Chemical Looping Combustion of Biomass: An Approach to BECCS

Abstract

The climate change challenge demands a commitment of combined strategies between global institutions, governments, companies and citizens. In order to reach 2015 Paris Agreement, greenhouse gas emissions need to be reduced. Any single technology is currently able to achieve atmospheric greenhouse concentration values for the purpose of climate change mitigation. Also carbon sinks will be needed to further this cause as well as Carbon Capture and Storage (CCS) technologies. In this sense, biomass represents an interesting alternative fuel for heat and power production as a carbon dioxide-neutral fuel. Moreover, if the CO2 generated during biomass combustion process was captured then negative-CO2 emissions would be reached. In this way, Bio-Energy with Carbon Capture and Storage (BECCS) technologies enable energy generation while CO2 is being removed from the atmosphere. Among the different options, Chemical Looping Combustion (CLC) is considered one of the most promising second generation CCS technologies due to its negligible energy and cost penalty for CO2 capture. In this work, three types of biomass were evaluated under CLC conditions: pine sawdust, olive stone and almond shell. Combustion experiments were performed in a continuous 500 Wth CLC unit at Instituto de Carboquímica (ICB-CSIC, Spain) using a highly-reactive low-cost iron ore as oxygen carrier (Tierga ore). During the experimental campaign, the effect of fuel reactor temperature (900-980 °C) on the combustion performance was analyzed. At the highest temperature tested (980 °C) a CO2 capture efficiency of 100% was reached with all the biomasses. However, the total oxygen demand followed no clear trend with temperature and the average value was close to 25%. The high volatile content of biomass compared to coal contributed to this effect. For a correct operation with biomass, further design measures should be taken to reduce the amount of unburned compounds at the outlet of the fuel reactor. In addition, tar and NOx measurements were done. No relevant drawbacks by the use of biomass in CLC were found related with other pollutants present in the system such as tar production or NOx emissions.