Quantitative study on thermal conversion behaviours and gas emission properties of biomass in nitrogen and in CO2/N2 mixtures by TGA/DTG and a fixed-bed tube furnace

Introducing CO2 in the pyrolysis medium could not only provide a route for CO2 sequestration but also potentially increase the carbon conversion efficiency. Herein, to reveal the effects of introducing CO2 in the pyrolysis medium alongside N2 on the thermal conversion behaviours of biomass, a series of pyrolysis/gasification experiments with/without CO2 in the pyroysis medium were conducted in a thermogravimetric analyser (TGA) and a self-established fixed-bed experimental system. The effects of reaction temperature, atmosphere and residence time on syngas emissions and compositions were elucidated in details. Introducing CO2 in the pyrolysis agent resulted in an additional consumption of residuals, promoting CO release due to char-CO2 reactions. During gasification, the total weight loss increased with increasing CO2 concentration. As the pyrolysis reaction was prolonged, the release of CO, CO2, CH4, and H2 occurred in chronological order. Reaction temperatures below 600 °C had negligible effects on CO emissions. For pyrolysis under N2, the H2 concentration in syngas increased obviously with increasing temperature, while that of CO2 presented the opposite trend, indicating that high temperature favoured H2 release while CO2 emissions could be inhibited. The particle residence time had no obvious influence on either gas emissions or yields in a CO2-containing atmosphere.