Biomass chemical looping gasification for syngas production using ilmenite as oxygen carrier in a 1.5 kWth unit

Abstract

Biomass Chemical Looping Gasification, BCLG, is a promising technology that uses lattice oxygen instead of expensive gaseous oxygen for high quality syngas production without CO2 emissions. In this work, 55 h of continuous operation in a 1.5 kWth BCLG unit using ilmenite as oxygen carrier and pine wood as fuel is reported. A new method for controlling the oxygen used in the syngas production through the control of the oxygen fed into the air reactor was used by first time in BCLG with satisfactory results. This method allows analysing the isolated effect of each one of the operating conditions: gasification temperature, TFR, steam-to-biomass ratio, S/B, and oxygen-to-biomass ratio, λ. This last parameter, λ, was the main factor affecting syngas production efficiency. Considering the high unconverted hydrocarbons usually obtained, a product gas composed by 37–40 % CO2; 27–30% H2; 17–21% CO; 10–12% CH4; and 2–3% C2-C3 with a syngas yield of 0.65 Nm3/kg dry biomass could be obtained for autothermal conditions. Tar generation was in the range 1.4–3.0 g/kg dry biomass (1–2.5 g/Nm3 d.b.), being lower than that reported by other gasification technologies. Despite its high reduction state in BCLG, ilmenite exhibited a good behaviour since remained with high reactivity during operation and no agglomeration problems were produced. However, outward migration of Fe observed in ilmenite decreased lifetime by a half during CLG operation in relation to chemical looping combustion conditions.