Evaluation of different oxygen carriers for biomass tar reforming (II): Carbon deposition in experiments with methane and other gases

摘要

This work is a continuation of a previous paper by the authors [1] which analyzed the suitability of the Chemical Looping technology in biomass tar reforming. Four different oxygen carriers were tested with toluene as tar model compound: 60% NiO/MgAl_2O_4 (Ni60), 40% NiO/MgAl_2O_4 (Ni40), 40% Mn_3O_4/Mg-ZrO_2 (Mn40) and FeTiO_3 (Fe) and their tendency to carbon deposition was analyzed in the temperature range 873-1073 K. In the present paper, the reactivity of these carriers to other compounds in the gasification gas is studied, also with special emphasis on the tendency to carbon deposition. Experiments were car ried out in a TGA apparatus and a fixed bed reactor. Ni-based carriers showed a tendency to form carbon in the reaction with CH_4, especially Ni60. The addition of water in H_2O/CH_4 molar ratios of 0.4-2.3 could decrease the carbon deposited, but not in the case of Ni60. Mn-based sample reacted with CH_4 almost completely and with low tendency to carbon deposition, while the Fe-based sample showed low reactiv ity. Ni40 showed more reactivity to CO than Mn40, although in both cases carbon was deposited, espe cially at 873 K. When H_2 was present, it reacted rapidly with both carriers, decreasing the amount of carbon deposited. The presence of CO_2 could also decrease the carbon deposited on Ni40 at 1073 K. According to both these and the previous results [1 ], it can be concluded that Mn40 is the most adequate for minimization of carbon deposition in Chemical Looping Reforming (CLR).