Surface adjustment of biochar by CO2 gasification under fixed and fluidized bed conditions

Abstract

This paper explores how torrefaction and CO2 gasification can be combined to create biochar with a high surface area from Pinus sylvestris wood pellets. Raw pellets were pretreated in a torrefaction process at 300 °C before conducting biomass CO2 gasification experiments under various operating conditions. Gasification was performed under fixed and fluidized bed conditions at temperatures between 800 to 900 °C and biomass residence times of 15 or 25 minutes. Biomass burn-off and BET surface areas were analyzed individually and combined to determine the surface yield per raw Pinus sylvestris feedstock. Higher temperatures, higher biomass residence times, and fixed bed conditions increased burn-off and BET surface areas up to 798 m²/g. Surface yield per raw biomass was instead found to be the highest from fluidized bed experiments, which yielded around 100 m²/gfeedstock after gasification at 850 to 900 °C.