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FOREWORD

Power is the most vital necessity for industrial and economical growth of any nation.Electricity can bring sea changes in quality of life of its society members. NTPC in itsendeavour for becoming most significant entity once again after 30 years of untiring andrelentless efforts, reaffirm its commitment towards making India a self-reliant nation inthe field of power generation. Having proven excellence in Operation & Maintenance of200 and 500MW units; for the first time we are going ahead with the commissioning of660MW units at our Sipat Project. This is a major step towards technologicaladvancement in power generation.

In the present time, efficient and economical power generation is the only answer torealise our ambitious plan. It is the need of the hour that available human resources whoare the at the whelm of the affairs managing the large thermal power plants havingsophisticated technology and complex controls, is to be properly channelised and trained.NTPC management firmly believes that skill and expertise up-gradation is a continuousprocess. Therefore, training gets utmost priority in our company.

Power Plant Simulators are the most effective tools ever created. This has computer basedresponse, creation incorporating mathematical models to provide real time environment,improves retentivity and confidence level to an optimum level in a risk-free, cost and timeeffective way.To supplement the hands-on training on panel and make the training moreeffective an operation manual in two volumes has been brought out.

The operation manual on 500MW plant provide the information comprehensively coveringall the aspects of Power Plant Operation which can be useful for fresh as well asexperienced engineers. It provides a direct appreciation of basics of thermal power plantoperation and enables them to take on such responsibility far more sincerely andeffectively.

I am pleased to dedicate these manuals (volume- I & II), prepared by CSTI members whichis a pioneer institute covering more than 7000 participants till date, to the fraternity ofengineers engaged in their services to power plant. The volume-I deals with the Plant &system description and II covers the operating instruction in a lucid way. I sincerely hopethat readers will find these manuals very useful and the best learning aid to them.

I believe that in spite of all sincere efforts and care of faculty members & staff, somearea of improvement might have remained unnoticed. Hence, your valuablesuggestions and comments will always be well received and acted upon.

( A. CHAUDHURI )GENERAL MANAGER

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CONTENTS

CHAPTERNO.

TOPIC PAGE NO

1.PLANT SIMULATION AND DATA

ACQUISITION SYSTEM7-17

2. BOILER AND AUXILIARIES19-120

3.CONDENSATE AND FEED

WATER SYSTEM121-174

4.CONDENSER AND EVACUATION

SYSTEM175-188

5. HP AND LP BYPASS SYSTEM 189-209

6. STEAM TURBINE AND AUXILIARIES 211-244

7. TURBINE GOVERNING SYSTEM 245-293

8. AUTOMATIC TURBINE TEST 295-319

9. TURBINE STRESS EVALUATOR 321-334

10.

GENERATOR, ITS AUXILIARIES AND

EXCITATION SYSTEM 335-393

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PLANT SIMULATIONAND

DATA ACQUISITION SYSTEM

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PLANT SIMULATION AND DAS

THE PLANT SIMULATION

The 500MW-training simulator is a complete full scope replica of the 500MW coal-firedunit-6 of Singrauli plant of NTPC, which creates the real time effects of the plant

operating conditions on the Unit Control Panel equipments. The actual plant, theequipments, the control systems - all are replaced by their mathematical models andmade to run through a real -time execution process of a computer to represent theexact plant dynamics through its process parameters on the Unit Control Panel.

THE SIMULATOR SYSTEM ARCHITECTURE

THE HARDWARE: - The simulator system is having the hardware organisation as per

fig.1

FIG-1 SIMULATOR HARDWARE ORGANISATION

UPS System: - It is a 55KVA UPS with 100 % stand by capacity, consisting of

Rectifiers, Inverters, Batteries, Stabilizer, Static By-pass Switch, AC distribution

panels, etc. It provides regulated power supply to the complete Simulator equipments.

The UPS is Supplied by M/S AEG , West Germany.

Computer system and peripherals: - The computer systems supplied are 32 bit

digital computers of Encore, USA. The supplied model 32 / 67 is ideally suited for the

real time simulation applications. The system mainly comprises of

Two computers for simulation of plant equipments (SIMULATION COMPUTER)

One computer for simulation of DAS tasks (DAS COMPUTER)

Shared memory systems (for coupling DAS and SIMULATION COMPUTERS)

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Various peripherals such as magnetic tape drives, disc drives, floppy drives,

system consoles, hard copy printers, line printers, Graphics systems (colour

monitors /controllers) video colour printer etc.

Set of cables for interconnecting the system and peripherals.

The computer system is based on a high speed synchronous bus (called asSELBUS) , on which the CPU and / or IPU are residing . It supports upto 16MB main memmory, Input Output Processor (IOP) and peripheral controllers. Itoffers 18 Selbus slots and four MPbus slots and peripheral space. This systemaccommodates 800 / 1600 / 3200 bpi streaming Mag tape units and over twoGigabytes of disk storage.

Control Panel: - a Simulator control panel with mounted instruments is replica of

Unit -6 of Singrauli Power Plant and is the main hardware of this Simulator. It

comprises of UCB section 1 to 3 and CSSAEP panels. Instruments mounted on these

panels represent the operation of the real plant processes which are simulated by thecomputer systems and the computed information is transmitted to these instruments

via Input / Output system.

In addition to various monitoring and recording equipments, the panels are also

equipped with control switches, indicating lamps, annunciation system and DAS

system.

Interface (Input / Output) System: - The I/O sub-system forms the interface

between the simulation computers and the UCB panels. The main function of the I/Osub system is to update the UCB output points with the current simulated value and

to report the state of the UCB inputs to the simulation computer. I/O sub-system

consists of four SIMTROLs catering the all sections of the UCB, associated Control

Room Equipment (CRE) power supply and special device interface modules.

Instructor Station: - Instructor station hardware comprises mainly of Instructor

station console and peripherals such as two monitors with keyboards, one video hard

copy printer, one remote control unit and one special function keyboard with back

lighted push buttons for activation of desired function.

With the help of remote control unit, certain functions can be initiated/stopped duringtraining session without the notice of the trainee and training session transients can

be hard copied on video printer for further analysis.

Data Acquisition System (DAS): - DAS comprises of three color CRTs mounted onUCB-2 panel having assigned as Utility, Alarm and Operation CRT. One additionalCRT is also provided on Operators desk. For documentation purposes Hard Copy

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printers are provided for Alarm and Utility CRT and a Logging line printer for massiveand fast documentation. Hard copy of the information from any of the DAS CRTs canalso be obtained on video printer through selector switches.

THE SOFTWARE: - The Simulator system is having the following software

organisation as per Fig.2

FIG-2 SIMULATOR SOFTWARE ORGANISATION

Computer operating System MPX-32: - The computers work on a Mapped Program

Executive (MPX-32) disk-oriented, multiprogramming Operating system, that supports

concurrent execution of multiple tasks in an interactive, batch and real timeenvironment. MPX provides memory management, terminal support, muliple batch

streams and intertask communication. It supports 16 MB physical memory address

space. An intergrated CPU scheduler and a swap scheduler provide efficient use of

main memory by balancing the task based on time distribution factors, software

priorities and task state queues.

Simulator Control & Executive System Software UNISYSTEM: - UNISYSTEM is a

Software tool for use in the developement of large-scale real time application

programs. It provides:

A data base to record and describe the variables, arrays and subroutine usedin a program.

A Modified FLECS compiler that is linked to the database to verify the

legitimacy of variable, arrey and subroutine names encountered in the code

being compiled.

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A data base manager program to handle the declaration of new variable, arrey,

and subroutine name. It also creats COMMON and EQUIVALENCE statements

needed to use the variable, arrey and subroutine names in programs.

A real time program scheduler to execute users programs on a real time basis.

A plotting program to display results obtained from execution of usersprograms.

Application Software for Plant system Simulator: - The total power plant system is

broadly divided into the following subsystems for math modeling purpose:

1. Boiler and Flue gas subsystem.

2. Boiler Water and Steam subsystem.

3. Fuel subsystem.

4. Condensate subsystem.

5. Feed Water subsystem.

6. Turbine subsystem.

7. Electrical subsystem.

Each of this subsystem is subdivided into Process interlock and control models based

on nature of the model function. These mathematical models are developed based onphysical laws of conservation of mass, energy and momentum.

The above mathematical models, converted in to the form of simulation software

models, are then integrated in a sequential manner to represent the power plant

dynamics in totality during all plant operating conditions including pre start-ups

checks, preheating, start-up (cold, warm and hot), shut down, power maneuvering,

normal operation and specified emergencies.

The extent of plant simulation is thorough enough to support the plant operators (the

trainees here) to fully participate in plant status evaluation, actual plant operation and

control of unusual transients.

Application Software for Data Acquisition System (DAS): - Plant computer

functions provided by actual plant computers have been duplicated in the simulator.

These are

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Alarm monitoring of analog and digital input signals and indication of abnormal

plant operating conditions.

Analog trend recording of operator selected analog inputs.

Logs such as hourly log, turbine run-up log etc.

CRT displays for analog, digital plant signals and group point displays, alarm

displays, etc.

Performance calculations.

Simulator Instruction Station Software: - Instructor station software is provided

with facility for monitoring, controlling simulator conditions and monitoring operator

(trainee) actions. It has provision to select all initial conditions and malfunctions and

the ability to manipulate external parameters.

Interface (Input/Output) System Software: - The I/O system application software

consists of tasks running on Simulation Computers and on SIMTROLs. The tasks

running on Simulation Computers perform: -

1. Input-Output Transmitting.

2. Misaligned switch checking.

3. Daily Operational Readiness Test.

The tasks running on SIMTROLs perform:

1. SEL Interface.

2. Input Transmitting.

3. Analog Output Updating

4. Digital Output Updating

5. Table Management

6. Watch Dog

7. Digital Input Scanning

8. Analog Input Scanning

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9. Analog/Digital Output Driving, etc,.

TRAINING FEATURES

The following features of the simulator facilitate a very effective training to the powerplant operators: -

Initialisation: - The simulator can be initialised to any one of 60 plant conditionsfrom where the training session can start. The instructor can choose the status /conditions of the running simulator (i.e., the plant) and save them as ICs (InitialConditions) through a special utility software at Instructor Station . A maximumnumber of 60 such selected plant conditions can be kept stored. Later on , any one ofthese stored conditions can be retrieved as an Initial Condition and the trainingsession can be started from that plant status . Thus the Initialisation facility providesthe flexibility in training by starting the session from any one of the 60 stored plantconditions as per the requirement / level of the trainees and saves time by eliminatingthe repeated exercise to bring the plant to the required condition again to start with.

Freeze/Run: - The FREEZE feature helps the instructor to freeze the plantsimulation and thus to bring the plant dynamics to a standstill condition.The plantoperation can be subsequently resumed from the last frozen status by using RUNcommand by the instructor. When the FREEZE command is issued from theInstructor Station, the simulation software under execution is stopped and theupdation of the simulation variables are suspended thereby creating an effect offreezing of the dynamic plant condition. This facilitates the instructor detailedexplanation on that particular stage of operation without allowing it to go unobserved

by the trainees on the panel.

Backtrack: - This facility enables the plant simulation status to traverse back allevents of operation for the past 60 minutes. The simulation data is continuously saved

for a period of 60 minutes at the interval of one minute each as 60 disc file records.Thus at any point of time, 60 data sets are available representing the plant status forthe preceding sixty minutes. The instructor can bring the simulator to any of theselast sixty plant conditions by BACKTRACKing to the desired problem time or byBACKTRACKing step-by-step from the present 1st record. Which is the current onesaved. If required, simulation session can continue from this backtracked recordstatus to facilitate repeated panel operation or to offer detail explanation to thetrainees.

Snapshot: - This feature enables the instructor to SNAP the plant status as acomplete record of all the simulation variables that represent the plant dynamics atthe time of snapping. These SNAPSHOT records, as disk files, can be saved with

identifying title, date & time and can be retreived any time in future as InitialConditions to commence the training session from that snapped plant condition. Atotal number of 60 SNAPSHOTs can be saved and stored as Initial Conditionsproviding wide range of flexibility in training.

Slow Time Mode: - This features enables the Instructor to slow down the dynamicsimulation to ten times slower than the real time. Thus in a SLOW MODE Simulation,a trainee can observe the fast transients or certain critical operations more precisely in

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order to analyse the dynamic behaviour and study the sequence of events therebyenhancing their knowledge and experience.

Fast Time Mode: - In this mode of simulation, certain time consuming plantoperations like turbine soaking, boiler heating, raising of condeser vacuum, furnacepurging, etc. are made to run ten times faster than the real time. Thus the instructor

can save the valuable panel time by attenuating the time taken in accomplishinglengthy plant operation stages and offer the saved time to the trainees for betterutilisation on the panel.

Malfunction: - This is the most valuable feature of the Simulator, which offers thetrainees a unique scope for experiencing a large number of malfunctions that occur ina power plant. The instructor can introduce malfunctions in single number or ingroups (the selection being dependent on the status of the plant) to simulate the realemergencies as faced by the operators on panel. The trainees are thus givenopportunities to tackle those malfunctions by taking suitable corrective operationsteps, which are, otherwise, rare events in an actual plant. A total number of 270malfunctions are available characterised into two types:

1. The Event type malfunctions: These can set the equipment/component failureat an optional pre-selected time.

2. The Severity type malfunctions:These can be started at an optional pre-selectedtime with the degree of severity (0-100%) and the gradient (time to reach thatseverity effects) choosen by the instructor.

The malfunctions available can be selected, activated and reset (cleared) by theinstructor without any intimation to the trainees on the panel, which supports arealistic operational environment.

Record & Replay: - The RECORD feature enables the instructor to record the trainingsession under progress for a period of two (2) hours. All the changed inputs from thepanel and the IS are recorded alongwith time on specified disk files. Maximum 4 nos ofrecords, each of two hours duration, can be stored. The storage can be initiated at anyinstant of time.

The REPLAY feature enables to replay the panel status as recorded earlier. Thus thetrainees can observe their previous performance on panel alongwith the instructorsexplanation and analysis. Any of the four-recorded sessions can be selected for replay.

Both RECORD & REPLAY functions can be paused and stopped in between.

Remote Function: - This function facilitates the instructor to perform any remote(field/local) operations, which are not carried out from main control room. The manualoperations of local equipments (e.g. F.O. pumps, valves, isolators, station supply

breakers, etc) are simulated from the instructor station for providing necessarypermissives and also for controlling process parameters.

Crywolf Alarm: -This feature enables the instructor to create false alarms by flashingwindows and by making audible cry wolf alarms even though such conditions do not

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exist in the plant under operation. With this facility trainees immediateresponse/reflexes can be tested. At a time, upto 16 numbers of alarms can be set andreset selectively by the instructor.

Override Panel Device: -Any device on the control panel can be OVERRIDENwith agiven value (for analog variables) or with a given status (for digital variables) by the

instructor at an optional preselected activation time. The value/status of theoverridden device remains constant until it is reset to normal operation or overriden

with a new value/status. A total number of 32 devices can be selected for overide at atime. The instructor can thus create maloperation of the instruments on the panel totest the trainees undergoing session.

External Parameters Manipulation: - This feature enables the instructor to changethe values of certain parameters that are not simulated in the software but affect theplant performance. External parameters (inputs) like the grid voltage, grid frequency,calorific value of fuels, etc can be assigned new values. The change will be achievedgradually within one minute. These inputs change the plant dynamics andperformance. Thus it offers the trainees scope of plant operation under different

conditions on a single platform.

Analog Output Reallocation: - Any analog output of the plant simulation can bereallocated to any other meter/recorder on the panel. This permits the instructor tocontinue the training in the event of some instrument failure on which someimportant parameters are displayed/recorded.

Parameters Monitoring: -Trends of important plant parameters (simulated variablesin engineering units) can be monitored on the instructors dedicated console to checkthe trainees performance on control panel for the duration selected. The instructorcan also change the higher and lower limits of the parameters selected during trenddisplay for better resolution in monitoring. A total number of 80 parameters can be

selected, deleted, and stopped for monitoring by the instructor to match hisrequirements. Limits of the selected parameter can be modified for better analysis.

Trainee Test: - This feature is the unique facility in simulator training by whichproficiency of operation personnel can be evaluated by the computer. The instructorcan assign the trainee a task on the panel and monitor his/her capacity to controlimportant parameters of the plant with a final assessment printout result if opted for.

At a time, maximum four nos. of tests can be conducted in parallel depending uponthe plant conditions and the tests selected. Each test has the following facilities to beselected.

Identification of the test by Instructors name, Trainees name & Exercise

number/Title,

Monitoring or Evaluation type,

Duration of the test (Run time),

Displaying the test parameters with updation by every one second,

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Trending of test parameters,

Deleting test parameters already selected,

Changing of Hi & Lo limits of the test parameters to monitor within a narrowrange.

Displaying of the test results on the Video Monitor.

Printing of the test results to get a hard copy.

Thus the trainees can get a feedback on themselves after completing the testprogram.

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BOILERAND

AUXILIARIES

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BOILER AND AUXILIARIES

SALIENT FEATURES OF 500 MW BOILER.

With increase in demand of power in India, new power projects are being constructed

with higher capacity and advanced technology for the better economy and reliability ofoperation.

Compared to other lower capacity Boilers supplied by BHEL, these 500 MW capacity boiler have incorporated certain special technical features which are detailed hereunder: -

CONTROLLED CIRCULATION SYSTEM

This is achieved by three numbers of glandless pump and wet motor installed in the

downcomer line after the suction manifold. These pump motor assemblies have single

suction and double discharge introduction of these pumps in the boiler system have

led to the designing of a furnace with lesser diameter tubes and high parameters

operating characteristics.

The advantages of the controlled circulation boiler over natural circulation boiler are

given below: -

Uniform drum cooling and heating. In controlled circulation boilers this is

possible because of arrangement of relief tubes inlets to the drum and the

internal baffles of the drum from both sides. The internal base plates are

arranged in such a way that it guides the steam water mixture from the relief

tubes along the whole circumference of the drum. The drum is therefore

uniformly heated and cooled.

Whereas in Natural Circulation Boiler, the arrangement of relief tubes and baffle

plates is only on one side of the drum and this imposes a constraint on uniform

heating of drum. Similar arrangement of relief as in controlled circulation boiler does

not exist in natural circulation (NC) boiler because in that case the relief required to be

taken over the drum and fed from both sides. This shall increase the pressure losses

in the riser tubes and also the hot static head requirement for start up. Since the

available head in NC Boiler is very less; efforts are always made to reduce the pressure

loss and improve the circulation. Second reason is to commence flow in the riser

tubes immediately after light up hot static head is kept as minimum as possible.

Rapid heating & cooling (start up & shut down): As mentioned in Para 1, thecontrolled circulation boiler does not impose any thermal constraints on thedrum and hence rapid cooling and heating of the boiler is possible. In NC

boiler, rise in saturation temperatures is limited to maximum of 110OC/hr.Hence, the controlled circulation boiler can be started at a rate two to threetimes faster than NC boilers.

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Better cleaning of boiler:For effective acid washing, the acid has to be kept at certain temperatureuniformly through the system. This is possible with the assistance of controlledcirculation.

Uniform expansion of pressure part and lower metal temperature:

This means lesser thermal stresses on the tubes. Because of controlledcirculation, lower diameter tubes are used, which result in high mass flow ratethereby preventing departure from nucleate boiling (DNB) maintains a lowermetal temperature.

USE OF RIFLE TUBES FOR FURNACE CONSTRUCTION

This is one of the extraordinary features of 500 MW capacity boilers. Because of theexcessive heat release in the burner zone of the furnace, the metal tubes constitutingthe furnace at that zone are exposed to the maximum temperature. This being a

water-cooled furnace, the steam water mixture inside the tubes should effectively

carry the heat from the burner zone of the furnace.

In this zone, the tubes have an internally cut spiral like a rifle bore so that when waterflows through the tubes, due to hot static heat, it takes a screwed path and attains acertain degree of spin by which the watness of the tube is always maintained. Thisprevents the tubes form departure from Nucleate boiling under all operating conditionof the boiler and increases the circulation ratio.

OVER FIRE AIR SYSTEM FOR NOX (OXIDES OF NITROGEN) CONTROL

Industrial growth in the recent years has necessitated the need to have a cleaner and

pollution free atmosphere, by controlling the production of industrial wastes with theapplication of improved technology. Power plants are the major sources of the

industrial pollution by virture of the stanch emission in the atmosphere. These

emissions contain mostly gases and dust particles, which have ill effect on the

ecological system. In the 500 MW capacity boiler design, this aspect has been given

due importance and certain technical improvements have been incorporated. These

are tilting tangential firing and over fire air system. Tangential firing helps in keeping

the temperature of the furnace low so that NOX emission is reduced considerably.

In addition to the above the over fire air is provided which is used as combustion

process adjustment technically for keeping the furnace temperature low and thereby

low Nox formation.

Each corner of the burner windbox is provided with two numbers of separate over fire

air compartments, kept one above the other and the over fire air is admitted

tangentially into the furnace.

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The over fire air nozzles has got tilting arrangement and compartment flow control

dampers for working in unison with the tilting tangential type burner system for

effective control of Nox formation.

AIR PRE-HEATER SYSTEM

As compared to trisector air pre-heater in 200 MW units, 500 MW units have been

incorporated with bisector air pre-heaters. This has been done for optimum utilisation

of space and also improved system layout. This has resulted in the flexibility and

efficient operation and maintenance of the air pre-heaters and the boiler as a whole.

PRIMARY AIR SYSTEM

The primary air system delivers air to the mills for coal drying and transportation ofcoal powder to furnace. The 500 MW units have two stage axial flow primary fans ascompared to radial fans in 200 MW units. By introducing axial flow fans, the systemefficiency has gone up as the axial flow fans consistently high efficiency at all

operating loads.

MILLING SYSTEM

In the 500 MW units at SSTPS, Raymonds Pressurised bowl mills have been installed. These are similar to the 200 MW mills except that 500 MW mills have vane wheelsurrounding the bowl and external lubrication unit. Introduction of vane wheel hasled to uniform distribution of primary air within the mill and less rejects. These millsare also supplied with weld overlay technology, which has increased the minimum

wear life of grinding parts to 6000 hrs.

I. D. FANS

Unlike 200 MW units, the 500 MW units have been supplied with radial type I.D. fans.These fans have a lower speed and are less susceptible to wear and tear due to theabrasive flue gases. The control of the I.D. fans is achieved through a variable speedhydraulic coupling and motorised inlet damper. By introducing variable speed controlthrough a hydraulic coupling the losses in the fan at various load has been minimisedand efficiency of the fan has remained high at all operating conditions.

ELECTROSTATIC PRECIPITATORS:

Electro static precipitators are installed in the 500 MW units for minimising theparticulate emission from the stack flue gases. There are four ESP passes for one unit

of 500 MW and each is independently operated. The emitting electrodes are changedat high-ve voltage DC and the gas while crossing this charged path gets jonised. Theionised ash particles of the gas are attracted towards the collecting electrode, which ismaintained at high +ve voltage. The ash collects at the collecting electrode and isperiodically tapped to dislodge the accumulated ash. The ash falls into the hopper,

which is evacuated by the ash handling system and taken out as slurry.

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TECHNICAL SPECIFICATION OF 500 MW BOILER

MAIN BOILER

GENERAL SPECIFICATION

Manufacturer : M/s BHEL (C.E. Design)

Type : Balanced Draft, Dry bottom,

Single drum, Controlled

Circulation plus.

Type of Firing : Tilting Tangential

Minimum load at which the steam generator

can be operated continously with complete

flame.

: 2 Mills at 50%

Minimum load at which the steam generator can be

operated continuosly with complete flame.

Stability with oil support (% MCR)

: 20%

Maximum load for which individual mill

beyond which no oil support is required

: 50%

FURNACE SPECIFICATION

Wall : Water Steam cooled

Bottom : Dry

Tube arrangement : Membrane

Explosion/Implosion withstand capacity

(MWG) at 67% yields point.

: + 660

Residence time for fuel particles in the

furnace.

: 3 second

Effective volume used to calculate the

residence time (M3)

: 14770

Height from furnace bottom ash hopper tofurnace roof (M)

: 63.65

Depth (M) : 15.289

Width (M) : 18.049

Furnace projected area (M2) : 7610

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Furnace volume (M3) : 14770

WATER WALLS

FRONT WALLS

Number : 283

OD (MM) : 51.00

Design thickness (MM) : 5.19

Pitch (MM) : 63.5

Actual thickness used (MM) : 5.6

Material : SA 210C

Total projected surface (M2) : 1160

Method of joining long tube : Butt weld

Total wt. of tubes (kgs) : 181000

Design pr. of tubes Kg/cm2 (ABS) : 207.3

Max. pressure of tubes Kg/cm2 (ABS) : 197.3

Design metal temp OC : 416

SIDEWALLS, REAR WALLS

& ROOF

Side walls Rear walls Roof

Number 444 283 142

OD (MM) 51 51 57

Design thickness (MM) 5.19 5.19 5.54Pitch (MM) 63.5 63.5 127

Actual thickness used 5.6 5.6 5.7

Total projected surface area

of tubes (M2)

1430 930 220

Method of joining long tubes. BUTT WELD BUTT WELD BUTT WELD

Total wt. of tubes (Kgs) 277000 186000 45000

Design Pr. of tubes Kgs/cm2

(ABS)

207.3 207.3 204.9

Max pr. of tubes Kgs/cm2

(ABS)

193.3 197.3 192.3

Design metal Temp oC 417 417 416

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WATER WALL HEADERS Lower drum WW outlet

No. of headers 1 5

Outside Dia (Dia (MM) 914 273

Design thickness (MM) 86 38.5

Actual thickness (MM) 89 45

Total wt. of headers (Kgs.) 166000 37300

Design pressure of headers kg/cm2 (ABS) 207.3 204.9

HEADERS Lower drum WW outlet

Max working pressure of headers Kg/cm2

(ABS)

197.3 192.4

Material specification SA-299 SA-106 Gr-B

DRUM

Material specification : SA-299

Design pressure Kg/cm2 (ABS) : 204.9

Design metal temp OC : 366

Max operating pressure Kg/cm2 (ABS) : 192.4

Actual thickness used for dished ends : 152.4

Overall length of Drum (MM) : 22070

OD of Drum (MM) : 2130

Internal dia (MM) : 1778Corrosion allowance (MM) : 0.75

Number of distribution headers : 6

No. of Cyclone separator : 96

No. Of Secondary driers : 96

Shroud material : Carbon Steel

Max permissible temp differential between any

two parts of the drum (oC).

: 50

Water capacity at MCR conditions (in seconds) between

normal and lowest water level permitted

(up to LL trip)

: 10

Drum wt. with internals (tonnes) : 237.00

Drum wt. without internals (tonnes) : 215.00

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BOILER WATER CIRCULATING PUMP

Number of pumps : (2 + 1)

CHARACTERISTICS

Type : Single suction doubledischarge

Design Pressure : 207.55 Kg/cm2

(2965 lbf/in2)

Design temp : 366.2oC(691oF)

NORMAL OPERATING DUTY

Sunction Pressure : 193.27 Kg/cm2 (2761

1bf/in2)

Suction temp. : 348.9oC(660oF)

Specific gravity at pump Suction

at pumping temp.

: 0.5993

Qty. pumped : 47994.2 lit/min (12679 u.s

gal/min)

Differerential HEAD : 28.65 M (94.00 ft)

Differential Pressure : 1.708 Kg/cm2 (24.4

1bf/ in2)

Minimumm NPSH required above

Vapour Pressure

: 16.15 M (53 ft)

Pump efficiency : 84% Hot duty

BHP absorbed : 215 Hot duty-358 Cold

duty

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MOTOR CHARACTERISITICS Hot duty Cold duty

Motor efficiency : 86% 88.6%

K.W. Input : 187 302

Power factor : 0.7 0.805

Overall efficiency : 72.2% 74.3%

Full load speed : 1450 rpm

Line current @ 6.6 KV : 23.3 amps 32.8 amps

Full load current : 36 amps

Motor starting current : 190 amps

Heat exchanger Hot duty

H.P. Inlet temp (max) : 55oC (130oF)

Allowable pr. drop : 0.7 kg/cm2 (10 1bf/in2)

Heat transfer - hot duty : 28980 kcal/hr. (115000 B.T.U./hr)

Heat transfer - cold duty : 30240 kcal/hr. (120000 B.T.U./hr)

H.P. cooling water flow : 200.62 lit/min (534.5 gal/min)

Weight (Approximate)

Pump case : 3541.2 kgs (7800 1bs)

Motor complete : 9534 kgs (21000 1bs)

Total weight : 13075.2 kgs (28800 1bs)

MOTOR CHARACTERISITICS

Type: : Wet Stator -Squirrel Cage

induction motor

Output : 400 H.P.

Service factor : 1.0

Winding : XLP

Motor case design temp. : 343.34OC (650OF)

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BOILER WATER CIRCULATION PUMPS

Each Boiler Water Circulation pump consists of a single stage centrifugal pump on a

wet stator induction motor mounted within a common pressure vessel. The vessel

consists of three main parts a pump casing, motor housing and motor covers.

The motor is suspended beneath pump casing and is filled with boiler water at full

system pressure. No seal exists between the pump and motor, but provision is made

to thermally isolate the pump from the motor in the following respect:

Thermal Conduction. To minimise heat conduction, a simple restriction in the

form of thermal neck is provided.

Hot Water Diffusion. To minimise diffusion of boiler water, a narrow annulus

surrounds the rotor shaft, between the hot and cold regions. A baffle ring

restricts solids entering the annulus.

Motor Cooling. The motor cavity is maintained at a low temperature by a heat

exchanger and a closed loop water circulation system, thus extracting the heat

conducted form the pump.

In addition, this water circulates through the stator and rotor bearings

extracting the heat generated in the windings and also provide bearing

lubrication. An internal filter is incorporated in the circulation system.

In emergency conditions, if low-pressure coolant to the heat exchanger fails, or

is inadequate to cope with heat flow from pump case, a cold purge can be

applied to the bottom of the motor to limit the temperature rise.

Pump

The pump comprises a single suction and dual discharge branch casing. The case is

welded into the boiler system pipework at the suction and discharge branches with the

suction upper most. Within the pump cavity rotates a key driven, fully shrouded,

mixed flow type impeller, mounted on the end of the extended motor shaft. Renewable

wear rings are fitted to both the impeller and pump case. The impeller wear ring is the

harder component to prevent galling.

Motor

The motor is a squirrel cage, wet stator, induction motor, the stator, wound with a

special watertight insulated cable. The phase joints and lead connections are also

moulded in an insulated material. The motor is joined to the pump casing by a

pressure tight flange joint and a motor cover completes the pressure tight shell.

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The motor shell contains all the moving parts, except for the impeller. Below the

impeller is situated an integral heat baffle which reduces the heat flow, a combination

of convection and conduction, down the unit. A baffle wear ring-cum sleeve above the

baffle forms a labyrinth with the underside of the impeller to limit sediment

penetration into the motor. Should foreign matter manage to pass the labyrinth device

into the motor enclosure, a filter located at the base of the cover end bearing housingstrains it out.

AUXILIARY COOLING CIRCUIT

The motor is provided with its own auxiliary cooling circuit, which besides cooling the

motor lubricates the bearings.

The water is continuously circulated through the bearings, motor windings and the

external heat exchanger, (cooler), by an auxiliary impeller (thrust disc) at the thrust

bearing end of the motor shaft. When the motor is stationary, thermo-syphonic

circulation takes place to remove conducted heat from the pump end of the motor.

BEARINGS

The motor rotor shaft is supported by water lubricated tilting pad type radial and

thrust bearings mounted on the stator shell, thus making the motor internals into a

separated construction independent of the motor pressure vessel.

INTER FILTER

A stainless steel woven wire strainer, fitted at the base of the reverse thrust plate,

filters the liquid in the motor before it is circulated through the bearings after passing

through the heat exchanger (cooler).

The filter should be cleaned at normal maintenance periods, removing anyaccumulation of foreign matter in the motor cover.

HEAT EXCHANGER

A heat exchanger (cooler) is fitted to dissipate the heat generated by the motorwinding.

Brackets are provided on the motor case to mount the heat exchanger.High-pressureoutlet and inlet-raised facings are situated bottom and top of the motor caserespectively for connection to high-pressure heat exchanger/motor case stub pipes.Inter - connecting pipework is short and direct with the heat exchanger mounted ashigh as possible to promote good thermo-syphonic circulation when the unit is on hotstandby.

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PURGE AND FILL PIPING

The purge and fill piping is used in association with boiler water circulation pumpsubmerged motors. Depending on valve positions it can be used for filling or emptyingthe motor cavity of water, or for emergency purging of the cavity to prevent the ingressof hot boiler water should a leak occur in the cooling water system, or a gasket failure

between pump and motor occur. Allowing high temperature boiler water to enter thecavity will damage the plastic insulation on the motor windings.

During normal operation water is taken from the S.H. & R.H. spray water system thenfed via a strainer and cooler before splitting three ways to service each circulationpump. If the pumps are to be filled when the S.H. spray water is out of service, atemporary connection can be made to take low pressure water from the reserve feed

water tank.

The valves, which service each circulation pump, can be opened and closed to makethe system operate in out modes.

Circulation pump filling. Water will flow through the filter then have itspressure and flow reduced through an orifice plate at the pump inlet. Drainlines down stream of the filter and the orifice will be closed.

Circulation pumps emptying. The isolating valve upstream of the drain orificewill be closed and water from the motor cavity will drain through open valves inthe drain line downstream of the orifice.

Piping blowdown. The isolating valve downstream of the filter will be closed anddrain line at the filter outlet open. Water will flow into the open drain.

Circulation pumps purging. Water will flow as described in the filling mode butthe orifice bypass line will be opened to augment the flow.

DRUM DESCRIPTION

Connections at both ends to the chemical clean pipework, and at three points along itslength to feed individual circulation pump suctions. Water will flow from the pumpsthrough two discharge pipes into the front leg of the water wall inlet headers at the

bottom of the furnace. Each discharge pipe is fitted with circulating pump dischargestop/check valves, which are controlled via sequence equipment to open and close asthe pump is taken in and out of service. If, however all three pumps are out of service,all of the valves will open to enable thermosyphonic circulation to take place. Initiating

any pump to restart will cause them all to close again then continue with the in andout of service regime. Controls for the pumps are located in the Contol room andcomprise a SEQUENCE pushbutton, ammeter and a DUTY/STANDBY selector. Pumpstatus is indicated on RUN/STOP lamps on the Firemen's Aisle Panel. The operatingregime for the boiler water circulation pumps is two-duty/one stanby.

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From the Waterwall inlet headers, water travels upwards through furnace wall tubing

via furnace upper front rear and side headers into riser tubes, which direct a

saturated steam/water mixture in to the steam drum. Furnace wall tubing is

manufactured from a combination of both smooth and rifled bore tubing which

permits the use of lower tube flow rates whilst still retaining full tube protection. The

required distribution of water to give the correct flow rates through the variousfurnace wall circuits is achieved and maintained by the use of suitably sized orifices

installed inside the water wall inlet headers at the inlet to each furnace wall tube.

Orifice size varies for different circuits or groups of circuits depending on the circuit

legth, arrangement and heat absorption. Perforated panel strainers are also located

inside the water wall inlet headers to prevent the orifices blicking and to ensure an

even distribution of water around the other inlet headers.

The saturated steam/water mixture enters the steam drum on both sides behind a

watertight inner plate baffle which directs the mixture around the inside surface of the

durm to provide uniform heating of the drum shell. This eliminates thermal stresses

from temperature differences through the thick wall of the drum, between the

submerged and unsubmerged protions. Having travelled around this baffle the

mixture enters two rows of steam enter the outer edge of the separator where it is

separated from the steam. Nearly dried steam leaves the separators and passes

through four rows of corrugated plate baskets where by low velocity surface contact

the remaining moisture is removed.

SUPER HEATERS & REHEATERS

SH LT

PENDENT

HORIZONTALSTAGE-1

PANEL

STAGE-II

PLATEN

STAGE-III

Type Convection Radiant Radiant

Platen (Drainable/Non-

drainable)

--- Non- drainable Non-

drainable

Pendant

(Drainable/Non-

Drainable)

Drainable --- ---

Horizontal Headers(Drainable/Non-

Drainable)

Drainable Drainable Drainable

Effective heating surface

area (M2)

12500 1660 1730

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Gas flow path area (M2) 147 --- 286

Max steam side

Metal temp (oC)

408 509 575

Max gas side metal temp

(oC)

450 570 690

Type of flow (counter or

parallel)

Counter Parallel Parallel

Mat of tube support SS SS SS

OD (MM) 51.00 44.5 54.00

Total Number of tubes 708 444 408

TUBE PITCH (MM)

Parallel to gas flow 101.6 54.00 63.5

Across gas flow 152.5 254.00 762

Method of joining long

tube

Total wt. of tubes (T)

REHEATERS

STAGE-1

RH RADIANT

WALL

STAGE-2

RH FINISHING PLATEN

RH INTER PENDENT

RH REAR PENDENT

Total heating surface (M2) 275 (proj.) 6200

Max operating pressure

(Kg/cm2)

47.68 47.00

Design pressure Kg/cm2

(ABS)

53.73 53.73

Max gas side metal temp oC 430 620

OD (MM) 63 63.5

Mean effecting length (perone

tube) MM (App)

17,500 27,000

Gross length (per one tube) MM

(App)

18300 38000

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Total number of tubes 248 644

Total Wt. (Kgs.) 423300

Method of Joining long tube

Headers

Max. Operating pressure

Kg/cm2 (ABS)

192.3 47.68

Design pressure (Kg/cm2)

(ABS)

204.9 53.73

Location (outside/inside gas

path)

Out side Out side

Total Wt. (Kgs.) 2111300 67000

SUPERHEATER AND REHEATER

The arrangement, tube size and spacing of the Superheater and Reheater elements areshown on the attached Schematic Flow Arrangement Diagram of Superheater andReheater.

SUPERHEATERS

The Superheater is composed of three basic stages of section; a Finishing PendantPlaten section, a Division Panel Section and a Low Temperature Section includingLTSH, the Backpass Wall and Roof Sections.

The finishing Section is located in the horizontal gas path above the furnace rear archtubes and consists of assemblies spaced on 76.2 centres across the furnace width.

The Division Panel Section is located in the furnace between the front wall andPendant Platen Section. It consists of six front and six rear panel assemblies.

The Low Temperature Sections and are located in the furnace rear Backpass above theEconomiser Section. They are composed of assemblies spaced on centres across thefurnace width.

The Backpass wall and Roof Section forms the side front and rear walls and roof of the

vertical gas pass.

REHEATER

The reheater is composed of 3 stages or sections, the Finishing Section the Front

Platen Section and the Radiant Wall Section

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The Finishing Section is located above the furnace arch between the furnace screen

tubes and the Superheater Finish. It consists of assemblies.

The Reheater Front and side Radiant Wall is composed of tangent tubes on centers

across the furnace width.

STEAM FLOW

The course taken by steam from the steam drum to the superheater finishing outlet

header can be followed on the attached illustrations, the Schematic Flow &

Arrangement of Superheater & Reheater. The elements, which make up the flow path

are essentially numbered consecutively. Where parallel paths exist, first one and then

the other circuit are numbered. The main steam flow is:

Steam drum - SH connecting tube - (1) -Radiant roof inlet header (2) - First pass roof

front (3)- Rear (4) - Radiant tube outlet header (5) - SH SCW inlet header side (6)Backpasss side wall tubes (7) & (8) - Backpass bottom headers (9), (10) & (11) -

Backpass Front, and rear (12) (21) - Backpass screen (13) Backpass roof (14)-

Backpass SH & Eco. supports (15) SH & Eco. support headers (16) - LTSH support

tubes (17) - SH Rear Roof tubes (18) - SHSC Rear wall tubes (19)- LTSH inlet header

(22) - LTSH banks (23) (24) - LTSH outlet headers (25) - SH DESH link (26) - SH DESH

(27) - Division panel (30) - Division Panel outlet header (31) - SH Pendent assembly

(34) - SH outlet header (35).

After passing through the high-pressure stages of the turbine, steam is returned to the

reheater via the cold reheat lines. The reheater desuperheaters are located in the cold

reheat lines. The reheat flow is.

Reheater radiant wall inlet header (38) (39) - radiant wall tubes (40) (41) reheaterassemblies (46) (47) - reheater outlet header (48) - Reheater load (49).

After being reheated to the design temperature, the reheated steam is returned to the

intermediate pressure section of the turbine via the hot reheat line.

PROTECTION AND CONTROL

As long as there is a fire in the furnace, adequate protection must be provided for the

Superheater and Reheater elements. This is especially important during periods whenthere is no demand for steam, such as when starting up and when shutting down.During these periods of no steam flow through the turbine, adequate flow through thesuperhteater is assured by means of drains and vents in the headers, links and mainsteam piping. Reheater drains and vents provide means to boil off residual water inthe reheater elements during initial firing of the boiler.

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ARRANGEMENT OF SUPERHEATER AND REHEATER

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Safety valves on the superheater main steam lines set below the low set drum safety valve, provide another means of protection by assuring adequate flow through thesuperheater if the steam demand should suddenly and unexpectedly drop Rehetersafely valves, located on the hot and cold reheat piping serve to protect the reheater ifsteam flow through the reheater is suddenly interrupted.

A power control valve on the superheater main steam line set below the low setsuperheater safety valve is provided as a working valve to given an initial indication ofexcessive steam pressure. This valve is equipped with a shut off valve to permitisolation for maintenance. The relieving capacity of the Power Control Valve is notincluded in the total relieving capacity of the safety valves required by the Boiler Code.

During all start-ups, care must be taken not to overheat the superheater or reheaterelements. The firing rate must be controlled to keep the furnace exit gas temperature

from exceeding 5400C. A thermocouple probe normally located the upper furnacesidewall should be used to measure the furnace exit gas temperatures.

NOTE:

Gas temperature measurements will be accurate only if a shielded, aspiratedprobe is used. If the probe consists of simple bare thermocouple, there will be

an error, due to radiation, rustling in a low temperature indication. At 588OCactual gas temperature, the thermocouple reading will be approximately 10degrees low. Unless very careful traverses are made to locate the point ofmaximum temperature, it is advisable to allow another 10 degrees tolerance,regardless what type of thermocouple probe is used.

The 540OC gas temperature limitation is based on normal start up conditions, when steam is admitted to the turbine at the minimum allowable pressure

prescribed by the turbine manufacturer. Should turbine rolling be delayed andthe steam pressure to permitted to build up the gas temperature limitation

should be reduced to 510OC when the steam pressure exceeds two thirds of thedesign pressure before steam flow through the turbine is established.

Thermocouples are installed on various superheater and reheater terminals tubes,

above the furnace roof, serve to give a continuous indication of element metal

temperatures during start-ups (superheater) and when the unit is carrying load

(Superheater and Reheater). In addition to the permanent thermocouples, on some

units temporary thermocouples provide supplementary means of establishing

temperature characteristics during initial operation.

Steam temperature control for Superheater and Reheater outlet is provided by means

of windbox nozzle tilts and desuperheaters.

DESUPERHEATERS

Super heater & Reheater temp Control

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SUPER HEATER ATTEMPRATOR

Type : Spray

Stage : One

Position in steam circuit : Between LT pendants

and SH panels.

Specification of material. : SA335 P12

Spray tube material : SA-213 T11

Super heater steam temp range that can be

maintained from 54.43% to 100% of Boiler MCR.

: 540 oC

Max spray water flow rate and corresponding steam

output (Kgs./hr.)

: 92,800 at 1566, 000Kgs./hr.

Min spray water flow rate and corresponding steam

out put Kg/hr. Reheat Emergency temp control

attemperator

: 47,000 at 1550,000Kg/hr.

REHEATER ATTEMPERATORTYPE : SPRAY

No. of stages of attemperator : One

Position in the steam circuit : Before RH Radiant wal

Specification of the Material : SA-106 Gr-B

Spray nozzle Material : SA-213T & SS Tips

HEADERS

Length mm : 18,000

Design Pr. (Kg/Cm2) (abs) : 209.8

Max Working Pressure (Kg/Cm2)(abs) : 196

GENERAL

Desuperheaters are provided in the superheater-connecting link and the reheater inletleads to permit reduction of steam temperature when necessary and to maintain the

temperatures at design values within the limits of the nozzle capacity.

Temperature reduction is accomplished by spraying water into the path of the steamthrough a nozzle at the entering end of the desuperheater. The spray water comesfrom the boiler feedwater system. It is essential that the spray water be chemicallypure and free of suspended and dissolved solids, containing only approved volatileorganic treatment material, in order reheater and carry-over of solids to the turbine.

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CAUTION:

During start up of the unit, if desuperheating is used to match the outlet steamtemperature to the turbine metal temperatures, care must be exercised so as not to

spray down below a minimum of 100 C above the saturation temperature at the

existing operating pressure. Desuperheating spray is not particularly effective at thelow steam flows of start up. Spray water may not be completely evaporated but becarried through the heat absorbing sections to the turbine where it can be the sourceof considerable damage. During start up alternate methods of steam temperaturecontrol should be considered.

The location of the desuperheaters helps to ensure against water carry - over to theturbine. It also eliminates the necessity for high temperature resisting materials inthe desuperheater construction.

SUPERHEATER DESUPERHEATERS

Two spray desuperheaters are installed in the connecting link between thesuperheater low temperature pendant outlet header and the superheater division

panel inlet headers.

REHEATER DESUPERHEATERS

Two spray type desuperheaters are installed in the reheater inlet lead near the

reheater radiant wall front inlet header.

ECONOMISER

Type : Non Steaming

Water side effecting heating surface area (M2) : 7810

Gas side effecting heating Surface area (M2) : 10210

Gas flow path area (M2) : 128

Design pressure of tubes Kg/cm2 : 209.8

OD of Tubes (MM) : 51.00

Actual thickness tubes (MM) : 5.6

Length of Tubes (MM) (App) : 2,15,000Pitch (MM) : 101.6

Total Wt. of Tubes (Kgs.) : 4,95,00

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BARE TUBE ECONOMISER

The function of the economiser is to preheat the boiler feedwater before it isintroduced into the Steam drum by recovering some of the heat of the flue gas leavingthe boiler. Refer the " Schematic Flow and Arrangement Diagram of Water & SaturatedSteam Circuits".

The economiser is located in the boiler backpass. It is composed of two banks of 156

parallel tube elemets (3) arragned in horizontal rows in such a manner that each row

is in line with the row above and below. All tube circuits originate from the inlet

header (2) and terminate at oulet headers (4) which are connected with the economiser

outlet header (7) through three rows of hanger tubes (6).

Feedwater is supplied to the economiser inlet head (1) (2) via feed stop and check

valves. The feedwater flow is upward through the economiser, that is, counterflow to

the hot flue gases. Most efficient heat transfer is, thereby, accomplished, while the

possibility of steam generation within the economiser is minimised by the upward

water flow. From the outlet header the feedwater is lead to the steam drum through

the economiser outlet links (5) (6).

The economiser recirculating lines, which connects the economiser inlet lead header

(2) with the furnace lower rear drum (14), provide a means of ensuring a water flow

through the economiser during startups. This helps prevent steaming. The valves in

these lines must be open during unit startup until continuous feed water flow is

established.

WATER COOLED FURNACE

WELDED WALL CONSTRUCTION

The furnace walls are composd of 51.0D. Tubes on 63.5" centers. The space between

the tubes is fusion welded to from a complete gas tight seal. Some of the tube ends are

swaged to a smaller diameter while other tubes are bifurcated where they are welded

to the outlet headers and lower drum nipples.

The furnace arch is composed of 63.5 O.D. fusion welded tubes, 76.2 (typical) centers.

The backpass walls and roof are composed of 63.5 O.D. fin welded tubes on 154.4

centers.

The furnace extended sidewalls is composed on O.D. fin welded tubes on 127 centers.

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The backpas front (furnace) roof is composed of 51.0. O.D. tubes, peg fin welded on

152.4 centers. The backpass rear roof is composed of 51.0 O.D tubes peg fin welded

on 152.4 centers.

All peg-finned tubes are normally backed with a plastic refractory and skin casing,

which is seal, welded to form a gas tight envelope.

Where tubes are spread out to permit passage of superheater elemets, hanger tubes,

observation ports, soot blowers, etc., the spaces between the tubes and openings are

closed with fin material so a completely metallic surface is exposed to the hot furnace

gases.

Poured insulation is used at each horizontal buckstay to form a continous band

around the furnace thereby preventing flue action of gases between the casing and

water walls.

BOTTOM CONSTRUCTION

Bottom designs used in these coal-fired units are of the open hopper type, often

referred to as the dry bottom typ. In this type of bottom construction two furnace

water walls, the front and rear walls, slope down toward the centre of the furnace to

form the inclined sides of the bottom. Ash and/or slag from the furnace is discharged

through the bottom opening into n ash hopper directly below it. A seal is used between

the furnace and hopper to prevent ambient air being drawn into the furnace and

disturbng combustion fuel/air rations. The seal is affected by dipping seal plates,

which are attached around the bottom opening of boiler furnace, into a water trough

around the top of the ash hopper. The depth of the trough and seal plates will

accommodate maximum downward expansion of the boiler (predicated (320.3 mms).

Feedwater enter the unit through the economizer elements (1) (2) (3) (4) (5) (6) and is

mixed with boiler water in the steam drum (7). Water flows from the drum (7) through

the downcomers (8) to the pump suction manofld (9). The boiler-circulating pump (10)

takes water from the suction manifold and discharges it, via the pump discharge lines

(12), into the furnace lower front inlet header (13). Furnace lower water wall right and

left side headers (15) assure proper distribution to the rear heater (14).

In the waterwall inlet headers the boiler water passes through strainers and thenthrough orifices, which feed the furnace wall tubes, the economiser recirculating lines.

The water rises through furnace wall tubes where it absorbs heat. The front wall tubes(16), rear tubes (17), rear wall hanger tubes (19), rear arch tubes (18), rear screentubes (21), extended sidewall tubes (2) and sidewall tubes (22) from parallel flowpaths.

The resulting mixture of water and steam collects in the waterwall outlet headers (23)

(24) (25) (26) and is discharged into the steam drum (7) through the riser tubes (27). In

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the steam drum the steam and water are separated (see "Drun Internals"), the steam

goes to the superheater (see "Supergeater and Reheater") and the water is reurned to

the waterside of the steam drum to be recirculated.

WATERWALL INLET HEADERS

The waterwall inlet headers are rectangular ring shaped manifold at the bottom of the

furnace. Downcoming pipes enter into the furnace lower front inlet header. Furnace

lower waterwall right and left side headers assure proper distribution to the rear

heads.

In the waterwall inlet headers the boiler water passes through screen and then

through orifices, which feed the furnace wall tubes.

The screen consists of a number of panels with 2/16" perforations. The panels aresecured in the inlet drums with clamps. The panels are made in sections to facilitate

removal and replacement.

Each orifice is installed on the orifice mount adapter tack welded to the drum interior

wall. A marman clamp holds the orifice on the orifice mount.

NOTES:

1. Initial boiling out and acid cleaning operation to be completed before installing

orifices.

2. Screens however must be installed

3. Orifice and screen assemblies retained on subsequent acid cleaning operation

and removed for inspection purposes only.

H.P. CHEMICAL DOSING SYSTEM

Intermittent H.P. Chemical dosing is used to inject Tri-sodium Phosphate (T.S.P.) intothe boiler water so that a phosphate reserve is maintained. T.S.P will precipitate any

undesirable hardness salts contained in the water into a form of free flowing sludge,

which can be removed by blowdown.

A solution of T.S.P. will be made ready in the mixing tank using a motor operated

stirrer and make up water as necessary. When prepared, the solution will be

transferred by gravity feed to the metering tank ready for injection into the boiler

steam drum in quantities determined by chemical analysis.

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The level of solution in the tanks can be observed through side mounted gaugeglasses. Further monitoring is provided by level switches which initiate an alarm

when the level in the metering tank is high / low. Drains from the gauge glasses andtank overflows empty into an open drains system.

Solution is pumped from the metering tank by one of the two 100 % duty H.P. dosingpumps (one standby) into the steam drum. Both pump system are indentical andinclude a suction filter and a discharge pressure relie valve. Each relief valvedischarges into the open drain system.

FUEL FIRING SYSTEM

INTRODUCTION

The information Contained in this chapter relates to the fuel (oil & coal) system and

fuel / combustion equipment under supply of BHEL for 500 MW boilers.

FUEL OIL SYSTEM

The fuel oil system prepares any of the two designated fuel oil for use in oil burners

(16 per boiler, 4 per elevation) to establish initial boiler light up of the main fuel

(pulverised coal) and for sustaining boiler low load requirements upto 15 % MCR load.

To achieve this, the system incorporates fuel oil pumps, oil heaters, filters, steam

tracing lines which together ensure that the fuel oil is progressively filtered, raised in

temperature, raised in pressure and delivered to the oil burners at the requisite

atomising viscosity for optimum combustion efficiency in the furnace.

COAL SYSTEM

The coal system prepares the main fuel (pulverised coal) for main boiler furnace firing. To achieve this the raw coal from overhead hopper is fed through pressurised coal valve, SECOAL nuclear monitor, and gravimetric feeder and into mills where it iscrushed and reduced to a pulverised state for optimum combustion efficiency. Thepulverised coal is mixed with a primary airflow, which carries the coal air mixture toeach of 4 corners of the furnace burner nozzles and into furnace.

BURNER NOZZLES

Both the oil and coal burner nozzles fire at a tangent to an imaginary circle at the

furnace centre. The turbulent swirling action this produces, promotes the necessarymixing of the fuels and air to ensure complete combustion of the fuel. A vertical tiltfacility of the burner nozzles, which is controlled by the automatic control system of

boiler, ensures a constituent reheat outlet steam temperature at varying boiler loads.

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TILTING TANGENTIAL FIRING SYSTEM

GENERAL

In the tangential firing system the furnace itself constitutes the burner. Fuel and airintroduced to the furnace through four windbox assemblies located in the furnacecorners. The fuel and air streams from the windbox nozzles are dissected to a firingcircle in the centre of the furnace. The rotative or cyclonic action that is characteristicof this type of firing is most effective in turbulently mixing the burning fuel in aconstantly changing air and gas atmosphere

AIR AND FUEL NOZZLE TILTS

The air and fuel stream are vertically adjustable by means of movable air deflectorsand nozzle tips, which can be tilted upward or downward through a total of approx.60 degrees. This movement is effected through connecting rods and tilting mechanismin each windbox compartment, all of which are connected to a drive unit at each

corner operated by automatic control. Provision is given in UCB to know the positionof nozzle tips during operation. The tilt drive units in all four corners operate inunison so that all nozzles have identical tilt positions.

WINDBOX ASSEMBLY

The fuel firing equipment consists of four windbox assemblies located in the furnace

corners.

Each windbox assembly is divided in its height into number of sections or

compartments. The coal compartments (fuel air compartment) contain air

(intermediate air compartments). Combustion air (secondary air) is admitted to theintermediate air compartment and each fuel compartment (around the fuel nozzle)

through sets of louvre dampers. Each set of dampers is operated by a damper drive

cylinders located at the side of the windbox. The drive cylinders at each elevation are

operated either remote manually or automatically by the Secondary Air Damper

Control System in conjunction with the Furnace Safeguard Supervisory System.

Some of the (auxiliary) intermediate air compartments between coal nozzles contains

oil gun. (Refer contract assembly drawing for details).Retractable High Energy Arc

(HEA) ignitors are located adjacent to the retractable oil guns. These ignitors directly

light up the oil guns.

Optical flames scanners are installed in flame scanner guide pipe assemblies in the

auxiliary are compartments. The scanners sense the ultraviolet (UV) radiation given

off by the flame and thereby prove the flame. They are used by Furnace safeguard

Supervisory System to initiate a master fuel top upon detection of flame failure in the

furnace.

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AIR FLOW CONTROL AND DISTRIBUTION

Total airflow control is accomplished by regulating fan dampers or fan speed. Airdistribution is accomplished by means of the individual compartment dampers. Theairflow to the air boxes can be equalised by observing and equalising the reading of the

flowmeters located in the hot air duct to windbox.

TOTAL AIR FLOW

In order to ensure safe light-off conditions, the pre-optional purge airflow (at least 30

% of full load volumetric air flow) is maintained during the entire warm-up period until

the unit is on the line and the unit load has reached the point where the airflow must

be increased to accommodate further load increase. To provide proper air distribution

for purging and suitable air velocities for lighting off, all auxiliary air dampers should

be open during the purge period, the lighting off and the warm-up period.

After the unit is on the line, the total required amount of air (total air flow) is a

function of the unit load. Proper airflow at a given load depends on the characteristics

of the fuel fired and the amount of excess air required (see note) to satisfactorily burn

the fuel. Excess air can be determined through flue gas analysis (Orsat

measurements).

The optimum excess air is normally defined as the O2 at the economiser outlet that

produces the minimum opacity. Operation below the optimum excess air will result in

high opacity due to unburned carbon where as operation above the optimum excess

air will result in high capacity due to excessive H2 SO4 condensation. Operation below

recommended range will result in excessive black smoke and operation above this

range will result in excessive white smoke.

NOTE: The most suitable amount of excess air for a particular unit, at a given load

and with a given fuel must be determined by experience. This is best done form

observation of furnace slagging conditions. Slagging tendency of a particular fuel may

dicatate an increase of operating excess air.

AIR FLOW DISTRIBUTION

The function of the windbox compartment dampers is to proportion the amount of

secondary air admitted to an elevation of fuel compartments in relationship to that

admitted to adjacent elevation of auxiliary air compartments.

Windbox compartment damper positioning affects the air distribution as follows:Opening up the fuel - air dampers or closing down the auxiliary air dampers increases

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the air flow around the fuel nozzle Closing down the fuel air dampers and opening theauxiliary air dampers decrease the air flow directly around the fuel stream.

Proper distribution of secondary air is important for furnace stability when lighting offindividual fuel nozzle, when firing at low rates and for achieving optimum combustioncondition in the furnace at all loads.

Proper distribution of secondary air also has an effect on the emission of pollutantsform coal fired units. As the unit increases the quantity of Nitrogen Oxide (NO)Produces in a furnace (due to the oxidation of nitrogen in the fuel) increases and theupper elevations of fuel nozzles are placed in service. The quantity of NO producedcan be reduced by limiting the amount of air admitted to the furnace adjacent to thefuel and increasing the quantity of air admitted above the fire (over fire air). When theunit has reached a predetermined load (app. 50 %) the over-fire air dampers shouldopen and modulate as a function of unit load until, at maximum continuous rating(MCR) when upto 15 % of the total air is admitted to the furnace as over fire air. Theoptimum ratio of over fire air to fuel and auxiliary air, as well as the optimum tiltposition of the over-fire air nozzles, to produce a minimum NO emission consitent with

satisfactory furnace performance must be determined through flue gas testing (i.e.measurement of NO) during initial operation of the unit.

The correct proportion of air between fuel compartment and auxiliary aircompartments depends primarily on the burning characteristics of the fuel. Itinfluences the degree of mixing, the rapidity of combustion and the flame pattern

within the furnace. The optimum distribution of air for each individual installationand for the fuel used must be determined by experience.

The wind-box compartments are normally provided with drive (except end aircompartments) so they may be operated by a secondary air damper and over-fire aircontrol system in conjuction with the furnace safeguard supervisory system. When on

automatic controls the system should provide modulation of the auxiliary air dampersas required to maintain a pre-set windbox-to-furnace differential pressure. The fuelair dampers should be closed prior to and during light off. When the fuel elevation isproven in service, the associated fuel-air dampers should open and be positioned inproportion to the elevation-firing rate. Normally the end air compartments are[provided with manual adjustment, which can be kept in the required position duringcommissioning of the unit.

FUEL OIL FIRING SYSTEM

FUELS

A coal-fired unit incorporates oil burners also to minimum oil firing capacity of 15 % ofboiler load for the reason of,

1. To provide necessary ignition energy to light-off coal burner

2. To stabilise the coal flame at low boiler/burner loads

3. As a safe start-up fuel and for controlled heat input during light-off.

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Auxiliary steam is utilised in boiler for following purposes:

For atomising the HFO at the oil gun.

For tank heating, main heating and heat tracing of HFO.

To preheat the combustion air at the steam coil air heater and to warm up the

main air heater (this reduces Sulphur-oxide condensation and thus cold end

corrosion of main air heater)

With above provisions and with proper oil, steam and combustion air parameters at

the burner, HFO is safely fired in a cold furnace

BURNER ARRANGEMENT

In a tangentially fired boiler, four tall windboxes (combustion air boxes) are arranged,

one at each corner of the furnace. The coal burners or coal nozzles are located at

different levels on elevations of the windboxes. The number of coal nozzle elevations

are equivalent to the number of coal mills. The same elevation of coal nozzle at 4

corners is fed from a single coal mill.

The coal nozzles are sandwitched between air nozzles or air compartments. That is,

air nozzles are arranged between coal nozzles, one below the bottom coal nozzle and

one above the top coal nozzle. If there are n numbers of coal nozzles per corner there

will be (n + 1) numbers of air nozzle per corner. The coal fuel and combustion air

streams from these nozzles or compartments are directed tangential to an imaginary

circle at the centre of the furnace. This creates a turbulent vortex motion of the fuelair and hot gases which promotes mixing ignition energy availability, combustion rate

and combustion efficiency.

The coal and air nozzles are tiltable 30 0 about horizontal, in unison, at all elevations

and corners. This shifts the flame zone across the furnace height for the purpose of

steam temperature control.

The air nozzle in between coal nozzles is termed as Auxiliary Air Nozzles, and the top

most and bottom most air nozzles as END Air Nozzles.

The coal nozzle elevation are designated as A,B, C,D etc., from bottom to top, the bottom end air nozzle as AA and the top end air nozzles as XX. The auxiliary air

nozzles are designated by the adjacent coal nozzles, like AB, BC, CD, DE ....... etc.

The four furnace corners are designated as 1,2,3, and 4 in clockwise direction looking

from top, and counting front water wall left corner as 1.

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During furnace purge, all the elevations of auxiliary and end air dampers are opened

to have uniform and through purging across the furnace volume.

BOILER LOW LOAD OPERATION

During initial operations upto about 30 % boilers loading (and also during furnacepurge) all the auxiliary and end air dampers modulate to maintain a predetermined

(approx. 40 mm WC) set point differential pressure between the windbox and furnace.

During this period also, 30-40 % of total airflow is maintained to have an air rich

furnace and to avoid possible unhealthy furnace conditions. Again all the auxiliary

and end air dampers are open to distribute the excessively admitted air away from the

operating burners and to pass only the necessary air behind the operating burners at

appropriate velocity, for successful burner light up and stable flames.

Around 40 mm of windbox of furnace differential is the pressure estimated as required

to admit 30-40 % of airflow with the entire auxiliary and end air dampers modulatingwith reasonable opening.

Whenever one or more oil burners are put into service the associated elevation of

auxiliary air dampers modulate as a function of oil header pressure, to provide

required combustion air. The other auxiliary air dampers continue to maintain 40

mm windbox to furnace differential.

At boiler load less than 30 % MCR, each elevation of oil burners shall not be loaded

more than 10 % MCR (if high capacity provided), since no adequate combustion air

will be available behind oil burners, under this operating conditions. If found

necessary total airflow may be marginally increased for better flame conditions.

BOILER LOAD ABOVE 30 %

When the unit load exceeds 30 % MCR, the differential set point is changed to a higher

setting (approx. 100 mm WC). Simultaneously, the auxiliary air dampers associated

with the coal or oil elevations not in service close in timed sequence starting with the

upper elevations of dampers and progressing to the lowest elevation.

The above 100 mm WC differential is the predicted value required to admit the total

secondary air at design air velocities with all dampers opened to reasonablepercentage.

When the unit load is reduced below 30 % loading, the auxiliary air dampers open in a

timed sequence starting with the lowest elevation of dampers. Simultaneously, the

differential set point change to its lower setting.

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burners. To achieve this the heater oil is circulated upto the burners and back to the

oil tank through HFO return lines, till adequate temperature is reached near the

burners.

For the above purpose there are two HFO recirculation loops. One is called the long

Recirculation, which is through the main trip valve, supply flow meter and flow control valve in the HFO supply line, supply ring header and HFO return lines. Long

recirculation is the effective one, which circulates oil right upto the burner valve inlet,

nears the corner risers.

Long recirculation is not possible if no control power is available and during mater fuel

trip. During such occasions the other partial recirculation loop called short

recirculation is employed. This later loop bypasses the boiler area piping and

connects the HFO return line to the HFO supply line before the HFO main trip valve

and supply flow meter, short recirculation valve is opened when the main trip valve is

closed, essentially for warming up the main lines. Before opening the main trip valve

or the first burner trip valve, the short recirculation valve is closed.

A HFO return trip valve (HORV) is installed in the long recirculation loop. With this

valve open, large volumes of HFO can be circulated upto the burners and initial

warming up of the pipings can be faster.

When one or more burners are firing (i.e. when HORV is shut) still a small amount of

hot oil is constantly recirculated through a restricting orifice arranged across HORV.

This constant recirculation keeps the HFO return line always warm, prevents

solidification of oil at dead ends and ensures uniform temperature in the piping. This

orifice is sized for a circulation flow rate of about 7 - 10 % of maximum oil firing rate.

During initial commissioning, this recirculation flow rate shall be checked and if foundnecessary orifice size be suitably changed or the regulating valve opening be adjusted.

The HFO return flow meter is installed across the HORV in series with the constant

recirculation orifice, rather than in the common return line, for better rangeability.

The flow metering should be accounted only when HORV is closed.

When the boiler is firing on coal or no oil burner is fired it is recommended to open

Heavy Oil Main Trip Valve and Return Valve to circulate the oil continuously. This will

enable the operator to cut in the oil gun immediately when required. The amount of

oil circulation however is to be restricted to avoid shooting up of tank temperatures

and hence the flow control valve may be throttled to reduce the return oil flow rate.

OIL FLOW CONTROL

This is remote manually done by varying oil flow control valve opening. The need for

varying the oil burner load and the normally adopted practice is described in the

following lines.

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SYSTEM REQUIREMENT

The maximum total output of oil burners is 30 % of the boiler MCR. This meets the

turbine synchronisation needs before firing coal burners.

Each oil burners capacity is about 2 % of boiler MCR.

For coal burner ignition and coal flame stabilisation a minimum oil burner output,

equivalent to 10-20 % of maximum coal burner capacity is required. This roughly

corresponds to 40 to 50 % rating of an oil burner.

For the exact capacities refer to performance data sheet (oil burners and ignitors)

The oil burner output is a function of oil pressure at the oil gun and the normal

turndown range of the oil burner is 3: 1.

For steam atomised oil burner, the oil pressure at the oil gun shall not fall below 2.5

kg/sq cm2(g) to ensure good atomisation and stable flames.

The oil burners have to be opted at loads, lower than the maximum rating for reasons

mentioned below.

1. During cold start-ups of the boiler, to have a controlled and gradually

increasing heat loading, to avoid temperature stresses on pressure part

materials, as dictated by boiler start up curves.

2. To conserve fuel oil by operating the oil burners just at the Coal flame

stabilisation requirements.

Oil Flow Control Valve and Minimum Pressure Control Valve Function

The oil header pressure is maintained constant at all loads, at the upstream of oil flow

control valve by a relieving type backpressure control valve installed after the pump.

The flow control valve essentially does the function of regulating the boiler fuel oil

firing rate. The valve opening can be varied from the remote depending upon the no of

burners firing and the firing rate. The minimum pressure control valve ensures a

smooth starting up boiler.

To start with, the Heavy Fuel Oil Heater Trip Valve and HORV are opened. Once the

temperature at the boiler front is adequate, the heavy fuel oil flow control valve is kept

at the predetermined minimum firing opening to restrict the firing rate. This can be

done by setting the required header pressure and maintaining the same through the

pneumatic pressure controller. The burner trip valves are then opened and burners

are put into service. The burners are operated only by pair mode.

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When more no of burners are brought into service the heavy fuel oil header pressure

will experience a sudden dip. The header pressure will be automatically maintained

by the pressure control loop in the flow control valve. If this pressure control loop is

not in service, it is always a good operators practice to increase the header pressure

before additional burners are brought into service.

The position transmitter or position limit switches mounted on the flow control valve

serve to indicate the status of opening of control valve. An UCB display of control

valve outlet pressure and the number of burners in service are the correct guidance