Densification, relaxation, and burning characteristics of rice straw and saw dust briquettes

Relationships between densification parameters and storage conditions on relaxation properties of briquettes were experimentally investigated. Densification of rice straw and saw dust was performed using a laboratory prototype densification apparatus operating in a uniaxial closed-die mode. Die diameters of 2.5 and 3.8 cm were used with die pressure ranging from 19-134 MPa. The expansion behavior of briquettes was studied in high and medium relative humidities. Rice straw briquettes showed 52-68% increase in length in the pressure range tested, which is 6-18% higher than for saw dust. Briquettes from the larger diameter die also showed 3-9% higher expansion compared to the smaller die. The change of moisture content of briquettes during storage delays the stabilization period and increases their expansion considerably. Combustion tests of briquettes were carried out in an isothermal thermogravimetric analyser. The burning rate of briquettes was found to compare favourably with wood. The main differences between wood and briquettes were found to be due to their difference in expansion during combustion and the anisotropic properties of wood. Rice straw and saw dust briquettes were found to increase in volume by almost 50% and 20%, respectively, during devolatilization. Analysis of quenched samples revealed that the devolatilization process in briquettes resembles that of thermally-thick wood.