A model has been developed for hot-gas filtration by candle filters, which includes incomplete removal of the filter cakes by the cleaning backpulses of compressed air. Operational data from the filtration system of the Integrated Gasification and Cleanup Facility at the Federal Energy Technology Center were analyzed with the model and used to estimate the cake permeability, thickness of cake left on the filter after each backpulse, and total cake thickness vs, time. The statistical R-2 for the fit of the incomplete-cleaning model was 0.93, compared to the R-2 = 0.78 previously obtained for a fit of the 'ideal filtration' model to the same data set.