Abstract: A method and apparatus for removing undesired compounds such as alkali compounds from a shaft furnace such as a blast furnace. The process and apparatus includes providing a plurality of intermediate exhaust conduits or manifolds within the shaft furnace for withdrawing some of the furnace gases which may be rich in alkali or other undesirable compounds from the furnace while allowing the balance of the gases of combustion to rise through the furnace. These conduits are positioned so that the temperature below the conduits is higher than the temperature at which the alkali compounds will volatilize and the temperature above the conduits is lower than the temperature at which the alkali compounds will condense so that the undesirable alkali compounds are in a vapor state when they are withdrawn from the furnace through the intermediate exhaust conduits.