CFB air-blown flash pyrolysis. Part II: Operation and experimental results

The main operational characteristics of a novel gasifier operating in the CFB mode are outlined in this paper, based on the experimental results from a total of 11 runs in the pyrolysis mode. The operation runs constituted the main experiments in the CFB reactor, carried out to derive meaningful mass balance and additional operational data for the CFB pyrolyzer. The experiments were conducted in varying operating conditions determined by the most important parameters, i.e., biomass flowrate, fluidizing gas flowrate, air factor, initial bed inventory), temperature in the CFB riser, vapor residence time and nominal air factor - or equivalence ratio, S_b. The results obtained showed that the reactor configuration successfully operated as a biomass fast pyrolysis system to maximize liquid yields reaching 61.50 wt% on a maf biomass basis, with the novel feature of providing for autothermal operation at 500 °C and with 0.46 s gas-vapor residence time, by utilizing the by-product char energy content in a single reactor. The reactor provides a very high specific throughput of 1.12-1.48 kg/h m² and the lowest gas-to-feed ratio of 1.3-1.9 kg gas/kg feed compared to other fast pyrolysis processes based on pneumatic reactors and has a good scale-up potential, providing significant capital cost reduction. Results to date suggest that the process is limited by the extent of char combustion. Future work should address resizing of the char combustor to increase overall system capacity, improve the solid separation and substantially increase liquid recovery.