Acid Gas and Tar Removal from Syngas of Refuse Gasification by Catalytic Reforming

Abstract

The existence of acid gas and tar in syngas of municipal solid waste gasification limits its downstream utilization as a clean energy source. Here, we investigated the catalytic removal of HCl and tar. The key parameters affecting the catalytic reaction, including space velocity, temperature, the amounts of active metals in the catalyst and the carrier material, were studied, targeting optimized operating conditions for enhanced syngas purification. The morphology, mineral phases, surface area and pore size before and after the reaction were investigated to understand the mechanism to dominate the reaction. The results showed that the removal rate of CaO adsorbent and HCl reached 96% at 400 °C. When the space velocity ratio was 1.0 and the temperature was 400 °C, HCl removal (97%) by NaAlO2 was even better. Nevertheless, clogging was observed for NaAlO2 via the BET test after reaction to jeopardize its durability. A level of 25% Ni doping on Zr1-x(Cex)O2 support provides high stability for tar removal. This is because the Zr1-x(Cex)O2 carrier has higher carbon deposition resistivity than the Al2O3 carrier. The EDX results confirmed that a large amount of C (79.3%) was accumulated on the commercial catalyst surface supported by Al2O3 (25% Ni-based). As for the temperature, a temperature higher than 800 °C could not enhance the efficiency of tar removal, likely due to catalyst deactivation. Carbon deposition and agglomeration are the two main causes of catalyst deactivation. At 800 °C, 25% Ni-based synthetic catalyst can convert 48.5 ± 19.4% tar to low molecular weight organic compounds. By contrast, such a conversion rate under the same temperature only accounted for 5.0 ± 6.8% based on a commercial catalyst. These insights point to the important role of catalyst support materials.