Low temperature chemical looping combustion of pyrolysis gases in a fixed bed reactor

Abstract

This study presents an experimental investigation into the feasibility of oxidizing biomass pyrolysis gases at relatively low temperatures using a chemical looping combustion (CLC) approach. The application of this alternative method would enable the capture of carbon from the pyrolysis gas stream, which is currently released into the atmosphere in most pyrolysis systems, as high-purity CO₂. In a fixed bed reactor, the reduction behavior of three different Cu-based oxygen carriers (OC) - pure CuO pellets, carulite and Al₂O₃-supported CuO - was evaluated to determine whether pyrolysis gases could be completely oxidized to CO₂ and H₂O within a temperature range of 600–650 °C and at weight hourly space velocities (WHSV) of 0.06–0.10 h⁻¹. Both CuO and carulite exhibited significant amounts of unconverted pyrolysis gases even during the initial stages of the reduction experiments. In contrast, Al₂O₃-supported CuO emerged as the most effective material, facilitating the complete oxidation of pyrolysis gases over extended reaction times. For this oxygen carrier, a decline in the combustion efficiency was only observed at very high (90 %) reduction conversions. Reduction/oxidation cycles for this most promising material were successfully demonstrated, with the oxygen carrier showing no signs of activity loss after 10 cycles. However, carbon deposition was detected under several experimental conditions, which could potentially reduce the carbon capture efficiency of the process.