Gasification experiments with railroad wood ties treated with creosote were conducted in a two-stage gasifier to produce a high caloric producer gas with low tar content. In the experiments, sand and dolomite as the bed material were compared, and the effects of temperature in a range from 666 to 818 degrees C and equivalence ratio from 0.19 to 0.52 were also investigated. Additionally, the effectiveness of additives (biomass-based activated carbon, coal-based activated carbon and dolomite) and their combination on the removal of tar were examined. As a result, the combination of dolomite as the bed material and coal-based activated carbon in the tar cracking zone gave the best performance with respect to tar removal. With this combination, the total amount of tar was reduced by 91.9%, compared to that obtained by using only sand as the bed material in the gasifier. Furthermore, the tar content in the producer gas was below 0.1 g/N m(3). Coal-based activated carbon also improved the production of hydrogen up to about 29 vol.%. The LHVs of most producer gases in these experiments were above 7 MJ/N m(3). (C) 2012 Elsevier Ltd. All rights reserved.