US Patent 7716850 Energy-efficient yankee dryer hood system

A paper machine configured as a swing machine capable of producing both light and heavy grades providing a Yankee hood split into a wet end half and a dry end half, at least one hood half being a flex-hood half wherein the supply for that half is capable of being run with either combustion heat or recycled heat and is capable of either recirculating the exhaust from the hood or discharging it to the atmosphere. The heater for the flex-hood half comprises both a primary combustion heat source and an indirect heat source capable of extracting by-product heat from another operation. The exhaust system for the flex hood half is capable of being run in either a straight through mode or in a recirculating mode.