Two-stage compression heat pump drying system with cascade utilization of exhaust air waste heat and air energy

Abstract

The present application relates to a two-stage compression heat pump drying system for step utilization of exhaust heat of exhaust air and air energy. The heat pump drying system is composed of a high-pressure stage compressor, a high-pressure stage throttling valve, a high-pressure stage evaporator, a low-pressure stage compressor, a low-pressure stage throttling valve, a low-pressure stage evaporator, a condenser, an exhaust air heat recovery device, a circulating water pump, a gas-liquid separator, an exhaust air fan and other components. The exhaust air heat recovery device recovers exhaust heat of exhaust air to provide heat source for the high-pressure stage evaporator, and outdoor air provides heat source for the low-pressure stage evaporator. Exhaust gas of the high-pressure stage compressor enters the condenser to release heat, so as to heat air sent to the drying chamber for hot air drying. When the low-pressure stage evaporator needs defrosting, exhaust gas of the high-pressure stage compressor enters the low-pressure stage evaporator through a bypass valve for hot gas defrosting as needed. The heat pump drying system can step utilize exhaust heat of exhaust air and low-temperature heat energy in the atmosphere, and has the advantages of high heating coefficient, high hot air temperature, fast defrosting speed, high efficiency and energy saving.

Description

Technical Field

[0001] This invention belongs to the field of hot air drying technology for materials, specifically involving a two-stage compression heat pump drying system that utilizes the waste heat of exhaust airflow and the cascade utilization of air energy. Background Technology

[0002] Hot air drying of materials is an energy-intensive operation. Energy consumption is even higher when the initial moisture content of the material is high, the required hot air temperature is high, and the amount of water to be removed is large. Air source heat pumps are energy-saving heating devices, but their heating performance is greatly affected by ambient temperature. At low ambient temperatures, the heating temperature of air source heat pumps decreases, heating power reduces, the coefficient of performance (COP) decreases, and defrosting time is prolonged.

[0003] During the material drying process, a large amount of high-temperature, high-humidity exhaust gas is discharged outside the drying room. Currently, for the recovery and utilization of low-grade waste heat in the exhaust gas, heat exchangers are mostly used to heat the heat medium to the required temperature using the exhaust gas, but the heat transfer temperature difference is small. Furthermore, due to the low thermal conductivity of the exhaust gas, its heat exchange performance is poor. Therefore, using heat exchangers to heat the heat medium with the exhaust gas not only results in low waste heat recovery efficiency but also high waste heat recovery costs. This, to some extent, limits the recovery and utilization of waste heat from the exhaust gas.

[0004] While using a dehumidified airflow source to provide a low-temperature heat source for the evaporator of an air-source heat pump can increase the evaporation temperature of the heat pump to some extent under low ambient temperatures, the high moisture content of the dehumidified airflow often leads to frequent frosting of the evaporator. This not only reduces the heating performance of the heat pump but also prolongs the defrosting time.

[0005] To effectively utilize the waste heat of exhaust airflow and improve the energy efficiency of heat pump hot air drying, it is necessary to seek new devices that can recover and utilize the waste heat of exhaust airflow, improve the heat pump heating coefficient, heating power and supply air temperature, and reduce defrosting time. These devices have significant application value and broad application prospects.

[0006] Therefore, this application proposes a two-stage compression heat pump drying system that utilizes the waste heat of the dehumidified airflow and the cascade utilization of air energy. Summary of the Invention

[0007] The purpose of this invention is to propose a two-stage compression heat pump drying system that utilizes the waste heat of the exhaust airflow and the low-temperature heat energy in the atmosphere in a cascade manner. The aim is to improve the heating coefficient and heating power of the heat pump, increase the air supply temperature of the heat pump, and reduce the defrosting time of the evaporator, thereby improving the thermal performance and energy utilization efficiency of the heat pump hot air drying.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] The two-stage compression heat pump drying system, which utilizes waste heat from dehumidified airflow and air energy in a cascade manner, includes main components such as a drying chamber, condenser, high-pressure stage compressor, low-pressure stage compressor, waste heat recovery unit for dehumidified airflow, low-pressure stage evaporator, high-pressure stage evaporator, and gas-liquid separator. The air outlet of the drying chamber is connected to the condenser via an air duct. A fresh air inlet is located at the bottom of the condenser. Refrigerant piping is installed on the condenser, and the gas-liquid separator, low-pressure stage evaporator, high-pressure stage evaporator, waste heat recovery unit for dehumidified airflow, low-pressure stage compressor, and high-pressure stage compressor are all installed on the refrigerant piping to form a waste heat utilization channel.

[0010] The dehumidification outlet of the drying chamber is connected to the waste heat recovery unit of the dehumidification airflow through the dehumidification duct.

[0011] Preferably, the discharge port of the high-pressure stage compressor is connected to the refrigerant inlet of the condenser via a refrigerant pipeline, the refrigerant outlet of the condenser is connected to the inlet of the high-pressure stage expansion valve via a refrigerant pipeline, and the outlet of the high-pressure stage expansion valve is connected to the inlet of the gas-liquid separator. The gaseous refrigerant that flashes out as the refrigerant flows through the high-pressure stage expansion valve is separated in the gas-liquid separator. The separated gaseous refrigerant enters the gas collector at the outlet of the high-pressure stage evaporator through a refrigerant pipeline, and after merging with the gaseous refrigerant from the high-pressure stage evaporator, it enters the gas collector at the inlet and outlet of the high-pressure stage compressor. Then, after merging with the gaseous refrigerant from the discharge port of the low-pressure stage compressor, it enters the suction port of the high-pressure stage compressor and enters the high-pressure stage compressor for compression.

[0012] Preferably, the liquid refrigerant separated from the gas-liquid separator enters the distributor and is divided into two loops. One loop enters the high-pressure stage evaporator, where it absorbs heat from the water in the exhaust gas waste heat recovery unit and evaporates. A circulating water pipe is installed between the high-pressure stage evaporator and the exhaust gas waste heat recovery unit. The refrigerant then enters the gas collector at the outlet of the high-pressure stage evaporator. The other loop flows sequentially through the low-pressure stage evaporator shut-off valve and the low-pressure stage throttle valve into the low-pressure stage evaporator. After absorbing heat from the outdoor air and evaporating, the refrigerant enters the low-pressure stage compressor for compression and is then discharged into the gas collector at the inlet and outlet of the high-pressure stage compressor.

[0013] The high-temperature, high-pressure superheated gaseous refrigerant, after undergoing two stages of compression, enters the condenser through the refrigerant pipeline from the exhaust port of the high-pressure compressor. Fresh air from the outside enters the condenser through the fresh air inlet and exchanges heat with the high-temperature, high-pressure superheated gaseous refrigerant. After being heated, it enters the drying chamber through the air outlet and exchanges heat and moisture with the material to be dried, resulting in a decrease in temperature and an increase in humidity. Finally, it is discharged from the dehumidification outlet of the drying chamber.

[0014] Preferably, the exhaust airflow from the exhaust port of the drying chamber enters the exhaust airflow heat recovery unit under the traction of the exhaust fan, where it exchanges heat with the water in the exhaust airflow waste heat recovery unit, releasing exhaust waste heat. After absorbing the exhaust waste heat, the water in the exhaust airflow waste heat recovery unit increases in temperature and flows through the high-pressure stage evaporator under the traction of the circulating water pump, providing a low-temperature heat source for the high-pressure stage evaporator.

[0015] Preferably, one end of the defrost bypass valve is connected to the refrigerant line at the discharge port of the high-pressure stage compressor, and the other end is connected to the refrigerant line at the inlet of the low-pressure stage evaporator. When the low-pressure stage evaporator needs to be defrosted, the defrost bypass valve opens, and part of the high-temperature exhaust gas from the high-pressure stage compressor enters the low-pressure stage evaporator, using the heat energy it carries to defrost, thereby increasing the defrost rate and reducing the defrost time.

[0016] Preferably, the exhaust airflow waste heat recovery unit is equipped with an exhaust pipe and an overflow pipe. Preferably, the exhaust airflow heat and moisture recovery unit is equipped with a drain pipe at the bottom, and a drain valve is installed on the drain pipe.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects:

[0018] This invention employs a novel two-stage compression heat pump cycle with throttling valves in series, evaporators in parallel, and a shared condenser. This not only utilizes the waste heat from the exhaust airflow and the low-temperature heat energy of the outdoor air in a cascade manner, but also effectively improves the heat pump's coefficient of performance (COP), heating power, and drying chamber supply air temperature, while reducing the compressor's compression work, increasing the evaporator defrosting rate, and reducing defrosting time. The two-stage compression heat pump drying system for utilizing the waste heat from the exhaust airflow and air energy in a cascade manner, as described in this invention, has advantages such as high COP, high hot air temperature, fast defrosting speed, and high energy efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the composition of the two-stage compression heat pump drying system of the present invention, which utilizes the waste heat of the dehumidified airflow and the cascade utilization of air energy.

[0020] Figure 1The numbers in the diagram represent the following in order: 1-Drying chamber, 2-Drying chamber air outlet, 3-Condenser, 4-High-pressure stage compressor, 5-High-pressure stage compressor inlet gas collector, 6-Low-pressure stage compressor, 7-Exhaust pipe, 8-Circulating water pump, 9-Dehumidification airflow waste heat recovery unit, 10-Overflow pipe, 11-Drain valve, 12-Drain pipe, 13-Low-pressure stage evaporator, 14-Dehumidification air duct, 15-Low-pressure stage throttling valve, 16-Dispenser, 17-Dehumidification fan, 18-Drying chamber exhaust outlet, 19-Refrigerant pipe, 20-High-pressure stage evaporator, 21-High-pressure stage throttling valve, 22-Circulating water pipe, 23-Air supply duct, 24-Fresh air inlet, 25-Gas-liquid separator, 26-High-pressure stage evaporator outlet gas collector, 27-Defrost bypass valve, 28-Low-pressure stage evaporator shut-off valve. Detailed Implementation

[0021] like Figure 1 As shown, to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention. Example

[0022] The two-stage compression heat pump drying system, which utilizes the waste heat from the exhaust airflow and the air energy in a cascade manner, includes the main components such as drying chamber 1, condenser 3, high-pressure stage compressor 4, low-pressure stage compressor 6, exhaust airflow waste heat recovery unit 9, low-pressure stage evaporator 13, high-pressure stage evaporator 20, and gas-liquid separator 25.

[0023] The air outlet 2 of the drying chamber 1 is connected to the condenser 3 via an air supply duct 23. A fresh air inlet 24 is provided at the bottom of the condenser 3. A refrigerant pipe 19 is provided on the condenser 3. A gas-liquid separator 25, a low-pressure evaporator 13, a high-pressure evaporator 20, a waste heat recovery unit 9 for exhaust airflow, a low-pressure compressor 6, and a high-pressure compressor 4 are provided on the refrigerant pipe 19 to form a waste heat utilization channel.

[0024] The dehumidification outlet 18 of the drying chamber 1 is connected to the waste heat recovery unit 9 of the dehumidification airflow through the dehumidification duct 14. The exhaust port of the high-pressure stage compressor 4 is connected to the refrigerant inlet of the condenser 3 through the refrigerant pipe 19. The refrigerant outlet of the condenser 3 is connected to the inlet of the high-pressure stage throttle valve 21 through the refrigerant pipe 19. The outlet of the high-pressure stage throttle valve 21 is connected to the inlet of the gas-liquid separator 25. The gaseous refrigerant that flashes out after the refrigerant flows through the high-pressure stage throttle valve 21 is separated in the gas-liquid separator 25. The separated gaseous refrigerant enters the gas collector 26 at the outlet of the high-pressure stage evaporator through the refrigerant pipe 19, and after merging with the gaseous refrigerant from the high-pressure stage evaporator 20, it enters the gas collector 5 at the inlet and outlet of the high-pressure stage compressor. Then, after merging with the gaseous refrigerant from the exhaust port of the low-pressure stage compressor 6, it enters the suction port of the high-pressure stage compressor 4 and is compressed by the high-pressure stage compressor 4.

[0025] The liquid refrigerant separated from the gas-liquid separator 25 enters the distributor 16 and is divided into two loops. One high-pressure loop enters the high-pressure evaporator 20, where it absorbs heat from the water in the exhaust gas waste heat recovery unit 9 and evaporates, then enters the gas collector 26 at the outlet of the high-pressure evaporator. The other low-pressure loop flows sequentially through the low-pressure evaporator shut-off valve 28 and the low-pressure throttling valve 15 into the low-pressure evaporator 13, where it absorbs heat from the outdoor air and evaporates, then enters the low-pressure compressor 6 for compression and is discharged into the gas collector 5 at the inlet and outlet of the high-pressure compressor. When the return air temperature of the drying chamber 1 is higher than the set value, the low-pressure evaporator shut-off valve 28 closes, and the low-pressure compressor 6 is de-energized and stops operating. When the return air temperature of the drying chamber 1 is lower than the set value, the low-pressure evaporator shut-off valve 28 opens, and the low-pressure compressor 6 is energized and runs.

[0026] One end of the defrost bypass valve 27 is connected to the refrigerant line 19 at the discharge port of the high-pressure stage compressor 4, and the other end is connected to the refrigerant line at the inlet of the low-pressure stage evaporator 13. When the low-pressure stage evaporator 13 needs to be defrosted, the defrost bypass valve 27 opens, and part of the high-temperature exhaust gas from the high-pressure stage compressor 4 enters the low-pressure stage evaporator 13, utilizing its heat energy for defrosting, thereby increasing the defrosting rate and reducing the defrosting time.

[0027] The high-temperature, high-pressure superheated gaseous refrigerant, after undergoing two stages of compression, enters the condenser 3 through the refrigerant pipe 19 from the exhaust port of the high-pressure stage compressor 4. Fresh air from outside enters the condenser 3 through the fresh air inlet 24, where it exchanges heat with the high-temperature, high-pressure superheated gaseous refrigerant. After being heated, it enters the drying chamber 1 through the drying chamber air outlet 2, where it exchanges heat and moisture with the material being dried, resulting in a decrease in temperature and an increase in humidity. Finally, it is discharged from the drying chamber exhaust outlet 18.

[0028] The exhaust airflow from the dehumidification outlet 18 of the drying chamber, driven by the dehumidification fan 17, enters the exhaust airflow heat recovery unit 9, where it exchanges heat with the water and releases waste heat. The water in the exhaust airflow waste heat recovery unit 9 absorbs...

[0029] After the waste heat from dehumidification is released, the temperature rises. Driven by the circulating water pump 8, the water flows through the high-pressure stage evaporator 20, providing a low-temperature heat source and increasing the evaporation temperature to improve the heat pump's heating power, coefficient of performance, and overall heating capacity. The dehumidified airflow releases waste heat in the water and is then discharged into the atmosphere through the exhaust pipe.

[0030] Furthermore, in this embodiment, the exhaust airflow waste heat recovery unit 9 is equipped with an exhaust pipe 7 and an overflow pipe 10 to facilitate exhaust and overflow.

[0031] The bottom of the dehumidification airflow heat and humidity recovery unit 9 is equipped with a drain pipe 12, and a drain valve 11 is installed on the drain pipe 12 for convenient drainage.

[0032] This invention employs a novel two-stage compression heat pump cycle with throttling valves in series, evaporators in parallel, and a shared condenser. This not only utilizes the waste heat from the exhaust airflow and the low-temperature heat energy of the outdoor air in a cascade manner, but also effectively improves the heat pump's coefficient of performance (COP), heating power, and drying chamber supply air temperature, while reducing the compressor's compression work, increasing the evaporator defrosting rate, and reducing defrosting time. The two-stage compression heat pump drying system for utilizing the waste heat from the exhaust airflow and air energy in a cascade manner, as described in this invention, has advantages such as high COP, high hot air temperature, fast defrosting speed, and high energy efficiency.

[0033] Working principle of this invention:

[0034] The heat pump employs a novel two-stage compression heat pump cycle with throttling valves in series, evaporators in parallel, and a shared condenser. It features a gas-liquid separator, a low-pressure stage evaporator circuit shut-off valve, and a defrost branch that bypasses the high-pressure stage compressor exhaust to the low-temperature stage evaporator. The low-pressure stage throttling valve is connected to the high-pressure stage throttling valve, and the low-pressure stage evaporator is connected to the high-pressure stage evaporator in parallel, sharing a single condenser. The low-temperature stage evaporator and the high-temperature stage evaporator use outdoor air and water from the exhaust gas waste heat recovery unit, respectively, as their low-temperature heat sources. By implementing a gas-liquid separator and parallel evaporator connection, the compression work of the low-pressure stage compressor is reduced. The defrost branch that bypasses the high-pressure stage compressor exhaust to the low-temperature stage evaporator utilizes a portion of the high-temperature exhaust gas from the high-pressure stage compressor for defrosting, thereby increasing the defrost rate and reducing defrost time. Water in the exhaust gas waste heat recovery unit exchanges heat and moisture with the exhaust gas from the drying chamber to recover waste heat from the exhaust gas. This waste heat is then supplied to the high-pressure stage evaporator via a circulating water pump, increasing the evaporation temperature, heating power, and coefficient of performance of the high-temperature stage evaporator. When the return air temperature of the drying chamber exceeds the set value, the low-pressure stage evaporator circuit shut-off valve closes, and the low-pressure stage compressor is powered off and stops operating. When the return air temperature of the drying chamber exceeds the set value, the low-pressure stage evaporator circuit shut-off valve opens, and the low-pressure stage compressor is powered on and runs.

[0035] The discharge port of the high-pressure stage compressor is connected to the refrigerant inlet of the condenser via a refrigerant pipeline. The refrigerant outlet of the condenser is connected to the inlet of the high-pressure stage expansion valve via a refrigerant pipeline. The outlet of the high-pressure stage expansion valve is connected to the inlet of the gas-liquid separator. The gaseous refrigerant that flashes out as the refrigerant flows through the high-pressure stage expansion valve is separated in the gas-liquid separator. The separated gaseous refrigerant enters the gas collector at the outlet of the high-pressure stage evaporator through a refrigerant pipeline, where it combines with the gaseous refrigerant from the high-pressure stage evaporator and then enters the gas collector at the inlet and outlet of the high-pressure stage compressor. Afterward, it combines with the gaseous refrigerant from the discharge port of the low-pressure stage compressor and enters the suction port of the high-pressure stage compressor for compression.

[0036] The liquid refrigerant separated from the gas-liquid separator enters the distributor and is divided into two loops. One loop (high-pressure stage loop) enters the high-pressure stage evaporator, where it absorbs heat from the water in the exhaust gas waste heat recovery unit and evaporates. It then enters the gas collector at the outlet of the high-pressure stage evaporator. The other loop (low-pressure stage loop) flows sequentially through the low-pressure stage evaporator shut-off valve and the low-pressure stage throttling valve into the low-pressure stage evaporator. After absorbing heat from the outdoor air and evaporating, it enters the low-pressure stage compressor for compression and is discharged into the gas collector at the inlet and outlet of the high-pressure stage compressor. When the return air temperature of the drying chamber is higher than the set value, the low-pressure stage evaporator shut-off valve closes, and the low-pressure stage compressor is powered off and stops operating. When the return air temperature of the drying chamber is lower than the set value, the low-pressure stage evaporator shut-off valve opens, and the low-pressure stage compressor is powered on and runs.

[0037] One end of the defrost bypass valve is connected to the refrigerant line at the discharge port of the high-pressure stage compressor, and the other end is connected to the refrigerant line at the inlet of the low-pressure stage evaporator. When the low-pressure stage evaporator needs defrosting, the defrost bypass valve opens, and part of the high-temperature exhaust gas from the high-pressure stage compressor enters the low-pressure stage evaporator, utilizing its heat energy for defrosting, thereby increasing the defrosting rate and reducing the defrosting time.

[0038] The high-temperature, high-pressure superheated gaseous refrigerant, after undergoing two stages of compression, enters the condenser through the refrigerant pipeline from the exhaust port of the high-pressure stage compressor. Fresh air from outside enters the condenser through the fresh air inlet, where it exchanges heat with the high-temperature, high-pressure superheated gaseous refrigerant. After being heated, it enters the drying chamber through the air outlet, where it exchanges heat and moisture with the material being dried, resulting in a decrease in temperature and an increase in humidity. Finally, it is discharged from the drying chamber's exhaust port.

[0039] The exhaust airflow from the drying chamber's exhaust vent is drawn by the exhaust fan into the exhaust airflow heat recovery unit, where it exchanges heat with the water, releasing waste heat. The water in the waste heat recovery unit absorbs this waste heat, increasing its temperature. Drawn by the circulating water pump, it flows through the high-pressure stage evaporator, providing a low-temperature heat source and raising the evaporation temperature to improve the heat pump's heating power, coefficient of performance, and overall heating capacity. After releasing waste heat in the water, the exhaust airflow is discharged into the atmosphere through the exhaust pipe.

[0040] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-stage compression heat pump drying system for cascade utilization of waste heat and air energy of a moisture-laden air stream, characterized in that: It includes a drying chamber (1), a condenser (3), a high-pressure stage compressor (4), a low-pressure stage compressor (6), a dehumidification airflow waste heat recovery unit (9), a low-pressure stage evaporator (13), a high-pressure stage evaporator (20), and a gas-liquid separator (25). The air outlet (2) of the drying chamber (1) is connected to the condenser (3) through the air supply pipe (23). A fresh air inlet (24) is provided at the bottom of the condenser (3). A refrigerant pipe (19) is provided on the condenser (3). A gas-liquid separator (25), a low-pressure evaporator (13), a high-pressure evaporator (20), a dehumidification airflow waste heat recovery device (9), a low-pressure compressor (6), and a high-pressure compressor (4) are provided on the refrigerant pipe (19) to form a waste heat utilization channel. The exhaust port of the high-pressure stage compressor (4) is connected to the refrigerant inlet of the condenser (3) through the refrigerant pipe (19). The refrigerant outlet of the condenser (3) is connected to the inlet of the high-pressure stage throttle valve (21) through the refrigerant pipe (19). The outlet of the high-pressure stage throttle valve (21) is connected to the inlet of the gas-liquid separator (25). The gaseous refrigerant that flashes out after the refrigerant flows through the high-pressure stage throttle valve (21) is separated in the gas-liquid separator (25). The separated gaseous refrigerant enters the gas collector (26) at the outlet of the high-pressure stage evaporator through the refrigerant pipe. After it is combined with the gaseous refrigerant from the high-pressure stage evaporator (20), it enters the gas collector (5) at the inlet and outlet of the high-pressure stage compressor. Then, it is combined with the gaseous refrigerant from the exhaust port of the low-pressure stage compressor (6) and enters the suction port of the high-pressure stage compressor (4) for compression. The liquid refrigerant separated from the gas-liquid separator (25) enters the distributor (16) and is divided into two loops. One loop enters the high-pressure stage evaporator (20), where it absorbs heat from the water in the exhaust gas waste heat recovery unit (9) and evaporates. A circulating water pipe (22) is installed between the high-pressure stage evaporator (20) and the exhaust gas waste heat recovery unit (9), and then enters the gas collector (26) at the outlet of the high-pressure stage evaporator. The other loop flows through the low-pressure stage evaporator shut-off valve (28) and the low-pressure stage throttle valve (15) in sequence and enters the low-pressure stage evaporator (13). After absorbing heat from the outdoor air and evaporating, it enters the low-pressure stage compressor (6) and is compressed before being discharged into the gas collector (5) at the inlet and outlet of the high-pressure stage compressor. The high-temperature and high-pressure superheated gaseous refrigerant, after two stages of compression, enters the condenser (3) through the refrigerant pipe (19) from the exhaust port of the high-pressure stage compressor (4). Fresh air from the outside enters the condenser (3) through the fresh air inlet (24) and exchanges heat with the high-temperature and high-pressure superheated gaseous refrigerant. After being heated, it enters the drying chamber (1) through the drying chamber air outlet (2) and exchanges heat and moisture with the drying material. The temperature decreases and the humidity increases, and then it is discharged from the drying chamber exhaust port (18). The drying chamber exhaust port (18) of the drying chamber (1) is connected to the exhaust airflow waste heat recovery unit (9) through the exhaust air duct (14).

2. The two-stage compression heat pump drying system for the cascade utilization of waste heat from dehumidified airflow and air energy as described in claim 1, characterized in that: The exhaust airflow discharged from the exhaust port (18) of the drying chamber enters the exhaust airflow heat and moisture recovery unit (9) under the traction of the exhaust fan (17), and exchanges heat with the water in the exhaust airflow waste heat recovery unit (9) to release exhaust waste heat. After absorbing the exhaust waste heat, the water in the exhaust airflow waste heat recovery unit (9) increases in temperature and flows through the high-pressure stage evaporator (20) under the traction of the circulating water pump (8), providing a low-temperature heat source for the high-pressure stage evaporator (20).

3. The two-stage compression heat pump drying system for the cascade utilization of waste heat from dehumidified airflow and air energy as described in claim 1, characterized in that: One end of the defrost bypass valve (27) is connected to the refrigerant pipe at the discharge port of the high-pressure stage compressor (4), and the other end is connected to the refrigerant pipe at the inlet of the low-pressure stage evaporator (13). When the low-pressure stage evaporator (13) needs to be defrosted, the defrost bypass valve (27) opens, and part of the high-temperature exhaust gas from the high-pressure stage compressor (4) enters the low-pressure stage evaporator (13) to perform defrosting using the heat energy it carries, thereby increasing the defrosting rate and reducing the defrosting time.

4. The two-stage compression heat pump drying system for the cascade utilization of waste heat from dehumidified airflow and air energy as described in claim 1, characterized in that: The exhaust airflow waste heat recovery unit (9) is equipped with an exhaust pipe (7) and an overflow pipe (10).

5. The two-stage compression heat pump drying system for the cascade utilization of waste heat from dehumidified airflow and air energy as described in claim 1, characterized in that: The bottom of the dehumidification airflow heat and moisture recovery unit (9) is equipped with a drain pipe (12), and a drain valve (11) is installed on the drain pipe (12).

Images