Energy and exergy analysis for torrefaction of pigeon pea stalk (cajanus cajan) and eucalyptus (eucalyptus tereticornis)

Abstract

Torrefaction of pigeon pea stalk and eucalyptus have been carried out in a tubular quartz reactor at a temperature range of 200–300 °C with constant residence time and heating rate under nitrogen atmosphere. Under moderate torrefaction (250 °C) solid yield for both types of biomass have been in the range of 63–64% with byproducts in the range of 19–29% (liquid) and 8–18% non-condensable gases (NCG). Maximum increase in HHV for pigeon pea stalk and eucalyptus have been 45.4 and 39.8%, respectively. HHV and water content of liquid product have been in the range of 7620–11200 kJ/kg and 52.8–83.5 wt%, respectively. NCG mainly consisted of CO2 and CO with former decreasing with increase in temperature. Energy and exergy value of solid product decreased while for NCG and liquid increased with increase in temperature. Energy and exergy value of solid have been highest followed by liquid and then NCG. CO has been the main contributor in the total energy and exergy of NCG. Exergy efficiency of solid product has been in the range of 52–54% under moderate torrefaction. Irreversibility increased with increase in temperature. Recuperation of energy from byproducts (liquid and NCG) could increase the energy recovery in solid by 8–9%.