Superheaters

Superheaters are heat exchangers in steam-generating boilers that raise saturated steam to a higher temperature above the saturation point corresponding to the drum pressure. Saturated steam leaving the boiler drum contains moisture; passing through a superheater transfers additional heat from hot flue gases to the steam, producing dry, high-temperature steam used for driving turbines and for process steam in industry. The degree of superheat is the difference between the actual steam temperature and the saturation temperature at the given pressure.

Most superheaters are tubular heat exchangers consisting of long bundles of tubes through which steam passes while hot flue gases flow externally. They are classified by location: radiant superheaters, located in the furnace’s radiant zone where they receive direct heat from combustion; and convection superheaters, located in the boiler’s convection pass where they are heated by flue gas after leaving the furnace. Variations include plate or platen-type designs and coil or straight-tube configurations.

Operating considerations include controlling steam temperature by adjusting fuel input and feedwater flow, monitoring tube metal temperatures to avoid overheating and creep, and ensuring corrosion resistance in exhaust gas environments. Materials are chosen for high-temperature strength and oxidation resistance.

Applications and benefits: superheaters are widely used in fossil-fuel-fired boilers and many high-pressure steam systems to improve turbine efficiency, reduce moisture-related blade erosion, and increase overall plant efficiency. Disadvantages include added fuel consumption for the extra heat, potential for overheating if control fails, and higher capital and maintenance costs due to more complex equipment.