Abstract: The generation of acid rain precursors, i.e., SO.sub.x and NO.sub.x, and slag during the combustion of a carbonaceous fuel, e.g., coal, is counteracted in a slagging combustor apparatus and process. The fuel is combusted in a primary combustor under substoichiometric combustion conditions and at a temperature greater than the fuel's ash fusion temperature. The substoichiometric combustion conditions suppress the formation of NO.sub.x. Most of the noncombustibles are separated from the gaseous products of combustion, in the form of liquid slag, to form treated gaseous combustion products having a noncombustible content that is substantially reduced with respect to the noncombustible content of the fuel. The temperature of the treated gaseous combustion as it leaves the primary combustion is above the ash fusion tmeprature of the fuel. A sorbent is introduced into the treated gaseous combustion products and calcined. The calcined sorbent removes SO.sub.x from the treated gaseous combustion products.