A semi-continuous process for combusting coke from catalyst particles in a fixed bed is improved by rejecting from the combustion process a high moisture content flue gas stream which is produced by the combustion of a relatively large proportion of the hydrogen in the coke that enters the combustion section during an early stage of combustion. By operating the early stage of combustion at conditions to increase the rate of combustion of the hydrogen in the coke relative to that of the carbon in the coke, the overall equilibrium level of water in a flue gas/recycle gas that circulates through the process is lowered. The high moisture content flue gas stream from the early stage of combustion is rejected separately from the process. Subdivision of the bed and separation of the flue gas streams can be easily accomplished in a vertically arranged catalyst particle bed by adding baffles to the recycle gas distribution space that subdivide the distribution space into separate chambers and by adding baffles to the flue gas collection space that subdivide the collection space into separate chambers. The amount of high moisture content flue gas withdrawn from the process can be equal to the amount of the make-up gas streams entering the flue gas/recycle gas loop.