Abstract: Method of operating a fixed bed dry bottom gasifier includes feeding coarse particulate coal with an average particle size of at least 1 mm and an ash fusion temperature increasing agent into a gasification chamber of the gasifier to form a coal bed, feeding a gasification agent into the gasification chamber, and gasifying the coarse particulate coal in the gasification chamber to produce synthesis gas as well as ash. The ash is collected in an ash bed below the coal, and the synthesis gas and the ash are removed from the gasification chamber.