Black liquor gasification is one of the promising alternatives to eliminate the drawbacks of the conventional recovery unit of the kraft process. A numerical model has been developed to simulate an industrial pilot scale entrained-flow gasifier currently operating at Tampere, Finland. The objective of the model is to investigate the effect of the key operating parameters on the efficiency of sulfate reduction during black liquor gasification. The results of the sensitivity analysis indicates that reduction is dependent of the ratio of the amount of carbon in black liquor to the amount of air being fed into the system, the reactor temperature and the initial particle size. Decreasing the air ratio can improve the efficiency of reduction. The rates of both reduction and carbon gasification increase with increasing in temperature. Higher reduction can be obtained by increasing the initial particle size. However, the values of those parameters need to be optimized based on the desired degree of sulfate reduction and the completion of carbon conversion. Economic considerations such as the length of the gasifier needed to achieve both high reduction efficiency and carbon conversion also need to be considered when selecting operating conditions. / Graduation date: 1994