Abstract
Waste mixture of food and plastics is one of the most refractory wastes, because conventional recycling techniques require the separation of the waste into each group before treatment. In this work, new recycling technique was developed to produce an excellent composite fuel using subcritical water. The waste mixture was agitated with sawdust as a plastic dispersed material in subcritical water at 200 °C and 1.6 MPa for 30 min, and the composite fuel particles with less than 20 mm in size were produced. The fuel had a high heating value close to that of coal and the fixed carbon ratio was 93 %. The fuel was dried in a short time of one third of conventional drying period. This was because a part of the surface tissue and cell wall of the biomass was decomposed by subcritical water and water inside the biomass was evaporated easily. The roles of subcritical water were the stabilization of the dispersed melting plastic particles, the removal of toxic elements such as chlorine and sulfur, and the saving of drying energy and the realization of high energy efficiency more than 4.When the composite fuel was pressed into pellet, the pellet fuel ignited easily and burned in a biomass stove stably for long time. The concentrations of the toxic compounds in the combustion gas were far below the emission standard of small boiler. The composite fuel was demonstrated to be safe and clean.
