The function of a boiler in the steam cycle is to convert water into steam. Reliability in operating naval boilers and associated equipment is important for the power plant to operate at maximum efficiency. The complex design of naval boilers requires a high degree of technical knowledge and skill on the part of the fireroom personnel responsible for boiler operations. All engineers should have some knowledge of the principles of combustion, how combustion occurs in a boiler, and the combustion requirements for operating a boiler more efficiently. You may want to review combustion in chapter 2 and 3 of this textbook.

This chapter describes boilers commonly used in propulsion plants of naval steam-driven surface ships. This information is general in nature and does not relate to any one class of ship. Chapter 221 of the Naval Ships' Technical Manual is the basic doctrine reference on boilers. For detailed information on the boilers in any particular ship, consult the manufacturer's technical manuals furnished with the boilers.

Upon completion of this chapter, you will have the knowledge to be able to identify and understand boiler terminology, the basic types of naval boilers and their operating principles, interpret gauges and indicators that aid in monitoring operating parameters of naval boilers, and understand boiler construction. You should be able to identify the major parts of a boiler and its functions. Also, you will learn about safety precautions that must be observed during boiler light-off.

BOILER TERMINOLOGY

Before studying the types of boilers used in propulsion plants aboard Navy ships, you need to know the boiler terms and definitions used most frequently by shipboard personnel. In this section we have listed some of the terms used in this chapter and by fireroom personnel on the job. It is not an all-inclusive list, but it will help form a basis for your understanding of the information presented on boilers.

Fireroom- The fireroom is a compartment containing boilers and the operating station for firing the boilers.

Boiler room- The boiler room is a compartment containing boilers but not containing the station for firing or operating the boiler.

Main machinery room- The main machinery room is a compartment containing boilers and the station for firing or operating the boilers and main propulsion engines.

Boiler operating station- The boiler operating station is a station from which a boiler or boilers are operated, applying particularly to the compartment from which the boilers are operated.

Steaming hours- Steaming hours is the time during which the boilers have fires lighted until fires are secured.

Boiler full-power capacity- Boiler fullpower capacity is specified in the contract specifications of a ship. It is expressed as the number of pounds of steam generated per hour at the pressure and temperature required for all purposes to develop contract shaft hp of the ship divided by the number of boilers installed. Boiler fullpower capacity is listed in the design data section of the manufacturer's technical manual for the boilers in each ship. It may be listed either as the capacity at full power or as the designed rate of actual evaporation per boiler at full power.

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 fullpower capacity.

Operating temperature- Operating temperature 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.