4) steel plant projects
TRANSCRIPT
-
8/22/2019 4) Steel Plant Projects
1/30
1
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.
-
8/22/2019 4) Steel Plant Projects
2/30
2
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
-
8/22/2019 4) Steel Plant Projects
3/30
3
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
-
8/22/2019 4) Steel Plant Projects
4/30
4
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.
-
8/22/2019 4) Steel Plant Projects
5/30
5
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
-
8/22/2019 4) Steel Plant Projects
6/30
6
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
-
8/22/2019 4) Steel Plant Projects
7/30
7
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.
-
8/22/2019 4) Steel Plant Projects
8/30
8
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
-
8/22/2019 4) Steel Plant Projects
9/30
9
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.
-
8/22/2019 4) Steel Plant Projects
10/30
10
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:
-
8/22/2019 4) Steel Plant Projects
11/30
11
- 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
-
8/22/2019 4) Steel Plant Projects
12/30
12
- 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
-
8/22/2019 4) Steel Plant Projects
13/30
13
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.
-
8/22/2019 4) Steel Plant Projects
14/30
14
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
-
8/22/2019 4) Steel Plant Projects
15/30
15
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.
-
8/22/2019 4) Steel Plant Projects
16/30
16
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
-
8/22/2019 4) Steel Plant Projects
17/30
17
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.
-
8/22/2019 4) Steel Plant Projects
18/30
18
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.
-
8/22/2019 4) Steel Plant Projects
19/30
19
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
-
8/22/2019 4) Steel Plant Projects
20/30
20
- 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.
-
8/22/2019 4) Steel Plant Projects
21/30
21
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.
-
8/22/2019 4) Steel Plant Projects
22/30
22
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.
-
8/22/2019 4) Steel Plant Projects
23/30
23
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.
-
8/22/2019 4) Steel Plant Projects
24/30
24
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.
-
8/22/2019 4) Steel Plant Projects
25/30
25
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
-
8/22/2019 4) Steel Plant Projects
26/30
26
- 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
-
8/22/2019 4) Steel Plant Projects
27/30
27
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.
-
8/22/2019 4) Steel Plant Projects
28/30
28
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.
-
8/22/2019 4) Steel Plant Projects
29/30
29
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.
-
8/22/2019 4) Steel Plant Projects
30/30
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)