Infrared drying
Another method of drying the micelles is an infrared drying process. In convection heating, the thermal conductivity between the gas and the colloidal particles, between the colloidal particles and the colloidal particles, and within the colloidal particles is very low, so the heat conduction is greatly limited. With infrared drying, because the molecules are exposed to infrared radiation, the absorbed energy is directly converted into thermal vibration, which means that the heating of the material is faster than in convective drying. In contrast to convection heating, infrared drying has an inverse temperature gradient in addition to the partial pressure difference between the ambient air and the moisture in the colloidal particles during the drying process. In general, the greater the temperature difference between the drying gas and the heated particles, the faster the drying process. Infrared drying time is usually 5min ~ 15min. At present, the infrared drying process has been designed as a turn-to-tube mode, that is, following a rotating tube with a threaded inner wall, the rubber particles are transported and circulated, and there are several infrared heaters in the central section of the rotating tube. In infrared drying, the power of the device can be selected with reference to the standard of 0.035 kWh/kg?0.105 kWh/kg.
As mentioned before, the difference in material moisture content will result in a difference in process parameters. In general, the difference in residual moisture content may be due to the different flow rate of different materials, so the interruption of the drying process or the startup or shutdown of the machine will cause different residence time. In the case of a fixed gas flow rate, the difference in the amount of material flow is generally represented by changes in the temperature profile and changes in the exhaust gas temperature. The dryer manufacturers measure in different ways and match the flow rate of the drying gas with the amount of material to be dried, thereby adjusting the temperature profile of the drying hopper so that the gel undergoes a stable residence time at the drying temperature.
In addition, the different initial moisture content of the material can also lead to instability of the residual moisture content. Because the residence time is fixed, a significant change in the initial moisture content will necessarily result in the same significant change in residual moisture content. If a stable residual moisture content is required, the initial or residual moisture content needs to be measured. Because the relevant residual moisture content is low, on-line measurement is not easy to perform, and the residence time of the material in the drying system is longer. Treating the residual moisture content as an output signal will cause system control problems, so the dryer manufacturers have developed a A new concept of control can achieve the goal of stable residual moisture content. This control concept aims at maintaining the stability of the residual water content, and uses the initial moisture content of the plastic, the dew point of the incoming and outgoing gas, the gas flow amount, and the rubber circulation rate as input variables, so that the drying system can be The differences in these variables are adjusted in time to maintain a stable residual moisture content.
Infrared drying and vacuum drying are new technologies in plastics processing. The application of these new technologies has greatly shortened the residence time of materials and reduced energy consumption. However, the innovative drying process is also relatively expensive. Therefore, in recent years, people are also working hard to increase the efficiency of traditional dehumidification gas drying. Therefore, in making investment decisions, accurate cost assessments should be conducted, not only to consider procurement costs, but also to consider piping, energy, space, maintenance, etc., in order to maximize the return on the smallest investment.