A kind of gas power generation and heat pump collaborative spraying line cascade heat recovery system and method

Abstract

The present application relates to a kind of gas power generation and heat pump collaborative spraying line cascade heat recovery system and method.The system includes gas power generation unit, heat pump unit and waste heat recovery unit.Gas power generation unit consumes gas to generate electric energy to drive heat pump unit, and the high-temperature flue gas generated by it is discharged into the rear section of dehydration drying channel to assist heating, and the waste heat of cylinder liner cooling water is stored in the medium-temperature water tank for preheating;Waste heat recovery unit recovers the waste heat of drying channel exhaust gas and workshop environment waste heat as the low-temperature heat source of heat pump unit;Heat pump unit includes medium-temperature heat pump and high-temperature heat pump, medium-temperature heat pump improves low-grade heat, and high-temperature heat pump further sends the medium-temperature heat to the front section of dehydration drying channel after upgrading.The present application breaks through the limitation of traditional direct heat exchange, by introducing multi-stage heat pump as intermediate upgrading link, forms "power generation energy supply→spraying waste heat→heat pump recovery→back supply spraying", energy closed loop, realizes the cascade matching of high, medium and low grade energy, significantly reduces heating energy consumption and improves workshop environment.

Description

Technical Field

[0001] This invention relates to the field of industrial energy conservation and carbon reduction technology, specifically to a cascade heat recovery system and method for a spraying line that combines gas-fired power generation and a heat pump. Background Technology

[0002] Spray coating production lines are a core component of surface treatment in industrial manufacturing, widely used in industries such as automobiles, home appliances, and building materials. Typical spray coating processes usually include pretreatment washing, dehydration and drying, powder coating, and curing, and are characterized by high energy consumption and high carbon emissions.

[0003] Currently, the heating system in spray coating lines commonly uses gas-fired hot air furnaces to directly burn natural gas, providing high-temperature hot air at 160℃~220℃ to the dehydration and drying channels and the curing channels. However, this traditional direct-fired heating method has significant technical drawbacks:

[0004] First, the mismatch between the heating temperature and process requirements leads to serious waste of "high quality used for low-quality purposes." Natural gas combustion flames reach temperatures of over 1000 degrees Celsius, yet it's only used to produce hot air at around 160 degrees Celsius. Furthermore, the dehydration and drying channels typically employ uniformly high-temperature heating throughout the entire process. In reality, the workpiece drying process includes different stages such as preheating evaporation, constant-rate drying, and slow-rate drying, with temperature requirements varying in stages. This uniformly high temperature not only exacerbates energy consumption but also causes significant heat loss, resulting in severe thermal pollution in the workshop.

[0005] Secondly, direct combustion produces high-temperature exhaust gases, resulting in significant direct heat loss. The waste gas generated during the spraying process (typically between 60°C and 80°C) is often directly discharged into the atmosphere through the exhaust hood, without any recovery of this low-grade waste heat.

[0006] To address the aforementioned high energy consumption issue, existing technologies have proposed several waste heat utilization solutions, such as introducing gas generator sets to utilize the waste heat generated by the cylinder liner water for preheating before spraying (e.g., patent CN207470313U). However, these existing improvement solutions still face core technological bottlenecks:

[0007] On the one hand, there is a lack of effective means to recover low-grade waste heat. Existing solutions generally adopt the traditional "direct waste heat exchange" method. Limited by the temperature difference heat transfer limitation of the second law of thermodynamics, direct heat exchange can only recover waste heat with a temperature higher than that of the heated medium. Faced with the large amount of low-grade waste gas (60℃~80℃) discharged from the spraying line and the heat dissipation of the workshop environment (about 30℃~40℃), traditional heat exchangers are powerless, resulting in this part of the waste heat being wasted.

[0008] On the other hand, the lack of an energy closed loop limits the overall energy efficiency improvement of the system. Existing waste heat utilization solutions are limited to a one-way linear utilization of "power generation → direct waste heat exchange → process preheating," failing to further enhance the waste heat generated by the spraying process itself and feed it back to the core high-temperature drying process, thus failing to form an energy closed loop throughout the workshop.

[0009] In summary, how to break through the physical bottleneck of traditional direct heat exchange methods, achieve the tiered matching of high, medium and low grade heat energy in the spraying line, and convert the dissipated process waste heat into usable heat energy to form a closed energy loop in the system is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0010] The purpose of this invention is to overcome the defects of the above-mentioned traditional processes and propose a cascade heat recovery system and method for a spraying line that combines gas power generation and heat pump, breaking through the bottleneck of traditional direct waste heat exchange and realizing cascade utilization of energy and systematic high-efficiency heat recovery.

[0011] This invention can be achieved through the following technical solutions:

[0012] On one hand, the present invention provides a cascade heat recovery system for a spraying line that combines gas power generation and heat pump, including a gas power generation unit, a heat pump unit, and a waste heat recovery unit.

[0013] Furthermore, the gas-fired power generation unit includes a gas generator, which is equipped with a generator high-temperature flue gas exhaust pipe and a cylinder liner water cooling circuit. The generator high-temperature flue gas exhaust pipe extends and is fluidly connected to the dehydration and drying channel (preferably, connected to the latter half of the drying channel) and the curing channel of the spraying line, providing direct heating of high-temperature waste heat; the cylinder liner water cooling circuit is circulated and connected to a medium-temperature water tank through a generator cylinder liner water cooling drive pump, and is used to store medium-temperature waste heat.

[0014] Furthermore, the heat pump unit includes a medium-temperature heat pump module and a high-temperature heat pump module arranged in a cascaded or stacked manner.

[0015] The medium-temperature heat pump module includes a medium-temperature heat pump module compressor, a medium-temperature heat pump module condenser, a medium-temperature heat pump module throttling element, and a medium-temperature heat pump module evaporator, which are connected in sequence by refrigerant pipelines.

[0016] The high-temperature heat pump module includes a high-temperature heat pump module compressor, a high-temperature heat pump module condenser, a high-temperature heat pump module throttling element, and a high-temperature heat pump module evaporator, which are connected in sequence by refrigerant pipelines. The high-temperature heat pump module condenser is arranged in the dehydration and drying channel (preferably in the first half of the drying channel), and provides high-temperature hot air to the drying channel through air circulation.

[0017] Furthermore, the waste heat recovery unit includes a waste gas heat recovery heat exchanger, a terminal cooling coil, and a low-temperature water tank. The waste gas heat recovery heat exchanger is arranged in the waste gas emission channel of the spraying line exhaust hood, and the terminal cooling coil is arranged in the spraying workshop environment. The waste gas heat recovery heat exchanger and the terminal cooling coil are connected in parallel through water pipelines, and a fluid circulation loop is established with the low-temperature water tank through a fourth circulation pump to collect the recovered low-grade heat into the low-temperature water tank; the low-temperature water tank is further circulated with the evaporator of the medium-temperature heat pump module through a third circulation pump, serving as a low-grade heat source for the medium-temperature heat pump module.

[0018] Furthermore, the medium-temperature water tank, the medium-temperature heat pump module condenser, and the high-temperature heat pump module evaporator are connected by a complex fluid flow relationship through multiple water flow paths, including a first circulation pump and a second circulation pump, to achieve flexible allocation of medium-temperature heat: the heat generated by the medium-temperature heat pump module condenser can be stored in the medium-temperature water tank through the water flow path, or directly flow into the high-temperature heat pump module evaporator side (at this time, the medium-temperature heat pump module condenser and the high-temperature heat pump module evaporator are a common intermediate heat exchanger) for heat exchange; the high-temperature heat pump module evaporator can absorb heat from the medium-temperature water tank or the medium-temperature heat pump module condenser through the water flow path.

[0019] Meanwhile, the medium-temperature water tank is connected to the water washing spray pump through a pipeline, and further fluidly connected to the water washing process pipeline of the pretreatment channel (preferably, connected to the last water wash) for preheating of the workpiece before spraying.

[0020] On the other hand, this invention discloses an operation control method based on the above system. Through the coordinated control of the gas-fired power generation unit, water pump network, and heat pump unit, the system includes the following operation modes and steps:

[0021] Step A (Gas-fired Power Generation Drive and Cascade Heating): Start the gas generator, consuming natural gas to produce electricity. This electricity powers the compressor of the heat pump unit and all circulating pumps in the waste heat recovery unit. Simultaneously, the approximately 500°C high-temperature flue gas discharged from the gas generator is directly introduced into the latter part of the dehydration and drying channel for high-temperature heating; the 80°C~90°C cylinder liner coolant generated by the gas generator circulates through the generator cylinder liner coolant driving pump, storing its heat in the medium-temperature water tank.

[0022] Step B (Waste Heat Upgrading and Heat Closed Loop): The fourth circulation pump is turned on, and the waste gas heat recovery heat exchanger and the terminal cooling coil absorb the waste heat from the exhaust gas and the waste heat from the workshop air, respectively, and collect them into the low-temperature water tank; the third circulation pump is turned on, and the medium-temperature heat pump module evaporator extracts low-grade heat from the low-temperature water tank. After the medium-temperature heat pump compressor does work, medium-temperature heat is produced on the condenser side of the medium-temperature heat pump; this medium-temperature heat is further transferred to the high-temperature heat pump module evaporator, and after being upgraded again by the high-temperature heat pump, high-temperature hot air of about 120°C is output by the high-temperature heat pump module condenser at the front of the dehydration and drying channel.

[0023] Step C (Dynamic Allocation Based on System Load): The flow of medium-temperature heat is flexibly allocated according to the different process loads of the pretreatment and drying sections of the spraying line. When the heat load of the dehydration and drying channel is high, the flow rates of the first and second circulation pumps are controlled to ensure that the heat generated by the medium-temperature heat pump condenser mainly flows to the high-temperature heat pump module evaporator. When the temperature of the pretreatment water washing section is lower than the process set value (e.g., 70℃), the medium-temperature water tank releases heat, and the water washing spray pump is turned on to draw hot water from the medium-temperature water tank to the final water washing process of the pretreatment for spray preheating. If the medium-temperature heat pump generates excess heat, the excess heat is stored in the medium-temperature water tank, which serves as a heat storage buffer hub for the energy allocation of the entire system.

[0024] Compared with the prior art, the present invention has the following significant advantages:

[0025] 1. Cascaded matching of energy grades: High-grade energy (electricity) generated by gas-fired power generation is used to drive the heat pump compressor, and its high-temperature flue gas, along with the heat generated by the high-temperature heat pump, is used for heating the drying tunnel; medium-grade energy (cylinder liner water at 80℃~90℃) from the waste heat of power generation is directly used for preheating of the pretreatment before spraying; the medium-temperature heat pump extracts low-grade heat from the exhaust gas and the workshop environment to make up for the medium-temperature heat gap in the system. This achieves the proper utilization of high, medium, and low-grade energy.

[0026] 2. Precise Matching of Dehydration and Drying Temperature Fields in Spray Painting Lines: Traditional spray painting hot air furnaces use direct combustion heating, requiring the overall drying tunnel temperature to be controlled at 160℃ or higher. This invention creates a three-stage differentially matched dehydration and drying temperature field through preheating of the pre-treated workpiece (approximately 70℃), a high-temperature heat pump heating section (approximately 120℃), and a gas generator waste heat heating section (approximately 150℃). This effectively reduces the average temperature and heat leakage loss within the tunnel, thereby significantly reducing the total heating energy consumption.

[0027] 3. A closed-loop energy utilization system is formed: the high-temperature exhaust gas (usually 60℃~80℃) discharged from the spraying oven is used as a low-temperature heat source for the heat pump. This "waste heat" is then upgraded and reused by the heat pump. This forms an energy closed loop of "power generation → waste heat generated by the spraying process → heat pump recovery → resupply to the spraying process", solving the overall energy utilization efficiency problem of the spraying workshop.

[0028] 4. Feasibility and Economic Efficiency of Engineering Modification: The main external energy input of this invention system is natural gas. The electricity required for the operation of the heat pump unit and various water pumps is generated and consumed by the gas generator. For spray painting lines that commonly use direct combustion of natural gas for heating, this system eliminates the need for expensive and cumbersome "power expansion" approvals and construction during energy-saving and carbon-reduction retrofits, significantly lowering the barrier to entry. Furthermore, in regions where natural gas prices are significantly lower than industrial electricity prices, this "gas-for-electricity, gas-electricity-heat synergy" system architecture achieves the optimal energy cost conversion ratio, bringing significant economic benefits to enterprises. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a traditional powder coating production line.

[0030] Figure 2 This is a schematic diagram of the cascade heat recovery system for the spraying line of the present invention (Example 1).

[0031] Figure 3 This is a schematic diagram of the cascade heat recovery system for the spraying line of the present invention (Example 2).

[0032] In the diagram: 0. Loading area; 1. Pre-treatment channel; 2. Dehydration and drying channel; 3. Powder spraying booth; 4. Curing channel; 5. Unloading area; 6. Production line; 7. Water washing; 8. Drying and heating hot air furnace; 9. Curing and heating hot air furnace; 10. Gas collection and exhaust hood; 11. Exhaust gas; 20. Gas generator; 21. Generator high-temperature flue gas; 22. Generator intake; 23. Generator cylinder liner water cooling circuit; 24. Generator cylinder liner water cooling drive pump; 26. Medium-temperature water tank; 27. Water washing spray pump; 28. 29. First circulation pump, 30. Second circulation pump, 31. High-temperature heat pump module compressor, 32. High-temperature heat pump module evaporator, 33. High-temperature heat pump module throttling element, 34. High-temperature heat pump module condenser, 35. Medium-temperature heat pump module compressor, 36. Medium-temperature heat pump module condenser, 37. Medium-temperature heat pump module throttling element, 38. Medium-temperature heat pump module evaporator, 39. Third circulation pump, 40. Low-temperature water tank, 41. Fourth circulation pump, 42. Waste gas heat recovery heat exchanger, 43. Terminal cooling coil. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 2 As shown, this embodiment provides a cascade heat recovery system for a spraying line that combines gas-fired power generation and heat pumps. It mainly consists of a gas-fired power generation unit, a multi-stage heat pump unit, and a waste heat recovery unit network coupled together.

[0036] Gas-fired power generation unit structure: The gas generator 20's intake end is connected to the generator intake 22 pipeline, and the electricity generated by its work is electrically connected to the compressor, water pump, and other electrical equipment in the system (the cable layout is not fully shown in the figure). The high-temperature exhaust gas generated by the gas generator 20 forms high-temperature flue gas 21 through anti-corrosion and heat-insulating pipelines, which is directly connected to the heating duct of the latter half of the dehydration and drying channel 2 and the curing channel 4. The cooling end of the gas generator 20 is connected to the generator cylinder liner water cooling circuit 23, which drives the generator cylinder liner water cooling pump 24 to circulate cooling water carrying 80℃~90℃ waste heat into the heat exchange coil (or direct water circulation) in the medium-temperature water tank 26 for heat storage.

[0037] The waste heat recovery unit structure includes a low-temperature water tank 39, a fourth circulation pump 40, a waste gas heat recovery heat exchanger 41, and a terminal cooling coil 42. The waste gas heat recovery heat exchanger 41 is located within the exhaust duct of the waste gas 11 collected from the solidification channel 4 and the dehydration and drying channel 2. The terminal cooling coil 42 is located in the workshop operating area as a fan coil unit (or other air conditioning terminal). The waste gas heat recovery heat exchanger 41 and the terminal cooling coil 42 are connected in parallel via a water collection pipe and driven by the fourth circulation pump 40, forming a low-temperature water circulation heat recovery flow path with the low-temperature water tank 39.

[0038] Heat pump unit and its coupling piping network structure:

[0039] Low-temperature heat extraction side: The low-temperature water tank 39 is connected to the third circulation pump 38 through a pipeline, which pumps the circulating water with recovered waste heat into the heat exchange side of the evaporator 37 of the medium-temperature heat pump module for heat release, and then flows back to the low-temperature water tank 39.

[0040] Medium-temperature heat pump circuit: The medium-temperature heat pump module compressor 34, medium-temperature heat pump module condenser 35, medium-temperature heat pump module throttling element 36 and medium-temperature heat pump module evaporator 37 are connected end to end by refrigerant copper pipes to form a closed circuit.

[0041] The high-temperature heat pump circuit consists of a high-temperature heat pump module compressor 30, a high-temperature heat pump module condenser 33, a high-temperature heat pump module throttling element 32, and a high-temperature heat pump module evaporator 31 (when a cascade heat pump configuration is adopted, the high-temperature heat pump module evaporator 31 and the medium-temperature heat pump module condenser 35 are common intermediate heat exchangers) forming a closed loop. The high-temperature heat pump module condenser 33 is preferably a finned tube air heat exchanger, directly integrated into the circulating fan airflow channel of the first half of the dehydration and drying channel 2.

[0042] Spray-coated water-washing coupling structure:

[0043] A water outlet pipe is led out of the medium-temperature water tank 26 and connected to the water washing spray pump 27. Then, through the spray pipeline, it is fluidly connected to the spray head array of the last water washing 7 in the pretreatment channel 1. This is used to directly preheat the workpieces on the production line 6 by spraying the residual heat of the cylinder liner water collected in the medium-temperature water tank 26 in the form of hot water pure water spray.

[0044] Furthermore, combined with Figure 2 This embodiment describes the operation method of the workpiece on the production line 6 using the above system and the implementation of the three-stage temperature field.

[0045] Step 1 (Pretreatment and Preheating): The workpiece to be coated enters the pretreatment channel 1. The medium-temperature water tank 26 collects the waste heat from the generator cylinder liner water. The water washing spray pump 27 delivers the hot water from the medium-temperature water tank 26 to the final water washing stage 7 for spraying. When the workpiece leaves the pretreatment channel 1, its temperature rises to about 70°C due to absorbing the sensible heat of the hot water, achieving the first stage of preheating.

[0046] Step 2 (Dehydration and Drying): The workpiece enters the dehydration and drying channel 2. Unlike traditional drying ovens where the entire oven is heated to 160℃ by a drying and heating hot air furnace 8, this solution creates a progressive temperature field within the drying channel:

[0047] Front section: After the workpiece is sprayed with hot water, the base temperature rises to about 70°C for basic evaporation;

[0048] Middle section: Air flows through the high-temperature heat pump module condenser 33 and is heated to about 120°C by dry hot air to blow on the workpiece, evaporating the main moisture on the surface;

[0049] Rear section: The high-temperature flue gas 21 introduced into the rear section of the gas generator maintains the internal air at approximately 150°C, providing the high temperature required for deep drying.

[0050] The three-stage temperature field precisely matches the physical process of water evaporation, significantly reducing unnecessary heat loss and energy consumption.

[0051] Step 3 (Energy Closed-Loop and Environmental Control): The exhaust gas 11 from the oven is no longer directly discharged, but instead passes through the exhaust gas heat recovery heat exchanger 41, where the heat is carried back to the system by the water circuit. Simultaneously, the heat emitted by the oven and curing furnace within the workshop is absorbed by the terminal cooling coil 42, reducing the temperature in the workshop's operating area and improving the working environment. The absorbed heat is ultimately supplied back to the drying channel by the heat pump unit, achieving a closed loop.

[0052] Example 2

[0053] This embodiment provides a cascaded heat recovery system for a painting line, parallel to Embodiment 1. In painting line scenarios requiring more flexible equipment layout and experiencing significant fluctuations in heat load across different process stages, this embodiment optimizes the distribution of heat sources and the coupling relationship between heat pumps. The main differences from Embodiment 1 are as follows:

[0054] First, the directional supply of waste heat from the generator exhaust: the high-temperature flue gas 21 generated by the gas generator 20 is only directionally supplied to the dehydration and drying channel 2 for heating, and does not provide auxiliary heating to the curing channel 4.

[0055] Differences and benefits: The high-temperature flue gas branch leading to the curing channel is eliminated, simplifying the layout of the corrosion-resistant and heat-insulating flue gas duct and reducing heat loss over long distances. Since the flue gas heat load only needs to meet the requirements of the later section of the dehydration drying tunnel, a smaller and lower-spec gas generator 20 can be used, thereby reducing the initial equipment investment of the system.

[0056] Second, the decoupling of medium and high temperature heat pumps and the star-shaped heat distribution network: In this embodiment, the direct cascaded heat exchange coupling structure between the medium temperature heat pump module and the high temperature heat pump module is eliminated. Instead, both are fluidly connected to the medium temperature water tank 26 to construct a star-shaped distribution network with the medium temperature water tank 26 as the energy hub.

[0057] The specific connection and operation methods are as follows:

[0058] 1) The cylinder liner water cooling circuit 23 of the gas generator stores the waste heat into the medium-temperature water tank 26 through circulation;

[0059] 2) After the condenser 35 of the medium-temperature heat pump module recovers and upgrades the low-grade waste heat, all the heat generated is transported through the water circuit and stored in the medium-temperature water tank 26.

[0060] 3) The intermediate heat source required by the evaporator 31 of the high-temperature heat pump module is uniformly drawn from the medium-temperature water tank 26 by a water pump and heat exchanged.

[0061] 4) The preheated hot water spray at the end of the pretreatment channel 1 is also heated by the water spray pump 27, which draws hot water from the medium-temperature water tank 26.

[0062] Differences and Benefits: This architecture breaks the rigid constraint that upstream and downstream heat pumps must operate in strict synchronization. Since there is often a time lag between the waste gas heat recovery (affected by exhaust volume) and the drying tunnel heating load (affected by workpiece output) in actual production, the medium-temperature water tank 26 acts as an "energy storage tank." The medium-temperature heat pump only needs to focus on storing heat in the water tank, while the high-temperature heat pump and pretreatment spray extract heat from the water tank according to their respective process requirements. The operation of each subsystem does not interfere with each other. This design significantly improves the system's operational flexibility, stability, and resistance to load fluctuations.

[0063] The above description of the embodiments is provided to enable those skilled in the art to understand and use the present invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A cascade heat recovery system for a spray painting line that integrates gas-fired power generation and a heat pump, characterized in that, include: Gas-fired power generation unit, used to consume gas to generate electricity and the associated high-temperature and medium-temperature waste heat; The heat pump unit is electrically connected to the gas-fired power generation unit and uses the electrical energy as the driving energy. Waste heat recovery units are located on the exhaust side of the spraying line and in the workshop environment to collect low-grade waste heat generated by the spraying process. The heating distribution pipeline is used to transport the high-temperature waste heat and medium-temperature waste heat generated by the gas-fired power generation unit, as well as the heat output after the heat pump unit is upgraded, to different temperature zones of the spraying line according to the process temperature requirements. The heat pump unit extracts low-grade heat from the waste heat recovery unit and heats and improves its quality, forming an energy closed loop of "power generation and energy supply → waste heat from spraying → heat pump recovery → return to spraying".

2. The spray painting line cascade heat recovery system according to claim 1, characterized in that, The spraying line includes at least a pretreatment channel (1), a dehydration and drying channel (2), a powder spraying chamber (3), and a curing channel (4). The medium-temperature waste heat from the gas-fired power generation unit is used to heat the pretreatment channel (1); the high-temperature heat output from the heat pump unit and the high-temperature waste heat from the gas-fired power generation unit are used to heat the dehydration and drying channel (2).

3. The spray painting line cascade heat recovery system according to claim 1, characterized in that, The gas-fired power generation unit is a gas generator (20), the medium-temperature waste heat is the heat generated by the cylinder liner water of the generator, and the high-temperature waste heat is the high-temperature flue gas of the generator (21). The gas generator (20) is connected to the medium-temperature water tank (26) through the generator cylinder liner water cooling circuit (23), and is in fluid communication with the pretreatment channel (1) through the water washing spray pump (27); the high-temperature flue gas (21) of the generator is directly connected to the dehydration and drying channel (2) through the pipeline.

4. The spray painting line cascade heat recovery system according to claim 3, characterized in that, The heat pump unit includes a medium-temperature heat pump module and a high-temperature heat pump module that form a cascaded or interconnected heating structure. The medium-temperature heat pump module absorbs the waste heat of the exhaust gas (11) and the waste heat of the workshop air through the waste heat recovery unit to generate medium-temperature heat. The high-temperature heat pump module obtains the medium-temperature heat from the condenser side of the medium-temperature heat pump module or the medium-temperature water tank (26), and generates high-temperature heat after further heating, which is then sent to the dehydration and drying channel (2).

5. The spray painting line cascade heat recovery system according to claim 4, characterized in that: The waste heat recovery unit includes a waste gas heat recovery heat exchanger (41) and a terminal cooling coil (42), which are circulatedly connected to a low-temperature water tank (39) via a fourth circulation pump (40); The medium-temperature heat pump module includes a medium-temperature heat pump module compressor (34), a medium-temperature heat pump module condenser (35), a medium-temperature heat pump module throttling element (36), and a medium-temperature heat pump module evaporator (37) connected in sequence. The medium-temperature heat pump module evaporator (37) absorbs heat from the low-temperature water tank (39) through a third circulation pump (38), and the medium-temperature heat pump module condenser (35) transfers heat to the medium-temperature water tank (26) or directly to the high-temperature heat pump module. The high-temperature heat pump module includes a high-temperature heat pump module compressor (30), a high-temperature heat pump module condenser (33), a high-temperature heat pump module throttling element (32), and a high-temperature heat pump module evaporator connected in sequence. The high-temperature heat pump module evaporator obtains medium-temperature heat, and the high-temperature heat pump module condenser (33) is arranged in the circulating air path of the dehydration and drying channel (2).

6. The spray painting line cascade heat recovery system according to claim 2, characterized in that, The dehydration and drying channel (2) contains three differentially matched drying temperature fields, which include, in sequence: The workpiece preheating section, which is sprayed with hot water from the pretreatment water, has a temperature of 60℃~80℃. The high-temperature heat pump heating section, heated by the heat pump unit, has a temperature of 100℃~130℃. The waste heat heating section, heated by the high-temperature flue gas emitted from the gas-fired power generation unit, has a temperature of 140℃~180℃.

7. A method for operating and controlling the cascade heat recovery system of a spraying line according to any one of claims 1-6, characterized in that, Includes the following steps: Step A: Start the gas-fired power generation unit to generate electricity to drive the heat pump unit, and at the same time, guide its high-temperature waste heat to the drying channel of the spraying line to heat it, and store the waste heat of the cylinder liner water in the medium-temperature water tank for pretreatment heating. Step B: Collect waste heat from the exhaust gas emitted from the dehydration and drying channel and waste heat from the workshop environment through the waste heat recovery unit; use a medium-temperature heat pump to absorb the low-grade heat to produce medium-temperature heat; and then use a high-temperature heat pump to further upgrade the medium-temperature heat to generate high-temperature hot air which is sent into the dehydration and drying channel. Step C: Adjust the power generation of the gas-fired power generation unit and the start-up, shutdown and frequency conversion operation of the heat pump unit according to the real-time temperature requirements of different stages of the spraying process to maintain the dynamic balance of energy cascade utilization.

8. The control method according to claim 7, characterized in that, In step B, the outlet air temperature of the condenser of the high-temperature heat pump module is controlled at 100℃ to 130℃, and the temperature of the high-temperature flue gas direct heating area of ​​the gas power generation unit is controlled at 140℃ to 180℃, thereby creating a stepped temperature field in the dehydration and drying channel.

9. The control method according to claim 7, characterized in that, In step B, during the process of recovering waste heat from the workshop air through the terminal cooling coil (42), the average temperature of the workshop is reduced simultaneously, providing a comfortable environment with localized cooling for the surrounding staff.

10. The control method according to claim 7, characterized in that, The medium-temperature water tank (26) serves as a system energy storage buffer hub: when the medium-temperature heat pump generates excess heat, the excess heat is stored in the medium-temperature water tank (26); when the temperature of the current processing water washing (7) is lower than the set value, hot water is drawn from the medium-temperature water tank (26) for heating; when the heat load of the dehydration and drying channel (2) increases, heat is preferentially drawn from the medium-temperature water tank (26) to supply the high-temperature heat pump module.

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