This section contains basic information on how electricity is created, what types of generators of electricity are used, and what are the inputs and outputs (wastes) of each phase of electric generation (pre-combustion, combustion, post-combustion and ancillary processes).

How is electricity generally created? Most thermal-operating plants employ a steam cycle, which consists of the sequence of energy conversions (illustration). Fuel and air are injected continuously into a furnace, where they are burned (if coal is used it must be pulverized first). The furnace is a metal box, which in a large electric plant can be 30 meters on a side and 30 meters high. The box is lined with tubes that make up the boiler. Water flows through them and is heated and is turned into steam by thermal energy transferred from the hot combustion products outside the tubes. The steam, which reaches pressures of 1000 lbs/psi (70 kgs/psc) and temperatures above 500 degrees C, is then directed into a steam turbine, usually in a series of stages?high pressure, medium pressure, and low pressure. A turbine is a device that that turns a fluid?s internal energy (associated with temperature and pressure) into the mechanical energy of a rotating shaft. The fluid can be a liquid, a gas, or a mixture; in a steam turbine it is mostly water vapor?a gas?with some liquid water appearing at the low-pressure end. The conversion from internal to mechanical energy is accomplished by arranging blades on a shaft in such a way that the working fluid is forced to turn them as it pushes its way from the high-pressure end of the device to the low-pressure end. Between the high-pressure stage and the medium- or low-pressure stage of the turbines in large thermal-power plants, the steam is usually returned to a special section of the boiler for reheat.

The turbine shaft is connected to a generator shaft, which, as it spins, forces electric conductors to move through a magnetic field produced by electromagnets. The motion of a conductor through a magnetic field induces electric voltages, which, when connected to an external circuit, drive currents. Generators used in typical power plants produce alternating current (the direction of the voltage and the current reverses repeatedly, going through about 60 complete cycles per second) at between 10,000 and 20,000 volts. The linked turbine and generator system is often called a turbogenerator.  

Basically, this is the process that thermal-operating plants employ to generate power. Although it seems like a simple process, it can quickly become one that is complicated and very wasteful (in terms of heat waste). To ensure smoothness, uncomplicatedness, and efficiency, it is recommended that an environmental management system (EMS) be implemented in each power generation plant.

What are the common types of generators? The majority of the electricity generated in the United States today is produced by steam turbine systems. Other fossil fuel prime movers commonly used include gas turbines and internal combustion engines. Still other power generation systems use a combination of the above, such as combined-cycle and cogeneration systems. The number of these systems being built is increasing as a result of the demands placed on the industry to provide economic and efficient systems. The type of system used at a facility is chosen based on the loads, the availability of fuels, and the energy requirements of the electric power generation facility. At facilities employing these systems, other ancillary processes must be performed to support the generation of electricity. These ancillary processes may include such supporting operations as coal processing and pollution control, for example.

Click on the operations and power generation processes listed below to get a more detailed description of each.

--Coal Processing

--Air Pollution Control Processes

The following represents the major ?inputs and outputs? as it pertains to the Pre-Combustion, Combustion, Post-Combustion and Ancillary phases of power generation.

Click on each category to view ?inputs and outputs?.

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