Convection recuperators (also referred to as "flue" or "canal" recuperators) are tubular heat exchangers that utilize convection heat transfer to preheat combustion air or gas for the purpose of saving fuel. By recovering heat from the hot waste gas exiting a furnace and transferring it to the combustion air feeding the burners, fuel usage can be reduced by an average of twenty-five percent (25%), and in many cases, greater savings are realized. Waste gas temperatures entering convection recuperators are usually in the 1500°F to 2000°F range, and combustion air preheat temperatures are usually in the 800°F to 1200°F range.
For high temperature industrial furnaces, such as steel reheat furnaces, recuperators are valuable tools for increasing furnace efficiency. Up to sixty percent (60%) of the available energy in the fuel may be carried out of the furnace in the waste gas, therefore, heat recovery is essential for fuel conservation and economical operation. With fuel costs rising, recuperation is certain to play a vital role in the future.
Convection recuperators are comprised of tube bundles with the tubes welded to the tube sheets to assure gas tightness. Tube arrangement, tube material and flow pattern are based on the specifics of each individual application, including temperatures, compositions, pressure drop limits and space availability. In a typical design, the hot waste gas from the furnace flows horizontally through the recuperator, passing outside of vertical tubes. Combustion air en route to the burners makes two or more passes inside the tubes in a counter cross-flow pattern.