Experiments on biomass gasification using chemical looping with nickel-based oxygen carrier in a 25 kWth reactor

•A new 25 kWth prototype was made in this study.•NiO was selected as oxygen carrier in the new prototype.•Gasification temperature, steam-to-biomass ratio and NiO content were investigated.•CaO-decorated NiO/Al2O3 was tested to produce high quality syngas.

Biomass gasification using chemical looping (BGCL) is an innovative biomass gasification technology, which utilizes lattice oxygen from oxygen carrier instead of molecular oxygen from air. This work attempted to investigate the BGCL performance with nickel-based oxygen carrier in a 25 kWth reactor. The new prototype is composed of a high velocity fluidized bed as an air reactor, a cyclone, a bubbling fluidized bed as a fuel reactor, and a loop-seal. At first, the major reactions in the process were presented and chemical reaction thermodynamics in the fuel reactor was analyzed. The NiO/Al2O3 oxygen carrier was then applied in the reactor. Different variables, such as gasification temperature, steam-to-biomass (S/B) ratio and NiO content, were analyzed. The carbon conversion efficiency increased smoothly within the temperature range of 650–850 °C, while the syngas yield reached the maximum of 0.33 Nm3kg−1 at 750 °C. Additionally, based on the tradeoff between carbon conversion efficiency and syngas yield, it was concluded that 30 wt.% was the optimal NiO content. Besides, in order to get high quality syngas with low CO2 emission, CaO-decorated NiO/Al2O3 oxygen carrier was investigated. Experimental results showed that the addition of CaO enhanced the biomass gasification process and increased the syngas yield.