Thermal Power Plant
(P.T.P.P. Parichha, Jhansi)
Six Weeks Industrial training in partial fulfillment for the
Bachelors of Technology
Submitted by :
Boiler Maintenance Division (BMD -ii)
SHREE GANESH Group of Institutions
Patiala-Nabha Road, Village Rakhra, Patiala
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
“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.
PARICHHA THERMAL POWER PLANT
INTRODUCTION OF THERMAL POWER PLANT
TECHNICAL DATA OF 110MW PLANT
MAIN PARTS OF POWER PLANT
BOWL MILL RAW COAL FEEDERAND ITS SPECIFICATION
FANS – PRIMARY AIR FAN, FORCE DRAUGHT FAN, INDUCED
DRAUGHT FAN WITH SPECIFICATION AND WORKING
HEATER – ECONOMIZER, PLATEN SH,LTSH,FINAL SH,
By Gagandeep Singh
Typical diagram of a coal-fired thermal power station
1. Cooling Tower
13. Feed water heater Hr
2. Cooling Water Pump .
14. Coal Conveyor
3. Transmission Line (3-Phase)
15. Coal Pulverizer
4. Step-Up Transformer (3-Phase)
16 Turbine Coal Hopper
5. Electrical Generator (3-Phase)
17 Boiler Steam Drum
6. Low Pressure Steam
18. Bottom Ash Hopper
7. Condensate Pump .
19. Super heater
8. Surface Condenser
20. Forced Draught (Draft) Fan
9. Intermediate Pressure Steam Turbine 21. Combustion Air Intake
10. Steam Control Valve
23. Air Preheater
12.High Pressure Steam Turbine.
26. Flue Gas Stack
26.Induced Draught (Draft) Fan .
TECHNICAL DATA OF 110MW PLANT
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.
Superheated outlet temp.
Steam pressure just before the stop valve
Steam temp. Just before stop valve
Pressure of steam
Temperature of steam before MP casing
Temperature of cooling water
Weight of rotor
Turing gear speed
Consumption make up
On the bank of the Betwa river in the Bundelkhand region of the district
On the Jhansi-Kanpur national highway no.25 near parichha railway station
Instillation capacity of unit Ist and IInd is 220 mw and for unit unit IIIrd & IVth
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 water source from Parichha reservoir, formed by upstream reservoir
Cooling water temp.- 30oc.
Water treatment plant capacity - 30tonnes/hour.
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
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
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
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
Fusion Welded Panels
Total Heating Surface
Higher Heating Value
Size Of Coal To Mill(mm)
Ph At 250
Specific Conductivity At 250
Total Silica (Sio2)
Ph At 25oc
Specific Electrical Conductivity At 25oc
Total Dissolved Solids
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
Coal based thermal power plant works on the principal of Modified Rankine Cycle.
Modified Rankine cycle
Components of Coal Fired Thermal Power Station:
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, they
are 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;
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.
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
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
The basic components of Boiler are: 1. Furnace and Burners
2. Steam and Superheating
a. Low temperature superheater
b. Platen superheater
c. Final superheater
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.
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.
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.
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
Final SH is of convection parallel glow type &pendent spaced.
The heat is absorbed in various elements in the following manner
Evaporation tubes in furnace (WW)
Pri and Sec SH in convection zone and Radiant
SH (platen) in radiant zone.
Pri and Sec RH in convection zone and
sometimes partly in radiant zone.
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
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.
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
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 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
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
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
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
The next series of fixed blades reverses the direction of the steam before it passes
to the second row of moving blades.
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.
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
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
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
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)
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
Can handle large volumes of gas flow with low pressure drop
High intial capital costs
Dry ESPs can only control particulate emissions, not gas compositon
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
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.
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
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.
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.
Connected as cation-shower-anion for most applications at medium to high
Connected as cation-anion, in case of low carbonate hardness or low flow
With a down-stream mixed bed filter, for reaching a very low residual salt
Regeneration upstream, for example floating bed or upcore, or downstream.
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(HCO 3)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:
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 (HCO 3-), 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:
NaOH + Cl [resin] → HO [resin] + NaCl
In additions to salts, like for example calcium chloride (CaCl 2) 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
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.
Standard design for small to large flow rates.
Not regenerative, with exchangable resin cartridges, for smallest flow rates.
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
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
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
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
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