Reduction of nickel oxide pellet by a H2-CO mixture accompanied by carbon deposition.

Abstract

The kinetics of the reduction of NiO pellet by H2–CO mixture is investigated in the temperature range from 873 to 1073 K where carbon deposition takes place simultaneously. To determine the respective rates of NiO reduction and carbon deposition, the weight change of the pellet and concentrations of CO2, H2O and CH4 in the exit gas were measured as a function of time.The reduction rate of NiO increases with increasing hydrogen content of the reducing gas. Carbon deposition occurs at the highest rate for a gas composition of 25% H2 and 75% CO. The reduction rate increases and the rate of carbon deposition decreases with increasing temperature.A reaction model in which the reduction, carbon deposition, methanation and the water gas shift reaction are taken into consideration is proposed. In the model it is assumed that the reduction proceeds according to the unreacted shrinking-core model and that the other reactions take place in the Ni layer. The experimental results agree closely with those calculated by using kinetic parameters obtained in previous studies.