A process for combustion of hydrocarbonaceous materials containing high levels of sulfur, fuel-bound nitrogen and low levels of ash which inhibits the emissions of oxides of nitrogen and sulfur, reduces solid waste disposal, and produces useable by-products. In the first step of the process, the hydrocarbonaceous material is burned in a fluidized bed into which a calcium based sorbent is introduced, producing a mixture of gaseous products of combustion and particulate matter, ash and calcium containing solids. In a second step of the process, the mixture of gaseous products of combustion and particulate matter is completely burned in a cyclonic combustion reactor. In a third step of the process, the ash and calcium-containing solids generated in the fluidized bed are withdrawn from the fluidized bed, cooled and contacted with steam in a regenerator producing calcium hydroxide, ash and unspent sorbent which are recycled to the fluidized bed.