Abstract: The invention relates to a method of operating a furnace with gas turbine exhaust as preheated combustion air, in which a gas seal is used. The gas seal housing may for example be a J-shaped tubular device depending from the duct through which the exhaust air flows to the burners, and is open at one end to the duct and open at the other end to the atmosphere. The variation permissible of duct pressure atop the seal in order to keep the seal intact is a function of the vertical range of the interface between the gases in the device and the difference in density between the two gases and can be controlled by adjustment of the damper setting. In normal operation the hot exhaust air flows to the furnace burners under the suction controlled by the damper. The seal is disrupted when the flow of exhaust air is reduced, the colder atmospheric air then being admitted and flowing to the burners so that the furnace continues in operation.

Abstract: Combustion air, prior to being introduced into the cracking furnace in a hydrocarbon pyrolytic conversion and separation system, is preheated by employing bottom pumparound, top pumparound and/or quench water streams diverting from the primary fractionator externally connected to the pyrolysis reactor in order to optimize the thermal efficiency of the overall process.