Combustion Characteristics of Husk Charcoal

Abstract

The authors developed a new device for the purpose of studying the combustion of various husk charcoal and experiments were conducted to obtain the relations between combustion and specific air flow rate G. The results were as follows.
1. Maximum combustion temperature T_p was related to specific air flow rate G. The value for T_p yielded the highest value of 1350°C when G was 0.56Nm³/min. kg. In order to decrease the value for T_p, in was required that the vales for G was sufficiently smaller than 0.56Nm³/min. kg. The suction aeration was the most recommended method to realize such condition.
2. The value for T_p was hardly related to the carbon ratio φ of the husk charcoal. The values T_p for moistened materials became slightly smaller than those of dried materials. The critical specific air flow rates G_p were nearly equal to 0.56Nm³/min kg for all experimental conditions.
3. Combustion propagation velocity was expressed as a power function of specific air flow rate G. Theoretical flame temperatures T_th which were calculated for boundless bed had a linear correlation to specific air flow rates G. If the specific air flow rate G increased. the steep increase was shown for both combustion propagation velocity V_f and maximum combustion temperature T_p, which might give an explosive combustion and a dangerously high temperature.
4. An exponential correlation was observed between theoretial excess air ratio m calculated from eq. (2) and specific air flow rate G. The values for m considering boundless bed approached 1.0 asymptotically, while more practical values for M_th which were calculated from using θ_f′ instead of θ_f in Fig. 2 took the value 2.0. When m took the value 1.0, the calculated value for T_th was 2550°C.
5. Theoretical flame temperature T_th′ was determined from the combustion propagation velocity V_f′ which was obtained by more practical combustion time θ_f′ The relation between the theoretical flame temperature T_th and the specific air flow rate G was similar to the relation between the observed maximum temperature T_p and the specific air flow rate G.
6. The deviations of V_f from the regression curve had a slight positive correlation as to the bulk densities ρ of the husk charcoal. So the bulk density ρ did not have a significant effect on the combustion characteristics of husk charcoal.