适宜炭化温度及时间改善生物质成型炭品质

Carbonization temperature and time improving quality of charcoal briquettes

为制备品质特性较佳的成型炭块,对螺杆挤出的生物质高密度成型燃料进行炭化,试验研究了炭化温度(400、450、500、550和600℃)、升温速率(2、6和10℃/min)和保持时间(60、120和180 min)对成型炭块的工业分析成分、热值和力学强度等品质指标的影响。随着炭化温度的提高,成型炭块的炭得率、挥发分含量降低,固定碳含量提高,热值增大;炭化温度550℃时热值达到最大值,为31.04 MJ/kg,抗压强度和抗跌碎强度均较好。升温速率对成型炭块的力学性能影响较大,升温速率越小,抗压强度越大;升温速率为2℃/min时,成型炭块表面裂纹少,抗压强度达最大值,为439.8 k Pa;相应地,抗跌碎强度亦较佳,为95.5%。保持时间为120 min时成型炭块具有较高的热值29.63 MJ/kg,较大的抗压强度192.1 k Pa和较好的抗跌碎强度96.7%,过长或过短的保持时间都不利于成型炭块品质的提升。

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.