Abstract: In order to be able to handle multiple fuels in a bubbling-bed fluidized bed combustor, a number of elements are combined together and a number of systems are described which utilize these elements in order to be able to appropriately process different types of fuels. With respect to the handling of multiple fuels by a bubbling-bed fluidized bed combustor which need not be reconfigured for each type of fuel, the combustor in the subject invention is provided with a closely-coupled pyrolyzer or gasifier. The close-coupled pyrolyzer not only permits the processing of virtually any type of fuel into two fuel streams which are immediately usable by the combustor but also has certain advantages in terms of reducing environmental pollutants. The above-mentioned close-coupled pyrolyzer also results in improved performance aside from the pollution aspects mentioned above.