A steam boiler is a vessel that contains water and a heat source powered by oil, coal or gas. The boiler transfers heat from the heat source to the water vessel, thereby turning the water into steam. This steam exits the vessel through a pipe and is transported to another location where it can be used for cleaning, to power equipment, to provide heat or for a number of other functions. A closed boiler system is one in which 100 percent of the steam is returned to the vessel in the form of water and reused. Closed boiler systems are very efficient and less costly to operate. However, some industrial processes contaminate the steam and prevent it from being reused. A boiler that does not return the used steam to the water vessel is called an open system.
Overview of Steam Boilers
Mechanics of Steam Boilers
The heat source in a boiler system is located in a separate compartment within the water vessel. The water vessel is attached to the heat source by metal rods, which heat the water directly and convert it to steam. The steam initially collects in an area above the water vessel known as the dome before exiting the boiler. The dome forces the steam to become highly condensed so that it will exit the boiler with a significant amount of pressure. Pressurized steam is particularly important for industrial applications such as powering turbines and other heavy equipment. All boilers have a safety valve, which allows excess steam to be released to prevent explosions. A boiler also contains a drain, which removes contaminants and sediment from the water vessel, and a chimney, which allows heat to escape once it has passed through the water vessel.
There are two main types of boilers: fire tubes and water tubes. In a fire tube boiler, heat is directed through metal rods that pass through the middle of the water vessel. The rods are arranged in banks so that the heat can pass through the vessel many times before escaping through the chimney. The fire tube system exposes the water to the maximum amount of heated surface and also has the maximum amount of water storage space. In a water tube boiler, the heat is directed through metal rods near the outside of the water vessel. Water tube boilers are vertical and have the ability to generate more units of steam per hour but also provide less water storage than fire tube configurations.