Negative CO2 emissions through iG-CLC of pinus residue in a continuous unit of 0.5 kWth using a natural Mn-based oxygen carrier

Abstract

The use of renewable fuels, as biomass, in the chemical looping combustion process becomes an attractive solution to bioenergy technology with CO₂ capture (BECCS). In this work, a manganese ore from Brazil (MnT1000) was evaluated as an oxygen carrier to promote the conversion of a pine residue biomass by the in-situ Gasification-Chemical Looping Combustion (iG-CLC) technology in a 0.5 kW_th continuous experimental unit installed at ICB-CSIC. The main parameters studied were the influence of fuel reactor temperature, air excess, and oxygen-to-biomass ratio on the performance of the MnT1000 evaluating CO₂ capture efficiency and total oxygen demand. Under all experimental conditions, CO₂ composition was higher than 84% at the fuel reactor outlet gas on a dry N₂-free basis. The unburned gases such as CH₄, CO and H₂ were present in low concentration, attributed to the high reactivity that MnT1000 has with H₂, CO and CH₄. In general, higher temperatures, higher oxygen excess ratio and lower oxygen-to-biomass ratio reduced the total oxygen demand, with no great influence on CO₂ capture efficiency. Most of the experiments showed capture efficiency above 90%, and a total oxygen demand in between 5.9 and 13.7% for the experimental conditions studied with low specific solid inventories (760 – 833 kg MW⁻¹). The amount of tar quantified in this study was low, corresponding to a total of 1.32 g Nm⁻³, composed mainly of naphthalene and phenanthrene. In all experimental conditions, MnT1000 showed promising behavior, its reactivity remained high and constant throughout whole operation and no agglomeration problems were observed.