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OPERATION AND MAINTENANCE SCHEDULE OF A STEAM TURBINE PLANT

ABSTRACT

Thermal electrical power generation is one of the major methods used in Egbin thermal station. Due to inconsistency and failure in the power supply in Nigeria, there is a need for a proper operation and maintenance schedule strategy of the various kinds of power plants accessories so as to facilitate their efficiencies and functionality. Egbin thermal station, which is one of the major power generating stations in Nigeria was used as a case study. The station has an installed capacity of 1320 MW consisting of 6 units of 220MW each. It is in the generating sector of the Power Holding Company of Nigeria (PHCN) which is the state owned Electric Power company. Egbin thermal station was commissioned on 11th May, 1985. Thermal electrical power generation is one of the major methods, used in Egbin thermal station. The major components of Egbin thermal station are boiler, steam turbine, condenser and the feed pumps. The objective of this research was to study and enumerate profound solutions in order to minimize the risk of failure and effectively manage the reliability of the substation equipment, stemming from a proper maintenance strategy. The operation and maintenance of Egbin Thermal station was examined and the conclusion was that it was challenged with insufficient Gas supply and restrictions, poor water quality and breakdown of two units due to boiler explosion in 2007, causing power generating plant to be shut down creating a 880 Mega Watts drop in power generation in the whole country. This occurrence has had a massive setback on the power plant, hence a proper maintenance strategy needs to be designed to curb the effect and develop a long lasting solution to prevent further potential disaster. Keywords: Power supply in Nigeria, steam turbine, thermal station, operation and maintenance Schedule of thermal station.

CHAPTER ONE

1. 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 the 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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