Regenerative air preheater installation

In a regenerative air preheater installation of the kind comprising a heat exchanger including a generally cylindrical rotary heat exchanging unit, connected to a driving motor and allowing fluids to flow therethrough in directions generally parallel to its rotary axis, and a stationary casing which surrounds the heat exchanging unit and is provided with axially opposite inlets and outlets for combustion air and flue gas defining two axial passageways for combustion air and flue gas, respectively, extending through the rotary heat exchanging unit, each such passageway being connected with its inlet and outlet in a duct for conveying a flow of combustion air and flue gas, respectively, through the heat exchanger, a branch duct connected to the flue gas duct to allow flue gas to be drawn off from the flue gas duct through said branch duct for subsequent use as an inert gas, the improvement comprising means to conduct away from the flue gas outlet of the heat exchanger at least a major portion of any air passing from the combustion air passageway to the flue gas passageway during the operation of the heat exchanger, said branch duct being connected to the flue gas duct at a point located downstream of the heat exchanger, as viewed in the direction of flow of flue gas through the gas duct, and means defining a passageway through which air may be conducted away from the flue gas outlet of the heat exchanger to a point in the flue gas duct located downstream of the branch duct connection.