Abstract:The maximum co-incineration ratio and the relative imposed sludge quantity of municipal sewage sludge with coal by using ordinary industrial boiler, especially for the coupled process of drying and co-incineration, are analyzed. The results show that the existing ideas about co-incineration of sludge with coal must be modified, i. e. first, the maximum co-incineration ratio is confined by the equivalent ash content rather than the equivalent water content, and it increases with the increase of the mass fraction of water in sludge, but the maximum relative disposed sludge quantity does not vary. Second, for the coupled process of drying and co-incineration, it consists of two distinct phases as the "co-incineration dominated phase" and the "drying dominated phase", and third, the relative disposed sludge quantity may increase with the increase of the mass fraction of water in desiccated material even in the drying dominated phase.