Intensified gasification of fuel cane bagasse for power production using solid oxide fuel cells

Abstract

Gasification of fuel cane bagasse the waste residue from an energy crop known as Fuel Cane was carried out in an intensified 50 kWe air-blown downdraft gasifier. The main objective of this study was to evaluate the feasibility of fuelling solid oxide fuel cells (SOFCs) with the syngas generated during gasification of this feedstock. Optimal operation of the gasifier system was evaluated in terms of syngas heating value, syngas yield, equivalence ratio, stability of gasifier operating zones and cold gas efficiency. Mass balances were calculated to examine the reliability of the results generated. Contaminants in syngas were investigated to assess the possible impact of the syngas produced on the SOFC system. The effect of CaO as a primary measure and sulphonated PolyHIPE polymer (PHP) as a novel secondary treatment process on tar production and conversion during gasification were investigated. Optimal gasification occurred at an equivalence ratio of 0.26 producing syngas with a heating value of 5.7 ± 0.6 MJ Nm-3 and syngas yield of 3.2-3.9 Nm3 kg-1. The air/fuel ratio was 1.17 Nm3 kg-1 (dry basis), cold gas efficiency 77-85 % and mass balances closures ranged from 92-94 %. Increasing the moisture content in the lower oxidation zone increased H2 production generating a medium heating value syngas suitable for power, liquid fuels and chemicals production. Tar concentration in the syngas was 621 ± 11 mg Nm-3 of which Class 1 tars comprised 3 %, the remainder was dominated by Class 2 and 5 tars. In-bed 6 wt% CaO reduced the tar yield by 35 %, increased the syngas yield by 37 % and reduced the tar dew point to 30-32 oC whereas sulphonated PHP had no effect on syngas yield but reduced the tar yield by 77 % and the tar dew point to 72.6 oC. Chemical fractionation studies showed that 30 % of the K released to the syngas was ‗captured‘ by aluminosilicates in the feedstock and retained in the ash. Potassium, HCl and H2S concentrations in the gas phase were 371 ± 62 mg m-3, 27 ± 8 mg m-3 and 40 ± 7 ppmv respectively. It is evident therefore that syngas from fuel cane bagasse can be used to power SOFCs, however a high potential for fouling of the SOFC anodes exist. Therefore a combination of primary and secondary syngas treatment systems for removal of Class 1, 2 and 5 tars as well as alkali metal sorbents will be essential for commercial operation of fuel cane bagasse fuelled SOFCs.