Production of Fischer-Tropsch hydrocarbons via oxygen-blown gasification of charred pinewood pellets

摘要

Thermochemical conversion of biomass to petroleum-equivalent liquid fuels is of particular practical interest since this approach would require practically no changes in existing engine technology and transportation infrastructure. This paper presents results of experimental studies aimed at the producing liquid hydrocarbons (C7 +) via a two-step process: gasification of charred pinewood pellets (CPP) followed by Fischer-Tropsch (FT) synthesis. The gasifier was operated in a semi-continuous updraft mode using a steam-oxygen mixture (in the range of [H2O]/[O-2] = 2.2-4.4 mol/mol) as an input oxidizing gas. The effect of gasification parameters, including the rate of oxygen flow and steam/oxygen molar ratio on the syngas yield and composition was determined. It was found that increasing oxygen flow rate into the gasifier (by a factor of 2.3) resulted in higher (by 32%) H-2/CO ratio while it had a minor effect on the CO/CO2 ratio in the syngas. Increasing the steam/oxygen ratio led to higher H-2/CO ratio in the syngas (up to 2.1 mol/mol) with slight decrease in the gasification rate of CPP. The water consumption rate was significantly reduced at higher steam/oxygen ratios (by almost half at [H2O]/[O-2] ratio of 4.4 mol/mol). The syngas from the gasifier was scrubbed of particulate matter and traces of oxygen and dried before it was directed to a FT synthesis reactor. FT synthesis reactor packed with cobalt-based catalyst featuring novel radial-flow design with improved heat-transfer characteristics was employed in this work. The integrated operation of the gasifier and FT reactor yielded mainly C7-C28 straight-chain hydrocarbons. The chain propagation probability (alpha) of the FT-hydrocarbon products estimated according to Anderson-Schulz-Flory (ASF) distribution model was about 0.8. (C) 2015 Elsevier B.V. All rights reserved.