Efficient heat pump dehumidifying dryer breaks through the single heat-reduction and dehumidification technology of heat pump dehumidifying dryer (most of them are used for air sensible heat-reducing under the condition of absorbing heat and low humidity). It uses air cooling and temperature-recovering 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.
Heat Pump Desiccant Drying Technology at Home and Abroad
Since the 1970s, the United States, Japan, France, Germany and other countries have conducted research on heat pump desiccation and drying, and the International Energy Center (IEA) has concentrated a large number of research results on heat pump drying technology. China also introduced this technology in the 1980s. The earliest and 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.
Development Trend and Prospect of Heat Pump Dehumidification and Drying Technology
Refrigerant replacement
Since HCFC-based refrigerants such as R22, which are commonly used in heat pump circulation systems, have a destructive effect on the ozone layer and the global climate, the research work has mainly focused on the single-working substance replacement R134a, the mixed working substance replacement R407c, and non-destructive green environment. Study on Natural Work Medium (CO2) in Heat Pump Drying Circulation System.
Improve 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 suitable for heat pump drying, it is also a research hotspot to try to increase the drying temperature. 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.
Application of phase change heat storage material in heat pump drying
The phase change material paraffin having a phase change temperature of 50-52° C. is placed in the bypass line from the condenser to the drying chamber, and the part of the heat that is discharged after the drying unit reaches the desired drying temperature is recovered. The test result shows that Variable materials used in heat pump drying have obvious energy-saving effects. When the average temperature of 45.degree. C. material is 24.5%, the phase change material is placed, drying and energy saving is 21.9%, and when the drying temperature is 50.degree. C., the average quality of the dried material. When the percentage is 35.5%, the phase change material is placed to dry and save energy 36.5%.
Heat pump and other methods combined drying system
Both microwave and infrared drying penetrate into the surface of the material to heat the material three-dimensionally, forming a positive and negative temperature field within the temperature range (consistent with the direction of motion of the water discharge material), but it is not conducive to the surface of the material at low temperatures. The elimination of the set water vapor and the introduction of the heat pump can well solve this problem. The low-temperature dry air produced by the heat pump can rapidly take away the moisture on the material surface and also ensure the quality of the finished product. The heat pump type vacuum drying device utilizes the heat pump evaporator to condense the moisture 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. The 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. %between.
Automatic control
Drying is an unsteady heat and mass transfer process. During the drying process, the value of control parameters at each state point is adjusted to a large extent. 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 system adjustment accuracy and sensitivity. Therefore, the combination of modern detection, sensing, and control technologies in 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.
Tungsten carbide roller has characteristics of good wear resistance, high temperature red hardness, thermal fatigue resistance and thermal conductivity and high strength , have been widely used in high-speed wire rod, bar, rebar, seamless steel tubes, etc. Domestic production of tungsten carbide roller materials mostly WC- Co, WC- Co- Ni- Cr two series, and the content of Co, Co- Ni - Cr is in the range of 6wt% ~ 30wt%. From the use of perspective, tungsten carbide rollers has good mechanical properties, its flexural strength up to 2200 MPa or more, shock toughness up (4 ~ 6) × 10^6 J/ m^2, Rockwell hardness (HRA) is up to 78 to 90, widely in the high-speed wire rod rolling process, which is much higher than single-slot chilled cast steel or high speed steel rolls.Tungsten carbide is made of Tungsten Carbide Powder and binder phase (such as drilling, nickel, etc.), and then pressing and sintering, regardless of the conditions under cold rolled or hot rolled has excellent wear resistance, tungsten carbide rollers has been widely used in pre-finishing mill and finishing of high-speed wire rod currently. On the performance of tungsten carbide roller in hot-rolling wire rod , the material must meet the following requirements:
1. Sufficient anti-fracture strength;
2. Good abrasion resistance;
3. The smooth surface finish;
4. Excellent corrosion resistance, thermal fatigue, thermal cracking performance.
Tungsten carbide roller rings can working in bad conditions , small profile rolling (especially rebar rolling) process conditions is harsher than the high-speed wire rod, and therefore corresponds to the profile rolling ,tungsten carbide rollers recommend using high binder phase carbide.
Tungsten carbide roller material design
Pre-finishing all vehicles roller should ensure its high toughness, strength, rigidity and thermal conductivity, followed before considering its wear resistance. When designing each vehicles roller, pre-finishing materials should choose carbide grades of Co, Co- Ni- Cr binder content is high (greater than or equal to 25wt%) , requiring an average WC grain size of coarse (5μm ~ 6μm), to obtain a higher shock toughness, proper strength and hardness. For the finishing of the roller movements, particularly the last two rollers of the finish rolling, which suffered load is small, and high relative velocity of the material to be pressed (80 m / min ~ 120 m / min). In this case, the wear resistance of the roller to be the most important requirements, and must ensure the strength , timpact toughness and hardness of a reasonable match, so the binder of Co / Ni content ratio and the average grain WC control of particle size and other factors must have greater control in front of different pre-finishing rolling roll.
Tungsten carbide roller category
According to the structure of tungsten carbide rollers, it can be divided into solid tungsten carbide roller and composite tungsten carbide roller. Solid tungsten carbide rollers have been widely used in pre-finishing and finishing stands high speed wire rod mill (including fixed reducing the rack, pinch roller rack). Composite tungsten carbide roller is made of cemented carbide and other materials, and it can be divided into tungsten carbide composite roll rings and solid tungsten carbide composite roller. Tungsten carbide composite roll rings mounted on the roller shaft; solid tungsten carbide composite roller will be directly cast in the roll axis to form a whole, a large load is applied to the rolling mill.
Tungsten carbide roller production process control
Tungsten carbide rollers produced by powder metallurgy method, the key to its process control is the chemical composition of the material and the mixture was prepared, pressed molding, sintering and deep processing and other preparation process parameters.
1. Preparation of starting material (WC focus quality): As the WC raw material and quality control of the use of different levels of quality may fluctuate, resulting in adverse effects on microstructure.
2. Preparation of the mixture: Mixture preparation is the key to the production process of the roller, the roller of failure modes - trachoma, mainly generated by this procedure.
3. Pressing: roller pressing is an important process of the roller mill.
4. Sintering: roller sintering is to determine the final quality of the roller production processes, use of advanced low-pressure sintering technology, HIP sintering technology can greatly improve the performance of roller.
5. Deep processing: deep processing rollers have a greater impact on the quality and accuracy of the roller surface.
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