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.

The authors thank the Spanish Ministry of Economy and Competitiveness (MINECO) for the funding received from the project ENE2014-56857-R) and FEDER for the financial support. A. Pérez-Astray thanks MINECO for the BES-2015-074651 predoctoral fellowship co-financed by the European Social Fund. T. Mendiara thanks for the ‘‘Ramón y Cajal’’ post-doctoral contract awarded by MINECO. The authors also thank PROMINDSA for providing the solid material used in this work.

8 Figures, 3 Tablas.-- © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

Peer reviewed