Reducing energy consumption in food drying: opportunities in desiccant adsorption and other dehumidification strategies

摘要

Drying is an energy intensive operation, accounting for about 15% of industrial energy consumption. Inaddition, the achievement of desired quality levels is of paramount importance in food drying. For a givendryer design, drying at high temperatures is the standard way of improving efficiency, but at the expense ofproduct quality. By dehumidifying the drying air, the capacity for moisture removal and hence, energyefficiency can be increased while drying at low temperatures. In refrigerant based systems, dehumidificationwould lead to loss of sensible heat in the drying air on the evaporator side coupled with the need to pump therefrigerant from the low temperature (evaporator) to the high temperature (condenser) sides. In desiccantbased systems, regeneration is required. Both processes involve energy expenditure. In this work, anassessment is made of the dehumidification drying techniques, vis-à-vis conventional convective drying interms of energy efficiency. Mathematical models are developed by means of which the energy efficiencies ofdifferent types of dehumidification dryers are expressed in terms of the efficiency of a conventionalconvective dryer operating at the same temperature. This permits the isolation of important design andoperational parameters specific to each dryer type which when optimized will improve energy efficiency forthe same product quality requirement and ensure better product quality while operating at the same energyefficiency as a conventional dryer. Desiccant dehumidification systems in particular have the addedadvantage of providing further opportunities for beneficial heat integration.