1.0 Introduction
This chapter gives a short introduction to the research subject and describes the classification of the power plant, existing power plants, location and their generated power in Nigeria. A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After which it passes through the turbine, the steam is condensed in a condenser; this is known as the Rankine cycle.
Steam turbines are devices used to convert the pressure energy of high pressure steam to kinetic and hence electrical energy in power plants and certain types of engines. While steam turbines might be one of the more revolutionary inventions in the power generation and conversion industry. High performance steam turbines of today are specialized in their design and incorporate many efficiency increasing technologies.
Steam turbine maintenance is of high importance to keep the steam turbines efficiency high and to conform to safety standards to avoid any unforeseen dangers. The steam turbine operates under high steam pressures, and has a number of moving parts that move at extremely high velocities. The nozzles and turbine blades are designed via careful analysis and the parts are manufactured to a high degree of finish and accuracy.
A steam power plant continuously converts the energy stored in fossil fuels i.e. coal, oil, etc. or fossil fuels e.g. uranium, thorium into shaft work and ultimately into electricity. The working fluid is “water” which is sometimes in the liquid phase and sometimes in the vapor phase during its cycle of operations.
A fossil fuelled power plant is an example of bulk energy converter from fuel to electricity using “water” as the working medium. The energy released by the burning fuel is transferred to water in the boiler to generate steam at high temperature, which then expands in the steam at high temperature, which then expands in the steam turbine to a low pressure to produce shaft work. The steam leaving the turbine is condensed into water in the “condenser” where cooling water from a river or sea circulates, carrying away the heat released during condensation. The water (condensate) is then feedback to the boiler by the pump and the cycle goes on repeating itself.
Steam turbine power plants operate on “Rankine cycle” for the production of electric power. If the steam from the waste heat boiler is used for process or space heating, the term “cogeneration” is the more correct terminology (simultaneous production of electric and heat energy).
Steam turbine plants generally have a history of achieving up to 95% availability and can operate for more than a year between shutdowns for maintenance and inspections. Their unplanned or forced outage rates are typically less than 2% or less than one week per year. Modern large steam turbine plants (over 500MW) have efficiencies of about 40-45%. These plants have installed cost between $800 (441 euros) and $2000/KW (1500 euros), depending on environmental permitting requirements.
This paper presents an assessment of the state of thermal plants in Nigeria, with a view to suggesting solutions to remedy the deteriorating states of the plants, in order to improve the power supply system in the country.
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