High quality, H2-rich syngas production from wood and miscanthus gasification in a novel stationary fluidized bed gasifier: An experimental investigation

Biomass will need to play a major role in the transition towards carbon neutrality in the energy sector. The conversion of biomass into syngas through gasification enables its usage in various applications including combined heat and power generation, production of sustainable hydrocarbon fuels and hydrogen generation. The compromise between producing syngas with both a high calorific value and low tar content remains challenging across various gasifier reactors. The rising co-current gasifier presents a novel reactor design that combines the advantages of the fixed and fluidized bed reactors in terms of the biomass conversion efficiency and quality of syngas produced. However, limited research has been conducted on this design, and its capabilities and limitations have not been characterised fully. This study presents an investigation of the performance of a rising co-current gasifier with two different feedstocks (wood and miscanthus pellets) over a range of operating conditions. The gasifier achieved an optimum balance between achieving a high magnitude of lower heating value (LHV) and a minimum tar content under different operating conditions. The LHV of syngas varied between 5.0 and 5.5 MJ/Nm3 for both materials, with the wood pellets achieving slightly higher values than the miscanthus. The equivalence ratio (ER) is estimated at 0.283–0.287 for wood pellets and at 0.319–0.339 for miscanthus. The gasifier achieved high cold gas efficiency (CGE) and carbon conversion efficiency (CCE), attaining maximum values of 83.1% and 98.0%, respectively. The H2 content in the syngas had a mean value of approximately 18%, with the H2/CO ratio in the range of 0.8–0.9. A minimum tar content of 14.7 mg/Nm3 of syngas was attained from the wood pellets at an air flow rate of 75 kg/h (ER = 0.285), while the maximum tar content of 163.5 mg/Nm3, was observed from the gasification of miscanthus pellets at a flow rate of 55 kg/h (ER = 0.319). It is worth highlighting that the gasification of miscanthus pellets imposed the additional challenge of bed agglomeration and the formation of channels in the bed, however fluidization at higher air flow rates can, at least in part, mitigate this problem.