cesc training

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Name of Organization: - CESC Ltd, Kolkata.

Name of station: - Budge Budge Generating

Station.

Details of Student: - SHANGARAB BERA

o FUTURE INSTITUTE OF

ENGINEERING &

MANAGEMENT

o MECHANICAL, 2nd YEAR

Duration of Training: - 2 weeks (4.07.2011-

16.07.2011).

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Acknowledgement

I wish to express my heartfelt gratitude towards Mr. Gopal Ghoshal (Jr.

Engineer, HRD) and Mr. Souren Bhattacharya (Consultant, HR) for their

invaluable guidance and constant encouragement during the tenure of my

training at BBGS.

I would also like to thank all the departmental managers and guides who have

helped me with valuable information and intricate technical details about the

plant and its various components without which the venture would have been

otherwise incomplete.

Mr. Rajarshi Chakraborty

(Manager OPS).

Mr Bimal Mukherjee

(Asst. Manager; F&A)

Mr Sibir Roy

(Manager E&I)

Mr Samir Banerjee

(Manager MMD)

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Signatures of officers.

DEPT:-HRD Mr. Souren Bhattacharya. (Consultant) ----------------------------------------------- Mr. Gopal Goshal (Jr.Engineer) ----------------------------------------------

DEPT:- OPERATIONS Mr. Rajarshi Chakraborty (Manager OPS). -----------------------------------------

----

DEPT:- FUEL AND ASH Mr. Bimal Mukherjee (Asst. Manager; F&A) ----------------------------------------

----

DEPT: - MMD Mr. Samir Banerjee (Manager MMD)

-------------------------------

--------------

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Generation and distribution of electricity since 1897. It is the second

company in the world to produce electricity commercially.

First thermal power generation company in India.

First power station to be constructed was the Old Southern Generating

station.

Initial licensed area was 14.44 sq. km. which has increased 567 sq. km

across Kolkata and suburbs over the past century.

Brought electricity to Calcutta 10 years after it has come in London.

First tunnel under Ganga for power transmission.

Over the past century the following power plants came up-Old Cossipore,

Mulajore, New Cossipore (100 MW), Titagarh (240 MW), New G

In 1989 CESC became a part of RPG group.

No. of consumers and employees are 2.3 million and 10000 (approx)

respectively.

Generation and substation capacity are 1225 MW & 6778 MVA.

Total transmission & distribution network-16909 ckt km.

Total revenue & profit in 2008 fiscal-3200 cr. & 410 cr.

The BBGS has maintained one of the highest PLFs in the country for the

last 5 years. It has been recognized as environment friendly by Govt. agencies

and received Silver National Award for Environment Management in

Thermal Power Station for 2008-09. It is the 1st plant in the world to receive

Carbon credits.

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CESC's Budge Budge plant registers highest PLF in 2005-06

During 2005-06 the Budge Budge plant of CESC Ltd, the flagship company of the RPG

Group, has registered the highest PLF (plant load factor) signifying the highest capacity

utilisation among all the thermal power stations in India.

This unit has also achieved the rare distinction of becoming the first coal fired thermal power

plant in the world to be registered under the UNFCCC (United Nations Framework

Convention for Climate Change) for carbon credits.

Addressing a press conference, Mr P.K. Basu, Executive Director (Generation) of CESC, said

that the PLF of the Budge Budge unit has gradually improved to 99.61 per cent in 2005-06

from around 75 per cent in 2001-02.

In 2003-04, PLF was 79.85 per cent and in 2004-05 it was 86.38 per cent. CESC has two

other units. The average PLF of the three units taken together will be over 85 per cent.

Commissioned between 1997 and 1999, the Budge Budge unit is the most modern generating

station of CESC. Its capacity is 2x250 MW.

"This is a major achievement for our unit. We are also taking several steps in effluent

management, ash utilisation and in becoming more environment friendly," Mr Basu said.

A project - chemical technology for boiler water treatment - at the Budge Budge plant has

been recognised under the UNFCCC. The project, which saved heat and ensured less of

burning coal, was validated by DNV.

"We have become the first coal fired thermal power plant in the world to get this recognition.

Moreover, the technology used in this project is developed in-house," he said.

This project will be generating 3,894 CER (carbon emission reduction) units every year for

CESC. The company has applied for two more projects and both are for its Titagarh plant.

According to Mr Basu, the company is targeting about 40,000 CER units every year.

Selling the CER units is not the only goal of CESC. "It adds a different dimension to the

operations of the organisation. The company has become more acceptable to several investors

across the globe," he said.

In the last financial year, CESC has exported 480 million units of power outside its

distribution area for an average price of Rs 2.20 per unit. In the first quarter of 2006-07, it has

exported 79 million units.

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About BBGS

The Budge Budge generating station is a state of the art facility which has won several

awards and accolades for its environmental friendly way of producing current. The capacity

stands out at 750 MW out of three units of 250 MW each.

It has consistently maintained one of the highest PLF in the country in the last five years. It

has been recognized by government agency as environment friendly and received silver

national award for environment management in thermal power station for 2008 to 2009. The

CDM project at Budge Budge is the first thermal project in the world to earn carbon credits.

Awards and Accolades

Budge Budge generating station won the national award of excellence for energy

management 2005 organized by CII and second prize in the national award for fly ash

utilization in 2005 organized by the government of India.

Budge Budge generating station won the Genentech environment excellence Gold award in

thermal power sector in 2006, 2007 and 2008 organized by Genentech foundation.

It received best power station award from the Prime Minister for achieving highest PLF in the

country in 2005 to 2006.

Dalal Street Journal recognized CESC as the one of the top 21 wealth creator from investors

viewpoint.

It has Ranked 57th in the business worlds 500 top corporate list.

It has also been ranked second as the most reliable HT supply in India by Central electricity

authority.

In the following pages we go into technical details about the Budge Budge generating station

which has four departments namely the operations, fuel and ash, electrical and

instrumentation.

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UNIQUE FEATURES OF BBGS

LARGEST COAL FIRED THERMAL POWER STATION OF CESC LTD.

USE OF CLARIFIED WATER FOR CONDENSER AND OTHER AUXILIARIES

VERTICAL DOWN SHOT FIRED BOILER HAVING NON TURBULENT,LOW NOX

BURNERS

USE OF GAS RECIRCULATION IN BOILER

USER OF HYDROGEN COOLING AND STATOR WATER COOLING FOR

GENERATOR(FIRST IN CESC)

USE OF COOLING TOWERS FOR CLOSED CIRCULATING WATER SYSTEM(FIRST

IN CESC)

USE OF ZERO DISCHARGE SYSTEM FOR BOTTOM ASH DISPOSAL

INCORPORATION OF ZERO EFFLUENT SYSTEM

INSTALLATION AND OPERATION OF A HIGH CONCENTRATION SLURRY

SYSTEM (HCSS).

BUDGE BUDGE GENERATING STATION

COMMERCIAL GENERATION

UNIT #1 07.10.97

UNIT #2 01.07.99

UNIT #3 28.01.10

FUEL SOURCE

ECL,BCCL,ICML & imported coals

FUEL REQUIREMENT 2.45 million tonnes of coal per annum

MODE OF TRANSPORTATION Rail

WATER SOURCE River Hooghly

LAND AREA 225 acres

ASH DUMPING AREA 91 acres

UNIT #1

TRIAL SYNCHRONIZATION 16.9.97

COMMERCIAL GENERATION 07.10.97

FULL LOAD GENERATION 26.02.98

Capacity 750 MW(3X250 MW) Location Pujali,Budge Budge,24 PGS(S),West Bengal

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UNIT #2




UNIT #3




OPERATIONS The Department of operations at the Budge Budge generating station is responsible for monitoring and issuing remote commands in case of manual mode of operation to various components for a smooth running of the power plant. It oversees the entire operation of the plant and ensures seamless integration between the various components which are in some cases situated far away from each other. It is helped by a centrally placed DCS which is continuously worked upon. To start with first of all we discuss a general working procedure of a steam power plant and then go into the details of some major equipment like boiler, turbine, generator, coal mills fans etc. These equipments and the entire water treatment process falls under the supervision of the Department of operations. We would be discussing about the working procedures and various working cycles of the different components that we come across.

General working procedure of a steam power plant. The steam power plant must first obtain heat. This heat must come from an energy source, and this varies significantly, often based on the plants location in the world. These sources of heat could be 1. A fossil fuelcoal, oil, or natural gas 2. A nuclear fuel such as uranium 3. Other forms of energy, which can include waste heat from exhaust gases of gas turbines; bark, wood, bagasse, vine clippings, and other similar waste fuels; by-product fuels such as carbon monoxide (CO), blast furnace gas (BFG), or methane (CH4); municipal solid waste (MSW); sewage sludge; geothermal energy; and solar energy Each of these fuels contains potential energy in the form of a heating value, and this is measured in the amount of British thermal units (Btus) per each pound or cubic feet of the fuel (i.e., Btu/lb or Btu/ft3) depending on whether the fuel is a solid or a gas. (Note: A British thermal unit is about equal to the quantity of heat required to raise one pound of water one degree Fahrenheit.) This energy must be released, and with fossil fuels, this is done through a carefully controlled combustion process. In a nuclear power plant that uses uranium, the heat energy is released by a process called fission. In both cases the heat is released and then

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transferred to water. This can be done in various ways, such as through tubes that have the water flowing on the inside. As the water is heated, it eventually changes its form by turning into steam. As heat is continually added, the steam reaches the desired temperature and pressure for the particular application. The system in which the steam is generated is called a boiler, or often commonly called a steam generator. Boilers can vary significantly in size and design. A relatively small one supplies heat to a building, and other industrial-sized boilers provide steam for a process. Very large systems produce enough steam at the proper pressure and temperature to result in the generation of 1300 megawatts (MW) of electricity in an electric utility power plant. Such a large power plant would provide the electric needs for over 1 million people.

Steam is generated in the boiler under carefully controlled conditions. The steam flows to the turbine, which drives a generator for the production of electricity and for distribution to the electric system at the proper voltage. Since the power plant has its own electrical needs, such as motors, controls, and lights, part of the electricity generated is used for these plant requirements. After passing through the turbine, the steam flows to the condenser, where it is converted back to water for reuse as boiler feedwater. Cooling water passes through the condenser, where it absorbs the rejected heat from condensing and then releases this heat to the atmosphere by means of a cooling tower. The condensed water then returns to the boiler through a

series of pumps and heat exchangers, called feedwater heaters, and this process increases the pressure and temperature of the water prior to its reentry into the boiler, thus completing its cycle from water to steam and then back to water. The type of fuel that is burned determines to a great extent the overall plant design. Whether it be the fossil fuels of coal, oil, or natural gas, biomass, or by-product fuels, considerably different provisions must be incorporated into the plant design for systems such as fuel handling and preparation, combustion of the fuel, recovery of heat, fouling of heat-transfer surfaces, corrosion of materials, and air pollution control.

BOILER A boiler (or steam generator, as it is commonly called) is a closed vessel in which water, under pressure, is transformed into steam by the application of heat. Open vessels and those generating steam at atmospheric pressure are not considered to be boilers. In the furnace, the chemical energy in the fuel is converted into heat, and it is the function of the boiler to transfer this heat to the water in the most efficient manner. Thus the primary function of a boiler is to generate steam at pressures above atmospheric by the absorption of heat that is produced in the combustion of fuel. With waste-heat boilers, heated gases serve as the heat source, e.g., gases from a gas turbine. A steam electric power plant is a

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means for converting the potential chemical energy of fuel into electrical energy. In its simplest form it consists of a boiler supplying steam to a turbine, and the turbine driving an electric generator. The ideal boiler includes:- 1. Simplicity in construction, excellent workmanship, materials conducive to low maintenance cost, high efficiency, and high availability 2. Design and construction to accommodate expansion and contraction properties of materials 3. Adequate steam and water space, delivery of clean steam, and good water circulation 4. A furnace setting conducive to efficient combustion and maximum rate of heat transfer 5. Responsiveness to sudden demands and upset conditions. The process of boiling water to make steam is a phenomenon that is familiar to all of us. After the boiling temperature is reached (e.g., 212F at an atmospheric pressure of 14.7 psia), instead of the water temperature increasing, the heat energy from the fuel results in a change of phase from a liquid to a gaseous state, i.e., from water to steam. A steam-generating system, called a boiler, provides a continuous process for this conversion. For most boiler or steam generator designs, water and steam flow through tubes where they absorb heat, which results from the combustion of a fuel. In order for a boiler to generate steam continuously, water must circulate through the tubes. Two methods are commonly used: (1) natural or thermal circulation and (2) forced or pumped circulation. For a forced circulation system a pump is added to the flow loop, and the pressure difference created by the pump controls the water flow rate. These circulation systems generally are used where the boilers are designed to operate near or above the critical pressure of 3206 psia, where there is little density difference between water and steam. There are also designs in the subcritical pressure range where forced circulation is advantageous, and some boiler designs are based on this technology. The steam-water mixture is separated in the steam drum. In small, low-pressure boilers, this separation can be accomplished easily with a large drum that is approximately half full of water and having natural gravity steam-water separation. In todays high-capacity, high-pressure units, mechanical steam water separators are needed to economically provide moisture-free steam from the steam drum. With these devices in the steam drum, the drum diameter and its cost are significantly reduced. At very high pressures, a point is reached where water no longer exhibits the customary boiling characteristics. Above this critical pressure (3206 psia), the water temperature increases continuously with the addition of heat. Steam generators are designed to operate at these critical pressures, but because of their expense, generally they are designed for large-capacity utility power plant systems. These boilers operate on the once-through principle, and steam drums and steam-water separation are not required.

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SUPERHEATERS Steam that has been heated above the saturation temperature corresponding to its pressure is said to be superheated. This steam contains more heat than does saturated steam at the same pressure, and the added heat provides more energy for the turbine for conversion to electric power, or in the case of process steam, more energy contained in a pound of steam for a more efficient process. For example, steam at a pressure of 700 psia has a saturation temperature of 503F. The heat content of this steam is 1201 Btu/lb. If this steam is heated further to, say, 700F, the steam is now superheated, and its heat content is 1345 Btu/lb. The degrees of superheat is the number of degrees above the saturation (or boiling) temperature at that pressure. In this example, the degrees of superheat is 197F (700503). A superheater surface is that surface which has steam on one side and hot gases on the other. The tubes are therefore dry with the steam that circulates through them. Overheating of the tubes is prevented by designing the unit to accommodate the heat transfer required for a given steam velocity through the tubes, based on the desired steam temperature. To accomplish this, it is necessary to have the steam distributed uniformly to all the superheater tubes and at a velocity sufficient to provide a scrubbing action to avoid overheating of the metal. Carry-over from the steam drum must be at a minimum. Superheaters are referred to as convection, radiant, or combination types. The convection superheater is placed somewhere in the gas stream, where it receives most of its heat by convection. As the name implies, a radiant superheater is placed in or near the furnace, where it receives the majority of its heat by radiation. The conventional convection-type superheater uses two headers into which seamless tubes are rolled or welded. The headers are baffled so that the steam is made to pass back and forth through the connecting tubes, which carry their proportioned amount of steam, the steam leaving at the desired temperature. The headers are small, and access to the tubes is achieved by removing handhole caps. With either the radiant or the convection-type superheater, it is difficult to maintain a uniform steam-outlet temperature, so a combination superheater is often installed. This is an older design, but it illustrates the concept. The radiant section is shown above the screen tubes in the furnace; the convection section lies between the first and second gas passages. Steam leaving the boiler drum first passes through the convection section, then to the radiant section, and finally to the outlet header. Even this arrangement may not produce the desired results in maintaining a constant steam temperature within the limits prescribed, and so a bypass damper, shown at the bottom of the second pass of the boiler, is used in this older design. A damper of this type can be operated to bypass the gas or a portion of the gas around the convection section, thus controlling the final steam-outlet temperature for various boiler capacities.

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STEAM TURBINES A heat engine is one that converts heat energy into mechanical energy. The steam turbine is classified as a heat engine, as are the steam engine, the internal combustion engine, and the gas turbine. Steam turbines are used in industry for several critical purposes: to generate electricity by driving an electric generator and to drive equipment such as compressors, fans, and pumps. The particular process dictates the steam conditions at which the turbine operates. The turbine makes use of the fact that steam, when passing through a small opening, attains a high velocity. The velocity attained during expansion depends on the initial and final heat content of the steam. This difference in heat content represents the heat energy converted into kinetic energy (energy due to velocity) during the process. The fact that any moving substance possesses energy, or the ability to do work, is shown by many everyday examples. A stream of water discharged from a fire hose may break a window glass if directed against it. When the speed of an automobile is reduced by the use of brakes, an appreciable amount of heat is generated. In like manner, the steam turbine permits the steam to expand and attain high velocity. It then converts this velocity energy into mechanical energy. There are two general principles by which this can be accomplished. In the case of the fire hose, as the stream of water issued from the nozzle, its velocity was increased, and because of this impulse, it struck the window glass with considerable force. A turbine that makes use of the impulsive force of high-velocity steam is known as an impulse turbine. While the water issuing from the nozzle of the fire hose is increased in velocity, a reactionary force is exerted on the nozzle. This reactionary force is opposite in direction to the flow of the water. A turbine that makes use of the reaction force produced by the flow of steam through a nozzle is a reaction turbine. In practically all commercial turbines, a combination of impulse and reactive forces is utilized. Both impulse and reaction blading on the same shaft utilize the steam more efficiently than does one alone. The turbine consists of a shaft, which has one or more disks to which are attached moving blades, and a casing in which the stationary blades and nozzles are mounted. The shaft is supported within the casing by means of bearings that carry the vertical and circumference loads and by axial thrust bearings that resist the axial movement caused by the flow of steam through the turbine. Seals are provided in the casing to prevent the steam from bypassing the stages of the turbine Blades. On the outer portion, or circumference, of each disk located on the shaft are blades where steam is directed and converted into work by rotation of the shaft. There are many blades in each turbine stage, and larger turbines have more stages. Blades generally are made from low carbon stainless steel; however, for high-temperature applications and where high moisture is expected, alloy steels are used to provide the strength and erosion resistance needed. Special coatings on the blades are often used where high erosion is anticipated. As the steam flows through the turbine, it expands and its volume increases. This increased volume is handled by having longer blades and thus a larger casing for each stage of the turbine. The turbine efficiency, as well as its reliable performance, depends on the design and construction of the blades. Blades not only must handle the steam velocity and temperature but also must be able to handle the centrifugal force caused by the high speed of the turbine. Any vibration in a turbine is significant because there is little clearance between the moving blades and the stationary

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portions on the casing. A vibration of the moving blades could cause contact with the stationary components, which would result in severe damage to the turbine. Vibration has to be monitored continuously and corrected immediately when required. Small turbines are housed in a single casing that admits high-pressure steam at one end, and low-pressure steam leaves at the back end of the turbine to the condenser or as steam for a process or heating. On large, high-pressure turbines, two or three separate casings are used, with the turbine having three sections: high pressure (HP), intermediate pressure (IP), and low pressure. The steam from the boiler passes through the HP section of the turbine. The exhaust steam from this section is returned to the boilers reheater, where it is reheated to generally the same superheated steam temperature as the HP steam but at a lower pressure. The steam is then returned to the IP section of the turbine. In some turbine designs, the HP and IP sections of the turbine are combined into one casing, and the steam flows in opposite directions in order to equalize the axial forces in the turbine. The IP turbine is used with boilers that have a reheat cycle, and this generally is found in large utility power plants. The IP turbine can use single or double flow depending on the pressure and steam flow. The LP turbine receives steam from either the HP turbine in nonreheat units or an IP turbine. Since the steam has expanded and its volume has increased significantly, the blades of the LP turbine are much longer than those of the HP and IP stages in order to handle the steam flow.

GOVERNORS A close control of turbine speed is essential from the standpoint of safety and satisfactory service. The same theory of centrifugal force that applied to steam engine flywheels also applies to the rotating elements of turbines. If the turbine runs at a speed far above that for which it was designed, the blading will be thrown out of the rotor. When a turbine is thrown apart in this manner, the resulting damage may be as great as, or even greater than, that caused by a boiler explosion. Turbines operating electric generators producing ac current must operate at constant speed (3600 or 3000 rpm). Some electrical appliances are seriously affected by a slight change of frequency in the power supply. The speed of the generator determines the frequency of the electric-current generator (60 Hz for 3600 rpm and 50 Hz for 3000 rpm). Even with generators producing dc current, a small change in speed will affect the voltage. There are two ways of changing the turbine supply of steam to meet the load demand. One consists of throttling the steam, by means of a valve, in such a

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manner that the pressure on the first-stage elements is changed with the load demand. Small turbines, like those shown in, have a main governor of the throttling type. The operating mechanism is driven directly by the main turbine shaft. Overload is taken care of by means of hand-operated valves that admit additional steam to the turbine. The other method uses several valves, governor-operated, that are opened separately to supply steam to secondary nozzles as the load increases. Economical partial-load operation is obtained by minimizing throttling losses. This is accomplished by dividing the first-stage nozzles into several groups and providing a separate valve to control the flow of steam to each group. Valves are then opened and closed in sequence, and the number of nozzle groups in service is proportional to the load on the unit. Valve seats are of the diffuser type to minimize pressure drop, and these valve seats are renewable. Single-seated valves are used, arranged in parallel within the steam chest and surrounded by steam at throttle pressure. The governor mechanism raises and lowers the valve-lift bar in a horizontal plane, opening the valves in sequence, with an unbalanced force tending to close the valves. In the oil-relay system, the governor operates a small valve that admits oil to and allows it to drain from a cylinder. This oil cylinder contains a piston that is connected, by means of a rod, to the steam valve mechanism. The governor admits oil either above or below the piston, depending on which way the load is changing. There is no connection between the governor and the governor-valve mechanism except by means of the oil cylinder. The movement of the governor is transmitted to the governor valves by the oil pressure. Oil is supplied to the governor system by the same pump that supplies oil to the turbine bearings. If this oil supply should fail, the governor valve would close and stop the turbine, thus preventing damage to the bearings. The hydraulically operated throttle valve is used to control the flow of steam when starting a turbine and in addition functions as an automatic stop valve in case of over speed. It cannot be opened nor can the turbine be started until after normal operating pressures for the turbine oiling system have been established. If oil pressure falls to an unsafe point, the valve automatically closes, and the flow of steam to the turbine is interrupted. A strainer is located within the valve to protect both the valve and the turbine. The emergency over speed governor is separate and independent of the speed governor. It functions to protect the unit from excessive speed by disengaging a trip at a predetermined speed, permitting the throttle valve to close. This trip may be reset and the throttle valve reopened before the turbine speed returns to normal. Large turbines are arranged frequently for extraction of steam at various points in the turbine. This extracted steam is used for feed water heating or other heating or process purposes, and thus a more economical cycle is obtained. One turbine design uses a grid-type extraction valve at normal pressure and temperature. This valve consists of a stationary port ring and a rotating grid. The rotating grid turns against the stationary ring and opens the ports in sequence. Thus simple hydraulic interconnections are obtained between the several components of the control system, such as the accurate and positive control of speed or the load carried by the unit, and of the extraction steam pressures. Where electric power generation is the prime consideration, condensing turbines are used. Openings are provided in the turbines for the extraction of steam for heating the feed water to the boilers. The change in speed of a turbine from no load to full load divided by the full-load speed is known as the speed regulation. A turbine with a full-load speed of 1764 rpm and a no-load speed of 1800 rpm would have a change of 36 rpm, or regulation of 2 percent. These types of turbines are used to drive mechanical equipment such as pumps, compressors, etc. For electricity production, the speed must be constant at either 3600 or 3000 rpm depending on 60- or 50-Hz

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applications. The governors of turbines operating electric generators are supplied with synchronizing springs. These are arranged to aid in moving the governor weights and lowering the turbine speed or to work against the governor weights and increase the turbine speed. The tension on the synchronizing spring is varied by means of a small motor (synchronizing motor). By adjusting the tension on this spring, the operator can change the load on the generator. Dashpots are frequently used in connection with turbine governors. They are used to keep the governor from over traveling because of the weight of the governor parts. When a governor adjusts the speed of a turbine and makes a change that an adjustment in the opposite direction is immediately necessary, the governor is said to hunt or over travel. In other cases dashpots are used to prevent the governor from operating too quickly. Friction or lost motion in the valve mechanism or, in some cases, too heavy or improperly installed dashpots will cause a turbine to hunt. Rapid changes in speed and the corresponding variation in load are referred to as surges. A governor mechanism must be adjusted as follows: The valve should be closed when the governor is in the closed position and opened the correct amount when it is in the open position. The speed adjustment must be such that the governor will be in the open position when the turbine is at rated speed, and the speed regulation (i.e., the change in speed from no load to full load) must be adjusted. Turbine governors require very little attention on the part of the operator. They must, however, be kept oiled and the joints kept working freely. With the oil-relay system, oil leaks must be stopped as soon as possible. The over speed trip must be checked at regular intervals. It is good practice to operate the over speed every time that the turbine is placed in service.

CONDENSORS The condenser is a major component of the power plant system. It receives exhaust steam from the last stage of a turbine and condenses it to water for reuse as feed water in the boiler system. For large utility turbines that have a design incorporating high-, intermediate-, and low-pressure sections, the exhaust steam comes from the low-pressure section of the turbine. There are two general types of condensers: 1) A direct contact type of condenser, where the cooling water is sprayed directly into the exhaust steam from the turbine, and the mixture of the water with the steam condenses the steam. 2) A surface condenser, in which the cooling water and exhaust steam remain separate. The vast majority of power plants use the water cooled surface condenser, and this book will describe its operation and not the direct-contact condenser because it has limited application. There are situations where air-cooled steam condensers are used instead of surface condensers, and these generally are necessary when cooling water is not readily available, such as in an arid region, or if a cooling tower is required, a plume from a tower is not acceptable. A description of the air-cooled condenser is given below in. In the condensing of steam, a vacuum is created. The vacuum reduces the backpressure on the turbine, and this reduction in backpressure increases the efficiency of the turbine. The cooling water absorbs the heat contained in the steam, and the volume of steam is greatly reduced when it is

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condensed into water. When a space filled with steam is cooled until the steam condenses, the resulting water occupies only a small portion of the volume, and a vacuum is created. By continually condensing the exhaust steam, the pressure is reduced below that of atmospheric pressure.

Surface condensers The surface condenser is a closed vessel filled with many tubes of small diameter. Cooling water from a lake, river, or other natural water source or from a cooling tower flows through the tubes, with steam from the turbine on the outside of the tube. The water flowing through the condenser may be once-through, or single-pass, or it may be made to reverse one or more times before being discharged. The surface condenser offers the following features: 1. It provides a low backpressure at the turbine exhaust, which maximizes the plant thermal efficiency and reduces the heat rate, and therefore the plants operating costs are reduced. 2. It allows the reuse of high-purity water in the boiler and turbine system, which also minimizes water treatment costs. 3. It de aerates the condensate, which minimizes the potential for corrosion. 4. It serves as a collection point for all condensate drains.

Air-cooled condensers Air-cooled condensers are used primarily when water availability is a problem. They are also used to meet the requirements for the discharge of water where so-called zero-discharge facilities are necessary. They also are used in areas where vapor plumes associated with cooling towers are to be eliminated. These vapor plumes might be objectionable if they ice up nearby roads or airport runways or cause fog like conditions or where communities find them aesthetically unacceptable. An air-cooled condenser also can simplify plant design and construction; however, its disadvantage is that its use results in a lower plant efficiency than a plant designed with a surface condenser and a cooling tower and therefore higher operating costs result.

ELECTRIC GENERATORS An electric generator works by electromagnetic induction in that it uses magnetism to make electricity. The power source is the steam turbine, a gas turbine, or in the case of a hydroelectric plant, a water driven turbine. It spins a coil, which is contained in the rotor of the generator, between the poles of a magnet or an electromagnet produced by the stator of the generator. As the coil of the rotor passes through the lines of force, an electric current flows through the coil to the main transformer and eventually to the transmission

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lines. The electric generator is a major piece of equipment in a power plant because it converts mechanical energy from the turbine to which it is connected into electric energy. Each generator incorporates the following major components: Frame.

Stator core and winding.

Rotor and winding Bearings.

Cooling system. Hydrogen gas is used to cool the windings in electric generators. More efficient operation results in the generator as compared with other methods because hydrogen provides high thermal conductivity. However, losses of hydrogen do occur through the generators rotor seals, and this requires makeup hydrogen. Most plants have hydrogen storage tanks that are replenished by truck deliveries, and some larger facilities have on-site production of hydrogen for increased convenience. The stator has a slotted and laminated silicon-steel-iron core. The winding of the stator is placed in the slots and consists of a copper strand configuration. Most frequently the stator is hydrogen cooled; however, small units may be air cooled and very large units can even be water cooled. The rotor is solid steel and has slots milled along the axis, as. A copper rotor winding is placed in the slots and is also cooled by hydrogen for this particular design. Cooling of the rotor is improved by sub slots and axial cooling passages. The rotor winding is restrained by wedges that are inserted into the slots. The rotor winding is supplied by dc current, either directly by a brushless excitation system or through collector rings. Bearings are located on each end of the rotor to provide the necessary support. The hydrogen is cooled by a water-cooled heat exchanger that is mounted on the generator or installed in a closed-loop cooling system. The dc current of the rotor generates a rotating magnetic field that induces an ac voltage in the stator winding. This voltage drives current through the load and supplies the electric energy.

COOLING TOWERS The amount of heat rejected from modern thermal power plants is significant in that it represents over 60 percent of the total heat input. Of this amount, 10 to 15 percent is rejected out the stack with the flue gas. Most of the balance (approximately 45 percent) results from the condensing of the exhaust steam from the turbine. Eventually, all this rejected heat is absorbed by the atmosphere, although the heat may first be rejected to a body of water such as a lake, river, or ocean. Heat-rejection systems are generally classified as once-through or closed: 1. Once-through systems. Water is withdrawn from a lake, river, or ocean and then pumped through the condenser, where its temperature is increased by 15 to 20F. The warmer water is then discharged back to its source. Evaporation from the natural water source to the atmosphere eventually cools this water. 2. Closed-loop systems. Heat is rejected to the atmosphere through the use of either a cooling tower or some form of outdoor body of water such as a spray pond or cooling lake. In many areas, the once-through cooling system is unacceptable for a new power plant. Either the site is already developed and the natural source of water cannot support another plant, or environmental restrictions prevent the use of this system. Therefore, nearly all new power plants use the closed-loop system for heat rejection and incorporate a cooling tower.

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Cooling ponds and lakes are found primarily at existing sites. The cooling pond, which is often called a spray pond, is the simplest type of closed-loop system. The circulating water is pumped into a pond or basin, where it provides water storage in addition to the cooling. The cooling pond is converted to a spray pond by locating a series of sprays above the water surface. The cooling water flows through piping and then vertically from the spray to form the shape of an inverted cone. This method of spraying provides uniform water distribution, which increases the area of exposure and improves the efficiency of the cooling as the spray droplets come into contact with the air and thereby are cooled. The problem with the spray pond is that the water is sprayed into the air; water particles in varying amounts are carried away by the wind, which results in the loss of water and can create a nuisance in a congested area. This problem has been reduced by the installation of a louvered fence around the pond. However, although spray ponds are still operational, they are limited due to location and to environmental issues because of the airborne spray. Modern facilities predominantly use either natural or mechanical draft cooling towers. In wet cooling tower systems, cooling water is circulated through the condenser and absorbs heat from the exhaust steam from the turbine. The heated cooling water is then circulated through a cooling tower, where the absorbed heat is rejected to the atmosphere by the evaporation of some of the circulating water. The cooled water is then returned to the condenser by a circulating water pump. Makeup water must be provided to replace the water lost during evaporation and during blow down, where contaminants are controlled. The cooling tower therefore performs the following major functions: 1. Removes the heat that the cooling water absorbed in the condenser. 2. Minimizes the use of cooling water. 3. Provides cooling water to the condenser to obtain high plant thermal efficiency.

19

ELECTROSTATIC PRECIPITATORS Approximately 80 percent of the ash from a pulverized-coal-fired boiler is carried through the boiler as fly ash, and about 50 percent of that is less than 10 micro m in size. This requires the use of electrostatic precipitators to capture the fly ash. In an electrostatic precipitator (ESP), dust-laden flue gas is distributed uniformly between rows of discharge electrodes and grounded collecting plates. A high-voltage dc current is applied to the electrodes, which causes the dust particles to become ionized and then to be attracted to the grounded collecting plate. These collected particles are removed periodically from the plates by a rapping system that generates vibrations and causes the collected dust to fall into the hoppers. Maximum efficiency is obtained by automatic control of the high voltage. The voltage is maintained at the maximum value without excessive sparking between the discharge electrodes and collecting plates. When sized and operated correctly, these collectors can remove more than 99.9 percent of the fly ash from the flue gases. However, the size of an ESP depends on a characteristic of ash known as the resistivity. This determines the susceptibility of the fly ash particles to the influence of the electrostatic field. Fly ash resulting from burning coal with a high sulfur content has a low resistivity and therefore is more easily collected, requiring a smaller precipitator than one designed to collect fly ash from a coal having a low sulfur content. Therefore, the proper sizing of a precipitator depends on knowing the various types of coal that will be used over the life of the plant. Otherwise, the precipitator might be too small if it were designed for high-sulfur coal, and in the future low-sulfur coal would be used. Other fuels such as wood, bark, or municipal solid waste (MSW) have similar resistivity characteristics, and these must be used for the proper sizing of an ESP. Because the gas velocities through an ESP are very low (approximately 5 ft/s), the draft loss is minimal, at about 0.5 in of water (gauge) through the precipitator, as compared with mechanical collectors. In general, there are two types of electrostatic precipitators currently in use, with variations in each of the designs. These designs can be classified as (1) weighted wire and (2) rigid frame. Perhaps the most important feature that differentiates precipitator designs is the manner in which the discharge electrodes are supported. The weighted-wire design attempts to hold the discharge electrode wires in a position uniform between the collecting plates by means of wire weights at the bottom of the individual wires. This design is also characterized by the two-point suspension system of the discharge electrodes for each bus section and by the top rapping of both the discharge electrodes and the collecting plates. With the arrival of large power plants requiring larger and taller precipitators to meet the more stringent emission requirements, the weighted-wire precipitator was found to be inadequate in many cases to provide the performance and reliability necessary. Long weighted wires had a high

20

incidence of failure, and subsequent bus section outages resulted, deteriorating performance and requiring plant outages for repair.

DM PLANT Since there is continuous withdrawal of steam and continuous return of condensate to the

boiler, losses due to blow down and leakages have to be made up to maintain a desired water level

in the boiler steam drum. For this, continuous make-up water is added to the boiler water system.

Impurities in the raw water input to the plant generally consist of calcium and magnesium salts

which impart hardness to the water. Hardness in the make-up water to the boiler will form deposits

on the tube water surfaces which will lead to overheating and failure of the tubes. Thus, the salts

have to be removed from the water, and that is done by a water demineralising treatment plant

(DM). A DM plant generally consists of cation, anion, and mixed bed exchangers. Any ions in the final

water from this process consist essentially of hydrogen ions and hydroxide ions, which recombine to

form pure water. Very pure DM water becomes highly corrosive once it absorbs oxygen from the

atmosphere because of its very high affinity for oxygen.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw water

input. However, some storage is essential as the DM plant may be down for maintenance. For this

purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-

up. The storage tank for DM water is made from materials not affected by corrosive water, such as

PVC. The piping and valves are generally of stainless steel. Sometimes, a steam blanketing

arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid

contact with air. DM water make-up is generally added at the steam space of the surface condenser

(i.e., the vacuum side). This arrangement not only sprays the water but also DM water gets

deaerated, with the dissolved gases being removed by an air ejector attached to the condenser.

In the following descriptions, there are specific technical details pertaining to Budge Budge Generating station. BOILER

Manufacturer M/S ABB ABL Limited, Durgapur, W.B.(Unit#1&2)

M/S BHEL (Unit#3)

Type Horizontal Single Drum, Natural Circulation, Water Wall Tube, Two Pass, Balanced Draft, Single Reheat, Pulverized Fuel Boiler with Common Cold PA Fan.

Furnace:- Unit#1&2 Unit#3

Width 17940 mm 14326 mm

Depth 17173 mm 11506 mm

Super Heater

Number 3 3

Type Primary/LTSH, Platen, Final

21

No of Safety valves Unit#1&2 Unit#3

At Drum 2 3

At Superheater 2 2

At CRH 4 1

At HRH 2 4

No of Air heater 3 2

No of F.D Fan 2 2

No of I.D Fan 3 2

No of P.A Fan 2 2

No of Coal Mills 6 5

Steaming Parameter 100% BMCR

Evaporation Of Boiler 805 Te/Hr

Max. Working Pressure Of Boiler 184 Kg/Cm2g

Final S/H Outlet Steam Pressure 152-155 Kg/Cm2g

Final S/H Outlet Steam Temperature 540 OC

Feed Water Temperature 247 OC

R/H Steam Flow 700 Te/Hr(unit#1&2) & 692.2 Te/Hr(unit#3)

R/H Max. Working Pressure 50 Kg/Cm2g

R/H Inlet Steam Pressure 39.8 Kg/Cm2g

R/H Inlet Steam Temperature 353 OC

R/H Outlet Steam Pressure 37.8 Kg/Cm2g

R/H Outlet Steam Temperature 540 OC

TURBINE

TURBINE No Of Cylinders HP - 1 Single Flow

IP - 1 Single Flow

TURBINE LP - 1 Double Flow

LP - 1 Double Flow 146.0 Kg/Cm2 Abs

5370C

35.7 Kg/Cm2 Abs

Reheat Temperature 5350C

Speed 3000 Rev/Min

Number Of Blading Stages

Unit#1&2 Unit#3

HP: 1 - Impulse 25- Reaction

18-50% Reaction

IP: 16-50% Reaction 17- Reaction

LP: 4-50% Reaction Per Flow, 3-

Variable Reaction 8- Reaction per flow

Steam conditions at 100% ECR load

HP Turbine : Inlet Unit#1&2 Unit#3

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Pressure 146.0 Kg/Cm2 Abs 147.0 Kg/Cm2 Abs

Temperature 5370C 5370C

HP Turbine : Outlet



IP Turbine : Inlet



IP Turbine :Outlet



LP Turbine : Inlet


Temperature 255.40C 3040C

LP Turbine : Outlet

Pressure 76 Mm Hg Abs 76 Mm Hg Abs

Temperature 480C 44.20C

Water Consumption Pattern (M3/Hr.) For Two units.

Avg. River Water Intake 1500

Avg. Evaporation (At 100% PLF) 1350

Avg. Blow-Down Water Used For Service Water, Fire

Water & Ashing Purposes

170

Avg. Clarified Water Intake For DM Plant 50

Avg. Effluent Water Produced After Regeneration Of DM

Plant Vessels

4

Avg. DM Water Produced 50

Avg. Waste Water (As Sludge) Produced 10

Avg. Holding Pond Water Intake To ISS (Recycled

Water)

250

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FUEL AND ASH The department of fuel and ash operations oversees the entire process of coal unloading, moving it to the stack yard and as well as the effective elimination of fly as well as bottom ash. A majority of the fly ash is at present exported to Bangladesh though barges for use in their cement plants.

COAL HANDLING SYSTEM The Coal Handling Plant has been designed for supplying coal to both the units of

250 MW each. Two (2) parallel conveyor streams, one working and one standby, each of 960 MTPH design capacity have been provided in the Coal Handling System.

Arrangements have been made for unloading of wagons in the yard either in Wagon Tippler Hoppers thru' Wagon Tipplers or In the Track Hoppers thru' bottom discharge wagons.

Coal of (-) 300 mm size will generally be received at site along with minimum 1 % oversize of (-) 1500 mm. Coal received in box type wagons will be unloaded by Rota side Wagon Tipplers WT -1 and/or WT2 to their common receiving hopper (WTH). The Wagon Tippler WI-2 shall be installed in future Feed to Wagon Tipplers will be by Side Arm Charger From the hopper WTH, coal will be fed to conveyor 1 C and 1 D. Feed to conveyor 1 C is done thru' Vibrating Feeders

VFD-1, 2 & 3 with Rack & pinion Gate (RPG) Nos. 1, 2 & 3 and Rod Gate (RG) Nos. 1, 2 & 3. Similarly, Conveyor 10 will be fed thru' VFD-4, 5 & 6, RPG-4, 5 & 6 and RG-4, 5 & 6. These are located below wagon Tippler Hopper.

From each of the conveyors 1C & 1D, coal will be fed to either of the conveyors 1A or 1B in TP-102 thru' Flap Gates FG-10A & 10B respectively. Conv.1A & 1B are extended backwards up to TP-101 to receive coal from Track Hopper thru' Conveyors 101 A/B, installed below Track Hopper.

Coal of (-) 300 mm size will also be received by bottom discharge wagons. Bottom discharge wagons will be unloaded automatically while in slow motion or in stationary condition on the track over Track Hopper.

Coal from Track Hopper will be scooped by four(4) Paddle Feeders PF1,2,3 & 4, two for each stream and will be fed to either conveyor 101 A or 101B. Conveyor 101A in turn will discharge to either of conveyors 1A or 1B thru' Flap Gate 1A. Similarly, conveyer 101B will discharge to either of conveyors 1A or 1B through Flap Gate - 1 B in underground TP-101.

Thus, conveyors 1A & 1B transport coal from both Wagon Tippler Hopper and Track Hopper.

Conveyer 1A & 1B transfer coal to TP-1 to either of conveyors 2A or 2B by Reversible Belt Feeders RBF-4A & RBF-4B respectively. Electromagnet EM-1 & EM-2 with trolley, mounted on monorail are provided in Pent House (PH) - 1 near TP-1 for removal of tramp

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iron from conveyer 1A & 1B respectively. Conveyors 2A & 2B convey coal to Primary Crusher House (PCH) where it feed coal to

the Rotary Breakers RB-1 A & RB-1 B respectively In RB-1A & RB-1 B coal is reduced from (-) 300 mm to (-) 100 mm

size and the output is collected on Reversible Belt Feeders RBF-1A & RBF-1B

respectively. Reject materials from Rotary Breakers RB-1A & RB-1B are discharged to Reject Conveyors RC-1 & RC-2 respectively. Conveyors RC-1 & RC-2 will in turn store the rejects in Reject Bins. From the Reject Bins, rejects will be disposed of periodically by trucks using Sector Gates G-1 & G-2.

Reversible Belt Feeder RBF-1A & 1B by running in one direction transfer coal to secondary crushers for further crushing and by running in reverse direction transfer coal to coal yard for stacking.

Reversible Belt Feeder RBF-1A & 1B by running In one direction will discharge coal to either of conveyors 3A or 3B by Flap Gates FG-2A & FG-2B respectively. While by running RBF-1A & 1B in reverse direction coal is transferred to either of conveyors 8A or 8B by Flap Gates FG-3A & FG-3B respectively.

Conveyors 3A & 3B convey coal to Secondary Crusher House (SCH) and transfer materials to either of the Double Deck vibrating screens DDVS-1A & 1B respectively thru' Flap Gates FG-3C, FG-3D & FG-4. By proper positioning of Flap Gates FG-3C, 3D & 4, Conveyor-3A can feed to either DDVS-1A or DDVS-1B. Similarly Conveyor - 3B can also feed to either DDVS-1A or 1B.

From Double Deck vibrating screens DDVS-1A & 1B oversize coal of (+) 20 mm is fed to Secondary Crushers SC-1A & SC-1B respectively. In the Secondary Crushers (-) 100 mm input coal is reduced to (-) 20 mm size. Now, (-) 20 mm output coal from Secondary Crushers SC-1A & 1B and undersize screen product of (-) 20 mm from DDVS-1A & 1B is transferred to either of conveyors 4A or 4B by Flap Gates FG-4A & FG4C and FG-4B & FG-4D respectively. In Line Magnetic separators ILMS-1A & 1B are installed on head ends of conveyors 3A & 3B respectively to separate tramp iron for protection of Crusher elements.

Conveyors 4A & 4B convey coal to TP-2 where conv. 4A transfers coal to either conveyor 5A or Reversible Belt Feeder RBF-2A by Flap Gate FG-5A. Similarly, conv. 4B transfers coal to either conveyor 5B or Reversible Belt Feeder RBF-2B by Flap Gate FG-5B.

RBF-2A & 2B by running in one direction will feed Conveyor 6A and by running in reverse direction will feed conveyor 6B. Conveyors 6A & 6B will be equipped with Travelling Trippers TT-1A & TT-1B respectively for Unit No. 1 bunker filling.

Conveyors 5A & 5B convey coal to TP-3 where they transfer coal to either of the Tripper conveyors 7A or 7B by FG-6A & RBF -3A and FG6B & RBF-3B respectively. Conveyors 7A & 7B are provided with Travelling Trippers TT-2A & TT-2B respectively for Unit NO.2 bunker filling. In TP-3 provisions are made to transfer coal from conveyors 5A & 5B to future conveyors 102A & 102B with the help of FG-6A & FG-6B respectively for bunker filling of future one unit.

Magnetic Detectors and Belt weighers, i.e. MD-1 & BW-3 and MD-2 & BW-4 are provided on conveyors 4A & 4B respectively near the Secondary Crusher House. Belt weighers BW-1 & BW-2 are installed on conveyors 2A & 2B respectively near TP-1.

The above describes about the flow path from unloading of raw coal in the yard to bunkering in the boiler bunkers. Facilities have been made also for stacking and reclaiming

25

of (-) 100 mm coal in the Coal Handling System. For stacking, coal of (-) 100 mm

size from Primary Crusher House With the help of RBF-1A & RBF-1B is taken by conveyors 8A & 8B to TP-4 where it is discharged to Stacker-Reclaimer Conveyor 10A Conveyor 10A convey coal to Stacker-Reclaimer STR-1 With the help of which stacking of (-) 100 mm coal is done in the coal yard as and when required.

Provision has been made in the Coal Handling System for future installation of conveyors 9A & 9B, Flap Gates FG-7A & 7B. TP-5, Stacker-Reclaimer Conveyor-10B and Stacker-Reclaime the above future provision, coal from Primary Crusher House can be stacked in the coal yard by Stacker-Reclaimer STR-2 also.

Reclaiming is done by transferring coal from coal yard to boiler bunkers with the help of Stacker-Reclaimer. For reclaiming, Stacker-Reclaimer STR-1 feeds coal from stock pile in the yard to conveyor 10A Conveyor 10A discharges in TP-4 to either of conveyors 110A or 11B by Flap Gate FG-8A unlike stacking, future provision for reclaiming has been made in the Coal Handling System. As per the future provision. Stacker-Reclaimer STR-2 will feed coal to conveyor-10B which will discharge coal in TP-S to either of the conveyors 11A or 11 B (to be extended as per future scheme) by Flap Gate FG-8B.

Conveyors 11 A & 11 B transfer reclaimed coal to conveyors 12A & 12B in TP-6 respectively. Conveyors 12A & 12B discharge to either of conveyors 3A or 3B in Primary Crusher House by Flap Gates FG-9A & 9B. From this point, reclaimed coal is taken to Secondary Crusher House & Boiler bunkers in the flow path as described earlier Flap Gates FG-9A & 9B can be positioned such that conveyors 12A or 12B can transfer coal to either of the conveyors 3A and 3B.

Facilities have been provided In the Coal Handling system for Emergency Reclaiming also. Emergency reclaiming IS done thru' Reclaim Hoppers which are located in the coal yard over conveyors 11A & 11B.

Each Reclaim Hopper is provided with two (2) nos. Vibrating Feeders (VFD), two (2) nos. Rack & Pinion Gates (RPG) and two(2) nos. Rod Gates (RG). For Emergency Reclaiming, four (4) nos. Reclaim Hoppers RH-1, 2,3 & 4 are provided along with VFD-7,8,9,10,11,12,13 & 14, RPG-l,8,9.10,11,12,13 & 14 and respective Rod Gates. However, RH-3 & 4, VFD & RPG -11,12,13 & 14 shall be installed in future. Emergency Reclaiming is done with the help of Bull Dozers by bull dosing of yard coal to Reclaim Hoppers and thereby transferring to conveyors 11 A or 11B by vibrating Feeders VFD-7,8,9 or 10.

Wagon tippler is provided with electronic integral weigh bridge where as, Track. Hopper lines are provided with electronic in motion weigh bridges.

Dust extraction, dust suppression and ventilation systems are provided for entire coal handling plant.

26

ASH HANDLING SYSTEM For a coal fired unit the ash generated after burning of coal is broadly divided into

three types. The heaviest part, clinker etc. are collected in Furnace bottom that is at Bottom Ash Furnace Hopper. Rest of the ash, called Fly ash, is carried away by flue gas, of which the coarser ash is collected in Economiser Hoppers and Air Heater Hoppers. Finer ash is further carried by flue gas to Electrostatic Precipitator, where Ash is separated from flue gas by imparting negative electrical charge to ash particles and then collecting at positive plate. Subsequently this ash is dislodged from positive plate by wrapping the plate Dislodged ash is collected in ESP Hoppers.

This huge ash thus collected at various hoppers needs a system for disposal. The system incorporated here is wet system for Bottom-Ash removal & dry system for Fly-Ash collection & removal. In other words the bottom ash is to be hydraulically conveyed in the form of slurry from the bottom ash hopper directly upto the Dewatering Bins the Ash Tank while the Fly Ash is to be pneumatically conveyed in dry state upto the intermediate Surge Hoppers and there from to Final Storage Silos. Ultimate disposal of both types of ash is to be by means of road trucks.

BOTTOM ASH HANDLING SYSTEM

Bottom ash of each down shot Steam Generating Unit is collected and quenched in

the respective water impounded bottom ash hopper having capacity 150 tones (on dry ash basis). For proper sealing of Furnace from outside atmosphere and at the same time for providing provision of thermal expansions of boiler from its startup to its Full-load, this bottom ash hopper utilises a continuous water trough around the top periphery which accepts a seal plate extending down from the Furnace.

The bottom ash hopper is shaped in the form of double-V and is provided with four(4) outlets which are connected to individual slurry stream. Each outlet is having individual discharging equipment consists of a Feed Gate, Clinker Grinder, Feed sump and Jet pump Feed Gate is Hydraulically operated. The clinker grinder reduces the clinker to average 25 mm size or below.

Out of four(4) parallel slurry streams for each bottom ash hopper normally one(1) stream is required for bottom ash removal and other three(3) steams remain-inactive Under normal operation, the removal of BA of two units is sequential. One setting tank is adequate for such normal operation However by using both the settling tank, operation of 2 jet pumps either from one unit Of from 2 units simultaneously is possible. It is also possible to operate simultaneously both V-sections outlets of each boiler. During ash removal the ash so collected is directed to the clinker grinders aided by high velocity water from the jetting nozzles. The clinker grinder serves to crush the large lumps of ash into specified sizes to facilitate effective conveying through pipe lines. The crushed ash in the form of slurry IS fed into the Jet pump via Feed sump and IS directly conveyed to the Dewatering Bin/Ash Tank by means of high pressure water supply at jet pump. The entire equipment below BA hopper e. 9 clinker grinder, jet pump and Issuing slurry pipes are placed in over ground (not In trench) around the Bottom Ash Hopper area.

There are two(2) slurry piping for each boiler. One slurry piping is dedicated to two

27

outlets, one from each V-section. One(1) of these piping is normally working. and the other remains as standby. The bottom ash removal is to be done normally once in a shift of eight hours and entire removal cycle is suppose to take 2.5 Hrs The removal capacity of bottom ash system for each unit is 60 tonnes/hr through one slurry stream. Continuous supply of water is to be maintained into the bottom ash hopper for quenching/refractory cooling which is suppose to be over flowing from the hopper and discharge into the overflow weir-box. Continuous make up water supply is provided into the seal through and the overflow is directly transported to the Dewatering Bin/Purchasers Ash Tank via the overflow transfer pump over ground Suction Tank. The downstream of B.A. system is equipt based on Closed loop Zero discharge" concept having both Dewatering Bins and Ash Tank" with anyone of these In operation at a time.

FLY ASH REMOVAL SYSTEM

First Stage Conveyance

Each boiler is having 28 nos. ESP hoppers (7 Fields x 4 hoppers) and 18 nos. Air Pre Heater Hoppers (3 nos. in Secondary AH.P, - 3 nos. in Primary A.P.H. - 3 nos. in Secondary A.P.H. in a row). Each fly ash hopper under precipitator or Air Heater is having one (1) number ash evacuation equipment in the form of vessel with pressure tight valve and in-built air lock arrangement. The ash evacuation equipment is hung from the Air Heater hopper/ESP structural to allow unobstructed truck movement under the hoppers. The ash inlet valve, known as dome valve, of this vessel is so sealed such that there is no interfere with the path of falling ash during "open- position i.e. during filling cycle and is having positive sealing between the hopper and ash evacuating equipment. This, during ash evacuation cycle there is no upward leakage of compressed air.

Ash evacuation equipment under each stage of ESP - Hoppers and AH Hoppers are placed in rows. First vessel/equipment of the row is known as "master vessel" and the subsequent vessels are known as "slave vessels. All the master vessels are provided with conveying air supply having min. pressure of 3.5 Bar. This conveying air line before terminating at one end of the master vessel having a tapping for the 'slave vessels, NRV, orifice plate and blow valve. This tapping line, known as blending line, is used to supply additional conveying air for evacuating the subsequent ash vessels and is having a common blow valve NRV, and' orifice plate & NRV for each termination at the ash conveying line. The other end of a master vessel is connected with 'the slave vessels in a row by means of ash conveying line. The total amount of Fly ash as generated in a unit is conveyed through these conveying lines to the Intermediate Surge Hoppers 1/2 situated approximately.200 meters always from the units. The total number of above conveying lines for a unit is as below:

For 1st, 2nd and 3rd Field ESP Hoppers, three independent ash conveying lines are

28

taken upto the Intermediate Surge Hopper. Each conveying line is thus connected with four ( 4) hours via the ash vessels of each field. For 4th, 5th, 6th & 7th Fields ESP Hoppers, a common ash conveying line is taken upto the Intermediate Surge Hopper. Ash Vessels of these hoppers are connected with four separate ash conveying lines for each of the 4th, 5th, 6th & 7th fields.

Ash conveying lines of 4th & 5th fields are connected with the common ash conveying line through a one way switch valve where as the ash conveying lines for E.S.P. fields 6 & 7 are connected through a 211 way switch valve. Thus the clearing of material in fields, 4,5,6 & 7 cannot be done simultaneously. And is to be done in cycle.

The Blow vessel and Ash Pump capacities are such that it permits the system to operate at less than 50,000 cycles per year. This reduces the system wear.

Silo Unloading System

As described earlier, three (3) nos. silos are provided for the two (2) units. Bottom of each silo is provided with four (4) independent ash discharge outlets for efficient loading of trucks.

Each ash discharge outlet of each silo is provided with suitable arrangement for smooth control of ash flow at the rate of 80 T/Hr. during loading of trucks. The arrangement is provided with suitable feeder to feed the ash at the specified rate on to tile rotary unloader.

Two (2) additional blanked and valve discharge connections on each silo are provided for future provision. These connections may be used for unloading spouts (for loading of container trucks) or alternatively, these connections may be used to install FUTURE long distance Fly ash pneumatic conveyors.

Water spraying arrangement is provided with control system for spraying and conditioning of ash for dust suppression during loading of ash trucks, Spray water for rotary un-loaders of ISH & Silos is taken from L. P/Make-Up water system.

The Fly ash silo unloading system is completely independent of Fly ash removal system from Intermediate Surge hoppers to the silos It is possible to unload any Fly ash silo through any discharge point.

Each of the three(3) Fly Ash R.C,C storage silos is having an effective storage capacity of 1750 tonnes of dry Fly ash where as each of the two(2) intermediate Surge Hoppers (steel construction) is having an effective storage of four(4) hours ash collection of one, Boiler (320 MT).

For venting out of conveying air, Bag type vent filter is provided at the top of each silo & also at the top of each ISH. These are provided to minimize solid particulate concentration of the surrounding atmosphere as per environmental norm.

Automatic system for on line pulse-jet cleaning of the bags is provided along with all required accessories, bag catchers, dust explosion arresting device, exhaust fan as necessary. Compressed air required for pulse jet operation is met from instrument air headers. Effluent air quality not exceeding 80 mgmslNm3 is achieved for this filter.

The material of bag is suitable for 150C continuous temperature with occasional excursion to 200C. Also, five (5) nos. vacuum/pressure relief valves - one(1) no. for each silo/ISH for protection of the same against excessive vacuum/pressure, is provided at the top of each silo/ISH.

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HIGH CONCENTRATION SLURRY SYSTEM

High Concentration Slurry System- is a new concept in the field of effective handling and

utilization of fly ash. It involves transportation of fly ash in the form of slurry of

homogeneous nature at a specific concentration (58% to 64% solid concentration). As the

ash slurry is used at a specific concentration and also it is a homogeneous mix, it maximises

the usage of the land area and takes care of the environmental consequences otherwise

likely in way of dust formation and contamination caused by ash laden effluent. The high-

density slurry is prepared by the Dosing and Mixing unit, conditioned in the Agitated

Retention Tank and then pumped to the site at a distance of 2.2 kms through a Pipeline by a

main line GEHO pump. At the mound area the slurry is discharged through a spigot and gets

spread over a very small area. The flow stops within a run of around 80 mts. only under a

natural angle of repose due to the consistency of the slurry. In this way a sloped surface is

formed. The homogeneous composition of the slurry ensures no water is released when the

slurry .is discharged at the mound area.

ELECTRICAL AND

INSTRUMENTATION

The Department of Electrical and instrumentation in Budge Budge generating station is responsible for proper distribution of electrical power for its own auxiliary uses as well as distribution towards substations. It also oversees calibration as well as tuning of various field instruments.

EHV POWER DISTRIBUTION & GENERATOR TRANSFORMER This system mainly consists of i) 132 KV SWITCHYARD and ii) GENERATOR TRANSFORMERS

132 KV SWITCHYARD (S/Y) There are two Main Buses (Bus I & II) and a Transfer bus in 132 KV Switchyard, receiving power from two generating Units (2 x 250 MW) of the Plant Power IS evacuated from 132 KV S/Y by several transmission lines (132 KV). Two numbers of Station Transformers (60 MVA each, 138/6.9/6.9 KV) are also connected to 132 KV S/Y and supply common services of the whole plant at 6.6 KV.

GENERATOR TRANSFORMERS (GT) Each generator is connected to its own GT, where generation voltage 165 KV is stepped up to 132 KV for feeding power to 132 KV switchyard. Generator output is connected directly

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through 16.5 KV isolated phase bus duct to LV side of 315 MVA GT which consists of three nos. of single phase 105 MVA. 138/3/16.5 KV Transformer bank connected as 'delta' in LV (16.5 KV) side and 'Star' in HV side so that Ynd11 vector group is achieved There is no circuit breaker between Generator and GT, but removable bus links are there in bus duct both at Generator and GT end. GT high voltage side is connected to 132 KV switchyard bus through HV circuit breaker Generator output, through GT is synchronized to the grid through this breaker.

6.6 KV DISTRIBUTION SYSTEM STATION TRANSFORMERS (ST) Plant common service load is supplied by two nos. Station Transformers, each of 60 MVA capacity, 132/6.9/6.9 KV. Each Station Transformer is fed from 132 KV switchyard and L.V. side has two 6.9 KV windings, each connected to 6.6 KV station switch gear through segregated phase bus duct HV neutral is directly grounded while both the LV-neutrals are grounded through resistance (9.9 Ohm ). Station Transformers are provided with ON load tap changer from + 6% to - 10% in 16 equal steps of 1 % each to maintain Station bus voltage at 6.6 KV (for variations in 132 KV grid). ST supply following common service loads of Plant:- a) Coal Handling Plant b) Ash Handling Plant c) DM Water Plant, Raw Water Plant, Clarified water Plant, Fire fighting, Fuel oil Plant d) Instrument & Plant Air Compressor Plant e) Station Aux. L.T. load like Station lighting, Ventilation & AC Plant etc BFP -8 motor (8.8 MW) of each unit is supplied from station bus 8 of each ST. Also unit auxiliary load is supplied from Station Transformers during Unit start up and shut down conditions.

UNIT TRANSFORMERS (UT) For power supply to unit auxiliary load, each unit is provided with one (1) number 40 MVA, 16.5/6.9/6.9 KV, Dynlynl Transformer, primary of which is tapped from Generator isolated phase bus by tee off bus duct. Unit Transformer has two secondary windings, each 6.9 KV rated but of 25 and 15 MVA capacity, feeding two separate 6.6 KV Unit Switchgears through segregated phase bus ducts.

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6.6KV STATION SWITCHGEAR Two separate 6.6KV switchgears (A &.B) are supplied from two 6.9 KV windings of each Station Transformer. Station Sw. Gr.1A is having a tie connection with Station Sw. Gr- 2A and similarly stn Bus 1B is having a tie with 2B. Also there are following tie connections between station and unit buses:- Sm. Sw. Gr 1A & Unit Sw. Gr. 1A Sm. Sw. Gr 1B & Unit Sw. Gr. 1B Stn. Sw. Gr 2A & Unit Sw. Gr. 2A Stn. Sw. Gr 2B & Unit Sw. Gr. 2B During Unit start up/shut down and Unit Transformer troubles, Unit load is supplied from station bus through these ties.

6.6KV UNIT SWITCHGEAR Each Generating Unit is having two Unit Sw. Gr. A & B. Unit Sw Gr A is again sectionalized in two halves with a bus coupler in between and one section is fed from UT, LVI winding (69 KV, 25 MYA) while the other section is having a tie connection from Station bus A.

415 V SYSTEM As in 6.6 kV system, 415 V power system has also been divided into two distinct system viz. Unit 415 V system and Station 415 V system. Unit 415 V system supplies power to auxiliaries directly connected with unit operation each unit has two 1600 kVA, 6.9/0.4 KV Unit Auxiliary Transformers fed from two sections of Unit Switch Gear. A (5.5 KV) Similarly for ESP L T load, two ESP transformers 2000 KV A each, is supplied from two sections of Unit switch gear - A Unit cooling tower L T load is supplies by two CT transformers, each 2 MVA capacity, fed from two sections of Unit switch gear - A Station 415 V systems supply the station common services like DM Plant, WTP, Intake Pump house, compressors, fuel oil plant, air conditioning and ventilation plants, lighting etc. Station Service PCC/MCCs have two incomers, (from two station transformers/station switch gear) and bus coupler)

220 V D.C. SYSTEM 220 V D.C. power supplies are provided in each unit to provide stable DC supply to following:-

i) Generator auxiliaries DC Seal Oil Pump. Excitation Cubicle, Generator back up panel.

ii) Generator Relay panel

iii) Turbine auxiliaries Emergency lub. Oil Pump, Jacking Oil Pump, Misc. Solenoids

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iv) Boiler auxiliaries D.C. scanner air fan, FSSS panel & Mise solenoids

v) 132 KV, 6.6 KV & 0.4 KV Switchgear

132 KV Relay panel. 132 KV control desk, 132 KV dose - trip operation., 6.6 KV Station & Unit bus - C.B. close trip operations relay auxiliary supply indications & annunciations

vi)

Emergency lighting

All above loads are supplied from D.C. distribution board charged from Battery Bank consisting of lead acid cells, constantly under charging by battery charger, AC power to which are supplied either from station auxiliary L T board (0.4 KV) and unit wise emergency MCC.

UNINTERRUPTED POWER SUPPLY (UPS) UPS system provides a regulated and uninterrupted single phase AC, 240 V, 50 Hz power supply within specified tolerances to critical station loads during normal and emergency operations. Each unit has its own UPS system which consists of: a) 60 KVA parallel redundant type UPS comprising of:- i) 2 x 100% capacity float cum boost charger ii) 2 x 100% capacity static inverter iii) 2 x 100% capacity static transfer switches iv) 1 x 100% manual bypass switch v) 1 x 100% UPS system battery b) 60 KV A servo type automatic voltage stabilizer with transformer c) 240 V A.C. Power Distribution Board comprising of MCCB at incoming & isolator fuse arrangement at outgoing feeders.

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D.G. SUPPLY There are two Diesel Generator sets, each 1000 kVA capacity, supplying unit emergency loads like lub Oil pumps, Turning gear drive, Jacking oil pumps and others. DG sets have brushless excitation system to maintain Generator voltage constant at any value within 5% of rated voltage DG distribution board charged from two DG sets in two sections with a bus coupler in between. From each section of DGDB, two 800 A feeders supply power to EMCC of Unit - I & II In addition there are feeders to D.G. auxiliary panel.

CONCLUSION

CESCs environmental management system focuses on continuous improvement and upgradation, with state-of-the-art principles and equipment, setting high targets and reviewing its performances. CESC recognizes its responsibility towards protecting the ecology, health and safety of the employees and consumers. The vacational training has been organized by the CESC limited and has been undertaken at the BUDGE BUDGE GENERATING STATION. The purpose of the vacational training is to get an industrial exposure in our engineering career. Students can learn a lot from different books about various subjects such as operations of a plant, various constituents of a plant, power production, power distribution etc. but a practical experience helps in better understanding and enhancement of knowledge in various subjects. I am grateful to CESC limited for organizing this vacational training.

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