The heating method of the vacuum belt dryer can be roughly divided into four types: heat transfer oil circulation heating, steam direct heating, hot water circulation heating and superheated water circulation heating.

Direct steam heating is currently the most widely used heating method, and is used by most manufacturers at home and abroad. In recent years, through continuous exploration and research, the direct steam heating technology of the vacuum belt dryer has made great progress, both in terms of temperature stability and utilization of heat energy.

The steam direct heating method also has the characteristics of large heating temperature range, generally can be controlled between 45 and 125 ° C. If the temperature continues to increase, it is not impossible, but the current domestic processing level seems to have a large manufacturing of the heating plate. Difficulties and risks. On the other hand, the steam pressure of the equipment used is not too high, and the maximum temperature can reach 125 ° C, which basically meets the requirements of most users.

Direct steam heating is faster than the other three heating methods, which can shorten the preparation time before production. Secondly, this heating method has fewer external components, small space, simple structure, and is convenient for maintenance, overhaul and maintenance.

Despite a lot of efforts by the manufacturers, the direct steam heating method is still the worst performing of the four methods in terms of temperature accuracy control. This is because it belongs to the gaseous heat medium and the pressure control. There are too many uncertainties involved. In the production process, steam-heated vacuum belt dryers often experience transient temperature rises and dips, which are difficult to accept for materials with strict heating temperature requirements or appearance color requirements.

Another disadvantage of direct steam heating is the problem of temperature difference and efficiency. Since the whole heating principle is a process from gas to condensate, the vector release caused by molecular activity is inevitable. This phenomenon will form on the heating plate and the pipe wall. The impact causes high-frequency continuous vibration, so that the track and the heating plate are always in incomplete contact state. Since the thermal conductivity is too low under vacuum conditions, the difference between the actual temperature of the heating plate and the surface temperature of the dried material is compared. Large, this is also the main reason for the low evaporation of steam heating equipment, especially for some large-scale multi-layer drying equipment, the temperature difference between the bottom layer and the top layer is more obvious, so the drying bed from top to bottom The amount of material can only be reduced in turn, otherwise it is difficult to ensure the uniform quality of the product, and the uniformity of the quality of the dried product caused by the temperature difference is relatively taboo for the user. Therefore, in the actual production, only the method of ensuring the quality to give up the capacity can be adopted.

In addition to the above mentioned cases, in recent years, some manufacturers have also made structural improvements to the steam direct type vacuum belt dryer. For example, the condensate waste heat from the steam conversion in the previous stage is distributed to the middle and the back stage to achieve the purpose of energy saving and emission reduction, but this can only be said to be a single design for some specific users. After all, there is a greater temperature difference in condensed water reuse. The problem, and the temperature distribution of the three-stage heating section is also limited, so it is not possible to use a point profile.