DRYING WITH SUPERHEATED STEAM

摘要

The principle of drying with superheated steam is known for a long time already, and differentrndesigns have been worked out and partly realised. The principle of the steam drying describedrnin this paper starts with superheated steam that is blown on to the products to be dried. Thernsuperheated steam transfers its sensible heat to the product and the water to be evaporated.rnThe superheated steam acts both as heat source and as drying medium to take away thernevaporated water. The majority of the superheated steam has to be recirculated and reheated.rnThe excess steam from this process, corresponding to the evaporated water, can be usedrnelsewhere in the process or plant, thus making an efficient energy recovery possible. Possiblernemissions from the drying process can be effectively removed by condensation.rnDrying by means of superheated steam impingement is one of the possible designs that is inrnprogress now for the paper industry. Work is going on with respect to this type of drying forrnother materials, especially food stuffs. At present experimental research at the laboratoryrnsteam dryer of TNO-MEP is carried out for vegetables, fries, herbs, etc.rnBesides the energy savings and environmental benefits, the oxygen free steam atmosphere andrnthe higher product temperatures in the dryer appear to have positive effects on the productrnqualities.rnModelling of the processes in food stuffs during steam drying is established, both on macrornand micro scale. In this paper examples and results of research on steam drying for specificrnproducts will be presented.