Three dimensional CFD models are developed to investigate the flow distribution, heat transfer and chemical reactions in a partially packed vessel. The vessel of interest is similar to a catalytic sulfur converter used for sweetening sour gas. The vessel considered is a large horizontal cylinder and contains a catalyst bed. The height of the bed is about one fourth of the vessel diameter and placed almost in the central region of the vessel. A gas stream enters the vessel, reacts over the catalyst before leaving it. The main reaction is that of H2S with SO2 to produce sulfur gas and water vapor. Flow in a three dimensional model of the unpacked vessel is simulated. The effects of flow rates and number of outlets were investigated and found to have a limited effect on the flow distribution. Flow in a partially packed vessel is also simulated without chemical reactions. Results show that packed beds act as a good flow distributor, however, there is still significant differences in the values of velocity across the various regions of the packed bed. The flow in a partially packed column with chemical reaction is also simulated. Limited kinetics information is available in the literature. A finite rate model is used to simulate the chemical reactions and the results show reasonable agreement with the available industrial data.