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Difference between revisions of "Superheated Steam Dryers"
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=== | ==Process== | ||
Closed loop system | |||
===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. | 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 | ===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. | 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 | ===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. | 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 | ===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. | 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. | ||