this embodiment, the temperature of the medium entering the heater unit 2 can be adjusted by opening and closing the first valve member 411 and the second valve member 51, and then the temperature of the primary air and the secondary air passing through the heater unit 2 can be adjusted to ensure the inlet air temperature of the air preheater 1 under different working conditions. It has good flexibility and can effectively reduce the corrosion of the cold end of the air preheater 1.

[0047] like Figure 1As shown, the low-pressure heating system of the steam turbine includes 6# low-pressure heater 71, 7# low-pressure heater 72 and 8# low-pressure heater 73. The inlet end of the first pipeline 4 is connected to the condensate outlet end of the 7# low-pressure heater 72, so that the condensate is used as a medium through the first branch 41 and the second branch 42 to enter the heater unit 2 and the low-temperature economizer 3.

[0048] Of course, steam from the low-pressure heater system can also be introduced into first pipe 4 as the medium. When condensate is introduced into first pipe 4 as the medium, heater unit 2 is a hot water heater, and no phase change occurs internally. This reduces vibration caused by the phase change, making heater unit 2 safer and quieter. This also ensures the medium volume, ensuring continuous and stable system operation, and preventing heater leakage from affecting the turbine vacuum, thereby ensuring safety.

[0049] like Figure 1 As shown, the outlet end of the first branch 41 is connected to the inlet end of the 6# low-pressure heater 71, and the outlet end of the second branch 42 is connected to the inlet end of the 8# low-pressure heater 73. That is to say, the condensate passing through the warm air unit 2 can be passed into the 8# low-pressure heater 73 along the second branch 42 after heat exchange with the primary air and secondary air. The condensate after heat exchange with the flue gas in the low-temperature economizer 3 and temperature increase can be passed into the 6# low-pressure heater 71 along the second pipeline 5. In this way, the steam extraction amount of the 7# low-pressure heater 72 is increased, and the steam extraction amount of the 6# low-pressure heater 71 is reduced. The steam extraction amount of the 6# low-pressure heater 71 is higher-quality steam than the steam extraction amount of the 7# low-pressure heater 72. Therefore, the working capacity of the steam turbine is increased and the economy is better.

[0050] Therefore, even during peak electricity consumption periods, condensate can be used as a medium to pass into the heater unit 2 and the low-temperature economizer 3. The power plant can operate the heater unit 2 all year round. The heater unit 2 plays a greater role in ensuring the inlet air temperature of the air preheater 1, thereby effectively reducing the cold end corrosion of the air preheater 1.

[0051] The waste heat utilization system provided in this embodiment safely increases the inlet air temperature of the air preheater 1 while utilizing the cooling source loss of the steam turbine, thereby improving the cycle efficiency. The power plant and operating personnel have no worries about the application of this technology. In this way, the condensation, ash adhesion, and corrosion of sulfuric acid dew in the flue gas and the deposition and corrosion of ammonium bisulfate can be completely avoided, thereby solving the serious problems of blockage and corrosion of the air preheater 1.

[0052] like Figure 1 As shown, the second branch 42 is further provided with a pressure pump 423. The condensed water after heat exchange with the air by the heater unit 2 is pressurized by the pressure pump 423 and then transported to the inlet of the 8# low-pressure heater 73.

[0053] like Figure 1 As shown, in the low-pressure heating system, the 6# low-pressure heater 71 and the 7# low-pressure heater 72 are connected through the medium pipeline 74. The waste heat recovery system also includes a three-way structure, which is connected to the position of suitable temperature in the medium pipeline 74. At the same time, the three-way structure is also connected to the inlet end of the first pipeline 4. The first pipeline 4 and the medium pipeline 74 are respectively provided with an isolation door 8 and an adjustment door 9. Among them, the isolation door 8 and the adjustment door 9 provided in the medium pipeline 74 are located on the side of the three-way structure facing the 6# low-pressure heater 71. The isolation door 8 is used to open and close the pipeline. During normal operation, the isolation door 8 is in a normally open state. The adjustment door 9 is used to adjust the size of the pipeline flow so that the resistance of each pipeline and branch is balanced to ensure the stability of the system operation. It can be adjusted according to actual conditions and has good flexibility.

[0054] Specifically, in this embodiment, there is no specific restriction on the location of the suitable temperature within the medium pipeline 74. It can be determined through heat balance calculation based on the inlet temperature requirements of the heater unit 2 and the low-temperature economizer 3. For example, the temperature difference between the suitable temperature and the inlet temperature of the low-temperature economizer 3 system is within the range of 65°C-90°C, specifically 70°C, 80°C, etc. If the temperature difference is too large, heat waste will result. If the temperature difference is too small, it may lead to insufficient heat, causing the inlet air temperature of the air preheater 1 to be too low, resulting in cold-end corrosion. Therefore, connecting the inlet end of the first pipeline 4 to the outlet side of the 7# low-pressure heater 72 can reduce the probability of cold-end corrosion in the air preheater 1 while reducing heat waste, achieving good energy-saving effects and economical efficiency.

[0055] A first thermometer 43, a first flowmeter 45 and a pressure gauge 46 are also provided on the inlet side of the first pipeline 4, wherein the first flowmeter 45 is used to detect the flow rate of condensed water passing through the first pipeline 4, the first thermometer 43 (which can be a thermal resistor) is used to detect the temperature of the condensed water entering the first pipeline 4, and the pressure gauge 46 is used to detect the pressure in the first pipeline 4. The first thermometer 43, the first flowmeter 45 and the pressure gauge 46 can monitor the condition of the condensed water drawn out by the low-pressure heating system of the steam turbine to ensure stable operation of the system.

[0056] like Figure 1 As shown, the waste heat utilization system also includes a third pipeline 6, one end of which is connected to the first pipeline 4, that is, the first pipeline 4 is provided with a three-way structure and is connected to one end of the third pipeline 6 through the three-way structure. The first pipeline 4 is also provided with a second thermometer 44, and the connection point between the third pipeline 6 and the first pipeline 4 is located on the upstream side of the second thermometer 44, and the third pipeline 6 is also provided with a regulating valve 61 and an on-off valve 62, wherein the on-off valve 62 is used to control the on-off of the third pipeline 6, and the regulating valve 61 is used to adjust the flow of condensed water passing through the third pipeline 6, and the flow direction of the condensed water in the third pipeline 6 is from the second branch 42 to one side of the first pipeline 4.

[0057] That is to say, the condensate after heat exchange with the primary air and secondary air of the heating unit 2 can be passed into the 8# low-pressure heater 73 along the first branch 41, and can also be passed into the first pipeline 4 along the third pipeline 6, mixed with the condensate in the first pipeline 4 to adjust the temperature, and then passed into the heating unit 2 and the low-temperature economizer 3 again, reducing the amount of condensate drawn out from the first pipeline 4, and having a good energy-saving effect.

[0058] The first valve member 411 , the second valve member 51 , the regulating valve 61 and the adjustment door 9 can be adjusted according to the detection result of the second thermometer 44 to ensure the temperature of the condensed water entering the heating unit 2 , and thus ensure the inlet air temperature of the air preheater 1 .

[0059] Since the temperature of the condensate introduced at the inlet end of the first pipeline 4 is relatively high, the temperature of the condensate entering the heater unit 2 and the low-temperature economizer 3 can be adjusted through the third pipeline 6. The second thermometer 44 provided in the first pipeline 4 is on the downstream side of the connection between the third pipeline 6 and the first pipeline 4, and is used to detect the temperature of the condensate entering the heater unit 2. The adjustment gate 9 and the regulating valve 61 provided in the third pipeline 6 can be adjusted according to the condensate temperature. When the condensate temperature detected by the second thermometer 44 is high, the second valve member 51 is closed and the regulating valve 61 is opened. At the same time, the adjustment gate 9 can be adjusted to reduce the flow rate of the condensate entering the first pipeline 4. When the condensate temperature detected by the second thermometer 44 is low, the regulating valve 61 can be closed and the second valve member 51 can be opened. At the same time, the adjustment gate 9 can be adjusted so that the temperature of the condensate detected by the second thermometer 44 is within the preset range, thereby ensuring the inlet air temperature of the air preheater 1.

[0060] The provision of the third pipeline 6 can further improve the flexibility of the condensed water temperature entering the heater unit 2, thereby ensuring stable operation of the system.

[0061] like Figure 1 As shown, a third thermometer 421 and a second flow meter 422 are further provided on the outlet side of the heater unit 2, which are respectively used to monitor the temperature and flow of the condensed water passing through the heater unit 2, so that the operator can monitor the condition of the condensed water passing through the heater unit 2 in real time. When the condensed water temperature detected by the second thermometer 44 exceeds the preset range and needs to be adjusted, the various regulating parts (including the regulating valve 61, the first valve part 411, the second valve part 51, and the adjustment door 9) can be adjusted according to the detection results of the first thermometer 43, the third thermometer 421, the first flow meter 45 and the second flow meter 422, so as to improve the adjustment efficiency and accuracy and ensure the stable operation of the system.

[0062] like Figure 1As shown, a fourth thermometer 413 is provided at the inlet of the low-temperature economizer 3 to detect the temperature of the condensate entering the low-temperature economizer 3 along the first branch 41. A third flowmeter is also provided at the outlet of the low-temperature economizer 3 to monitor the flow rate of the condensate entering the low-temperature economizer 3 along the first branch 41, allowing operators to monitor the overall system operation status in real time. Furthermore, a third valve 424 is provided at the outlet of the second branch 42 of the heater unit 2 to control the opening and closing of the second branch 42.

[0063] In this embodiment, the types of the heating unit 2 and the low-temperature economizer 3 are not limited. The heating unit 2 is preferably a steel-aluminum fin heat exchanger, which has high heat exchange capacity, low system resistance, and good corrosion resistance. The low-temperature economizer 3 is preferably a flue gas molten salt heat exchanger. Molten salt has the advantages of high heat storage density, low viscosity, low cost, and long life, making it an excellent heat transfer and storage medium. Excess flue gas waste heat can be stored in the flue gas molten salt heat exchanger and then exchanged with condensate through the molten salt, further saving the exhaust volume of the 6# low-pressure heater 71. When the second valve 51 is in the open state, the condensate, after absorbing the heat of the molten salt, can heat the primary and secondary air, increasing the inlet temperature of the air preheater 1 and preventing blockage. Molten salt can also be used for peak regulation to absorb the growing amount of new energy. Molten salt heat storage can not only meet the needs of deep peak regulation of thermal power generation and absorb new energy, but also save energy and reduce consumption, so that the boiler always maintains a relatively ideal state and reduces coal consumption.

[0064] The heater unit 2 is also equipped with a differential pressure transmitter (not shown). This transmitter is used to monitor the pressure difference between the air inlet and outlet of the heater unit 2. This allows the operator to monitor the operating status of the heater unit 2 in real time and ensure that the overall pressure drop on the air side does not exceed a preset pressure drop. If the pressure drop is too large, it may cause the entire flue gas channel to operate, thereby affecting the stability of boiler combustion. Specifically, in this embodiment, there is no limit on the preset pressure drop and it can be set according to actual conditions, such as 350Pa.

[0065] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A waste heat utilization system, characterized in that: It includes a boiler, a steam turbine, an air preheater (1), a heating unit (2), a low-temperature economizer (3), a first pipeline (4) and a second pipeline (5); The flue gas outlet of the boiler is connected to the air preheater (1) and the low-temperature economizer (3) in sequence through a flue gas pipeline (10); The heating unit (2) is in communication with the air preheater (1); The outlet end of the first pipeline (4) is provided with a first branch (41) and a second branch (42); the first branch (41) is connected to the low-temperature economizer (3) and a first valve (411); the first valve (411) is located on the downstream side of the low-temperature economizer (3); the second branch (42) is connected to the heating unit (2); the second pipeline (5) is connected between the low-temperature economizer (3) and the heating unit (2), and the second pipeline (5) is provided with a second valve (51); The inlet end of the first pipeline (4), the outlet end of the first branch (41), and the outlet end of the second branch (42) are respectively connected to the low-pressure heater system of the steam turbine.

2. The waste heat utilization system according to claim 1, characterized in that: The inlet end of the first pipeline (4) is connected to the condensate outlet end of the 7# low-pressure heater (72) of the low-pressure heater system of the steam turbine, and the outlet end of the second branch (42) is connected to the inlet end of the 8# low-pressure heater (73) of the low-pressure heater system.

3. The waste heat utilization system according to claim 2, characterized in that: The outlet end of the first branch (41) is communicated with the inlet end of the 6# low-pressure heater (71) of the low-pressure heater system.

4. The waste heat utilization system according to claim 3, characterized in that: The low-pressure heater system further includes a medium pipeline (74) communicating between the 6# low-pressure heater (71) and the 7# low-pressure heater (72); The waste heat utilization system further includes a three-way structure, the three-way structure being connected to the medium pipeline (74) and to the inlet end of the first pipeline (4); The first pipeline (4) and the medium pipeline (74) are respectively provided with an isolation door (8) and an adjustment door (9) on the side facing the 6# low-pressure heater.

5. The waste heat utilization system according to claim 4, characterized in that: The inlet side of the first pipeline (4) is also provided with a first thermometer (43), a first flow meter (45) and a pressure gauge (46).

6. The waste heat utilization system according to claim 5, characterized in that: The invention also includes a third pipeline (6), one end of which is connected to the first pipeline (4), and the other end of which is connected to the outlet of the heater unit (2). The third pipeline (6) is provided with a regulating valve (61). The first pipeline (4) is also provided with a second thermometer (44). The connection point between the third pipeline (6) and the first pipeline (4) is located on the upstream side of the second thermometer (44).

7. The waste heat utilization system according to claim 4, characterized in that: A third thermometer (421) and a second flow meter (422) are also provided on the outlet side of the heating unit (2).

8. The waste heat utilization system according to any one of claims 1 to 7, characterized in that: The heating unit (2) is a steel-aluminum fin heat exchanger.

9. The waste heat utilization system according to any one of claims 1 to 7, characterized in that: The low-temperature economizer (3) is a flue gas molten salt heat exchanger.

10. The waste heat utilization system according to any one of claims 1 to 7, characterized in that: The heating unit (2) is also provided with a pressure differential transmitter, and the pressure differential transmitter is used to detect the pressure difference between the air inlet and the air outlet of the heating unit (2).

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