Positive and negative pressure heat pump drying system and its control method based on the whole process of material drying

Abstract

This invention belongs to the field of heat pump system design and operation control technology. It proposes a positive and negative pressure heat pump drying system and its control method based on the entire material drying process. An air duct is located at the end of the drying chamber furthest from the heat pump dryer, and a material cart is located at the end closest to the heat pump dryer. A positive pressure fan is installed at the air inlet of the air duct, and a buffer zone is provided between the material cart and the air outlet of the air duct. A negative pressure fan is installed at the end of the drying chamber located at the end of the material cart furthest from the buffer zone. During system operation, the speeds of the positive and negative pressure fans are controlled according to the material placement density and moisture content. By controlling the speed of the positive pressure fan, the problem of materials being blown off by the circulating air in the later stages of drying can be avoided. Simultaneously, considering the moisture content to control the fan speed ensures the dehumidification capacity within the drying chamber.

Description

Technical Field

[0001] This invention belongs to the field of heat pump system design and operation control technology, and particularly relates to a positive and negative pressure heat pump drying system and its control method based on the entire material process. Background Technology

[0002] In agriculture and industry, heat pump drying has replaced traditional coal-fired drying methods, which is of great significance to sustainable energy development. The significant advantages of heat pump drying are reduced energy consumption and carbon emissions, and its application prospects are broad. With social development and the diversification of drying product demand, the requirements for heat pump drying systems are also increasing.

[0003] The inventors discovered that in current heat pump drying systems, materials with significant weight changes during the drying process, such as flower petals, become lighter in the later stages of drying and are easily blown off by the circulating air. For such materials, the control of the air velocity in the drying chamber needs to be carefully managed in the later stages of drying. However, traditional heat pump drying systems mostly use positive pressure air supply, which has high air pressure and air velocity. If the air supply speed is reduced, it can easily lead to insufficient heat or dehumidification capacity in the drying chamber. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a positive and negative pressure heat pump drying system and its control method based on the entire material drying process. According to the material properties, material placement density, and material moisture content, the operating status of the positive and negative pressure fans is controlled, reducing the impact of wind speed on the material's weight loss in the later stages of drying, while ensuring the dehumidification capacity of the drying chamber.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a positive and negative pressure heat pump drying system based on the entire material process, employing the following technical solution:

[0006] A positive and negative pressure heat pump drying system based on the entire material process includes a drying chamber body and a heat pump dryer installed at one end of the drying chamber body.

[0007] Inside the drying chamber, an air supply duct is provided at the end away from the heat pump dryer, and a material cart is provided at the end closer to the heat pump dryer; a positive pressure fan is provided at the air inlet of the air supply duct, and a buffer zone is provided between the material cart and the air outlet of the air supply duct; inside the drying chamber, a negative pressure fan is provided at the end of the material cart away from the buffer zone.

[0008] The positive pressure fan and the negative pressure fan are connected to a controller; the controller is used to control the speed of the positive pressure fan and the speed of the negative pressure fan according to the material placement density and the material moisture content.

[0009] Furthermore, the drying chamber body is provided with a drain outlet.

[0010] Furthermore, the drying chamber body is also equipped with a fresh air valve, a dehumidification vent, and an operating electrical box; the dehumidification vent is connected to a dehumidification fan via a pipe.

[0011] Furthermore, when the moisture content of the material on the material cart is higher than the preset moisture content value, the water discharge rate is higher than the preset water discharge rate, the material mass is higher than the preset mass, and the material placement density is greater than the preset density, the positive pressure fan is controlled and the negative pressure fan is turned off; otherwise, the positive pressure fan is controlled to turn off and the negative pressure fan is turned on.

[0012] Furthermore, images of the materials on the material cart are acquired in real time; the material placement density is equal to the ratio of the area of ​​all materials in the image to the total area of ​​the material cart used to place the materials.

[0013] Furthermore, when the controller controls the speed of the positive pressure fan and the speed of the negative pressure fan: the target temperature and target moisture content of the drying chamber are set; in the initial stage of drying, the positive pressure fan is turned on, and the material is dried by positive pressure air supply, and the compressor in the heat pump dryer is controlled to run at full frequency; when the water rate is less than the product of the preset maximum water output rate and the first correction coefficient, the target deviation of the water output rate is calculated, and the speed of the positive pressure fan is adjusted; when the water rate is less than the product of the preset maximum water output rate and the second correction coefficient, the positive pressure fan is turned off, and the negative pressure fan is turned on and runs at full speed; when the water rate is less than the product of the preset maximum water output rate and the third correction coefficient, the target deviation of the water output rate is calculated, and the speed of the negative pressure fan is adjusted until the target moisture content is reached, and then the operation is stopped; the first correction coefficient is greater than the second correction coefficient, and the second correction coefficient is greater than the third correction coefficient.

[0014] Furthermore, in the initial drying stage, the compressor frequency inside the heat pump dryer is controlled to meet the set target temperature according to the target deviation.

[0015] Furthermore, the water discharge rate is equal to the ratio of the difference in moisture content at two different times to the time difference between the two times.

[0016] To achieve the above objectives, in a second aspect, the present invention also provides a control method for a positive and negative pressure heat pump drying system based on the entire material process, employing the following technical solution:

[0017] A control method for a positive and negative pressure heat pump drying system based on the entire material process is provided. The system employs the positive and negative pressure heat pump drying system based on the entire material process as described in the first aspect, including: controlling the rotation speed of the positive pressure fan and the rotation speed of the negative pressure fan according to the material placement density and the material moisture content.

[0018] Furthermore, the target temperature and target moisture content of the drying room are set; in the initial stage, the positive pressure fan is turned on, and the material is dried by positive pressure air supply. The compressor of the heat pump dryer is controlled to run at full frequency to meet the target temperature set in the drying room; the target deviation is calculated, and the compressor frequency of the PID heat pump dryer is adjusted to meet the set drying room temperature.

[0019] Calculate the real-time water output rate; when the water output rate is less than or equal to the first preset value, calculate the target deviation of the water output rate based on the first correction coefficient, and adjust the speed of the positive pressure fan through PID control; otherwise, the positive pressure fan runs at full speed; when the water output rate is less than or equal to the second preset value, turn off the positive pressure fan and turn on the negative pressure fan at full speed, using negative pressure air supply for drying; when the water output rate is less than or equal to the third preset value, calculate the target deviation of the water output rate based on the third correction coefficient, and adjust the speed of the negative pressure fan; until the drying chamber reaches the target moisture content, stop operation;

[0020] Among them, the first preset value is greater than the second preset value, the second preset value is greater than the third preset value, and the first correction coefficient is greater than the second correction coefficient.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The present invention provides an air supply duct at one end of the drying chamber away from the heat pump dryer and a material cart at the other end closer to the heat pump dryer. A positive pressure fan is installed at the air inlet of the air supply duct, and a buffer zone is provided between the material cart and the air outlet of the air supply duct. A negative pressure fan is installed at the end of the drying chamber located away from the buffer zone of the material cart. During system operation, the speed of the positive pressure fan and the speed of the negative pressure fan are controlled according to the material placement density and the material moisture content. By switching the positive pressure fan and controlling its speed, the problem of materials being blown off by the circulating air in the later stage of drying can be avoided. At the same time, the fan speed is controlled by considering the moisture content, thus ensuring the dehumidification capacity of the drying chamber.

[0023] 2. This invention can select the appropriate fan circulation according to the material properties, material placement density and material moisture content. In addition, the fan circulation can be switched according to the hourly exhaust moisture content during the drying process, reducing the impact of the drying chamber wind speed on the material, meeting the drying requirements, and is highly flexible and practical. During the drying process, it can make a real-time dynamic response to the changes in ambient temperature required by the process, which can fully meet the process requirements, achieve better drying effect and save energy and reduce consumption. Attached Figure Description

[0024] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0025] Figure 1 This is a schematic diagram of the system structure of Embodiment 1 of the present invention;

[0026] Figure 2 This is a schematic diagram of the positive pressure fan circulation principle in Embodiment 1 of the present invention;

[0027] Figure 3 This is a schematic diagram of the negative pressure fan circulation principle in Embodiment 1 of the present invention;

[0028] Figure 4 This is a diagram of the adjustment model for Embodiment 1 of the present invention;

[0029] Figure 5 This is a system operation control diagram of Embodiment 1 of the present invention;

[0030] The components include: 1. Heat pump dryer; 2. Positive pressure fan; 3. Negative pressure fan; 4. Material cart; 5. Fresh air valve; 6. Exhaust air outlet; 7. Drain outlet; 8. Control box; 9. Exhaust fan; and 10. Drying room body. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] Example 1:

[0034] During the drying process, materials such as flower petals, whose mass changes significantly, become extremely light in the later stages of drying and are easily blown off by the circulating air. Therefore, controlling the airflow velocity within the drying chamber is crucial for these materials in the later stages of drying. However, traditional heat pump drying systems often use positive pressure airflow, resulting in high air pressure and velocity. If the airflow velocity is reduced, it can easily lead to insufficient heat or dehumidification capacity in the drying chamber.

[0035] To address the aforementioned issues, this embodiment provides a positive and negative pressure heat pump drying system based on the entire material process. It employs positive and negative pressure circulating air supply and can be installed independently or in combination, meeting diverse production needs, assisting heat pump drying companies in upgrading their product technology, and promoting the efficient application and sustainable development of heat pump drying technology. Figure 1 As shown, the system includes a heat pump dryer 1, a positive pressure fan 2, a negative pressure fan 3, a material cart 4, a fresh air valve 5, a dehumidification vent 6, a drain outlet 7, an operating electrical box 8, a dehumidification fan 9, and the drying chamber body 10, etc.

[0036] Optionally, a heat pump dryer 1 is located at one end of the drying chamber body 10; an air supply duct is provided at the end of the drying chamber body 10 away from the heat pump dryer 1, and a material cart 4 is provided at the end closer to the heat pump dryer 1; a positive pressure fan 2 is provided at the air inlet of the air supply duct, and a buffer zone is provided between the material cart 4 and the air outlet of the air supply duct; a negative pressure fan 3 is provided at the end of the drying chamber body 10 located away from the buffer zone of the material cart 4.

[0037] In some embodiments, the positive pressure fan 2 and the negative pressure fan 3 are connected to a controller; the controller is used to control the rotation speed of the positive pressure fan 2 and the rotation speed of the negative pressure fan 3 according to the material placement density and the material moisture content.

[0038] During system operation, the controller controls the speed of the positive pressure fan 2 and the speed of the negative pressure fan 3 according to the material placement density and material moisture content. By controlling the speed of the positive pressure fan 2, the problem of materials being blown off by the circulating air in the later stage of drying can be avoided. At the same time, the fan speed is controlled by taking the moisture content into account, thus ensuring the dehumidification capacity in the drying room.

[0039] In some embodiments, the drying chamber body 10 is further provided with a drain outlet 7 for draining accumulated water from the drying chamber body 10. The drying chamber body 10 is also provided with a fresh air valve 5, a dehumidification vent 6, and an operating electrical box 8, etc.; the dehumidification vent 6 is connected to a dehumidification fan 9 via a pipe. The controller can be located in the operating electrical box, and the controller is also connected to the dehumidification fan, etc. The positive pressure fan 2 and the negative pressure fan 3 are arranged side by side, and the number of the positive pressure fan 2 and the negative pressure fan 3 can be selected according to actual conditions. An air handling buffer zone is provided between the heat pump dryer, the positive pressure fan 2, and the negative pressure fan 3. The area where the material cart 4 is located is the material area; optionally, the dehumidification fan 9 is an axial flow dehumidification fan, the positive pressure fan 2 can be an axial flow fan installed at the upper part of the drying chamber, and the positive pressure area supplied by the fan is the material area; the negative pressure fan 3 is an axial flow fan installed at the lower part of the drying chamber, and the negative pressure area drawn by the fan is the material area.

[0040] In some embodiments, the heat pump dryer 1 can be implemented using conventional equipment. In this embodiment, optionally, the heat pump dryer 1 includes a compressor, a liquid receiver, an electronic expansion valve, a gas-liquid separator, an indoor condenser, a dehumidifying evaporator, a solenoid valve, and a dehumidifying fan, etc. Its working principle is as follows: the high-temperature, high-pressure refrigerant discharged from the compressor flows through the indoor condenser to release heat, then flows through the liquid receiver, and after being throttled by the electronic expansion valve, becomes a low-temperature, low-pressure refrigerant. It then enters the dehumidifying evaporator to evaporate and absorb heat, and finally enters the compressor through the gas-liquid separator, thus completing the cycle.

[0041] Based on the drying system, a drying system control method is also provided, including two modes: positive pressure air supply and negative pressure air supply. Optionally, the positive pressure circulating air supply mode is mainly used in the initial stage of material drying, when the material has high moisture content and high water output rate, high material quality, and high material density. At this time, the positive pressure fan 2 located above the material is turned on, and the high-temperature, high-speed airflow is sent to the positive pressure buffer zone behind the material through the upper air duct. Then, the high-temperature, high-speed airflow flows through the material area to dry the material. The humid air generated during drying is discharged from the room by the exhaust fan 9, completing the positive pressure drying cycle. In the later stage of drying, when the material has low moisture content, low water output rate, and low material quality, the positive pressure fan 2 is turned off, and the negative pressure fan 3 is turned on, adopting the negative pressure circulating air supply mode. At this time, the negative pressure fan 3 located in front of the material supplies air, and the area behind the material is in the negative pressure buffer zone. The airflow flowing through the material has a low velocity and a high temperature, and the humid air generated after drying is discharged from the room by the exhaust fan 9, completing the negative pressure drying cycle.

[0042] In some embodiments, when the moisture content of the material on the material cart 4 is higher than a preset moisture content value, the water discharge rate is higher than a preset water discharge rate, the material mass is higher than a preset mass, and the material placement density is greater than a preset density, the positive pressure fan is controlled and the negative pressure fan is turned off; otherwise, when the moisture content of the material on the material cart 4 is not higher than a preset moisture content value, the water discharge rate is not higher than a preset water discharge rate, the material mass is not higher than a preset mass, and the material placement density is not greater than a preset density, the positive pressure fan is controlled to turn off and the negative pressure fan is turned on. Optionally, the material moisture content, water discharge rate, and material mass can be directly collected by preset humidity sensors, moisture content sensors, and mass sensors, or obtained through conventional technical methods based on the collected data; the material placement density can be achieved through image acquisition and processing technology, for example, by acquiring images of the material on the material cart 4 in real time and calculating the ratio of the area of ​​all materials in the image to the total area of ​​the material cart 4 used to place the materials, as the placement density. The preset values ​​such as preset water discharge rate, preset mass, preset density, and preset moisture content can be determined and adjusted based on experiments, historical data, or experience.

[0043] In some embodiments, the system control method may include the following steps:

[0044] S1. Set the target temperature of the drying room. T set and target moisture content d set Real-time monitoring of moisture content in the drying room. d and drying room temperature T Optionally, temperature and humidity sensors can be installed in the drying room to monitor humidity and temperature.

[0045] S2. In the initial drying stage, turn on the positive pressure fan 2 to dry the material using positive pressure airflow. Simultaneously, control the compressor to run at full frequency, prioritizing the achievement of the target temperature set in the drying chamber. T set ; then according to γ =( T set - T ) / T set The target deviation is calculated by multiplying by 100%, and the frequency of the heat pump compressor is controlled by PID to meet the set target temperature.

[0046] S3, according to the formula v =( d i - d j ) / t ij Calculate the real-time water output rate, where d i and d j The first i and j Moisture content at any given time t ij For the first i and j The time difference between moments.

[0047] S4, when v ≤ a × v max When, in the formula, v max This represents the maximum water output rate during the drying process, which typically occurs in the initial stage. a This is the first correction factor, typically taken as 0.5; according to σ a =( a × v max - v ) / ( a × v max The deviation from the target water output rate is calculated by multiplying the result by 100%, and the positive pressure fan speed is adjusted using PID control. Conversely, the positive pressure fan runs at full speed.

[0048] S5, when v ≤ b × v max At that time, among them, bThe second correction factor is typically between 0.2 and 0.4. At this point, the material moisture content is low, and the material mass is relatively small. In this case, the positive pressure fan 2 is turned off, and the negative pressure fan 3 is turned on and runs at full speed, using negative pressure airflow for drying. Conversely, the operation is controlled according to step S4.

[0049] S6, when v ≤ c × v max hour, c This is the third correction factor, which is generally taken as 0.1; according to σ c =( c × v max - v ) / ( c × v max The deviation from the target water output rate is calculated by multiplying the deviation by 100%, and the speed of the negative pressure fan 3 is adjusted using PID control. Conversely, the operation is controlled according to step S5. Optionally, the linear relationship between the target deviation and the fan speed can be determined in advance using historical or experimental data, and the corresponding speed can be selected for control according to the target deviation.

[0050] S7. Continue until the drying room reaches the target moisture content. d set When the time comes, the program will stop running.

[0051] Example 2:

[0052] This embodiment provides a control method for a positive and negative pressure heat pump drying system based on the entire material process. It adopts the positive and negative pressure heat pump drying system based on the entire material process as described in Embodiment 1, including: controlling the rotation speed of the positive pressure fan and the rotation speed of the negative pressure fan according to the material placement density and the material moisture content.

[0053] like Figure 2 As shown, when the material has a high moisture content and a high water discharge rate, positive pressure fan 2 is turned on, while negative pressure fan 3 is turned off. Figure 3 As shown, when the material has low moisture content and low water discharge rate, the negative pressure fan 3 is turned on, while the positive pressure fan 2 is turned off.

[0054] like Figure 5 As shown, the optional system operation control methods are as follows:

[0055] S1. Set the target temperature for the drying chamber. T set =25℃, target moisture content d set =15%; simultaneously monitor the moisture content of the drying room in real time. d and drying room temperature T .

[0056] S2. In the initial stage, the positive pressure fan is turned on to dry the material using positive pressure airflow. Simultaneously, the compressor is controlled to run at full frequency, prioritizing the achievement of the drying chamber's set temperature. T set ; then according to γ =( T set - T ) / T set The target deviation is calculated by multiplying by 100%, and the frequency of the heat pump compressor is controlled by PID to meet the set drying room temperature.

[0057] S3, Calculation v max =40g / s, calculate the real-time water output rate. v =( d i - d j ) / t ij .

[0058] S4, when v When ≤20g / s, according to σ a =( a × v max - v ) / ( a × v max ) × 100% to calculate the deviation from the target water output rate. a The correction factor is typically set to 0.5; the speed of the positive pressure fan is adjusted using PID control. Conversely, the positive pressure fan runs at full speed.

[0059] S5, when v When the moisture content is ≤12g / s, the material moisture content is low and the material mass is relatively small. At this time, the positive pressure fan is turned off and the negative pressure fan is turned on and run at full speed to dry the material using negative pressure air supply. Otherwise, the operation is controlled according to step S3.

[0060] S6, when v When ≤4g / s, according to σ c =( c × v max - v ) / ( c × v max ) × 100% to calculate the deviation from the target water output rate. cThe correction factor is typically set to 0.1; the speed of the negative pressure fan is adjusted using PID control. Conversely, operation is controlled according to step S5.

[0061] S7. Continue until the drying room reaches the target moisture content. d set When the time comes, the program will stop running.

[0062] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A positive and negative pressure heat pump drying system based on the entire material process, characterized in that, It includes a drying chamber body and a heat pump dryer installed at one end of the drying chamber body; Inside the drying chamber, an air supply duct is provided at the end away from the heat pump dryer, and a material cart is provided at the end closer to the heat pump dryer; a positive pressure fan is provided at the air inlet of the air supply duct, and a buffer zone is provided between the material cart and the air outlet of the air supply duct; inside the drying chamber, a negative pressure fan is provided at the end of the material cart away from the buffer zone. The positive pressure fan and the negative pressure fan are connected to a controller; the controller is used to control the speed of the positive pressure fan and the speed of the negative pressure fan according to the material placement density and the material moisture content. When the moisture content of the material on the material cart is higher than the preset moisture content value, the water discharge rate is higher than the preset water discharge rate, the material mass is higher than the preset mass, and the material placement density is greater than the preset density, the positive pressure fan is controlled and the negative pressure fan is turned off; otherwise, the positive pressure fan is controlled to turn off and the negative pressure fan is turned on.

2. The positive and negative pressure heat pump drying system based on the entire material process as described in claim 1, characterized in that, The drying chamber body is equipped with a drainage outlet.

3. The positive and negative pressure heat pump drying system based on the entire material process as described in claim 1, characterized in that, The drying room body is also equipped with a fresh air valve, a dehumidification vent, and an operating electrical box; the dehumidification vent is connected to a dehumidification fan through a pipe.

4. The positive and negative pressure heat pump drying system based on the entire material process as described in claim 1, characterized in that, Images of the materials on the material cart are acquired in real time; the material placement density is equal to the ratio of the area of ​​all materials in the image to the total area of ​​the material cart used to place the materials.

5. The positive and negative pressure heat pump drying system based on the entire material process as described in claim 1, characterized in that, When the controller controls the speed of the positive pressure fan and the speed of the negative pressure fan: it sets the target temperature and target moisture content of the drying room; In the initial drying stage, the positive pressure fan is turned on to dry the material using positive pressure airflow, and the compressor inside the heat pump dryer is controlled to run at full frequency. When the water rate is less than the product of the preset maximum water output rate and the first correction coefficient, the deviation of the water output target is calculated, and the speed of the positive pressure fan is adjusted. When the water rate is less than the product of the preset maximum water output rate and the second correction coefficient, the positive pressure fan is turned off, and the negative pressure fan is turned on and runs at full speed. When the water rate is less than the product of the preset maximum water output rate and the third correction coefficient, the deviation of the water output target is calculated, and the speed of the negative pressure fan is adjusted until the target moisture content is reached, at which point the operation stops. The first correction coefficient is greater than the second correction coefficient, and the second correction coefficient is greater than the third correction coefficient.

6. The positive and negative pressure heat pump drying system based on the entire material process as described in claim 5, characterized in that, In the initial drying stage, the compressor frequency inside the heat pump dryer is controlled to meet the set target temperature according to the target deviation.

7. The positive and negative pressure heat pump drying system based on the entire material process as described in claim 5, characterized in that, The water discharge rate is equal to the ratio of the difference in moisture content at two different times to the time difference between the two times.

8. A control method for a positive and negative pressure heat pump drying system based on the entire material process, characterized in that, The positive and negative pressure heat pump drying system based on the entire material process as described in any one of claims 1-7 is adopted, including: controlling the rotation speed of the positive pressure fan and the rotation speed of the negative pressure fan according to the material placement density and the material moisture content.

9. The control method for a positive and negative pressure heat pump drying system based on the entire material process as described in claim 8, characterized in that, Set the target temperature and target moisture content of the drying room; in the initial stage, turn on the positive pressure fan and use positive pressure air supply to dry the material, and control the compressor of the heat pump dryer to run at full frequency to meet the target temperature set in the drying room; Calculate the target deviation and ensure that the compressor frequency of the PID heat pump dryer meets the set drying room temperature; Calculate the real-time water output rate; When the water output rate is less than or equal to the first preset value, the deviation from the target water output rate is calculated based on the first correction coefficient, and the speed of the positive pressure fan is adjusted through PID control; otherwise, the positive pressure fan runs at full speed. When the water output rate is less than or equal to the second preset value, the positive pressure fan is turned off, and the negative pressure fan is turned on and runs at full speed, using negative pressure air supply for drying. When the water output rate is less than or equal to the third preset value, the deviation from the target water output rate is calculated based on the third correction coefficient, and the speed of the negative pressure fan is adjusted. Operation stops when the drying chamber reaches the target moisture content. Among them, the first preset value is greater than the second preset value, the second preset value is greater than the third preset value, and the first correction coefficient is greater than the second correction coefficient.

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