Analysis of Drying Characteristics and Cost of High-Capacity Vacuum-Drying Food Waste Disposal System Using Steam

Purpose This study was conducted to develop a high-capacity vacuum-drying food waste disposal system that uses steam and to identify its drying characteristics and cost through an experiment. Methods A drying system with a drying capacity of 10,000 kg/h was fabricated that used the steam generated by a boiler as a drying heat source. Its performance was verified, and the drying cost was analyzed through a drying experiment in which water and mixtures (sawdust, flour, and water) were used as experimental materials. Results The results of the drying experiment showed that the input steam temperature was 193.2 °C, and that the average drying speeds were 19.65%/h for water and 3.89%/h for the mixtures. The drying speed increased as the drying progressed, and it reached a moisture content of 20% (wb) or less after drying without a drying delay caused by moisture condensation. The drying energy rate that represents the ratio of the drying energy consumption to the input energy was as high as 88.90% for water and 99.23% for the mixtures, on average. The total drying time was 5.5 h for water and 18.5 h for the mixtures on average, which were significantly shorter compared with that of the hot-air drying method. Conclusions The drying speed, water content after drying, drying energy rate, and total drying time were significantly improved compared with those of the case of converting steam to hot air when the boiler steam was directly used as a drying heat source for the disposal of large-volume food waste with high water content. The drying cost was also not significantly different from that of the methods that use electricity or gas as a heat source, indicating that the developed system can be used for the disposal of large volumes of food waste.