Gasification of low-rank solid fuels with thermochemical energy recuperation for hydrogen production and power generation

The steam gasification of carbonaceous solid fuels allows thermochemical energy recuperation and chemical heat pumping that greatly improve the efficiencies of combined-cycle power generation and hydrogen production. These functions are realized in the practical gasification of the fuels by enhancing steam consumption and thermal energy utilization, while suppressing oxygen consumption, i.e., by using two-stage gasifiers (TSGs) that separate pyrolysis of the fuel and steam reforming/gasification of volatiles/ char from partial or full combustion of the residual char. Single-gas-flow and dual-gas-flow TSGs are best for converting low-rank fuels, such as biomass or lignite, using steam-oxygen and steam-air, respectively. There are requirements for maximizing the efficiencies of gasification with TSGs, such as fuel-to-gas conversion by pyrolysis and steam reforming/gasification above a certain level to balance the heat between the endothermic and exothermic sections (reactors), and the complete decomposition of tar without oxygen/air. The results of previous studies on biomass/lignite pyrolysis and the steam gasification/ reforming of tar/char show the potential TSGs. However, few of those studies have shown that TSGs can meet these requirements simultaneously. Therefore, more knowledge is needed to predict and control the fuel conversion characteristics in TSGs.