There are a number of technical terms used in connection with steam generation. Some of these commonly used terms you should know are as follows:

"Degree" is defined as a measure of heat intensity.

"Temperature" is defined as a measure in degrees of sensible heat. The term sensible heat refers to heat that can be measured with a thermometer.

"HEAT" is a form of energy measured in British thermal units (Btu). One Btu is the amount of heat required to raise 1 pound of water 1 degree Fahrenheit at sea level.

"Steam" means water in a vapor state. DRY SATURATED STEAM is steam at the saturation temperature corresponding to pressure, and it contains no water in suspension. WET SATURATED STEAM is steam at the saturation temperature corresponding to pressure, and it contains water particles in suspension.

The "QUALITY" of steam is expressed in terms of percent. For instance, if a quantity of wet steam consists of 90 percent steam and 10 percent moisture, the quality of the mixture is 90 percent.

"SUPERHEATED STEAM" is steam at a temperature higher than the saturation temperature corresponding to pressure. For example, a boiler may operate at 415 psig (pounds per square inch gauge). The corresponding saturation temperature for this pressure is 483F, and this will be the temperature of the water in the boiler and the steam in the drum. (Charts and graphs are available for computing this pressure-temperature relationship.) This steam can be passed through a superheater where the pressure remains about the same, but the temperature will be increased to some higher figure.

Q1. When heat is applied to water, what physical change occurs?

Q2. How is a "degree" of heat defined?

Q3. As long as the pressure in a boiler is held constant, what factor remains the same in the boiler?

BOILER DESIGN REQUIREMENTS

Learning Objective: Describe the design requirements for boilers.

A boiler must meet certain requirements before it is considered satisfactory for operation. Three important requirements for a boiler are as follows:

1. The boiler must be safe to operate.

2. The boiler must be able to generate steam at the desired rate and pressure.

3. The boiler must be economical to operate.

NOTE Make it a point to familiarize yourself with the boiler code and other requirements applicable to the area in which you are located.

Design rules for boilers are established by the ASME (American Society of Mechanical Engineers). These rules are general guidelines used by engineers when designing boilers. These rules require that for economy of operation and to generate steam at the desired rate and pressure, a boiler must have the following attributes:

Adequate water and steam capacity

Rapid and positive water circulation

A large steam generating surface

Heating surfaces that are easy to clean on both water and gas sides

Parts accessible for inspection

A correct amount and proper arrangement of heating surface

A firebox for efficient combustion of fuel

Q4. What three requirements must a boiler meet before being considered satisfactory for operation?

Q5. What organization has established guidelines for designing boilers?

TYPES OF BOILERS

Learning Objective: Identify the different types of boilers and describe the operation of each.

The Utilitiesman is concerned primarily with the FIRE-TUBE type of boiler, since it is the type generally used in Seabee operations. However, the WATER- TUBE type of boiler may occasionally be used at some activities. The information in this chapter primarily concerns the different designs and construction feature: of fire-tube boilers.