Miscellaneous Mechanical Components
Boilers are commonly used at large facilities to act as primary or backup steam
sources. The source of heat that generates the steam varies, but the basic
operation of the boiler is the same. This chapter will summarize the operation
of a boiler.
DESCRIBE the basic operation of a boiler.
IDENTIFY the following components of a typical boiler:
The primary function of a boiler is to produce steam at a given pressure and temperature. To
accomplish this, the boiler serves as a furnace where air is mixed with fuel in a controlled
combustion process to release large quantities of heat.
The pressure-tight construction of a
boiler provides a means to absorb the heat from the combustion and transfer this heat to raise
water to a temperature such that the steam produced is of sufficient temperature and quality
(moisture content) for steam loads.
Two distinct heat sources used for boilers are electric probes and burned fuel (oil, coal, etc.)
This chapter will use fuel boilers to illustrate the typical design of boilers. Refer to Figure 9
during the following discussion.
The boiler has an enclosed space where the fuel combustion takes place, usually referred to as
the furnace or combustion chamber. Air is supplied to combine with the fuel, resulting in
combustion. The heat of combustion is absorbed by the water in the risers or circulating tubes.
The density difference between hot and cold water is the driving force to circulate the water
back to the steam drum. Eventually the water will absorb sufficient heat to produce steam.
Steam leaves the steam drum via a baffle, which causes any water droplets being carried by the
steam to drop out and drain back to the steam drum. If superheated steam is required, the steam
may then travel through a superheater. The hot combustion gasses from the furnace will heat
the steam through the superheater's thin tube walls. The steam then goes to the steam supply
system and the various steam loads.