Chemical looping gasification of biomass char using iron ore as an oxygen carrier

Chemical looping gasification (CLG), employing the oxygen carriers to replace the gasification agents for solid fuels gasification, is viewed as a promising gasification technology thanks to its low cost for producing high quality synthesis gas. In the present work, natural iron ore is applied as an oxygen carrier for CLG of biomass char in a fixed-bed reactor. The Redox reactions between biomass char and iron ore can occur even under inert atmosphere, but the char conversion is low due to inadequate contact of solid-solid phases, resulting in a low reaction rate. In order to improve the char conversion rate, mixture of steam and iron ore is used as gasification agent in the CLG of biomass char. An optimal mass ratio of oxygen carrier to biomass char and a suitable amount of steam addition are determined. It is observed that biomass char gasification with the mixture of iron ore and steam increases the carbon conversion by 80%, and attains three times gas yield as much as the char gasification with individual iron ore. The cyclic performance of iron ore is also discussed. The carbon conversion and gas yield shows a mild downtrend with the increase of cycle numbers due to a slight decrease of specific surface area of oxygen carrier, caused by the thermal sintering and ash deposition. However, iron ore still maintains a satisfactory reactivity after 20 cycles (∼52 h), indicating that it is a good oxygen carrier candidate for char gasification.