Efficient heat pump desiccant dryer breaks through the single heat-reduction and dehumidification technology of heat pump dehumidifying dryer (most of the air is used for sensible heat cooling under the condition of heat absorption and low humidity), and uses air cooling and heat recovery design to realize double-effect dehumidification and dehumidification than general heat pump. Dryer energy-saving above the operating costs, high-efficiency heat pump dehumidifying dryer can fully meet the needs of different industries drying process. Therefore, heat pump dehumidification and drying is the development direction of energy-saving and emission reduction in the low- and middle-temperature drying industry.

The most commonly used fields for drying equipment are pharmaceuticals and foods. The requirements for drying equipment in these two fields are relatively high. There are specific requirements for the materials, structure and processing quality of the drying equipment used, and there are also strict requirements for drying equipment and drying systems. The health index requirements, therefore, need to continue through technological innovation to meet the increasing demand in the field of application, which is China's drying equipment industry must take the path of breakthrough development. However, at this stage, the drying capacity of China's drying equipment manufacturing enterprises is generally low, and the enterprises that can introduce new technologies and new products with independent intellectual property rights are poor, resulting in slow development of drying technology. The fundamental reason is that the level of technological innovation is not enough. Industry companies should strengthen their research in automation, manufacturing processes, and materials and materials design in the technological direction.

Research status of heat pump dehumidification drying technology at home and abroad Since the 1970s, the United States, Japan, France, Germany and other countries have conducted research on heat pump dehumidification and drying, and the International Energy Center (IEA) has concentrated on a large number of researches on heat pump drying technology. Achievements. China also introduced this technology in the 1980s. The earliest and the most widely used is the drying of wood. Since the heat pump drying temperature is close to natural drying, it has gradually been applied to the drying of food and agricultural and sideline products in recent years. In the meantime, good economic benefits have been achieved and the added value of the products has been greatly improved. In particular, the implementation of energy conservation and environmental protection policies by the Chinese government has greatly promoted the development of heat pump dehumidification and drying technologies.

Heat Pump Desiccant Drying Technology Development Trends and Prospects Replacement of Refrigerants Since H22 refrigerants such as R22, which are commonly used in heat pump circulation systems, have destructive effects on the ozone layer and the global climate, the research work has mainly focused on the single-working substance replacement R134a. R407c, a working substance substitute, and a non-destructive, environmentally friendly, green working fluid (carbon dioxide) in heat pump drying cycle systems.

Increasing drying temperature The temperature of heat pump drying is mostly concentrated between 40°C and 60°C. In order to expand the range of drying materials that can be used for heat pump drying, trying to increase the drying temperature is also a research hotspot. At present, the commonly used method is to further increase the temperature of the air heated by the condenser through the auxiliary heating system. Although this method is simple and effective, the energy consumption is significantly increased. To solve this problem, the heat pump drying should be aimed at the refrigeration workers. Conditions and air circulation conditions using composite working medium, research and development of high temperature and high pressure refrigeration compressors, in order to increase the condensing temperature, so as to meet the higher drying temperature requirements.

The use of phase change heat storage material in heat pump drying is accomplished by placing paraffin phase change material with a phase change temperature of 50-52°C in the bypass line of the condenser to the drying chamber, and recovering the drying unit to reach the desired drying temperature. The part of the heat discharged, the test results show that the phase change material used in heat pump drying has obvious energy-saving effect, when the drying temperature is 45 °C, the average mass percentage of the material is 24.5, the phase change material is placed, drying and energy-saving 21.9; when the drying temperature For 50 °C, the average mass percentage of the dry material is 35.5, place the phase change material dry energy-saving 36.5.

Heat pump and other methods combined drying system microwave and infrared drying penetrate the material surface into the three-dimensional heating of the material, forming a high temperature outside the positive temperature field (consistent with the direction of movement of the water discharge material), but at low temperatures It is not conducive to the elimination of water vapor enriched on the surface of the material. The introduction of the heat pump can solve this problem very well. The low-temperature dry air produced by the heat pump can quickly take away the moisture on the surface of the material and also ensure the quality of the finished material. The heat pump type vacuum drying device utilizes the heat pump evaporator to condense the water discharged from the material, which can reduce the load of the vacuum equipment. Compared with the electric heating type vacuum drying device, the operation cost of the heat pump type vacuum drying device is only 1/5.

Solar energy and heat pump combined drying in areas with sufficient solar energy can achieve good energy-saving effects. Fujian Provincial Forestry Research Institute developed a solar-heat pump combined drying device. The experimental results show that the energy-saving rate of the device is 15-47.8 percent. between.

The automatic control of drying is an unsteady process of heat and mass transfer. During the drying process, the value of the control parameters at each state point is greatly adjusted. Manual adjustment is difficult and the control accuracy is low. The development of computer hardware and software technology has provided convenience for the computer's automatic collection, display and preservation of data and automatic monitoring of parameters. According to material dehydration conditions and environmental conditions timely regulation of drying process parameters, will help improve energy efficiency and product quality, can reduce manual monitoring, control errors, reduce system adjustment lag, improve the system's regulation accuracy and sensitivity. Therefore, the combination of modern detection, sensing, and control technologies for heat pump drying processes enables full-automatic artificial intelligence control of the drying process, thereby reducing operating costs and drying energy consumption and improving product quality.

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