Chemical-looping combustion of raw syngas from biomass steam gasification – Coupled operation of two dual fluidized bed pilot plants

Product gas from a 100 kW fuel power dual fluidized bed (DFB) steam gasifier for solid biomass was used as fuel for chemical looping combustion in a continuously operated dual circulating fluidized bed (DCFB) 120 kW chemical looping combustion (CLC) pilot plant. The two pilot units were coupled through a hot product gas fan. Olivine was used as bed material in the gasifier and a synthetic oxygen carrier containing 9 wt% CuO was used as oxygen carrier in the CLC unit. Standard wood pellets with a water content of 6 wt% were used as primary fuel. In the gasifier, conditions were kept constant at 850 °C and a steam/fuel ratio of 1.6 kg/kg dry biomass. Two operating conditions were employed at 850 °C and 900 °C in the fuel reactor of the CLC unit. The composition was monitored with respect to CO, CO2, H2, and CH4 for product gas, fuel reactor exhaust gas and air reactor exhaust gas. Also, H2S and SO2 were measured in the product gas and CLC off gas streams. A product gas with 41.9 vol% (db) H2, 31.2 vol% (db) CO, 17 vol% (db) CO2, and 7.8 vol% (db) CH4 was obtained from the gasifier. While CH4 conversion in CLC was between 53% and 64%, almost full conversion of the CO and H2 contained in the product gas were achieved. The effect of temperature was significant only with respect to CH4 conversion. Analysis of particulate matter in product gas and CLC off gas streams indicate that fines contained in the product gas tend to pass through the CLC unit. No performance drop was evident during the experiment, which lasted for 10 h. It can be concluded that it is possible to couple two DFB systems in a robust way when using a high temperature fan and that biomass gasifier product gas can be effectively converted to CO2 and H2O in CLC using copper-based oxygen carriers.