Superheated Steam Dryers
Superheated Steam Drying is an environmental and energy saving drying technology.
Process
Closed loop system
The Superheated dryer is a closed loop pneumatic conveying type. The wet solids are fed into the flow of pressurised superheated transport steam by means of a pressure tight rotary valve, plug screw or similar.
Indirect heating
The transport steam is superheated indirectly via a tubular heat exchanger, by a heating media such as medium pressure steam, flue gases or thermal oil. Also, electrical heating can be applied.
Fast drying
In the subsequent drying ducts, moisture is vapourized from the product, forming excess transport steam and lowering its degree of superheat. Normally the residence time in the system is 5-60 seconds only. For some materials a second superheater is necessary to achieve the required dryness.
Energy recovery
Primary consumption is about 750 kWh/ton evaporated water without any heat recovery. 70-90% of the energy is recoverable by re-using generated steam in another process, for heating purposes, or by using Mechanical Vapour Recompression. With a condensing turbine the generated steam can produce about 200 kWh electricity per ton evaporated water.