1 heat pump low temperature drying device principle and characteristics Hubei ruiyate Automobile Co.,Ltd , https://www.ruiyateworkingtruck.com
With the improvement of processing requirements for biological materials, low-temperature processing (≤60 ℃) of pharmaceutical preparations (such as pills), bioactive products (such as blood products), mushroom products (such as mushrooms) and other agricultural and sideline products are the basic trends [1]. Drying is the basic process of biological materials processing, application of low temperature drying device can better maintain its color, smell, taste and nutrition, texture, to ensure the quality of biological material processing is of great significance.
Currently used in low-temperature drying methods, freeze-drying, high cost of microwave drying, vacuum drying temperature is not easy to do too low, the natural weather directly affected by the weather, the use of moisture absorbent (molecular sieve, silica gel, etc.) Biological materials. Therefore, developing a new type of low temperature drying device with good drying quality (between freeze-drying and hot air drying), moderate initial investment, low operation cost and short drying time has a positive effect on the development of low temperature processing of biological materials. Heat pump low temperature drying device can meet the basic requirements [2].
The combination of heat pump and drying device can recover the exhaust heat (including the sensible heat of air and the latent heat of water vapor) of the drying device to make the drying air of low temperature (20 ℃ to 60 ℃) and improve the material drying process to achieve Drying system integration, high efficiency, green. To heat pump fluidized bed drying device, for example, the principle shown in Figure 1. The working process of the device is as follows: the low-temperature drying air generated by the heat pump at about 20 DEG C to 60 DEG C enters the fluidized bed under the circumstance of the circulation fan.
In the fluidized bed, the low-temperature drying air exchanges heat and moisture with the material to be dried to absorb the moisture in the material into damp cold air and enter the heat pump evaporator. In the heat pump evaporator, the humid cool air is further cooled below the dew point temperature to condense the moisture therein into dry cool air and into the heat pump condenser. In the heat pump condenser, the dry cold air is heated to a low temperature of about 20 ℃ ~ 60 ℃ dry air, circulating fan to increase the pressure and then into the fluidized bed to start the next cycle. This cycle of operation, to achieve continuous drying of materials.
From the above, heat pump low temperature drying device has the following salient features:
(1) low energy consumption. The heat used to cool the cold air mainly comes from the waste heat of the fluidized bed exhaust from the heat pump evaporator. The power consumption of the heat pump compressor is very small, only 1/3 to 1/10 of the heating air energy of the drying device, and the device has high energy efficiency , Operating costs can be significantly reduced.
(2) low temperature drying air absorption capacity. In the heat pump evaporator by freezing and condensation method to remove air moisture, heat pump evaporator dry cold air when the moisture content is very small (0 ℃, about 4g steam / kg dry air), heated to 20 ℃ ~ 60 ℃ to get a certain degree of hygroscopic ability of low temperature air (when heated to 40 ℃, the moisture absorption capacity of about 45g steam / kg dry air; and direct heating of ambient air used to dry the material, the ambient temperature set at 20 ℃ , Relative humidity of 80%, heated to 40 ℃ moisture absorption capacity of about 35g steam / kg dry air). The lower the drying temperature required for the material, the better it is to use a heat pump to dehumidify - the advantage of heating to provide cold, dry air. Especially when the required dry material temperature, humidity is lower than the local ambient temperature and humidity (hot and humid summer), the direct use of ambient air heating is no longer viable.
(3) the quality of the material drying is good. The degradation reaction of the active ingredients, nutrients and bioactive components of the material generally has an exponential relationship with the temperature. The low temperature drying of the heat sensitive material is an important means to ensure the quality of the material to be dried. This is of great benefit to the slowdown of the drying load and the drying load The drying stage is of particular importance [3,4]. In addition, the heat pump fluidized bed drying device is a closed circulation method using a drying medium (such as air, etc.), which can reduce the load of the air purification device. If necessary, an inert gas such as nitrogen can be used as the drying medium, Operation and other methods to reduce the oxidation of materials in the drying process and reduce the loss of aroma of tea, spices and other materials in the drying process, therefore, heat pump fluidized bed drying equipment for heat-sensitive materials, materials containing easy oxidation components, volatile components The material is particularly suitable.
2 heat pump low temperature drying device development method
The main purpose of heat pump low temperature drying device developed two: reduce operating costs and improve the quality of drying. According to the characteristics of water movement in the drying of different materials, heat pump low temperature drying device can be divided into two categories, the device structure and development of different content.
2.1 Reverse-type heat pump drying device development
This type of heat pump drying device multi-system heat pump and the current widely used drying device (such as fluidized bed, spray, revolving drum, drying room, belt drying device, etc.) combined with the drying process of moisture content in the material movement and heat transfer In the opposite direction. Such heat pump drying device drying heat-sensitive materials, the drying device in the constant speed drying device inlet air temperature may be higher, but the material temperature is maintained at a low (below 60 ℃) [5]; In the desiccation drying section dryer inlet Low temperature drying air below 60 ℃. The key to its development is the integration of heat pump and drying device to strengthen the drying process, improve heat pump efficiency, reduce heat pump costs and heat pump variable conditions to adapt to technology (constant speed drying section provides high temperature dry air, slow down the drying section to provide low temperature Dry air) so that the heat pump throughout the drying process can efficiently provide the required temperature of the drying air, to ensure that the material is low temperature drying.
The basic structure of the general When the hot air temperature is not dry than 100 ℃, the heat pump system can be fully applied to recover the exhaust heat of the drying device to heat the drying air, the basic principle shown in Figure 1, the heat pump compressor is the device's energy consumption components.
⑵ energy-efficient drying device into the air temperature of 100 ℃, exhaust temperature of 70 ℃, the heat pump energy efficiency (EER) is about 4, that is, heat pump fluidized bed drying device is the same size of electric heating flow 25% of the bed drying device. When the inlet air temperature is lower, the energy saving effect of the heat pump low temperature drying device is better (when the temperature difference between the intake and exhaust air is the same).
(3) Technical Economy Taking a fluidized bed drying device with a heating capacity of 100 kW as an example, the electricity charge is 0.8 yuan / kWh and the drying device works 10 hours a day. The heat pump drying device saves electricity cost about a month 15,000 yuan, the drying device to join the heat pump system or the use of heat pump system to transform the existing drying device, the payback period is about 3 to 5 months.
⑷ parts heat pump fluidized bed (and spray, drying room, with) dry heat pump evaporator, heat pump condenser finned tube heat exchanger can be used, the average heat exchanger heat transfer temperature difference of 10 ~ 15 ℃ ; Heat pump drum drying device, the condenser can be casing, shell and tube, plate type, heat transfer temperature difference of 5 ~ 10 ℃.
(5) heat pump working fluid Heat pump circulating working fluid should adopt environmentally friendly non-azeotropic mixture (NARM), such as R227ea / R141b, etc., to ensure better energy efficiency, working pressure, safety, heat exchanger temperature changes inside and outside the medium Matching [6].
⑹ Other current heat pump air temperature provided by heating air is generally lower than 100 ℃, when the constant speed drying phase requires hot air of higher temperature (such as spray drying device), you need to use the new high temperature heat pump technology [7] . For small and medium-sized steam compression heat pump, the options include electric energy near Carnot cycle technology, oil-free lubrication technology, wet compression technology, gas or oil-powered gas or fuel-powered heat pump technology; for large installations , Can consider oil, gas, coal as energy absorption heat pump technology.
2.2 forward type heat pump drying device development
Drying materials such drying device, the material in the direction of movement of water and heat flow in the same direction or by vacuum to form a driving force of water movement. Heat pump and such drying devices (such as microwave, infrared, vacuum drying device, etc.), the purpose is to ensure the quality of the material under the premise of drying, reducing drying energy consumption, and strengthen the drying process, shorten the drying time to make up for lack of simple drying device , The key to its development is the effective combination of the dehumidification heating function of the heat pump and the heating and dehumidification function of the drying device.
â‘´ temperature To ensure the quality of the drying of heat-sensitive materials, the drying temperature is generally not high, the drying conditions are relatively gentle, the required heat pump related technologies and components are more mature, heat pump cycle of the optional range, such as R134a, R227ea, R142b, R600 and its mixture can better meet the requirements of various types of heat pump drying devices in this temperature range [6].
⑵ heat pump microwave and infrared drying device Both microwave and infrared drying penetrate into the material surface for three-dimensional heating of the material to form the temperature within the high and low external temperature field (with the water discharge material movement of the same direction) advantages can be achieved in The lower the temperature of the material of high quality drying, but the material surface is enriched with water vapor removal, drying costs, large (especially for microwave drying) is restricting the application of unfavorable factors. The introduction of heat pump can better overcome the above shortcomings, the use of heat pump made of low-temperature drying air to ensure the quality of the material dry, but also quickly take away the surface of the material moisture, the microwave or infrared energy is mainly used to drive water from the inside out Of the movement, the water vaporization and removal of the heat pump to complete the formation of complementary complementary integration, so that the heat pump microwave or infrared drying device has the material drying quality, time is short, low energy consumption, easy to achieve large-scale and other comprehensive advantages.
⑶ heat pump vacuum drying device Heat pump vacuum drying device can be used by similar freeze-drying device structure. The use of heat pump evaporator as a cold trap, so that the material discharged in the heat pump evaporator condensation coagulation can greatly reduce the load on the vacuum equipment (vacuum equipment is only used to exclude non-condensable gases); the use of heat pump condenser heating material provided Evaporation of moisture in the material required to discharge the heat. Compared with electric heated vacuum drying device, heat pump vacuum drying device with (running costs) only 1/5.
3 heat pump low temperature drying device application analysis
Application opportunities: Heat pump and microwave, infrared, vacuum and other low-temperature drying device combination can significantly reduce the cost of drying,
Materials with relatively low added value can also be dried at low temperatures to improve the quality of the dry and extend the range of materials that are suitable for use, extending the range of materials available to a large chunk of low value added materials. Heat pumps, combined with medium- and high-temperature drying units such as fluidized beds, provide high moisture absorption and dry strength at relatively low temperatures, allowing previously unsuitable thermosensitive materials to be dried and expanding the range of applicable materials , About to expand its range of applicable materials to heat-sensitive materials. The successful integration of heat pumps with various types of drying devices can significantly reduce the energy consumption of the drying process and improve the economy of dry products and the market competitiveness of products [8].
Market positioning: In summary, the heat pump low-temperature drying device and freeze-drying device, medium and high temperature thermal drying device, the drying quality of the material and the initial investment are between the two, while the lowest dry operating costs can be used as not Ideal for a wide range of materials that withstand high temperatures but do not have to freeze-dry.
Technical key: The key to the application and promotion of heat pump low temperature drying equipment is the enhancement of the heat and mass transfer process between low temperature drying air and material, the structural optimization of heat pump low temperature drying equipment, the condition control of heat pump low temperature drying equipment, Low-temperature drying device function integration.
4 conclusions and recommendations
Heat pump low temperature drying device for a large number of thermosensitive materials provide an ideal method of drying, affecting the application and promotion of the main factors is the initial investment and reliability, the main solution is through the drying and heat pump in close cooperation in two areas, Based on a thorough grasp of typical drying process and heat pump dehumidification heating process, through the highly integrated structure and function of the system, the modularity, greenness and intelligence of the device are realized. The initial investment is similar to that of the conventional device, and the material adaptation Good quality, low energy consumption, easy to master the technology, material quality and good drying high-level heat pump low temperature drying device.