Boiler overload capacity— Boiler overload capacity is specified in the design of the boiler. It is usually 120 percent of boiler full-power capacity, for either steaming rate or firing rate, as specified for the individual installation.
Superheater outlet pressure— Superheater outlet pressure is the actual pressure at the superheater outlet at any given time.
Steam drum pressure— Steam drum pressure is the actual pressure carried in the boiler steam drum at any given time.
Operating pressure— Operating pressure is the constant pressure at which the boiler is being operated. This pressure may be carried at either the steam drum or the superheater outlet, depending on the design feature of the boiler. Operating pressure is specified in the manufacturer’s technical manual.
Design pressure— Design pressure is the maximum pressure specified by the boiler manufacturer as a criterion for boiler design. Design pressure is not the same as operating pressure. It is somewhat higher than operating pressure. Design pressure is given in the manufacturer’s technical manual for the particular boiler.
Design temperature— Design temperature is the maximum operating temperature at the superheater outlet at some specified rate of operation. For combatant ships the specified rate of operation is normally full- power capacity.
Operating temperature— Operating tem- perature is the actual temperature at the superheater out let. Operating temperature is the same as design temperature ONLY when the boiler is operating at rate specified in the definition of design temperature.
Boiler efficiency— The efficiency of a boiler is the Btu’s per pound of fuel absorbed by the water and steam divided by the Btu’s per pound of fuel fired. In other words, boiler efficiency is output divided by input, or heat used divided by heat available. Boiler efficiency is expressed as a percent.
Superheater surface— The superheater surface is that portion of the total heating surface where the steam is heated after leaving the boiler steam drum.
Economizer surface— The economizer surface is that portion of the total heating surface where the feed water is heated before it enters the boiler steam drum.
Total heating surface— The total heating surface area is the area of the generating, economizer, and superheater tube banks exposed in the boiler furnace. These tubes are that part of the heat transfer that exposes one side to combustion gases and the other side to the water or steam being heated.
