Low-temperature heat storage and multifunctional heat pump drying system and method

Abstract

The invention provides a low-temperature heat storage and multifunctional heat pump drying system and method. The low-temperature heat storage and multifunctional heat pump drying system comprises a refrigerant loop, a hot air loop, a hot water circulation loop and a control unit. The refrigerant loop is a closed cycle formed by sequentially connecting a compressor, a main condenser, an auxiliary condenser, a heat storage condenser, a throttling valve and an evaporator through pipelines; the hot air loop comprises a main drying air path and a pre-drying air path; the hot water circulation loop is connected with the heat storage condenser and a medium and low temperature heat storage unit; a four-way reversing valve is arranged in the main drying air path, a bypass air duct connected with the evaporator in parallel is arranged in the hot air loop, and an air valve is arranged on the bypass air duct. The control unit is in signal connection with the four-way reversing valve, the air valve and a circulating water pump in the hot water circulation loop and used for controlling reversing of dry airflow, adjusting the opening degree of a bypass air duct and controlling starting and stopping of hot water circulation. According to the technical scheme, the whole-process optimization of the drying process can be realized.

Description

Technical Field

[0001] This invention relates to the field of heat pump drying technology, and in particular to a low-temperature heat storage and multifunctional heat pump drying system and method. Background Technology

[0002] Currently common material drying methods include hot air drying, vacuum freeze drying, microwave drying, and infrared drying. These methods have varying degrees of problems in practical applications, such as significant environmental impact, high equipment costs, high energy consumption, or unsatisfactory drying efficiency. In contrast, heat pump drying technology, due to its advantages of high drying efficiency, low energy consumption, and environmentally friendly operation, is gradually becoming an important choice in the drying field. This technology achieves efficient heat generation through the thermodynamic cycle of the working fluid, absorbing low-grade heat energy in the evaporator, compressing it, and releasing high-grade heat energy in the condenser.

[0003] However, existing heat pump drying technology still has significant shortcomings. First, the drying process mostly adopts a constant temperature method throughout, which makes it difficult to match the water loss characteristics of materials at different drying stages (such as the rapid evaporation period of free water and the slow diffusion period of bound water), often leading to problems such as uneven drying, low efficiency, and decreased product quality.

[0004] Secondly, for closed-loop heat pump drying systems, there is a technical bottleneck in the initial startup phase: the low temperature of the air returning from the drying chamber results in a low evaporator inlet temperature and limited evaporation temperature, making it difficult to quickly raise the condenser outlet temperature to the required high temperature. Existing technologies generally use electric heating for secondary heating, which is not only energy-intensive and costly but also affects the overall system efficiency. Some solutions attempt to use external high-temperature heat storage devices to assist in heating, but these have drawbacks such as high cost, complex structure, and large footprint. Currently, there is a lack of effective solutions for rapid initial heating without significantly increasing energy consumption.

[0005] In addition, existing heat pump drying processes often use a fixed airflow direction, which can lead to inconsistent drying levels of the same batch of materials at different locations (such as the air inlet and outlet), thus affecting the overall drying quality.

[0006] Furthermore, existing closed-loop heat pump drying systems suffer from high temperature and low humidity air discharged from the drying chamber during the later stages of drying, due to the single hot air circulation. If all of this air is still sent to the evaporator, it will result in low evaporator dehumidification efficiency, with a large amount of cooling capacity wasted on air cooling rather than effective dehumidification, leading to problems such as increased system energy consumption, decreased energy efficiency, and frequent compressor start-stop.

[0007] In summary, existing technologies have significant room for improvement in terms of energy efficiency control, drying curve matching, initial rapid heating and drying capacity, and drying uniformity. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a low-temperature heat storage and multifunctional heat pump drying system and method to achieve full-process optimization of the drying process.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a low-temperature heat storage and multifunctional heat pump drying system, comprising: a refrigerant circuit, a hot air circuit, a hot water circulation circuit, and a control unit; The refrigerant circuit consists of a compressor, main condenser, auxiliary condenser, heat storage condenser, expansion valve, and evaporator connected in sequence through pipelines to form a closed loop. The hot air circuit includes a main drying air path and a pre-drying air path; The main drying air path is connected in sequence to the main drying chamber, the evaporator and the main condenser, forming the main circulating air duct for drying materials. The pre-drying air path is connected in sequence to the pre-drying chamber and the auxiliary condenser, forming a circulating air duct that uses the waste heat discharged by the auxiliary condenser to pre-dry the material. The hot water circulation loop connects the heat storage condenser to a medium-low temperature heat storage unit, which is used to store the waste heat generated by the heat storage condenser in the form of hot water in the heat storage unit during system operation, and to use the stored heat to increase the temperature of the medium entering the evaporator when the system is started. The main drying air path is equipped with a four-way reversing valve, and the hot air circuit is equipped with a bypass ventilation duct connected in parallel with the evaporator, and the bypass ventilation duct is equipped with an air valve. The control unit is connected to the four-way reversing valve, the air valve, and the circulating water pump in the hot water circulation loop, respectively, and is used to control the reversal of the drying airflow, adjust the opening of the bypass ventilation duct, and control the start and stop of the hot water circulation.

[0010] In a preferred embodiment, the hot water circulation loop is equipped with a circulating water pump and a heat exchanger. The heat exchanger is located at the inlet of the evaporator and is used to preheat the medium about to enter the evaporator using the hot water stored in the medium-low temperature heat storage unit.

[0011] In a preferred embodiment, the system employs a staged drying process, wherein the material is first pre-dried at low temperature in the pre-drying chamber using waste heat from an auxiliary condenser to remove free water, and then transferred to the main drying chamber for high-temperature main drying to remove bound water.

[0012] The present invention also provides a low-temperature heat storage and multifunctional heat pump drying method, which, based on the aforementioned low-temperature heat storage and multifunctional heat pump drying system, includes the following steps: When the system is started, the refrigerant circulates in the refrigerant circuit, releasing heat in the main condenser to provide high-temperature heat to the main drying air path, and releasing heat in the auxiliary condenser to provide low-temperature heat to the pre-drying air path. During system operation, the hot water circulation loop is controlled to store the waste heat generated by the heat storage condenser in the medium and low temperature heat storage unit; When the system starts up in the next operating cycle, the heat stored in the medium and low temperature heat storage unit is transferred to the front end of the evaporator inlet to preheat the medium entering the evaporator, so as to increase the evaporation temperature and condensation temperature at the beginning of the system startup. The material to be dried is placed in the pre-drying chamber and the main drying chamber in sequence. The waste heat of the auxiliary condenser is used to pre-dry the material at a low temperature, and then the high-temperature hot air provided by the main condenser is used to dry the material, thus completing the staged drying process.

[0013] In a preferred embodiment, during the main drying stage, the airflow direction through the main drying chamber is periodically switched by controlling a four-way reversing valve installed in the main drying air path to ensure uniform drying of the material.

[0014] In a preferred embodiment, during the later stages of drying, when the return air temperature from the main drying chamber is high and the humidity is low, the opening of the bypass duct connected in parallel with the evaporator is adjusted to allow part of the return air to bypass the evaporator.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention, through an integrated system architecture and a coherent workflow, uses waste heat recovery for pre-drying, medium and low temperature heat storage for rapid start-up, air direction switching for uniform drying, and air volume bypass for end-stage energy efficiency optimization, forming a complete, efficient, energy-saving, and high-quality heat pump drying solution that covers the entire process from start-up to operation and from the early stage to the end stage. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the system structure of a preferred embodiment of the present invention; Figure 2 This is a structural diagram of the four-way valve for the reversing air duct according to a preferred embodiment of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] It should be noted that the following detailed descriptions are illustrative 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.

[0019] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0020] This invention aims to overcome the problems of slow initial heating, high energy consumption in the later stages of drying, uneven drying and poor drying quality caused by constant temperature drying and fixed air ducts in existing drying technologies. It provides a multifunctional heat pump drying system solution based on low-temperature thermal storage. In existing technologies, closed-loop heat pump drying systems typically require an auxiliary condenser to discharge approximately 20%-30% of waste heat to maintain a stable drying chamber temperature, resulting in energy waste. Constant temperature drying modes are difficult to adapt to changes in the thermal and moisture characteristics of materials at different drying stages, affecting drying quality, while variable temperature drying increases system energy consumption. In the initial startup phase, the system relies heavily on electric heating or high-temperature thermal storage for auxiliary heating, resulting in low energy efficiency and high cost. Fixed air ducts easily cause uneven heating of materials. Furthermore, in the later stages of drying, due to high return air temperature and low humidity, all return air entering the evaporator leads to decreased dehumidification efficiency and wasted cooling capacity, further reducing system energy efficiency and increasing energy consumption. To this end, the present invention proposes the following technical solutions: 1) A pre-drying chamber is set up at the auxiliary condenser to recover the waste heat from the discharge for staged pre-drying of materials, thereby improving energy utilization efficiency; 2) The condenser 2 set up in the system is used to store medium and low temperature heat energy in the heat storage unit through hot water circulation; when the system starts up in the next operating cycle, the stored hot water is transported to the evaporator inlet for preheating, thereby increasing the evaporation temperature and condensation temperature, and realizing rapid and low energy consumption start-up; 3) Four-way reversing valves are configured at the inlet and outlet of the drying chamber in the hot air circuit to realize the controllable switching of the drying airflow direction, ensuring uniform drying of the same batch of materials; 4) A bypass duct is added in the hot air circuit, and the operating conditions in the later stage of drying are optimized by adjusting the bypass ratio, thereby improving the overall energy efficiency and stability of the system.

[0021] refer to Figure 1-2 The system of this invention includes a refrigerant circuit, a hot air circuit, a hot water circulation circuit, and a control unit. The refrigerant circuit includes a compressor 1, a main condenser 2, an auxiliary condenser 3, a heat storage condenser 4, a throttling valve 5, and an evaporator 6. The hot air circuit is divided into a main drying air path and a pre-drying air path. The main drying air path connects the main drying chamber 7, the evaporator 6, and the main condenser 2, while the pre-drying air path connects the pre-drying chamber and the auxiliary condenser 3. The hot water circulation circuit connects the heat storage condenser 4 and the medium-low temperature heat storage heat exchanger 8. The control unit coordinates the operation of each component.

[0022] The core workflow of the method of this invention is as follows: Phase 1: System Startup and Rapid Warm-up During system startup (especially cold start), the control unit first activates the hot water circulation loop, pumping the medium-low temperature hot water 9 stored in the heat storage unit to the medium-low temperature heat exchanger 8 located at the evaporator inlet. This hot water is used to preheat the air (or cooling medium) about to enter the evaporator 6, thereby directly increasing the evaporator inlet temperature. The increase in evaporation temperature causes the condensation temperature to rise accordingly, enabling the main condenser 2 to output high-temperature hot air in a short time. This solves the problem of slow temperature rise and reliance on auxiliary heating in the initial stage of heat pump drying system startup, achieving low-energy-consumption and rapid startup.

[0023] Phase Two: Phased Coordinated Drying Operation After the system is running normally, the refrigerant circulation simultaneously provides heat to the main condenser 2, auxiliary condenser 3 and heat storage condenser 4.

[0024] Pre-drying stage: The low-temperature heat generated by the auxiliary condenser 3, which is usually discarded as waste heat in traditional systems, is introduced into the pre-drying air path to perform preliminary drying on the materials placed in the pre-drying chamber 10. This stage mainly removes easily evaporable free water from the materials, realizing the recovery and utilization of waste heat.

[0025] Main drying stage: The pre-dried material is transferred to the main drying chamber 7. High-grade hot air generated by the main condenser 2 circulates in the main drying air path, performing high-temperature deep drying on the material to remove bound water. This staged drying process (low-temperature pre-drying + high-temperature main drying) better suits the drying characteristics of the material, improving drying quality and efficiency with the same energy consumption.

[0026] Thermal storage process: At the same time, the heat generated by the thermal storage condenser 4 is continuously stored in the thermal storage unit through the hot water circulation loop, accumulating energy for the rapid start-up of the next working cycle.

[0027] Phase 3: Optimized Operation and Uniform Drying Airflow direction switching ensures uniformity: During the main drying stage, the control unit controls the four-way reversing valve in the main drying air path to switch the direction of the hot air flowing through the main drying chamber according to a set cycle, thereby eliminating the problem of uneven drying of materials on the inlet and outlet sides caused by fixed airflow direction and improving the drying uniformity of the entire batch of materials.

[0028] Bypass regulation improves energy efficiency in the later stages of drying: At the end of the drying process, the material moisture content is very low, and the return air discharged from the main drying chamber 7 has a high temperature and low humidity. If all of this air enters the evaporator 6, it will result in low dehumidification efficiency and wasted cooling capacity. At this time, the control unit adjusts the opening of the bypass duct's upper air valve, allowing a portion of the high-temperature, low-humidity return air to bypass the evaporator 6 and mix with the air that has been cooled and dehumidified by the evaporator 6. This operation optimizes the air conditions entering the evaporator 6, improves the effective dehumidification efficiency of the evaporator 6, avoids frequent compressor start-stop cycles, and significantly reduces the system's operating energy consumption in the later stages of drying.

[0029] The airflow direction switching in the duct is accomplished by a four-way valve. Figure 2 The diagram shows the structure of a four-way reversing valve. This valve changes the airflow path by controlling the swing angle of an internal baffle. When the baffle rotates 45° to the left, hot air enters through the bottom port of the valve body and exits through the left port, causing the airflow direction into the drying chamber to be from left to right. The high-temperature, high-humidity air discharged from the right side of the drying chamber enters through the top port of the valve body and exits through the right port, eventually returning to the heat pump unit. When the baffle rotates 45° to the right, hot air still enters through the bottom port of the valve body, but exits through the right port. At this time, the airflow direction in the drying chamber reverses, becoming from right to left. The air discharged from the left side of the drying chamber enters through the top port of the valve body, exits through the left port, and flows back to the heat pump unit. Through this structure, the four-way reversing valve achieves the periodic switching of the airflow direction in the drying chamber, thereby improving the uniformity of material drying.

[0030] Combination Figure 1 In practical implementation, the control unit of this system can be a PLC or a microprocessor. During the first drying cycle, the heat storage unit has no heat at initial startup. The initial startup can be completed through short-term electric auxiliary heating or extended preheating time, allowing the stored energy to be utilized in subsequent cycles. The switching cycle of the four-way reversing valve, the opening adjustment logic of the bypass valve (e.g., PID control based on sensor feedback of return air humidity), and the start-up and shutdown temperature conditions of the hot water circulation can all be implemented by preset programs or algorithms within the control unit. The entire workflow (start-up preheating -> staged drying and heat storage -> airflow switching -> final bypass adjustment) can be automatically executed by the control unit, achieving intelligent and efficient drying operations.

[0031] 1. Existing heat pump drying systems generally rely on auxiliary condensers 3 to directly release excess heat into the environment, resulting in energy waste; at the same time, conventional drying processes mostly adopt constant temperature drying throughout the process, which cannot match the actual water loss pattern of the material (fast in the early stage and slow in the later stage), affecting the drying quality.

[0032] This invention recovers the waste heat emitted from the auxiliary condenser 3 and uses it in a matching low-temperature pre-drying chamber to achieve phased pre-drying of materials. This design not only recovers the originally discarded waste heat but also optimizes the drying process through a pre-drying stage with no additional energy consumption, making the drying process more in line with the material's water loss characteristics, thereby improving the drying quality.

[0033] 2. Existing technologies typically employ electric auxiliary heating or high-temperature heat storage to achieve rapid temperature rise in the initial drying stage, which generally suffer from high energy consumption and difficulty in implementation.

[0034] This invention adds a medium-low temperature heat storage unit using water as the heat storage medium. This unit is connected to the heat storage condenser 4 via a hot water circulation pipeline. During system operation, the waste heat of the heat storage condenser 4 is used to heat and store hot water. When the system restarts, the stored hot water is pumped to the inlet of the evaporator 6 to preheat the medium entering the evaporator 6, thereby effectively increasing the evaporation temperature and indirectly increasing the system condensation temperature. This achieves rapid heating of the entire drying circuit and significantly reduces initial start-up energy consumption.

[0035] 3. Existing drying technologies typically employ fixed airflow directions, which can easily lead to uneven airflow distribution within the drying chamber, affecting the uniformity of material drying.

[0036] This invention incorporates a four-way reversing valve in an independent air duct to enable controllable switching of the direction of the drying hot air flow, ensuring uniform drying of materials from different locations within the same batch.

[0037] 4. In the later stages of drying, existing closed-loop heat pump drying systems experience high return air temperature and low humidity. Sending all the return air into the evaporator leads to a decrease in dehumidification efficiency, waste of cooling capacity, and reduced system energy efficiency.

[0038] This invention designs a bypass duct in the hot air circuit and optimizes the air state entering the evaporator by adjusting the bypass ratio, thereby improving the overall energy efficiency of the system in the later stage of drying.

Claims

1. A low-temperature heat storage and multifunctional heat pump drying system, characterized in that, include: Refrigerant circuit, hot air circuit, hot water circulation circuit and control unit; The refrigerant circuit consists of a compressor, main condenser, auxiliary condenser, heat storage condenser, expansion valve, and evaporator connected in sequence through pipelines to form a closed loop. The hot air circuit includes a main drying air path and a pre-drying air path; The main drying air path is connected in sequence to the main drying chamber, the evaporator and the main condenser, forming the main circulating air duct for drying materials. The pre-drying air path is connected in sequence to the pre-drying chamber and the auxiliary condenser, forming a circulating air duct that uses the waste heat discharged by the auxiliary condenser to pre-dry the material. The hot water circulation loop connects the heat storage condenser to a medium-low temperature heat storage unit, which is used to store the waste heat generated by the heat storage condenser in the form of hot water in the heat storage unit during system operation, and to use the stored heat to increase the temperature of the medium entering the evaporator when the system is started. The main drying air path is equipped with a four-way reversing valve, and the hot air circuit is equipped with a bypass ventilation duct connected in parallel with the evaporator, and the bypass ventilation duct is equipped with an air valve. The control unit is connected to the four-way reversing valve, the air valve, and the circulating water pump in the hot water circulation loop, respectively, and is used to control the reversal of the drying airflow, adjust the opening of the bypass ventilation duct, and control the start and stop of the hot water circulation.

2. The low-temperature heat storage and multifunctional heat pump drying system according to claim 1, characterized in that, The hot water circulation loop is equipped with a circulating water pump and a heat exchanger. The heat exchanger is located at the inlet of the evaporator and is used to preheat the medium that is about to enter the evaporator using the hot water stored in the medium-low temperature heat storage unit.

3. The low-temperature heat storage and multifunctional heat pump drying system according to claim 1, characterized in that, The system employs a staged drying process. The material is first pre-dried at a low temperature in the pre-drying chamber using the waste heat from the auxiliary condenser to remove free water, and then transferred to the main drying chamber for high-temperature main drying to remove bound water.

4. A low-temperature heat storage and multifunctional heat pump drying method, characterized in that, A low-temperature heat storage and multifunctional heat pump drying system based on any one of claims 1 to 3 includes the following steps: When the system is started, the refrigerant circulates in the refrigerant circuit, releasing heat in the main condenser to provide high-temperature heat to the main drying air path, and releasing heat in the auxiliary condenser to provide low-temperature heat to the pre-drying air path. During system operation, the hot water circulation loop is controlled to store the waste heat generated by the heat storage condenser in the medium and low temperature heat storage unit; When the system starts up in the next operating cycle, the heat stored in the medium and low temperature heat storage unit is transferred to the front end of the evaporator inlet to preheat the medium entering the evaporator, so as to increase the evaporation temperature and condensation temperature at the beginning of the system startup. The material to be dried is placed in the pre-drying chamber and the main drying chamber in sequence. The waste heat of the auxiliary condenser is used to pre-dry the material at a low temperature, and then the high-temperature hot air provided by the main condenser is used to dry the material, thus completing the staged drying process.

5. The low-temperature heat storage and multifunctional heat pump drying method according to claim 4, characterized in that, During the main drying stage, the direction of airflow through the main drying chamber is periodically switched by controlling the four-way reversing valve installed in the main drying air path to ensure uniform drying of the material.

6. The low-temperature heat storage and multifunctional heat pump drying method according to claim 4, characterized in that, In the later stages of drying, when the return air temperature from the main drying chamber is high and the humidity is low, the opening of the bypass duct connected in parallel with the evaporator is adjusted to allow part of the return air to bypass the evaporator.

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