THERMODYNAMIC ANALYSIS OF THE ENERGY SAVING POTENTIAL OF SUPERHEATED STEAM DRYING

There is potential for large energy saving by using superheated steam (SHS) drying instead of conventional air drying. SHS drying is operated in a recycle and purge mode, whereby a quantity of exhaust SHS equivalent to the water evaporated from the product is purged and the rest recycled. The energy saving potential is due partly to eliminating the need to heat from ambient temperature and partly to the ability to recover energy from the purged SHS. Energy can be obtained from the purged SHS by heat transfer to a process fluid, or by compressing a portion of the purged SHS to a pressure such that its’ latent heat of evaporation can be transferred to the recycled SHS in order to obtain dryer inlet SHS temperature. The thermodynamic analysis quantifies this energy saving potential, and evaluates the effect of process parameters, such as dryer inlet SHS temperature.