A semi-continuous process for combusting coke from catalyst particles in a fixed bed is improved by segregating flue gas from the combustion process into a high moisture content flue gas stream which is withdrawn from the process and a relatively low moisture content flue gas stream which is combined with an oxygen-containing make-up gas and recycled to the process. When coke is combusted in a fixed bed to which catalyst is added at an inlet and withdrawn from an outlet on a semi-continuous basis, hydrogen from the coke is quickly combusted whereas less volatile coke components are more slowly combusted. As a result, flue gas passing through the catalyst that has just entered the bed will have the highest water concentration. By separately recovering the flue gas stream having this high moisture content, the overall equilibrium level of water in a flue gas/recycle gas that circulates through the process is lowered. Segregation of flue gas can be easily accomplished in a vertically arranged catalyst bed by adding a baffle to the flue gas collection space that subdivides the collection space into separate chambers. The amount of high moisture content withdrawn from the process can be equal to the amount of make-up gas entering the flue gas/recycle gas loop. A larger amount of high moisture content flue gas than that vented from the process can be collected with the non-vented gas passing through a drier and other treatment steps before re-entering the process as part of the make-up gas. Using the unvented portion of the high moisture content flue gas increases the efficiency of using driers since a relatively large amount of water can be removed from a small volume of flue gas.