This type of recuperator consists in two cylinders of similar diameter made with heat resistant steel and insulated outside with ceramic fiber and rock-wool.
The heat exchanging area is the anular space formed between the two concetric cylinders. In fact, the hot waste gas passes through the inner tube heating the steel till 700°C and the combustion air passes through the anular space cooling the steel and heating up itself till 400°C.
The stainless steel inside of the recuperator is avalaiable in two qualities: AISI 310S and 253MA.The double shell recuperator is used in single modules.This kind of recuperator is used for Day Tank furnaces of dimensions up to 4 tons/day.The double shell recuperator has a overheating safety system installed on the refractory material of the chimney.
This system consists in a stack base motorized valve, that through a cold air flow, regulates the temperature of the waste gas in the chimney in case of overheating, and cooling the recuperator in case of stop of combustion air flow (due to black out or electroventilator breakage)