Heat pump coupling type sludge low-temperature vacuum dewatering and drying system and use method

Abstract

The invention relates to the technical field of sludge treatment, in particular to a heat pump coupling type sludge low-temperature vacuum dewatering and drying system and a using method. The system comprises a heat pump subsystem, a drying device, a gas-liquid separator and a control subsystem, the heat pump subsystem comprises an evaporator, a compressor and a condenser, a cooling heat exchange pipeline is arranged in the evaporator, an inlet of the cooling heat exchange pipeline is connected with a negative pressure steam outlet of the drying device, and an outlet of the cooling heat exchange pipeline is connected with an inlet of the gas-liquid separator. A heating heat exchange pipeline is arranged in the condenser, the heating heat exchange pipeline is connected into the drying equipment to form a high-temperature hot water circulation loop, the evaporator, the compressor and the condenser are sequentially connected to form a heat pump circulation loop, the control subsystem is electrically connected with the compressor, and the control subsystem controls the high-temperature hot water circulation loop and the heat pump circulation loop to be switched on and off. According to the heat pump coupling type sludge low-temperature vacuum dewatering and drying system and the using method, heat of negative pressure steam can be efficiently and stably utilized.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, and in particular to a heat pump coupled low-temperature vacuum dewatering and drying system for sludge, and a method for using the system. Background Technology

[0002] When performing low-temperature vacuum dewatering and drying of sludge, see [link / reference]. Figure 1 The drying equipment 1 (such as a filter press) needs to be heated with high-temperature hot water to accelerate the evaporation of water in the sludge. The negative pressure steam evaporated from the sludge needs to enter the heat exchanger 2 to cool down and form a gas-liquid two-phase water before being discharged. Then, the gas-liquid separator 3 separates the gas-liquid two-phase water into sewage and waste gas and discharges them separately.

[0003] Currently, see Figure 1 In heat exchanger 2, the heat exchange medium used to cool the negative pressure steam is greywater. The greywater, pumped into heat exchanger 2 by greywater transfer pump 4, still has a relatively low temperature (generally 15-25℃) after heat exchange and heating, making it unsuitable for direct use as a high-grade heat source. Therefore, the greywater, carrying residual heat, is often directly discharged to the wastewater treatment plant's outlet, resulting in a significant waste of heat. However, using a conventional heat pump to extract heat from the greywater faces problems of low thermal efficiency and poor stability. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a heat pump-coupled low-temperature vacuum dewatering and drying system for sludge, and its usage method, which can efficiently and stably utilize the heat of negative pressure steam.

[0005] The present invention adopts the following technical solution:

[0006] This invention provides a heat pump coupled low-temperature vacuum dehydration and drying system for sludge, comprising a heat pump subsystem, drying equipment, a gas-liquid separator, and a control subsystem. The heat pump subsystem includes an evaporator, a compressor, and a condenser. The evaporator is equipped with a cooling heat exchange pipeline, the inlet of which is connected to the negative pressure steam outlet of the drying equipment, and the outlet of which is connected to the inlet of the gas-liquid separator. The condenser is equipped with a heating heat exchange pipeline, which is connected to the drying equipment to form a high-temperature hot water circulation loop. The evaporator, compressor, and condenser are sequentially connected to form a heat pump circulation loop. The control subsystem is electrically connected to the compressor and controls the on / off state of the high-temperature hot water circulation loop and the heat pump circulation loop.

[0007] Preferably, a medium temperature sensor is installed at the medium inlet and outlet of the evaporator, a mass flow meter is installed on the heating heat exchange pipeline, and a hot water temperature sensor is installed at the inlet and outlet of the heating heat exchange pipeline. The heat pump subsystem also includes an auxiliary evaporator, which is equipped with an auxiliary heat exchange pipeline connected to the greywater discharge pipeline. The auxiliary evaporator, compressor, and condenser are connected in sequence to form an auxiliary heat pump circulation loop. The control subsystem is electrically connected to the medium temperature sensor, the hot water temperature sensor, and the mass flow meter, and the control subsystem controls the on / off state of the auxiliary heat pump circulation loop and the greywater discharge pipeline.

[0008] Preferably, an auxiliary solenoid valve and an auxiliary expansion valve are sequentially connected on the pipeline extending from the medium outlet of the condenser to the medium inlet of the auxiliary evaporator in the auxiliary heat pump circulation loop, and an auxiliary check valve that unidirectionally flows to the inlet of the compressor is provided at the medium outlet of the auxiliary evaporator. Both the auxiliary solenoid valve and the auxiliary expansion valve are electrically connected to the control subsystem.

[0009] Preferably, a reclaimed water pump with frequency conversion function is installed on the reclaimed water discharge pipeline, and the reclaimed water pump is electrically connected to the control subsystem.

[0010] Preferably, the heat pump circulation loop has a main solenoid valve and a main expansion valve connected in sequence on the pipeline extending from the medium outlet of the condenser to the medium inlet of the evaporator, and a main check valve that unidirectionally flows to the inlet of the compressor is provided at the medium outlet of the evaporator. Both the main solenoid valve and the main expansion valve are electrically connected to the control subsystem.

[0011] Preferably, a hot water tank is provided on the high-temperature hot water circulation loop, and the heating heat exchange pipeline is connected to the hot water tank to form a low-temperature water circulation sub-loop. The hot water tank is connected to the drying equipment to form a high-temperature water circulation sub-loop. The control subsystem controls the on / off of the low-temperature water circulation sub-loop and the high-temperature water circulation sub-loop.

[0012] Preferably, a hot water pump is installed on the low-temperature water circulation sub-loop, and a hot water circulation pump is installed on the high-temperature water circulation sub-loop. Both the hot water pump and the hot water circulation pump are electrically connected to the control subsystem.

[0013] The present invention also provides a method of using the above-mentioned heat pump coupled sludge low-temperature vacuum dewatering and drying system, comprising the following steps:

[0014] S1: Set the minimum and maximum limits for the temperature difference between the inlet and outlet of the evaporator medium within the control subsystem;

[0015] S2: The control subsystem monitors the compressor's operating status in real time. If the compressor is not under full load, the control subsystem controls the heat pump circulation loop to be turned on and continue to work. If the compressor is under full load, proceed to step S3.

[0016] S3: The control subsystem receives the detection data from the medium temperature sensor on the evaporator and calculates the medium temperature difference. The control subsystem also receives the detection data from the mass flow meter and hot water temperature sensor on the heating heat exchange pipeline and calculates the heat balance. If the medium temperature difference is lower than the limit low value, or if the medium temperature difference is between the limit low value and the limit high value and the heat balance is lower than -10%, the auxiliary heat pump circulation loop is then activated and continues to work. If the medium temperature difference is higher than the limit high value, the control subsystem triggers a fault alarm for the drying equipment.

[0017] Preferably, when the compressor is under full load, if the medium temperature difference recovers to the compressor's low return temperature and the thermal balance is greater than -5%, the control subsystem controls the auxiliary heat pump circulation loop to shut down.

[0018] Preferably, the calculation steps for the thermal balance in step S3 are as follows:

[0019] Step 1: Calculate the actual heating capacity Q of the condenser h Q h =c×m×ΔT, where c is the specific heat capacity of the water in the heating heat exchange pipeline, m is the mass flow rate of the water in the heating heat exchange pipeline, and ΔT is the temperature difference between the inlet and outlet of the heating heat exchange pipeline.

[0020] Step 2: Calculate the actual cooling capacity Q of the heat pump subsystem d Q d =Q h -P w , where Q h P represents the actual heating capacity of the condenser. w This refers to the actual input power of the compressor;

[0021] Step 3: Calculate the thermal balance degree, which is... Among them, Q d Q represents the actual cooling capacity of the heat pump subsystem. s This refers to the rated cooling capacity of the heat pump subsystem.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The heat pump-coupled low-temperature vacuum dehydration and drying system for sludge of this invention can directly extract heat from negative pressure steam using the evaporator in the heat pump subsystem. This negative pressure steam is then cooled and condensed. The condensed gas-liquid two-phase water enters a gas-liquid separator for separation before being discharged. Meanwhile, the heat pump medium in the heat pump circulation loop absorbs heat in the evaporator and then enters the compressor for compression and heating. It then enters the condenser to heat the low-temperature hot water in the heating heat exchange pipeline before re-entering the drying equipment via a high-temperature hot water circulation loop for sludge dehydration and drying. Thus, the heat pump-coupled low-temperature vacuum dehydration and drying system of this invention forms a closed-loop heat system, enabling efficient and stable utilization of the heat from the negative pressure steam.

[0024] The method of using the heat pump coupled sludge low-temperature vacuum dewatering and drying system of the present invention involves controlling the subsystem to rationally configure the on / off state of the heat pump circulation loop and the auxiliary heat pump circulation loop within the heat pump subsystem. This allows the heat provided by the negative pressure steam to be insufficient to meet the operating requirements of the drying equipment, while simultaneously connecting the heat pump circulation loop and the auxiliary heat pump circulation loop, using greywater as a backup heat source. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a low-temperature vacuum dewatering and drying system for sludge in the existing technology.

[0026] Figure 2 This is a schematic diagram of a heat pump coupled low-temperature vacuum dewatering and drying system for sludge in an embodiment of the present invention.

[0027] The reference numerals in the attached figures are explained as follows:

[0028] 1. Drying equipment; 10. Auxiliary expansion valve

[0029] 2. Heat exchanger 11. Auxiliary circuit check valve

[0030] 3. Gas-liquid separator; 12. Medium water pump

[0031] 4. Reclaimed water transfer pump; 13. Main line solenoid valve

[0032] 5. Evaporator 14. Main expansion valve

[0033] 6. Compressor; 15. Main circuit check valve

[0034] 7. Condenser; 16. Hot water tank

[0035] 8. Auxiliary evaporator; 17. Hot water pump

[0036] 9. Auxiliary solenoid valve; 18. Hot water circulating pump Detailed Implementation

[0037] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0038] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0040] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] See Figure 2 This embodiment provides a heat pump coupled low-temperature vacuum dehydration and drying system for sludge, including a heat pump subsystem, a drying device 1, a gas-liquid separator 3, and a control subsystem. The heat pump subsystem includes an evaporator 5, a compressor 6, and a condenser 7. The evaporator 5 is equipped with a cooling heat exchange pipeline, the inlet of which is connected to the negative pressure steam outlet of the drying device 1, and the outlet of which is connected to the inlet of the gas-liquid separator 3. The condenser 7 is equipped with a heating heat exchange pipeline, which is connected to the drying device 1 to form a high-temperature hot water circulation loop. The evaporator 5, compressor 6, and condenser 7 are connected in sequence to form a heat pump circulation loop. The control subsystem is electrically connected to the compressor 6 and controls the on / off state of the high-temperature hot water circulation loop and the heat pump circulation loop.

[0042] The heat pump-coupled sludge low-temperature vacuum dehydration and drying system of this embodiment can directly extract heat from the negative pressure steam using the evaporator 5 in the heat pump subsystem. The negative pressure steam is then cooled and condensed. The condensed gas-liquid two-phase water enters the gas-liquid separator 3 for separation before being discharged. Meanwhile, the heat pump medium in the heat pump circulation loop absorbs heat in the evaporator 5 and then enters the compressor 6 for compression and heating. It then enters the condenser 7 to heat the low-temperature hot water in the heating heat exchange pipeline and re-enters the drying equipment 1 through the high-temperature hot water circulation loop for sludge dehydration and drying. Thus, the heat pump-coupled sludge low-temperature vacuum dehydration and drying system of this embodiment forms a closed-loop heat system, thereby enabling efficient and stable utilization of the heat from the negative pressure steam.

[0043] It should be noted that, in this embodiment, the control subsystem preferably adopts a PLC controller; in addition, the evaporator 5 should be designed and calculated according to the highest heat exchange peak value of negative pressure steam cooling and condensation to ensure system safety.

[0044] Preferably, in this embodiment, the gas-liquid separator 3 is provided with a waste gas discharge pipe and a waste liquid discharge pipe. After the condensed gas-liquid two-phase water enters the gas-liquid separator 3, the separated gas enters the waste gas treatment device through the waste gas discharge pipe, and the separated liquid enters the subsequent water treatment stage through the waste liquid discharge pipe.

[0045] Preferably, see Figure 2 The evaporator 5 is equipped with a medium temperature sensor at the medium inlet and outlet, a mass flow meter at the heating heat exchange pipeline, and a hot water temperature sensor at the inlet and outlet of the heating heat exchange pipeline. The heat pump subsystem also includes an auxiliary evaporator 8, which is equipped with an auxiliary heat exchange pipeline connected to the greywater discharge pipeline. The auxiliary evaporator 8, compressor 6, and condenser 7 are connected in sequence to form an auxiliary heat pump circulation loop. The control subsystem is electrically connected to the medium temperature sensor, the hot water temperature sensor, and the mass flow meter, and controls the on / off state of the auxiliary heat pump circulation loop and the greywater discharge pipeline.

[0046] Under normal operating conditions, the hot water used by the drying equipment 1 for sludge dewatering and drying is heated by the heat pump circulation loop. When the heat extracted from the negative pressure steam is insufficient to meet the operating requirements of the drying equipment 1, the control subsystem can control the auxiliary heat pump circulation loop to start, using greywater as a backup heat source.

[0047] Preferably, see Figure 2 The auxiliary heat pump circulation loop is connected in sequence to an auxiliary solenoid valve 9 and an auxiliary expansion valve 10 on the pipeline extending from the medium outlet of the condenser 7 to the medium inlet of the auxiliary evaporator 8. An auxiliary check valve 11 that unidirectionally flows to the inlet of the compressor 6 is provided at the medium outlet of the auxiliary evaporator 8. Both the auxiliary solenoid valve 9 and the auxiliary expansion valve 10 are electrically connected to the control subsystem.

[0048] See Figure 2 The circulation of the heat pump medium in the auxiliary heat pump loop is as follows: after cooling, the heat pump medium is discharged from the medium outlet of the condenser 7 and passes through the auxiliary solenoid valve 9 and the auxiliary expansion valve 10 in sequence. Then it enters the auxiliary evaporator 8 to exchange heat with the greywater in the greywater discharge pipeline and is heated. Then it enters the compressor 6 through the auxiliary check valve 11 to be pressurized and heated. After that, it re-enters the condenser 7 from the compressor 6 to release heat and heat the low-temperature hot water in the high-temperature hot water circulation loop.

[0049] Preferably, see Figure 2 A variable frequency drive (VFD) greywater pump 12 is installed on the greywater discharge pipeline, and the greywater pump 12 is electrically connected to the control subsystem. The control subsystem controls the operation of the greywater pump 12 to deliver greywater to the auxiliary evaporator 8. The greywater that has cooled down after heat exchange is then discharged normally through the greywater discharge pipeline. Furthermore, the greywater pump 12's VFD function allows the auxiliary heat pump circulation loop to adjust not only through its own auxiliary expansion valve 10, but also through the greywater pump 12 to adjust the greywater flow based on calculated heat balance, ensuring optimal operation of the auxiliary heat pump circulation loop.

[0050] Preferably, see Figure 2 In the heat pump circulation loop, a main solenoid valve 13 and a main expansion valve 14 are connected in sequence on the pipeline extending from the medium outlet of the condenser 7 to the medium inlet of the evaporator 5. A main check valve 15 that unidirectionally flows to the inlet of the compressor 6 is provided at the medium outlet of the evaporator 5. Both the main solenoid valve 13 and the main expansion valve 14 are electrically connected to the control subsystem.

[0051] See Figure 2 The circulation of the heat pump medium in the heat pump loop is as follows: after cooling, the heat pump medium is discharged from the medium outlet of the condenser 7 and passes through the main solenoid valve 13 and the main expansion valve 14 in sequence. Then it enters the evaporator 5 to exchange heat with the negative pressure steam in the cooling heat exchange pipeline and is heated. Then it enters the compressor 6 through the main check valve 15 to be pressurized and heated. After that, it re-enters the condenser 7 from the compressor 6 to release heat and heat the low temperature hot water in the high temperature hot water loop.

[0052] It should be noted that when the control subsystem controls the operation of the heat pump circulation loop, the flow rate of the heat pump medium is regulated through the main expansion valve 14.

[0053] Preferably, see Figure 2A hot water tank 16 is installed in the high-temperature hot water circulation loop. Heating and heat exchange pipes are connected to the hot water tank 16 to form a low-temperature water circulation sub-loop. The hot water tank 16 is connected to the drying equipment 1 to form a high-temperature water circulation sub-loop. The control subsystem controls the on / off state of the low-temperature and high-temperature water circulation sub-loops. In actual use, the low-temperature hot water exchanges heat with the heat pump medium in the condenser 7 in the low-temperature water circulation sub-loop to raise its temperature, while the high-temperature water circulation sub-loop transports the high-temperature hot water from the hot water tank 16 to the drying equipment 1 for sludge dewatering and drying.

[0054] Preferably, see Figure 2 A hot water pump 17 is installed on the low-temperature water circulation sub-loop, and a hot water circulation pump 18 is installed on the high-temperature water circulation sub-loop. Both the hot water pump 17 and the hot water circulation pump 18 are electrically connected to the control subsystem. The control subsystem can control the start of the hot water pump 17 and the hot water circulation pump 18. The hot water pump 17 can transport low-temperature hot water from the hot water tank 16 to the condenser 7 for heating, and the heated high-temperature hot water then flows back to the hot water tank 16. The hot water circulation pump 18 can transport high-temperature hot water to the drying equipment 1 for sludge dewatering and drying. After the water in the sludge is dried and evaporated, it becomes negative pressure steam and is discharged from the negative pressure steam outlet. The high-temperature hot water is cooled down and then flows back to the hot water tank 16.

[0055] This embodiment also provides a method for using the above-mentioned heat pump coupled sludge low-temperature vacuum dewatering and drying system. See [link to relevant documentation]. Figure 2 And includes the following steps:

[0056] S1: Set the minimum and maximum limits for the temperature difference between the inlet and outlet of the evaporator medium within the control subsystem;

[0057] S2: The control subsystem monitors the working status of compressor 6 in real time. If compressor 6 is not in full load state, the control subsystem controls the heat pump circulation loop to be turned on and continue to work. If compressor 6 is in full load state, then proceed to step S3.

[0058] S3: The control subsystem receives the detection data from the medium temperature sensor on the evaporator 5 and calculates the medium temperature difference. The control subsystem also receives the detection data from the mass flow meter and the hot water temperature sensor on the heating heat exchange pipeline and calculates the heat balance. If the medium temperature difference is lower than the limit low value, or if the medium temperature difference is between the limit low value and the limit high value and the heat balance is lower than -10%, the auxiliary heat pump circulation loop is then turned on and continues to work. If the medium temperature difference is higher than the limit high value, the control subsystem triggers a fault alarm for the drying equipment 1.

[0059] It should be noted that in step S3, when the medium temperature difference is lower than the limit low value, it indicates that the heat pump circulation loop extracts insufficient heat from the negative pressure steam and needs to supplement the heat source, that is, additional greywater needs to be used as the heat source; when the medium temperature difference is between the limit low value and the limit high value and the thermal balance is lower than -10%, it indicates that the heat pump circulation loop extracts insufficient heat from the negative pressure steam and still needs to supplement the heat source, that is, additional greywater still needs to be used as the heat source; when the medium temperature difference is higher than the limit high value, it indicates that the drying equipment 1 may have a malfunction and has exceeded the optimal operating conditions.

[0060] Better, see Figure 2 In this embodiment, when the auxiliary heat pump circulation loop is used, the greywater pump 12 needs to be turned on first, and the auxiliary solenoid valve 9 and the auxiliary expansion valve 10 need to be turned on after a certain delay. In this way, the thermal balance of the heat pump subsystem is relatively small when the auxiliary heat pump circulation loop is running.

[0061] Preferably, when the compressor 6 is under full load, if the medium temperature difference recovers to the low return temperature of the compressor 6 and the thermal balance is greater than -5%, it indicates that the cooling and heating loads have reached a balance, and the control subsystem controls the auxiliary heat pump circulation loop to shut down.

[0062] See Figure 2 When the heating and cooling loads reach equilibrium and the auxiliary heat pump circulation loop is shut down, the auxiliary solenoid valve 9 is closed first, and after a certain delay, the greywater pump 12 is shut down to reduce energy consumption.

[0063] Preferably, the calculation steps for the thermal balance in step S3 are as follows:

[0064] Step 1: Calculate the actual heating capacity Q of condenser 7 h Q h =c×m×ΔT, where c is the specific heat capacity of the water in the heating heat exchange pipeline, specifically taken as 4.1868 kJ / (kg·K); m is the mass flow rate of the water in the heating heat exchange pipeline, in kg / h, obtained from on-site monitoring; ΔT is the temperature difference between the inlet and outlet of the heating heat exchange pipeline, in K, obtained from on-site monitoring;

[0065] Step 2: Calculate the actual cooling capacity Q of the heat pump subsystem d Q d =Q h -P w , where Q h The actual heating capacity of condenser 7, in kW, is obtained through calculation in step one; P w This is the actual input power of compressor 6, in kW, obtained from on-site monitoring.

[0066] Step 3: Calculate the thermal balance degree, which is... Among them, Q d Q represents the actual cooling capacity of the heat pump subsystem, expressed in kW, and is calculated in step two. s The rated cooling capacity of the heat pump subsystem is expressed in kW, and the inherent parameters of the heat pump subsystem are also given.

[0067] In summary, the heat pump coupled sludge low-temperature vacuum dehydration and drying system and its usage method of the present invention utilizes a heat pump subsystem to directly extract low-grade heat from the drying equipment 1, and transfers it to high-temperature hot water through the circulation of the heat pump medium as the drying heat source for the drying equipment 1, thereby avoiding heat waste and improving the operating efficiency and stability of the heat pump subsystem.

[0068] The above description is only a preferred embodiment of the present invention. 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 invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A heat pump coupled low-temperature vacuum dewatering and drying system for sludge, characterized in that, The system includes a heat pump subsystem, a drying device (1), a gas-liquid separator (3), and a control subsystem. The heat pump subsystem includes an evaporator (5), a compressor (6), and a condenser (7). The evaporator (5) is equipped with a cooling heat exchange pipeline. The inlet of the cooling heat exchange pipeline is connected to the negative pressure steam outlet of the drying device (1), and the outlet of the cooling heat exchange pipeline is connected to the inlet of the gas-liquid separator (3). The condenser (7) is equipped with a heating heat exchange pipeline. The heating heat exchange pipeline is connected to the drying device (1) to form a high-temperature hot water circulation loop. The evaporator (5), the compressor (6), and the condenser (7) are connected in sequence to form a heat pump circulation loop. The control subsystem is electrically connected to the compressor (6) and controls the on / off state of the high-temperature hot water circulation loop and the heat pump circulation loop.

2. The heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 1, characterized in that, The evaporator (5) is equipped with a medium temperature sensor at the medium inlet and outlet, a mass flow meter is installed on the heating heat exchange pipeline, and a hot water temperature sensor is installed at the inlet and outlet of the heating heat exchange pipeline. The heat pump subsystem also includes an auxiliary evaporator (8), which is equipped with an auxiliary heat exchange pipeline. The auxiliary heat exchange pipeline is connected to the greywater discharge pipeline. The auxiliary evaporator (8), the compressor (6), and the condenser (7) are connected in sequence to form an auxiliary heat pump circulation loop. The control subsystem is electrically connected to the medium temperature sensor, the hot water temperature sensor, and the mass flow meter, and the control subsystem controls the opening and closing of the auxiliary heat pump circulation loop and the greywater discharge pipeline.

3. The heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 2, characterized in that, The auxiliary heat pump circulation loop is connected in sequence to an auxiliary solenoid valve (9) and an auxiliary expansion valve (10) on the pipeline extending from the medium outlet of the condenser (7) to the medium inlet of the auxiliary evaporator (8). An auxiliary check valve (11) is provided at the medium outlet of the auxiliary evaporator (8) to unidirectionally flow to the inlet of the compressor (6). Both the auxiliary solenoid valve (9) and the auxiliary expansion valve (10) are electrically connected to the control subsystem.

4. The heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 2, characterized in that, The greywater discharge pipeline is equipped with a greywater pump (12) with frequency conversion function, and the greywater pump (12) is electrically connected to the control subsystem.

5. The heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 1, characterized in that, The heat pump circulation loop has a main solenoid valve (13) and a main expansion valve (14) connected in sequence on the pipeline extending from the medium outlet of the condenser (7) to the medium inlet of the evaporator (5). A main check valve (15) that unidirectionally flows to the inlet of the compressor (6) is provided at the medium outlet of the evaporator (5). Both the main solenoid valve (13) and the main expansion valve (14) are electrically connected to the control subsystem.

6. The heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 1, characterized in that, A hot water tank (16) is provided on the high-temperature hot water circulation loop. The heating heat exchange pipeline is connected to the hot water tank (16) to form a low-temperature water circulation sub-loop. The hot water tank (16) is connected to the drying equipment (1) to form a high-temperature water circulation sub-loop. The control subsystem controls the on / off state of the low-temperature water circulation sub-loop and the high-temperature water circulation sub-loop.

7. The heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 6, characterized in that, A hot water pump (17) is installed on the low-temperature water circulation sub-loop, and a hot water circulation pump (18) is installed on the high-temperature water circulation sub-loop. Both the hot water pump (17) and the hot water circulation pump (18) are electrically connected to the control subsystem.

8. A method of using the heat pump coupled low-temperature vacuum dewatering and drying system for sludge as described in any one of claims 2-4, characterized in that, Includes the following steps: S1: Set the minimum and maximum limits for the temperature difference between the inlet and outlet of the evaporator (5) medium within the control subsystem; S2: The control subsystem monitors the working status of the compressor (6) in real time. If the compressor (6) is not in full load, the control subsystem controls the heat pump circulation loop to be turned on and continue to work. If the compressor (6) is in full load, then proceed to step S3. S3: The control subsystem receives the detection data of the medium temperature sensor on the evaporator (5) and calculates the medium temperature difference. The control subsystem receives the detection data of the mass flow meter and the hot water temperature sensor on the heating heat exchange pipeline and calculates the heat balance. If the temperature difference of the medium is lower than the limit low value, or if the temperature difference of the medium is between the limit low value and the limit high value and the thermal balance is lower than -10%, then the auxiliary heat pump circulation loop will be turned on and continue to work; if the temperature difference of the medium is higher than the limit high value, then the control subsystem will trigger the drying equipment (1) fault alarm.

9. The method of using the heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 8, characterized in that, When the compressor (6) is under full load, if the medium temperature difference recovers to the low return temperature of the compressor (6) and the thermal balance is greater than -5%, the control subsystem controls the auxiliary heat pump circulation loop to shut down.

10. The method of using the heat pump coupled low-temperature vacuum dewatering and drying system for sludge according to claim 8, characterized in that, The calculation steps for the thermal balance in step S3 are as follows: Step 1: Calculate the actual heating capacity Q of the condenser (7) h Q h =c×m×ΔT, where c is the specific heat capacity of the water in the heating heat exchange pipeline, m is the mass flow rate of the water in the heating heat exchange pipeline, and ΔT is the temperature difference between the inlet and outlet of the heating heat exchange pipeline. Step 2: Calculate the actual cooling capacity Q of the heat pump subsystem d Q d =Q h -P w , where Q h P represents the actual heating capacity of the condenser (7). w This refers to the actual input power of the compressor (6); Step 3: Calculate the thermal balance degree, which is... Among them, Q d Q represents the actual cooling capacity of the heat pump subsystem. s This refers to the rated cooling capacity of the heat pump subsystem.

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