A waste gas treatment closed cycle waste heat recovery energy saving device

Abstract

The application discloses a waste gas treatment closed circulation waste heat recovery energy-saving device, which comprises a waste gas treatment unit and a closed heat exchange circulation unit.

Description

Technical Field

[0001] This invention specifically relates to a closed-loop waste heat recovery energy-saving device for waste gas treatment. Background Technology

[0002] Industrial processes such as electroplating, chemical processing, pickling, semiconductor manufacturing, and PCB manufacturing generate large amounts of acid mist waste gas containing components such as sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid. This type of waste gas is highly corrosive and toxic. Direct emission would severely pollute the atmospheric environment, corrode surrounding equipment and buildings, and endanger the health of operators and nearby residents. Therefore, it must undergo strict treatment to meet standards before it can be discharged.

[0003] Currently, the mainstream treatment processes for acid mist exhaust gas include three categories: absorption, adsorption, and condensation. Among them, condensation separates gaseous acid mist and water vapor by cooling the exhaust gas below the acid mist dew point, condensing them into liquid droplets. It has advantages such as high treatment efficiency, no secondary pollution, and the ability to recover acid resources, making it particularly suitable for high-concentration, low-volume acid mist exhaust gas treatment scenarios. However, existing condensation treatment systems have the following significant drawbacks: existing systems mostly adopt the mode of directly introducing high-temperature exhaust gas into the evaporator for deep cooling. The inlet temperature of acid mist exhaust gas is usually 30-40℃, while the dew point temperature required for condensation is mostly 0-10℃. The evaporator needs to bear the cooling load across the entire temperature range, resulting in high refrigeration unit power, low operating COP, and energy consumption accounting for more than 80% of the total system operating cost, which seriously restricts the widespread application of condensation methods. Summary of the Invention

[0004] In view of the deficiencies of the existing technology, the technical problem to be solved by the present invention is to provide a closed-loop waste heat recovery energy-saving device for waste gas treatment.

[0005] A closed-loop waste heat recovery energy-saving device for waste gas treatment includes a waste gas treatment unit and a closed-loop heat exchange cycle unit.

[0006] The waste gas treatment unit is provided with an inlet pipe, a first waste heat recovery coil, an evaporator, a gas-liquid separator, a second waste heat recovery coil, and an exhaust pipe in sequence along the waste gas flow direction.

[0007] The closed-loop heat exchange unit includes a circulating pump, a heat exchange medium, a first heat exchange pipeline, and a second heat exchange pipeline; the medium flow chamber of the first waste heat recovery coil, the second heat exchange pipeline, the medium flow chamber of the second waste heat recovery coil, the first heat exchange pipeline, and the circulating pump are connected in sequence to form a closed-loop circulation circuit.

[0008] The heat exchange medium is filled in the internal cavity of the closed-loop circulation circuit;

[0009] The first waste heat recovery coil is used to pre-cool the high-temperature acid mist waste gas input from the intake pipe, while the heat exchange medium inside the coil absorbs heat from the waste gas and increases its temperature.

[0010] The evaporator is used to cool the pre-cooled acid mist exhaust gas, causing the acid mist components in the exhaust gas to condense into droplets.

[0011] The gas-liquid separator is used to separate condensed acid liquid and saturated water vapor in the cooled waste gas.

[0012] The second waste heat recovery coil is used to reheat the separated low-temperature clean waste gas, while the heat exchange medium inside the coil releases heat to cool it down.

[0013] The circulating pump is used to drive the heat exchange medium to circulate in a closed loop, thereby realizing the cyclic exchange of heat between the first waste heat recovery coil and the second waste heat recovery coil.

[0014] In one embodiment, the closed-loop heat exchange circulation unit further includes an expansion tank, a shut-off valve, and a safety valve; the expansion tank is connected between the first heat exchange pipeline and the inlet of the circulation pump via a tee joint to balance pressure fluctuations in the closed-loop circulation circuit; both the inlet and outlet ends of the medium in the closed-loop circulation circuit are equipped with shut-off valves, and the safety valve is located at the outlet end of the circulation pump for overpressure protection of the circuit.

[0015] In one embodiment, both the first waste heat recovery coil and the second waste heat recovery coil adopt a corrosion-resistant finned tube structure, and turbulence structures are respectively provided inside the first waste heat recovery coil and the second waste heat recovery coil; the turbulence structure is a continuous equal pitch or variable pitch ribbon-shaped spiral.

[0016] In one embodiment, the system further includes an automatic control unit, which comprises a PLC controller, a first temperature sensor, a second temperature sensor, a third temperature sensor, a fourth temperature sensor, and a frequency converter driver. The first temperature sensor is disposed in the intake pipe and is used to detect the initial temperature of the intake exhaust gas. The second temperature sensor is disposed in the pipe between the first waste heat recovery coil and the evaporator and is used to detect the temperature of the exhaust gas after pre-cooling. The third temperature sensor is disposed in the pipe between the evaporator and the gas-liquid separator and is used to detect the temperature of the exhaust gas after cooling. The fourth temperature sensor is disposed in the pipe between the second waste heat recovery coil and the exhaust pipe and is used to detect the temperature of the exhaust gas after reheating. The frequency converter driver is electrically connected to the circulating pump and is used to adjust the speed and output flow of the circulating pump. The PLC controller is electrically connected to the first temperature sensor, the second temperature sensor, the third temperature sensor, the fourth temperature sensor, and the frequency converter driver.

[0017] In one embodiment, the automatic control unit further includes an electric flow regulating valve, a pressure sensor, and a differential pressure sensor; the electric flow regulating valve is disposed on the second heat exchange pipeline for finely regulating the circulation flow rate of the heat exchange medium; the pressure sensor is disposed at the outlet end of the circulating pump for detecting the operating pressure of the closed circulation loop; the two ends of the differential pressure sensor are respectively connected to the medium inlet and medium outlet of the first waste heat recovery coil for detecting the pressure difference across the coil; the PLC controller is electrically connected to the electric flow regulating valve, the pressure sensor, and the differential pressure sensor.

[0018] In one embodiment, the bottom of the gas-liquid separator is connected to a condensate recovery tank via a drain pipe. A drain solenoid valve is installed on the drain pipe. An online pH meter and a liquid level sensor are installed inside the condensate recovery tank. The online pH meter, liquid level sensor, and drain solenoid valve are all electrically connected to a PLC controller.

[0019] In one embodiment, the exhaust gas treatment unit further includes a pre-filter and a demister. The pre-filter is connected between the air inlet pipe and the first waste heat recovery coil, and the pre-filter is a polypropylene pleated filter element. The demister is located between the gas-liquid separator and the second waste heat recovery coil, and the demister is a wire mesh demister or a baffle plate demister.

[0020] In summary, the advantages of this invention over the prior art are:

[0021] This invention addresses the core deficiency of existing condensation systems where the evaporator bears the full-temperature-range cooling load. This device achieves internal closed-loop heat transfer through a closed-loop heat exchange cycle unit: the first waste heat recovery coil pre-cools the high-temperature acid mist exhaust gas, recovering the sensible heat of the exhaust gas that would otherwise be directly wasted, thereby reducing the temperature of the exhaust gas entering the evaporator, reducing the evaporator's cooling load, significantly reducing the power consumption of the refrigeration unit, and lowering the total power consumption of the system, thus completely solving the industry pain point of excessively high operating costs in condensation systems; at the same time, the second waste heat recovery coil uses the recovered heat to reheat the low-temperature clean exhaust gas, eliminating the need for additional energy consumption to heat the exhaust gas, and avoiding the extra energy consumption of traditional systems that require the addition of electric heaters or steam heaters to prevent white smoke from the chimney;

[0022] Furthermore, the heat exchange medium flows in a completely closed loop, without any direct contact with the acid mist exhaust gas, which fundamentally eliminates the problem of the heat exchange medium being corroded and contaminated by acid mist, and also avoids secondary pollution to the exhaust gas treatment system and the environment caused by heat exchange medium leakage; the closed loop system does not require frequent replenishment of the heat exchange medium, greatly reducing maintenance and significantly improving operational stability.

[0023] Furthermore, both the first and second waste heat recovery coils adopt corrosion-resistant finned tube structures, which are suitable for the highly corrosive working conditions of acid mist exhaust gas and have a long service life. The ribbon-shaped spiral turbulence structure set inside the tube can destroy the laminar boundary layer of the heat exchange medium, causing the heat exchange medium to generate strong turbulence, thereby increasing the heat transfer coefficient and achieving higher heat exchange efficiency under the same heat exchange area, which can reduce the size of the equipment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the frame of a closed-loop waste heat recovery energy-saving device for waste gas treatment in one embodiment of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0026] like Figure 1 The present invention preferably provides a closed-loop waste heat recovery energy-saving device for waste gas treatment, comprising a waste gas treatment unit and a closed-loop heat exchange circulation unit; the waste gas treatment unit is provided with an inlet pipe 1, a first waste heat recovery coil 2, an evaporator 3, a gas-liquid separator 4, a second waste heat recovery coil 5, and an exhaust pipe 6 arranged sequentially along the waste gas flow direction; the closed-loop heat exchange circulation unit includes a circulation pump 7, a heat exchange medium, a first heat exchange pipeline, and a second heat exchange pipeline; the medium flow chamber of the first waste heat recovery coil 2, the second heat exchange pipeline, the medium flow chamber of the second waste heat recovery coil 5, the first heat exchange pipeline, and the circulation pump 7 are sequentially connected to form a closed-loop circulation circuit; the heat exchange medium is filled in the closed-loop circulation circuit. Within the internal cavity of the loop: the first waste heat recovery coil 2 is used to pre-cool the high-temperature acid mist exhaust gas input from the inlet pipe 1, while the heat exchange medium inside the coil absorbs heat from the exhaust gas and raises its temperature; the evaporator 3 is used to cool the pre-cooled acid mist exhaust gas, causing the acid mist components in the exhaust gas to condense into droplets; the gas-liquid separator 4 is used to separate the condensed acid liquid and saturated water vapor in the cooled exhaust gas; the second waste heat recovery coil 5 is used to reheat the separated low-temperature clean exhaust gas, while the heat exchange medium inside the coil releases heat to lower its temperature; the circulating pump 7 is used to drive the heat exchange medium to circulate in a directional manner within the closed loop, realizing the cyclic exchange of heat between the first waste heat recovery coil 2 and the second waste heat recovery coil 5.

[0027] Specifically, a fan can be added to the exhaust pipe so that the exhaust gas can be drawn in through the intake pipe and discharged through the exhaust pipe. This device achieves the purification treatment of acid mist exhaust gas through the exhaust gas treatment unit and realizes the internal closed-loop recovery and utilization of exhaust gas heat through the closed heat exchange cycle unit. The two work together to achieve extreme energy saving while ensuring the acid mist treatment effect.

[0028] High-temperature acid mist exhaust gas enters the exhaust gas treatment unit through the inlet pipe. It first flows through the first waste heat recovery coil, where it exchanges heat with the low-temperature heat exchange medium inside the coil. The exhaust gas is pre-cooled, and the heat exchange medium absorbs heat and heats up. The pre-cooled exhaust gas enters the evaporator for deep cooling, and the temperature drops below the acid mist dew point. The acid mist components and most of the water vapor in the exhaust gas condense into droplets. Subsequently, the exhaust gas enters the gas-liquid separator, where the condensed acid liquid is separated from the exhaust gas. The separated acid liquid is recovered to the condensate recovery tank. The separated low-temperature clean exhaust gas flows through the second waste heat recovery coil, where it exchanges heat with the high-temperature heat exchange medium inside the coil. The exhaust gas is reheated and then discharged through the exhaust pipe in compliance with standards. The heat exchange medium releases heat and cools down. Driven by the circulating pump, the cooled heat exchange medium flows back to the first waste heat recovery coil through the first heat exchange pipeline to absorb heat from the high-temperature exhaust gas again. This cycle repeats continuously, achieving a continuous transfer of heat between the first and second waste heat recovery coils.

[0029] Furthermore, the closed-loop heat exchange circulation unit also includes an expansion tank 8, a shut-off valve, and a safety valve; the expansion tank 8 is connected between the first heat exchange pipeline and the inlet of the circulation pump via a three-way connector to balance the pressure fluctuations of the closed-loop circulation circuit; both the medium inlet and outlet ends of the closed-loop circulation circuit are equipped with shut-off valves, and the safety valve is located at the outlet end of the circulation pump for overpressure protection of the circuit.

[0030] Specifically, the expansion tank is connected to the first heat exchange pipeline and the inlet of the circulating pump via a three-way connector, and is filled with inert gas at a certain pressure. When the heat exchange medium in the closed-loop circuit expands due to temperature increase, the excess volume enters the expansion tank, compressing the inert gas inside. When the heat exchange medium contracts due to temperature decrease, the inert gas in the expansion tank expands, pushing the heat exchange medium back into the circulation loop. This automatically balances the pressure fluctuations caused by temperature changes in the closed-loop circuit, preventing system damage due to excessively high or low pressure. The shut-off valves at the medium inlet and outlet of the closed-loop circuit can be closed during system installation, inspection, or maintenance to cut off the flow of the heat exchange medium, facilitating equipment disassembly and replacement.

[0031] The safety valve is located at the outlet of the circulating pump. When the system operating pressure exceeds the set safety threshold, the safety valve automatically opens to release pressure and discharge excess heat exchange medium. It automatically closes after the system pressure returns to the normal range, effectively preventing safety accidents such as system rupture due to overpressure and ensuring the safe and stable operation of the system.

[0032] Furthermore, both the first waste heat recovery coil 2 and the second waste heat recovery coil 5 adopt a corrosion-resistant finned tube structure, and turbulence structures are respectively provided inside the first waste heat recovery coil 2 and the second waste heat recovery coil 5; the turbulence structure is a continuous equal pitch or variable pitch ribbon-shaped spiral.

[0033] Specifically, the first and second waste heat recovery coils adopt a corrosion-resistant finned tube structure. The fins can significantly increase the heat exchange area on the waste gas side and improve the gas-liquid heat exchange efficiency. At the same time, the finned tubes are made of corrosion-resistant materials, which can resist long-term corrosion from acid mist waste gas and extend the service life of the equipment.

[0034] The continuous, constant-pitch or variable-pitch ribbon-like spiral turbulence structure installed inside the tube generates strong rotation and turbulence in the heat exchange medium as it flows through the tube. This disrupts the laminar boundary layer formed at the tube wall, allowing for thorough mixing of the high-temperature heat exchange medium at the tube center with the low-temperature heat exchange medium at the tube wall. This significantly improves the heat transfer coefficient inside the tube, thereby enhancing the overall heat exchange efficiency of the coil. The variable-pitch ribbon-like spiral can generate turbulence of varying intensities in different tube sections according to changes in the flow velocity and temperature of the heat exchange medium, further optimizing the heat exchange effect.

[0035] Furthermore, it also includes an automatic control unit, which comprises a PLC controller, a first temperature sensor, a second temperature sensor, a third temperature sensor, a fourth temperature sensor, and a frequency converter driver. The first temperature sensor is installed in the intake pipe 1 to detect the initial temperature of the intake exhaust gas. The second temperature sensor is installed in the pipe between the first waste heat recovery coil 2 and the evaporator 3 to detect the temperature of the exhaust gas after pre-cooling. The third temperature sensor is installed in the pipe between the evaporator 3 and the gas-liquid separator 4 to detect the temperature of the exhaust gas after cooling. The fourth temperature sensor is installed in the pipe between the second waste heat recovery coil 5 and the exhaust pipe 6 to detect the temperature of the exhaust gas after reheating. The frequency converter driver is electrically connected to the circulating pump and is used to adjust the speed and output flow of the circulating pump. The PLC controller is electrically connected to the first temperature sensor, the second temperature sensor, the third temperature sensor, the fourth temperature sensor, and the frequency converter driver.

[0036] Specifically, the first temperature sensor detects the initial temperature of the high-temperature exhaust gas in the intake pipe in real time, the second temperature sensor detects the temperature of the pre-cooled exhaust gas at the outlet of the first waste heat recovery coil in real time, the third temperature sensor detects the temperature of the exhaust gas after deep cooling at the outlet of the evaporator in real time, and the fourth temperature sensor detects the emission temperature of the exhaust gas after reheating at the outlet of the second waste heat recovery coil in real time, and transmits all temperature signals to the PLC controller.

[0037] The PLC controller, based on preset control logic, compares the difference between the actual detected temperature and the set target temperature, and outputs a control signal to the frequency converter driver. The frequency converter driver adjusts the speed and output flow of the circulating pump according to the control signal: when the inlet air temperature rises or the pre-cooled temperature is higher than the set value, the circulating pump speed is increased, the circulation flow of the heat exchange medium is increased, and the pre-cooling effect of the first waste heat recovery coil and the heat recovery effect of the second waste heat recovery coil are enhanced; when the inlet air temperature decreases or the pre-cooled temperature is lower than the set value, the circulating pump speed is reduced, the circulation flow of the heat exchange medium is reduced, energy waste caused by excessive heat exchange is avoided, and the system achieves energy-saving operation.

[0038] Furthermore, the automatic control unit also includes an electric flow regulating valve, a pressure sensor, and a differential pressure sensor; the electric flow regulating valve is installed on the second heat exchange pipeline and is used to finely regulate the circulation flow rate of the heat exchange medium; the pressure sensor is installed at the outlet end of the circulating pump and is used to detect the operating pressure of the closed circulation loop; the two ends of the differential pressure sensor are respectively connected to the medium inlet and medium outlet of the first waste heat recovery coil 2 and are used to detect the pressure difference between the two ends of the coil; the PLC controller is electrically connected to the electric flow regulating valve, the pressure sensor, and the differential pressure sensor.

[0039] Specifically, the electric flow regulating valve is installed on the second heat exchange pipeline and works in conjunction with the frequency converter to achieve a combination of coarse and fine adjustment of the heat exchange medium circulation flow: the frequency converter achieves a wide range of coarse adjustment of the flow by adjusting the speed of the circulating pump, and the electric flow regulating valve achieves a small range of fine adjustment of the flow by changing the valve opening, so that the circulation flow of the heat exchange medium can accurately match the heat exchange requirements under different operating conditions, further improving the control accuracy and energy saving effect of the system.

[0040] The pressure sensor monitors the system operating pressure at the outlet of the circulating pump in real time and transmits the pressure signal to the PLC controller. When the system pressure is lower than the set lower limit, the PLC controller issues an alarm signal, indicating that there may be a leak in the system. When the system pressure is higher than the set upper limit, the PLC controller controls the safety valve to open and release pressure, and at the same time reduces the speed of the circulating pump to ensure system safety.

[0041] The differential pressure sensor detects the pressure difference between the medium inlet and outlet of the first waste heat recovery coil in real time and transmits the differential pressure signal to the PLC controller. When the differential pressure exceeds the set value, it indicates that the inner wall of the coil may be scaled or blocked. The PLC controller issues a cleaning alarm signal to remind the staff to clean and maintain the coil in time to ensure the heat exchange efficiency of the coil.

[0042] Furthermore, the bottom of the gas-liquid separator 4 is connected to a condensate recovery tank via a drain pipe. A drain solenoid valve is installed on the drain pipe. An online pH meter and a liquid level sensor are installed inside the condensate recovery tank. The online pH meter, liquid level sensor, and drain solenoid valve are all electrically connected to the PLC controller.

[0043] Specifically, the condensed acid separated by the gas-liquid separator flows into a condensate recovery tank for storage through a drain pipe. A level sensor monitors the liquid level in the condensate recovery tank in real time and transmits the signal to a PLC controller. When the liquid level reaches the set upper limit, the PLC controller opens the drain solenoid valve to discharge the acid from the recovery tank for reuse in the production process. When the liquid level drops to the set lower limit, the PLC controller closes the drain solenoid valve to stop the discharge, thus achieving automatic discharge of the condensate.

[0044] An online pH meter monitors the pH value of the acid solution in the condensate recovery tank in real time and transmits the pH signal to the PLC controller. When the pH value exceeds the set range, it indicates that the purity of the condensed acid solution may not meet the reuse requirements. The PLC controller issues an alarm signal to remind staff to conduct timely testing and treatment to ensure the quality of the recovered acid solution.

[0045] Furthermore, the exhaust gas treatment unit also includes a pre-filter and a demister. The pre-filter is connected between the air inlet pipe 1 and the first waste heat recovery coil 2, and the pre-filter uses a polypropylene pleated filter element. The demister is located between the gas-liquid separator 4 and the second waste heat recovery coil 5, and the demister is a wire mesh demister or a baffle plate demister.

[0046] Specifically, the pre-filter is connected between the air inlet pipe and the first waste heat recovery coil. It uses a polypropylene pleated filter element, which can effectively filter solid particulate impurities in the exhaust gas, prevent solid particles from entering the subsequent waste heat recovery coil and evaporator, causing coil blockage, reduced heat exchange efficiency or evaporator scaling and damage, and extend the service life of the core equipment.

[0047] The demister is installed between the gas-liquid separator and the second waste heat recovery coil. It adopts a wire mesh demister or a baffle plate demister, which can further capture the tiny acid mist droplets and water mist that the gas-liquid separator cannot completely separate, improve the acid mist removal rate, and ensure that the exhaust gas meets the standards. At the same time, it avoids tiny droplets from entering the second waste heat recovery coil, which would cause coil corrosion and a decrease in heat exchange efficiency.

[0048] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A closed-loop waste heat recovery energy-saving device for waste gas treatment, characterized in that, Includes an exhaust gas treatment unit and a closed-loop heat exchange cycle unit; The waste gas treatment unit is provided with an inlet pipe (1), a first waste heat recovery coil (2), an evaporator (3), a gas-liquid separator (4), a second waste heat recovery coil (5), and an exhaust pipe (6) in sequence along the waste gas flow direction. The closed heat exchange circulation unit includes a circulation pump (7), a heat exchange medium, a first heat exchange pipeline, and a second heat exchange pipeline; the medium flow chamber of the first waste heat recovery coil (2), the second heat exchange pipeline, the medium flow chamber of the second waste heat recovery coil (5), the first heat exchange pipeline, and the circulation pump (7) are connected in sequence to form a closed circulation loop. The heat exchange medium is filled in the internal cavity of the closed-loop circulation circuit; The first waste heat recovery coil (2) is used to pre-cool the high-temperature acid mist waste gas input into the inlet pipe (1), and at the same time, the heat exchange medium in the pipe absorbs the heat of the waste gas and raises the temperature. The evaporator (3) is used to cool down the pre-cooled acid mist exhaust gas, so that the acid mist components in the exhaust gas condense into droplets; The gas-liquid separator (4) is used to separate condensed acid liquid and saturated water vapor in the cooled waste gas; The second waste heat recovery coil (5) is used to reheat the separated low-temperature clean waste gas and raise its temperature, while the heat exchange medium in the coil releases heat to lower its temperature. The circulating pump (7) is used to drive the heat exchange medium to circulate in a closed loop, so as to realize the heat exchange between the first waste heat recovery coil (2) and the second waste heat recovery coil (5).

2. The waste gas treatment closed-loop waste heat recovery energy-saving device according to claim 1, characterized in that: The closed-loop heat exchange circulation unit also includes an expansion tank (8), a shut-off valve and a safety valve; the expansion tank (8) is connected between the first heat exchange pipeline and the inlet of the circulation pump (7) through a three-way connector to balance the pressure fluctuation of the closed-loop circulation circuit; the medium inlet and outlet ends of the closed-loop circulation circuit are both equipped with shut-off valves, and the safety valve is located at the outlet end of the circulation pump for overpressure protection of the circuit.

3. The waste gas treatment closed-loop waste heat recovery energy-saving device according to claim 1, characterized in that: The first waste heat recovery coil (2) and the second waste heat recovery coil (5) both adopt a corrosion-resistant finned tube structure, and a turbulence structure is respectively provided in the tubes of the first waste heat recovery coil (2) and the second waste heat recovery coil (5); the turbulence structure is a continuous equal pitch or variable pitch ribbon spiral.

4. The waste gas treatment closed-loop waste heat recovery energy-saving device according to claim 1, characterized in that: It also includes an automatic control unit, which includes a PLC controller, a first temperature sensor, a second temperature sensor, a third temperature sensor, a fourth temperature sensor, and a frequency converter; the first temperature sensor is installed in the intake pipe (1) to detect the initial temperature of the intake exhaust gas; the second temperature sensor is installed in the pipe between the first waste heat recovery coil (2) and the evaporator (3) to detect the temperature of the exhaust gas after pre-cooling; the third temperature sensor is installed in the pipe between the evaporator (3) and the gas-liquid separator (4) to detect the temperature of the exhaust gas after cooling; the fourth temperature sensor is installed in the pipe between the second waste heat recovery coil (5) and the exhaust pipe (6) to detect the temperature of the exhaust gas after reheating; the frequency converter is electrically connected to the circulating pump to adjust the speed and output flow of the circulating pump; the PLC controller is electrically connected to the first temperature sensor, the second temperature sensor, the third temperature sensor, the fourth temperature sensor, and the frequency converter.

5. The waste gas treatment closed-loop waste heat recovery energy-saving device according to claim 4, characterized in that: The automatic control unit also includes an electric flow regulating valve, a pressure sensor, and a differential pressure sensor; the electric flow regulating valve is installed on the second heat exchange pipeline and is used to finely regulate the circulation flow of the heat exchange medium; the pressure sensor is installed at the outlet end of the circulating pump and is used to detect the operating pressure of the closed circulation loop; the two ends of the differential pressure sensor are respectively connected to the medium inlet and medium outlet of the first waste heat recovery coil (2) and are used to detect the pressure difference between the two ends of the coil; the PLC controller is electrically connected to the electric flow regulating valve, the pressure sensor, and the differential pressure sensor.

6. The waste gas treatment closed-loop waste heat recovery energy-saving device according to claim 1, characterized in that: The bottom of the gas-liquid separator (4) is connected to a condensate recovery tank via a drain pipe. A drain solenoid valve is installed on the drain pipe. An online pH meter and a liquid level sensor are installed inside the condensate recovery tank. The online pH meter, liquid level sensor, and drain solenoid valve are all electrically connected to the PLC controller.

7. The waste gas treatment closed-loop waste heat recovery energy-saving device according to claim 1, characterized in that: The exhaust gas treatment unit also includes a pre-filter and a demister. The pre-filter is connected between the air inlet pipe (1) and the first waste heat recovery coil (2). The pre-filter uses a polypropylene pleated filter element. The demister is located between the gas-liquid separator (4) and the second waste heat recovery coil (5). The demister is a wire mesh demister or a baffle plate demister.

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