Katsuhiko Yokohama

Novel Drying Process Based on Self-Heat Recuperation Technology

Significant amounts of energy are used in the conventional methods for drying wet carbonaceous materials such as biomass, low-rank coals, sludge, and manure, because the latent heat for evaporating water is large. An innovative drying process, based on self-heat recuperation technology that recovers not only latent heat but also sensible heat, was developed to save drying energy. Water contained in a wet sample is heated to its boiling point, and the resulting steam is superheated. The superheated steam is compressed to provide a temperature difference for heat exchange. The condensation heat of the compressed steam is exchanged with the evaporation heat of the water from the wet sample. The sensible heat of the compressed steam is utilized to raise the temperature of both evaporated steam (superheating) and water contained in the wet sample (preheating). In addition, the sensible heat of the dried sample is recovered by gas to improve the overall energy efficiency. The amount of energy required for the proposed system was determined using a commercial process simulation tool, PRO/II (v. 8.1, Invensys plc, London, UK). The proposed drying process based on self-heat recuperation was found to drastically reduce the energy consumption to 13.7% of the energy consumption of the conventional drying process with heat recovery.