Experimental study and modeling of heavy tar steam reforming

In this paper, the elimination of heavy tar by steam reforming at high temperature was studied with experiments and numerical simulation. The experiments were conducted in a tube reactor with five model compounds at temperatures of 1273-1673 K, steam of 0-40 vol% and sample weight of 3-20 mg with residence time of 2 s. The simulation was performed with the plug flow model in CHEMKIN program based on a kinetic model that consists of > 200 chemical species and 2000 elementary step-like reactions. The results of experiments indicate that increasing temperature will accelerate the decomposition of heavy tar; moisture could significantly prompt the decomposition of heavy tars, but not so efficient above 20 vol%; less sample could help the decomposition of heavy tar; longer residence time can slightly increase the decomposition of heavy tar. At high temperature (1573 K or above), the heavy tar is mainly cracked into two parts: the one carbon molecules (CO and CO2) and the soot at the beginning of reactor. Then the soot decomposes into CO, CO2 and H-2 by steam reforming. The conversion and kinetic data of heavy tar can be divided by two temperature sections. The carbon conversion degrees of different model compounds from 1173 K to1473 K are close with similar trends, which may be represented by a universal kinetic model. Our results provide an insight in the understanding of the heavy tar decomposition and give the necessary information for the designation and operation of the tar cracker to eliminate heavy tar.