Active and passive cooperative spraying line cascade heat recovery system and control method thereof

Abstract

The invention relates to an active and passive cooperative spraying line cascade heat recovery system and a control method thereof. The system comprises a normal-temperature heat pump, a medium-temperature heat pump, a high-temperature heat pump, a high-temperature water tank, a heat preservation channel and a heat recovery channel, the normal-temperature heat pump recycles waste heat of workpieces at an outlet of the drying channel for degreasing heating, the medium-temperature heat pump further recycles waste heat of the workpieces behind the curing channel in a stepped mode, the high-temperature heat pump assists the drying boiler to provide high-temperature hot air and store redundant heat to the high-temperature water tank, and the high-temperature water tank and the heat preservation channel conduct preheating and heat preservation on the workpieces at an inlet of the drying channel. The heat recovery channel recovers waste heat of outlet workpieces of the curing channel for inlet workpiece heating. The system achieves multiple operation modes through switching of different water flow paths, and heat is flexibly distributed. Through cooperative operation of the multiple stages of heat pumps, efficient matching and utilization of heat are achieved, a flexible and reliable operation mode is achieved, energy consumption is remarkably reduced, the working environment of a workshop is improved, and remarkable environmental protection benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial energy conservation and carbon reduction, and in particular to an active and passive coordinated spray line cascade heat recovery energy-saving system and a control method thereof. Background Art

[0002] The spraying line is an automated production system used for surface coating treatment. It is also a type of industrial production line with high energy consumption and high carbon emissions. There is an urgent need to develop green spraying technology that saves energy, reduces carbon emissions and is environmentally friendly.

[0003] The spraying line uses powder spraying or plastic spraying to form a uniform and dense protective coating on the surface of the workpiece through a specific process. This technology has been widely used in many industrial fields such as automobile manufacturing, furniture production, and architectural decoration. Figure 1 As shown in the figure, the traditional powder spraying line mainly includes pre-treatment, dehydration and drying, powder spraying, powder solidification, natural cooling and other process.

[0004] The standard process flow for this spray coating line is as follows: Workpieces enter the assembly line from the loading area and are moved by a motor-driven chain. First, the workpieces enter the degreasing and water washing channel, where a degreaser removes surface oil and other organic contaminants. Two-stage water washing removes residual degreaser and other impurities. Silane treatment improves the coating's adhesion and corrosion resistance, and two further water washes remove residual silane. The workpieces then enter the drying channel, where high-temperature circulating hot air removes residual moisture from the surface. After natural cooling, they enter the powder spray booth, where powder coating is applied by manually operated manual spray guns. Finally, they enter the curing channel, where the powder on the workpiece surface melts, levels, and solidifies into a film at a higher air temperature. After natural cooling, the finished product is discharged from the unloading area.

[0005] Different processes require different temperature conditions. Degreasing requires a temperature of around 30°C to ensure optimal degreasing agent activity. This heat is provided by a dedicated degreasing boiler, primarily operated during the lower winter temperatures. Drying and curing require high temperatures of 120-160°C and 180-220°C, respectively, supplied by separate drying and curing boilers. Powder coating and unloading procedures, on the other hand, are performed at room temperature.

[0006] Traditional processes rely on simple, reliable boilers to directly power each high-temperature process. After the high-temperature treatment, the workpieces cool naturally to room temperature. This, coupled with the fact that continuous boiler operation consumes significant amounts of natural gas and other fossil fuels, also results in the heat from the high-temperature workpieces being dissipated directly into the workshop environment during the natural cooling process. This not only wastes heat but also raises the ambient temperature, impacting worker comfort and productivity. According to statistics, the average daily energy consumption of a powder coating line using traditional processes exceeds 2,000 RMB. Energy-saving heat recovery solutions are urgently needed to reduce production costs and improve energy efficiency.

[0007] Heat pumps, as an energy-saving technology, are widely used in the heat recovery field. However, their direct use in the aforementioned spray line heat recovery application presents challenges. Firstly, spray lines involve multiple processes, each with distinct heat recovery requirements. This results in differences in both the amount of recovered heat and the quality of the recovered heat. Furthermore, the processes are relatively dispersed, making uniform recovery difficult. Secondly, a significant portion of the heat to be recovered is residual heat carried by the workpiece's own heat capacity. This heat must be removed through an intermediate medium (air or water) before it can be recovered by the heat pump. This constitutes indirect heat recovery, further increasing the difficulty. Summary of the Invention

[0008] The purpose of the present invention is to overcome the defects of the above-mentioned traditional process and to propose an active and passive coordinated spray line cascade heat recovery system and its control method to achieve cascade utilization of heat and efficient heat recovery.

[0009] The present invention can be achieved through the following technical solutions:

[0010] In one aspect, the present invention provides a coordinated active and passive cascade heat recovery system for a spray painting line, comprising an active heat recovery subsystem and a passive heat recovery subsystem. The active heat recovery subsystem comprises a distributed arrangement of a normal temperature heat pump, a medium temperature heat pump, and a high temperature heat pump, as well as a high temperature water tank and an insulation channel. The passive heat recovery subsystem comprises a heat recovery channel.

[0011] Furthermore, the ambient temperature heat pump includes a compressor, a condenser, an expansion valve, and an evaporator. The condenser is a plate heat exchanger connected to the degreasing water tank via a circulating water circuit. The evaporator is a fin-tube heat exchanger located at the outlet of the drying channel.

[0012] Preferably, the refrigerant of the normal temperature heat pump can be a normal temperature refrigerant such as R410A, R32, etc.

[0013] Furthermore, the medium-temperature heat pump includes a compressor, a condenser, an expansion valve, and an evaporator. The condenser is a plate heat exchanger. The evaporator is a finned-tube heat exchanger, located at the outlet of the heat recovery channel. Preferably, because the production line leading to the heat recovery channel outlet is long, multiple medium-temperature heat pumps can be deployed along the production line to achieve efficient cascaded heat recovery.

[0014] Preferably, the refrigerant of the medium-temperature heat pump can be a medium-temperature refrigerant such as R134a, R1234yf, etc.

[0015] Furthermore, the high-temperature heat pump comprises a compressor, condenser, subcooler, expansion valve, and evaporator. The condenser is a finned-tube heat exchanger, arranged in series or parallel with the drying boiler within the drying duct to provide high-temperature circulating hot air. Both the subcooler and evaporator are plate-type heat exchangers.

[0016] Preferably, the refrigerant of the high-temperature heat pump can be a high-temperature refrigerant such as R245fa, R1233zd, etc.

[0017] Furthermore, the heat preservation channel is arranged between the degreasing and washing channel and the drying channel, and a plurality of circulating fan coils are arranged inside. Preferably, the circulating fan coils use variable speed fans, and the air volume provided can be changed according to the moving speed of the workpiece.

[0018] Furthermore, the high-temperature water tank is connected to the final water washing process via a branch line; is circulated to the plate heat exchanger of the high-temperature water tank via a fourth water flow path; and is circulated to several circulating fan coils within the insulation channel via a fifth water flow path. A third water pump is disposed on the fifth water flow path.

[0019] Furthermore, the heat recovery channel is arranged between the powder spraying room and the curing channel, and is provided with a plurality of circulating fans inside. Preferably, the circulating fans are variable speed fans, and the air volume provided can be changed according to the moving speed of the workpiece.

[0020] Furthermore, the medium-temperature heat pump, high-temperature heat pump, and plate heat exchanger of the high-temperature water tank are interconnected via multiple water flow paths. The first water flow path sequentially flows through the first water pump, the AC port of three-way ball valve I, the high-temperature heat pump evaporator, the CA port of three-way ball valve IV, and the medium-temperature heat pump condenser. The second water flow path sequentially flows through the second water pump, the plate heat exchanger of the high-temperature water tank, the BC ports of three-way ball valve III, the high-temperature heat pump subcooler, and the AC port of three-way ball valve II. The B port of three-way ball valve I is connected to the B port of three-way ball valve II, and the B port of three-way ball valve IV is connected to the A port of three-way ball valve III. Thus, a third water flow path sequentially flows through the first water pump, the AB ports of three-way ball valve I, the BC ports of three-way ball valve II, the second water pump, the plate heat exchanger of the high-temperature water tank, the BA port of three-way ball valve III, the BA port of three-way ball valve IV, and the medium-temperature heat pump condenser. Different water flow paths can be switched by controlling the opening and closing of different ports of four three-way ball valves.

[0021] On the other hand, the present invention provides a control method for a spray line cascade heat recovery system with active and passive coordination. By switching between different water flow paths, this technical solution includes the following operating modes:

[0022] Mode A: The medium-temperature heat pump supplies heat to the high-temperature heat pump. Part of the heat from the high-temperature heat pump is used to heat the circulating air in the drying channel, and the other part is used to heat the high-temperature water tank. In this mode, the first and second water flow paths operate, driven by the first and second water pumps, respectively. The heat generated on the condensing side of the medium-temperature heat pump is absorbed by the evaporating side of the high-temperature heat pump through the first water flow path. Part of the heat generated by the high-temperature heat pump provides high-temperature circulating hot air for the drying channel, and the other part is stored in the high-temperature water tank through the second water flow path. Part of the heat from the high-temperature water tank is used for the high-temperature spray in the final stage of water washing, and the other part is used to keep the workpieces warm in the insulation channel. This mode is the main operating mode of the heat recovery system.

[0023] Furthermore, in this mode, the system components are as follows: the medium-temperature heat pump and the high-temperature heat pump are both on, the first water pump and the second water pump are on, the ac port of the three-way ball valve I is open, the ac port of the three-way ball valve II is open, the bc port of the three-way ball valve III is open, and the ca port of the three-way ball valve IV is open.

[0024] Furthermore, the system control method in this mode is to control the outlet water temperature by adjusting the capacity of the medium-temperature heat pump, with a typical target value of 60°C. The condensation heat of the high-temperature heat pump is used for drying, while the subcooling heat is stored in the high-temperature water tank. By adjusting the capacity of the high-temperature heat pump and the heat distribution ratio on the condensing side, the condenser outlet air temperature and subcooler outlet water temperature are controlled, with typical target values of 120°C and 80°C.

[0025] Mode B: The medium-temperature heat pump supplies heat to the high-temperature heat pump, with all heat from the high-temperature heat pump used for the drying duct. In this mode, only the first water flow path operates, driven by the first water pump. Heat generated by the condensing side of the medium-temperature heat pump is absorbed by the evaporating side of the high-temperature heat pump through the first water flow path. The heat generated by the high-temperature heat pump provides high-temperature circulating hot air for the drying duct. The system operates in this mode when there is sufficient heat in the high-temperature water tank.

[0026] Furthermore, in this mode, the system components are as follows: the medium-temperature heat pump and the high-temperature heat pump are both on, but the high-temperature heat pump's subcooler is off. The first water pump is on, and the second water pump is off. The ac port of three-way ball valve I is open, and the ca port of three-way ball valve IV is open. The abc ports of three-way ball valve II and three-way ball valve III are both closed.

[0027] Furthermore, the system control method in this mode is to control the outlet water temperature by adjusting the capacity of the medium-temperature heat pump, with a typical target value of 60°C. The condenser outlet air temperature is controlled by adjusting the capacity of the high-temperature heat pump, with a typical target value of 120°C.

[0028] Mode C: The medium-temperature heat pump supplies heat to the high-temperature water tank. In this mode, only the third water path operates, driven by the first and second water pumps. Heat generated on the condensing side of the medium-temperature heat pump is used via the third water path to heat the high-temperature water tank, preheating and maintaining the temperature of workpieces at the drying channel inlet. This mode is suitable for the initial stage of production line startup.

[0029] Furthermore, in this mode, the system components are in the following states: the medium-temperature heat pump is on, the high-temperature heat pump is off. The first and second water pumps are both on. Ports ab of three-way ball valve I are open, port bc of three-way ball valve II is open, port ba of three-way ball valve III is open, and port ba of three-way ball valve IV is open.

[0030] Furthermore, the control method of the system in this mode is: controlling the outlet water temperature by adjusting the capacity of the medium-temperature heat pump, with a typical target value of 80°C, and storing it in a high-temperature water tank.

[0031] D Mode: Part of the heat generated by the medium-temperature heat pump is used to heat the high-temperature heat pump, and the remaining heat is used to heat the high-temperature water tank. In this mode, the first and third water flow paths operate, driven jointly by the first and second water pumps. Part of the heat generated on the condensing side of the medium-temperature heat pump is absorbed by the evaporating side of the high-temperature heat pump through the first water flow path, while the remaining heat is used to heat the high-temperature water tank through the third water flow path. The system operates in this mode when a large amount of waste heat is to be recovered at the outlet of the heat recovery channel. At this time, all the heat from the high-temperature heat pump is used to heat the drying channel, significantly reducing the output of the drying boiler.

[0032] Furthermore, in this mode, the system components are as follows: the medium-temperature heat pump and the high-temperature heat pump are both on, but the high-temperature heat pump subcooler is off. The first and second water pumps are on. Ports abc of three-way ball valves I and IV are both open, port bc of three-way ball valve II is open, and port ba of three-way ball valve III is open.

[0033] Furthermore, in this mode, the system's control method is to adjust the medium-temperature heat pump's capacity to control its outlet water temperature, with a typical target value of 80°C. Part of the hot water flows through the high-temperature heat pump evaporator, while the remaining hot water flows through the plate heat exchanger in the high-temperature water tank. This increases the high-temperature heat pump's evaporation temperature and system capacity.

[0034] Mode E: The high-temperature heat pump draws heat only from the high-temperature water tank. The water flow path in this mode operates identically to Mode D, except that the medium-temperature heat pump is shut down, and heat from the high-temperature water tank is absorbed by the evaporation side of the high-temperature heat pump through the first water flow path. This mode is typically used when the system is about to shut down, but can also serve as an emergency mode if the medium-temperature heat pump fails to start.

[0035] Furthermore, in this mode, the system components are as follows: the high-temperature heat pump is on, but its subcooler is off, and the medium-temperature heat pump is off. The first and second water pumps are on. Ports abc of three-way ball valves I and IV are both open, port bc of three-way ball valve II is open, and port ba of three-way ball valve III is open.

[0036] Furthermore, in this mode, the system's control method is as follows: since there is no heat input into the high-temperature water tank, the water tank temperature decreases as the high-temperature heat pump continues to extract heat. When the high-temperature water tank temperature falls below a set value (e.g., 40°C), the high-temperature heat pump is shut down. At this point, the heat in the high-temperature water tank is almost completely used up, and the heat recovery system is about to shut down completely.

[0037] The present invention discloses an active and passive coordinated cascade heat recovery system for a spraying line, which has the following beneficial effects:

[0038] This energy-saving heat recovery system fully realizes active and passive heat recovery.

[0039] Active heat recovery:

[0040] a) A normal-temperature heat pump is located next to the degreasing water tank. Its evaporator absorbs waste heat lost to the ambient air from the workpieces at the drying channel outlet, achieving indirect heat recovery. Its condenser heats the degreasing water tank to provide heat energy for the degreasing process, ensuring temperatures in the pre-degreasing and main degreasing processes remain between 30°C and 40°C. The normal-temperature heat pump primarily operates in winter, when ambient temperatures are lower.

[0041] b) A medium-temperature heat pump is located at the outlet of the heat recovery channel, actively recovering waste heat from the workpiece through circulating air. Multiple medium-temperature heat pumps are arranged sequentially along the workpiece's travel direction, achieving cascaded heat utilization along the way. A single medium-temperature heat pump can be a single-stage system or other more efficient system configurations. The recovered heat is ultimately absorbed by the evaporation side of the high-temperature heat pump via the first water flow path or heated by the third water flow path in a high-temperature water tank.

[0042] c) A high-temperature heat pump assists the drying boiler in providing the high-temperature circulating hot air required for drying moisture, reducing the load on the drying boiler and, consequently, natural gas consumption. The high-temperature heat pump's evaporator draws heat from the condensing side of the medium-temperature heat pump via the first water flow path. Part of this heat is used to provide high-temperature circulating hot air for the drying duct, while the remainder is stored in a high-temperature water tank via the second water flow path. In special circumstances, the high-temperature heat pump can also draw heat directly from the high-temperature water tank.

[0043] d) The heat in the high-temperature water tank serves two purposes. One portion is used to improve the spray conditions in the final wash stage, raising the workpiece temperature with high-temperature hot water. The other portion is supplied via the fifth water flow path to the circulating fan coils within the insulation channel. These circulate hot air within the insulation channel to maintain a high temperature for the hot workpieces before they enter the drying channel. Preheating the workpieces at the drying channel inlet reduces the load on the high-temperature heat pump and drying boiler within the drying channel. Furthermore, the high-temperature water tank's heat storage capacity ensures stable system operation.

[0044] Passive heat recovery: Driven by the circulating fan in the heat recovery channel, the circulating air transfers the waste heat carried by the workpiece at the curing outlet to the workpiece at the curing inlet, increasing the temperature of the workpiece at the curing channel inlet, thereby reducing the load of the curing boiler.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] 1. Achieve efficient and matched utilization of heat. Through the active + passive heat recovery system, the waste heat at the drying channel outlet is used for degreasing heating, the waste heat at the curing channel outlet is used for inlet preheating and drying channel heating, and the excess heat is further used for preheating and insulation of the drying channel inlet, forming a complete heat recovery chain.

[0047] 2. Flexible and reliable operation. Despite the distributed layout of the multi-stage heat pumps, the medium-temperature heat pump, high-temperature heat pump, and high-temperature water tank are connected through multiple circulating water circuits. Different circulating water circuits are switched through three-way ball valves to achieve various operating modes. The system operation and control are flexible, stable, and reliable.

[0048] 3. Significantly reduced energy consumption. By using a normal temperature heat pump to replace the degreasing boiler, a high temperature heat pump to assist the drying boiler in heating, and a heat recovery channel to reduce the load on the curing boiler, the overall energy consumption of the spraying line has been greatly reduced, and the average daily energy consumption cost has also been significantly reduced.

[0049] 4. Improved workshop working environment. By effectively recovering and utilizing the waste heat of the workpiece, the heat loss to the workshop environment is reduced, the workshop temperature can be reduced by 5~8℃, and the working comfort of workers is significantly improved.

[0050] 5. It has significant environmental benefits. The heat recovery system reduces the use of gas boilers, reduces natural gas consumption, and reduces the emission of greenhouse gases such as carbon dioxide, which is in line with the development trend of green manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the traditional powder spraying line structure.

[0052] Figure 2 This is a schematic structural diagram of the active and passive coordinated spray line cascade heat recovery system of the present invention.

[0053] Figure 3 This is a schematic structural diagram of the heat recovery system of the present invention operating in mode A.

[0054] Figure 4 This is a schematic structural diagram of the heat recovery system of the present invention operating in mode B.

[0055] Figure 5 This is a schematic structural diagram of the heat recovery system of the present invention operating in C mode.

[0056] Figure 6 This is a schematic structural diagram of the heat recovery system of the present invention operating in D mode.

[0057] Figure 7 This is a schematic structural diagram of the heat recovery system of the present invention operating in E mode.

[0058] In the figure: 1. Loading area, 2. Assembly line, 3. Degreasing and washing channel, 4-1. Pre-degreasing, 4-2. Main degreasing, 5. Silane treatment, 5-1. Water washing I, 5-2. Water washing II, 5-3. Water washing III, 5-4. Water washing IV, 6. Drying channel, 7. Drying boiler, 8. Degreasing water tank, 9. Degreasing boiler, 10. Curing channel, 11. Curing boiler, 12. Powder spraying room, 13. Unloading area, 14. Normal temperature heat pump (14-1 compressor, 14-2 condenser, 14-3 expansion valve, 14-4 evaporator), 15. Medium temperature heat pump (15-1 compressor, 15-2 condenser, 15-3 expansion valve, 15-4 evaporator), 16. High temperature heat pump (16-1 compressor, 16-2 condenser, 16-2' subcooler, 16-3 expansion valve, 16-4 evaporator), 17, high-temperature water tank, 17-1, plate heat exchanger of high-temperature water tank, 18, insulation channel, 19, circulating fan coil, 20, heat recovery channel, 21, circulating fan, 22-1, first water pump, 22-2, second water pump, 22-3, third water pump, 23-1, three-way ball valve I, 23-2, three-way ball valve II, 23-3, three-way ball valve III, 23-4, three-way ball valve IV, W-1, first water flow path, W-2, second water flow path, W-3, third water flow path, W-4, fourth water flow path, W-5, fifth water flow path.

[0059] Among them: a, b, c are the three conduction ports of the three-way ball valve. DETAILED DESCRIPTION

[0060] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention. Based on the embodiments described in the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention.

[0061] Example 1

[0062] This embodiment provides a spray line cascade heat recovery system with active and passive coordination (such as Figure 2 ), mainly including an active heat recovery subsystem and a passive heat recovery subsystem. The active heat recovery subsystem includes a normal temperature heat pump 14, a medium temperature heat pump 15, a high temperature heat pump 16, a high temperature water tank 17, and a heat preservation channel 18. The passive heat recovery subsystem is the heat recovery channel 20.

[0063] Furthermore, the ambient temperature heat pump 14 comprises a compressor 14-1, a condenser 14-2, an expansion valve 14-3, and an evaporator 14-4, which are connected in sequence. Condenser 14-2 is a plate heat exchanger connected to the degreasing water tank 8 via a circulating water circuit. Evaporator 14-4 is a finned tube heat exchanger placed at the outlet of the drying channel.

[0064] Furthermore, the medium-temperature heat pump 15 includes a compressor 15-1, a condenser 15-2, an expansion valve 15-3, and an evaporator 15-4, which are connected in sequence. The condenser 15-2 is a plate heat exchanger, and the evaporator 15-4 is a finned tube heat exchanger, which is placed at the outlet of the heat recovery channel.

[0065] Furthermore, the high-temperature heat pump 16 comprises a compressor 16-1, a condenser 16-2, a subcooler 16-2', an expansion valve 16-3, and an evaporator 16-4, connected in sequence. Condenser 16-2 is a finned-tube heat exchanger placed at the bottom of the drying duct and connected in series with the drying boiler 7. This means that the circulating air within the drying duct flows sequentially through the high-temperature heat pump condenser 16-2 and the drying boiler 7, converting it into high-temperature hot air. Both the subcooler 16-2' and evaporator 16-4 of the high-temperature heat pump are plate-type heat exchangers.

[0066] Furthermore, the heat preservation channel 18 is located between the degreasing water washing channel 3 and the drying channel 6 and is equipped with several circulating fan coils 19. The high-temperature water washing tank 17 is connected to the water washing IV 5-4 via a branch line; it is circulated to the plate heat exchanger 17-1 of the high-temperature water tank via a fourth water flow path W-4; and it is circulated to the several circulating fan coils 19 via a fifth water flow path W-5.

[0067] Furthermore, the heat recovery channel 20 is provided between the powder spraying room 12 and the curing channel 10 , and a plurality of circulation fans 21 are provided inside.

[0068] Furthermore, the medium-temperature heat pump's condenser 15-2 and the high-temperature heat pump's evaporator 16-4 are connected by a first water flow path W-1, which sequentially flows through the first water pump 22-1, the ac port of three-way ball valve I 23-1, the high-temperature heat pump's evaporator 16-4, the ca port of three-way ball valve IV 23-4, and the medium-temperature heat pump's condenser 15-2. The high-temperature heat pump's subcooler 16-2' and the high-temperature water tank's plate heat exchanger 17-1 are connected by a second water flow path W-2, which sequentially flows through the second water pump 22-2, the high-temperature water tank's plate heat exchanger 17-1, the bc port of three-way ball valve III 23-3, the high-temperature heat pump's subcooler 16-2', and the ac port of three-way ball valve II 23-2. The condenser 15-2 of the medium-temperature heat pump and the plate heat exchanger 17-1 of the high-temperature water tank are connected by a third water flow path W-3. The third water flow path W-3 flows sequentially through the first water pump 22-1, the ab port of the three-way ball valve I 23-1, the bc port of the three-way ball valve II 23-2, the second water pump 22-2, the plate heat exchanger 17-1 of the high-temperature water tank, the ba port of the three-way ball valve III 23-3, the ba port of the three-way ball valve IV 23-4, and the condenser 15-2 of the medium-temperature heat pump.

[0069] By adjusting the opening and closing of different ports of the four three-way ball valves 23-1 to 23-4, switching between different water flow paths can be achieved. This technical solution includes the following operating modes:

[0070] A mode ( Figure 3 ): The medium-temperature heat pump 15 supplies heat to the high-temperature heat pump 16. Part of the heat from the high-temperature heat pump 16 is used to dry the duct 6, and the other part is used to heat the high-temperature water tank 17. In mode A, the system components are as follows: the medium-temperature heat pump 15 and the high-temperature heat pump 16 are both on, and the first water pump 22-1 and the second water pump 22-2 are on. The ac port of the three-way ball valve I 23-1 is open, the ac port of the three-way ball valve II 23-2 is open, the bc port of the three-way ball valve III 23-3 is open, and the ca port of the three-way ball valve IV 23-4 is open. The first water flow path W-1 and the second water flow path W-2 are in operation. In mode A, the system is controlled by adjusting the capacity of the medium-temperature heat pump 15 to control its outlet water temperature, with a typical target value of 60°C. The condenser outlet air temperature and the subcooler outlet water temperature are controlled by adjusting the capacity of the high temperature heat pump 16 and the heat distribution between the condenser 16 - 2 and the subcooler 16 - 2 ′, with typical target values being 120° C. and 80° C.

[0071] B mode ( Figure 4 ): The medium-temperature heat pump 15 supplies heat to the high-temperature heat pump 16, and all the heat of the high-temperature heat pump 16 is used for the drying channel. In mode B, the status of the system components is as follows: the medium-temperature heat pump 15 and the high-temperature heat pump 16 are both turned on, but the high-temperature heat pump subcooler 16-2' stops working. The first water pump 22-1 is turned on, and the second water pump 22-2 is turned off. The ac port of the three-way ball valve I 23-1 is open, and the ca port of the three-way ball valve IV 23-4 is open. The first water flow path W-1 is running. In mode B, the system is controlled by adjusting the capacity of the medium-temperature heat pump 15 to control its outlet water temperature, with a typical target value of 60°C. The condenser outlet air temperature is controlled by adjusting the capacity of the high-temperature heat pump 16, with a typical target value of 120°C.

[0072] C Mode ( Figure 5 ): the medium-temperature heat pump 15 supplies heat to the high-temperature water tank 17. In mode C, the status of the system components is: the medium-temperature heat pump 15 is on, and the high-temperature heat pump 16 is off. The first water pump 22-1 and the second water pump 22-2 are on. The ab port of the three-way ball valve I 23-1 is connected, the bc port of the three-way ball valve II 23-2 is connected, the ba port of the three-way ball valve III 23-3 is connected, the ba port of the three-way ball valve IV 23-4 is connected, and the third water flow path W-3 is in operation. In mode C, the system is controlled by adjusting the capacity of the medium-temperature heat pump 15 to control its outlet water temperature, with a typical target value of 80°C, and stored in the high-temperature water tank 17.

[0073] D Mode ( Figure 6The heat generated by the medium-temperature heat pump 15 is partially supplied to the high-temperature heat pump 16, and the remaining portion is supplied to the high-temperature water tank 17. In D mode, the system components are as follows: the medium-temperature heat pump 15 and the high-temperature heat pump 16 are both on, but the high-temperature heat pump subcooler 16-2' is off. The first water pump 22-1 and the second water pump 22-2 are on. The abc ports of the three-way ball valve I 23-1 and the three-way ball valve IV 23-4 are both open, the bc port of the three-way ball valve II 23-2 is open, and the ba port of the three-way ball valve III 23-3 is open. The first water flow path W-1 and the third water flow path W-3 are operating. In D mode, the system is controlled by adjusting the capacity of the medium-temperature heat pump 15 to control its outlet water temperature, with a typical target value of 80°C. Some of the hot water flows through the high-temperature heat pump evaporator 16-4, while the remaining hot water flows through the plate heat exchanger 17-1 of the high-temperature water tank.

[0074] E Mode ( Figure 7 ): The high-temperature heat pump 16 takes heat from the high-temperature water tank 17. In E mode, the status of the system components is: the high-temperature heat pump 16 is turned on, but the high-temperature heat pump subcooler 16-2' stops working, and the medium-temperature heat pump 15 is turned off. The first water pump 22-1 and the second water pump 22-2 are turned on. The status of the three-way ball valve and the operation of the water flow path in this mode are the same as those in D mode. The control method of the system in E mode is: when the temperature of the high-temperature water tank 17 is lower than the set value (such as 40°C), the high-temperature heat pump 16 is turned off. At this time, the heat in the high-temperature water tank is almost used up, and the heat recovery system is about to be completely shut down.

[0075] The working process of the spraying line in this embodiment is as follows:

[0076] The workpiece to be sprayed enters the assembly line 2 from the loading area 1, and its temperature is about 30℃.

[0077] Step 1: The workpiece enters the degreasing and water-washing channel 3. Pre-degreasing 4-1 and main degreasing 4-2 remove surface oil and other organic contaminants. Water washes I 5-1 and II 5-2 remove residual degreasing agent and other impurities. Silane treatment 5 improves the coating's adhesion and corrosion resistance, and water wash III 5-3 removes residual silane. Water wash IV 5-4 uses 80°C hot water spray, allowing the workpiece to reach a temperature of 75°C upon exiting the degreasing and water-washing channel 3. After a slight cooling process, the workpiece enters the heat-insulating channel 18, where heated circulating air is generated by several circulating fan coils 19 to maintain a high ambient temperature within the channel, thereby maintaining a temperature of approximately 70°C before entering the drying channel 6.

[0078] Step 2: The workpieces enter the drying tunnel 6 for dehydration and drying. High-temperature circulating hot air at 120-160°C is generated by the high-temperature heat pump 16 and the drying boiler 7. After leaving the drying tunnel 6, the workpieces are naturally cooled to room temperature before being powder-coated in the powder spray booth 12.

[0079] Step 3: The workpiece enters the heat recovery channel 20. Under the action of the circulating fan 21, the residual heat of the workpiece leaving the curing channel 10 on the other side is dissipated in the heat recovery channel 20 and preheats the inlet workpiece. Finally, the workpiece is heated to about 60°C.

[0080] Step 4: The workpiece enters the curing channel 10 for powder leveling and curing. Curing boiler 11 generates circulating hot air at a temperature of 180-220°C. The workpiece then exits the curing channel 10 and enters the heat recovery channel 20, where heat is transferred to the incoming workpiece. After exiting the heat recovery channel 20, the workpiece remains at approximately 60°C, where it is subjected to cascaded heat recovery via multiple medium-temperature heat pumps 15 arranged along the way.

[0081] Finally, the workpiece temperature drops to about 30°C, which is the normal temperature, and the finished product is output from the unloading area.

[0082] Compared with the traditional workflow, the differences and benefits of this embodiment are as follows:

[0083] In the first step, high-temperature hot water spraying and heat preservation are used to preheat the workpiece and increase its temperature before entering the drying channel, so as to reduce the heating load of the dehydration and drying channel.

[0084] In the second step, the high-temperature heat pump 16 is used to partially or completely replace the drying boiler 7 , with the purpose of reducing the output of the drying boiler 7 or even replacing the drying boiler 7 .

[0085] In the third step, a heat recovery channel 20 is used to use the heat at the outlet of the curing channel for inlet preheating through circulating air, ultimately increasing the temperature of the workpiece before it enters the curing channel to reduce the load of the curing boiler 11.

[0086] In the fourth step, multiple medium-temperature heat pumps 15 are used to further recover the waste heat at the outlet of the curing channel through circulating air, provide heat for the high-temperature heat pump 16 and the high-temperature water tank 17, and improve the workshop environment.

[0087] The above description of the embodiments is intended to facilitate understanding and use of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. 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 present invention should be within the scope of protection of the present invention.

Claims

1. An active and passive coordinated spray line cascade heat recovery system, characterized in that: include: A passive heat recovery subsystem comprising a heat recovery channel (20) disposed between the outlet and inlet of the curing channel of the production line, for directly transferring workpiece heat between the outlet and inlet of the curing channel to preheat the inlet workpiece; Active heat recovery subsystem, which includes: A normal temperature heat pump (14) provided at the outlet of the drying channel to recover waste heat from the workpiece; A medium-temperature heat pump (15) disposed at the outlet of the heat recovery channel (20) to recover waste heat from a higher-temperature workpiece; A high-temperature heat pump (16) for providing high-temperature heat to the drying channel; a high-temperature water tank (17) for storing high-temperature heat; and a heat preservation channel (18) for preheating and keeping warm the workpieces before entering the drying channel using the heat of the high-temperature water tank (17); The heat recovered by the normal temperature heat pump (14) is used for the heating demand of the degreasing process of the production line, and the heat recovered by the medium temperature heat pump (15) is used to provide a heat source to the high temperature heat pump (16) and / or to supply heat to the high temperature water tank (17). The high temperature heat pump (16) supplies heat to the drying channel and / or to the high temperature water tank (17). The high temperature water tank (17) supplies heat to the insulation channel (18). A multi-stage waste heat recovery and cascade utilization relationship is formed within the active heat recovery subsystem and between the active heat recovery subsystem and the passive heat recovery subsystem.

2. The active and passive coordinated spraying line cascade heat recovery system according to claim 1 is characterized in that: The invention is applied to a spraying production line, wherein the production line comprises at least a degreasing and washing section, a drying channel, a powder spraying section, and a curing channel arranged in sequence. A heat recovery channel (20) is arranged between the powder spraying section and the curing channel, and a heat preservation channel (18) is arranged between the degreasing and washing section and the drying channel.

3. The active and passive coordinated spraying line cascade heat recovery system according to claim 1 is characterized in that: The normal temperature heat pump (14) is arranged at the outlet of the drying channel, and recovers the waste heat of the workpiece through air circulation. The generated heat is used to heat the degreasing water tank to ensure the process temperature of the degreasing process. The medium-temperature heat pump (15) is arranged at the outlet of the heat recovery channel (20), with at least one medium-temperature heat pump, and optionally multiple medium-temperature heat pumps arranged along the direction of movement of the workpiece, to achieve step-by-step utilization of heat along the way through air circulation, and to supply heat to the high-temperature heat pump (16) and / or the high-temperature water tank (17). The high-temperature heat pump (16) is arranged at the bottom of the drying channel and obtains heat from the condensing side of the medium-temperature heat pump (15) and / or the high-temperature water tank (17) to assist the heating boiler of the drying channel in providing high-temperature circulating hot air and / or storing heat in the high-temperature water tank (17). The high-temperature water tank (17) and the heat preservation channel (18) are used for preheating and heat preservation of workpieces at the inlet of the drying channel.

4. The active and passive coordinated spraying line cascade heat recovery system according to claim 1 is characterized in that: The normal temperature heat pump (14) and the degreasing water tank are connected in a heat exchange manner via a fluid circulation loop. The medium-temperature heat pump (15) condenser is connected to the high-temperature heat pump (16) evaporator and the high-temperature water tank (17) in a heat exchange manner via a fluid circulation loop. The high-temperature heat pump (16) condenser is connected to the drying channel via an air circulation heat exchange method, and the high-temperature heat pump (16) subcooler is connected to the high-temperature water tank (17) via a fluid circulation loop heat exchange method. The high-temperature water tank (17) is fluidically connected to the water washing section of the spraying line via a pipeline, and the high-temperature water tank (17) is connected to the internal circulation fan coil in the heat preservation channel (18) via a water channel.

5. The active and passive coordinated spraying line cascade heat recovery system according to claim 1 is characterized in that: The normal temperature heat pump (14) comprises a compressor, a condenser, an expansion valve and an evaporator, the condenser is a refrigerant-water heat exchanger, and the evaporator is a refrigerant-air heat exchanger. The medium-temperature heat pump (15) comprises a compressor, a condenser, an expansion valve and an evaporator, the condenser is a refrigerant-water heat exchanger, and the evaporator is a refrigerant-air heat exchanger. The high-temperature heat pump (16) includes a compressor, a condenser, a subcooler, an expansion valve and an evaporator, the condenser is a refrigerant-air heat exchanger, the subcooler is a refrigerant-water heat exchanger, and the evaporator is a refrigerant-water heat exchanger. The heat preservation channel (18) is internally provided with a plurality of circulating fan coils to generate hot air circulation. The heat recovery channel (20) is internally provided with a plurality of circulating fans to generate hot air circulation.

6. The active and passive coordinated spraying line cascade heat recovery system according to claim 1 is characterized in that: The active heat recovery subsystem further includes a fluid circulation loop connecting the medium-temperature heat pump (15), the high-temperature heat pump (16) and the high-temperature water tank (17): a first flow path (W-1) connecting the condenser of the medium-temperature heat pump (15) and the evaporator of the high-temperature heat pump (16); A second flow path (W-2) connecting the high-temperature heat pump (16) subcooler and the high-temperature water tank (17) heat exchanger; A third flow path (W-3) connects the medium-temperature heat pump (15) condenser and the high-temperature water tank (17) heat exchanger. The circuit is provided with a switching valve group, which includes a plurality of multi-way valves (23-1 to 23-4). The switching valve group controls the flow path connection state by switching the ports, and changes the fluid flow direction to achieve multiple operating modes.

7. The control method of the active and passive coordinated spray line cascade heat recovery system according to claim 6 is characterized in that: By switching between different fluid paths, the system includes the following operating modes: Mode A: The medium-temperature heat pump (15) supplies heat to the high-temperature heat pump (16) through the first flow path (W-1); part of the heat of the high-temperature heat pump (16) is used for drying the channel, and part is stored in the high-temperature water tank (17) through the second flow path (W-2); Mode B: the medium-temperature heat pump (15) supplies heat to the high-temperature heat pump (16) through the first flow path (W-1), and all the heat of the high-temperature heat pump (16) is used for the drying channel; Mode C: the medium-temperature heat pump (15) supplies heat to the high-temperature water tank (17) through the third flow path (W-3), and the high-temperature heat pump (16) is turned off; Mode D: The medium-temperature heat pump (15) supplies heat to the high-temperature heat pump (16) and the high-temperature water tank (17) at the same time; E mode: The high-temperature heat pump (16) takes heat from the high-temperature water tank (17), and the medium-temperature heat pump (15) is turned off.

8. The control method of the active and passive coordinated spray line cascade heat recovery system according to claim 7 is characterized in that: The temperature distribution is controlled by adjusting the operating parameters of each heat pump: when the medium-temperature heat pump (15) is turned on, the medium-temperature heat pump (15) is adjusted to control the temperature to the set outlet water temperature; when the high-temperature heat pump (16) is turned on, the high-temperature heat pump (16) is adjusted to control the temperature to the set condenser outlet air temperature; when the high-temperature heat pump subcooler is working, the heat distribution of the high-temperature heat pump (16) is adjusted to control the temperature to the set outlet water temperature.

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