A power plant (or power station) is a system or facility that uses a renewable or non-renewable primary energy source to generate electricity. The main function of a power plant is electricity generation, which it achieves using energy extracted from any of various sources. This article discusses power plant definition, components and electricity generation process, according to the outline below;
Power Plant Definition: 6 Ways to Define Power Plants
To give an alternative power plant definition within the same context, it is possible to mildly describe the generating mechanism involved, as follows;
A power plant is a rotary, turbine or dynamo-driven system that works to convert energy from a source to electricity for utility purposes.
Multiple options exist with respect to the energy sources used to generate electricity. These sources can be mentioned in the power plant definition;
A power plant is an industrial facility which is driven by fossil fuels like coal and diesel, as well as renewable resources like solar, wind, biomass, converted biofuel, and geothermal, and which uses these resources to generate electricity.
Power plant definition in terms of equipment and components, is given as follows;
A power plant is a facility or component of an energy system that consists of reactors, turbines, alternators and generators which work to generate electricity from a fuel.
The applications of power plants can be used to define them, as follows;
A power plant is an energy system that is used for cogeneration (heat and power generation) as well as electricity supply for industrial, commercial and domestic purposes.
Lastly, power plant definition can be can be given with reference to the existing types;
A power plant is an electricity generation facility, which may be categorized into various types such as nuclear, diesel-driven, coal-driven, solar, geothermal, wind, gas-driven and hydroelectric power plants .
Components of a Power Plant
The three main parts of a conventional power plant are the fuel storage, turbine and generator. Other components include boiler, condenser, drum, draft, cooling tower, circulating water pump, re-heater, economizer, water treatment unit, penstock, fore-bay and tail-race.
These components are discussed below;
1). Fuel Storage as one of the Power Plant Components
The fuel storage unit is very important in a power plant because it safely houses the energy source in such a manner that it can be easily supplied to the system.
Fuel storage systems may vary in size and design, based on the type and capacity of the power plant. As such, these two factors (type and capacity) must be considered when designing a fuel storage system for a power plant.
Before a power plant can be used to generate electricity, the energy source must be fed into the fuel storage unit.
In cases where the energy source is nuclear fuel or biomass, a reactor may be used as fuel storage and conversion system. For liquid and gaseous energy sources, the fuel storage unit may take the form of a reservoir or tank, which houses these fluids.
The turbine produces mechanical energy that is used to generate electricity .
It usually occurs in the form of a rotary component that can be driven into motion by hydraulic force provided from the fuel or energy source. For a turbine to function optimally, it is often equipped with blades that interact with the hydraulic force to cause rotation.
The most common form of energy conversion which is induced by the turbine in a power plant is kineto-mechanical or kinetic-to-mechanical conversion, where a fluid provides kinetic energy from the fuel, and the turbine converts this to mechanical energy in the form of rotary motion.
Based on the hydraulic pressure and kinetic energy of the fluid, power plant turbines can be classified into low, medium and high-pressure types.
3). Generator as one of the Power Plant Components
As its name implies, the function of a generator in a power plant is electricity generation.
It achieves this basically by the induction of electric currents using mechanical energy provided by the turbine. Power plant generators work by electromagnetic induction , which is a principle by which electricity is induced when a conductor rotates in a magnetic field.
Generators comprise of prime mover, magnet, and alternator. The prime mover is the rotary part, which transmits mechanical energy from the turbine to the generator. The magnet may be a permanent magnet or an electromagnet, and its main function is to create the magnetic field required for electromagnetic induction.
In most cases, the generator in a power plant produces alternating current (AC), because this is the more usable form of electricity than its counterpart; direct current (DC).
Alternating current is produced by the alternator, whose primary function is to reverse the direction of the induced potential difference thereby producing a constantly-changing current output.
4). Boiler as one of the Power Plant Components
In a power plant, the boiler serves the purpose of combustion, heat transfer and hydraulic pressure production .
Boilers are found in power plants that use hydraulic heating and pressure mechanisms to drive the turbine. These include plants where the fuel is coal or biomass, among other options, and where the turbine is driven by steam and/or flue gases.
In the boiler, a hydraulic fluid like water is heated with energy from combustion of the fuel/energy source. Vapor formed as a result of this boiling is released and brought into contact with the turbine or prime mover of the power plant, so as to produce electricity.
5). Condenser as one of the Power Plant Components
Condensers are made up of tubes through which a cooling fluid flows.
The role of the condenser in a power station is basically to reduce the temperature of the exhaust vapor and flue gases from the system .
These gases are usually released after they have come in contact with the turbine. By cooling, the condenser conserves the hydraulic fluid(s) of the power plant and ensures that they are effectively recycled with minimal losses.
The condenser also regulates the temperature of the system, thereby preventing problems that may occur due to overheating.
6). Drum as one of the Power Plant Components
The drum is found mainly in steam power plants.
Its serves as a reservoir for the hydraulic fluid. In a drum, the water and steam are usually contained at high pressure. This helps to separate the two different phases from each other, while ensuring that steam (and/or flue gases) can be effectively released to the turbine.
In a conventional steam power plant, the drum is positioned before the turbine, so that steam from this component can be used to produce mechanical energy which causes the turbine to experience motion.
7). The Draft
The term ‘draft’ in a power plant is used to describe the concept, components and mechanisms related to fluid flow and hydraulic pressure.
As a component or set of components, a draft in a power plant is a tube, fan or pump system that controls the flow and regulates the pressure of fluids within the plant.
Draft tubes usually connect the turbine to the tail-race or outlet of the power plant, so that vapor and flue gases are effectively discharged from the system.
The draft tube may be used to send these flue gases and vapors through a fluid treatment or cleaning apparatus, which can remove toxins before the fluid is ejected into the environment. Alternatively it can be used to supply and regulate the pressure of fluid in the boiler.
Power plant draft fans can be classified as induced or forced draft fans based on the manner of their operation; where induced type is used to eject gaseous fluids and forced type is used to supply air to the boiler, for combustion.
8). Cooling Tower
Cooling tower is especially needed in power plants that use steam turbines to generate electricity.
Like the condenser, cooling towers play the primary role of temperature regulation. However, unlike condensers which function by condensation, cooling towers function by evaporation.
The principle behind the usage of cooling tower in a power station, is that as water (or any other hydraulic fluid) evaporates, the remaining fluid in the system experiences a drop in temperature.
Additionally, the cooling tower works alongside the condenser of the power station, to further cool ejected fluid and return it to the system for reuse . This is achieved by reducing the temperature of the circulating (cooling) fluid in the condenser chambers or tubes.
Cooling towers are often associated with large-scale power plants that use energy sources like coal, nuclear and biomass. The vapor released by the cooling tower may have environmental effects , since it is likely to include water vapor and carbon-bearing gases.
9). The Circulating Water Pump as one of the Power Plant Components
Circulating pump is a subcomponent which works with the condenser by supplying water for cooling, from a source. This source may be natural or artificial, and is always stationed in close proximity to the power plant.
In order to serve its purpose, the water source must be of high volume. The pump(s) must also be capable of providing sufficient pressure to drive the fluid through the circulating system. Overall design of this component depends on the scale and type of the power plant.
10). Re-Heater as one of the Power Plant Components
The re-heater plays the key role of optimizing the temperature of the hydraulic fluid in the system.
When steam is produced by the boiler and used to mobilize the turbine, it loses some of its heat in the process. The role of the re-heater is to increase the temperature of this steam or vapor, so as to enable it remain effective.
In power plants that are equipped with re-heaters, the energy efficiency of the system is usually relatively-high.
The economizer is a component whose function is to conserve energy in the power plant, while electricity is being generated.
This is achieved through heat recovery. Economizers basically recover heat from the flue gases and vapor released from the boiler, and applies this heat to the feed-water of the same boiler .
What this mechanism does is to reduce the overall amount of energy that is used to heat the hydraulic fluid and drive the turbine, thereby increasing the efficiency of the boiler and the entire power plant system.
The function of the economizer can also be described with terms like heat capture and cogeneration, as it involves the capture and utilization of waste heat.
12). Water Treatment Unit
Water from the boiler which is turned to vapor and used to drive the turbine; usually requires some form of treatment before it can be either reused or discarded.
This is because the water comes in contact with the boiler and turbine equipment in the course of its circulation.
Contaminants in such water will most likely include suspended particles and dissolved solids. The water treatment unit usually includes coagulants and softeners, which help to segregate the contaminants.
Other treatment mechanisms can also be integrated into this component, such as the use of membrane filtration.
13). Penstock as one of the Components of a Power Plant
In power stations, a penstock is an of various pipes or conduits that serve as transmission equipment for hydraulic fluid, usually from the boiler or inlet to the turbine.
The design of a penstock may include inclined flow pathways and fortified walls which serve to optimize the transmission of fluid.
14). Fore-bay as one of the Power Plant Components
As the name implies, a fore-bay is a reservoir of water which occurs before a larger water body.
In the same vein, an after-bay is a reservoir which occurs after a larger body of water.
The fore-bay can be described as a kind of surge tank, based on its function. Water from this reservoir is carried into the power system (to the boiler) by penstocks. In hydroelectric power plants, the fore-bay serves as a reservoir from which water is recycled (used to drive the turbine, then treated) for power generation.
The tailrace or tail-race is an outlet from which hydraulic fluid exits the plant.
It is usually designed with the appropriate diameter and resistant material to withstand outflow. The main purpose of this component is to control the emission pattern for water from the plant, by preventing scouring, silting and other possible drawbacks.
Tailrace is most commonly used in hydroelectric power stations due to the large volumes of water that come in contact with the turbine or wheel.
Electricity Generation in a Power Plant: An outline of the Process
Electricity is generated in a power plant in three steps, which include primary energy conversion, kinetic energy conversion and electromagnetic induction.
These steps are each discussed below;
1). Primary Energy Conversion
This is the first stage in the process of electricity generation in a power plant.
Primary energy is energy from the fuel or renewable resource that is being used by the power station. These sources may be fossil fuels, biomass, solar, wind or geothermal, among others.
In primary energy conversion, energy from the primary fuel or resource is extracted; which is used for electricity generation.
Combustion is a typical process by which primary conversion takes place, and it involves the burning of a fuel to produce heat energy. Energy from renewable resources may also occur in the form of heat.
2). Kinetic Energy Conversion
Kinetic energy conversion occurs when the energy from the fuel is used to energize a fluid through heating.
This phase of the electricity generation process usually occurs in the boiler or combustion chamber of a power plant.
Water or any other suitable fluid is heated with energy derived from the primary source or fuel. As a result, the fluid vaporizes to form steam or flue gas which is energetic and possesses significant amounts of kinetic energy.
3). Electromagnetic Induction
Electromagnetic induction is the final step in the process of electricity generation in a power station or plant.
Kinetic energy from the heated fluid is used to drive a mechanical component, such as a turbine. This leads to the production of mechanical energy in the form of motion.
Electromagnetic induction occurs when the moving component is placed in a stationary magnetic field, leading to the induced flow of electrons and the generation of electricity.
In order for electromagnetic induction to be possible, the power plant must be equipped with an electric generator which contains a permanent or electromagnet that provides the stationary field. The amount of power that can be generated (that is the capacity) depends on the scale of the power plant and the features of the generator.
A power plant is a system which is designed to generate electricity from a primary source, through energy conversion and electromagnetism.
Parts of a power plant include;
- Fuel Storage
- Cooling Tower
- Circulating Water Pump
- Water Treatment Unit
Electricity is generated in a power station through the following three steps;
- Primary Energy Conversion
- Kinetic Energy Conversion
- Electromagnetic Induction
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