Pyrolysis of torrefied crop residue: Optimization using response surface methodology and benefits of bio-char in co-combustion with coal

Abstract

The present study includes optimizing process parameters using response surface methodology (RSM) for the pyrolysis of torrefied pigeon pea stalk to maximize its bio-oil yield. Substantial improvements have been observed in terms of calorific value (29–34% increase), water content (29–33% decrease), and oxygen content (9–12% decrease) for the bio-oil obtained from the pyrolysis of torrefied biomass compared to raw biomass. The results obtained in the present study indicate that the torrefaction of raw biomass could increase the effectiveness of hydrodeoxygenation (HDO) significantly. Hence, it could help achieve desired properties even in a single stage HDO compared to two stages HDO, leading to substantial cost reduction. Furthermore, bio-char from torrefied biomass has a better fuel ratio (FR), less particulate emission, and higher fuel value index (FVI) compared to bio-char from raw biomass and shows better compatibility with bituminous coal in co-combustion. Also, as much as 13.4% and 41.7% reduction in required fuel feed rate and ash production rate have been observed for 60% blending of bio-char with bituminous coal. The yield of pyrolytic gas decreased; however, on the qualitative front, the concentration of CH4 and H2 increased with CO2 being decreased significantly.