Accelerating wet torrefaction rate and ash removal by carbon dioxide addition

In this study, CO2 was employed as an environment friendly catalyst for wet torrefaction of fresh Norwegian forest residues. The effects of CO2 addition on the yield and the properties of hydrochar were experimentally studied and compared with the base case, wet torrefaction in N-2. The results showed that wet torrefaction in CO2 and N-2 has similar effects on the improvement in the fuel properties of biomass. However, CO2 was found to improve the reactivity of forest residues during wet torrefaction, producing the same hydrochar yield at less severe conditions compared with N-2. The hydrochars produced in CO2 had lower heating value and energy yield, but better grindability and hydrophobicity, compared with those in N-2. More importantly, CO2-enriched wet torrefaction can remove up to 60-69% of the ash content in the forest residues, compared to only 14-26% for wet torrefaction in N-2. (C) 2015 Elsevier B.V. All rights reserved.