Learning Objectives: Describe the principles and theory of steam generation. Identify different types of boilers and the design requirements for boilers. Describe the purpose and operation of the different types of boilers and their fittings and accessories. Describe the methods and procedures for the testing and treatment of boiler water. Describe methods and procedures involved in fireside and waterside cleaning.
A boiler is an enclosed vessel in which water is heated and circulated, either as hot water or steam, to produce a source for either heat or power. A central heating plant may have one or more boilers that use gas, oil, or coal as fuel. The steam generated is used to heat buildings, provide hot water, and provide steam for cleaning, sterilizing, cooking, and laundering operations. Small package boilers also provide steam and hot water for small buildings.
A careful study of this chapter can help you acquire useful knowledge of steam generation, types of boilers pertinent to Seabee operations, various fittings commonly found on boilers, and so on. The primary objective of this chapter is to lay the foundation for you to develop skill in the operation, maintenance, and repair of boilers.
Learning Objective: Describe the principles and theory of steam generation.
To acquaint you with some of the fundamentals underlying the process of steam operation, suppose that you set an open pan of water on the stove and turn on the heat. You find that the heat causes the temperature of the water to increase and, at the same time, to expand in volume. When the temperature reaches the BOILING POINT (212F or 100C at sea level). a physical change occurs in the water; the water starts vaporizing. When you hold the temperature at the boiling point long enough, the water continues to vaporize until the pan is dry. A point to remember is that THE TEMPERATURE OF WATER DOES NOT INCREASE BEYOND THE BOILING POINT. Even if you add more heat after the water starts to boil, the water cannot get any hotter as long as it remains at the same pressure.
Now suppose you place a tightly fitting lid on the pan of boiling water. The lid prevents the steam from escaping from the pan and this results in a buildup of pressure inside the container. However, when you make an opening in the lid, the steam escapes at the same rate it is generated. As long as water remains in the pan and as long as the pressure remains constant, the temperature of the water and steam remains constant and equal.
The steam boiler operates on the same basic principle as a closed container of boiling water. By way of comparison, it is as true with the boiler as with the closed container that steam formed during boiling tends to push against the water and sides of the vessel. Because of this downward pressure on the surface of the water, a temperature in excess of 212F is required for boiling. The higher temperature is obtained simply by increasing the supply of heat; therefore, the rules you should remember are as follows:
1. All of the water in a vessel, when held at the boiling point long enough, will change into steam. AS LONG AS THE PRESSURE IS HELD CONSTANT, THE TEMPERATURE OF THE STEAM AND BOILING WATER REMAINS THE SAME.
2. AN INCREASE IN PRESSURE RESULTS IN AN INCREASE IN THE BOILING POINT TEMPERATURE OF WATER.
A handy formula with a couple of fixed factors will prove this theory. The square root of steam pressure multiplied by 14 plus 198 will give you the steam temperature. When you have 1 psig of steam pressure, the square root is one times 14 plus 198 which equals 212F which is the temperature that the water will boil at 1 psig.Continue Reading