Devolatilization of residual biomasses for chemical looping Gasification in Fluidized Beds Made up of Oxygen-Carriers

Abstract

The chemical looping gasification of residual biomasses-operated in fluidized beds composed of oxygen-carriers-may allow the production of biofuels from syngas. This biomassto- fuel chain can contribute to mitigate climate change, avoiding the accumulation of greenhouse gases in our atmosphere. The ongoing European research project Horizon2020 CLARA (G.A. 817841) investigates wheat-straw-pellets (WSP) and raw-pine-forest-residue (RPR) pellets as feedstocks for chemical looping gasification. This work presents experimental results from devolatilizations of WSP and RPR, in bubbling beds made of three different oxygen-carriers or sand (inert reference), at 700, 800, 900 °C. Devolatilization is a key step of gasification, influencing syngas quality and quantity. Tests were performed at laboratory-scale, by a quartz reactor (fluidizing agent: N2). For each pellet, collected data allowed the quantification of released gases (H2, CO, CO2, CH4, hydrocarbons) and mass balances, to obtain gas yield (ηav), carbon conversion (XavC), H2/CO ratio (λav) and syngas composition. A simplified single-first order-reaction model was adopted to kinetically analyze experimental data. WSP performed as RPR; this is a good indication, considering that RPR is similar to commercial pellets. Temperature is the dominating parameter: at 900 °C, the highest quality and quantity of syngas was obtained (WSP: ηav= 0.035-0.042 molgas gbiomass-1, XavC = 73-83%, λav= 0.8-1.0); RPR: ηav= 0.036-0.041 molgas gbiomass-1, cav C = 67-71%, λav= 0.9-1.0), and oxygencarries generally performed better than sand. The kinetic analysis suggested that the oxygen-carrier ilmenite ensured the fastest conversion of C and H atoms into gases, at tested conditions.