Rice husk biomass torrefied without carrier gas: influence on physico-thermal properties as co-combusted renewable fuel

In the present investigation, rice husk biomass torrefaction was carried out in an electrically preheated rotating screw reactor without any carrier gas up to a temperature of 300 °C. The torrefied product is characterized by various properties. It is observed that volatile matter decreases, and fixed carbon increases with increasing torrefaction temperature. The calorific value increases from 15.27 to 19.16 MJ/kg and bulk density from 110 to 270 kg/m³ at temperature 300 °C. On pulverization of torrefied product, bulk density is improved to 550 kg/m³. The hard grove grindability index, which is an essential property of the biomass when used with the combination of subbituminous coal for co-firing, for rice husk is 15, and it was increased to 37 after the torrefaction at 300 °C. The burning profile of torrefied products suggests that reactivity reduces due to a change in the microstructure of rice husk. The combustion index of coal and RH280 (rice husk torrefied at 280 °C) was calculated as 7.1 × 10⁻⁸ and 10.6 × 10⁻⁸ mg²min⁻² C⁻³. The combustion index of coal blend with 10, 20, and 30% of RH280 is 7.14, 7.20, and 8.29 10⁻⁸ mg²min⁻² C⁻³. The increase in the combustion index of blend w.r.t. subbituminous coal is due to the lower ignition temperature of the torrefied product. The change in co-combustion properties is owing to mutual interaction between torrefied products and subbituminous coal.