Project

On

Thermal Power Plant

(P.T.P.P. Parichha, Jhansi)

for

Six Weeks Industrial training in partial fulfillment for the

Bachelors of Technology

in

Mechanical Engineering

Submitted to: Submitted by :

Avedhesh Kumar Gagandeep Singh

Executive Engineer 100721132601

Boiler Maintenance Division (BMD -ii) Mechanical Engineering

+SHREE GANESH Group of Institutions

Patiala-Nabha Road, Village Rakhra, Patiala

ACKNOWLEDGEMENT

We great sense of pleasure & joy fills you heart as we present my dissertation “Boiler

maintenance division –II in Parichha Thermal Power Project, Jhansi”. We could not have

dream of this Endeavour in the absence of internal knowledge.

We thanks to the management of Parichha Thermal Power Project, Jhansi for providing me

the best of facilities of opportunities we express mine profound sense of gratitude to mine

respectable.

“Er. Avedesh Kumar” (Executive Engineer) BMD-II

“Er. Jitendra Nigam” (Assistant Engineer) BMD-II

“Er. Ashish Katiyar” (Junior Engineer) BMD-II

For granting me the permission to undergo the training period in Power Plant.

(Signature)

Gagandeep Singh

CONTENTS

PARICHHA THERMAL POWER PLANT

INTRODUCTION OF THERMAL POWER PLANT

SALIENT FEATURES

TECHNICAL DATA OF 110MW PLANT

MAIN PARTS OF POWER PLANT

BOILER

GENERATOR

TURBINE

FUEL HANDLING

ASH HANDLING

BOWL MILL RAW COAL FEEDERAND ITS SPECIFICATION

FANS – PRIMARY AIR FAN, FORCE DRAUGHT FAN, INDUCED DRAUGHT FAN WITH SPECIFICATION AND WORKING

ELECTROSTATIC PRECIPITATOR

HEATER – ECONOMIZER, PLATEN SH,LTSH,FINAL SH,AIR PREHEATER(APH)

CONDERSER

HOTWELL

DEMINERALISATION PLANT

DEARATOR

SAFETY PRECAUTION

Plant overview

By Gagandeep Singh

 Typical diagram of a coal-fired thermal power station

1. Cooling Tower 13. Feed water heater Hr2. Cooling Water Pump . 14. Coal Conveyor3. Transmission Line (3-Phase) 15. Coal Pulverizer4. Step-Up Transformer (3-Phase) 16 Turbine Coal Hopper5. Electrical Generator (3-Phase) 17 Boiler Steam Drum6. Low Pressure Steam 18. Bottom Ash Hopper7. Condensate Pump .  19. Super heater 8. Surface Condenser 20. Forced Draught (Draft) Fan 9. Intermediate Pressure Steam Turbine 21. Combustion Air Intake10. Steam Control Valve 22.Reheater 11. Deaerator 23. Air Preheater12.High Pressure Steam Turbine. ,24Economiser25. Precipitator 26. Flue Gas Stack26.Induced Draught (Draft) Fan .

TECHNICAL DATA OF 110MW PLANT

BOILER

Manufacture : BHARAT HEAVY ELECTRICALTTD ,Truchrapilli, Tamil Nadu,Tilting tangential burners, balanced draught , fusion welded furnace, natural circulation, dry bottom with direct fire pulverized coal from mill and steam reheating arrangement, HP and LP steam by passing system has been included.

Capacity : 375ton/hrs.

Design pressure : 158.2kg/cm2

Superheated outlet

pressure : 138kg/cm2

Superheated outlet temp. : 535o c

TURBINE

Manufacturer : BHEL Hydrerabad

Rated output 110mwMW

Economical output 95MW

Steam pressure just before the stop valve 130bar

Steam temp. Just before stop valve 535.54oc

Pressure of steam 33.63bar

MP casing

Temperature of steam before MP casing 534.54 Oc

Temperature of cooling water 33.36 Oc

Weight of rotor HP-5500kg

MP-11000kg

LP-24000lg

Turing gear speed 65rpm

Consumption make up 0.35kg/hrs

Salient features

Location

On the bank of the Betwa river in the Bundelkhand region of the district

Jhansi (U.P.).

On the Jhansi-Kanpur national highway no.25 near parichha railway station

(CR).

Technical

Instillation capacity of unit Ist and IInd is 220 mw and for unit unit IIIrd & IVth

is 420mw.

Work on the another plant with double of present plant capacity is in progress.

In 2x110mw units boiler are of radiant dry bottom, natural circulation and

vertical water tube type with single reheat 380tonnes/hour of steam at the

139kg/cm2 540 oc .

Turbine and turbo alternators of 110mw.

Cooling system

Cooling water source from Parichha reservoir, formed by upstream reservoir

at Matatiladukwan.

Cooling water temp.- 30oc.

Water treatment plant capacity - 30tonnes/hour.

Outdoors substation

Power transformer (2)-120MV.

Auto transformer (2):-75VA.

Outgoing feeders (2):-at 220KV and (3)132 KV.

Introduction to FANS

The air we need for combustion in the furnace and the flue gas that we mast evacuate would not possible without using fans. A fan is capable of imparting energy to the air/gas in the form of a boost in pressure. We overcome the losses through the system by means of this pressure boost. The boost is dependent on density for a given fan at a given speed. The higher the temperature, lower is the boost. Fan performance ( Max capability) is represented as volume Vs. pressure boost. The basic information needed to select a fan are:

Air or Gas flow kg/hr. Density(function of temperature and pressure) System , resistance(losses)

Types of fans used in plant

Force Draught Fan:

Force draught fans supply air necessary for fuel combustion and must be sized to handle the stoichiometric air plus the excess air needed for proper burning of the specified fuel. In addition ,they provide air make up for heater leakage and for some sealing air requirement. FD fans supply the total airflow except when an atmospheric suction primary fan is used.

In the balanced draught units. The required static head for the FD fans is the sum of all the series resistance in the secondary air system including duct . steam air heater , air heater, air metering device, hot air duct , wind box, and damper , for pressurized units additional loss from the furnace to the stack outlet must also be included.

FD fans operate in the cleanest environment associated with a boiler and are generally the quietist and most efficient fans in the plant. they are particularly well suited for high speed operation. Radial airflow or variable pitch fans are preferred foe FD fans.

FD fans specification

No. of units 2

Rating continuous

RPM 980

Power 360kw

Voltage 6600kv

Q 56.2m3 /s

Δ P 457KP/m2

Motor specification

Power 360KW

RPM 991

PRIMARY AIR FAN

These fans are large pressure fans which supply the air need to dry and transport coal either directly from the coal mills to the furnace or to the intermediate bunker. These fns maybe located before or after the milling equipment. The most common applications are primary air fans, hot air fans and pulveriser exhauster fans.

The function of primary air fan is to supply the primary air used for drying and carrying coal to the boiler from mills.

Air discharge from fan is divided into two parts , one passes through a air preheater(APH)then through agate into PA duct. The second goes to the cold air duct the mix of both is used to carry the pulverized coal to the boiler.

PA fans specification

No. of units 2

RPM 1480

Power 750kw

Voltage 6600kv

Q 36.8m3 /s

Δ P 368KP/m2

Motor specification

Power 750KW

RPM 490

Rating continuous

Induced draught fan

Induced draught fans evacuate combustion product from the boiler furnace by creating sufficient negative pressure to establish a slight suction in the furnace (5to 10 of w.c.), as such these fans must have enough capacity to accommodate any infiltration caused by the negative pressure in the equipment down stream of the furnace and by seal leakage in air heaters.

Induced draught fans are horizontal single stage double suction centrifugal type and coupled with a driving motor through a hydraulic coupling.

Evacuate combustion product from the boiler furnace by creating sufficient negative pressure to establish a slight suction in the furnace.

Specification of ID FAN

No. of units 3

RPM

Power kw

Voltage kv

Q m3 /s

Δ P KP/m2

Motor specification

Power KW

RPM

Rating continuous

Furnace Specification

Type Fusion Welded Panels

Depth 7.696m

Width 10.135m

Volume 2250m3

Economizer

Type Bare Tube

Total Heating Surface 3233m2

Arrangement In Line

Fuel

Fixed Carbon 27.5%

Volatile Matter 28.00%

Moisture 11.00%

Ash 33.00%

Sulphur 0.50%

Grindability (HG) 50.00

Higher Heating Value 3850 Joule/Kg

Size Of Coal To Mill(mm) 20mm

Chemicals Parameters

Ph At 250 8.8-9.2

Specific Conductivity At 250 0.3s/Cm(Max)

Oxygen 0.0007

Total Iron 0.001ppm(Max)

Total Copper 0.005ppm(Max)

Total Silica (Sio2) Nil

Hydrazine 0.01-0.02ppm

Permanganate Consumption Nil

Oil Not Permissible

Boiler Water

Ph At 25oc 9.1-10.1

Specific Electrical Conductivity At 25oc 200s/Cm(Max)

Total Dissolved Solids 100 ppm(Max)

Phosphate Residual 5-10 ppm

Silica (Sio2) 1.0ppm(Max)

In a coal based power plant coal is transported from coal mines to the power plant

by railway in wagons or in a merry-go-round system. Coal is unloaded from the

wagons to a moving underground conveyor belt. This coal from the mines is of no

uniform size. So it is taken to the Crusher house and crushed to a size of 20mm.

From the crusher house the coal is either stored in dead storage( generally 40 days

coal supply) which serves as coal supply in case of coal supply bottleneck or to the

live storage(8 hours coal supply) in the raw coal bunker in the boiler house. Raw

coal from the raw coal bunker is supplied to the Coal Mills by a Raw Coal Feeder.

The Coal Mills or pulverizer pulverizes the coal to 200 mesh size. The powdered

coal from the coal mills is carried to the boiler in coal pipes by high pressure hot air.

The pulverized coal air mixture is burnt in the boiler in the combustion zone.

Generally in modern boilers tangential firing system is used i.e. the coal nozzles/

guns form tangent to a circle. The temperature in fire ball is of the order of 1300

deg.C. The boiler is a water tube boiler hanging from the top. Water is converted to

steam in the boiler and steam is separated from water in the boiler Drum. The

saturated steam from the boiler drum is taken to the Low Temperature Superheater,

Platen Superheater and Final Superheater respectively for superheating. The

superheated steam from the final superheater is taken to the High Pressure Steam

Turbine (HPT). In the HPT the steam pressure is utilized to rotate the turbine and the

resultant is rotational energy. From the HPT the out coming steam is taken to the

Reheater in the boiler to increase its temperature as the steam becomes wet at the

HPT outlet. After reheating this steam is taken to the Intermediate Pressure Turbine

(IPT) and then to the Low Pressure Turbine (LPT). The outlet of the LPT is sent to

the condenser for condensing back to water by a cooling water system. This

condensed water is collected in the Hotwell and is again sent to the boiler in a

closed cycle. The rotational energy imparted to the turbine by high pressure steam is

converted to electrical energy in the Generator.

Diagram of a typical coal-fired thermal power station

Principal

Coal based thermal power plant works on the principal of Modified Rankine Cycle.

Modified Rankine cycle

Components of Coal Fired Thermal Power Station:

COAL PREPARATION

i)Fuel preparation system: In coal-fired power stations, the raw feed coal from the

coal storage area is first crushed into small pieces and then conveyed to the coal

feed hoppers at the boilers. The coal is next pulverized into a very fine powder, so

that coal will undergo complete combustion during combustion process.

** pulverizer is a mechanical device for the grinding of many different types of materials. For example, theyare used to pulverize coal for combustion in the steam-generating furnaces of fossil fuel power plants.Types of Pulverisers: Ball and Tube mills; Ring and Ball mills; MPS; Ball mill; Demolition.

Dryers: they are used in order to remove the excess moisture from coal mainly wetted during transport. As the presence of moisture will result in fall in efficiency due to incomplete combustion and also result in CO emission. Magnetic separators: coal which is brought may contain iron particles. These iron particles may result in wear and tear. The iron particles may include bolts, nuts wire fish plates etc. so these are unwanted and so are removed with the help of magnetic separators.The coal we finally get after these above process are transferred to the storage site.Purpose of fuel storage is two – Fuel storage is insurance from failure of normal operating supplies to arrive.

Storage permits some choice of the date of purchase, allowing the purchaser to

take advantage of seasonal market conditions. Storage of coal is primarily a

matter of protection against the coal strikes, failure of the transportation system &

general coal shortages.

There are two types of storage:

1. Live Storage (boiler room storage): storage from which coal may be withdrawn

to supply combustion equipment with little or no remanding is live storage. This

storage consists of about 24 to 30 hrs. of coal requirements of the plant and is

usually a covered storage in the plant near the boiler furnace. The live storage

can be provided with bunkers & coal bins. Bunkers are enough capacity to store

the requisite of coal. From bunkers coal is transferred to the boiler grates.

2. Dead storage- stored for future use. Mainly it is for longer period of time, and it is

also mandatory to keep a backup of fuel for specified amount of days depending

on the reputation of the company and its connectivity.There are many forms of

storage some of which are –

1. Stacking the coal in heaps over available open ground areas.

2. As in (I). But placed under cover or alternatively in bunkers.

3. Allocating special areas & surrounding these with high reinforced concerted

retaking walls.

BOILER AND AUXILIARIES

A Boiler or steam generator essentially is a container into which water can be fed

and steam can be taken out at desired pressure, temperature and flow. This calls for

application of heat on the container. For that the boiler should have a facility to burn

a fuel and release the heat. The functions of a boiler thus can be stated as:-

1. To convert chemical energy of the fuel into heat energy

2. To transfer this heat energy to water for evaporation as well to steam for

superheating.

The basic components of Boiler are: -

1. Furnace and Burners

2. Steam and Superheating

a. Low temperature superheater

b. Platen superheater

c. Final superheater

ENERGY CYCLE

The energy cycle in the thermal power plant involves transfer of heat by one method or another – viz radiation , conduction and convection

The boiler may be conveniently divvied into three exchange zones.

THE FURNANCE:

Here the direct radiant heat and high temperature gaseous products of combustion (flue gases).From the burring of fuel is used in the generation of steam from the feed water. The radiant SH are also placed in the radiant a heat zone to provide the steam with medium to high degree of superheat. The heat transfer in the Furnace zone is both by radiation.

COVENTION ZONE

The gases leave the furnace zone and enter the convention zone with reduced temperature. The heat transfer from the flue gases to the steam is through convention mechanism, Superheater and Reheater elements occupy this zone.

THE RECOVERY ZONE:

with relatively cooler flue gases, the heat is abstracted effectively

By cooler fluids such as steam with low superheat and feed water .The LTSH and Economizer are placed in this zone, at the tail –and of the zone the air heaters recover the sensible heat from the flue gases to the extent that the losses to the chimney are minimum and the flue gas temperature is high enough at APH exit to avoid condensation of sulphurdioxide and corration.

SUPERHEATERS:

Low temprature SH (LTSH) is convection mixed flow type with upper &lower banks.

Platen SH is of radiant parallel flow type, hanging from top & supported by their

header.

Final SH is of convection parallel glow type &pendent spaced.

The heat is absorbed in various elements in the following manner

Sensible heat Economizers

Latent heat Evaporation tubes in furnace (WW)

Superheat Pri and Sec SH in convection zone and Radiant

SH (platen) in radiant zone.

Reheat Pri and Sec RH in convection zone and

sometimes partly in radiant zone.

Economiser

It is located below the LPSH in the boiler and above pre heater. It is there to improve

the efficiency of boiler by extracting heat from flue gases to heat water and send it to

boiler drum.

Advantages of Economiser include

1) Fuel economy: – used to save fuel and increase overall efficiency of boiler plant.

2) Reducing size of boiler: – as the feed water is preheated in the economiser and

enter boiler tube at elevated temperature. The heat transfer area required for

evaporation reduced considerably.

Feed Water Heating And Deaeration

The feed water used in the steam boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinning steam turbine. The total feed water consists of recirculated condensate water and purified makeup water. Because the metallic materials it contacts are subject to corrosion at high temperatures and pressures, the makeup water is highly purified before use. A system of water softeners and ion exchange demineralizers produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter.

Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal water storage section).

The water flows through a series of six or seven intermediate feed water heaters, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Typically, the condensate plus the makeup water then flows through a deaerator that removes dissolved air from the water, further purifying and reducing its corrosiveness. The water may be dosed following this point with hydrazine, a chemical that removes the remaining oxygen in the water to below 5 parts per billion .It is also dosed with pH control agents such as ammonia or morpholine to keep the residual acidity low and thus non-corrosive. 

AIR PREHEATER

The heat carried out with the flue gases coming out of economiser are further

utilized for preheating the air before supplying to the combustion chamber. It is a

necessary equipment for supply of hot air for drying the coal in pulverized fuel

systems to facilitate grinding and satisfactory combustion of fuel in the furnace.

APH is tri sector chamber

Schematic diagram of APH

REHEATER

Power plant furnaces may have a reheater section containing tubes heated by hot

flue gases outside the tubes. Exhaust steam from the high pressure turbine is

rerouted to go inside the reheater tubes to pick up more energy to go drive

intermediate or lower pressure turbines.

STEAM TURBINES

Steam turbine generator

Rotor of a modern steam turbine, used in a power station

MOUNTING OF A STEAM TURBINE PRODUCED BY SIEMENS

A modern steam turbine generator installation

Working Principles

High pressure steam is fed to the turbine and passes along the machine axis through multiple rows of alternately fixed and moving blades. From the steam inlet port of the turbine towards the exhaust point, the blades and the turbine cavity are progressively larger to allow for the expansion of the steam.The stationary blades act as nozzles in which the steam expands and emerges at an increased speed but lower pressure. (Bernoulli's conservation of energy principle - Kinetic energy increases as pressure energy falls). As the steam impacts on the moving blades it imparts some of its kinetic energy to the moving blades. 

There are two basic steam turbine types, impulse turbines and reaction turbines, whose blades are designed control the speed, direction and pressure of the steam as is passes through the turbine. 

Steam turbines have been used predominantly as prime mover in all thermal power

stations. The steam turbines are mainly divided into two groups: -

1. Impulse turbine

2. Impulse-reaction turbine

Impulse Turbines

The steam jets are directed at the turbine's bucket shaped rotor blades where the pressure exerted by the jets causes the rotor to rotate and the velocity of the steam to reduce as it imparts its kinetic energy to the blades. The blades in turn change change the direction of flow of the steam however its pressure remains constant as it passes through the rotor blades since the cross section of the chamber between the blades is constant. Impulse turbines are therefore also known as constant pressure turbines.The next series of fixed blades reverses the direction of the steam before it passes to the second row of moving blades.

Reaction Turbines

The rotor blades of the reaction turbine are shaped more like aerofoils, arranged

such that the cross section of the chambers formed between the fixed blades

diminishes from the inlet side towards the exhaust side of the blades. The chambers

between the rotor blades essentially form nozzles so that as the steam progresses

through the chambers its velocity increases while at the same time its pressure

decreases, just as in the nozzles formed by the fixed blades. Thus the pressure

decreases in both the fixed and moving blades. As the steam emerges in a jet from

between the rotor blades, it creates a reactive force on the blades which in turn

creates the turning moment on the turbine rotor, just as in Hero's steam engine.

(Newton's Third Law - For every action there is an equal and opposite reaction

The turbine generator consists of a series of steam turbines interconnected to each

other and a generator on a common shaft. There is a high pressure turbine at one

end, followed by an intermediate pressure turbine, two low pressure turbines, and

the generator. The steam at high temperature (536 ‘c to 540 ‘c) and pressure (140 to

170 kg/cm2) is expanded in the turbine.

CONDENSER

The condenser condenses the steam from the exhaust of the turbine into liquid to

allow it to be pumped. If the condenser can be made cooler, the pressure of the

exhaust steam is reduced and efficiency of the cycle increases. The functions of a

condenser are:-

1) To provide lowest economic heat rejection temperature for steam.

2) To convert exhaust steam to water for reserve thus saving on feed water

requirement.

3) To introduce make up water.

We normally use surface condenser although there is one direct contact condenser

as well. In direct contact type exhaust steam is mixed with directly with D.M cooling

water.

BOILER FEED PUMP

Boiler feed pump is a multi stage pump provided for pumping feed water to

economiser. BFP is the biggest auxiliary equipment after Boiler and Turbine. It

consumes about 4 to 5 % of total electricity generation.

No. of units - 2

COOLING TOWER

The cooling tower is a semi-enclosed device for evaporative cooling of water by

contact with air. The hot water coming out from the condenser is fed to the tower on

the top and allowed to tickle in form of thin sheets or drops. The air flows from

bottom of the tower or perpendicular to the direction of water flow and then exhausts

to the atmosphere after effective cooling.

The cooling towers are of four types: -

1. Natural Draft cooling tower

2. Forced Draft cooling tower

3. Induced Draft cooling tower

4. Balanced Draft cooling tower

FAN or draught system

In a boiler it is essential to supply a controlled amount of air to the furnace for

effective combustion of fuel and to evacuate hot gases formed in the furnace

through the various heat transfer area of the boiler. This can be done by using a

chimney or mechanical device such as fans which acts as pump.

i) Natural draught

When the required flow of air and flue gas through a boiler can be obtained by the

stack (chimney) alone, the system is called natural draught. When the gas within the

stack is hot, its specific weight will be less than the cool air outside; therefore the unit

pressure at the base of stack resulting from weight of the column of hot gas within

the stack will be less than the column of extreme cool air. The difference in the

pressure will cause a flow of gas through opening in base of stack. Also the chimney

is form of nozzle, so the pressure at top is very small and gases flow from high

pressure to low pressure at the top.

ii) Mechanized draught

There are 3 types of mechanized draught systems

1) Forced draught system

2) Induced draught system

3) Balanced draught system

Forced draught: – In this system a fan called Forced draught fan is installed at the

inlet of the boiler. This fan forces the atmospheric air through the boiler furnace and

pushes out the hot gases from the furnace through superheater, reheater,

economiser and air heater to stacks.

Induced draught: – Here a fan called ID fan is provided at the outlet of boiler, that

is, just before the chimney. This fan sucks hot gases from the furnace through the

superheaters, economiser, reheater and discharges gas into the chimney. This

results in the furnace pressure lower than atmosphere and affects the flow of air

from outside to the furnace.

Balanced draught:-In this system both FD fan and ID fan are provided. The FD fan

is utilized to draw control quantity of air from atmosphere and force the same into

furnace. The ID fan sucks the product of combustion from furnace and discharges

into chimney. The point where draught is zero is called balancing point.

ASH HANDLING SYSTEM

The disposal of ash from a large capacity power station is of same importance as

ash is produced in large quantities. Ash handling is a major problem.

i) Manual handling: While barrows are used for this. The ash is collected directly

through the ash outlet door from the boiler into the container from manually.

ii) Mechanical handling: Mechanical equipment is used for ash disposal, mainly

bucket elevator, belt conveyer. Ash generated is 20% in the form of bottom ash and

next 80% through flue gases, so called Fly ash and collected in ESP.

iii) Electrostatic precipitator: From air preheater this flue gases (mixed with ash)

goes to ESP. The precipitator has plate banks (A-F) which are insulated from each

other between which the flue gases are made to pass. The dust particles are ionized

and attracted by charged electrodes. The electrodes are maintained at

60KV.Hammering is done to the plates so that fly ash comes down and collect at the

bottom. The fly ash is dry form is used in cement manufacture.

An electrostatic precipitator is air pollution control device used to separate solid particulate matter from a contaminated air stream. Contaminated air flows into an ESP chamber and is ionized by electron emitting electrodes; also known as the corona chamber. The suspended particles are charged by the electron field and migrate to a collection plate. Accumulate particulate matter is removed from the collection plates at periodic intervals by rapping or hitting the plates with rappers (mallets type hammers). Heavy particles fall to the base of the ESP where hoppers hold the removed particles for disposal.

There are typically three types of ESP units: dry negative corona units, wet negative corona units and wet positive corona units. Dry negative corona units have inherently better voltage/current characteristics, are utilized more frequently and will be the main focus of this website; however, wet negative corona units will be discussed for their applicative differences. The following is a small list of typical industrial applications for ESPs.

Refuse & sewerage sludge dryers and incinerators Coal- and oil-fired boilers, coal driers and coal mills

Production plants for the cement, limestone, gypsum, pulp and paper industry (kilns, mills, driers and coolers)

Electro-metallurgical, chemical, gas and detergent manufacturing plants

SO2, SO3, acid mist and ammonia control (wet ESPs)

ESP Advantages:

ESPs are very efficient (up to 99% efficiency), even for small particals They are generally more ecnomical than other particulat control devices:

Operating costs are reduced by low energy consumption, minimal maintanence requirements and reduced cost on spare parts

Can be designed to handle wet and dry gas compositions for a wide range of gas temperatures

Can handle large volumes of gas flow with low pressure drop

ESP Disadvantages:

High intial capital costs Dry ESPs can only control particulate emissions, not gas compositon

emisions

Once installed, ESPs take up a lot of space and cannot be easily redesigned

May not work properly on high electrical resistive particals

ESP Operation and Basic Design

A dry negative corona ESP, is designed to generate and disperse negative electrons through suspended electrodes (wires). Excess electrons migrate from the corona toward a positve (grounded) collection plate. Electrons are readily adsorbed onto passing electronegative gas molecules and particals. As the electrons are accumulated on the dust particles they are transported and deposited on to the collection plate. Below is a typical dry gas flow schematic of an ESP.

As dust particles collect on the grounded plate, they transfer their charge thus completing the electrical circuit. Particles are retained on the plate by friction and the constant collection and transfer of particle electrons. As the dust layer increases, electron conduction is dampened by the resistance. The measure of resistance is known as resistivity. Resistivity has a strong influence on particle collection efficiency..

Rapping System

To improve collection efficiency and ensure proper functional use of the precipitator, a rapping system is applied to the collection plates and electrodes to dislodge the collected dust layer. A falling weight or fixed rotating hammer raps the collection plates, causing a vibration that knocks off the dust layer. The dust drops into steeply sloped hoppers, which are periodically emptied for disposal. The collection plates should be smooth enough to prevent frictional resistance during rapping removal and have sufficient oscillation behavior to ensure particle dislocation across the length of the plate. Each plate is rapped individually to minimize the escape of dust particles from the system. Rapping intervals are dependent upon gas flow composition, corona voltage, and precipitator size.

ESP Sizing

The volumetric flow rate and gas stream composition are the two important empirical factors for determining a precipitator design. The velocity component, other wise known as the migration velocity, is the dominate factor which helps to determine the dust removal efficiency. The following parameters can also effect the migration velocity component:

Particle chemical composition and electrical resistivity Gas stream humidity

Gas stream temperature

Particle size distribution (Within the range of 0.01 mm to 100 mm)

Fly ash content at the precipitator inlet

Fly ash content at the precipitator outlet

The inlet gas stream typically has a high temperature and may require pretreatment. Flue gas conditioning should be considered to facilitate particle collection. By spraying water into the flue gas, the fly ash is cooled to an efficient precipitator operating temperature. In addition, this increases the gas humidity which lowers the dust resistivity. Particle resistivity is material, temperature and humidity dependent and should be thoroughly understood for proper ESP design.

DEMINIRILASTION PLANT

In a demineralisation plant, salts dissolved in water are removed by ion exchange processes. The exchange products react to water. Regeneration of the ion exchange resins is conducted with acid and lye.

Picture: Demineralisation plant, consisting of a cation exchanger, a degasser, and an anion exchanger. With regeneration tanks for acid and lye.

Design Variants

Connected as cation-shower-anion for most applications at medium to high flow capacity

Connected as cation-anion, in case of low carbonate hardness or low flow capacity

With a down-stream mixed bed filter, for reaching a very low residual salt content

Regeneration upstream, for example floating bed or upcore, or downstream.

Process Description

Salts dissolved in water are dissociated, meaning they are seperated into positively charged cations and negatively charged anions. For example, when dissolved in water, calcium hydrocarbonate (Ca(HCO3)2) is dissociated into the cation calcium (Ca2+) and the anion hydrogen carbonate (HCO3

-).

In a demineralisation plant, those salts dissolved in water are removed by an ion exchange process. For this purpose, the to be demineralised water flows through vessels filled with ion exchange resin. First through a cation exchanger filled with acidic ion exchange resin, then through an anion exchanger filled with alkaline ion exchange resins. The acidic ion exchange resin in the cation exchanger has hydrogen ions (H+) attached to it, while hydroxide ions (HO-) are attached to the alkaline resin in the anion exchanger.

While flowing through the acidic resin bed in the cation exchanger, dissolved kations, like calcium (Ca2+), magnesium (Mg2+) or sodium (Na+), are exchanged for the attached hydrogen ions. This happens as follows, with the examples of sodium chloride and calcium hydrogen carbonate:

NaCl + H [resin] → HCl + Na [resin]Ca(HCO3)2 + 2H [resin] → 2H2CaCO3 +Ca [resin]

The reaction products in these examples are hydrochloric acid (HCl) and carbonic acid (H2CaCO3). A part of the carbonic acid exists in free form, meaning as gas molecule, while another part is bound, meaning it exists as dissociated ions. The

free carbonic acid can be removed from the water with a degasser. By doing so, load is taken from the downstream anion exchanger.

The ion exchange process in the anion exchanger is similar to that in the cation exchanger. Anions like for example hydrocarbonate (HCO3

-), sulphate (SO42-) or

chloride (Cl-) are exchanged for hydroxide ions. This happens as follows, with the example of chloride as anion of hydrochloric acid:

HCl + HO [resin] → H2O + Cl [resin]

The product of this reaction is water (H2O).

In case of depletion, the ion exchange resins are regenerated. The acidic resin of the cation exchanger is regenerated with hydrochlorid acid (HCl), the alkaline resin of the anion exchanger is regenerated with caustic soda (NaOH). The regeneration process for example proceeds as follows:

2HCl + Ca [resin] → 2H [resin] + CaCl2NaOH + Cl [resin] → HO [resin] + NaCl

In additions to salts, like for example calcium chloride (CaCl2) and sodium chloride (NaCl), the regeneration effluent often also contains excess acid or lye. Before being discharged into the sewer system, acidic or alkaline waste water needs to be neutralised.

Overview

A mixed bed filter serves for fine purification of demineralised water, or for demineralisation of smaller amounts of water. This is achieved by ion exchange, with the resin bed consisting of a mixture of acidic and alkaline resins. Regeneration is conducted with acid and lye.

Picture: Mixed bed filter. To the left frontal view of valve and piping arrangement. To the right schematic view during regeneration.

Design Variants

Standard design for small to large flow rates. Not regenerative, with exchangable resin cartridges, for smallest flow rates.

Process Description

The ion exchange process in a mixed bed filter does chemically work as described under demineralisation. However, the mixed bed filter is filled with both strongly acidic and strongly alkaline ion exchange resin at the same time. During operation, the different resin types are mixed with eached other. This basically works like a series of many small connected cation and anion exchangers, and thus results in a very high demineralisation effect.

For regeneration, the resins are first seperated with water, by making use of their different specific weights. The strongly acidic cation exchange resin is regenerated upstream with acid, the strongly alkaline anion exchange resin is regenerated

downstream with acid. The regeneration effluent is drained from the transitional region between the two resin types. Often, the effluent contains an excess of acid or lye, and accordingly needs to be neutralised before being discharged into the sewer system. After regeneration, air is used to intermix the two resin types with each other again.

Compared to other ion exchange processes, the amount of excess chemicals required for regeneration of a mixed bed filter is significantly higher. That is why a mixed bed filter is usually only used for polishing, for example of already demineralised water or condensante, with an accordingly long service life between regenerations.

Generator

Generator or Alternator is the electrical end of a turbo-generator set. It is generally

known as the piece of equipment that converts the mechanical energy of turbine into

electricity. The generation of electricity is based on the principle of electromagnetic

induction.

Advantages of coal based thermal Power Plant

They can respond to rapidly changing loads without difficulty

A portion of the steam generated can be used as a process steam in different

industries

Steam engines and turbines can work under 25 % of overload continuously

Fuel used is cheaper

Cheaper in production cost in comparison with that of diesel power stations