Chemical Looping Combustion of different types of biomass in a 0.5 kWth unit

•40 h of biomass combustion accomplished in a 0.5 kWth CLC unit.•Pine, olive stone and almond shell were used as fuel.•100% CO2 capture without carbon stripper was achieved.•Total oxygen demand was 25-30%, mostly generated by unburned volatiles.•Tar contribution to the total oxygen demand was estimated as 1 percentage point.

Chemical Looping Combustion (CLC) using renewable solid fuels appears as an important option to reach negative carbon emissions. In this work, three types of forest and agricultural residues (pine sawdust, olive stone and almond shell) were tested between 900-980 °C in a 0.5 kWth unit with an iron ore as oxygen carrier (Tierga ore) working under In situ Gasification-Chemical Looping Combustion (iG-CLC) mode. Specific solids inventories lower than 1000 kg/MWth were tested as they were consider more representative of what can be used in a larger CLC unit. CO2 represented about 70% in the fuel reactor outlet gas stream, followed by unburnt compounds: H2, CO and CH4. CO2 capture efficiencies increased with the fuel reactor temperature achieving almost 100% of capture with the three biomasses at temperatures above 950 °C. In contrast, no clear trend with the fuel reactor temperature was observed for the total oxygen demand, achieving values about 25%. The major contribution to this value comes from the unburned volatiles with a small contribution coming from tar (≈ 1%). Regarding tar, naphthalene was the major compound found at the different operating conditions. The present results support the consideration of the CLC process with biomass (bio-CLC) as a promising Bio-Energy with Carbon Capture (BECCS) technology.