Regenerative, Rotary Air Preheaters
The Ljungstrom heat exchanger (C-E Air Preheater, Combustion Engineering) is a large rotating basket of heat transfer elements. Hot flue gas heats the elements as they pass through the flue gas chamber. The elements then pass through seals into the incoming air chamber and give up heat to the combustion air. The exchanger is usually mounted on the ground; thus, it needs plot space. It requires ducting for both flue gas and air as well as a power supply and cooling for bearings. Flue gas must be diverted if the exchanger stops rotating; otherwise it can be damaged by overheating. Seal maintenance is required to minimize air leakage. There will always be some leakage; design of ducts and fans must accommodate it. The Ljungstrom-type exchanger is considered quite reliable and is in wide use.