UNIT 1 PART 3 PDF

ENIR 11 ENERGY AND ENVIRONMENTAL ENGINEERING Different type of conventional power plant  POWER PLANT A power plant is an industrial facility used to generate electric power with the help of one or more generators which converts different energy sources into electric po...

ENIR 11 ENERGY AND ENVIRONMENTAL ENGINEERING Different type of conventional power plant  POWER PLANT A power plant is an industrial facility used to generate electric power with the help of one or more generators which converts different energy sources into electric power. Electricity is a secondary energy source, which means that electricity is obtained from the conversion of other primary sources of energy, such as coal, natural gas, nuclear, solar, or wind energy. The energy sources used to make electricity can be renewable or non-renewable, but electricity itself is neither renewable or non- renewable. The power plant is the location in which the energy conversions take place. Traditionally, large power plants have been located in sub-urban regions away from cities, as they need a vast area of land and sometimes water. All electricity produced in a power plant is alternating current (AC).  Thermal power plant Thermal power plant or steam power plant is a generating station which converts heat energy of fossil fuels into electrical energy. Generally bituminous, brown or peat type coal are used as the fuel for coal based thermal power plant. In a thermal power plant, coal is burnt in a big boiler which produces steam at high pressure and temperature. This steam is passed through a steam turbine which converts steam's heat energy into mechanical energy. The steam turbine acts as a prime mover and it is coupled to an alternator. Now alternator collects the mechanical energy from the steam turbine and convert into electrical energy. In this power plant, steam turbine sometimes acts as an auxiliary equipment's like pumps, strokes etc. Though thermal efficiency and overall efficiency of thermal power plant is comparatively less than other power plant like nuclear power plant but still it is very popular. The only reason behind that, is coal. It is very cheap and easily available as well. Still, now maximum energy is supplied by the coal-based thermal power plant.  TYPES OF THERMAL POWER PLANT 1. Condensing Type Thermal Power Plant:- In Condensing type thermal power plant, discharges exhaust steam is coming to a condenser which creates suction at very low pressure and it allows the expansion of steam in the turbine to a very low pressure. As a result, turbine's efficiency increases. This type of thermal power plant plays an important role where there is a question of availability of pure water. Because condensed steam water in the condenser can be re-circulated to the boiler with the help of pumps. This plant extracts more energy from per kg of steam and develops the greater amount of power according to the size of turbine. Condensing type plants are used to supply electrical energy all type's of consumers (domestic, industrial and commercial). Since this type of plant is very economical, so it is used both hydro power plant and thermal power plants for economical power supply all the time. The condensing type system is also used in central power plant. 2. Non-Condensing Type Thermal Power Plant:- In non-condensing type thermal power plant, exhaust steam is coming from turbine and steam pressure greater the atmospheric pressure. This type of thermal power plant, a continuous supply of fresh feed water is required. Industrial and Captive power plants are the non-condensing types. In industries, steam is used for process purpose and it is also used in the steam turbine for generation of electrical energy. This types of thermal power plant is basically small capacity power plants (nearly 10 MW). Block Diagram of Thermal Power Plant Different stages of power plant: (i) Coal and Dust Handling Arrangement Coal storage Coal handling Ash handling Ash storage Transportation Boiler plant plant plant plant coal Coal pulverization combustion and process ash formation (ii) Steam Generating Plant Utilize flue gas heat to increase air temp (increased thermal effic and steam capacity per sq m) Air preheater Economiser Boiler Superheater Steam turbine Utilize flue gas Steam with dried and heat to increase high temp and superheated feed water temp pressure steam (increased efficiency and prevent blade corrosion) (iii) Steam Turbine (iv) Alternator Generator (v) Feed Water (vi) Cooling Arrangement Rankin Cycle. In a thermal power plant, coal is coming from coal storage and burnt in the boiler. It converts water into steam. This steam is expanded in the prime-mover (i.e. turbine) which produces mechanical power driving the alternator coupled to the turbine. The steam is expanded again the turbine and usually condensed in the condenser to be fed into the boiler. But in real practice, the conversion of heat from coal combustion into electrical energy needs some modern arrangements and improvements, in which it will run in proper working efficiency. 1. Fuel and Ash Circuit:- The fuel (coal) is transported from supply points to power station by roads, rails or water and is stored in coal storage plant. Generally, coal is delivered into power station by rail wagon but in a case of small power plants, it may be transported by road or water. After that this coal is stored in the coal storage plant. From the coal storage plant, it is conveyed to the coal handling plant. In the coal handling plant, coal is pulverised (i.e. crushed into small pieces) to increase its surface tension to help rapid combustion without using a large amount of excess air. This pulverised coal is taken into boiler bunkers by conveyer belt. Coal is now stored into the boiler bunker and fall into the hoppers by gravity. From the hopper, required amount of coal either fall on the grate or fall into the coal spreaders. If it is fall to the coal spreaders, maximum coal combustion is done in the air and remaining portion burnt at the rear end of the grate. The grate is types of boiler, where combustion is controlled by its speed. The grate is made a move from rear end to front end with the help of spreaders or without spreaders; it is move from front to rear. The total coal combustion in the grate is controlled by its speed. After complete combustion of coal, ash is delivered to the ash storage plant by scrap conveyors for disposal. Generally, it is seen that a 100 MW power plant which operates 10% to 12% load factor may burn 20,000 tons of coal per month and ash is produced nearly 2000 to 3000 tons per month. 2. Air and Fuel Gas Circuit:- The thermal power plant consists of a boiler and other auxiliary equipment which is required to utilize the air and flue gases. The air is coming from the atmosphere by a forced or induced draught fan through the air pre- heater. In the air-preheater, air is heated by the heat of flue gases which passing to the chimney. This flue gases are passing through boiler, super heater, air per heater and finally exhausted to the atmosphere through the chimney. The boiler is an essential equipment of the thermal power plant operation. In the boiler, heat is produced by coal combustion, is utilized to convert water into steam at high pressure and temperature. The steam is the wet condition in the boiler and it is converted dry and superheated condition by the flue gases when it is passed through the superheater. Superheated steam means the steam temperature is above the boiling point of water and this will provide added advantages to the turbine. This steam is increased the overall efficiency of the turbine and protect the turbine's blade from corrosion. Economiser and air preheater are such type of devices which extract the heat from flue gases on their way to a chimney and increased the temperature of the feed water. Economiser is basically a feed water heater which recovers heat from flue gases and increase the temperature of the fed water before it is supplied to the boiler. Air is also supplied for the coal burning. Air preheater also extracts the heat from flue gases when it is passed in it. Air preheater increases the heat of air as well as improves the overall efficiency of the turbine. It also increases the steam capacity per square meter of boiler surface. Now this dry and superheated steam is fed to the blades of steam turbine through the main valve. Here steam energy is converted to the mechanical energy. 3. Feed water and steam circuit:- Condensed steam is coming out of the turbine and the condensate is extracted from the condenser by the condensate extraction pump. Exhaust steam is passed through the low-pressure feed water heater where its temperature is raised by the bled steam. The feed water is now pumped by deaerator to high- pressure feed water heater where this feed water is heated by the heat from bled steam extracted at suitable point of steam turbine. Deaerator is to reduce dissolved oxygen content in the feed water. Feed water is pumped into the boiler and it is passing through the economiser where it is heated by the heat of flue gases. This will increase the overall efficiency. Some steam and water are lost when it is passed through the different component of the system. Turbine is directly coupled to the alternator which converts the mechanical energy of turbine into electrical energy and delivers the electrical output to the bus bar. 4. Cooling water circuit:- Cooling water is supplied from a natural source of supply such as river, channel, sea, etc. This water is circulated through the condenser for condensing the steam. It will increase the overall efficiency of the plant. The circulating water absorbs heat from the exhaust steam and becomes hot. This hot water is coming out from the condenser and discharged at a suitable position like a lake, river etc. To ensure the availability of cold water throughout the year, a cooling tower is used. During the scarcity of water, hot water of condenser is passed to the cooling tower where it is cooled. The circulation of cooling water to the condenser is to maintain low pressure in the condenser.  SITE FOR THERMAL POWER STATIONS Cost and Type of Land : cheap (rural areas) and the land bearing capacity of should be adequate to install heavy machinery Availability of Water : A large amount of water is required for condensers 560 × 103 kg of water is required for every 1 tonne of coal burnt. ----bank of a river or near a canal Supply of Fuel : near the coal mines so that transportation cost of fuel is minimum. Nearness to Load Centre : In order to reduce the transmission cost, the plant should be located near the center of the load. This is particularly important that dc supply system is adopted. Distance from Populated Area : The plant should be located at a considerable distance from the populated area to minimise pollution Ample Space : future expansion Disposal of Ash : Facility for the disposal of ash. ADVANTAGES OF THERMAL POWER PLANT: The fuel (i.e. coal) is used is quite cheap. Less initial cost as compared to the other generating stations of the same capacity. It requires less space as compared to the hydro-electric power station. The cost of generation is lesser than the Diesel power station. According to the demand, the load can be changed frequently without any difficulty. Thermal Power plant can be installed anywhere irrespective of the availability of fuels. Fuel can be transferred to the site of the plant by rail, road etc. This type of plants is installed near load centre. Thermal Power plant can be run with overload condition (around 25%). DISADVANTAGES OF THERMAL POWER PLANT: It pollutes the atmosphere due to the production of a large amount of smoke. Maintenance cost and operating cost is high. A Huge amount of water is required. Running cost is high as compared to the diesel power plant. Coal handling and ash disposal is quite difficult.  Hydroelectric power plant Hydroelectric power is developed by utilizing the potential energy of water. In hydroelectric power plant, water is stored in a dam called hydroelectric dam which is located upper level from the ground especially any hilly areas. Water head is created by construction the dam across any river or lake. This type of water head store huge potential energy. The water fall into water turbine and the potential energy of water is converted into kinetic energy. Kinetic energy is converted into mechanical energy at the turbine shaft. A hydroelectric generator or alternator is coupled with turbine shaft to convert mechanical energy into electrical energy. The power P is developed- Here, W = Specific weight of water in kg/m3 Q = Rate of flow of water in m3/s H = Height of fall or head in meters η = Overall efficiency of operation Block diagram of hydroelectric power plant  Working Principle of hydroelectric power plant Hydroelectric power plant is becoming very popular nowadays to full feel rapid increasing demand of electric power day by day. Every country is trying to develop more Hydro Electric Power Station to full fill their demand for electricity. In other hand fossils, fuels ( i.e. coal,oil, and gas) are limited stock in the world and these fuels are expensive. So hydroelectricity may be a good alternative electrical source. So in a single word we can say,a generating Station which utilizes the potential energy of high-level water for the generating of electrical energy is known as hydropower plant or hydroelectric power plant. conventional hydroelectric facilities- rely on a head difference created by man-made dams and obstructions. Two types of systems that are considered conventional are hydroelectric dams and tidal dam. unconventional hydroelectric facilities- rely on hydroelectric discharge or on a small head differential. Some examples of unconventional hydropower facilities are low head hydro, run-of- the-river systems, instream hydro, and kinetic tidal. Working principle of hydroelectric power plant depends on the conversion of hydraulic energy into electrical energy. Hydroelectric power station needs huge amount of water at sufficient head all the time. So a hydroelectric dam is constructed across the river or lake. An artificial storage reservoir where water is stored, is placed back side of the dam. This reservoir creates sufficient water head. A pressure tunnel is placed in between the reservoir to valve house and water is coming from reservoir to penstock via this tunnel. An automatic controlling sluice valve is placed in valve house and it controls water flow to the power station and the letter cuts off supply of water in case the penstock bursts. Penstock is a huge steel pipe in which water is taken from valve house to turbine. A surge tank is also provided just before the valve house for better regulation of water pressure in the system. Now water turbine converts hydraulic energy into mechanical energy and an alternator which is couple to the water turbine converts this mechanical energy into electrical energy. Run off river power plants without pondage water is not available all the time. not suitable for constant steady load. There is no pondage or storage facility available in such type of power plant. Plant is placed in such a area,where water is coming directly from the river or pond. This type of hydroelectric power plant is called run off power plant without pondage. Plant produces hydro electricity only when water is available. Run off river power plants with pondage This type of plant is used to increase the capacity of pond. The pond is used as a storage water of hydro electric power plant. Increased the pond size means more water is available in the plant, used fluctuating load period depending on the size of pondage. Reservoir power plants (with head) Water is stored behind the dam and water is available throughout the year even in dry season. very efficient and it is used both base and peak load period a. Low head hydro electric power plant water head height is below 30 meters dam construction is essential. No surge tank is required for this plant, dam itself discharge the surplus water from the river. large diameter and low length pipe is used for this plant b. Medium head hydro electric power plant water head height is above 30 meters to 300 meters A forebay is used for medium head hydro electric power plant. Which act as a surge tank. Forebay is tapped with the river and water is led to the turbine via penstock. c. High head hydro electric power plant head of this power plant is more than 300 meters. For high head more than 500 meters,Pelton wheel turbine is used and for lower head Francis turbine is useful. a. Base load hydro electric power plant Base load plant is suitable for constant load. load factor of this plant is high Run off river plants without pondage and reservoir plants are used as base load plants. b. Peak load hydro electric power plant (as they have storage facility) This plant is suitable for peak load curve of power system. Run off river plants with pondage and Reservoir plants can be used as peak load plants. c. Pumped storage hydro electric power plant for the peak load two types of water pond is used,called upper head water pond and tail water pond.T wo water ponds are connected each other by a penstock. During the off load period, surplus energy of this plant is utilized to pumping the lower head pond water to upper head pond water. This extra water is used to generate energy at pick load periods. By doing this arrangement,same water is used again and again. SITE SELECTION FOR HYDROELECTRIC POWER PLANT 1.Water Availability: Main fuel of this plant is water. So, such plant should be located nearer to river, canal etc. where sufficient water is available all the time. 2.Water Storage: Storage of water in a suitable reservoir or dam has to be placed by a careful geological study of the area to get the maximum advantage of that water. Dam should be located across the river to get continuous water supply throughout the year specially in a dry season. The storage capacity of dam can be determined by hydrograph or mass curve or using analytical method. Adequate facilities of erection a dam and storage of water are two important matters for site selection of hydro electric power plant. 3.Water Head: It is an important point for site selection of hydroelectric power plant. Water head is directly related to the cost of generation of electric power. If effective head is increased, water storage has to be reduced as well as capital cost of the plant is reduced. 4.Distance from the load center: Since it is located away from the load center, more transmission line is required to supply the power. To avoid the line loss and economical power supply, distance of such plant should need more attention. 5.Transportation Facilities: Good transportation facilities must be available to any hydro electric power plant, so that necessary equipment should be reached easily. 6.Availability of land: Hydro electric power plant needs enough space. It should be kept in mind that land cost must be cheap. Advantages Since water is the main source of energy, so no fossil fuels are required. This plant is neat and clean and no smoke or as disposal is required. It is the cheapest operating and maintenance cost as compared to the other power plants because water is freely available in the world. It is very reliable, robust and has a longer life app rocks 45 to 60 years. This plant can start instantly. It can start hydroelectric power with fluctuating load demand. The efficiency does not fall at the age of this plant. There is no standby loss in this plant. At the initial time of construction highly skilled engineers are required and after that only few experience persons can run the plant. This plant also serves to help in irrigation and Flood control etc. Since this plants are located remote area so land is available and competitively cheaper rates. Disadvantages Such plant requires large area High construction cost is required due to construction of dam. When experience skilled engineers are required to build this plant Scenes such plant is located as from the load areas, long transmission line is required to transmit this hydroelectric power. It doesn't supply constant hydroelectricity due to the availability of water. In transition, power supply is most affected.  Nuclear power plant It can produce a huge amount of electrical energy from relatively small amount of nuclear fuel as compared to other conventional types of power stations. It is seen that complete fission of 1 kg nuclear fuel like uranium-235 would produce energy equivalent to 4000 tonnes of high-grade coal. Although nuclear fuels (like uranium, thorium) are difficult to recover and these are expensive too but nuclear fuel cost is considerably less than the conventional steam power station. Fuel cost of nuclear power plant is generally 40% cheaper than a conventional steam power station. Nuclear energy is converted to electrical energy is known as a nuclear power plant. NUCLEAR CHAIN REACTION PROCESS: Uranium-235 is natural and it will give higher fission percentage too. Some other fissionable materials (U-233, PU-239) are present in the world. U-235 is the most common isotope to use for a nuclear chain reaction. it produces comparatively higher amount of energy and heat from the other fissionable materials. 235 + 10n = 13956Ba + 9436Kr + 3 10n 92U In the above reaction, it is shown that a heavy nucleus uranium-235 strikes one neutron and it produce alternative three neutrons. These three neutrons again strikes U-235 which produce nine neutrons and striking nine neutrons produce another twenty-seven neutrons and so on, showing in the picture A single fission reaction generates a large amount of energy, so the complete nuclear chain reaction process will generate many times greater energy. It is seen that one fission reaction of U-235 release nearly 200 MeV of energy. 200MeV energy: 200 X 1.6 X 10-13 = 3.2 X 10-11joules (or watt-seconds)  Working Principle of nuclear power plant 1.Nuclear Reactor 2.Heat Exchanger 3.Steam Turbine 4.Alternator Nuclear reactor is used to produce heat and heat exchanger performs to convert water into steam by using the heat generated in nuclear reactor. This steam is fed into steam turbine and condensed in condenser. Now steam turbine is turn to run an electric generator or alternator which is coupled to steam turbine and thereby producing electric energy. Block Diagram of Nuclear Power Plant 1. Nuclear Reactor:- Nuclear reactor, where nuclear fuel is subjected to nuclear fission. By the braking of uranium atom, tremendous amount of heat energy and radiation is formed in the reactor and the chain reaction is continuously running until it is controlled by a reactor control chain reaction. A large amount of fission neutrons are removed in this process, only small amount of fission uranium is used to generate the electrical power. The nuclear reactor is cylindrical type shape. Main body of reactor is enclosed by reactor core, reflector and thermal shielding. It prevent reactor wall from getting heated. It is also used to protect alpha ( α), bita (β) , gama (γ) rays and neutrons which are bounce back at the time of fission within the reactor. Mainly Nuclear reactor consists, some fuel rods of uranium, moderator and control rods. Fuel rods are made of the fission materials and released large number of energy at the time of bombarding with slow moving neutrons. Moderator consists full of graphite which is enclosed by the fuel rods. Moderator maintains the chain reaction by releasing the neutrons in a suitable manner before they mixed with the fissile materials. Control rods are made of boron-10 and cadmium or hafnium which is a highly neutron absorber and it is inserted into the nuclear reactor. When control rods are push down into the reactor core, it absorbs most of fission neutrons and power of the reactor is reduced. But when it is pulling out from the reactor, it releases the fission neutrons and power is increased. Real practice, this arrangement depends upon according to the requirement of load. A coolant, basically sodium metal is used to reduce the heat produce in the reactor and it carries the heat to the heat exchanger. 2. Heat Exchanger:- Coolant is used to raise the heat of the heat exchanger which is utilised in raising the steam. After that, it goes back to the reactor. 3. Steam Turbine:- Steam is coming from the heat exchanger to fed into the steam turbine through the valve. After that the steam is exhausted to the condenser. This condensed steam is fed to the heat exchanger through feed water pump. 4. Alternator:- Steam turbine is coupled to an alternator which converts mechanical energy to electrical energy. The output of alternator produces electrical energy to bus bars via major electrical apparatus like transformer, circuit breakers, isolators etc. ADVANTAGES OF NUCLEAR POWER PLANTS There are lots of advantages of nuclear power plant as compared to other power plants. Since the requirement of fuel is very small, so the cost of fuel transportation, storage etc. is small. Nuclear power plant needs less space as compared to any other power station of the same size. Example: A 100 MW nuclear power station needs 38 - 40 acres of land whereas the same capacity coal based thermal power plant needs 120-130 acres of land. This type of power plant is very economical to produce large electric power. Nuclear power plant can be located near load center because bulk amount of fuel (like water, coal) is not required. Nuclear power is most economical to generate large capacities of power like 100 MVA or more. It produces huge amount of energy in every nuclear fission process. Using a small amount of fuel, this plant produces large electrical energy. This plant is very reliable in operation. Since, the large number of nuclear fuel is available in this world. So, a nuclear power plant can generate electrical energy thousands of years continuously. Nuclear Power Plant is very neat and clean as compared to a steam power plant. The operating cost is low at this power plant but it is not affected for higher load demand. Nuclear power plant always operates a base load plant and load factor will not be less than 0.8. DISADVANTAGES OF NUCLEAR POWER PLANTS Initial installation cost is very high as compared to the other power station. Nuclear fuel is very much expensive and it is difficult to recover. Capital cost is higher in respect of other power station. Good technical knowledge is required to operate such type plant. So, salary bill and other maintenance cost will be higher to operate such of a plant. There is a chance to spread of radioactive pollution from this type of plant. Nuclear Reactor does not response efficiently with the fluctuating load demand. So, it is not suited for varying the load. Cooling water requirement is twice than a coal based steam power plant.