Experimental evaluation and modeling of steam gasification and hydrogen inhibition in Chemical-Looping Combustion with solid fuel

Artikel i vetenskaplig tidskrift, 2012

A Chemical-Looping Combustion (CLC) system is composed of two fluidized bed reactors, an air reactor and a fuel reactor. Oxygen is transferred from the air to the fuel by solid oxygen carrier particles circulating between these two reactors. By this arrangement, the N2 from the air is kept separated from the fuel gases as a part of the process and an almost pure stream of CO2 is obtained from the fuel reactor. This work investigates and models the influence of the steam and hydrogen concentration in the fuel reactor on the rate of solid fuel conversion in Chemical-Looping Combustion. Two kinds of fuel were examined, Swedish wood char and El Cerrejon bituminous coal (Colombian coal). Four different bed materials have been used in the reactor, ilmenite, nickel and oxide scales as an oxygen carrier and quartz sand for gasification experiments. The temperature was 970 °C for all experiments. Different fractions of steam and hydrogen were added to the fluidizing stream. Additionally, gasification experiments of fuel particles pretreated in mixtures of H2 and N2 were performed in order to determine the reversibility of the observed hydrogen inhibition. The results show that the best models for describing the behavior of steam gasification and fuel conversion in Chemical-Looping Combustion for a Swedish wood char and the El Cerrejon coal is the oxygen exchange model. For both fuels, it can be seen that higher steam concentration increases the rate of char conversion and, higher hydrogen concentration decreases the rate as a result of hydrogen inhibition. No irreversible hydrogen inhibition could be observed.