Co-combustion properties of torrefied rice straw-sub-bituminous coal blend and its Hardgrove Grindability Index

Combustion behavior of rice straw torrefied at 300 °C for different residence time and their blends with sub-bituminous coal was investigated. The torrefied product and its blends were characterized for fuel properties and Hardgrove Grindability Index (HGI). Also, the torrefied product is characterized fordensity, proximate and ultimate analysis, energy yield, and structural analysis by Raman spectroscopy. The calorific value data of blend shows its value is equivalent to the value of sub-bituminous coal, i.e., 17.21 MJ/kg. On the other hand, HGI of torrefied product is 40–45 and that of coal is 80. On blending, the value of HGI up to a certain ratio shows the synergetic effect while higher content of the torrefied product in blend demonstrated non-additivity behavior and it is dominated by coal as a consequence of density difference between torrefied product and coal. Characteristic combustion parameter for blends reveals the synergetic behavior. It is found that the blend of torrefied products and sub-bituminous coal at a ratio of 10:90 and 20:80 had ignition and burnout temperature almost close to coal sample. The ignition and burnout temperature of 10:90 of torrefied product at 300 °C for 60 and 120 min are 295 °C and 507 °C, 301 °C and 505 °C whereas that of sub-bituminous coal is 325 and 515 °C. The change in the fuel properties of the blend suggests there is a certain degree of interaction that occurred during combustion.