4) Steel Plant Projects

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    Chapter - 1

    PROFILE OF VISAKHAPATNAM STEEL PLANT

    1.1 INTRODUCTION

    The economy of a nation depends on core sector industries like iron and steel. Steel is the basic

    input for construction, machines building and transport industries. Keeping in view the

    importance of steel the Visakhapatnam Steel Plant with foreign collaborations was constructed in

    the public sector in the post independence era. The decision of the Government to set up an

    integrated steel plant was laid down by the then Prime Minister Smt. Indira Gandhi. The Prime

    Minister laid the foundation stone on 20th

    January, 1971.

    The consultant, M/s M N Dastur & Co (Pvt) Ltd. submitted a techno-economic

    feasibility report in February 1972, and detailed project report for the plant, with an annual

    capacity of 3.0 million ton of liquid steel. The Government of India and USSR signed an

    agreement on 12th

    June 1979 for the co-operation in setting up 3.0 million ton integrated Steel

    Plant. The project was estimated to cost to Rs. 3, 897.28 crores based on prices as on 4th

    Quarter

    of 1981. However, on completion of the construction and commissioning of the whole Plant in

    1992, the cost escalated to Rs. 8, 755 crores based on prices as on 2nd

    Quarter of 1994.

    Visakhapatnam Steel Plant is one of the most modern steel plants in the country. The

    plant was dedicated to the nation on 1st

    August 1992 by the then Prime Minister, Sri

    P.V.Narasimha Rao. New technology, large-scale computerization and automation etc, are

    incorporated in the Plant at the international levels and attain such labour productivity, the

    organizational manpower has been rationalized. The manpower in the VSP has been limited to

    16,416 employees. The plant has the capacity of producing 3.0 million tons of liquid steel and

    2.656 million tons of saleable steel. It has set up two major Blast Furnaces, the Godavari and the

    Krishna, which are the envy of any modern steel making complex.

    1.2 CORPORATE PLAN

    1.2.1 Vision

    To be a continuously growing world-class company.

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    We shall:

    Harness our growth potential and sustain profitable growth. Deliver high quality and cost competitive products and be the first choice of

    customers.

    Create an inspiring work environment to unleash the creative energy of people. Achieve excellence in enterprise management. Be a respected corporate citizen, ensure clean and green environment and

    develop vibrant communities around us.

    1.2.2 Mission

    To attain 16 million tons liquid steel capacity through technological up gradation,

    operational efficiency and expansion, to produce steel at international standards of cost and

    quality, and to meet the aspirations of the stakeholders.

    1.2.3 Objectives

    Objectives are measurable performance outcomes of the company and emanate from the

    Vision. The focus areas emerging from the analysis of SWOT Matrix are the basis for

    formulating the company objectives. They are

    Expand plant capacity to 6.3 MT by 2008-09, with the mission to expand furtherin subsequent phases as per the Corporate Plan.

    Sustain gross margin to turnover ratio > 25%. Be amongst top five lowest cost steel producers in the world by 2009-10. Achieve higher levels of customer satisfaction than competitors. Instill right attitude amongst employees and facilitates them to excel in their

    professional, personal and social life

    1.2.4 Core Values

    Commitment Customer Satisfaction

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    Continuous Improvement Concern of Environment Creativity and Innovation

    VSP takes all necessary actions for the fulfilment of regulatory requirements. It has

    dedicated departments for this purpose. Energy conservation, environmental preservation, safety

    in work place, and occupational health gets highest priority in the company. Some of the

    policies in this regard are reproduced below.

    1.3 COMPANYS CORPORATE SOCIAL RESPONSIBILITY

    RINLs concern for the society is reflected in its vision, mission, objectives and core

    values. The statement, We shall be a respected corporate citizen, ensure clean and green

    environment and develop vibrant communities around us forms a part of the vision of the

    company. Concern for environment is one the five core values. One of the companys

    objectives is to ensure zero effluents discharge by 2005-06 and contribute to improving quality

    of life (health, literacy and water) in at least one village every year. A comprehensive policy on

    Corporate Social Responsibility (CSR) has been formulated and processed for approval of the

    Board.

    Major Sources of Raw Materials

    Iron Ore lumps & fines Bailadilla, Chhattisgarh

    BF Lime Stone Jaggayyapeta, A.P

    SMS Lime Stone Jaisalmer, Rajasthan

    BF Dolomite Dubai

    SMS Dolomite Madharam, A.P

    Manganese Ore Chipuripalli, A.P

    Boiler Coal Talcher, Orissa

    Coking Coal Australia

    Water supply Yeluru canal, Andhra Pradesh

    Power supply Captive power plant

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    Main Productions of Visakhapatnam Steel Plant

    S No Steel Products By Products1. Angles Nut coke2. Billets Coke dust3. Channels Coal tar4. Beans Anthracene oil5. Squares H P Naphalene6. Flats Benzene7. Rounds Toluene8. Rebars Zylene9. Wire rods Wash oil10. Granulated slag11. Lime fines12. Ammonium Sulphate

    1.4 TECHNOLOGICAL HIGHLIGHTS

    First shore based integrated steel plant. Selective crushing with pneumatic separation of coal blend. 7 Metre tall Coke Ovens. Dry Quenching of hot coke and production of steam and power from hot

    inert gases.

    3200 M3 Blast Furnace having bell-less top equipment with conveyorcharging.

    Granulation of 100% molten slag at the Cast House. B.F. top pressure recovery turbine for power generation. Desulphurisation facilities for pre-treatment of hot metal. Sub lance measurement of dynamic blowing control with computer. 100% continuous casting of liquid steel.

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    High capacity, high speed, computer controlled multi-line mills. Use of on-line heat treatment Temp core processes for reinforcement

    bars.

    Use of No twist rolling and controlled cooling Stelmore of wire rods.

    First integrated steel plant to receive ISO 9002 certification for all itsproducts.

    1.5 POLLUTION CONTROL & ENVIRONMENTAL PROTECTION

    Elaborate measures have been adopted to combat air and water pollution in

    Visakhapatnam Steel Plant. In order to be Eco friendly Visakhapatnam Steel Plant has

    planted more than 3 million trees in area of 35 square kilo meters and incorporated

    various technologies at a cost of Rs 460 crores and control measures.

    Production Performance (000 Tonnes)

    Year Hot metal Liquid steel Saleable steelLabor productivity

    (Tonnes /year)

    2000-01 3,165 2,909 2,507 211

    2001-02 3,485 3,083 2,757 226

    2002-03 3,941 3,356 3,056 260

    2003-04 4,055 3,508 3,169 262

    2004-05 3,920 3,560 3,173 265

    2005-06 4,153 3,603 3,237 282

    2006-07 4,046 3,606 3,290 285

    2007-08 3,913 3,322 3,074 287

    2008-09 3,546 3,145 2,01 297

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    Commercial Performance (Rs. Crores)

    Year Sales turnover Domestic sales Exports

    2001-02 4,081 3,710 371

    2002-03 5,059 4,433 626

    2003-04 6,174 5,406 768

    2004-05 8,181 7,933 248

    2005-06 8,469 8,026 443

    2006-07 9,126 8,702 424

    2007-08 10,433 9,283 950

    2008-09 10,411 10,333 781

    Financial Performance (Rs. Crores)

    Year Gross Margin Cash profit Net profit

    1998-99 15 (-) 346 (-) 457

    1999-00 252 (-) 130 (-) 562

    2000-01 504 153 (-) 291

    2001-02 690 400 (-75)

    2002-03 1,049 915 521

    2003-04 2,073 2,024 1,547

    2004-05 3,271 3,260 2,008

    2005-06 2,383 2,355 1,252

    2006-07 2,633 2,584 1,363

    2007-08 3,498 2.414 1.942

    200-09 2,300 2,264 1,958

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    1.6 WELFARE AMENITIES

    Modern township with all amenities has been developed with 8032 quarters to house the

    plant employees and other agencies in 11 sectors. The township is having best facilities in terms

    of drinking water supply, drainage, roads, modern hospital, community centre, parks, schools,

    shopping complexes, recreational facilities etc. to cater to the needs of the employees.

    1.7 ACHIEVEMENTS AND AWARDS

    The efforts of VSP have been recognized at various forums. Some of the major awards

    received by VSP are in the area of energy conservation, environment protection, safety, quality,

    Circles, Rajbhasha, MOU, sports and a number of awards at the individual level. Some of the

    important awards received by VSP are:

    ISO-9001-2000, ISO-14001 and OHSAS-18001 for all the Operational units ofthe plant.

    SCOPE Award for- Best Turnaround : 2001. Best Enterprise Award from SCOPE, WIPS : 2001-02. Environment Excellence Award from Greentech Foundation for Energy

    conservation : 2002.

    ISTD Award for "Best HR Practices" :2002. Ispat Suraksha Puraskar (1

    st

    Prize) for longest Accident Free Period 1991-94.

    Indira Priyadarshini Vriksha Mitra Award : 1992-93. Nehru Memorial National Award for Pollution Control :1992-93 & 1993-94. EEPC Export Excellence Award : 1994-95.

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    CII (Southern Region) Energy Conservation Award : 1995-96. Golden Peacock (1st Prize) "National Quality Award-96" IIM in the National

    Quality Competition : 1996.

    Steel Ministers' Trophy for "Best Safety Performance" :1996. Selected for 'World Quality Commitment Award-1997 of J*Ban, Spain. Gold Star Award for Excellent Performance in Productivity. Udyog Excellence Gold Medal Award for Excellence in Steel Industry. Excellence Award for outstanding performance in Productivity Management,

    Quality & Innovation.

    Best Labour Management Award from the Govt. of AP. Prime Ministers Trophy for "Best Integrated Steel Plant-2002-03. Best Enterprise Award from SCOPE for surpassing MOU targets-2003-04. "Organizational Excellence Award" for 2003-04 by INSSAN. "World Quality Commitment International Star Award" in the Gold category

    conferred by Business Initiative Directions, Paris.

    National Energy Conservation Award, 2004 and Special Prize from Ministry ofPower, Govt. of India.

    Mini Ratna status in PSE by Government of India on 26-05-2006. Won prestigious Prime Ministers Trophy for "Best Integrated Steel Plant 2005-06

    second time.

    The above awards are besides a number of awards at the local, regional & national level

    competitions in the area of Quality Circles, Suggestion Schemes etc. VSP has been bestowed

    with several national accolades significant among them being:

    National Energy Conservation Award for the 6th time in succession. National

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    Award for Excellence in Water Management.

    ICWAI Award for excellence in Cost Management. Viswakharma Rashtriya Puraskar Awards (6 out of 32 at the national level). FAPCCI Best Industrial Productivity Award. INSAAN National Award for Organisational Excellence Best CEO Award

    1.8 EXPANSION PLAN

    Presently the Plant is operating at higher efficiency levels surpassing the rated capacities thus

    achieving 4.04 Mt of Hot Metal, 3.6 MT of Liquid Steel and 3.2 MT of Saleable Steel i.e. 122%,

    120% & 122% of the respective rated capacities. The Organization has become net positive in

    2005-06, having wiped out all accumulated losses and registered Rs. 1363 Crores net profit after

    taxes in 2006-07. In line with the vision in National Steel Policy envisaging 110 MT steel by

    2019-20, Vizag Steel is also planning to expand its capacity. Considering the buoyancy in

    domestic steel market for long products, which is the product mix of VSP and the high

    acceptance of VSPs brand image in the market, an expansion plan has been proposed. The

    expansion plan of doubling the capacity of the plant has been cleared in a record time of 10months and the entire Vizag Steel collective is totally geared up for completing the expansion in

    the stipulated 36 months. The consultant is in place and the funds are in hand. The expansion

    should give a strong footing for VSPs growth. The expansion programme is progressing well as

    per plans and the present focus is on creating an enabling infrastructure such as roads, water,

    power etc., for smooth execution. Also thrust is on finalization of the specifications and

    placement of orders. To leverage from our brand leadership in the long segment category,

    expansion has been cast to enhance volumes in the long product category.

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    CHAPTER2

    THERMAL POWER PLANT

    2.1The three main constituents of a thermal power plant

    2.1.1 Boiler: Pulverized coal along with combustion air is fired in the Boiler where

    chemical energy of fuel is converted into heat energy to generate steam from DM

    (De-Mineralized) water.

    2.1.2

    Turbine: Steam at high pressure and temperature is then fed to the Turbinewhere heat energy of steam is converted into mechanical energy by rotating

    the turbine. The outlet steam from the turbine is condensed in the condenser.

    The condensed DM water is re-used in the boiler. Condenser is an indirect

    type heat exchanger where steam is condensed by sea water passing through

    the condenser tubes.

    2.1.2 Generator: Turbine and generator are coupled together. As the turbinerotates, the generator too rotates. The generator generates power as electric

    excitation is applied.

    Generated power at 21kv is stepped up to 400Kv and then fed to grid via the switch yard.

    Thermal power plant uses a dual cycle i.e. vapor and liquid cycle. It is a closed cycle where the

    working fluid can be used again and again. Here the cycle used is RANKINE CYCLE which

    includes feed water heating, super heating of steam.

    It becomes economical by increasing the cycle efficiency. By super heating the steam before it is

    expanded, the Rankine cycle efficiency can be increased. The use of super heated steam also

    ensures longer life of turbine blade because of the absence of erosion from high velocity water

    particles that are suspended in water vapor.

    Other factors which effect thermal efficiency are:

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    - Initial steam pressure- Initial steam temperature- Condenser vacuum- Feed water temperatures

    Modern thermal power station involves three major systems namely generation of steam in

    boiler, conversion of heat energy to mechanical energy in turbine, power generation in generator

    and transmission of generated electric power.

    2.2 GENERATION OF STEAM

    Generation of steam involves the following systems

    - Draft system

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    - Fuel system- Water system- Ash system

    2.2.1 DRAFT SYSTEM

    This system consists of primary air and secondary air. There are three types of fans in balanced

    draft system viz. primary air fan (PA), forced draught air fan (FD) and induced draught fan (ID).

    PA fan takes atmospheric air, a part of which is sent to air-preheaters for heating while a part

    goes directly to the mill which is regulated for mill outlet temperature control. Atmospheric air

    from FD fan is heated in the air-preheaters and sent to the furnace as secondary air for

    combustion. ID fans suck out the combustion products in the system and release the same to the

    atmosphere through air preheaters and electro static precipitators (ESP).

    2.2.2 FUEL SYSTEMCoal from the mines is transported and is unloaded in the coal handling plant. This coal is

    transported to the coal bunkers with the help of conveyers after crushing them to optimum sizes.

    Then it is carried to mills by coal feeders. This coal is pulverized in the mill, where it is ground

    to powder form. This crushed coal is taken away to the furnace through coal pipes with the help

    of hot and cold air mixture from primary air fan. Light diesel oil (LDO) is used initially and then

    heavy fuel oil (HFO) is taken over. After boiler becomes sufficiently hot and desired ignition

    temperature is reached coal is fired in the boiler. Once sufficient coal mills are taken into service

    LDO and HFO firing will be stopped.

    2.2.3 WATER SYSTEMDM water from boiler feed pump passes through economizer and reaches the boiler water walls

    and due to the density difference between steam and water the water flows through water wall

    tubes to the drum. In case of bigger size boilers additional circulating water pumps are used to

    create sufficient flow of water. Water is partly converted into steam as it rises up in the furnace.

    This steam and water mixture passes to the boiler drum where steam is separated from water and

    sent to the super heaters where steam gets super heated before entering the turbine. Steam after

    performing work loses its heat and pressure energy and enters condenser where it is condensed to

    water. This condensate is recycled for steam generation. Water deficit due to vapor losses or

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    leakages is made up with make up water. The steam leaving the turbine is passed through

    condenser in which steam is converted to condensate water. Cooling of steam is effected by

    supply of sea water through condenser tubes. Sea water after picking up heat from steam is

    further cooled in cooling towers and returned in closed cycle.

    2.2.4 ASH SYSTEM

    Flue gases from the furnace is extracted by ID fan and passes through economizer, air preheaters

    and goes through electrostatic precipitator where ash particles are separated from the flue gas and

    the flue gases are thrown out of the chimney. The ash collected in ESP hoppers is mixed with

    water to form slurry and is dumped in an open area (ash pond) in case of wet system. In dry

    system fine ash collected is disposed through vacuum system into separate bunkers.

    2.3 CONVERSION OF HEAT ENERGY TO MECHANICAL ENERGY

    Super heated steam from boiler passes through the turbine through control valves in three

    different stages i.e. high pressure cylinder and low pressure cylinder.

    The steam leaving the HP cylinder goes to LP cylinder. At this stage the steam loses its

    temperature and pressure. The decrease in the pressure and temperature occurs as the steam

    transmits energy to shaft and performs work thus rotating the turbine shaft

    2.4 GENERATION AND LOADING DESPATCH OF ELECTRIC POWER

    When the turbine rotates generator also rotates. So when the rotor is rotated, the lines of

    magnetic flux cut through the stator windings. This induces an electromagnetic force in stator

    windings and electricity is generated.

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    CHAPTER - 3

    BOILER & ITS AUXILIARIES

    3.1 INTRODUCTION

    The boiler is a radiant reheat, controlled circulation, single drum type unit. Boiler is fitted with

    tilting tangential pulverized coal and oil burners, high energy arc ignitors, light diesel and heavy

    fuel oil burners. Boiler includes many sub systems for conversion of chemical energy of fuels

    into heat energy in the form of steam. The steam generated is sent to the turbine for converting

    heat energy of steam into mechanical energy thereby rotating the turbo-generator.

    3.2SAILENT FEATURES OF BOILER

    PRESSURE PARTS

    Feed water from feed control station to the boiler passes through the economizer and then to the

    drum from where it flows through boiler circulating water pumps (BCW) into furnace water wall

    circuits returning to the drum as steam/water mixture. The steam and water gets separated in the

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    drum. The water follows the above path whereas steam separated passes through steam cooled

    water wall and super heater circuits. Super heater temperature control is provided by spray

    attemperation. The exhaust steam from the HPT goes to LPT.

    PULVERISED COAL SYSTEM

    The system for direct firing of pulverized coal utilizes bowl mills to pulverize the coal and a

    tilting tangential system to admit the pulverized coal together with air required for combustion to

    the furnace. The pulverized coal and air discharged is directed to the centre of the furnace to

    form a firing circle which is initially ignited by a suitable ignition source at the nozzle exit.

    Above a predictable loading condition the ignition becomes self sustaining.

    AIR / DRAFT SYSTEM

    PRIMARY AIR SYSTEM

    The primary air draught plant supplies hot air and cold air to the coal mills to dry and convey

    pulverized coal to the burners. The primary system consists of two primary air (P.A) fans, two

    steam coil air-preheaters (S.C.A.P.H) two regenerative type primary air pre heaters. Each fan,

    which is of sufficient rating to support the load, discharges through a SCAPH into a common bus

    duct that has four outlets, two directing air into primary air-preheater for heating and then to the

    mills, two direct cold air straight to the pulverizing mills. The SCAPHs are located in the PA fandischarge ducts to ensure that the primary air combined with coal temperature does not fall

    below the specified minimum to protect against cold end erosion.

    SECONDARY AIR SYSTEM

    The secondary air draught plant supplies the balance of air required for pulverized coal

    combustion, air for fuel oil combustion, and over fire air to minimize the production of nitrous

    oxide. The secondary air system consists of two forced draft (FD) fans, two steam coil air pre

    heaters and two regenerative type secondary air preheaters. Control of unit air flow is obtained

    by positioning the FD fans while the distribution of secondary air from wind box compartment to

    the furnace is controlled by secondary air dampers. The SCAPHs are located in the FD fan

    discharge ducts to ensure that the secondary air does not fall below the specified minimum to

    protect against cold end erosion.

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    FUEL GAS SYSTEM

    The fuel gas draught plant draws hot flue gases from the furnace to the chimney by means of ID

    fan. Flue gas is passed through an economiser and regenerative air preheaters to improve the

    boiler efficiency, and through electrostatic precipitators to keep dust emission from the chimney

    within prescribed limits.

    SOOT BLOWING SYSTEM

    On-line gas side cleaning of boiler tubes and regenerative air-heaters is done using wall blowers

    and long retractable soot blowers.

    3.3PRESSURE PARTS3.3.1ECONOMISER

    The heat from the flue gases is absorbed by the economizer which otherwise would leave the

    boiler as waste heat. This heat is added to the feed water before water enters the boiler. In

    modern boilers used for power generation, LP & HP feed water heaters are used to increase the

    efficiency of the turbine unit and feed water temp and hence relative size of the economiser is

    less. The economiser is continuous loop type and water flows in upward direction and gas in

    downward direction.

    3.3.2 DRUM AND DRUM INTERNALS

    The function of boiler drum is to separate water and steam from the saturated steam & water

    mixture. The walls of the furnace absorb radiant heat from the furnace after the combustion and

    this mixture is then discharged into the drum. The drum is located on the upper surface of the

    boiler. The steam and water gets separated by means of turbo separators and primary and

    secondary screens.

    The boiler drum forms a part of the circulation of the boiler. Boiler water circulates from the

    steam drum into unheated down comer pipes, then from the pipes into heated furnace wall tubes

    back into the drum.

    The drum serves two functions, the first one being that of separating steam from the mixture of

    water and steam discharged into it. Secondly the drum houses all the equipments used for the

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    purification of steam after being separated from water. This purification equipment is commonly

    referred to as the drum internals.

    The drum internals may consist of baffle arrangements, devices which change the direction of

    flow of steam and water mixture, separators employing spinning action for removing water from

    steam and screen dryers. These devices are used in conjunction with other to remove impurities

    from steam leaving the boiler drum.

    3.3.3 FURNACE

    A boiler furnace is housed in the space within the boiler in which fuel is burnt and from which

    the combustion products are removed through a series of exhaust components before and finally

    getting discharged into the atmosphere. There is a separate chamber engulfed with water tube

    walls on all four sides in which the combustion process takes place isolated and confined so as to

    sustain controlled combustion. The firing system can be classified into direct firing system and

    indirect firing or intermediate bunker system.

    Direct firing systemHot air whose temperature can be controlled with the help of cold primary air is permitted to

    flow through the mill which is fed with required coal. The air dries the coal and the fine coal is

    carried by the air through the coal burner to the combustion chamber.

    Indirect firing systemThe combustion products pass through a series of super heater, re-heater tubes, economiser

    before escaping out from the boiler in the second pass.

    3.3.4 WATER CIRCULATION SYSTEM IN BOILER Natural circulation systemThe circulation in this type of system takes place by means of thermo-syphon principle due to

    different temperatures existing. The down comers contain relatively cold water, whereas the riser

    tube contain steam and water mixture whose density is comparatively less.

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    Controlled circulation systemThe circulation is to be assisted with mechanical pumps called controlled circulation (BCW)

    pumps beyond the pressure of 110kg/cm2. With the increase in the pressure the density

    difference between steam and water decreases. This is to overcome the frictional losses. Orifice

    plates are used to regulate the flow through various tubes. This system is applicable in high sub

    critical regions.

    3.3.5 WATER WALLSWater walls serve as the only means of heating and evaporating the feed water supplied to the

    boiler from the economiser. Water walls consist of vertical tubes and are connected at the top

    and bottom to headers. These tubes receive water from boiler drum with the help of down

    comers. Boiler water walls absorb approximately 50% of heat released by combustion of fuel in

    the furnace

    3.3.6 BURNER PANELBurners help for the combustion process to take place. The pulverized coal is mixed with

    primary air flow which carries the coal air mixture to each of four corners of the furnace burner

    nozzles and into furnace. There are a total of 36 pulverized coal burners for corner fired boilers,

    nine burners per corner in the four corners and 20 oil burners provided each in between two

    pulverized fuel burners. All the nozzles of the burners are interlinked and are moved by burner

    tilt mechanism in unison. Burner tilt mechanism helps in positioning fire balls for temperature

    control. The boiler is fed up with light diesel oil and heavy fuel oil during initial start up of

    boiler. The high energy arc ignitors are used to ignite the oil. The ignition temperature varies for

    different fuels depending upon its properties. Raising the temperature of the fuel to its ignition

    temperature brings about combustion. Ignitors are used to ignite the fuel.

    3.3.7 SUPER HEATERThere are three stages of super heater besides the sidewalls & extended sidewalls. The first stage

    consists of low temperature super heater of connection flow type with upper and lower banks

    located above economiser assembly in rear pass. The second stage super heater consists of platen

    super heater. The third stage super heater consists of final super heater coil which is of radiant,

    convection and parallel flow type.

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    3.4 PULVERISED COAL SYSTEM3.4.1 COAL BUNKERS

    These are used for the storage of crushed coal coming from the coal handling system. Coal from

    mines comes in different sizes. These are crushed to a size less than 25mm size in crusher houses

    and sent to coal bunkers. These bunkers are located on the top of the mills so as to aid in gravity

    feeding of coal.

    3.4.2 FEEDERSThe purpose of the feeders is to transport coal from RC bunkers to the mills at the desired rate.

    The raw crushed coal is delivered from bunker to the individual feeder which in turn feed the

    coal at a controlled rate to the pulveriser. Feeder at TPP is gravimetric type and conveys coal

    through belt. Speed of feeder can be regulated and rate of coal fed to the mill is varied to meet

    the demand from the boiler.

    3.4.3 MILLSMills pulverize coal to desired fineness and fed to the furnace for combustion. Coal trapped in

    between bowl and rollers gets crushed and required crushing pressure is provided by springs in

    journal assembly. Pulverized fuel firing is a method where the coal is reduced to a required

    fineness such that 70 to 80% passes through a 200 mesh sieve. Crushed coal is carried byprimary air through classifiers and fine coal is sent through pipes directly to burners and then to

    the boiler for combustion. When discharged into the combustion chamber, the mixture of air and

    coal ignites and burns in suspension. The different types of mills are.

    Medium speed mills such asbowl mills, ball mills are normally of vertical spindle type andoperate between 30 to 100 rpm

    The mills at TPP are of Bowl mill type. This is one of the most advanced design of coal

    pulverizer presently manufactured. The advantages of this mill are

    - Lower power consumption- Reliability- Minimum maintenance

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    - Can be operated at various coal flows

    Coal is fed from the feeders to the grinding zone of the mill where it is ground. Primary air enters

    at the bottom dries and transports coal from mill to boiler. Coarser coal gets separated in the

    classifier assembly and it falls back into the grinding zone. Fine coal along with air mixture

    flows to boiler for combustion. Foreign material falls into the scrapper chamber at bottom of mill

    which is removed and sent to reject bunker.

    3.5 AIR AND DRAFT SYSTEM3.5.1 FAN

    Fans are used to produce the air we need for the combustion in the furnace. They are also used

    to evacuate the flue gases produced after combustion.

    PA FanAir flow from PA fans is regulated by blade pitch mechanism depending upon the demand from

    the boiler. These are axial reaction two stage fans which supply primary air to the mills. Primary

    air gets preheated in air pre heater before entering mill. Primary air dries the moisture content in

    coal and also helps in transporting coal from mills to boiler for combustion.

    FD FanThe FD fans are designed for handling secondary air for the boiler. Air from FD fan is called

    secondary air and is supplied to the boiler for combustion. Secondary air gets preheated in air pre

    heater before entering boiler. Air flow from FD fans is regulated by blade pitch mechanism

    depending upon the demand from the boiler.

    ID FanThese fans draw the flue gases from furnace and sends to chimney and then to atmosphere. The

    flow is regulated by means of inlet guide vanes or variable frequency drive mechanism.

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    Seal air FanThese are used to supply seal air to the mills to prevent ingress of coal dust into gear box

    lubrication oil. Seal air fans take suction from primary air ducts.

    DRAFT SYSTEM

    The term draft denotes the difference between the atmospheric pressure and the pressure in the

    furnace. Depending on the draft used, they are classified as

    - Natural draft- Induced draft- Forced draft- Balancing draft system

    Natural draftIn natural draft system units the pressure differentials are obtained by constructing tall chimneys

    so that vacuum is created in the furnace. Due to the pressure difference air is admitted into the

    furnace.

    Induced draftIn this system air is admitted due to natural pressure difference and the flue gases are taken out

    by means of induced draft fans.

    Forced draftA set of forced draft fans are made use of for supplying air to the furnace and so the furnace is

    pressurized. The flue gases are taken out due to the pressure difference between the furnace and

    the atmosphere.

    Balance draftHere a set of induced and forced draft fans are utilized in maintaining a vacuum in the furnace.

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    3.6 Air pre-heaterAir pre-heaters transfer heat from flue gases to cold primary or secondary air by means of

    rotating heating surface elements. Flue gas from boiler enters on one half of APH dissipating

    heat to the heating elements. When these heating elements come in contact with the coal primaryor secondary air, the air gets heated thus entering boiler at elevated temperature. This results in

    lesser heat energy requirement for combustion hence improving boiler efficiency.

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    3.7 Electrostatic precipitatorESP consists of large chamber in which collecting electrodes (which are plates) and discharged

    electrodes (thin wires) are suspended alternatively. The flue gas passing between the collecting

    and emitting electrodes gets charged and ionized due to corona effect. The suspended ash in theflue gas gets charged and gets collected in the collecting electrodes. ESP is used in the boiler to

    precipitate the dust in the flue gas which reduces the pollution which otherwise results in health

    hazards. The efficiency of modern ESPs is of the order of 99.9%.

    3.8 ChimneyThese are tall RCC structures of height 180mts and form the final outlet of the flue gases which

    escape to the atmosphere at higher elevations.

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    CHAPTER4

    TURBINE & ITS AUXILIARIES

    4.1 INTRODUCTION

    The turbine is a three cylinder, reaction, condensing type with regenerative system of feed water

    heating. It is coupled directly to the generator. The turbine is a single shaft machine with separate

    High Pressure (HP), Low Pressure (LP) turbines. The HPT is a single cylinder having 24+1

    stages and LPT are 25 stages respectively. The steam produced in the boiler is sent to the turbine

    where heat energy is converted into mechanical energy.

    4.2 WORKING PRINCIPLE

    A steam turbine consists of two parts - cylinder and the rotor. The cylinder contains fixed blades,

    vanes and nozzles that direct steam into the moving blades carried by the rotor. Each fixed blade

    set is mounted in diaphragms located in front of each disc on the rotor. The rotor is a rotating

    shaft that carries the moving blades on the outer edges of either discs or drums. The blades rotate

    as the rotor revolves.

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    In a multiple stage turbine, steam at high pressure and temperature enters the first row of fixed

    blades or nozzles through an inlet valve. As the steam passes through fixed blades or nozzles it

    expands and its velocity increases. The high velocity jet of steam strikes the first set of moving

    blades. The kinetic energy of steam changes into mechanical energy, causing the shaft to rotate.

    The steam then enters the next set of blades and strikes the next row of moving blades.

    As the steam flows through the turbine, its pressure and temperature decreases, while its volume

    increases. The decrease in the pressure and temperature occurs as the steam transmits energy to

    shaft and performs work. After passing through the last turbine stage, the steam exhaust into the

    condenser where it forms condensate which is recycled.

    4.3H.P TURBINEThe outer casing is of barrel type and has neither axial nor a radial flange. An axially split guide

    blade carrier is arranged in the barrel type casing and is kinematically supported. The HP turbine

    is provided with a balance piston in the admission side to counteract the axial thrust forces

    exerted in the direction of flow of steam. The exhaust steam from HPT flows back to the boiler

    and passes through re-heater coils. The hot re-heat steam is then admitted into the LPT

    4.4 LP TURBINE

    The casing of double flow LP cylinder is of three shell design. The shells are axially split and of

    rigid welded construction.

    4.4TURBINE COMPONENTS4.5.1 ROTOR

    The rotor is machined from single (Cr-Mo-V) steel forging with integral discs. This specially

    designed by the BHEL for TPP.

    4.5.2 BLADESBlades are the costliest elements of the turbine. Blades fitted in the stationary part are called

    guide blades or nozzles and those fitted in the rotor are called moving or working blades. The

    following are three main types of blades

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    - Cylindrical (of constant profile- Twisted and varying profile blades.

    4.5.3 COUPLINGSCouplings are required between any two rotors since it is made in small parts due to forging

    limitations and other technological and economic reasons. The coupling permits angular

    misalignment, transmit axial thrust and ensures axial location.

    4.5.4 BEARINGSThe HP rotor is supported by two bearings, a journal bearing at the front end of the turbine and a

    combined journal and thrust bearing directly adjacent to the coupling with the LP rotor. The

    combined journal and thrust bearing incorporates a journal and a thrust bearing which takes up

    residual thrust from both directions. The bearing temperatures are measured by thermocouples in

    the lower shell directly under the white metal lining.

    4.6 TURBINE AUXILIARIES

    The turbine cycle can be viewed in the form of different systems. They are:

    - Lube oil system- Control fluid system- Condenser- Vacuum Pumps- Condensate extraction pump- De-aerator

    4.6.1 LUBE OIL SYSTEMThis consists of main oil pump, auxiliary oil pump, emergency DC oil pump and jacking oil

    pump. When the machine is running, the main oil pump situated in the bearing pedestal draws oil

    from the main oil tank by injectors and conveys it to the system for lubrication purposes. When

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    the main and auxiliary oil pumps fails, the lubrication oil is maintained by a DC driven

    emergency oil pump. This system fulfills the following functions:

    - Lubricating and cooling the bearings- Jacking up the shaft at low speeds. This enables the complete rotor assembly

    to be raised or floating in the bearing during turbine generator start up and

    shut down. This prevents damage to the bearing when shaft speeds are too

    low for hydro dynamic lubrication to take place.

    4.6.2 CONTROL FLUID SYSTEMThe turbine governing system is supplied with fire resistant control fluid and this system is

    independent of the lube oil system. The control fluid tank contains fire resistant control fluid

    pumps necessary for the governing system. Apart from its function, it also de-aerates the control

    fluid system. Control fluid pumps are situated on the control fluid tank and immerse with the

    pump bodies into the tank. They draw from the deepest point in order to supply control fluid that

    is as free of air as possible. The control fluid tank is provided with a local level indicator and

    level switches with which the maximum and minimum levels of the control fluid can be

    transmitted. A storage space is provided between the operating levels of the control fluid, which

    corresponds to the normal contents of the tank. This can accommodate the fluid in the entire

    control fluid system when the turbine is shut down.

    4.6.3 CONDENSORThese are surface type condensers with two-pass arrangement. Cooling water is pumped into

    each condenser by a vertical cooling water pump through inlet pipe. To ensure healthy

    cleanliness of the condenser tubes on line tube cleaning is done where in balls are sent through

    the tubes which removes the scales. Steam looses its latent heat to the cooling water in the steam

    side of condenser. This condensate is collected in the hot-well welded to the bottom of the

    condenser and sent back to system by condensate extracting pumps.

    4.6.4 VACCUM PUMPSThe purpose of vacuum pump is to evacuate air and other non condensing gases from the

    condenser and thus maintain vacuum in the condenser. There are two pumps.

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    4.6.5 CONDENSATE EXTRACTION PUMP

    The steam after condensing in the condenser, known as condensate, is extracted out of the hot

    well by condensate extraction pump and taken to the de-aerator through drain cooler, gland

    steam condenser and series of LP heaters. Steam from de-aerator or auxiliary steam header is

    supplied to the end seal of the turbine so as to prevent ingress of atmospheric air into the turbine

    through the end clearances. The gland steam cooler extracts this steam supplied to the end seals.

    4.6.6 DE-AERATORThe presence of certain gases like oxygen, carbon dioxide and ammonia dissolved in water is

    generally considered harmful because of their corrosive attack on metals, particularly at elevated

    temperatures. The condensate admitted at the top of de-aerator column flows downwards through

    the spray walls and trays which are designed to expose to the maximum water surface for

    efficient scrubbing to affect the liberation of associated gases. Steam enters from the underneath

    of the trays and flows in counter direction of condensate. While flowing upwards through the

    trays, scrubbing and heating is done. Thus the liberated gases move upwards along with the

    steam. Steam gets condensed above the trays and in turn heats the condensate. Liberated gases

    escapes to the atmosphere from the orifice opening meant for it.

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    CHAPTER5

    GENERATOR & ITS AUXILIARIES

    5.1 INTRODUCTION

    Generator is used to transform mechanical energy to electrical energy. Turbo generator for

    500MW units are two pole water and hydrogen gas cooled generator. The two pole generator

    uses direct water cooling for stator winding, phase connections & bushings and direct hydrogen

    cooling for rotor winding. The generator frame is pressure resistant and gas tight equipped with

    one stator end shield on each side. The hydrogen coolers are arranged vertically inside the

    turbine end stator end shield.

    5.2WORKING PRINCIPLE

    The A.C generator is based upon the principle of electromagnetic induction and consists

    generally of a stationary part called stator and a rotating part called rotor. The stator houses the

    armature windings while the rotor houses the field windings. When the rotor is rotated, the lines

    of magnetic flux cut through the stator windings. This induces an emf in the stator windings.

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    RESULT

    On an average Thermal Power Plant at Visakhapatnam Steel Plant produces 250MW of power

    for the plant use and provide 6000 m3/hr cold blast to Blast Furnace Department and hot water to

    Rolling Mills.

    FUTURESCOPE

    Thermal Power Plant at Visakhapatnam Steel Plant releases hot air into the atmosphere whose

    temperature is around 2000C.

    By reducing the 2000

    C temperature of the released gases into the atmosphere to atleast 1800

    C the

    company can get an annual profit of 20crores. (Case study done by Visakhapatnam Steel Plant

    employees)