SAIMAA UNIVERSITY OF APPLIED SCIENCES Faculty of Technology Department Of Mechanical Engineering and Production Technology KEHINDE BOLAJI OKWUEJUNTI EMEKA Operation and Maintenance Schedule of a Steam Turbine Plant (A Case Study of Egbin Thermal Power Station) Thesis 2014 1" " ABSTRACT' Kehinde Bolaji Okwujuenti Emeka Operation and Maintenance Schedule of a Steam Turbine Plant, 99 pages, 2 –appendices Saimaa University of Applied Sciences, Lappeenranta Technology, Degree Programme in Mechanical Engineering and Production Technology Thesis 2014 Supervisor: Jukka Nisonen 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 " " 2" " CONTENTS ' ABSTRACT ....................................................................................................................................... 2" 1. INTRODUCTION ........................................................................................................................... 4" 1.1 The major components of a steam power plant ...................................................................... 5" 1.1.1 Steam turbine .................................................................................................................... 6" 1.1.2 Boiler ................................................................................................................................. 7" 1.1.3 Condenser ....................................................................................................................... 10" 1.2 Classification of power plant ................................................................................................. 12" 1.3 Existing power stations, location and their generated power in nigeria ................................ 15" 2 POWER PLANT ........................................................................................................................... 17" 2.1 HISTORY ON MAJOR TYPES OF POWER PLANT ............................................................ 18" 2.1.1 Steam Power Plant ......................................................................................................... 18" 2.1.2 Gas Power Plant ............................................................................................................. 20" 2.1.3 Hydropower plant ............................................................................................................ 21" 3 OPERATION AND MAINTENANCE OF A STEAM POWER PLANT CYCLE ............................. 25" 3.1 The carnot vapor cycle ........................................................................................................... 25" 3.2 Rankine cycle: The ideal for vapor power cycles ................................................................... 27" 3.3 OPERATIONS ........................................................................................................................ 28" 3.4 Energy analysis of the steam cycle ....................................................................................... 29" 3.5 Reheat cycle .......................................................................................................................... 33" 3.6 Regenerative cycle ................................................................................................................. 34" 3.7 Maintenance of steam power plant accessories .................................................................... 35" 3.7.1 Maintenance of boiler ........................................................................................................ 39" 3.7.2 General Requirements for a Safe and Efficient Boiler Room .......................................... 40" 3.7.3 Maintenance of steam turbine ......................................................................................... 41" 4 PERFORMANCE ANALYSIS OF A STEAM POWER PLANT .................................................... 46" 4.1 Formula .................................................................................................................................. 47" 5 SUMMARY AND CONCLUSIONS ............................................................................................... 69" REFERENCES ................................................................................................................................ 71" Appendix ......................................................................................................................................... 72" POWER HOLDING COMPANY OF NIGERIA PLC, EGBIN ELECTRIC POWER BUSINESS UNIT.72" " 3" " 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 4" " 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. 1.1 The major components of a steam power plant " " • Turbine (High, Intermediate and Low pressure). • Boiler (Economizer, Evaporator, Drum and Super heater). • Generator • Condenser • Feed pumps " 5" " 1.1.1 Steam turbine " Steam turbines are machines that are used to generate mechanical (rotational motion) power from the pressure energy of steam. Steam turbines are the most popular power generating devices used in the power plant industry primarily because of the high availability of water, moderate boiling point, cheap nature and mild reacting properties. The most widely used and powerful turbines of today are those that run on steam. From nuclear reactors to thermal power plants, the role of the steam turbine is both pivotal and result determining. A steam turbine is basically an assemblage of nozzles and blades. Steam turbines are not only employed to operate electric generators in thermal and nuclear power plants to produce electricity, but they are also used (a) to propel large ships, submarines and so on, and (b) to drive power absorbing machines like large compressors, blowers, fans and pumps. Turbines can be condensing or non-condensing, depending on whether the back pressure is below or equal to the atmospheric pressure. For small units without reheat, the steam turbine may consist of a single turbine when the steam expanding through the turbine exhausts to a condenser or a process line. For a large unit without reheat, the steam may expand through an initial section and then exhaust to a condenser or to a process. The initial turbine is designated as the high-pressure (HP) turbine and the second turbine the low-pressure (LP) turbine. For a single reheat cycle, the steam from the boiler flows to the HP turbine where it expands and is exhausted back to the boiler for reheating. The reheat steam coming from the boiler flows to the intermediate-pressure (IP) or reheat turbine where it expands and exhausts into a crossover line that supplies steam to double-flow LP turbine (O. I. Okoro, and T. C. Madueme, Renewable Energy, vol. 29, pp.1599-1610, 2004). 6" " Figure 1a. Steam turbine """"""""""""""""""""""""" " """"""""""""""""""""""""""""""""""""""""""""Figure 1b. Condensing steam turbine ' 1.1.2 Boiler " A boiler generates steam at the desired pressure and temperature by burning fuel in its furnace. Boilers are used in both fossil-fuel and nuclear-fuel electric generating power stations. A boiler is a complex integration of furnace, super heater, reheater, boiler or evaporator, economizer, and air preheater along with various auxiliaries such as pulverizers, burners, fans, stokes, dust collectors and precipitators, ash-handling equipment, and chimney or stack. The boiler is where phase change (or evaporator) occurs from liquid (water) to vapour (steam), essentially at constant pressure and temperature (The Control of Boilers, 2nd Edition, Sam G. Dukelow, 1991). 7" " Figure 2. Boiler The components of a boiler include • Economizer: An economizer is a heat exchanger which raises the temperature of the feed water leaving the highest pressure feed water heater to about the saturation temperature corresponding to the boiler pressure. This is done by hot flue gases exiting the last super heater or reheater at a temperature varying from 370°C to 540°C. • Evaporator: is where phase change occurs from liquid (water) to vapour (steam), essentially at constant pressure and temperature. • Drum: Made from high carbon steel with high tensile strength and its working involves temperatures around 390ºC and pressures well above 350 psi (2.4MPa). The separated steam is drawn out from the top section of the drum and distributed for process. Further heating of the saturated steam will make superheated steam normally used to drive a steam turbine. 8" " Saturated steam is drawn off the top of the drum and re-enters the furnace in through a super heater. The steam and water mixture enters the steam drum through riser tubes, drum internals consisting of demister separate the water droplets from the steam producing dry steam. The saturated water at the bottom of the steam drum flows down through the down comer pipe, normally unheated, to headers and water drum. Its accessories include a safety valve, a water- level indicator and level controller. The feed-water of the boiler is also fed to the steam drum through a feed pipe extending inside the drum, along the length of the steam drum. A steam drum is used without or in the company of a mud-drum/feed water drum which is located at a lower level. A boiler with both steam drum and mud/water drum is called a bi-drum boiler and a boiler with only a steam drum is called a mono-drum boiler. The bi-drum boiler construction is normally intended for low pressure-rating boiler while the mono-drum is mostly designed for higher pressure-rating(Fundamentals of Engineering Thermodynamics" Moran and Shapiro, Published by Wiley). • Super heater: The super heater is a heat exchanger in which heat is transferred to the saturated steam to increase its temperature. It raises the overall cycle efficiency. In addition it reduces the moisture content in the last stages of the turbine and thus increases the turbine internal efficiency. In modern utility high pressure, more than 40% of the total heat absorbed in the generation of steam takes place in the super heaters. So large surface area is required for superheating of steam (Pearsons, Sir Charles A, “The Steam Turbine” p.20-22). 9" " Figure 3. Superheater 1.1.3 Condenser " • Condenser: The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases. The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate (water) by flowing over the tubes. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain vacuum. For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100 °C where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensable air into the closed loop must be prevented. Typically the cooling water causes 10" "