Torrefaction of wheat stubble into pellets for solid biofuels
The high domestic consumption of firewood produces a high level of pollution, producing wheat stubble. The habitual practice of burning wheat stubble also contributes to this pollution.
Wheat stubble biomass has an irregular size, low density and low calorific value, among others. By means of a torrefaction process (thermal process carried out at moderate temperatures in an inert environment), a significant increase in retained energy and calorific value was obtained at moderate operating conditions below 150ºC.
Wood biomass is a fuel widely used for domestic heating. This high consumption of wood directly affects air pollution and usually people are exposed to concentrations of Particulate Matter below 2.5 µm (PM2.5) above 20 mg/m3. Some countries are currently investing in the generation of pellets as an alternative to forest biomass, as wheat stubble can be abundant. Moreover, the usual practice for eliminating this stubble is burning, which generates a great environmental impact. Despite the unpromising characteristics of this biomass (irregular size, low density, low calorific value, among others), the Universidad de la Frontera has optimised a torrefaction process (a thermal process carried out at moderate temperatures in an inert environment) to generate pellets from wheat stubble. The pellet (black pellet) produced at pilot scale with this torrefied biomass was characterised according to the European standard ISO 17225-1 (2014). An increase in bulk density from 469 kg/m3 to 568 kg/m3 was achieved due to the torrefaction pre-treatment.
Market deployment considerations