Preheater

A preheater is a device that raises the temperature of a cold fluid by exchanging heat with a hotter fluid or solid. Preheaters are used to recover energy from waste or hot streams and to reduce the energy required by a processing unit. They improve overall plant efficiency, reduce fuel consumption, lower emissions, and can minimize thermal shock to downstream equipment.

Common forms include: air preheaters, which transfer heat from exhaust gases to incoming combustion air in boilers and gas turbines; feedwater heaters in steam cycles, which warm condensate or feedwater using extraction steam or hot process streams; and exhaust or process preheaters that warm oils, gases, or other process streams before entering furnaces or reactors. Some systems employ regenerative media, such as heat wheels, or recuperative shell-and-tube heat exchangers.

Design and operation: Most preheaters are heat exchangers. Key factors are heat transfer area, flow arrangement, pressure drop, material compatibility, and resistance to fouling and corrosion. Efficiency is influenced by temperature approach, heat transfer coefficient, and residence time. Maintenance focuses on cleaning fouling deposits and preventing corrosion.

Applications: Preheaters are widely used in power generation, cement manufacture, petroleum refining, petrochemical processing, steel and glass production, and other processes that benefit from energy recovery. They contribute to reduced fuel use and emissions, but add capital cost and may introduce pressure losses or flow restrictions.