Carbonization temperature and time improving quality of charcoal briquettes

Abstract: Energy crisis and environmental pollution make it attractive to find an environmentally friendly and renewable energy source to substitute fossil fuels. Charcoal briquettes produced from sawdust densified fuels by carbonization, which are often applied in barbecue field, can not only meet the demands of energy but also protect forest resources and maintain the ecological balance. Properties of charcoal powder were reported to be influenced by carbonization conditions such as temperature, heating rate and residence time, while the studies on those of charcoal briquettes were rare, especially the mechanical behavior and combustion performance. Cedarwood sawdust was used to produce high density, virgate briquette by using spiral pipe hot extrusion equipment. The parameters of briquette: screenshot size was 60 mm ×60 mm, and the length was 60 mm, the hole diameter was 22 mm, the average density was 1.24 g/m3, average mass was 240 g. In order to prepare charcoal briquettes with good transportation and combustion performances, Chinese fir sawdust briquettes were carbonized at the temperature of 400, 450, 500, 550 and 600℃, heating rate of 2, 6 and 10℃/min, and residence time of 60, 120 and 180 min, respectively. The effects of temperature, heating rate and residence time on the compression resistance, shatter resistance, calorific value, and ash content of charcoal briquettes were investigated. Results showed that with the carbonization temperature increasing, the yield of charcoal briquettes decreased from 37.33% at 400℃ to 29.62% at 600℃, whereas the calorific value slightly increased from 26.40 MJ/kg at 400℃ to 31.04 MJ/kg at 550℃. Charcoal briquettes appeared to have a high calorific value at the temperature of 550℃ as well as a relatively good property in compression resistance (143.7 kPa) and shatter resistance. The compression resistance and shatter resistance were significantly improved with the decrease of heating rate. Compression resistance reached the maximum value of 439.8 kPa and crack occurred rarely on the surface of charcoal briquettes at heating rate of 2℃/min as well as the best shatter resistance. A residence time of 120 min could be the better choice, for it exhibited the least ash content of 6.27%, the highest fixed carbon content of 69.08%, the highest calorific value of 29.63 MJ/kg and the highest compression resistance of 192.1 kPa, respectively. These results can supply some technical support for the production of good quality charcoal briquettes.