Sludge drying device based on transcritical CO2 heat pump cycle

Abstract

The invention belongs to the technical field of sludge drying, and discloses a transcritical CO2 heat pump cycle-based sludge drying device, which is characterized in that an outlet of a compressor is communicated with an inlet of the compressor through a first heat exchange channel of a primary gas cooler, a first heat exchange channel of a secondary gas cooler, a throttle valve and a first heat exchange channel of an evaporator; an air return outlet is communicated with an inlet of a first heat exchange channel of the heat release heat exchanger, an outlet of the first heat exchange channel of the heat release heat exchanger is divided into two paths, one path is communicated with an upper-layer air supply inlet through a second heat exchange channel of the first-stage gas cooler and an upper-layer air supply fan, and the other path is communicated with an upper-layer air supply outlet. And the other path is communicated with a lower-layer air supply inlet through a first heat exchange channel of the heat regenerator, a second heat exchange channel of the evaporator, a second heat exchange channel of the heat regenerator, a second heat exchange channel of the secondary gas cooler and a lower-layer air supply fan. Basic requirements of sludge drying can be met, and performance optimization is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sludge drying, and particularly relates to a sludge drying device based on a transcritical CO2 heat pump cycle. BACKGROUND

[0002] Energy consumption and carbon emission indicators in various fields of industrial production are widely valued, and energy-saving and environment-friendly researches begin to develop in more specific aspects.

[0003] The environmental protection industry, as a pillar of ecological civilization construction, has a very large energy consumption demand; in the process of treating sludge in the environmental protection industry, the sludge needs to be dried to a certain humidity or below before landfill, and the energy consumption in the treatment process is largely dependent on the drying method, so the sludge drying has also transformed from mainly consuming primary energy to using electric energy. The emergence of heat pump drying provides technical route support for the above transformation and can well adapt to the current national strategic deployment and policy requirements.

[0004] At present, there is little research on sludge drying heat pump systems, and there is a huge energy efficiency improvement space, so it is urgent to propose a sludge drying heat pump system with higher energy efficiency and environmental protection to optimize the performance of existing sludge drying heat pump systems. SUMMARY

[0005] The purpose of the present application is to provide a sludge drying device based on a transcritical CO2 heat pump cycle to solve one or more of the above technical problems. The technical solution disclosed in the present application can meet the basic requirements of sludge drying and achieve performance optimization, with advantages such as high efficiency, economy, etc.

[0006] To achieve the above purpose, the present application adopts the following technical solutions:

[0007] The present application provides a sludge drying device based on a transcritical CO2 heat pump cycle, comprising: a transcritical CO2 heat pump cycle system and a drying air system; wherein,

[0008] In the transcritical CO2 heat pump cycle system, the outlet of the compressor is connected in communication with the inlet of the compressor through the first heat exchange channel of the primary gas cooler, the first heat exchange channel of the secondary gas cooler, the throttling valve and the first heat exchange channel of the evaporator;

[0009] The drying air system comprises: a multilayer sludge drying chamber, a heat-releasing heat exchanger and a regenerator; wherein the multilayer sludge drying chamber is provided with a sludge inlet, a sludge outlet, an upper layer air supply inlet, a lower layer air supply inlet and an air return outlet; the air return outlet is connected with the inlet of the first heat exchange channel of the heat-releasing heat exchanger, the outlet of the first heat exchange channel of the heat-releasing heat exchanger is divided into two paths, one path is connected with the upper layer air supply inlet through the second heat exchange channel of the primary gas cooler and the upper layer air supply fan, and the other path is connected with the lower layer air supply inlet through the first heat exchange channel of the regenerator, the second heat exchange channel of the evaporator, the second heat exchange channel of the regenerator, the second heat exchange channel of the secondary gas cooler and the lower layer air supply fan; wherein the second heat exchange channel of the heat-releasing heat exchanger is used for passing in cooling water.

[0010] Further improvement of the technical scheme of the present application is that the water cooling tower is further included; wherein,

[0011] The outlet of the water cooling tower is connected with the inlet of the water cooling tower through the circulating water pump and the second heat exchange channel of the heat-releasing heat exchanger.

[0012] Further improvement of the technical scheme of the present application is that in the design process of the sludge drying device, the structural parameters of the heat-releasing heat exchanger and the design value of the water flow of the water cooling tower are calculated according to the heat-releasing amount calculation expression; wherein the heat-releasing amount calculation expression is:

[0013] Q=f1(m,t,V1,V2);

[0014] Q=f2(κ,V3,T3,d3);

[0015] In the formula, m represents the mass of sludge to be dried; t represents the time for completing sludge drying; V1 represents the air supply amount of the upper path; V2 represents the air supply amount of the lower path; κ is the structural parameter of the heat-releasing heat exchanger; V3 represents the water flow of the water cooling tower; T3 represents the air return temperature after the air of the upper path and the lower path is converged; and d3 represents the air return humidity after the air of the upper path and the lower path is converged.

[0016] Further improvement of the technical scheme of the present application is that in the step of calculating the structural parameters of the heat-releasing heat exchanger and the water flow of the water cooling tower according to the heat-releasing amount calculation expression,

[0017] The optimal heat-releasing amount is obtained by finding the optimal value of Q=f1(m,t,V1,V2) in the defined domain with the system cycle COP as the optimization target.

[0018] Further improvement of the technical scheme of the present application is that the data acquisition system is further included; wherein,

[0019] The data acquisition system is used to acquire the compressor speed, sludge moisture content at the sludge outlet, throttle valve opening, exhaust pressure, air volume at the upper and lower air inlets, water volume in the second heat exchange channel of the heat exchanger, evaporation temperature and superheat of the evaporator, inlet enthalpy of the heat exchanger, and outlet enthalpy of the heat exchanger.

[0020] A further improvement to the technical solution of the present invention is that it further includes: a control system; wherein,

[0021] The control system is used to perform real-time negative feedback control of the sludge drying device based on parameters acquired by the data acquisition system and combined with PID control. Specifically, the power consumption and speed of the compressor are used to control the sludge moisture content at the sludge outlet to meet the discharge requirements. The upper and lower air supply fans are used to control the air volume entering the primary and secondary gas coolers, respectively. The opening degree of the throttle valve is used to control the superheat in the evaporator. In addition, the extreme value search control is used to achieve automatic optimization of the evaporation temperature of the heat pump system by controlling the water flow rate of the heat exchanger.

[0022] A further improvement to the technical solution of this invention lies in the fact that, during the process of controlling the airflow entering the primary gas cooler and the secondary gas cooler using the upper-layer air supply fan and the lower-layer air supply fan respectively, the expression for the optimal airflow ratio between the upper and lower layers is:

[0023] ω best =f(T) 1,in ,d 1,in ,T 2,in ,d 2,in ,T 1,out ,d 1,out ,T 2,out ,d 2,out );

[0024] In the formula, ω best The optimal air volume ratio for air supply to the upper and lower floors; T 1,in Indicates the inlet temperature of the air supply; T 2,in Indicates the inlet temperature of the lower air supply line; T 1,out Indicates the outlet temperature of the air supply system; T 2,out Indicates the outlet temperature of the air supply line; d 1,in Indicates the relative humidity at the air supply inlet; d 2,in Indicates the relative humidity at the lower air supply inlet; d 1,out Indicates the relative humidity at the air supply outlet; d 2,out This indicates the relative humidity at the lower air supply outlet.

[0025] A further improvement to the technical solution of this invention lies in that, in the process of controlling the airflow entering the primary gas cooler and the secondary gas cooler respectively using the upper-level air supply fan and the lower-level air supply fan, ω is calculated. bestThe optimal value of the sum of heat exchange amounts of the first-stage gas cooler and the second-stage gas cooler in the feasible region is taken as an optimization target, and an optimal air volume ratio is obtained.

[0026] Further improvement of the technical scheme is that in the process of automatically optimizing the evaporation temperature of the heat pump system by the heat-releasing heat exchanger water side flow size of the extremum search control, the implementation steps of the extremum search control include:

[0027] A high-frequency sinusoidal disturbance signal S1(t) = a1sin(ω1t) + … + a i sin(ω i t) + … + a n sin(ω n t) is applied to the evaporation temperature of the heat pump system; wherein a i and ω i are the amplitude and frequency of the i-th signal respectively, and n represents the total order;

[0028] The heat pump COP signal following the high-frequency disturbance signal is filtered through a high-pass filter to filter out the direct current component, and the remaining signal is demodulated by a signal S2(t) = sin(ω1t+α1) + … + sin(ωit+α i ) + … sin(ω n t+α n ) having the same frequency as the high-frequency sinusoidal disturbance signal, the continuously changing sinusoidal signal is converted into a signal having a direct current gradient signal component, and the high-order term in the signal is filtered through a low-pass filter to retain the gradient term; wherein α i is a set phase deviation angle for compensating for the phase difference after filtering.

[0029] An integrator is used to form a proportional-integral control loop with the low-pass filtered direct current gradient signal component as the input, and after multiple calculations, the optimal evaporation temperature point is found when the input is 0, the heat pump system is controlled to maintain the optimal evaporation temperature condition, and the optimal control of the entire sludge drying device is realized.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] The present application provides a sludge drying device based on a transcritical CO2 heat pump cycle, which comprises a transcritical CO2 heat pump cycle system and a drying air system; wherein the transcritical CO2 heat pump cycle system comprises a compressor, a condenser, an evaporator and an expander. sThe heat pump circulation system realizes efficient heat energy conversion and recycling through the specific connection mode of the compressor, the first-stage gas cooler, the second-stage gas cooler, the throttling valve and the evaporator, and the unique circulation structure provides a basis for improving energy efficiency, compared with the traditional heat pump system, energy can be more effectively utilized in the sludge drying process, and energy loss is reduced; in addition, the drying air system adopts a plurality of sludge drying chambers, and a unique air supply and return air path is arranged, the return air first passes through the heat bleeding heat exchanger, and then is divided into two paths and enters the upper and lower air supply inlets after being treated differently, the two-layer air supply mode can accurately control the air supply temperature and humidity according to the requirements of different levels of the sludge drying chamber, and higher drying efficiency is realized, so that the overall energy efficiency is improved, and the urgent needs of the sludge drying industry for energy efficiency improvement are met. In conclusion, the sludge drying device based on the transcritical CO2 heat pump circulation disclosed in the present application can realize the dehumidification and drying of sludge by using the heat pump heating mode, and has the advantages of high efficiency and energy saving; the CO2 heat pump system has very high heating energy efficiency, can realize good drying function, and has great application potential, but there is no sludge drying equipment applying CO2 heat pump in the industry at present; in view of the above situation, in the new scheme provided in the present application, CO2 is applied as the refrigerant of the heat pump system, CO2 is a pure natural refrigerant and is more environmentally friendly, meets the requirements of the refrigerant replacement policy, the CO2 heat pump system can generate more heat and obtain circulating air with higher temperature, and the two-layer air supply mode is adopted to realize higher energy efficiency of the drying effect. Further supplementary explanation, the system of the present application has an optimal upper and lower air volume ratio, an optimal heat bleeding amount and an optimal evaporation temperature when the air volume ratio, the heat bleeding amount and the evaporation temperature reach the optimal values, the heat pump drying system can work in the highest energy efficiency operating condition.

[0032] In the preferred scheme of the present application, during the design process of the sludge drying device, the design values of the structure parameters of the heat bleeding heat exchanger and the water flow of the water cooling tower are calculated according to the heat bleeding calculation expression. By considering multiple influencing factors such as sludge mass, drying time, air supply volume, etc., the parameters of each component of the system can be accurately designed to ensure that the system reaches the best performance in actual operation, and a specific design method is provided for performance optimization of the existing sludge drying heat pump system.

[0033] In the preferred scheme of the present application, a data acquisition and control system is also provided; wherein the data acquisition system is introduced to obtain key parameters such as compressor speed, sludge moisture content, throttle valve opening, exhaust pressure, air supply volume, water volume, evaporation temperature and superheat, inlet and outlet air enthalpy, etc. The control system then performs real-time negative feedback control on the sludge drying device according to these parameters, combined with PID control and extremum seeking control. By accurately controlling the operating parameters of each component, the optimization design of the entire drying system is realized, and the system performance is further improved. In summary, the optimization design of the entire drying system is realized by measuring and controlling the evaporation temperature of the heat pump system.

[0034] In the preferred technical scheme of the present application, the multi-layer sludge drying chamber of the drying air system and the unique air supply path design enable the upper and lower air supply to be independently controlled according to different stages and needs of sludge drying; for example, the upper air supply can be used for rapid drying of the sludge surface, and the lower air supply can penetrate into the sludge interior to promote water evaporation; this layered air supply method can more uniformly and efficiently remove water from the sludge, greatly improving the drying efficiency and achieving higher energy-efficient drying effects compared to the traditional single air supply method. Further, through the optimal air volume ratio expression of the upper and lower air supply, considering multiple factors such as the temperature and relative humidity of the air supply inlet and outlet, the optimal air volume ratio is calculated to be the optimal value within the feasible domain, with the heat exchange capacity of the first-stage gas cooler and the second-stage gas cooler as the optimization target. This optimization method can ensure that the upper and lower air supply volumes reach the optimal proportion, further improving the drying energy efficiency and enabling the system to maintain efficient operation under different operating conditions.

[0035] In the preferred technical scheme of the present application, the evaporation temperature of the heat pump system is one of the key parameters affecting system performance. By accurately measuring and controlling the evaporation temperature, the heat pump cycle process can be optimized, the heating coefficient of performance (COP) of the heat pump can be improved, and thus the energy efficiency of the entire drying system can be improved. In addition, the extremum seeking control (ESC) technology is used to apply a high-frequency sinusoidal disturbance signal to the evaporation temperature of the heat pump system. Through a series of signal processing and control links such as high-pass filter, demodulation processing, low-pass filter and integrator, the optimal evaporation temperature point is found, and the heat pump system is controlled to maintain at this operating condition. This real-time optimization control method can automatically adjust the evaporation temperature according to the changes in system operating state and environmental conditions, ensuring that the system is always in the best performance state and realizing the optimization design of the entire drying system. In summary, the extremum seeking control is embedded to realize the control of the evaporation temperature and the real-time optimization control of the system performance. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the present application or the prior art, the drawings needed to be used in the following embodiments or prior art description will be briefly introduced; obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0037] Figure 1 is a schematic diagram of a sludge drying device based on a transcritical CO2 heat pump cycle in an embodiment of the present application;

[0038] Figure 2 is a schematic diagram of air volume ratio optimization logic in an embodiment of the present application;

[0039] Figure 3 is a schematic diagram of heat dissipation optimization logic in an embodiment of the present application;

[0040] The explanatory description of the reference numerals in the drawings is as follows:

[0041] 1, compressor; 2, first-stage gas cooler; 3, second-stage gas cooler; 4, throttle valve; 5, evaporator; 6, heat regenerator; 7, multi-layer sludge drying chamber; 8, heat dissipation heat exchanger; 9, water cooling tower; 10, upper-layer air supply fan; 11, lower-layer air supply fan. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions in the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application; obviously, the described embodiment technical solutions are some embodiments of the present application, but not all the embodiments.

[0043] Based on the technical solutions disclosed in the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0044] Please refer to Figure 1 The sludge drying device based on a transcritical CO2 heat pump cycle disclosed in the embodiments of the present application comprises: a transcritical CO2 heat pump cycle system and a drying air system; wherein,

[0045] The transcritical CO2 heat pump cycle system comprises a compressor 1, a first-stage gas cooler 2, a second-stage gas cooler 3, a throttling valve 4 and an evaporator 5; wherein the outlet of the compressor 1 is connected with the inlet of the compressor 1 through the first heat exchange channel of the first-stage gas cooler 2, the first heat exchange channel of the second-stage gas cooler 3, the throttling valve 4 and the first heat exchange channel of the evaporator 5;

[0046] The drying air system comprises a multi-layer sludge drying chamber 7, a heat-releasing heat exchanger 8 and a regenerator 6; wherein the multi-layer sludge drying chamber 7 is provided with a sludge inlet, a sludge outlet, an upper-layer air supply inlet, a lower-layer air supply inlet and an air return outlet; the air return outlet is connected with the inlet of the first heat exchange channel of the heat-releasing heat exchanger 8, the outlet of the first heat exchange channel of the heat-releasing heat exchanger 8 can be divided into two paths through a three-way valve, one path is connected with the upper-layer air supply inlet through the second heat exchange channel of the first-stage gas cooler 2 and an upper-layer air supply fan 10, and the other path is connected with the lower-layer air supply inlet through the first heat exchange channel of the regenerator 6, the second heat exchange channel of the evaporator 5, the second heat exchange channel of the regenerator 6, the second heat exchange channel of the second-stage gas cooler 3 and a lower-layer air supply fan 11; the second heat exchange channel of the heat-releasing heat exchanger 8 is used for passing cooling water.

[0047] In a further preferred technical solution, a water cooling tower 9 is further included; wherein the outlet of the water cooling tower 9 is connected with the inlet of the water cooling tower 9 through a circulating water pump and the second heat exchange channel of the heat-releasing heat exchanger 8.

[0048] In the technical solution provided by the embodiment of the present application, in the transcritical CO2 heat pump cycle system, the refrigerant is compressed from the inlet to the outlet of the compressor 1, flows through the first-stage gas cooler 2 and the second-stage gas cooler 3, becomes a low-temperature and low-pressure liquid through the throttling device (i.e. the throttling valve 4), and finally returns to the inlet of the compressor 1 after flowing through the evaporator 5, forming a closed cycle; in the drying air system, the air supply entering the multi-layer sludge drying chamber 7 is divided into upper-layer air supply and lower-layer air supply, and the air return output from the multi-layer sludge drying chamber 7 is divided into two paths, one path is heated through the first-stage gas cooler 2 and then returns to the multi-layer sludge drying chamber 7 through the upper-layer air supply inlet, becoming the upper-layer air supply; the other path is cooled and water is separated through the heat-releasing heat exchanger 8 and the evaporator 5, and then is heated through the second-stage gas cooler 3 and returns to the multi-layer sludge drying chamber 7 through the lower-layer air supply inlet, becoming the lower-layer air supply.

[0049] As a preferred embodiment of the technical solution of the present application, a control system is further included; wherein the outlet sludge moisture content is controlled by the compressor speed mainly through PID by collecting signals such as compressor speed, outlet sludge moisture content, throttling valve opening degree, exhaust pressure, air volume, water volume, heat release heat exchanger inlet air enthalpy, heat release heat exchanger outlet air enthalpy and the like, and the exhaust pressure is controlled by the throttling valve opening degree.

[0050] In one embodiment of the present application, the preset position of the sludge drying device based on transcritical CO2 heat pump cycle is provided with temperature and pressure measuring points, and the sludge drying device is controlled in real time by negative feedback through the actual state of the measuring points combined with PID control; wherein the water content of the sludge outlet is controlled to meet the discharge requirements by the compressor power consumption and speed, the air volume entering the first and second air coolers is controlled by the upper and lower air supply fans respectively, and the superheat degree in the evaporator is controlled by the opening degree of the throttle valve, and the automatic optimization of the evaporation temperature of the heat pump system is realized by the flow rate of the water side of the heat-releasing heat exchanger combined with extreme value search control.

[0051] In a specific example of the technical solution, for certain sludge inlet and outlet temperature and humidity boundary conditions, under the condition that the total air supply volume is determined, i.e. the fan power consumption is determined, there is an optimal air volume ratio for the two-layer air supply mode for different drying chamber structures and air outlet modes. The currently commonly used drying chamber structures and air outlet modes mainly include three-layer upper air, three-layer middle air, four-layer upper air, and four-layer middle air. Different structures and air outlet modes mainly affect the final air outlet temperature and humidity of the upper and lower air supply, so the air volume ratio is a function of the upper air outlet temperature and humidity and the lower air outlet temperature and humidity.

[0052] For the optimal air volume ratio ω of the upper and lower paths, there is the following relationship:

[0053] Total air volume V0: V0=V1+V2;

[0054] Air volume ratio ω: ω=V1 / V2;

[0055] Optimal air volume ratio relationship: ω best =f(T 1,in ,d 1,in ,T 2,in ,d 2,in ,T 1,out ,d 1,out ,T 2,out ,d 2,out )

[0056] Wherein, V1 is the upper air supply air volume / (m 3 / h); V2 is the lower air supply air volume / (m 3 / h); T 1,in is the upper air supply inlet temperature / ℃; T 2,in is the lower air supply inlet temperature / ℃; T 1,out is the upper air supply outlet temperature / ℃; T 2,out is the lower air supply outlet temperature / ℃; d 1,in is the upper air supply inlet relative humidity / %; d 2,in is the lower air supply inlet relative humidity / %; d 1,out is the upper air supply outlet relative humidity / %; d 2,outRelative humidity of the outlet of the down air supply.

[0057] In the case of given sludge import and export boundary conditions, the air volume ratio is adjusted by the import and export state of the air supply, the import and export enthalpy difference of the upper and lower routes is increased as much as possible, the outlet temperature is reduced, the outlet relative humidity is increased, and thus the drying effect is improved. In the specific exemplary technical solution, the optimal value of the equation ω best =f(T 1,in ,d 1,in ,T 2,in ,d 2,in ,T 1,out ,d 1,out ,T 2,out ,d 2,out ) in the feasible region is obtained, and the optimal air volume ratio is obtained.

[0058] In the embodiment of the application, the size of the system heat-releasing heat exchanger and the flow of the water cooling tower of the heat-releasing heat exchanger are optimized and designed, and the use of the equipment size and the water flow is reduced as much as possible, so that the production and use costs are reduced, and the return air temperature after heat release is effectively improved. The structural parameter κ of the heat-releasing heat exchanger and the water flow V3 of the cooling water tower jointly affect the heat-releasing amount of the system, different systems have different heat-releasing demands, the required heat-releasing amount Q can be obtained through simulation calculation, and based on this, the corresponding water flow and heat exchanger structure can be designed.

[0059] In the specific exemplary technical solution of the application, the required heat-releasing amount Q has the following relationship:

[0060] Q=f1(m,t,V1,V2);

[0061] Q=f2(κ,V3,T3,d3);

[0062] Wherein, m is the mass of the sludge to be dried, t is the time for completing the drying of the sludge, V1 is the air volume of the upper air supply / (m 3 / h), V2 is the air volume of the lower air supply / (m 3 / h), V3 is the water flow of the cooling tower / (m 3 / h), T3 is the return air temperature after the air of the upper and lower routes is converged, and d3 is the return air humidity after the air of the upper and lower routes is converged.

[0063] In the specific exemplary technical solution, the structural parameter of the heat-releasing heat exchanger and the size of the water flow of the cooling tower can be calculated for a specific drying system through the two relationship formulas, and the heat-releasing heat exchanger and the cooling water flow can be reduced as much as possible under the working condition of meeting the maximum heat-releasing amount. Wherein, the optimal value of the equation Q=f1(m,t,V1,V2) in the defined region is obtained, and the optimal heat-releasing amount is obtained.

[0064] There is an optimal evaporation temperature when the heat pump system is running, and the evaporation temperature is directly affected by the heat dissipation, which can be directly regulated by the size of the heat dissipation. The system uses a set of PI controllers to control the outlet sludge moisture content to remain unchanged by adjusting the compressor speed, and embeds an extremum search control logic, which can automatically optimize the evaporation temperature by adjusting the heat dissipation, so that the heat pump system works at the optimal evaporation temperature and the cycle COP is maximum.

[0065] In the technical scheme of the embodiment of the application, the implementation steps of the extremum search control logic are as follows:

[0066] Firstly, a high-frequency sinusoidal disturbance signal is applied to the evaporation temperature of the heat pump system Wherein a i and ω i are the amplitude and frequency of the signal, respectively;

[0067] Secondly, the heat pump COP signal following the high-frequency disturbance signal is filtered through a high-pass filter to filter out the direct current component, and the remaining signal is demodulated with a signal having the same frequency as the disturbance signal After demodulation, the continuously changing sinusoidal signal is converted into a signal with a direct current gradient signal component, and then the high-order term in the signal is filtered through a low-pass filter to retain the gradient term, wherein α i is a set phase deviation angle used to compensate for the phase difference after filtering;

[0068] Thirdly, an integrator is used to form a proportional-integral control loop with the low-pass filtered direct current gradient signal component as the input, and after multiple calculations, the optimal evaporation temperature point is found when the input is 0, and the heat pump system is maintained at the optimal evaporation temperature condition to achieve optimal control of the entire drying system.

[0069] The extremum search control is an advanced adaptive control method, which does not require an accurate system model, and finds the optimal control parameters by introducing a disturbance signal into the system and according to the response of the system. In the technical scheme of the application, it is applied to the control of the evaporation temperature of the heat pump system, which can effectively overcome the shortcomings of the traditional control method depending on the system model, and improve the accuracy and robustness of the control. The application adjusts the evaporation temperature of the heat pump system by applying a high-frequency sinusoidal disturbance signal. Gradient information related to system performance is extracted using high-pass filter, demodulation processing and low-pass filter signal processing technology. The integrator forms a proportional-integral control loop according to the gradient information, and continuously adjusts the evaporation temperature until the optimal evaporation temperature point is found. This real-time optimization control process can ensure that the system can quickly and accurately achieve the best performance under different working conditions, and improve the stability and energy efficiency of the system.

[0070] Please see Figure 2 In this embodiment of the invention, given the boundary conditions of the sludge inlet and outlet, the air volume ratio is adjusted by changing the inlet and outlet states of the air supply to maximize the enthalpy difference between the upper and lower paths, reduce the outlet temperature, and increase the outlet relative humidity, thereby improving the drying effect. Specifically, through... Figure 2 The specific process for optimizing the method shown is as follows:

[0071] The first step is to input the system structure parameters and initial state parameters, and set the air volume ratio to the lower limit value, i.e., ω(0) = ω min The system is calculated, and the output is saved as follows: COP, SMER, energy consumption per ton of sludge, and enthalpy difference Δh between the inlet and outlet of the upper and lower air passages. up (0) and Δh down (0);

[0072] Step 2: Within a certain upper and lower limit range, increase the air volume ratio by a step size Δω, and set the air volume ratio ω(i) = ω in each iteration. min +i*Δω, calculated under the new airflow ratio, outputting and saving the enthalpy difference Δh between the inlet and outlet of the upper and lower airflow paths. up (i) and Δh down (i) Calculate and compare Δh(i) = Δh in each iteration. up (i)+Δh down The value of the total enthalpy difference Δh(i) is selected by considering the magnitude of (i).

[0073] Step 3: Output the air volume ratio when the total enthalpy difference Δh(i) is maximized, and use it as the optimal air volume ratio.

[0074] Please see Figure 3 In this embodiment of the invention, the specific process of optimizing the heat dissipation and heat exchange method is as follows:

[0075] The first step is to input the system structure parameters and initial state parameters, and set the heat exchanger water flow rate to the lower limit value, i.e., Q(0) = Q. min The system performs calculations and outputs and saves the system's COP, SMER, and the heat exchange capacity of the heat exchanger, i.e., the heat released.

[0076] Step 2: Within a certain upper and lower limit range, increase the heat dissipation and heat exchange capacity by a step size ΔQ, and set the air volume ratio Q(i) = Q in each iteration. min +i*ΔQ, calculate under the new air volume ratio, output and save the system performance parameters SMER, COP and heat transfer rate Q(i), calculate and compare the magnitude of heat transfer rate Q(i) in each iteration, and select the heat transfer rate Q(I) that results in the best performance.

[0077] Step 3: Determine the heat dissipation at which the output performance is optimal, and use this as the optimal heat dissipation.

[0078] In the technical scheme provided by the embodiment of the present application, the heat pump drying system has the characteristics of complex structure and real-time working condition change, and there is only one optimal evaporation temperature when the system is running, so the corresponding control logic can be used to realize real-time optimization control of the system and performance optimization. In the exemplary technical scheme of the embodiment of the present application, a group of PI controllers are used to control the outlet sludge moisture content to remain unchanged by adjusting the compressor speed, and the extremum search control logic is embedded, the heat bleeding amount can be changed by adjusting the water flow of the heat bleeding heat exchanger, so as to realize automatic optimization of the evaporation temperature, so that the heat pump system works at the optimal evaporation temperature and the cycle COP is maximum.

[0079] Finally, it should be noted that: the above examples are only used to illustrate the technical scheme of the present application, but not to limit it, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: the specific embodiments of the present application can still be modified or replaced by the equivalent, without departing from the spirit and scope of the present application. Any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A sludge drying apparatus based on transcritical CO2 heat pump cycle, characterized by, The application relates to a sludge drying device. The cross-critical CO2 heat pump circulation system is connected with a drying air system. The cross-critical CO2 heat pump circulation system comprises a compressor (1), a first-stage gas cooler (2), a second-stage gas cooler (3), a throttling valve (4), an evaporator (5) and a heat recovery unit (6). The drying air system comprises a multilayer sludge drying chamber (7), a heat-releasing heat exchanger (8) and the heat recovery unit (6).

2. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 1, characterized in that, The multilayer sludge drying chamber (7) is provided with a sludge inlet, a sludge outlet, an upper-layer air supply inlet, a lower-layer air supply inlet and an air return outlet. The air return outlet is connected with the inlet of the first heat exchange channel of the heat-releasing heat exchanger (8). The outlet of the first heat exchange channel of the heat-releasing heat exchanger (8) is divided into two paths.

3. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 2, characterized in that, One path is connected with the upper-layer air supply inlet through the second heat exchange channel of the first-stage gas cooler (2) and an upper-layer air supply fan (10). The other path is connected with the lower-layer air supply inlet through the first heat exchange channel of the heat recovery unit (6), the second heat exchange channel of the evaporator (5), the second heat exchange channel of the heat recovery unit (6), the second heat exchange channel of the second-stage gas cooler (3) and a lower-layer air supply fan (11). The second heat exchange channel of the heat-releasing heat exchanger (8) is used for inputting cooling water. The application further comprises a water cooling tower (9).

4. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 3, characterized in that, The outlet of the water cooling tower (9) is connected with the inlet of the water cooling tower (9) through a circulating water pump and the second heat exchange channel of the heat-releasing heat exchanger (8). In the design process of the sludge drying device, the structural parameters of the heat-releasing heat exchanger (8) and the water flow size of the water cooling tower (9) are calculated according to a heat-releasing amount calculation expression.

5. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 1, characterized in that, The heat-releasing amount calculation expression is Q=f1(m, t, V1, V2). Q=f2(κ, V3, T3, d3). In the expression, m represents the mass of sludge needing to be dried, t represents the time needed for completing sludge drying, V1 represents the air supply amount of the upper path, V2 represents the air supply amount of the lower path, kappa is the structural parameter of the heat-releasing heat exchanger, V3 represents the water flow of the water cooling tower, T3 represents the air return temperature after the air of the upper path and the lower path is converged, and d3 represents the air return humidity after the air of the upper path and the lower path is converged.

6. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 5, characterized in that, In the step of calculating the structural parameters of the heat-releasing heat exchanger (8) and the water flow size of the water cooling tower (9) according to the heat-releasing amount calculation expression, the optimal heat-releasing amount is obtained by taking the system cycle COP as the optimization target and solving the optimal value of Q=f1(m, t, V1, V2) in the defined domain. The application further comprises a data acquisition system. The data acquisition system is used for acquiring the rotating speed of the compressor (1), the sludge moisture content of the sludge outlet, the opening degree of the throttling valve (4), the exhaust pressure, the air amount of the upper-layer air supply inlet and the lower-layer air supply inlet, the water amount of the second heat exchange channel of the heat-releasing heat exchanger (8), the evaporation temperature and the superheat degree of the evaporator (5), the inlet air enthalpy value of the heat-releasing heat exchanger (8) and the outlet air enthalpy value of the heat-releasing heat exchanger (8). The application further comprises a control system. The control system is used for controlling the rotating speed of the compressor (1), the opening degree of the throttling valve (4), the air supply amount of the upper-layer air supply inlet and the lower-layer air supply inlet, the water amount of the second heat exchange channel of the heat-releasing heat exchanger (8), the evaporation temperature and the superheat degree of the evaporator (5), the inlet air enthalpy value of the heat-releasing heat exchanger (8) and the outlet air enthalpy value of the heat-releasing heat exchanger (8). The control system is used for real-time negative feedback control of the sludge drying device according to parameters acquired by the data acquisition system and in combination with PID control; wherein the sludge moisture content of the sludge outlet is controlled by using the compressor power consumption and rotating speed to meet the discharge requirements, the air volume entering the primary gas cooler and the secondary gas cooler is controlled by using the upper air supply fan and the lower air supply fan respectively, the superheat degree in the evaporator is controlled by using the throttling valve opening degree, and the automatic optimization of the evaporation temperature of the heat pump system is realized by using the extreme value search control and the water side flow size of the heat release heat exchanger.

7. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 6, characterized in that, In the process of controlling the air volume entering the primary gas cooler and the secondary gas cooler by using the upper air supply fan and the lower air supply fan respectively, the expression of the optimal air volume ratio of the upper and lower air supply is: ω best = f(T 1,in ,d 1,in ,T 2,in ,d 2,in ,T 1,out ,d 1,out ,T 2,out ,d 2,out ) where ω best is the optimal air volume ratio of the upper and lower air supply; T 1,in represents the inlet temperature of the upper air supply; T 2,in represents the inlet temperature of the lower air supply; T 1,out represents the outlet temperature of the upper air supply; T 2,out represents the outlet temperature of the upper air supply; d 1,in represents the relative humidity of the inlet of the upper air supply; d 2,in represents the relative humidity of the inlet of the lower air supply; d 1,out represents the relative humidity of the outlet of the upper air supply; d 2,out represents the relative humidity of the outlet of the lower air supply.

8. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 7, characterized in that, The process of controlling the air volume entering the first-stage gas cooler and the second-stage gas cooler by the upper air supply fan and the lower air supply fan respectively, through solving ω best The optimal air volume ratio is obtained by taking the sum of the heat exchange amounts of the first-stage gas cooler and the second-stage gas cooler as the optimization objective in the feasible region.

9. A sludge drying apparatus based on transcritical CO2 heat pump cycle according to claim 6, characterized in that, In the process of realizing the automatic optimization of the evaporation temperature of the heat pump system by using the extreme value search control and the water side flow size of the heat release heat exchanger, the implementation steps of the extreme value search control include: A high frequency sinusoidal perturbation signal S1(t) = a1sin(ω1t) +... + a i sin(ω i t) +... + a n sin(ω n t); where a i and ω i are the amplitude and frequency of the i-th order signal, respectively, and n represents the total order number. A high frequency sinusoidal perturbation signal S1(t) = a1sin(ω1t) +... + a i sin(ω i t) +... + a n sin(ω n t); where a i and ω i are the amplitude and frequency of the i-th order signal, respectively, and n represents the total order number. The heat pump COP signal followed by the high-frequency disturbance signal is filtered through a high-pass filter to filter out the direct current component, and the remaining signal is demodulated with a signal S2(t)=sin(ω1t+α1)+…+sin(ωit+α i ) having the same frequency as the high-frequency sinusoidal disturbance signal, and the continuously changing sinusoidal signal is converted into a signal having a direct current gradient signal component, and then the high-order terms in the signal are filtered through a low-pass filter to retain the gradient term; wherein α n is a set phase deviation angle for compensating for the phase difference after filtering. n i ​​ An integrator is used to form a proportional integral control loop with an input being a low-pass filtered direct current gradient signal component, and after multiple calculations, when the input is 0, the optimal evaporation temperature point is found, the heat pump system is controlled to maintain the working condition of the optimal evaporation temperature, and the optimal control of the entire sludge drying device is realized.

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