Since the majority of electrical power produced today is from coal-fired systems, we will discuss the basic operation of this type of system. In a steam plant that produces electrical power, most of the operations are used for rotating the steam turbine. Remember that in any steam plant, heat must be produced. This heat produces steam, which moves the steam turbine, which produces a rotary motion, which finally produces electrical power.
Figure 4-2 shows the layout of a typical coal-fired electrical power plant. Notice that it is located near a river, so that cooling water can be easily provided. The water is also used to produce steam to operate the steam turbine that rotates the generator unit. The maximum efficiency of the coal-fired plant of today is approximately 40 percent when using a powdered-coal spraying process. Efficiency is calculated as: where power output is electrical power produced.
Coal requires extensive handling equipment. The coal itself must be handled, and then the ash and dust particles must be removed. At the power plant, the coal is moved to overhead hoppers by means of conveyor belts. These hoppers may typically be as large as eight stories high. The coal usually is fed into pulverizing mills by means of gravity. It is ground to a consistency similar to that of face powder, using the method discussed previously. The powdered coal is then dried using plant exhaust gases, and then blown into a furnace. The coal is ordinarily blown through a tangential or “T” burner into the furnace. These burners are placed in the four corners of a square furnace to create the turbulence needed for complete combustion.