Torrefied fuel pellets from solid waste of sugar industry

The preparation of fuel pellets from the filter cake waste from the sugar industry was studied. Pelletization by a hydraulic press at a pressure of 20 to 50 bar (2 to 5 MPa) was used to produce fuel pellets with a diameter of 1 cm and height of 1. 25 cm. Energy efficiency of the resulting pellets was improved by thermal treatment called “torrefaction”. During this process, the samples were heated to between 200 and 300°C for 0.5 to 2 h under a nitrogen atmosphere. The properties of fuel pellets including calorific value, bulk density, pellet density, proximate analysis, and compressive strength were characterized. The results demonstrated that the minimum pressure needed to produce the pellets without binder was 30 bar. The calorific value was between 13,954–14,468 kJ/ kg for the resulting fuel pellet, which was significantly higher than that of the unpelletized raw material (11,197 kJ/ kg). The fuel pellets had bulk density and pellet density of between 300–440 kg/m3 and 720–890 kg/m3, respectively. Increasing the time and temperature of torrefaction resulted in the lower yields of pellets. Fuel pellets maintain their shape and did not break under the applied torrefaction conditions. Torrefied pellets resulted in higher calorific value of 16,552–22,642 kJ/kg, higher carbon content, lower pellet and bulk densities compared to the fuel pellet without thermal treatment. The compressive strength of torrefied pellets decreased due to the delicate nature of the sample. The suggested conditions for optimal torrefied pellet in thermal and physical properties are 300°C and 1 h. The prepared fuel pellets showed comparable heating values to other fuels, and had properties in agreement with Thailand standards. Therefore, filter cake as a solid waste from production process of sugar has potential as raw material for the production of solid fuel pellets.