Effects Of Bio-asphalt And Hydrothermal Carbonization On Sawdust Pelletization And Fuel Qualities

The short of raw material, high energy consumption and poor qualities have been the problems that stunt the development of pellet fuel industry. In our research, waste biomass(camphor wood and Chinese fir) were choosed as materials and two different pretreatment processes were applied to make the feedstock of pellet fuel.(1) The addition of different mass ratio of bio-asphalt.(2) Under different subcritical conditions for hydrothermal carbonization. The blends of bio-asphalt and sawdust, hydrothermal biochars were further compacted into pellets. The main objective of the present study is to identify the influence of two pretreatment processes on energy consumption for compaction and extrusion, density, Meyer hardness, moisture uptake and combustion characteristics of pellet fuel. Results are as follows:1) Energy consumption of compaction is decreased with increasing bio-asphalt dosage. When adding 20wt% bio-asphalt, Energy consumption of compaction reduced by 44%. While a marked decrement of extrucion energy consumption were obtained in the range of 0-5% and extrucion energy consumption of pellet reduced by 39%~73%. While increasing dosage of bio-asphalt(>5%) further has little effect on energy consumption of extrucion. When adding 5wt% bio-asphalt, The maximum densities of pellets were also obtained around bio-asphalt dosage of 5%. The maximum densities of pellets produced from camphor wood and Chinese fir were 1130 kg/m3 and 1150 kg/m3 respectively. In the temperature of 30 ℃, relative humidity of 90% environment, the moisture uptake of pellet was decreased with the increment of bio-asphalt dosage from 0% to 20%, and the equilibrium moisture absorption content of pellet produced from camphor wood and Chinese fir were reduced by 13.14% and 8.33% respectively. While the higher heating value of pellet was identified as an opposite trend. Furthermore, pellet fuel’s ignition temperature can be reduced with the addition of bio-asphalt, which can improve the stability and continuity of pellet’s combustion.2) Pellets made from HTC biochar have higher energy consumption of compaction and extrusion, higher pellet density, Meyer hardness and hydrophobicity property compared to their raw materials. In addition, mass density, Meyer hardness and hydrophobicity of HTC biochar pellets increased with increasing HTC temperature. While mass density of pellets increased with increasing HTC temperature firstly from 200 ℃ to 240 ℃ and then decreased at 260 ℃. The maximum densities of pellets produced from camphor biochars and Chinese fir biochars were 1274 kg/m3 and 1213 kg/m3 respectively. After 260 ℃ hydrothermal carbonization of sawdust, The Meyer hardness of hydrochar pellets were 3.1~5.5 times of pellets produced from raw sawdust, and the equilibrium moisture absorption content of hydrochar pellets were decreased 66.3%~70.2% compared to pellets produced from raw sawdust. The hydrochar pellets combusted at elevated temperatures and wide temperature ranges compared to biomass pellets. The present study demonstrated that hydrothermal carbonization(HTC) combined with pelletization provides an alternative for solid bio-fuel production from biomass resources, especially for the abundant agricultural residues.