Co-pyrolysis of low-grade bituminous coal and algal biomass in a rotary kiln: Effect of coal/algae ratio and kiln temperature on the yield and composition of the resultant oils

Abstract

Co-use of coal with biomass does not only help reduce the carbon footprint from coal-based energy generating systems but also creates opportunities of improving the synthesis of liquid fuels and valuable chemicals via simple pyrolysis processes. Co-pyrolysis of a low-grade coal and algal biomass was performed in a rotary kiln with the aim of assessing the effect of coal/algae blending ratio and kiln temperature on the yield and composition of the resultant oils. Current industrial continuous pyrolysis units operate at intermediate pyrolysis heating rates, as such, the rotary kiln used in this study operated in the heating rates range of 100 – 500 ᵒC/min. For a given reactor temperature, the yield of pyrolysis oil increased with an increase in algae loading. For example, at 550 ᵒC, the yields from coal, coal/algae (90/10), coal/algae (80/20), coal/algae (60/40) and pure algae were 6.9%, 9.6%, 15.1%, 16.3% and 40%, respectively. The oil synthesised from coal contained a high proportion of paraffins. On the other hand, the oil synthesised from algal biomass contained a high proportion of fatty acid esters (28.8 – 32.6%) and alcohols (17.6 – 20.8%). The oil synthesised from coal-algae blends contained compounds found in both coal and algae oils with an increased proportion of PAH and PANHs. It was found that for pyrolysis of all samples, an increase in the reactor temperature resulted in an increase in concentration of PAH and PANHs.