A sludge drying system based on heat pump and its thermodynamic optimization design method

Abstract

The present invention discloses a sludge drying system based on a heat pump and a thermodynamic optimization design method thereof. In the sludge drying system based on a heat pump, the outlet of the compressor is connected to the inlet of the compressor through the refrigerant channel of the first condenser, the refrigerant channel of the second condenser, the expansion valve, and the refrigerant channel of the evaporator in sequence; in the drying chamber, the sludge inlet is connected to the sludge outlet through a drying conveyor belt, the upper air outlet is connected to the middle air outlet, and the middle air outlet is connected to the lower air outlet; the middle air outlet is divided into two paths after passing through the air duct of the heat release device, one path is connected to the upper air outlet through the air duct of the first condensation, and the other path is connected to the lower air outlet through the high-temperature side air duct of the sensible heat exchanger, the air duct of the evaporator, the low-temperature side air duct of the sensible heat exchanger, and the air duct of the second condensation in sequence. The method of the present invention can complete the overall optimization design of the heat pump drying system under certain operating conditions, sludge demand and structural characteristics.

Description

Technical Field

[0001] The invention belongs to the technical field of heat pump application, and in particular relates to a heat pump-based sludge drying system and a thermodynamic optimization design method thereof. Background Art

[0002] With the continuous development of economy and society, the total supply of cold and hot energy in the transportation field and industrial, commercial and civil fields has continued to increase year by year. Considering the low efficiency and high pollution characteristics of traditional primary energy direct combustion heating, there is a strong demand for technological progress and industrial transformation in the field of refrigeration and heating in the industrial, commercial and civil fields in modern life.

[0003] In the field of distributed drying, the primary energy direct combustion heating method still occupies an absolute dominant position. Not only is the direct energy utilization efficiency far less than 100%, but also a large amount of waste gas and waste residue are discharged under the conditions of distributed combustion. Therefore, the promotion of heat pump technology in this field is of great significance for energy saving and environmental protection.

[0004] Different from the technical points in the application background of traditional heat pump water heaters, heat pump heating, etc., the heat pump system in the drying field not only relies on the condenser to output heat to the outside, but also relies on the evaporator to provide cooling capacity for the circulating air, so as to precipitate the moisture in the circulating air and ensure that it enters the drying room in a low-humidity state and ensures the drying effect. This requires a new system optimization design according to the heat pump drying system process.

[0005] In summary, given the special working conditions in the drying field, conventional heat pump design methods (heat pump water heaters, heat pump heating, etc.) cannot meet the needs of the drying system, and new design methods are urgently needed. Summary of the invention

[0006] The purpose of the present invention is to provide a heat pump-based sludge drying system and a thermodynamic optimization design method thereof to solve one or more of the above-mentioned technical problems. The method provided by the present invention can complete the overall optimization design of the heat pump drying system under certain operating conditions, sludge demand and structural characteristics, find the optimal operating thermodynamic parameters and ensure the lowest energy consumption per ton of sludge during the operation process.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a heat pump-based sludge drying system, comprising: a compressor, a first condenser, a second condenser, a sensible heat exchanger, an evaporator, an expansion valve, a heat release device and a drying chamber;

[0009] The outlet of the compressor is connected to the inlet of the compressor via the refrigerant channel of the first condenser, the refrigerant channel of the second condenser, the expansion valve, and the refrigerant channel of the evaporator in sequence;

[0010] The drying chamber is provided with a sludge inlet, a sludge outlet, an upper air outlet, a middle air outlet, a lower air outlet and a drying conveyor belt; in the drying chamber, the sludge inlet is connected to the sludge outlet via the drying conveyor belt, the upper air outlet is connected to the middle air outlet, and the middle air outlet is connected to the lower air outlet; the middle air outlet is divided into two paths after passing through the air duct of the heat release device, one path is connected to the upper air outlet via the first condensation air duct, and the other path is connected to the lower air outlet via the high-temperature side air duct of the sensible heat exchanger, the air duct of the evaporator, the low-temperature side air duct of the sensible heat exchanger, and the second condensation air duct in sequence.

[0011] A further improvement of the present invention is that it also includes:

[0012] A water cooling tower, wherein a water outlet of the water cooling tower is connected to a water inlet of the water cooling tower through a water channel of the heat release device.

[0013] A further improvement of the present invention is that the drying conveyor belts are arranged in layers.

[0014] A further improvement of the present invention is that during operation:

[0015] A part of the circulating air enters the drying room from the upper air outlet of the drying room, passes through several layers of drying conveyor belts and reaches the middle air outlet; another part of the circulating air enters the drying room from the lower air outlet of the drying room, passes through several layers of drying conveyor belts and reaches the middle air outlet;

[0016] After the two parts of circulating air are mixed, they enter the heat release device to dissipate heat to the circulating cooling water. The medium-temperature circulating air after heat dissipation is divided into two parts, one part of which is passed into the first condenser to absorb the heat of the refrigerant, and then returns to the upper air outlet of the drying chamber; the other part first passes through the high-temperature side of the sensible heat exchanger to release part of the heat, and then passes into the evaporator to release heat and precipitate water, and then passes through the low-temperature side of the sensible heat exchanger again and absorbs the heat of the high-temperature side. The heated circulating air passes through the second condenser to raise the temperature to a high temperature and low humidity state, and finally returns to the lower air outlet of the drying chamber.

[0017] A further improvement of the present invention is that the medium in the refrigerant channel is R134a.

[0018] The present invention provides a thermodynamic optimization design method for a heat pump-based sludge drying system, comprising the following steps:

[0019] Obtain the required boundary conditions, operating conditions, geometric structure of the sludge drying system and the structural form of the drying chamber for sludge products;

[0020] Set the compressor speed, total circulating air flow, upper and lower air volume ratio, volumetric efficiency and isentropic efficiency of the compressor, subcooling degree of the heat pump system, exhaust pressure of the heat pump system, suction pressure of the heat pump system, superheat degree of the heat pump system, and outlet temperature of the low-temperature side after waste heat recovery; based on the set conditions, calculate the heating capacity, COP, circulating air temperature of the two-layer inlet, evaporator water removal, and heat exchange temperature of the heat ventilator of the drying system, SMER, and energy consumption per ton of mud;

[0021] Determine whether the sludge outlet parameters meet the feedforward requirements. If not, feedback is used to adjust the compressor speed of the heat pump system, increase a step from the current value, and continue the calculation; if the sludge outlet dryness meets the requirements, determine the difference between the system ton sludge energy consumption and the preset value. If it is less than the preset value, save all current assumed thermodynamic parameters and thermodynamic calculation results as the existing optimal values ​​for the current calculation stage; if it is greater than or equal to the preset value, skip the saving step and directly determine whether the low-temperature side outlet temperature after waste heat recovery has reached the maximum value. If it has not reached the maximum value, increase the low-temperature side outlet temperature after waste heat recovery by a step and continue the calculation; if it has reached the maximum value, determine whether the superheat of the heat pump system has reached the maximum value. If it has not reached the maximum value, increase Superheat, increase the value by one step, and continue the calculation; if it has reached the maximum value, determine whether the suction pressure of the heat pump system has reached the maximum value, if it has not reached the maximum value, increase the suction pressure, increase the value by one step, and continue the calculation; if it has reached the maximum value, determine whether the air volume ratio of the heat pump system has reached the maximum value, if it has not reached the maximum value, increase the air volume ratio, increase the value by one step, and continue the calculation; if it has reached the maximum value, determine whether the total air volume of the heat pump system has reached the maximum value, if it has not reached the maximum value, increase the total air volume, increase the value by one step, and continue the calculation; if it has reached the maximum value, end the entire calculation process, and the final output result is the optimal operating state of the system corresponding to the lowest ton of mud energy consumption in all iterative calculation steps.

[0022] A further improvement of the present invention is that the demand boundary conditions of the sludge product include the sludge processing volume, the sludge inlet moisture content and the sludge outlet moisture content; the operating conditions include the ambient temperature and the ambient humidity; the structural form in the drying chamber includes the number of drying conveyor belts, air inlet and air outlet information.

[0023] A further improvement of the present invention is that the compressor speed includes a lower limit of the speed, an upper limit of the speed and an adjustment step; the total circulating air flow includes a lower limit of the total air volume, an upper limit of the total air volume and an adjustment step; the two-layer air volume ratio includes a lower limit of the air volume ratio, an upper limit of the air volume ratio and an adjustment step; the suction pressure of the heat pump system includes a lower limit of the suction pressure, an upper limit of the suction pressure and an adjustment step; the superheat of the heat pump system includes a lower limit of the superheat, an upper limit of the superheat and an adjustment step; the low-temperature side outlet temperature after waste heat recovery includes a lower limit of the outlet temperature, an upper limit of the outlet temperature and an adjustment step.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In the technical solution provided by the present invention, an innovative double-layer parallel drying chamber structure with two inlets and one outlet is proposed. Through the structural innovation of the segmented hot air inlet, not only the average hot air temperature in the drying chamber is significantly improved, but also the air resistance caused by the air flow process in the drying chamber is effectively reduced, thereby greatly reducing the power consumption of the circulating fan.

[0026] In existing conventional heat pumps, the evaporation side (cooling side) and the condensation side (heating side) are in two different environmental areas, exchanging heat with different heat exchange media respectively, and both sides can be designed and optimized separately; in the present invention, in view of the special working conditions in the drying application field, an optimization design method different from the conventional heat pump system is proposed. The evaporation side (cooling side) and the condensation side (heating side) exchange heat with the air in the same circulation loop. This part of the wet air is first cooled (water is analyzed out) and then heated. Therefore, it is a strong coupling process, which is essentially different from the traditional design optimization scheme. The method provided by the present invention can complete the overall optimization design of the heat pump drying system under certain operating conditions, sludge requirements and structural characteristics, find the optimal operating thermodynamic parameters and ensure the lowest energy consumption per ton of sludge during the operation process, which can provide theoretical reference for equipment manufacturers and suppliers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art; obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 is a schematic diagram of a heat pump-based sludge drying system provided by the present invention;

[0029] Figure 2 It is a schematic flow chart of a thermodynamic optimization design method for a sludge drying system provided in an embodiment of the present invention;

[0030] In the figure, 1, compressor; 2, first condenser; 3, second condenser; 4, sensible heat exchanger; 5, evaporator; 6, expansion valve; 7, heat release device; 8, water cooling tower. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0032] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0034] See also Figure 1 A sludge drying system based on a heat pump is provided in an embodiment of the present invention, comprising: a compressor 1, a first condenser 2, a second condenser 3, an expansion valve 6, an evaporator 5, a sensible heat exchanger 4, a heat release device 7 and a plurality of dryer conveyor belts; wherein the sludge drying system comprises a refrigerant circuit, a cooling water circuit, a circulating air circuit and a sludge conveying channel; the heat pump can select an R134a heat pump or the like.

[0035] In the refrigerant circuit of the embodiment of the present invention, the outlet of the compressor 1 is connected to the inlet of the first condenser 2, the outlet of the first condenser 2 is connected to the inlet of the second condenser 3, the outlet of the second condenser 3 is connected to the inlet of the expansion valve 6, the outlet of the expansion valve 6 is connected to the inlet of the evaporator 5, and the outlet of the evaporator 5 is connected to the inlet of the compressor 1, completing the circulation loop of the refrigerant;

[0036] The cooling water circuit of the embodiment of the present invention specifically refers to the cooling water circuit between the heat release device 7 and the water cooling tower 8, and the water inlet and outlet of the heat release device 7 are connected to the water inlet and outlet of the water cooling tower 8 respectively;

[0037] The circulating air circuit of the embodiment of the present invention is divided into two parallel cycles, wherein one part of the circulating air enters the drying chamber from the upper layer of the drying chamber (the chamber where the dryer conveyor belt is located), and reaches the middle outlet position of the drying chamber after passing through several layers of the dryer conveyor belt; another part of the circulating air enters the drying chamber from the lower layer of the drying chamber, and also reaches the middle outlet position of the drying chamber after passing through several layers of the dryer conveyor belt. The two circulating airs are mixed and uniformly enter the heat release device 7 to dissipate heat to the circulating cooling water. After heat dissipation, the medium-temperature circulating air is divided into two parts, one part of which is passed into the first condenser 2 to absorb the heat of the refrigerant, and then returns to the upper air outlet of the drying chamber; the other part first passes through the high-temperature side of the sensible heat exchanger 4 to release part of the heat, and then is passed into the evaporator 5 to release a large amount of heat and precipitate a large amount of water at the same time, and then passes through the low-temperature side of the sensible heat exchanger 4 again and absorbs the heat on the high-temperature side. The circulating air after gradually heating up passes through the second condenser 3 to increase the temperature to a high-temperature and low-humidity state, and finally returns to the lower air outlet of the drying chamber to complete the air circulation circuit;

[0038] The sludge conveying channel of the embodiment of the present invention refers to the whole process of sludge entering and leaving the drying chamber, wherein the sludge to be dried enters the sludge conveyor belt on the top layer from the sludge inlet of the top layer dryer conveyor belt, then flows through each layer of the conveyor belt in turn and falls to the next layer of the conveyor belt, and finally flows out from the sludge outlet of the bottom conveyor belt.

[0039] The core invention of the technical solution provided by the embodiment of the present invention is that a condenser in a conventional heat pump system is split into a first condenser and a second condenser, and the hot air is also divided into two paths, which are heated by two condensers respectively and sent into the drying room from the top and bottom at the same time, which can meet the special working conditions requirements in the drying field.

[0040] In a further preferred scheme provided by an embodiment of the present invention, the dryer conveyor belt in the drying chamber is divided into two parts, the upper part is the preheating section of the sludge, which may include 1 to 2 layers of dryer conveyor belts in total, and is heated and dried by the high-humidity circulating air that has not been dehydrated and flows through the first condenser 2; and the lower part is the main water removal and heating section of the sludge, which may include 2 layers of dryer conveyor belts in total, and is heated and dried by the low-humidity circulating air that has been dehydrated and flows through the second condenser 3.

[0041] In a further preferred solution provided by an embodiment of the present invention, the environmentally friendly working fluid R134a is used as the working medium in the heat pump system to provide a higher working temperature range.

[0042] In the sludge drying system based on R134a heat pump provided by the embodiment of the present invention, a total of three circulating air inlets and outlets are arranged in the drying chamber, respectively at the upper end, the middle part and the lower end of the drying chamber; the lower end of the drying chamber is always the circulating air inlet, receiving the low-humidity circulating air that has been dehydrated and flows through the second condenser 3; and the functions of the air outlets at the upper end and the middle part of the drying chamber can be interchanged. Figure 1 In the structural schematic diagram shown, the upper end of the drying chamber is the circulating air inlet, which receives the high-humidity circulating air without dehydration flowing through the first condenser 2, and the middle air outlet of the drying chamber is the circulating air outlet. The two parts of the circulating air merge in the middle and leave the drying chamber from the middle air outlet at the same time; in addition, when the upper air outlet and the middle air outlet of the drying chamber are switched, the high-humidity circulating air without dehydration flowing through the first condenser 2 can enter the drying chamber from the middle air outlet of the drying chamber, be fully mixed with the circulating air entering from the lower air outlet of the drying chamber, flow upward, and flow out of the drying chamber from the upper air outlet of the drying chamber, and then return to the heat release device 7 to complete the air circulation.

[0043] See also Figure 2 The present invention provides a thermodynamic optimization design method for a sludge drying system based on an R134a heat pump, comprising the following steps:

[0044] From the very beginning, it is necessary to input the required boundary conditions of the sludge product (sludge processing volume, sludge inlet moisture content and sludge outlet moisture content, etc.), operating conditions (ambient temperature, ambient humidity, etc.), the geometric structure of the entire drying system, etc., and secondly, it is necessary to determine the specific structural form used in the drying room (the number of conveyor belts included in the upper sludge preheating section, upper and lower air inlet and middle outlet, or middle and lower air inlet and upper outlet, etc.), and then start the design work.

[0045] In the design process, the compressor speed of the heat pump system is first assumed (including the lower limit of the speed, the upper limit of the speed and the adjustment step), and then the total flow rate of the circulating air is assumed (including the lower limit of the total air volume, the upper limit of the total air volume and the adjustment step), and then the two-layer air volume ratio is assumed (including the lower limit of the air volume ratio, the upper limit of the air volume ratio and the adjustment step), and then the volumetric efficiency and isentropic efficiency of the heat pump compressor are assumed, and then the subcooling of the heat pump system is assumed, and then the exhaust pressure of the heat pump system is assumed, and then the suction pressure of the heat pump system is assumed (including the lower limit of the suction pressure, the upper limit of the suction pressure and the adjustment step), and then the superheat of the heat pump system is assumed (including the lower limit of the superheat, the upper limit of the superheat and the adjustment step), and then the Assume the outlet temperature of the low-temperature side after waste heat recovery (including the lower limit of the outlet temperature, the upper limit of the outlet temperature and the adjustment step), and then according to all the assumed conditions, it can be brought into the heat pump cycle simulation model to calculate the heating capacity, COP, circulating air temperature of the two-layer inlet, evaporator water removal and other thermodynamic parameters of the heat pump system, and then brought into the overall model of the drying room to calculate the temperature after the heat exchanger of the drying system, SMER (water removal per unit energy consumption), energy consumption per ton of sludge and other information, to determine whether the sludge outlet parameters meet the feedforward requirements. If not, feedback is used to adjust the speed of the compressor of the heat pump system, increase a step from the current value, and continue the calculation. If the sludge outlet dryness meets the requirements, the difference between the system energy consumption per ton of sludge and the preset value is determined. If it is less than the preset value, all current assumed thermodynamic parameters and thermodynamic calculation results are saved as the existing optimal values ​​in the current operation stage; if it is greater than or equal to the preset value, the saving step is skipped, and it is directly determined whether the low-temperature side outlet temperature after waste heat recovery has reached the maximum value. If it has not reached the maximum value, the low-temperature side outlet temperature after waste heat recovery is increased by a step length, and the calculation is continued; if it has reached the maximum value, it is further determined whether the superheat of the heat pump system has reached the maximum value. If it has not reached the maximum value, the superheat is increased by a step length, and the calculation is continued; if it has reached the maximum value, then Further determine whether the suction pressure of the heat pump system has reached the maximum value. If it has not yet reached the maximum value, increase the suction pressure by a step and continue the calculation. If it has reached the maximum value, further determine whether the air volume ratio of the heat pump system has reached the maximum value. If it has not yet reached the maximum value, increase the air volume ratio by a step and continue the calculation. If it has reached the maximum value, further determine whether the total air volume of the heat pump system has reached the maximum value. If it has not yet reached the maximum value, increase the total air volume by a step and continue the calculation. If it has reached the maximum value, terminate the entire calculation process, and the final output result is the optimal operating state of the system corresponding to the lowest energy consumption per ton of mud in all iterative calculation steps.

[0046] In the embodiment of the present invention, after the thermodynamic parameters such as heating capacity and air outlet temperature are calculated by the heat pump model, with the help of the two-stage condenser model, it is necessary to adjust the actual supercooling degree by the temperature after heat release, and to adjust the actual exhaust pressure value by the circulating air flow on both sides. In addition to the system model design ideas, it is also necessary to cooperate with the sub-item models of the components to finally complete the complete calculation work. The sub-item models of each part include the compressor three-efficiency model, condenser model, evaporator model, waste heat recovery heat exchanger model, heat discharge heat exchanger model, drying room heat and mass transfer model, etc. According to the above heat exchanger models, the heat exchanger optimization design that needs to be carried out includes the heat discharge heat exchanger optimization design, the first condenser and 2 optimization design, the evaporator optimization design, and the waste heat recovery device optimization design. The conventional heat exchanger calculation and optimization design methods are adopted in the above process, so the present invention application will not be repeated.

[0047] In the technical solution provided by the present invention, a two-inlet and one-outlet double-layer parallel drying chamber structure is innovatively proposed. Through the structural innovation of the segmented hot air inlet, not only the average hot air temperature in the drying chamber is significantly improved, but also the air resistance caused by the air flow process in the drying chamber is effectively reduced, and the power consumption of the circulating fan is greatly reduced; a structural form in which the middle air outlet and the upper air outlet of the drying chamber can be interchanged with each other is creatively proposed, which can easily realize the mode switching between the middle and lower air inlet and upper air outlet (pure countercurrent air supply drying combined with intermediate one-time reheating) form and the upper and lower air inlet and middle air outlet (cross-flow air supply combined with preheating / drying two-stage) form during the drying process, providing convenience for mode switching for different sludge types and sludge drying requirements; an innovative thermodynamic optimization design scheme for the R134a heat pump system suitable for the closed sludge drying system is proposed. Under the premise of determining the operating conditions, external requirements, and structural dimensions, by performing several iterative calculations in the thermodynamic model, the optimal operating state corresponding to the lowest ton of sludge energy consumption of the heat pump drying system can be quickly found, and all thermodynamic parameters under the optimal state can be output for reference.

[0048] In summary, the embodiment of the present invention provides a thermodynamic optimization design method for a sludge drying system based on an R134a heat pump, which is suitable for the thermodynamic optimization design of a closed double-layer parallel sludge drying system. It can establish an effective thermodynamic model of the drying system under the premise of determining the operating conditions, external requirements, and structural dimensions, and through several iterative calculations in the thermodynamic model, it can quickly find the optimal operating state corresponding to the lowest energy consumption per ton of sludge of the heat pump drying system, and output all thermodynamic parameters under the optimal state. It can match the structural parameters and optimize the thermodynamic parameters of the heat pump system under special needs in the drying field, and significantly reduce the operating energy consumption of the sludge heat pump drying system, greatly improve the energy efficiency of the drying system, and make important contributions to energy conservation and emission reduction in the drying field.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A thermodynamic optimization design method for a sludge drying system based on a heat pump, characterized in that: The sludge drying system based on a heat pump comprises: a compressor (1), a first condenser (2), a second condenser (3), a sensible heat exchanger (4), an evaporator (5), an expansion valve (6), a heat release device (7) and a drying chamber; the outlet of the compressor (1) is connected to the inlet of the compressor (1) via the refrigerant channel of the first condenser (2), the refrigerant channel of the second condenser (3), the expansion valve (6), and the refrigerant channel of the evaporator (5); the drying chamber is provided with a sludge inlet, a sludge outlet, an upper air outlet, a middle air outlet, a lower air outlet, and a lower air outlet. The sludge inlet is connected to the sludge outlet via the drying conveyor belt, the upper air outlet is connected to the middle air outlet, and the middle air outlet is connected to the lower air outlet; the middle air outlet is divided into two paths after passing through the air duct of the heat release device (7), one path is connected to the upper air outlet via the first condensation air duct, and the other path is connected to the lower air outlet via the high-temperature side air duct of the sensible heat exchanger (4), the air duct of the evaporator (5), the low-temperature side air duct of the sensible heat exchanger (4), and the second condensation air duct in sequence; The thermodynamic optimization design method of the heat pump-based sludge drying system comprises the following steps: Obtain the required boundary conditions, operating conditions, geometric structure of the sludge drying system and the structural form of the drying chamber for sludge products; Set the compressor speed, total circulating air flow, upper and lower air volume ratio, volumetric efficiency and isentropic efficiency of the compressor, subcooling degree of the heat pump system, exhaust pressure of the heat pump system, suction pressure of the heat pump system, superheat degree of the heat pump system, and outlet temperature of the low-temperature side after waste heat recovery; based on the set conditions, calculate the heating capacity, COP, circulating air temperature of the two-layer inlet, evaporator water removal, and heat exchange temperature of the heat ventilator of the drying system, SMER, and energy consumption per ton of mud; Determine whether the sludge outlet parameters meet the feedforward requirements. If not, feedback is used to adjust the compressor speed of the heat pump system, increase a step from the current value, and continue the calculation; if the sludge outlet dryness meets the requirements, determine the difference between the system ton sludge energy consumption and the preset value. If it is less than the preset value, save all current assumed thermodynamic parameters and thermodynamic calculation results as the existing optimal values ​​for the current calculation stage; if it is greater than or equal to the preset value, skip the saving step and directly determine whether the low-temperature side outlet temperature after waste heat recovery has reached the maximum value. If it has not reached the maximum value, increase the low-temperature side outlet temperature after waste heat recovery by a step and continue the calculation; if it has reached the maximum value, determine whether the superheat of the heat pump system has reached the maximum value. If it has not reached the maximum value, increase Superheat, increase the value by one step, and continue the calculation; if it has reached the maximum value, determine whether the suction pressure of the heat pump system has reached the maximum value, if it has not reached the maximum value, increase the suction pressure, increase the value by one step, and continue the calculation; if it has reached the maximum value, determine whether the air volume ratio of the heat pump system has reached the maximum value, if it has not reached the maximum value, increase the air volume ratio, increase the value by one step, and continue the calculation; if it has reached the maximum value, determine whether the total air volume of the heat pump system has reached the maximum value, if it has not reached the maximum value, increase the total air volume, increase the value by one step, and continue the calculation; if it has reached the maximum value, end the entire calculation process, and the final output result is the optimal operating state of the system corresponding to the lowest ton of mud energy consumption in all iterative calculation steps.

2. The thermodynamic optimization design method of a heat pump-based sludge drying system according to claim 1 is characterized in that: The demand boundary conditions of the sludge product include the sludge processing volume, the sludge inlet moisture content and the sludge outlet moisture content; the working conditions include the ambient temperature and the ambient humidity; the structural form in the drying room includes the number of drying conveyor belts, air inlet and air outlet information.

3. The thermodynamic optimization design method of a heat pump-based sludge drying system according to claim 1 is characterized in that: The compressor speed includes a lower speed limit, an upper speed limit and an adjustment step; the total circulating air flow includes a lower total air volume limit, an upper total air volume limit and an adjustment step; the two-layer air volume ratio includes a lower air volume ratio limit, an upper air volume ratio limit and an adjustment step; the heat pump system suction pressure includes a lower suction pressure limit, an upper suction pressure limit and an adjustment step; the heat pump system superheat includes a lower superheat limit, an upper superheat limit and an adjustment step; the low-temperature side outlet temperature after waste heat recovery includes a lower outlet temperature limit, an upper outlet temperature limit and an adjustment step.

4. The thermodynamic optimization design method of a heat pump-based sludge drying system according to claim 1 is characterized in that: The heat pump-based sludge drying system also includes: A water cooling tower (8), wherein a water outlet of the water cooling tower (8) is connected to a water inlet of the water cooling tower (8) via a water channel of the heat release device (7).

5. The thermodynamic optimization design method of a heat pump-based sludge drying system according to claim 1, characterized in that: The drying conveyor belts are arranged in layers.

6. The thermodynamic optimization design method of a heat pump-based sludge drying system according to claim 1, characterized in that: When the heat pump-based sludge drying system is in operation: A part of the circulating air enters the drying room from the upper air outlet of the drying room, passes through several layers of drying conveyor belts and reaches the middle air outlet; another part of the circulating air enters the drying room from the lower air outlet of the drying room, passes through several layers of drying conveyor belts and reaches the middle air outlet; After the two parts of circulating air are mixed, they enter the heat release device (7) to dissipate heat to the circulating cooling water. After heat dissipation, the medium-temperature circulating air is divided into two parts, one of which is passed into the first condenser (2) to absorb the heat of the refrigerant, and then returns to the upper air outlet of the drying chamber; the other part first passes through the high-temperature side of the sensible heat exchanger (4) to release part of the heat, and then passes into the evaporator (5) to release heat and precipitate water, and then passes through the low-temperature side of the sensible heat exchanger (4) again and absorbs the heat of the high-temperature side. The heated circulating air then passes through the second condenser (3) to raise the temperature to a high temperature and low humidity state, and finally returns to the lower air outlet of the drying chamber.

7. The thermodynamic optimization design method of a heat pump-based sludge drying system according to claim 1, characterized in that: The medium in the refrigerant channel of the heat pump-based sludge drying system is R134a.

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