Hot air drying equipment for bulk materials, especially plastic granules, includes valves controlling air flow recirculated between drying chamber and drying agent chamber

摘要

Two three-way valves (11, 19) are used to control the recirculated air flow. These connect the drying air blower (9) pressure side to the input side (13) of the drying heater, via a bypass line (29). With the drying agent chamber (14), the regeneration air blower (34) forms an independent regeneration circuit with fresh air supply. One valve (11) is located in the pressure line (10) between the pressure side of the drying air blower (9) and the air supply side (13) of the drying agent chamber (14). The other valve (19) is located between the outlet side (18) of the drying agent chamber (14) and the inlet side of the drying heater (23). In one position, the valves (11, 19) interrupt the air supply to the drying agent chamber (14) and the connection between the drying agent chamber and the inlet side of the drying heater (23). They simultaneously form a connection between the pressure side of the drying air blower (9) and the inlet side of the drying heater (23). In the other position, air supply from the drying air blower is sent to the inlet of the drying agent chamber and the connection between this chamber and the inlet side of the drying heater is opened. Simultaneously, direct connection between the pressure side of the drying air blower and the inlet side of the drying air heater is interrupted. In this position, the fresh air supply through the regeneration blower is interrupted. Further details of the valving and pipework are provided, in accordance with the foregoing principles. Temperature sensors are provided to control the process. Salient features include impulse modulation of DC motors to control the drying air quantity and minimize frictional heating in the blower. A controlled cooling phase is employed. When heating the drying agent, the temperature is limited to below 360[deg] C. The air blower is also used for pneumatic conveying, to transfer bulk material into the drying vessel. One drying agent chamber is able to remove moisture from several drying vessels. An independent claim IS INCLUDED FOR the corresponding method of drying.