DECOMPOSITION OF TAR MODEL COMPOUND TOLUENE BY TREATMENT WITH THE HIGHTEMPERATURE HYDROGEN/OXYGEN FLAME

摘要

A complete decomposition of all organic molecules generated as a result of biomass gasification intosimple inorganic species like CO and H_2 (syngas) means both an improved energy efficiency and technologicalrobustness of the process of renewable synthesis gas (syngas) production. The syngas could be then converted intosynthetic fuels, chemicals or electricity. A contamination of the produced syngas with polyaromatic hydrocarbons(PAH) promotes an origination of tar which, when the temperature of the gas becomes lower, deposits on the innersurfaces of the downstream equipment inducing its fouling and possibly its failure. A non-catalytic method of tardecomposition includes mixing of gasification products with plasma gas (usually air) generated by its heating toextremely high temperatures (5000°C and higher) in a high-voltage electrical field. Combustion products attemperatures of the oxy-fuel flames could be also considered as plasma due to a presence of ionized particles, radicalsand free electrons. The effect of continuous injection of the hydrogen/oxygen high-temperature flame into the blendof gases containing toluene in order to decompose the latter has been studied in the present work. Toluene in themixture with nitrogen and steam (reaction mixture) was selected as a tar model compound because it has beenregarded by many researchers as a precursor of heavier polyaromatic compounds in high temperature gasificationprocesses. The experimental results indicate that treatment of the reaction mixture with the stoichiometrichydrogen/oxygen flame leads to the reforming of toluene into H_2 and CO. A certain excess of oxygen in the flamepromotes almost complete toluene decomposition into syngas in the regime of its partial oxidation. In spite of somereduction in the amount of syngas produced, that excess oxygen in the hydrogen/oxygen flame could be efficientlyapplied to the syngas contaminated with tars; this allows the original syngas heating value to remain unchanged. Amechanism of hydrogen/oxygen flame influence on tar destruction/decomposition pathways is also discussed.Hydrogen and oxygen could be technically produced by electrolysis of water. The efficiency of electricity utilizationto make the hydrogen/oxygen flame in order to decompose volatile organic compounds and tars will be a subject forour following studies.