Abstract: Sulfur is readily and efficiently removed from solid fuel in a boiler installation which comprises a hearth for burning and thereby gasifying the solid fuel, the hearth including a grid supporting a fluidized bed of the solid fuel spread thereover, and a tubular boiler body superimposed on, and integral with, the hearth, the boiler body including a lower portion receiving the gasified fuel from the hearth, an upper portion, a common transverse wall dividing the tubular boiler body into the lower and upper portions, and a burner extending into the upper boiler body portion near the dividing transverse wall and receiving a supply of secondary combustion air. A conduit connects the lower boiler body portion to the burner for feeding the gasified fuel therefrom to the burner, and dust removing and desulfurization cyclones in the conduit remove dust and sulfur from the gasified fuel.