Experimental and kinetic study of the NO-reduction by tar formed from biomass gasification, using benzene as a tar model component

The present work studies the combustion of biomass syngas to characterize the NO-reduction by tar, benzene being selected as the representative model tar component. Experiments were carried out in a tubular flow reactor at atmospheric pressure and at different operating conditions i.e. an equivalence ratio of 0.5 to 2.5, temperatures between 1173 K and 1673 K and a reaction residence time of 50 to 100 ms. Kinetic parameters were determined from the experimental results. A simplified scheme of NO-reduction by benzene was presented and the effects of operating variables were concluded. The NO conversion is favored by an oxygen-rich condition, and the reduction efficiency falls with the rise of equivalence ratio, especially in the range of 0.5–1.0. Although high temperature enhances the reduction reactions, soot formation at high temperatures (1573 K, 1673 K) will seriously hinder the reduction of NO, which should be prevented. The ideal temperature is about 1473 K. 50 ms is found to be an insufficient residence time for the reduction. An increased contact time is of higher benefit at 1673 K where the heterogeneous reactions between NO and graphitized heavy hydrocarbons have a lower reaction rate. High pre-exponential factors and low activation energies are achieved under oxygen-rich conditions.