Design Superheater of Steam Boiler

Superheater is a device for producing superheated steam, typically a group of tubes exposed to heat through which steam is passed. Its purpose is to add additional heat to the steam. Thus a superheater is employed in the steam boiler to add additional energy into steam and raise its temperature. The function of superheater are increase the capacity of the steam boiler, eliminates erosion of the steam turbine, reduces steam consumption of the steam turbine.

Superheater is the tube banks that attain the highest temperatures in a steam boiler and consequently require the greatest care in the design, fabrication, and construction to ensure that the permissible metal temperatures are never exceeded. The final sections of superheater must be placed in the highest gas temperatures, which calls for adopting the most appropriate high-temperature alloy for the tubing from considerations of metal temperatures, fouling due to ash compounds and corrosion due to salts in ash.

The most important aspects of the design of superheater are: uniform distribution of steam and gas across all the sections to minimize unbalance of flows, optimally high steam velocity in all the tubes to keep the metal temperatures as low as possible, and minimum steam pressure losses. Superheater pressure drop is normally limited to 8% of outlet pressure to reduce the pumping load.

The superheater is usually drainable along a single loop of an inverted U. As the required
superheat increases or a larger control range is desired, a double inverted U-type superheater may have to be adopted, making the heater nondrainable. The superheater in a package steam boiler is largely convective. The degree of control range is also not as large as in field-erected steam boilers. Occasionally, a loop is pushed into the furnace space to achieve higher temperature.

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