Ntpc Report

Summer Training Report


By:

Prateek BahlMAE (7th Sem.)


Acknowledgements

This project involved the collection and analysis of information from a wide variety of sources and the efforts of many people beyond me. Thus it would not have been possible to achieve the results reported in this document without their help, support and encouragement.

I will like to express my gratitude to the following people for their help in the work leading to this report:

Project supervisors: for their useful comments on the subject matter and for the knowledge I gained by sharing ideas with them.

Project Coordinator: for organizing and coordinating the B. Tech. Projects’ 2010.


Contents

Introduction About The Company Evolution Of NTPC Thermal Power Plant Generation Of Electricity

Boiler Maintenance Department (BMD) Description Boiler Auxiliaries Technical Data On Pulverizing Plant Description Of Equipments

Plant Auxillary Maintenance (PAM) Hydrogen Plant Cooling Tower Water Treatment Plant Compressor House Ash Handling Plant

Turbine Maintenance Department (TMD) Turbine Cycle Turbine Auxiliaries Design Of Steam Turbine

Coal Handling Department (CHD) Transportation System Handling System Equipments


About The Company

Corporate Vision:

“A world class integrated power major, powering India's growth with increasing global presence.”

Core Values:

B- Business ethicsC-Customer focusO-Organizational & professional prideM-Mutual respect & trustI-Innovation & speedT-Total quality for excellence

NTPC Limited is the largest thermal power generating company of India, Public Sector Company. It was incorporated in the year 1975 to accelerate power development in the country as a wholly owned company of the Government of India. At present, Government of India holds 89.5% of the total equity shares of the company and the balance 10.5% is held by FIIs, Domestic Banks, Public and others. Within a span of 31 years, NTPC has emerged as a truly national power company, with power generating facilities in all the major regions of the country.


Evolution Of NTPC

1975: NTPC was set up in 1975 with 100% ownership by the Government of India. In the last 30 years, NTPC has grown into the largest power utility in India.

1997: In 1997, Government of India granted NTPC status of “Navratna’ being one of the nine jewels of India, enhancing the powers to the Board of Directors.


2004: NTPC became a listed company with majority Government ownership of 89.5%.NTPC becomes third largest by Market Capitalization of listed companies

2005: The Company rechristened as NTPC Limited in line with its changing business portfolio and transforms itself from a thermal power utility to an integrated power utility.

NTPC is the largest power utility in India, accounting for about 20% of India’s installed capacity.

Thermal Power PlantA thermal power station consists of all the equipment and a subsystem required to produce electricity by using a steam generating boiler fired with fossil fuels or befouls to drive an electric generator. Some prefer to use the term ENERGY CENTER because such facilities convert form of energy like nuclear energy, gravitational potential energy or heat energy (derived from the combustion of fuel) into electrical energy. Typical diagram of a coal power thermal power station-

Cooling water pump Three phase transmission line Step up transformer Electrical generator Low pressure steam Boiler feed water pump Surface condenser Intermediate pressure steam turbine Steam control valve High pressure steam turbine Deaerator feed water heater Coal conveyer Coal hopper Coal pulverizer Boiler steam drum Boiler ash hopper


Super heater Force draught (draft) fan Reheater Combustion air intake Economizer Air preheater Precipitator Induced draught (draft) fan Fuel gas stack

The description of some of the components above is as follows:

Cooling towers:

Cooling towers are evaporative coolers used for cooling water. Cooling tower use evaporation of water to reject heat from processes such as cooling the circulating water used in oil refineries, chemical plants, power plants, etc. The tower vary in size from small roof – top units to very large hyperboloid structures that can be up to 200 meters tall and 100 meters in diameter, or rectangular structure that can be over 40 meters tall and 80 meters long. Smaller towers are normally factory built while larger ones are constructed on site. The primary use of large, industrial cooling tower system is to remove the heat absorbed in the circulating water system used in power plants, petroleum refineries, petrochemical and chemical plants, natural gas processing plants and other industrial facilities.

The absorbed heat is rejected to the atmosphere by the evaporation of some of the cooling water in mechanical forced – draft or induced draft towers or in natural draft hyperbolic shaped cooling towers as seen at most nuclear power plants.

Three phase transmission line:

Three phase electric power is a common method of electric power transmission. It is a type of polyphase system mainly used for power


motors and many other devices. In a three phase system, three circuits reach their instantaneous peak values at different times. Taking one conductor as reference, the other two conductors are delayed in time by one-third and two-third of cycle of the electrical current. This delay between phases has the effect of giving constant power over each cycle of the current and also makes it impossible to produce a rotating magnetic field in an electric motor. At the power station, an electric generator converts mechanical power into a set of electric currents one from each electromagnetic coil or winding of the generator. The currents are sinusoidal functions of time, all at the same frequency but offset in time to give different phases. In a three phase system, the phases are spaced equally giving a phase separation of one-third of one cycle. Generators output at a voltage that ranges from hundreds of volts to 30,000 volts. At the power station. Transformers step-up this voltage for suitable transmission. After numerous further conversions in the transmission and distribution network, the power is finally transformed to standard mains voltage i.e. the household voltage. The power may already have been split into single phase at this point or it may be still three phase. Where the step-down is three phase. The output of the transformer is usually star connected with the standard mains voltage being the phase neutral voltage.

Electrical generator:

An electrical generator is a device that coverts mechanical energy to electrical energy, using electromagnetic induction whereas electrical energy is converted to mechanical energy with the help of electric motor. The source of mechanical energy may be a reciprocating turbine steam engine. Turbines are made in variety of sizes ranging from small 1 hp(0.75 kW) used as mechanical drives for pumps, compressors and other shaft driven equipment to 2,000,000 hp(1,500,000 kW) turbines used to generate electricity.

Boiler Feed Pump:

A Boiler Feed Pump is a specific type of pump used to pump water into steam boiler. The water may be freshly supplied or retuning condensation of steam produced by the boiler. These pumps are normally high pressure units that use suction from a condensate return system and can be of centrifugal pump type or positive displacement type. Construction and Operation feed water pumps range in size upto many horsepower and the electric motor is usually separated from the


pump body by some form of mechanical coupling. Large industrial condensate pumps may also serve as the feed water pump. In either case, to force water into the boiler, the pump must generate sufficient pressure to overcome the steam pressure developed by the boiler. This is usually accomplished through the use of centrifugal pump. Feed water pumps usually run intermittently and are controlled by a float switch or other similar level-sensing device energizing the pump when it detect a lowered liquid level in the boiler substantially increased. Some pumps contain a two stage switch. As liquid lowers to the trigger point of the first stage, the pump is activated.

If the liquid continues to drop (perhaps because the pump has failed, its supply has been cut-off or exhausted, or its discharge is blocked),the second stage will be triggered. This stage may switch off the boiler equipment (preventing the boiler from running dry and overheating), trigger an alarm or both.

Control valves:

Control Valves are the valves used within industrial plants and elsewhere to control operating conditions such as temperature, pressure, flow and liquid level by fully or partially opening or closing in response to signals received from controllers that compares a “set point” to a “process variable” whose value is provided by sensors that monitor changes in such conditions. The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems.

Deaerator:

A Deaerator is a device for air removal and used to remove dissolved gases from boiler feed water to make it non-corrosive. A deaerator typically includes a vertical domed deaeration section as the deaeration feed water tank. A steam generating boiler requires that the circulating steam, condensate and feed water should be devoid of dissolved gases, particularly corrosive ones and dissolved or suspended solids. The gases will give rise to corrosion of the metal. The solids will deposit on heating surfaces giving rise to localized heating and tube ruptures due to overheating. Deaerator level and pressure must be controlled by adjusting control valves-the level by regulating condensate flow and pressure by regulating steam flow. Most deaerators guarantee that if operated properly, oxygen in deaerated water will not exceed 7ppb by weight.


Feed Water Heater:

A feed water heater is a power plant component used to pre heat water delivered to a steam generating boiler. Feed water heater improves the efficiency of the system. This reduces plant operating costs and also helps to avoid thermal shock to boiler metal when the feed water is introduced back into the steam cycle. Feed water heaters allow the feed water to be brought upto the saturation temperature very gradually. This minimizes the inevitable irreversibility associated with heat transfer to the working fluid(water). A belt conveyer consists of two pulleys, with a continuous loop of material- the conveyer belt that rotates around them. The pulleys are powered, moving the belt and the material on the belt forward. Conveyer belts are extensively used to transport industrial and agricultural material, such as grain, coal, ores, etc.

Pulverizer:

A pulverizer is a device for grinding coal for combustion in a furnace in a fossil fuel power plant.

Boiler Steam Drum:

Steam Drums are a regular feature of water tube boilers. It is reservoir of water/steam at the top end of the water tubes in the water-tube boiler. They store the steam generated in the water tubes and act as a phase separator for the steam/water mixture. The difference in densities between hot and cold water helps in the accumulation of the “hotter”-water/and saturated –steam into steam drum. Made from high-grade steel (probably stainless) and its working involves temperatures 390’C and pressure well above 350psi (2.4MPa). The separated steam is drawn out from the top section of the drum. Saturated steam is drawn off the top of the drum. The steam will re-enter the furnace in through a super heater, while the saturated water at the bottom of steam drum flows down to the mud- drum /feed water drum by down comer tubes accessories include a safety valve, water level indicator and fuse plug. A steam drum is used in the company of a mud-drum/feed water drum which is located at a lower level. So that it acts as a sump for the sludge or sediments which have a tendency to the bottom.

Super Heater:


A Super heater is a device in a steam engine that heats the steam generated by the boiler again increasing its thermal energy and decreasing the likelihood that it will condense inside the engine. Super heaters increase the efficiency of the steam engine, and were widely adopted. Steam which has been superheated is logically known as superheated steam; non-superheated steam is called saturated steam or wet steam; Super heaters were applied to steam locomotives in quantity from the early 20th century, to most steam vehicles, and so stationary steam engines including power stations.

Economizers:

Economizer, or in the UK economizer, are mechanical devices intended to reduce energy consumption, or to perform another useful function like preheating a fluid. The term economizer is used for other purposes as well. Boiler, power plant and heating ventilating and air conditioning. In boilers, economizer are heat exchange devices that heat fluids , usually water, up to but not normally beyond the boiling point of the fluid. Economizers are so named because they can make use of the enthalpy and improving the boiler’s efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used the fill it (the feed water). Modern day boilers, such as those in cold fired power stations, are still fitted with economizer which is decedents of Green’s original design. In this context they are turbines before it is pumped to the boilers. A common application of economizer is steam power plants is to capture the waste hit from boiler stack gases (flue gas) and transfer thus it to the boiler feed water thus lowering the needed energy input, in turn reducing the firing rates to accomplish the rated boiler output. Economizer lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection.

Air Preheater:

Air preheater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler). The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the fuel gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature allowing


simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack.

Precipitator:

An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device that removes particles from a flowing gas (such As air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices, and can easily remove fine particulate matter such as dust and smoke from the air steam. ESP’s continue to be excellent devices for control of many industrial particulate emissions, including smoke from electricity-generating utilities (coal and oil fired), salt cake collection from black liquor boilers in pump mills, and catalyst collection from fluidized bed catalytic crackers from several hundred thousand ACFM in the largest coal-fired boiler application. The original parallel plate-Weighted wire design (described above) has evolved as more efficient ( and robust) discharge electrode designs were developed, today focusing on rigid discharge electrodes to which many sharpened spikes are attached , maximizing corona production. Transformer –rectifier systems apply voltages of 50-100 Kilovolts at relatively high current densities. Modern controls minimize sparking and prevent arcing, avoiding damage to the components. Automatic rapping systems and hopper evacuation systems remove the collected particulate matter while on line allowing ESP’s to stay in operation for years at a time.

Fuel gas stack:

A Fuel gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called fuel gases are exhausted to the outside air. Fuel gases are produced when coal, oil, natural gas, wood or any other large combustion device. Fuel gas is usually composed of carbon dioxide (CO2) and water vapor as well as nitrogen and excess oxygen remaining from the intake combustion air. It also contains a small percentage of pollutants such as particulates matter, carbon mono oxide, nitrogen oxides and sulfur oxides. The flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so as to disperse the exhaust pollutants over a greater aria and thereby reduce the concentration of the pollutants to the levels required by governmental environmental policies and regulations.


Electricity Generation Process(A Basic Overview)

At NTPC (Badarpur) the man two paths are the flue gas or air cycle and steam or condensate paths.

Capital Overhaul

NTPC has been in news due to extensive load sheds in many areas in Delhi and the main cause behind these load sheds was the capital overhaul of one of 210 MW units. Unit IV was under an extensive check, which has caused shut down of the plant and the plant, was dismantled completely to change the old parts and cleaning up the whole unit. But capital overhaul has no meaning because such a deep checking of the plant happens once in five to seven years.

How Electricity Is Generated?

Thermal power station burns fuel and uses the resultant heat to raise steam which drives the TURBO GENERATOR. The fuel may be ‘fossil’ (coal, oil, natural gas) or it may be fissionable, whichever fuel is used, the objective is same to convert the mechanical energy into electricity by rotating a magnet inside a set of winding.

Coal to Steam


Its other raw materials are air and water. The coal brought to the station by trains or by other means, travels handling plant by conveyer belts, travels from pulverizing mills, which grind it as fine as the face powder of size upto 20 microns. The finely produced coal mixed with preheated air is then blown into the boiler by a fan called primary air fan where it burns more like a gas than as a solid, in the conventional domestic or industrial grate, with additional amount of air, called secondary air supply, by forced draft fan.

As coal is ground so finally the resultant ash is also a fine powder. Some of it binds together to form pumps, which falls into ash pits at the bottom of the furnace. The water-quenched ash from the bottom is conveyed to pits for subsequent disposal or sale. Most of ash, still in fine particle form is carried out of boilers to the precipitator as dust, where electrodes charged with high voltage electricity trap it. The dust is then conveyed to water to disposal area or to bunker for sale while the clean flue gases are passed on through IP fans to be discharged through chimneys.

The heat released from the coal has been absorbed by the many kilometers tubing which line the boiler walls. Inside the tubes the boiler feed water, which is transformed by heat into steam high temperature and pressure. The steam superheated in further tubes (super heaters) passes to turbine where it is discharged through the nozzle on the turbine blades. Just as the energy of wind turns the sail of the windmill, the energy of steam striking the blade makes the turbine rotate.

Coupled to the end of the turbine is the rotor of the generator. The rotor is housed inside the stator having heavy coils of the bars in which electricity is produced through the movement of magnetic field created by the rotor. Electricity passes from stator windings to step-up transformer which increases its voltage so that it can be transmitted efficiently over lines of grid.

The steam which has given up its heat energy is changed back into water in a condenser so that it is ready for re-use. The condenser contains many kilometers of tubing through which cold water is constantly pumped. The steam passing around the tubes loses heat. Thus it is rapidly changed back into water.


But, the two lots of water, that is, the boiler feed and cooling water must never mix. Cooling water is drawn from river- bed, but the boiler feed water must be absolutely pure, far purer than the water we drink (de-mineralized water), otherwise it may damage the boiler tubes.

Boiler Maintenance Department(BMD)

From Atmosphere

P.A Fans

Air Pre-Heaters

Hot P.A Fans

Cold P.A Fans

Seal Air Fans

Pulverized Bowl Mill

Furnace


Description

The second stage of Badarpur Thermal Power Station consists of two units of 210MW each. The boilers are manufactured and supplied by B.H.E.L. It is of “semi outdoor type” single drum, natural circulation, two- pass vertical membrane water wall construction, reheat dry bottom , tangentially fired furnace using pulverized fuel and having a maximum continuous rating of 700 T/ hr. at working pressure of 137 kg/cm2 and final steam temperature of 540*c . The boiler is equipped with six Raymond Bowl mills, two PA fans, forced Draught (FD) fans, two Induced Draught (ID) fans, two regenerative type air-heaters, dust collecting plants and other accessories. This boiler is direct fired having six elevations of coal and three elevations of oil. The first pass of boiler is combustion chamber enclosed with water walls of fusion welded construction on all four sides. In addition, there are four water walls platens to increase the radiant heating surface. Besides this the platen pendant super heater, reheater section are also suspended in furnace i.e., combustion chamber.

The second pass is surrounded by steam cooled walls on all four sides as well as roof of boilers. Feed water is supplied to the steam drum through the economizer links. The steam and water mixture from the water wall plantens are collected in boiler drum where the steam is separated and led to various super heater stages. The boiler drum houses turbo separators and driers.


Each turbo separator consists of primary and secondary stages. The primary stage of two concrete cans spinner blades impart a centrifugal motion to the mixture of steam and water thereby throwing the water particles, hence forcing the steam outside. The water particles gets arrested by a skin of lip above the spinner blades and return to lower part of the drum through annular space between two cans. Further the steam proceeds to the secondary separator stage which consists of two opposed banks of closely spaced corrugated sheets. The entrained water is separated out and steam moves up to the scrubber for final separation.

Specifications:

Main boiler At 100% load

Evaporation : 700 T/hr. Feed water temp. : 247 0CFeed water economizer : 276 0C

Steam temperature

Drum : 341 0CSuper heater outlet : 540 0CRe-heater inlet : 332 0CRe-heater outlet : 540 0C

Steam pressure

Drum design : 158.2 kg/cm2

Drum operating : 149.7 kg/cm2

Super heater outlet : 137.0 kg/cm2

Reheater inlet : 26.35 kg/cm2

Reheater outlet : 24.50 kg/cm2


Fuel

CoalFixed carbon : 38%Volatile matter : 26%Moisture : 8%Grindability : 50% hard groove

Furnace

Width : 13.868 m Depth : 10.562 mHeight : 42.797 mVolume : 5210 m3

Boiler Auxiliaries

Furnace:

It is the primary part of the boiler where the chemical energy of fuel is converted to thermal energy by combustion.

Major factors that assist for efficient combustion are time of residence (fuel) inside the furnace and turbulence which causes rapid mixing between fuel and air.

The furnace of the boiler may be P.E. fired dry bottom furnace, slag type furnace, oil fired furnace. Normally about 65% of furnace volume is enough for an oil fired boiler as compared to the corresponding P.F fired boiler.

Boiler Drum:

Drum is of fusion welded design with hemi-spherical dished ends. It is provided with manholes and cover. The drum is provided with stubs for welding all the connecting tubes i.e. down comers, risers, pipes, saturated steam outlet. The function of steam drum internal is


to separate the water from the steam generated in furnace walls and to reduce the dissolved solid contents of the steam to below the prescribed limit of 1ppm and also take care of sudden change of steam demand from boiler.

Wet steam entering the drum is collected in a compartment, formed by internal baffles. From this compartment the steam is first fed through two rows of turbo separators consisting of primary and secondary stages. The primary stage is formed by two concentric cans. Spinner blades imparts the centrifugal motion to the mixture of steam and water flowing through the inner can, thereby throwing the water to the outside and forcing the steam to the inside, then the steam proceeds to the secondary separator stage.

The secondary stage consists of two opposed banks of closely spaced thin corrugated sheets which direct the steam and force the remaining entrained water against the corrugated plates. Since the velocity is relatively low, this water does not get picked again, but runs down the plates and off the second stage lips at the two steam outlets.

From the secondary separators the steam flows upwards to the series of screen dryers extending in layers across the length of drum. The screen performs the final stage of separation.

Drum Internal:

The boiler drum internal consists of the following equipments arranged inside the drum of MW unit-

Cyclone steam separator: In this system, steam water mixture is admitted tangentially. The water forms a layer against the cylinder walls and the steam of less density moves to the core of the cylinder and the water goes to the drum.

Phosphate dozing line: All small pipe with no. of small holes along its Length is used to distribute the chemical into drum. The phosphate is fed by a small high pressure pump in the compartment to remove silver impurities.


Feed water distribution: The salt compartment is fed with water from clean compartment through special holes in the dividing partitions.

Drier: These are used as a second stage separation to remove almost all water from the steam passing through the super heater. The drier consists of closely packed strips of steal with steam passing through strips making one or more sharp changes of direction and throwing the heavier water particles in to contact with the strip. The water runs the drier and is returned to boiler water. The velocity of steam through the drier must not be high else there will be chance of water entering and hence the drier would get overloaded.

Girth baffler: It guides steam-water mixture from the riser to the separator. At the same time it keeps the bulk of water in the drum free from disturbance by steam bubbles.

Dry box: At the top of the drum is a compartment used to collect the dry steam from drier and distribute it to super heater off take tubes. Sometimes they are also known as super saturated tubes because they carry dry saturated steam.

Attemperator: It is also known as desuperheater. This provides direct heat exchange with feed water which by passing through the economizer is sprayed in to steam flow.

Water walls: Water flows to the water walls from the boiler drum by natural circulation. The front and the two side water walls constitute the main evaporation surface.

Reheater:

Reheater is used to raise the temperature of steam from which a part of energy has seen extracted in high pressure turbine. This is another method of increasing the cycle efficiency. Reheating requires additional equipment i.e., heating surface connecting boiler and turbine piping


safety equipment like safety valve non-return valve, isolating valve, high pressure feed pump etc.

Types Of Super Heater And Reheater:

These heating can be classified into convection and radiant type according to heat transfer process. Even though the surface gets heated by both types, the ratio between them varies according to location and temp. of the flue gases at the location. The reheaters and super heaters placed above the furnace which can view the flame are called radiant type. The other type is called convection type. As the radiant surface are located in high temp. Region, they are widely pitched to reduce the velocity of gas and the grinding the surfaces by the ash.

Super heaters and reheaters can be arranged either horizontally or allowed to be hung vertically. The vertical arrangement is simpler in supporting and allowed for expansion and this arrangement is called pendant type.

Specifications:

Rear convection super heater:

Upper bank : 15 mLower bank : 05 mTerminal tube : 26.5mHeating surface : 556 m2

Plant super heater:

Weight : 76.3 T No. of coil : 29Heating surface : 9445 m2

Pendant super heater:

Weight : 69 T


No. of coil : 119Heating surface : 1036 m2

Reheater:

Outlet heater : 42 mFront assembly : 35 mRear assembly : 26 mHeating surface : 850 m2

De-super heater:

De-super heater are provided in the super heater connecting links and the cool reheater lines to permit reduction of steam temperature and is necessary to maintain the temp. at design values within the limits of nozzles capacity.

Temperature reduction is accomplished by injecting spray water in to the path of the steam through the nozzle. Maintenance of de-super heater is not needed, even then they should be inspected in 2-2.5 yrs. Spray nozzles and lines are the wearing parts of the super heater. Excessive noise observed in de-super heater in service means wear in nozzles or lines.

Specifications:

Super heater of de-super heater:

Design pressure : 154.50 kg/cm2

Design temp. : 430 0CType : Spray Type

Reheater of de-super heater:


Design pressure : 33.50 kg/cm2

Design temperature : 345 0CType : Spray Type

Economizer:

The function of an economizer in a steam generating unit is to absorb heat from the flue gases and add as a sensible heat to the feed water before the water enters the evaporation circuit of the boiler.

Earlier economizers were introduced mainly to recover the heat available in flue gases that leaves the boiler and provision of this addition heating surface increase the efficiency of steam generation by increasing the temp. of feed water to the boiler and hence also named as feed water heater.

Air preheater:

Air preheater absorbs waste heat from the flue gases and transfers this heat to incoming cold air, by means of continuously rotating heat transfer element of specially formed metal plates. Thousands of these high efficiency elements are spaced compactly arranged within 12 section shaped compartments of a radially divided cylindrical shell, called the rotor. Special sealing arrangements are provided in the air preheater to prevent leakage between the air and gas sides.

The air preheater heating surface elements are provided with two types of cleaning arrangements, soot blower to clean normal deposits, and washing arrangements to clean the elements when soot blowing alone cannot keep them clean.


Specifications:

No. of air preheater : 2 per unitHeating surface area : 1900 eachRotor drive motor : 15 hpSpeed reduction ratio : 110:1

Technical Data On Pulverizing Plant

Milling Circuit:

Each boiler is provided with 3 identical closed milling circuits with suction type drum mills with partial recirculation of vapours in the circuit and with the pulverized coal bunkers. Regulated quality of vapory is recirculated in the milling circuit and the remaining is burnt in the boiler through vapour burners.

Pulverizing plant:

Fuel data:

Type Bituminous

Calorific value : 4727 kcal/kgMoisture content : 7.5%Volatile matter : 43%Ash content : 32%Inlet size of coal to mill : 20mmDrying medium : hot flue gasesTemp. of flue gases : 480 0C


Description Of Individual Equipment:

1. Lower part of raw coal bunker: The outlet end of raw coal bunker, which is not included in our scope of delivery, is to be provided with a flange for mixing needle type raw coal bunker closure.

2. Raw coal bunker closure: The raw coal bunker closer is of needle type. No. of steel tubes (needles) are arranged in arrow and is guided is a frame. Each tube can be operated individually by hands. By operating a group of needle at a time, it is possible to avoid bridge formation in bunkers.

3. Raw coal chain feeder: The raw coal chain feeder transports coal from the raw coal bunker to the inlet chute leading to the pulverizer. Raw coal, which is precrushed in coal crusher to the required size, is conveyed to R.C. bunker by the coal handling equipment. A needle type hand operated bunker closure is interred posed between the bottom of R.C. bunker and top of the chain feeder.

The assembly consists of:

Hand operated bunker closure Feed hopper


Tension head Driving head Spacers Double link chain Driving unit Supporting base frames

The feeder casing is of welded construction duly stiffened and supported on steel frames and is lined replaceable steel plates, which are screwed to the feeder casing. A welded double link chain fabricated from high tensile steel, moves on wheels, mounted on shafts in the tension and driving heads. The upper part of the casing is provided with removable covers at suitable places. The link chain can be taken out through the rear side opening of the feeder, after removing the cover. Any slackness in the chain is compensated by volute springs in the tension head.

The chain sweeps the raw coal falling on the top plate of the feeder, on to the bottom plate and scraps it off to the raw coal chute. The height of the coal bed above the top plate can be adjusted manually by means of lever operated damper. The damper inside the chain feeder is bolted to a shaft, which protrudes out of the casing. A lever is keyed to the shaft outside and can be operated by hand and can be set in any desired position. The max. and min. heights of coal bed over the top plate are 200mm and 120mm respectively. Signaling equipment indicates the absence of the coal flow in the feeder. The signaling system consists of paddle mounted on a shaft onside the chain feeder. The shaft projects out of the casing and has levered screwed to it. The paddle normally rests over the top of the coal bed on the bottom plate. When there is no coal flow, the paddle assumes a vertical position making the lever to contact a limit switch suitably located and this gives an indication of no coal flow in the control room. The main shaft in the driving head is connected to the driving unit, consisting of a vibrater, a gear box and a motor mounted as a single unit. The chain wheel on the driving head shaft is provided with a gear which will shear off and disconnect the driving mechanism, if there is any over load in the feeder, the speed of the chain feeder is automatically regulated by actuating the control spindle of the variator by the servomotor. Rubber wires are provided both in tension and driving head to scrap off the coal dust from the moving chain.

TECHNICAL DATA


Type of feeder : chain type R 600 Width of feeder : 600 mmLength : 18,700 mmSpeed variation : 0.0503-0.151 m/sec

Functions of chain feeder: the chain feeder serves for conveying the coal from R.C. bunker to the mill. The quality of raw coal feed in to the mill can be controlled effectively by the speed control of the variation drive. The drive is a positive one and contains gear box, positively infinite variator and as an integral unit. The raw coal falls by gravity on top plate of the chain feeder and is carried on by the moving chain to the bottom part of the feeder from where it is dragged to the outlet chute of the chain feeder. Provision is made to take out raw coal samples from the feeder by means of spoon. The main shaft in the driving head is connected to the driving unit by means of a double raw roller chain.

Drum mill:

Drum mill consists of:

Single compartment mill drum Antifriction bearing Mill drive Fuel inlet and discharge elbows Foundations frame for drive and bearing Ball charge Lubricating equipment for mill bearing

Mill drum: Mill drum shell is fabricated from thick plates provided with fabricated ends and flange for bolting the gear rim. The entire inside surface of the mill is provided with armour plates, which is fastened to the drum shell by bolts with 10mm thick asbestos mill board interposed between armour plates and mill shell.

The hollow journals on both sides of the mill drum are provided with fabricated armour inserts with helix inside.


Antifriction bearing: The entire mill drum with mill journals supported and rotates on two antifriction bearing. Fixed bearing is on the other side. The free is designed to take up the axial and is lubricated by forced lubrication. Suitable thermometer is provided to indicate the temperature of oil. Labyrinth seals prevent the leakage of oil from the bearing. The pedestals of bearing are bolted to base frame.

Mill drive: It consists of:-

HT motor: Squirrel cage, induction motor totally enclosed, air cooled circuit machine.

Reduction gear box: It is of robust construction with single stage reduction. The gear box has a built in cooling coil for circulating water, which cools the oil in gear box.

Gear rim: Gear rim is machined from steel casting and is made up of two half pieces bolted together. The whole rim is bolted to the flange on the mill drum.

Grid type flexible couplings: The coupling consists of the grooved discs or hubs mounted one on the driven shaft and other on the drive shaft, interconnected by a grid spring.

Foundation frame for drive and bearing:

The foundation frames are fabricated from thick steel sections. The frame under the drive consists of three parts with precisely machined mating surfaces bolted together.

The whole foundation frame is leveled on a concrete, bolted to the foundation and grouted.

Ball charge:


The ball charge of the mill consists of three different sizes of forged steel balls. The quantity of bal fitting will be around 24 to 26% of volume of mill drum. The ball charge for each mill consists of:

Diameter 40mm : 22500 kgDiameter 50mm : 20000 kgDiameter 60mm : 10000 kgTotal : 52500 kg

During operation only balls with diameter 60mm are added and will be approx. 500 kg/week.

Specifications for mill balls:

Ball diameter : 40mm 50mm 60mmWeight per ball : 0.26 kg 0.15 kg 0.89 kgTolerance in mm : + 3 + 3 + 3


Plant Auxiliary Maintenance(PAM)

Plant Auxiliary Maintenance understands that the maintenance work of various auxiliaries outside the main plant or generation unit, essential for proper running of plants.There are seven such Auxiliary which comes under PAM: Hydrogen Plant Water Treatment Plant- I & II (PAM only undertakes maintenance

work of Treatment Plant and not the Operational Work) Compressor House Control Structure Pump House Cooling Tower Ash Slurry Pump House Fire Fighting Systems (Plant has a water line running throughout,

which should always be filled with water for firefighting)

Hydrogen Plant

Hydrogen Gas is used for generation cooling so supply of pure hydrogen in power station is essential for generation filling and maintenance of hydrogen gas pressure inside the generator casing.

Description:


Hydrogen is prepared by electrolysis of pure De-mineralized water in an electrolytic cell. When DC is passed through water, it decomposes the water into two elements 1volume oxygen and 2volume hydrogen. Pure distill water is bad conductor of electricity but if acid or salt is added it becomes a good conductor. To make economical use of electrolysis of water a solution called electrolyte has to be used which is passed through the electrolyte Hydrogen is given out of negative electrode. The Hydrogen gas is collected in Low Pressure Holder form the Low Pressure Holder the gas is taken through pipe to the High Pressure Compressor. The Compressor is a 3 stage Compressor. The gas is compressed and filled in cylinders. The gas pressure in a fully filled cylinder is 120Kg/cm*cm. From each and every cylinder the gas sample is taken & analysed by the Chemistry Department. If the Hydrogen gas purity is less than 97%, the gas is considered to be unfit for use and is discharged into the atmosphere. Oxygen produced in the process is let off to atmosphere.

The gas produced also contains some amount of moisture in it therefore, form the HP Compressor Hydrogen gas is make to flow through after coolest, which as moisture separator columns and then to a point filling station.

The Hydrogen filled cylinders containing Hydrogen of rated purity then sent to the plant for general cooling plant for dosing the Chlorine into canal for removed of fungus form the condenser.

There are two separate centrifugal pumps which are used for the suction of filtered water form the WTP and used for cleaning the screens. These pumps are known as screen work pumps. These gives supply to nozzle water traveling water screen and as well as manual cleaning of screens placed after the control structure for arresting any left over impurities in the water moving farther in the intake channel and used as cooling water in condenser.

The Compressor used in the Compressor House are of “Horizontal Double Acting Double Cylinder type. In these compressors there are two cylinders, The High Pressure and Low Pressure. The Cylinders have two different Pistons but are connected to a common lead.

To start with the suction of the low pressure cylinders is from atmosphere through air filters. There are 6 inlets to the low pressure cylinders through air can enter the cylinder in low pressure cylinder the


atmosphere air is compressed to a pressure of 1.5to 2kg/cm*cm. The temperature of air again rises due to frictional heat about 150deg.celsius. To cool down this compressed air the hot air after discharging from high pressure cylinder is again passed through after cooler. The compressed air is then collected in tanks and supply is given to common header. The basic difference between the plant air compressor have ail lubricating system between the piston and cylinder due to which there are always some air particles or decuples in the air. But in the instrument air compressors the piston rings and inner surface of the cylinder are made up of Teflon and thus there is no need of oil lubrication as Teflon at high temperature has lubrication precipitate.

But instruments air also containing certain amount of moisture. To remove this moisture, the compressor air from the compressor is passed through AIR DRY UNITS. These units contain silica gel and activated Alumina Bed (2 in numbers) are remains in service and other in regeneration. Both the air dry units are connected through a three way valve. Suppose A is service the silica gel will absorb moisture and air will become dry. One air drying unit will get exhausted in six hours, thus after six hours the unit A will get exhausted and supplied to unit Band unit B will now be in operation for next six hours and unit A will be regeneration process. The time of regeneration is also six hours thus by the time unit B will get exhausted unit A will be regenerated.

The efficiency of compressor is governed by the extent of cooling of air inter coolers and other coolers.

The Capacity of : KG Khosla Machine Compressor is 14.2mcu/min. KIRLOSKAR Compressor 18mcu/min PLANT AIR Compressor 30mcu/min.

Cooling Tower

Water is required in the Thermal Power Station for various purposes. Filtered water is used for bearing cooling, drinking and other general uses, whereas ordinary unfiltered water is used for condenser cooling and ash disposal purposes. Main sources of water supply are river, reservoirs, natural lakes and canals, wells for small stations and the oceans for coastal plants.


Cooling tower are important components of thermal plants where a limited supply of make up water is only available Cooling Tower thus provide flexibility for selections of sides for thermal power station even though Capital Investment and tunning costs are generally on the high side.

Broadly Speaking Cooling Tower are of two types: Mechanical Draft Cooling Tower Natural Draft CoolingTower

Mechanical Draft Cooling Tower :Two Types viz. Forced Draft Cooling Tower Induced Draft Cooling Tower

Forced Draft Cooling Tower

In this case, motor driven fans located at the base the top of the tower are open to the air vapour discharge. The main drawbacks in these types of tower are that exit velocity is 10W and this result in re-circulating hot air into the fan intake. Thus the efficiency of the tower is reduced. The other disadvantages of forced draft towers are:

1. High velocity from the fan located at the base makes it difficult to distribute air evenly over the whole of the packing.

2. Low height, low velocity of air and 10W wind velocity generally results in re-circulating of hot air.

3. There is rapid growth of fungus.

Induced Draft Cooling Tower

These days, it is preferred to use induced Draw Cooling Tower where the fan is located at the top and air enters from the openings located at ground level. Air mixed with vapours is discharged through a fan stack located at the top of the tower. In this case, moist air is discharged higher in the atmosphere thereby dispensing to a greater distance from the tower.

Cold water is collected in the pond located below the cooling tower where make up water is also discharged.

Hyperbolic Natural Draft Cooling Tower


These are hyperbolic RCC structures supported on RCC columns. Most of structure is empty shell but the lower portion of shelf is open to allow the air.

A pond is constructed below the towers to catch the cooled water for circulation. As the warm water falls in the stack it gives its heat to the air there which becomes lighter than the ambient air and a draft is created due to chimney.

In BTPS, induced draft type cooling towers are used. There are three stages of Cooling Tower as:

Stage I Stage II Stage III

There are four Pumps used for Stage I, Two Pumps are used for Stage II and Stage III. All Pumps are vertical in their flow.

The Cooling Towers are brought into operation in two Situations:

During rainy season the water from the canal is very muddy therefore the water in a plant is used in a closed cycle with the help of cooling tower.

During Summer season, the supply of water is limited; therefore cooling towers are brought into act.

Water Treatment Plant

The water treatment plant in the power house is used to provide de-mineralised water to the boiler so as to avoid sealing. The source of water in water treatment plant is either the River water or Ground water. The River water is mainly used in the BTPS and main source is the Agra Canal. As the River water contains various types of impurities, therefore it becomes necessary to purify the water and the task is handled by water treatment plant. The impurities in water can be classified in the following types.

Suspended Impurities Dissolved Impurities Gaseous Impurities Organic Matter.


Removal Of Impurity

Suspended Impurities: The large sized impurities are arrested by the traveling water screens at inlet. For the removal of smaller size impurity the water is stored in reservoir and kept still as a result of which the impurities settle down. The process is taken out in ‘CLEARIFOCULATOR’ it is a big tank where water is stored and some chemicals are mixed with it. It consists of two concentric tanks. The diameter of outer tank is about 30m. Firstly, the raw water is fed to the control tank from the bottom. This is done so that the water is properly agitated from the central tank the water comes into the outer tank now in order to felicitate the settling process a solution of Alum is fed to the water through a pipeline. Actually, the Alum is a chemical, which felicitate fifth formation. All the suspended impurities stick to these forth and get collected at the bottom of the tank and this mass is known as sludge. In the external tank four stirrers are installed. These agitation provide proper mixing of water and Alum solution. The excessive settling in the tank is not allowed, as it will become difficult to remove it form the tank. Therefore the sludge is drained two times in 8hours. A drain valve is provided for removal of sludge, the drain valve may choke due to the blockage of sludge in the drain. Thus, back flushing of line drain is done by a high pressure water line. Thus, the clarified water gets collected at the top of the surface of outer tank, which gets collected in trough around the tank on being over flown in the tank. The clarified water is unsuitable for drinking purposes. A part of this water is used in the plant for cooling purpose and rest and remaining part can be used in more purified form for drinking purposes after filtration.

Filtration: Filtration of clarified water is done in the sand bed containing alternate layer of wood, charcoal and sand. The number of sand beds depends on capacity of Water Treatment Plant generally 4-5 beds are used for small plants. The size of charcoal decreases with height. After filtration water is stirred in two tanks the clarified water tank and filtered water tank.

Removal Of Organic Matter: Organic impurities in water include the bacterial and other microorganism. The various methods removal of organic matter are by passing chlorine, UV rays and Ozone. The chlorine gas is available in high pressure yellow coloured cylinder. The chlorination is done in the clearifoculator. But the gas is not fed directly to water. The chlorine dosing is done through ejector, which


consists of a conversing-diverging nozzle. In the conversing nozzle the high pressure water at low velocity is converted low pressure water at high velocity which is approximately equal to sonic velocity. A tapping is given at the junction and chlorine cylinder is attached to this tapping due to vacuum pressure at the junction. The gas is sucked into the water and in the divergent part this high velocity is again converted to high pressure.

Removal Of Dissolved Impurities: The requirement for power plant is totally demineralized water thus, the water should not contain any dissolved impurity or minerals. The minerals and elements commonly present in the water are CaCO3, CaHCO3, MgCO3, MgHCO3, CaCl2, MgCl2 and Phosphorus etc. for the removal of dissolved impurities filtered water is taken to demineralized tank.

There are five such tanks:

Activated Carbon Filter Cation Exchanger Degasifier Anion Exchanger Mixed Bed

Activated Carbon Filter: To neutralize chlorine in water, The water is passed through activated carbon filter. It consists of as capsule shaped tower, which is about 5m high and contains a bed of activated coal. The chlorine gets collected in the bed in HCl form. After sometime the carbon bed gets exhausted. For regeneration the inlet and outlet valves are closed and the back washing of the bed is done by passing water at high pressure in opposite direction and the HCl is washed awayin drain. The regeneration is necessary after 16hours.

Cation Exchanger: In the Cation Exchanger the cations present in water such as Ca2+, Mg2+, Al3+, Na+, and K+ are removed. In cation battery there is sand like resin, which is in granular form but sands is lighter than the resin material. The composition of the resin is never disclosed by Supplier Company basically it is polystyrene sulphorate. The resin is in RH for. Positive ion reacts with resin free water is removed and hydrogen is replaced. Capacity of resins 850Tonnes in the power station


Maximum quantity of water 50T/H. thus regeneration is necessary after every 16hours.

For regeneration inlet and outlet values of water is closed and 5%HCl solution is added to the cation exchanger and regeneration is allowed for 55min. on addition HCl, CaCl2 etc. are formed and are reached by back washing by feeding High Pressure from bottom.

Degasifier: In this whatever Carbon dioxide is dissolved in water removed. In the degasifier the partial pressure of carbon dioxide is decreased to zero and thus carbon dioxide gas escapes in the atmosphere. Thus, the dagasifer works on the principle of Henry’s law of partial pressure.

Anion Exchanger: The anion resins are basically are amines technically the anion resin used in the anion exchanger is named as DAN IP. After sometimes the anion battery gets exhausted and has tobe regenerated. Life of this battery is 14-15hours, having maximum capacity of 700tonnes. The regeneration is done by adding 5%set of NaOH to the resin for 30min. approx.

Mixed Bed: Before feeding into the boiler the water should be totally free from minerals. The water is finally passed through the mixed bed filled in a battery. The competition of mixed bed is not fixed. It contains both cation exchange resin and anion exchange resin.

Regeneration Process of Battery Carried out in Following Way:

Back Washing Regeneration of Anion Battery Regeneration of Cation Battery Again Rinse the battery Again final rinsing of particle like HCl and NaOH Fixed Mixing is done by passing compressed air into the bed.

Finally after all this process, De-min. water of PH 7 and Silica content .02% and conductivity .01 is obtained. The De-Min. Water thus produced by water treatment plant is stored in tanks.

Compressor House:


Two types of air is generally used in the power plant are: The plant air or station air Instrumental air.

The Plant Air may be somewhat impure and contains moisture oil particles etc. it is used for general purposes in plant there are:

Sand blasting of turbine blades Filter cleaning of main oil tank Light oil atomization in igniter gun Opening of gates in 210MW unit for mixing of hot primary air.

In the 210MW units there are certain pneumatic machines which require extremely pure compressed air free from any moisture and oil content. These include motors for air preheater and certain valve operation thus instrumental air is used in pneumatic instruments.There are three compressor houses in the power plants:

Station air compressor house the compressor installed in this house is used for producing compressed plant air. All the three compressors are of consolidated pneumatic Sales Corp. made.

At the end of 4th unit, there are 2Kg Khosla made instrumental air compressors which are used for instrumental air.

The compressors used in the compressor house are of horizontal type, double acting and two cylinder type. The high pressure and low pressure cylinders. The cylinders have two different pistons. But are connected to a common lead.

To start with the suction of the low pressure cylinder is from atmosphere through air filters. There are 6 inlets to the low pressure cylinder. In the low pressure cylinder the atmosphere air and compressed to a pressure of 1.5Kg/cm2. The temperature of air rises due to frictional heat about 150deg. Celsius.

Ash Handling Plant

Bottom Ash Cleaning System:


This is a continuous in which bottom ash is collected in who bottom ash hoppers. From the bottom ash hoppers it is continuously dropped on two water impounded scrapper conveyers one for each hoppers which in turn transfer the bottom ash to two cylinder grinders. The clinkers grinders crush the bottom ash to appropriate size and the crushed clinkers fall into sluice trench where high pressure water jets have been fitted at suitable locations convey the mixture of ash and water through the system of sluice trenchen and into the air slurry pump for outward disposal by ash slurry pumps.

Fly Ash:

It is the waste product or residue obtained after burning of coal. The following are the methods that are employed at BTPS to control the manage fly ash.

Fly ash is made to mix with water to form slurry which is then put alone with stack pipe of ash, which are covered by plantation.

Electrostatic precipitator has been installed which help a lot in reducing the pollution.

Coal is washed before burning to reduce amount of ash produced.

Ash Disposal System And Its Utilization:

The ash produced during the process of power generation is being put to productive use (utilization level of more than 30%) for purposes like filling of low lying areas, landscaping, raising of ash types and manufacturer of other ash based products like of bricks etc. The station utilized 6.3lack tones of ash than the generated with utilization 14.24MT

Supply of dry ash to M/s Ballapur industries, as a first stage towards utilization of ash dry ash evacuated system capacity 250tones /day

For manufacturing of bricks using fly ash the stati9on was pioneer in setting up an ash brick demonstration plant in 1993 with capacity 8000bricks/year. To meet the total captive brick requirement with ash bricks and to meet the expended demand of bricks for outside agencies, the station augmented ash brick many capacity.


Land filling, BTPS has taken initiative for filling of low lying areas with ash and had been successful in land filling at 10C’s LBG bottling plant near village Madanpur Khad, 70000MT of pond ash has been used during 1999-2000 for above purpose.

Ash from the station has been used for construction rail (DMRC) and DND Highway.

Turbine Maintence Department(TMD)

From Boiler Drums

L.T.S.H

Palten S.H

Final S.H

Main Steam Line

H.P.Turbine

C.R.H Line

I.P.Turbine

L.P.Turbine

To Condensate


Turbine

Turbine Cycle:

Fresh steam from the boiler is supplied to the turbine through the emergence stop valve from the stop valve steam is supplied to four control valves situated on high pressure cylinder at front bearing end. After expansion through 20 stages of H.P. cylinders , steam flows to the central part of L.P. cylinder through two cross over pipes of 900-mm dia. each from the central part of L.P. cylinder the exhaust steam enters the condenser or welded direct to exhaust part of turbine.

Turbine is provided with regenerative system of feed water heating. Heated steam is extract3ed from 7 non-regulated bleed points of the turbine from L.P. condensate of 6kg/cm 2 absolute pressure.

Steam at 1.01 to 1.03 Kg/cm2 is supplied to gland steam seals of the turbine from the deaerator trough a collector where the pressure of the steam is regulated . From the end chambers of seals the air steam mixture is sucked out with the help of special steam ejector.

From the condenser, the condensate is pumped to deaerator with the help 3*50% capacity condensate pumps through 2*100% capacity ejector and four L.P. heaters condensate while passing through the main ejector condense the air steam mixture sucked out from condenser. A portion of the main condensate is passed through gland steam cooler to condense the steam from air steam mixture sucked out from the gland seal of turbine.

Drain of L.P. heater no.’s 2 , 3and 4 are in cascade and is finally pumped to the main line of condensate with the help of drip pumps . The drain of L.P. heater no. 1 is connected directly to the condenser.


Turbine Auxillaries:

Vacuum System

Condensor: 2 per 200MW unit at exhaust of L.P. turbine. Ejector: One starting and two main ejectors connected to a

condenser located near turbine. CW Pump: 2 per unit.

Condensate System

Condensate Pumps: 3 per unit each located near the condenser hot well.

Low Pressure Heaters: Normally 4 in no. with no. 1 located at the upper part of the condenser and no. 2, 3and 4 around 4m level.

Deaerator: One per unit located around 18m level.

Feed Water System

Boiler Feed Pump: 3 per unit each located in 0m level in TG bay. High Pressure Heater: normally 3 in no. Drip Pump: 2 in no. , each situated beneath L.P. heater.

Turbine Lub. Oil System

It consists of main oil pump (mop), starting oil pump (sol), AC stanby pumps and emergency DC pump (1 each unit).

Range: Up to 2000 KW


Application: Pump Drive, Blower DriveSugar Cane Mill & Fibrizor Drives FD & ID Fan Drives Compressors, Exhausters Power Generation

Design Of Steam Turbine:

Emergency Stop Valve:

Steam from boiler is supplied to the turbine through an emergency stop valve. This valve is operated by a hydraulic servomotor that shuts off steam supply to the turbine when turbo-set is tripped. The sheet is made up of molybdenum-chromium-vanadium steel casting on cradle. This valve is connected to the four control valves.

High Pressure Cylinder:

High pressure cylinder of the turbine consists of two parts. The front part is made of high creep resisting chromium-molybdenum-vanadium steel casting. The rear part is made of special carbon steel casting. The two parts are connected with a vertical joint. Each part consists of two halves having a horizontal joint. The horizontal joint is secured with the help of studs and nuts. Four steam chests, two on top and two on the sides are welded to the nozzle boxes, which are welded to the cylinder at the front bearing end. The steam chests accommodate four control valves to regulate the flow of steam to the turbine according to the load.

The high pressure cylinder comprises of 20 stages, the first being the governing stage. The nozzle apparatus of the first stage is welded. In high pressure zone the material for the body and blades are of chromium-molybdenum-vanadium steel and in lower temp. Zones the blades are of stainless steel whereas body is of alloy steel and mild steel.

Low Pressure Cylinder:

The L.P. cylinder is of double flow type with two exhaust opening. Each flow comprises of five stages .it consists of three parts i.e. one middle


part and two exhaust parts. The middle part is grey iron casting and the two exhaust parts are fabricated from wieldable mild steel. Steam from H.P. cylinder flows through two cross-over pipes fabricated out of weld able steel. Suitable compensators have been provided to allow expansion. Necessary mercury thermometers are provided to measure temp. of steam at L.P. exhaust.

Condensor:

There are two surface type condensers which are both air and water tight, with an equalizing pipe between them . The condenser steam inlet, the expansion being taken up by the spring on which condensers are seated. Each condenser has separate inlet and outlet of cooling water to facilitate cleaning of the cooling tubes with 50-60% load on turbojet. it is also provided with an inlet for dematerialized make up water . In the upper part of each condenser, two sections of L.P. heater no.1 are installed. These two sections connected in parallel and steam is supplied from the same bleed point.

Specifications:

Cooling surface : 4000m2(each) Pressure : 0.098kg/cm2

Consumption of cooling water : 800m3/hr.No. of water flows for each condenser : 2No. of tubes : 7700Tube material : Brass

Starting Ejector:

It is provided for creation of vacuum in condenser. The ejector is supplied with steam from the deaerator at the rate of 1100kg/hr.

Main Ejector:

These ejectors are capable of removing 60kgs of dry air per hr. The ejector is provided with necessary pressure and vacuum gauges for measurement of steam pressure and thermometers for measurement of temp. at the inlet and outlet of the condensate and of air-steam mixture.


Condensate Pumping Sets:

Three condensate pumps 50% efficient are installed at ground level for pumping the condensate from the condenser to the deaerator through L.P. heaters. Two pumps are normally in operation and third on serves as standby.

Regenerative Equipment:

L.P. Heater No.1:

Heater no.1 is installed inside the condenser. It is horizontal type consisting of two sections, one is connected in parallel and steam is supplied from the same bleed. The heaters have u-shaped brass tubes rolled with brass tube plates.

Specifications:Heating surface : 200m2

Bleed steam pressure : 0.408kg/cm2

Tube design pressure : 15kg/cm2

No. of tubes : 524No. of paths : 4

L.P. Heater No. 2, 3 & 4:

The three heaters are of surface type. They are designed for vertical mountings and are supported at 5m level. They are of welded construction with u-shaped brass tubes rolled with plates. Water flows inside the tube system from outside. The tubes are designed for the full pressure developed by main condensate pump. Two level transmitters will be connected to each heater, one for remote level indication in local panel and other for automatic level control.

Specifications:Heating surface : 180m2

Tube design pressure : 5kg/cm2

Tube design temp. : 1550CShell design pressure : 5kg/cm2

Shell design temp. : 7600C


High Pressure Heaters No. 5, 6 & 7:

These heaters are also surface type , and are designed for vertical mounting and are supported at zero level. Each heater comprises of a spiral tube and the spiral coils. Feed water flows inside the coils of the spiral tube system and heating system washes the tube from outside.

Specifications:NO.5 NO.6 NO.7

Heating surfaces are : 275 275 275Max. bleed steam pressure (kg/cm2): 11 21 23 Max. bleed steam temp. (0C) : 300 350 410Tube design temp. : 225 225 250Tube design pressure : 180 180 180No. of spiral tubes : 272 272 272

Drain Coolers:

Drain cooler is of horizontal welded construction designed for cooling the drain of L.P. heater no. 3. part of main condensate passes through and takes off the heat from the drain of L.P. heater no. 3 . the tubes are of brass rolled in steam tube plates .

Thermometers for measuring temp. of condensate at inlet and outlet of drain are provided.

Gland Steam Coolers:

It cools the air steam mixture sucked from the turbine gland seals. It is of horizontal type and is in two sections. An ejector mounted on the cooler maintains a constant vacuum in the first section. It also sucks the remaining air-steam mixture from first section to second , where the air is let off and steam is condensed. A part of main condensate after the main ejector flows through the cooler tube system drains from cooler is led to condenser through an expander and siphon.

Drip Pumping Sets:

The two pumps are installed at ground level for pumping the bleed. Condensate from L.P. heater no.2 into main condensate line.


Feed Water Pump:

Each 100MW boiler unit is provided with three electrically feed pumping sets of capacity 245tons/hr. it is a multistage barrel type of pump. The inner body is vertically spurt and tightened together by bolts and encased in a heavy outer barrel. Both the suction and discharge are on the top of the pump. On the discharge side the barrel is closed by a high pressure cover. The sealing of pressure on two sides is done by providing special mechanical seals.


COAL HANDLING PLANT(CHP)

From Jharia Mines

Railway Wagon

BTPS Wagon Tippler

Magnetic Separator

Crusher House

Coal Stack Yard

R C Bunker

R C Feeder

Bowl Mill

To Furnace


Coal And Transportation

As coal is the prime fuel for a thermal power plant adequate emphasis need to be given for its proper handling and storage also, it is equally important to have a outstand glow of this fuel to maintain uninterrupted power generation.

Coal Transportation System (Mgr.)

Each of NTPC project requires transportation of large quantity of coals from the coal mines to power station site of the order of 30000 tons per day for a typical 2000 MW station. This enormous coal requirement is being met ITOrll opm cost mines. Techno economic study conducted for coal transportation from mines to power station have revealed that captain merry go round (MGR) rail transportation system is most economic and is also reliable. This system calls for high speed load outstation at the mines which have the following advantages:

High loading enables loading of trains quickly this achieving high turnover of wagons and reduction in rolling stock requirement.

Top opm railway wagons are loaded with maximum possible load consistently and accurately.

Simple loading arrangement at a simple point avoids the need for by marshaling yard with cumbersome operational system.

The high speed load outstation consists of one or more loading silos depending upon the coal requirement of the linked power station. The loading capacity of the loading silo is such that is adequate to fill at least one complete rake of wagon and in some cases two rakes.

Coal Handling System

In the coal handling system of NTPC station, three coal path are normally available for direct of coal.

Path A………………………………from track hopper to boiler bunkerPath B………………………………from track hopper to stock yardPath C………………………………from stock Yard to boiler bunker


The storage facilities at the stockyard have been provided only for crushed coal. The coal handling system is design to provide 100% stand by for all equipments and conveyers.

The 200 mm coal as received at the track hopper is feed to the crusher house for crusher of 50% capacity is provided and these are preferred to two crushers of 100% capacity because of increased reliability and possible higher availability.

A series of parallel conveyers thereafter are designed either to carry crushed coal directly to the boiler bunkers or to divert it to the stockyard. To feed coal into bunkers, mobile trippers have been provided over bunkers on conveyers.

The coal mills and thereafter, also the bunker conveyer of 200 MW units of the earlier projects are provided between boiler and turbo-generator building. However, for better mill maintenance, accessibility and to reduce coal dust nuisance the turbine plant area, coal mills, and bunker conveyers are now being place between boiler and electrostatic precipitator.

Coal Handling System Equipments

The various equipments involved in coal handling system have been described in this section:

Idlers: These essentially consist of rolls made out of seamless steel tube enclosed fully at each end and fitted with stationary shaft, antifriction bearing and seals. The idlers support the belt and enable it to travel freely without much frictional losses and also keep the belt properly trained.

Pulleys: These are made of mild steel. Rubber lagging is provided to increase the friction factor in between the belt and the pulley.

Conveyer belt: The conveyer belt consists of layers or plies of fabric duck, impregnated with rubber and protected by a rubber cover on both sides and edges. The fabric duck supplies the strength to withstand the tension created in carrying the load while the cover protects the fabric carcass. Heat resistant belting is always recommended for handling material at a temperature over 66”C

Drive unit: This comprises of motor coupled to reduction gear box with the help of flexible coupling on the high speed shaft of the gear


box with the provision of fluid coupling on the input side, the motor starts under no load conditions and the conveyer moves only when the motor reaches its full speed. This also eliminates the starting shock on the conveyer components.

Scrapper: Conveyer are provided with scrappers at a distance pulley in order to clean the carrying side of the belt built up material on idlers rolls. It is important that care should be taken to ensure that the scrapper is held against the belt due to remove material without causing damage to the belt due to excessive force exerted by the wiper.

The following categories of scrapper are in common use:-- Steel blade Rubber or fabric blades Nylon brush Compressed air blast.

Crusher: The roles of crusher are to crush the coal from 240mm to 20mm size of coal received from the vibrating screen. This is accomplished by means of granulators. These granulators are of ring type and there are about 37 crushing elevations. In each of these elevations, there are 4 granulators; 2 plain types and 2 tooth type. These have been arranged in such a way that 2 of the some types are not side by side. Normally, these crushers have capacity of around 600 tons.

Vibrating screen: The function of vibrating screen is to send the coal size less than 250mm to the crusher. The screen is operated by 4 V-belt connected to motor.

Magnetic separator: This is an electromagnet placed above the conveyer to attract magnetic materials. Over this magnet there is one conveyer to transfer these materials to chute provided for dumping at ground level.

Vibrating feeder: This is used to held coal on the underground conveyer belt from where coal goes to bunker. Coal from the stock yard with the help of bull dozer is taken to the vibrating feeder via. Reclaim hopper.


Tippler: A tippler is provided in the conveyer to stack the material at desired location on either side or along the conveyer with the help of chute fitted with the tripper itself. The tripper is provided with wheels which move on rails, parallel to conveyer. These trippers are of 3 types: Motorized Belt propelled/ manually operated Winch driven.

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