Optimizing Energy Efficiency in Low Temperature Drying by Zeolite Adsorption and Process Integration

Drying is an energy intensive process, with low efficiencies, particularly at low drying temperatures required for heat-sensitive products. This work presents an energy efficient method for drying heat-sensitive products based on drying air dehumidification by zeolites and process integration. Two optimization approaches are considered: sequential and simultaneous. In the sequential approach, a zeolite adsorption dryer is optimized for energy efficiency, subject to product temperature and final moisture constraints using the zeolite, drying and regeneration air flowrates as well as the regeneration air inlet temperature as decision variables. Heat is then optimally recovered from the process exhaust streams using pinch analysis. In the simultaneous method, heat recovery is considered an integral part of the drying process and the entire system simultaneously optimized. Since the heat recovery stream properties are now unknown a priori, the pinch point is not unique but determined by optimization. The sequential and simultaneous methods reduce energy consumption by about 45 % and 55 % respectively, compared to a conventional convective dryer at the same drying temperature of 50 °C