A waste heat recovery type heat pump drying system

Abstract

The utility model relates to the field of cereal drying, and specifically discloses a waste heat recovery type heat pump drying system, which comprises an air inlet pipe, a heat pump and a drying bin. The heat pump comprises an evaporator and a condenser. The drying bin is arranged at the air outlet end of the air inlet pipe. The evaporator and the condenser are arranged in sequence along the airflow direction in the air inlet pipe. An air outlet pipe is arranged on the drying bin. An auxiliary heating device is arranged on the pipe section in front of the evaporator on the air inlet pipe. A heat exchanger is arranged between the air inlet pipe and the air outlet pipe. The heat exchanger is arranged on the pipe section of the air inlet pipe in front of the auxiliary heating device. The heat exchanger is used for exchanging heat between the air flowing out of the air outlet pipe and the air flowing into the air inlet pipe. A fan is arranged on the air inlet pipe. The heat pump drying system has high energy consumption and low drying efficiency.

Description

Technical Field

[0001] This utility model relates to the field of grain drying, specifically to a waste heat recovery heat pump drying system. Background Technology

[0002] With the development of large-scale agricultural production, the demand for efficient drying of various grains such as corn, wheat, and rice is increasing. Heat pump drying technology, due to its advantages in energy saving and environmental protection, has become an important development direction for grain drying.

[0003] In the prior art, a heat pump drying system includes an air inlet pipe, a heat pump, and a drying chamber; the heat pump heats the air entering through the air inlet pipe, and the heated air is sent into the drying chamber by a fan to dry the grains inside the drying chamber.

[0004] In existing heat pump drying systems, the hot and humid air discharged from the drying chamber is directly discharged through the exhaust pipe, resulting in energy waste, high operating costs, and a low COP value for the heat pump system. The heating temperature range of the heat pump drying system is narrow, making it difficult to adapt to the drying temperature requirements of different grains. For example, the suitable drying temperature for wheat is 40-50℃, while corn requires 50-60℃. There is a lack of efficient auxiliary heating devices, resulting in a significant decrease in drying efficiency at low temperatures, and excessively long drying cycles for high-moisture grains. Utility Model Content

[0005] The purpose of this invention is to provide a waste heat recovery heat pump drying system to address the above problems, thereby solving the issues of high energy consumption and low drying efficiency in existing heat pump drying systems.

[0006] To achieve the above objectives, this utility model discloses a waste heat recovery heat pump drying system, which includes an air inlet pipe, a heat pump, and a drying chamber. The heat pump includes an evaporator and a condenser. The drying chamber is located at the outlet end of the air inlet pipe, and the evaporator and condenser are arranged sequentially on the air inlet pipe along the airflow direction. An exhaust pipe is provided on the drying chamber. An auxiliary heating device is provided on the section of the air inlet pipe in front of the evaporator. A heat exchanger is provided between the air inlet pipe and the exhaust pipe, and the heat exchanger is located on the section of the air inlet pipe before the auxiliary heating device. The heat exchanger is used to exchange heat between the air flowing out of the exhaust pipe and the air flowing in of the air inlet pipe. A fan is provided on the air inlet pipe.

[0007] With the above structure, the evaporator not only transfers heat from the air to the refrigerant within it, allowing the refrigerant to absorb heat and heat up, then be compressed and heated by the compressor before releasing heat through the condenser, thus increasing the heating temperature of the heat pump; it also dehumidifies the air flowing through the evaporator via the intake pipe. The condenser heats the dehumidified air from the evaporator, creating dry, hot air. The fan facilitates the entry of this dry, hot air into the drying chamber and drives air circulation throughout the entire waste heat recovery heat pump drying system, ensuring thorough contact between the grains and the dry, hot air, removing moisture and creating humid, hot air, thus improving drying efficiency. The heat exchanger recovers heat from the humid, hot air as it exits through the exhaust pipe, preventing energy waste; it also preheats the cold air entering the intake pipe, increasing the intake temperature and thus improving the heat pump's COP value and reducing energy consumption. The auxiliary heating device further preheats the air after it has been preheated by the heat exchanger, further increasing the air temperature and improving the heat pump's heating temperature and start-up efficiency.

[0008] As a further improvement of this utility model, the heat exchanger is provided with two air passages; the inlet pipe includes an inlet section and a connecting section, the section of the inlet pipe before the heat exchanger is the inlet section, and the section of the inlet pipe between the heat exchanger and the auxiliary heating device is the connecting section; the exhaust pipe includes an inlet section and an outlet section, the section of the exhaust pipe from which air enters the heat exchanger is the inlet section, and the section of the exhaust pipe from which air exits the heat exchanger is the outlet section; the inlet section and the connecting section are connected to one air passage on the heat exchanger, and the inlet section and the outlet section are connected to the other air passage on the heat exchanger. With this structure, all the air flowing in through the inlet pipe and all the air exiting through the exhaust pipe can enter the heat exchanger, making the heat exchange between the hot air in the exhaust pipe and the cold air in the inlet pipe more complete, improving waste heat recovery, and reducing heat loss.

[0009] As a further improvement of this invention, the airflow directions in the two air passages inside the heat exchanger are opposite. This structure maximizes the utilization of the heat transfer area, resulting in more thorough and rapid heat exchange and maximizing waste heat recovery. This effectively reduces the heating load of the heat pump and increases its COP value.

[0010] As a further improvement of this utility model, a branch pipe is provided on the exhaust pipe; one end of the branch pipe is connected to the exhaust pipe, and the other end is connected to the section of the air inlet pipe between the auxiliary heating device and the evaporator; the branch pipe is used to allow part of the air discharged from the exhaust pipe to flow through the evaporator. With this structure, the branch pipe allows part of the hot, humid air discharged from the exhaust pipe to flow through the evaporator, transferring heat to the refrigerant in the evaporator, thus realizing heat recovery and reuse, thereby increasing the heating temperature of the heat pump and improving the energy efficiency of the entire waste heat recovery heat pump drying system.

[0011] As a further improvement of this invention, a vent is provided at the bottom of the evaporator to discharge the condensate formed after the air is cooled by the evaporator. This structure effectively prevents the condensate from accumulating in the evaporator, thus avoiding water accumulation being carried into the drying chamber by the airflow and affecting the drying effect.

[0012] As a further improvement of this invention, the auxiliary heating device consists of one or more PTC heating units. Using this structure, the PTC heating unit is made of zirconia ceramic with a high-temperature resistant insulating layer coated on its surface, featuring rapid heating, good thermal stability, and no open flame. This not only enhances safety and reliability but also provides the PTC heater with adaptive adjustment capabilities, resulting in higher preheating stability.

[0013] As a further improvement of this utility model, a fan is located between the evaporator and the condenser to deliver air heated by the condenser into the drying chamber. With this structure, the fan can directly blow air onto the condenser, effectively avoiding resistance to airflow from other components and allowing the airflow to fully penetrate the entire condenser. Furthermore, the fan's rotation increases the flow rate of the hot, dry air inside the drying chamber, resulting in more thorough contact between the grain and the hot, dry air, effectively improving the drying efficiency of the grain within the drying chamber.

[0014] As a further improvement of this invention, the drying chamber is equipped with multiple drying layers. This structure effectively increases the contact area between the grain and the hot, dry air, allowing for full contact between the two and improving drying efficiency.

[0015] As a further improvement of this invention, an observation window for monitoring the grain's condition is provided on the side wall of the drying chamber. This structure allows operators to directly and in real-time observe the drying status of the grain inside the drying chamber without opening the chamber door. This not only effectively avoids heat loss and interruptions in the drying process caused by frequent opening of the chamber for inspection, but also allows for timely assessment of the grain's drying status to determine whether intervention is necessary, thereby ensuring the quality of the dried grain.

[0016] As a further improvement of this utility model, the heat pump drying system also includes a controller with a touch screen. The controller is electrically connected to the auxiliary heating device, the heat pump, and the fan. Sensors electrically connected to the controller are installed inside the air inlet pipe, the drying chamber, and the exhaust pipe. These sensors are temperature and humidity sensors. With this structure, the touch screen allows manual selection of grain type and corresponding drying parameters. The temperature and humidity sensors can collect real-time data on grain temperature and humidity, as well as inlet and outlet air temperature and humidity. The controller can control the heating power of the auxiliary heating device, the operating frequency of the heat pump, and the speed of the fan.

[0017] In summary, the beneficial effects of this utility model are as follows: the heat exchanger recovers heat from the humid air flowing through it as it is discharged through the exhaust pipe, avoiding energy waste; it also preheats the cold air entering the intake pipe, increasing the intake temperature and thus improving the COP value of the heat pump and reducing energy consumption. The auxiliary heating device further preheats the air after it has been preheated by the heat exchanger, further increasing the air temperature and thus improving the heating temperature and start-up efficiency of the heat pump. Furthermore, the auxiliary heating device adopts a modular design, allowing for flexible adjustment of heating power and widening the system's heating temperature range (40-65℃), adapting to the drying needs of various grains such as corn, wheat, and rice. Through branch pipes, some of the humid air discharged from the exhaust pipe flows through the evaporator, transferring heat to the refrigerant in the evaporator, achieving heat recovery and reuse, thereby increasing the heating temperature of the heat pump and improving the energy efficiency of the entire waste heat recovery heat pump drying system. This allows it to adapt to the drying needs of different grains, meeting the requirements of large-scale and diversified grain drying. The evaporator transfers heat from the air to the refrigerant within it. The refrigerant absorbs heat and heats up, then is compressed and heated by the compressor before releasing heat through the condenser, thus increasing the heating temperature of the heat pump. Furthermore, the evaporator dehumidifies the air flowing through the intake pipe. The condenser then heats the dehumidified air, creating dry, hot air. A fan circulates this dry, hot air into the drying chamber and drives air circulation throughout the entire waste heat recovery heat pump drying system. This ensures thorough contact between the grains and the dry, hot air, removing moisture and creating humid, hot air, thus improving drying efficiency. The controller provides precise control of the drying process, enhancing both drying quality and efficiency. The entire waste heat recovery heat pump drying system features a rational structural design, excellent drying uniformity, and effectively prevents grain scorching and uneven moisture content. It is suitable for large-scale agricultural production and has broad application prospects. This system solves the problems of high energy consumption, low drying efficiency, and poor adaptability to different grain types in existing heat pump drying systems, making it difficult to meet the needs of large-scale, diversified grain drying. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of this utility model.

[0019] The arrows in the diagram indicate the airflow direction in the intake pipe 1; here, we define the end where air enters the intake pipe 1 as the front and the end where it enters the drying chamber 6 as the rear. The air in the intake pipe 1 flows from front to back and enters the drying chamber 6.

[0020] In the diagram: 1. Inlet pipe, 100. Inlet section, 101. Connecting section, 2. Exhaust pipe, 200. Connecting section, 201. Discharge section, 202. Branch pipe, 3. Heat exchanger, 4. Auxiliary heating device, 5. Heat pump, 51. Evaporator, 52. Compressor, 53. Condenser, 54. Throttling valve, 55. Refrigerant circulation pipeline, 56. Exhaust port, 6. Drying chamber, 7. Fan, 8. Controller, 9. Touch screen, 10. Sensor. Detailed Implementation

[0021] The specific embodiments of this utility model will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this utility model, but are not intended to limit its scope.

[0022] Reference Figure 1In some embodiments of this utility model, a waste heat recovery heat pump drying system includes an air inlet pipe 1, a heat pump 5, and a drying chamber 6. The heat pump 5 includes a compressor 52, a condenser 53, a throttling valve 54, an evaporator 51, and a refrigerant circulation pipeline 55. The compressor 52 is preferably a variable frequency compressor, and the throttling valve 54 is preferably an electronic throttling valve. The refrigerant is preferably R410A high-efficiency refrigerant, which has a heat exchange efficiency 10%-15% higher than traditional refrigerants and is environmentally friendly and pollution-free. The variable frequency compressor can adjust its operating frequency according to the drying load, preferably 30-70Hz, to achieve on-demand energy output. The condenser 53 is equipped with a flow equalization device to ensure uniform distribution of dry and hot air and improve drying uniformity. The electronic throttling valve can adjust the refrigerant flow rate in real time to adapt to the heat exchange requirements under different operating conditions. The drying chamber 6 is located at the outlet end of the air inlet pipe 1. The evaporator 51 and condenser 53 are arranged sequentially along the airflow direction in the air inlet pipe 1. The drying chamber 6 is equipped with an exhaust pipe 2. An auxiliary heating device 4 is installed on the section of the air inlet pipe 1 in front of the evaporator 51. The auxiliary heating device 4 can be a resistance wire heater, a PTC heating unit, etc., preferably a PTC heating unit. The auxiliary heating device 4 adopts a modular design, consisting of one or more independent PTC heating units, each with a rated power of 3kW. The PTC heating unit adopts a honeycomb structure, is made of zirconia ceramic PTC, and has a high-temperature resistant insulating layer on its surface. It features rapid heating, good thermal stability, and no open flame. The PTC heating unit can flexibly adjust the heating power according to the drying requirements. It can be activated in low-temperature environments or when drying high-moisture grains to further increase the inlet air temperature to 20-30℃, ensuring that the heat pump 5 operates under suitable conditions and expanding the heating temperature range of the heat pump 5 to 40-65℃. A heat exchanger 3 is provided between the intake pipe 1 and the exhaust pipe 2; in one embodiment, the heat exchanger 3 is a plate heat exchanger. In another embodiment, the heat exchanger 3 adopts a shell-and-tube heat exchanger structure, with the shell material being corrosion-resistant aluminum alloy and the heat exchange tubes being copper-nickel alloy, which has the characteristics of high heat exchange efficiency and anti-condensation. The second embodiment is preferred. The heat exchanger 3 is located on the section of the intake pipe 1 before the auxiliary heating device 4, and the heat exchanger 3 is used to exchange heat between the air flowing out of the exhaust pipe 2 and the air flowing in of the intake pipe 1; a fan 7 is provided on the intake pipe 1.

[0023] Through the above structure, the evaporator 51 not only transfers heat from the air to the refrigerant within it, allowing the refrigerant to absorb heat and heat up, then compress and heat up again via the compressor 52, before releasing heat through the condenser 53, thus increasing the heating temperature of the heat pump 5; it also dehumidifies the air flowing through the evaporator 51 via the intake pipe 1. The condenser 53 heats the dehumidified air from the evaporator 51, forming dry, hot air. The fan 7 promotes the dry, hot air into the drying chamber 6 and drives the air circulation throughout the waste heat recovery heat pump drying system, ensuring full contact between the grains and the dry, hot air, removing moisture and forming humid, hot air, thus improving drying efficiency. The heat exchanger 3 transfers the heat from the humid, hot air discharged from the exhaust pipe 2 to the cold air in the intake pipe 1, achieving heat recovery from the humid, hot air flowing through the heat exchanger 3 as it is discharged from the exhaust pipe 2, avoiding energy waste; it also preheats the cold air entering the intake pipe 1, increasing the intake temperature and thus improving the COP value of the heat pump 5, reducing energy consumption. The auxiliary heating device 4 further preheats the air after it has been preheated by the heat exchanger 3, thereby increasing the temperature of the air and thus improving the heating temperature and start-up efficiency of the heat pump 5.

[0024] Reference Figure 1 In some embodiments of this utility model, the heat exchanger 3 is provided with two air passages; the inlet pipe 1 includes an inlet section 100 and a connecting section 101, the section of the inlet pipe 1 before the heat exchanger 3 is the inlet section 100, and the section of the inlet pipe 1 between the heat exchanger 3 and the auxiliary heating device 4 is the connecting section 101; the exhaust pipe 2 includes an inlet section 200 and an outlet section 201, the section of the exhaust pipe 2 through which air enters the heat exchanger 3 is the inlet section 200, and the section of the exhaust pipe 2 through which air exits the heat exchanger 3 is the outlet section 201; the inlet section 100 and the connecting section 101 are connected to one air passage on the heat exchanger 3, and the inlet section 200 and the outlet section 201 are connected to the other air passage on the heat exchanger 3. With this structure, the air flowing into the inlet pipe 1 and the air exiting the exhaust pipe 2 can both enter the heat exchanger 3 completely, making the heat exchange between the hot air in the exhaust pipe 2 and the cold air in the inlet pipe 1 more complete, improving the waste heat recovery effect, and reducing heat loss.

[0025] Reference Figure 1 In some embodiments of this invention, the airflow directions in the two air passages inside the heat exchanger 3 are opposite. This structure maximizes the utilization of the heat transfer area, resulting in more thorough and rapid heat exchange and maximizing waste heat recovery. This effectively reduces the heating load of the heat pump 5 and improves its COP value.

[0026] Reference Figure 1In some embodiments of this utility model, a branch pipe 202 is provided on the exhaust pipe 2; one end of the branch pipe 202 is connected to the exhaust pipe 2, and the other end is connected to the section of the air inlet pipe 1 between the auxiliary heating device 4 and the evaporator 51; the branch pipe 202 is used to allow part of the air discharged from the exhaust pipe 2 to flow through the evaporator 51. Through this structure, the branch pipe 202 allows part of the hot and humid air discharged from the exhaust pipe 2 to flow through the evaporator 51, transferring heat to the refrigerant in the evaporator 51, realizing heat recovery and reuse, thereby increasing the heating temperature of the heat pump 5 and improving the energy efficiency of the entire waste heat recovery heat pump drying system.

[0027] Reference Figure 1 In some embodiments of this utility model, the bottom of the evaporator 51 is provided with a vent 56 for discharging condensate formed after the air is cooled by the evaporator 51. Through this structure, the vent 56 discharges the condensate formed in the evaporator 51, which can effectively prevent condensate from accumulating in the evaporator 51, thereby avoiding water accumulation being carried into the drying chamber 6 by the airflow and affecting the drying effect.

[0028] Reference Figure 1 In some embodiments of this invention, the auxiliary heating device 4 comprises one or more PTC heating units. The PTC heating unit can be an independent PTC heating element or a PTC heater module integrating insulation, thermal conductivity, and electrodes. The PTC heating unit is made of zirconia ceramic with a high-temperature resistant insulating layer coated on its surface, featuring rapid heating, good thermal stability, and no open flame. This structure not only enhances safety and reliability but also provides the PTC heater with adaptive adjustment capabilities and higher preheating stability.

[0029] Reference Figure 1 In some embodiments of this invention, a fan 7 is positioned between the evaporator 51 and the condenser 53 to deliver air heated by the condenser 53 into the drying chamber 6. The adjustable speed of the fan 7 is preferably 3-8 m / s, ensuring sufficient contact between the hot, dry air generated by the condenser 53 and the grain. This structure allows the fan 7 to directly blow air onto the condenser 53, effectively avoiding resistance to airflow from other components and ensuring the airflow fully penetrates the entire condenser 53. Furthermore, the rotation of the fan 7 increases the flow rate of the hot, dry air within the drying chamber 6, resulting in more thorough contact between the grain and the hot, dry air, thus effectively improving the drying efficiency of the grain within the drying chamber 6.

[0030] Reference Figure 1 In some embodiments of this invention, the drying chamber 6 has multiple drying layers inside. This structure effectively increases the contact area between the grain and the hot, dry air, allowing the hot, dry air to fully contact the grain and improving drying efficiency.

[0031] Reference Figure 1In some embodiments of this invention, the side wall of the drying chamber 6 is provided with an observation window for observing the state of the grain. This structure allows operators to directly and in real-time observe the drying status of the grain inside the drying chamber 6 without opening the chamber door. This not only effectively avoids heat loss and interruption of the drying process caused by frequent opening of the chamber for inspection, but also allows for timely assessment of the grain drying status to determine whether intervention is necessary, thereby ensuring the quality of the dried grain.

[0032] Reference Figure 1 In some embodiments of this utility model, the waste heat recovery heat pump drying system further includes a controller 8, which is equipped with a touch screen 9. The controller 8 is electrically connected to the auxiliary heating device 4, the heat pump 5, and the fan 7. Sensors 10 electrically connected to the controller 8 are installed inside the air inlet pipe 1, the drying chamber 6, and the exhaust pipe 2. The sensors 10 include temperature sensors and / or humidity sensors. When the temperature sensor in the air inlet pipe 1 detects that the air inlet temperature is lower than the temperature threshold, the controller 8 turns on the PTC heating unit to heat the air inlet, thereby increasing the evaporation pressure of the evaporator 51 and improving the unit's energy efficiency. When the evaporation pressure is too high or the grain temperature is too high, the controller 8 turns off the PTC heating unit. When the temperature and humidity sensors in the drying chamber 6 report that the temperature is too high or the humidity is too low, the controller 8 turns off the PTC heating unit and reduces the frequency of the variable frequency compressor to lower the temperature of the grain layer and prevent the grain from deteriorating or overheating. Through this structure, the touch screen 9 allows manual selection of grain type and corresponding drying parameters; temperature and humidity sensors can collect real-time data on grain temperature, humidity, and inlet / outlet air temperature and humidity; the controller 8 can control the frequency of the variable frequency compressor, the start / stop status of the PTC heating unit, and the speed of the fan 7 based on the data collected by the sensors. (This only protects the entire waste heat recovery heat pump drying system device, not the method or algorithm).

[0033] Reference Figure 1The working principle of this utility model is as follows: After starting the waste heat recovery heat pump drying system, the type of grain and the corresponding drying parameters are selected via the touch screen 9; cold air from the outside enters the heat exchanger 3 through the air inlet pipe 1, and the cold air entering through the air inlet pipe 1 exchanges heat with the hot and humid air discharged through the exhaust pipe 2 in a counter-current manner to achieve preliminary preheating. If the temperature does not reach the set value after preheating by the heat exchanger 3, the auxiliary heating device 4 is activated to reheat the air. The heated air flows through the evaporator 51, where the refrigerant absorbs heat from the air and rises in temperature. It is then compressed and heated by the compressor 52, and the condenser 53 releases heat to generate dry and hot air that meets the drying requirements. The dry and hot air enters the drying chamber 6 under the action of the fan 7, passes through the grain layer, and carries away the moisture from the grain to form hot and humid air. When the hot and humid air is discharged through the exhaust pipe 2, part of the hot and humid air recovers heat through the heat exchanger 3; the remaining hot and humid air flows through the evaporator 51, and after being cooled by the evaporator 51, it forms condensate, which is discharged from the exhaust port 56; the controller 8 controls the frequency of the variable frequency compressor, the start and stop status of the PTC heating unit, and the speed of the fan 7 according to the data collected by the sensor, so as to achieve precise control of the drying process.

[0034] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present utility model, and these improvements and substitutions should also be considered within the protection scope of the present utility model.

Claims

1. A waste heat recovery heat pump drying system, comprising an air inlet pipe (1), a heat pump (5), and a drying chamber (6); the heat pump (5) includes an evaporator (51) and a condenser (53); the drying chamber (6) is located at the air outlet of the air inlet pipe (1), characterized in that, The evaporator (51) and condenser (53) are arranged sequentially on the inlet pipe (1) along the airflow direction in the inlet pipe (1); the drying chamber (6) is provided with an exhaust pipe (2); an auxiliary heating device (4) is provided on the pipe section of the inlet pipe (1) in front of the evaporator (51); a heat exchanger (3) is provided between the inlet pipe (1) and the exhaust pipe (2), and the heat exchanger (3) is located on the pipe section of the inlet pipe (1) before the auxiliary heating device (4). The heat exchanger (3) is used to exchange heat between the air flowing out of the exhaust pipe (2) and the air flowing in of the inlet pipe (1); a fan (7) is provided on the inlet pipe (1).

2. The waste heat recovery heat pump drying system as described in claim 1, characterized in that, The heat exchanger (3) is provided with two air passages; the air inlet pipe (1) includes an air inlet section (100) and a connecting section (101). The section of the air inlet pipe (1) before the heat exchanger (3) is the air inlet section (100), and the section of the air inlet pipe (1) between the heat exchanger (3) and the auxiliary heating device (4) is the connecting section (101); the exhaust pipe (2) includes an inlet section (200) and an outlet section (201). The section of the exhaust pipe (2) through which air enters the heat exchanger (3) is the inlet section (200), and the section of the exhaust pipe (2) through which air exits the heat exchanger (3) is the outlet section (201); the air inlet section (100) and the connecting section (101) are connected to one air passage on the heat exchanger (3), and the inlet section (200) and the outlet section (201) are connected to the other air passage on the heat exchanger (3).

3. The waste heat recovery heat pump drying system as described in claim 2, characterized in that, The air flows in opposite directions in the two air passages inside the heat exchanger (3).

4. The waste heat recovery heat pump drying system as described in claim 3, characterized in that, A branch pipe (202) is provided on the exhaust pipe (2); one end of the branch pipe (202) is connected to the exhaust pipe (2), and the other end is connected to the section of the intake pipe (1) between the auxiliary heating device (4) and the evaporator (51); the branch pipe (202) is used to allow part of the air discharged from the exhaust pipe (2) to flow through the evaporator (51).

5. The waste heat recovery heat pump drying system as described in claim 4, characterized in that, The bottom of the evaporator (51) is provided with a vent (56) for discharging condensate formed after the air is cooled by the evaporator (51).

6. The waste heat recovery heat pump drying system as described in claim 1, characterized in that, The auxiliary heating device (4) consists of one or more PTC heating units.

7. The waste heat recovery heat pump drying system as described in claim 1, characterized in that, The fan (7) is located between the evaporator (51) and the condenser (53) and is used to send the air heated by the condenser (53) into the drying chamber (6).

8. The waste heat recovery heat pump drying system as described in claim 1, characterized in that, The drying chamber (6) has multiple drying layers inside.

9. The waste heat recovery heat pump drying system as described in claim 8, characterized in that, The drying chamber (6) has an observation window on its side wall for observing the state of the grain.

10. The waste heat recovery heat pump drying system as described in any one of claims 1 to 9, characterized in that, The heat pump drying system also includes a controller (8), which is equipped with a touch screen (9); the controller (8) is electrically connected to the auxiliary heating device (4), the heat pump (5) and the fan (7); the air inlet pipe (1), the drying chamber (6) and the exhaust pipe (2) are all equipped with sensors (10) electrically connected to the controller (8), and the sensors (10) include temperature sensors and / or humidity sensors.

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