Abstract In the present study, the rate of reduction in the direct reduction moving bed reactor of a MIDREX plant has been studied. The reactor was modeled by a one-dimensional, nonisothermal, steady-state model. The three interface unreacted shrinking core model accounting for different iron oxides reduction was used for describing the reaction behaviors at the pellet scale. The quasi steady state assumption was used to calculate the gas species concentrations at the interfaces. The effects of external and internal mass transfer resistance through the pellets and heat transfer on the overall rate of reduction were considered. The results of the model were validated with the data of the Khorasan Steel plant (Neyshabur, Iran). The model results show good agreement with the plant data. The effect of gas and solid flow rates, feed gas properties, and pellet characteristics on the reactor performance were investigated using the model.

Abstract The reaction of calcium oxide with carbon dioxide is one of the most important methods for the capture and concentration of greenhouse gas from the flue gases of industrial plants. In this work, the carbonation reaction of CaO obtained from various sources with CO2 was investigated by a thermogravimetric method. These sources include commercial lime or CaO, CaCO3, Ca(OH)2, CaC2O4.H2O, a synthesized nanoporous sorbent, limestone and acetic acid washed limestone. The effect of structural parameters of the sorbents on the reactivity and CO2 capture capacity were studied using pore size distribution data. Also, the changes in the solid texture during the carbonation reaction were investigated. It was found that there is a direct relation between the pore volume of the sorbents and their reactivity. It was found that sintering is one of the main reasons for decreased activity in the carbonation/calcination cycles.