Presentation on theme: "steam power plant A Presentation On Rakesh kumar Assistant professor"— Presentation transcript:
1 steam power plant A Presentation On Rakesh kumar Assistant professor By :-Rakesh kumarAssistant professorElectrical Engineering Department.BABA HIRA SINGH BHATTAL INSTITUTE OF ENGINEERING AND TECHNOLOGY LEHRAGAGA DISTT.SANGRUR (Pb.)
2 Essentials of Steam Power Plant Equipment A steam power plant must have following equipment :(a) A furnace to burn the fuel.(b) Steam generator or boiler containing water. Heat generated in the furnace is utilized to convert water into steam.(c) Main power unit such as an engine or turbine to use the heat energy of steam and perform work.(d) Piping system to convey steam and water.
3 (a) Feed water and steam flow circuit. (b) Coal and ash circuit. The flow sheet of a thermal power plant consists of the following four main circuits :(a) Feed water and steam flow circuit.(b) Coal and ash circuit.(c) Air and gas circuit.(d) Cooling water circuit.
4 A steam power plant using steam as working substance works basically on Rankine cycle. Steam is generated in a boiler, expanded in the prime mover and condensed in the condenser and fed into the boiler again.
5 The different types of components used in steam power plant (a) High pressure boiler.(b) Prime mover .(c) Condensers and cooling towers .(d) Coal handling system .(e) Ash and dust handling system .(f) Draught system .(g) Feed water purification plant .(h) Pumping system .(i) Air preheater, economizer, super heater, feed heaters.
6 Types of steam Generators Horizontal vertical or inclined.Fire tube or water tube.Externally fired or internally fired.Forced circulation and natural circulation.High pressure or low pressure boiler.
7 Dalton’s lawThe partial pressure pressure of each constituent is that pressure which the gas would exert if it occupied alone that volume occupied by the mixture at the same temperature.
8 Factors that should be considered while selecting the boiler Working pressure and quality of steam required.Steam generation rate.Floor area available.The portable load factor.Erection facilities.
9 Properties of good steam generators It should be absolutely reliable.It should occupy minimum space.It should be light in weight.Capable of quick starting.Erection of boiler should be simple.
10 CLASSIFICATION OF STEAM POWER PLANTS Steam Power Plants are Classified asBy fuel.By prime mover.By cooling tower.
11 CLASSIFICATION OF STEAM POWER PLANTS Steam Power Plants are also Classified as;Central stations; the electrical energy available from these stations is meant for sale to the consumers who wish to purchase it.Industrial/ captive power stations; this type of power station is run by the manufacturing company for its own use and its output is not available for general sale.
12 Comparison between jet and surface condenser Jet condenser; low manufacturing cost. Low upkeeps, requires small floor space and more auxiliary power required.surface condenser; high manufacturing cost. high upkeeps, requires large floor space and less auxiliary power required.
13 Advantages of feed water heaters Feed water heating improves overall plant efficiency.Quantity of steam produced by the boiler is increase.Thermal stress due to cold water entering the boiler drum are avoided.Chance of boiler corrosion are decrease.
14 classification of dust collectors Dust collectors are Classified as;Mechanical dust collectors;Wet type(scrubbers).Spray type, packed type and impingement type.(b) Dry type.Gravitational separators, cyclone separators,electrical dust collectors;Rod type and plate type.
15 DIFFERENT TYPES OF BOILERS USED IN STEAM POWER PLANTS horizontal, vertical or inclined.fire tube and water tube .Externally or internally fired.Forced or natural circulation.High pressure or low pressure.Stationary or portable.Single-tube and multi-tube.
17 Steam Turbine Power Plant hot gasessuperheatedsteamcompressedwaterSteam Generator(Boiler / Furnace)SteamTurbineCPumpGenCondensersaturatedwatersaturatedsteamcooling water
18 Schematic arrangement of equipment of a steam power station. Coal received in coal storage yard of power station is transferred in the furnace by coal handling unit. Heat produced due to burning of coal is utilized in converting water contained in boiler drum into steam at suitable pressure and temperature. The steam generated is passed through the superheater.
19 Superheated steam then flows through the turbine Superheated steam then flows through the turbine. After doing work in the turbine the pressure of steam is reduced. Steam leaving the turbine passes through the condenser which is maintained the low pressure of steam at the exhaust of turbine.
20 Steam pressure in the condenser depends upon flow rate and temperature of cooling water and on effectiveness of air removal equipment.Water circulating through the condenser may be taken from the various sources such as river, lake or sea. If sufficient quantity of water is not available the hot water coming out of the condenser may be cooled in cooling towers and circulated again through the condenser.Bled steam taken from the turbine at suitable extraction points is sent to low pressure and high pressure water heaters.
21 Air taken from the atmosphere is first passed through the air pre-heater, where it is heated by flue gases. The hot air then passes through the furnace.The flue gases after passing over boiler and superheater tubes, flow through the dust collector and then through economiser, air pre-heater and finally they are exhausted to the atmosphere through the chimney.
22 Disadvantage of steam power plant Maintenance and operating cost are high.Long time required for erection and putting into action .Large quantity of water is required.Great difficulty experienced in coal handling .Efficiency decreases rapidly below about 75 percent load.
23 Mechanical equipment in Thermal power station. BOILERSUPER HEATERECONOMISERAIR PREHEATERTURBINECONDENSER
24 SuperheaterThe superheater consists of a superheater header and superheater elements. Steam from the main steam pipe arrives at the saturated steam chamber of the superheater header and is fed into the superheater elements.Superheated steam arrives back at the superheated steam chamber of the superheater header and is fed into the steam pipe to the cylinders. Superheated steam is more expansive.
25 Advantages of superheated steam Capacity to do work is increased without increasing its pressure.High temperature of super heated steam results in an increase in thermal efficiency.Heat losses due to condensation of stem on cylinder walls are avoided to a great extent.Does not produce corrosion effect on turbine.
26 Superheater It is a heating device. It is used to raise temp of steam at const pressure.It removes even last traces of moisture.
27 Classification of super heater Convection.Radiation.Combination of convection and radiation.
28 ReheaterThe function of reheater is similar to the superheater in that it serves to elevate the steam temperature. Primary steam is supplied to the high pressure turbine.After passing through the high pressure turbine, the steam is returned to the steam generator for reheating (in a reheater) after which it is sent to the low pressure turbine. A second reheat cycle may also be provided.
29 Soot BlowersThe fuel used in thermal power plants causes soot and this is deposited on the boiler tubes, economizer tubes, air pre heaters, etc.This drastically reduces the amount of heat transfer of the heat exchangers. Soot blowers control the formation of soot and reduce its corrosive effects.The types of soot blowers are fixed type, which may be further classified into lane type and mass type depending upon the type of spray and nozzle used.
30 CondenserThe use of a condenser in a power plant is to improve the efficiency of the power plant by decreasing the exhaust pressure of the steam below atmosphere.Another advantage of the condenser is that the steam condensed may be recovered to provide a source of good pure feed water to the boiler and reduce the water softening capacity to a considerable extent. A condenser is one of the essential components of a power plant.
31 Functions of Condensers The main purposes of the condenser are to condense the exhaust steam from the turbine for reuse in the cycle and to maximize turbine efficiency by maintaining proper vacuum.As the operating pressure of the condenser is lowered (vacuum is increased), the enthalpy drop of the expanding steam in the turbine will also increase. This will increase the amount of available work from the turbine (electrical output).
32 Cooling TowerThe importance of the cooling tower is felt when the cooling water from the condenser has to be cooled.The cooling water after condensing the steam becomes hot and it has to be cooled as it belongs to a closed system. The Cooling towers do the job of decreasing the temperature of the cooling water after condensing the steam in the condenser.
33 Cooling Towers have one function : Remove heat from the water discharged from the condenser so that the water can be discharged to the river or re-circulated and reused.
34 A cooling tower extracts heat from water by evaporation A cooling tower extracts heat from water by evaporation. In an evaporative cooling tower, a small portion of the water being cooled is allowed to evaporate into a moving air stream to provide significant cooling to the rest of that water stream.
35 Cooling Towers are commonly used to provide lower than ambient water temperatures and are more cost effective and energy efficient than most other alternatives.The smallest cooling towers are structured for only a few litres of water per minute while the largest cooling towers may handle upwards of thousands of litres per minute. The pipes are obviously much larger to accommodate this much water in the larger towers and can range up to 12 inches in diameter.
36 Advantages of regenerative cycle Improve overall plant efficiency.Protect boiler corrosion.Avoid the thermal stresses due to cold water entering the boiler .Increased the quantity of steam produced by boiler.
37 Function of economizer To extract a part of heat from the fuel gas coming out of the boiler.To use heat for heating feed water to the boiler.To increases the efficiency of boiler.
38 The economizer is a feed water heater, deriving heat from the flue gases. The justifiable cost of the economizer depends on the total gain in efficiency. In turn this depends on the flue gas temperature leaving the boiler and the feed water inlet temperature.
39 Air Pre-heaterThe flue gases coming out of the economizer is used to preheat the air before supplying it to the combustion chamber. An increase in air temperature of 20 degrees can be achieved by this method. The pre heated air is used for combustion and also to dry the crushed coal before pulverizing.
40 Advantages of mechanical handling Higher reliability.Less labour required.Operation is easy and smooth.Economical for large capacity plant.Losses in transport are minimised.Easily started.
41 Disadvantages of mechanical handling Need continuous maintenance and repair.Capital cost of plant is increased.
44 Total Heat Total Work Loss??? Where??? Work Steam Turbine Power Plant hot gasessuperheatedsteamTotalcompressedwaterSteam GeneratorWorkoutLoss???Where???SteamTurbineCPumpWorkinGenCondensersaturatedwatersaturatedsteamcooling water
45 2nd Law of Thermodynamics when heat is converted into work, According to the2nd Law of Thermodynamicswhen heat is converted into work,part of the heat energy must be wastedPower generationtypeUnit size (MW)Energy wasted (MW)Diesel engine7 – 22Gas Turbine36 – 78Steam Turbine120 – 560Combined (ST & GT)150 – 380Nuclear (BWR & PWR)330 – 760R. Shanthini Aug 2010
47 How can We Increase the Efficiency of the Rankine cycle? Rankine cycle efficiency can be increased by increasing average temperature at which heat is transferred to the working fluid in the boiler or decreasing the average temperature at which heat is rejected from the working fluid in the condenser. That is, the average fluid temperature should be as high as possible during heat addition and as low as possible during heat rejection.
48 The three ways by which efficiency of the Rankine cycle can be increased are : (a) Lowering the condenser pressure.(b) Superheating the steam to high temperatures.(c) Increasing the boiler pressure.
49 The thermal efficiency of the Rankine cycle can be increased by increasing the average temperature at which heat is added to the working fluid and/or by decreasing the average temperature at which heat is rejected to the cooling medium. The average temperature during heat rejection can be decreased by lowering the turbine exit pressure.
50 Consequently, the condenser pressure of most vapor power plants is well below the atmospheric pressure. The average temperature during heat addition can be increased by raising the boiler pressure or by superheating the fluid to high temperatures. There is a limit to the degree of superheating, however, since the fluid temperature is not allowed to exceed a metallurgically safe value.
51 Superheating has the added advantage of decreasing the moisture content of the steam at the turbine exit. Lowering the exhaust pressure or raising the boiler pressure, however, increases the moisture content. To take advantage of the improved efficiencies at higher boiler pressures and lower condenser pressures, steam is usually reheated after expanding partially in the high-pressure turbine.
52 This is done by extracting the steam after partial extraction in the high-pressure turbine, sending it back to the boiler where it is reheated at constant pressure, and returning it to the low-pressure turbine for complete expansion to the condenser pressure.
53 The average temperature during the reheat process, and thus the thermal efficiency of the cycle, can be increased by increasing the number of expansion and reheat stages. As the number of stages is increased, the expansion and reheat processes approach an isothermal process at maximum temperature. Reheating also decreases the moisture content at the turbine exit.
54 Another way of increasing the thermal efficiency of the Rankine cycle is by regeneration. During a regeneration process, liquid water (feed water) leaving the pump is heated by some steam bled off the turbine at some intermediate pressure in devices called feed water heaters.
55 The two streams are mixed in open feed water heaters, and the mixture leaves as a saturated liquid at the heater pressure. In closed feed water heaters, heat is transferred from the steam to the feed water without mixing.
56 The production of more than one useful form of energy (such as process heat and electric power) from the same energy source is called cogeneration. Cogeneration plants produce electric power while meeting the process heat requirements of certain industrial processes.
57 This way, more of the energy transferred to the fluid in the boiler is utilized for a useful purpose. The faction of energy that is used for either process heat or power generation is called the utilization factor of the cogeneration plant.
58 The overall thermal efficiency of a power plant can be increased by using binary cycles or combined cycles. A binary cycle is composed of two separate cycles, one at high temperatures (topping cycle) and the other at relatively low temperatures.
59 The most common combined cycle is the gas-steam combined cycle where a gas-turbine cycle operates at the high-temperature range and a steam-turbine cycle at the low-temperature range. Steam is heated by the high-temperature exhaust gases leaving the gas turbine. Combined cycles have a higher thermal efficiency than the steam- or gas-turbine cycles operating alone.
60 Selection of plant site The selection of plant site for thermal power plant compared with hydro-power plant is more difficult as it involves number of factors to be considered for its economic justification.A few important factors to be considered for the selection of thermal power plants.
61 Selection of plant site AVAILABILITY OF COAL.Huge quantity of coal is required for large thermal plants.ASH DISPOSAL FACILITIES.SPACE REQUIREMENT.NATURE OF LAND.AVAILABILITY OF WATER.
62 Selection of plant site TRANSPORT FACILITYIES.AVAILABILITY OF LABOUR.PUBLIC PROBLEMS.SIZE OF THE PLANT.
63 ABOUT ELECTROSTATIC PRECIPITATOR Nowadays, the environment protection has become a crucial problem and the authorities are requested to set increasingly more stringent limits , one of which is the emissions from the industrial plants of solid particulate and other gaseous pollutants.
64 ABOUT ELECTROSTATIC PRECIPITATOR What is ESPElectrostatic precipitator (ESP) is a widely used device in so many different domains to remove the pollutant particulates, especially in industrial plants.
65 HOW ESP WORKS Main process of ESP Generally, the processes of electrostatic precipitator are known as three main stages: particle charging, transport and collection.
66 Schematic of wire-plate ESP Schematic of wire-plate electrostatic precipitator
67 Mechanism of ESPMechanism of electrostatic precipitator
68 PROCESS OF Particle charging Particle charging is the first and foremost beginning in processes.As the voltage applied on precipitator reach threshold value, the space inside divided into ionization region and drift region.
69 The electric field magnitude around the negative electrode is so strong that the electrons escape from molecule.Under the influence of electric field, the positive ions move towards the corona, while the negative ions and electrons towards the collecting plates.
70 Particle transportIn the moving way, under the influence of electric field, negative ions cohere and charge the particles, make the particles be forced towards collecting-plate.
71 Particle collectionAs soon as the particles reach the plate, they will be neutralized and packed by the succeeded ones subsequently. The continuous process happens, as a result, particles are collected on the collecting plate.
72 Introduction What is a Boiler? Vessel that heats water to become hot water or steamAt atmospheric pressure water volume increases 1,600 timesHot water or steam used to transfer heat to a processA boiler is an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam.When water at atmospheric pressure is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be an equipment that must be treated with utmost careThe hot water or steam under pressure is then usable for transferring the heat to a process.
73 The boiler is a rectangular furnace about 50 feet (15 m) on a side and 130 feet (40 m) tall. Its walls are made of a web of high pressure steel tubes about 2.3 inches (58 mm) in diameter.
74 A boiler should fulfill the following requirements Safety : The boiler should be safe under operating conditions.(b) Accessibility : The various parts of the boiler should be accessible for repair and maintenance.(c) Capacity : The boiler should be capable of supplying steam according to the requirements.
75 (d) Efficiency : To permit efficient operation, the boiler should be able to absorb a maximum amount of heat produced due to burning of fuel in the furnace.(e) It should be simple in construction and its maintenance cost should be low.(f) Its initial cost should be low.(g) The boiler should have no joints exposed to flames.(h) The boiler should be capable of quick starting and loading.
76 Introduction BOILER Figure: Schematic overview of a boiler room STEAM TO PROCESSEXHAUST GASVENTSTACKDEAERATORECO- NOMI- ZERPUMPSBOILERAs you can see, the boiler system comprises of a feed water system (click and circle will appear); a steam system (click and 2 circles will appear); as well as a fuel system (click and circle will appear).This is a schematic overview of a boiler room:The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are:(1) Condensate or condensed steam returned from the processes and(2) Makeup water (treated raw water) which must come from outside the boiler room and plant processes. For higher boiler efficiencies, an economizer preheats the feed water using the waste heat in the flue gas.The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges.The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system.VENTBURNERWATER SOURCEBLOW DOWN SEPARATORFUELBRINECHEMICAL FEEDSOFTENERSFigure: Schematic overview of a boiler room
77 What Type of Boilers Are There? Types of BoilersWhat Type of Boilers Are There?Fire Tube BoilerWater Tube BoilerPackaged BoilerFluidized Bed (FBC) BoilerStoker Fired BoilerPulverized Fuel BoilerWaste Heat BoilerThermic Fluid Heater (not a boiler!)There are different types of boilers based on different fuels and with various capacities.(Questions to audience) What type of boilers do you know of? What kind of boilers do you use in the industry where you work? (Discussion)(Click once and boiler types will appear) We will look closer at the following types of boilers: Fire Tube Boiler, Water Tube Boiler, Packaged Boiler, Fluidized Bed Boiler, Stoker Fired Boiler, Pulverized Fuel Boiler and Waste Heat Boiler.
78 According to flow of water and hot gases : (a) Water tube The boilers can be classified according to the following criteria.According to flow of water and hot gases :(a) Water tube(b) Fire tube.
79 Type of Boilers 1. Fire Tube Boiler Relatively small steam capacities (12,000 kg/hour)Low to medium steam pressures (18 kg/cm2)Operates with oil, gas or solid fuelsTo begin with, we will look at the fire tube boiler:This is generally used for relatively small steam capacities and at low to medium steam pressures.The steam rates for fire tube boilers are up to 12,000 kg/hour with pressures of 18 kg/cm2.Fire tube boilers can operate on oil, gas or solid fuels.The figure illustrates how a fire tube boiler works. The fuel is burned and heats up the water to steam which is turn channeled to the process. Today, most fire tube boiler are in a packaged construction for all fuels.
80 Type of Boilers 2. Water Tube Boiler Used for high steam demand and pressure requirementsCapacity range of 4,500 – 120,000 kg/hourCombustion efficiency enhanced by induced draft provisionsLower tolerance for water quality and needs water treatment plantIn a water tube boiler, boiler feed water flows through the tubes and enters the boiler drum. The circulated water is heated by the combustion gases and converted into steam at the vapour space in the drum. These boilers are selected when the steam demand as well as steam pressure requirements are high as in the case of process cum power boiler / power boilers.Most modern water boiler tube designs are within the capacity range 4,500 – 120,000 kg/hour of steam, at very high pressures. Many water tube boilers are of “packaged” construction if oil and /or gas are to be used as fuel. Solid fuel fired water tube designs are available but packaged designs are less common.The features of water tube boilers are:Forced, induced and balanced draft provisions help to improve combustion efficiency.Less tolerance for water quality calls for water treatment plant.Higher thermal efficiency levels are possible
81 3. Packaged Boiler Comes in complete package Features High heat transferFaster evaporationGood convective heat transferGood combustion efficiencyHigh thermal efficiencyClassified based on number of passesOil BurnerTo ChimneyDoes anyone recognize what type of boiler this is? (Click once and name will appear) This is a packaged boiler. More specifically, it is a typical 3 pass, oil fired packaged boiler.The packaged boiler is so called because it comes as a complete package. Once delivered to a site, it requires only the steam, water pipe work, fuel supply and electrical connections to be made to become operational.Package boilers are generally of a shell type with a fire tube design so as to achieve high heat transfer rates by both radiation and convection.The features of packaged boilers are:Small combustion space and high heat release rate resulting in faster evaporation.Large number of small diameter tubes leading to good convective heat transfer.Forced or induced draft systems resulting in good combustion efficiency.Number of passes resulting in better overall heat transfer.Higher thermal efficiency levels compared with other boilers.These boilers are classified based on the number of passes - the number of times the hot combustion gases pass through the boiler.
82 Working of power plantPulverized coal is air-blown into the furnace from fuel nozzles at the four corners and it rapidly burns, forming a large fireball at the center. The thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter.
83 The water circulation rate in the boiler is three to four times the throughput and is typically driven by pumps. As the water in the boiler circulates it absorbs heat and changes into steam at 700 °F (371 °C) and 3,200 psi
84 The water enters the boiler through a section in the convection pass called the economizer. From the economizer it passes to the steam drum. Once the water enters the steam drum it goes down to the lower inlet water wall headers.
85 From the inlet headers the water rises through the water walls and is eventually turned into steam due to the heat being generated by the burners located on the front and rear water walls (typically). As the water is turned into steam/vapor in the water walls, the steam/vapor once again enters the steam drum.
86 The steam/vapor is passed through a series of steam and water separators and then dryers inside the steam drum The steam separators and dryers remove water droplets from the steam and the cycle through the water walls is repeated. This process is known as natural circulation.
87 super heaterFossil fuel power plants can have a super heater and/or re-heater section in the steam generating furnace. In a fossil fuel plant, after the steam is conditioned by the drying equipment inside the steam drum, it is piped from the upper drum area into tubes inside an area of the furnace known as the super heater,
88 which has an elaborate set up of tubing where the steam vapor picks up more energy from hot flue gases outside the tubing and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves before the high pressure turbine.
89 CondenserThe 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.
90 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.
91 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-condensible air into the closed loop must be prevented.
92 The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.
93 The condenser tubes are made of brass or stainless steel to resist corrosion from either side. Nevertheless they may become internally fouled during operation by bacteria or algae in the cooling water or by mineral scaling, all of which inhibit heat transfer and reduce thermodynamic efficiency.
94 Many plants include an automatic cleaning system that circulates sponge rubber balls through the tubes to scrub them clean without the need to take the system off-line.
95 Re heaterPower plant furnaces may have a re heater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the re heater tubes to pickup more energy to go drive intermediate or lower pressure turbines.
96 Main pollutants from a power system Non –toxic dustSulphurous anhydrideCarbon monoxideNitrogen dioxideSoot (fly ash)Hydrogen sulphidePollution can be define as the contamination of soil, air and water with undesirable amount of material and heat.
97 Acid rain; the rain which contain acid as its constituents, brings all the acid down from high above the environment.Contaminant; it is the another name of pollution. It is undesirable substances which may be physical, chemical or biological.Pollutant; these are undesirable substances present in the environment these can be NO2, SO2, CO2,smoke,salt, bacteria.
98 Bad effects of thermal pollution Lot of heat is injected into biosphere from thermal power plant, through exhaust gases and waste water. The major problem is the effect of discharge of large quantity of heated wasted water into natural water basins. Hot water raises the temperature and disturbs the natural ecological balance
99 Advantages of combined operation of plants Greater reliability of supply to the consumers.Avoid complete shut down.The overall cost of energy per unit of an interconnected system is less.There is a more effective use of transmission line facilities.Less capital investment required.Less expenses on supervision, operation and maintenance.
100 Due to limited generating capacity diesel power stations is not suitable for base load plants. Nuclear power stations is not suitable for peak load plants.Incremental rate curve shows that as output power increases, cost of plant also increases.