Unit1 COALBASEDPOWER PLANTS

ME 6701
POWER PLANT ENGINEERING
UNIT I COAL BASED THERMAL POWER
PLANTS
UNIT 2 : DIESEL, GAS TURBINE AND
COMBINED CYCLE POWER PLANTS
UNIT 3 : NUCLEAR POWER PLANTS
UNIT 4 : POWER FROM RENEWABLE
ENERGY
UNIT 5 : ENERGY, ECONOMIC AND
ENVIRONMENTAL ISSUES OF POWER
PLANTS
1
S.PALANIVEL ASSOCIATE PROF./MECH ENGG
KAMARAJ COLLEGE OF ENGG. & TECH. VIRUDHUNAGAR(Near)

COURSE OBJECTIVE
• Providing an overview of Power
Plants and detailing the role of
Mechanical Engineers in their
operation and maintenance.
2

UNIT 1 : POWER PLANT ENGG.
• ELECTRICITY
• ENERGY
• EASY TO PRODUCE,
• TRANSPORT,
• USE & CONTROL
• MOSTLY TERMINAL FORM OF ENERGY FOR
TRANSMISSION & DISTRIBUTION
• IT HAS TO BE CONSUMED AT THE MOMENT
OF GENERATION
3

TYPES OF POWER PLANTS
• THERMAL
• HUDRAULIC
• GAS TURBINE
• NUCLEAR
• GEO THERMAL
4

BASIC FLOW DIAGRAM OF POWER PLANT
5S.PALANIVEL ASSOCIATE PROF./MECH ENGG

6

POWER PLANT CIRCUITS
• STEAM CIRCUIT
• CONDENSATE & FEED WATER CIRCUIT
• COAL CIRCUIT
• AIR CIRCUIT
• ASH CIRCUIT
• CIRCULATING WATER CIRCUIT
• D.M. WATER CIRCUIT
7

STEAM CIRCUIT
• Steam from Boiler drum ,
• further heated in super heaters,
• fed into HP Turbine, outlet of HP turbine
goes to
• Reheaters, Temperature of steam increased
• fed into Intermediate pressure Turbine
• then to LP Turbine
• certain amount of stem extracted and used
to preheat Feedwater
8

CONDENSATE & FEED WATER CIRCUIT
• Exhaust of LP turbine condensed by circulating water
becomes condensate
• Condensate heated in LP heaters
• Preheated Condensate, further heated and its
dissolved oxygen are liberated at deaerator thro
deaeration
• Feed water stored in deaerator pumped by Boiler
feed water pumps to Boiler drum thro HP heaters and
Economisers.
• From condenser till reaching Boiler drum it is kept as
water by rising temp & pressure of water.
9

COAL CIRCUIT
• Coal received thro rail/ship/Mines are stored in yard
• Coal from yard transported to Coal handling
Receiving Bunkers ( capacity of minimum 2days
storage)
• Coal from receiving bunkers crushed to a specified
size say upto 80 mm by crushers and fed into Boiler
Bunkers. To avoid entry of iron material, magnetic
separators are used.
• From Boiler bunkers, coal fed into individual mills by
boiler feeders, Mills powdered the coal as minute
particles, pulversied coal fed into Furnace.
• By varying the speed of the boiler feeders, coal input
to Boiler is varied. 10

AIR CIRCUIT
• Air required for firing is drawn from
atmosphere thro forced draught fans.
• Drawn air is preheated in Air preheaters,
preheated air is used for many purposes.
• Combustible gas called flue gases are sucked
by Induced draught fans and let out to
atmosphere thro high rise stack after passing
thro Electrostatic Precipitators.
• Temp. of outlet Air is kept above 140 deg. C
to avoid cold end corrosion.
11

ASH CIRCUIT
 There are two types of ash generated in Boiler
as Bottom ash and fly ash
 Unburnt carbon materials are collected at the
bottom of the furnace as bottom ash in slag
conveyors and continuously removed thro scrapper
conveyors. Scrapped bottom ash are collected in
trucks and disposed off.
 Fly ash coming out with flue gases are collected at
electro static precipators. Fly ash are collected at
Ash vessel at the bottom of ESP and transported to
Ash Silo thro pneumatic conveying.
 Ash from Ash silo are disposed off by trucks.
12

CIRCULATING WATER CIRCUIT
• Steam at the exhaust of the LP turbine is condensed by circulating
water.
• Cold circulating water pumped (or) drawn from sea /river into
Condenser as inlet to condense the steam
• After condensing the steam , the cold water gets heated and the
hot circulating water is taken from condenser outlet to Cooling
tower
• Hot circulating water will then enter into cooling tower and gets
cooled by air travelling in opposite direction to water flow. Cooled
water gets collected at the cooling tower basin.
• Cold water pumped from cooling tower basin to condenser
• In places where circulating water is taken from sea or river, hot
water either sent back to sea or river if it is permitted by authorities
or cooled at the cooling tower.
• Certain quantity of water is added at the basin to make up
evaporation losses in cooling tower 13

DM WATER CIRCUIT
• Raw water taken from river or from bore water is firstly
removed/ filtered of suspended solids /sediments
• Filtered water will be processed in ION EXCHANGERS to
remove unwanted salts
• D.M. water will be made either thro Ion exchange process or
distillation processes or reverse osmosis (RO) processes.
• D.M water thus produced will be kept stored in condensate
storage tanks.
• From condensate storage tanks, DM water is added as make
up thro DM water make up pumps while the plant is running
by taking signals from condenser level.
• While starting up of unit or for filling up the Boiler , it can be
done by a dedicated line from DM make up water pumps .
14

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20

Induced Draft Cooling Tower
• Air will be sucked into Cooling Tower Cells thro Fans fixed at
the top of the cell.
• Hot Water will be admitted below the fan in the Cooling
tower thro uprisers.
• Hot Water will be made to fall as fine water droplets nozzles.
• Hot Water will fall from top to bottom and air will travel from
bottom to top, cooled water will get collected at the Cooling
Tower basin.
• Drift eliminators are fixed below the fan and above the hot
water channel to avoid of carrying over of water droplets
• Fans are made of FRB blades and run by electric motors
S.PALANIVEL ASSOCIATE PROF./MECH
ENGG KAMARAJ COLLEGE OF ENGG. &
TECH. VIRUDHUNAGAR(Near)
22

23
Natural
Draught
Cooling
Tower

24

Natural Draft Cooling Tower
• Air will be sucked into Cooling Tower due tonatural draft
• Hot Water will be admitted at the throat of the Cooling
tower thro uprisers.
• Hot Water will be made to fall as fine water droplets thro
nozzles falling on splashers placed .
• Hot Water will fall from top to bottom and air will travel
from bottom to top, cooled water will get collected at the
Cooling Tower basin.
• Drift eliminators are fixed above the hot water channel to
avoid of carrying over of water droplets
25

• Range of Cooling :Difference between hot
water (Condenser outlet) and Cold water
(Condenser inlet).Desired RC is 10 deg.of
Celsius
• Approach : Design temp. difference between
coldwater at Cooling tower and wet bulb
temp. Desired approach is below6deg.Celsius
26

Draught System
• A fuel-heated boiler must provide air to
oxidize its fuel.
• Early boilers provided this stream of air, or
draught, through the natural action of
convection in a chimney connected to the
exhaust of the combustion chamber.
• Since the heated flue gas is less dense than
the ambient air surrounding the boiler, the
flue gas rises in the chimney, pulling denser,
fresh air into the combustion chamber.
27

• Most modern boilers depend on mechanical
draught rather than natural draught.
• This is because natural draught is subject to
outside air conditions and temperature of
flue gases leaving the furnace, as well as the
chimney height.
• All these factors make proper draught hard
to attain and therefore make mechanical
draught equipment much more reliable and
economical.
28

• Types of draught can also be divided into
induced draught, where exhaust gases are
pulled out of the boiler;
• forced draught, where fresh air is pushed
into the boiler; and balanced draught, where
both effects are employed.
• Natural draught through the use of a
chimney is a type of induced draught;
• mechanical draught can be induced, forced
or balanced.
29

• There are two types of mechanical induced
draught.
• The first is through use of a steam jet. The
steam jet oriented in the direction of flue gas
flow induces flue gases into the stack and
allows for a greater flue gas velocity
increasing the overall draught in the furnace.
• This method was common on steam driven
locomotives which could not have tall
chimneys.
30

• The second method is by simply using an
induced draught fan (ID fan) which removes
flue gases from the furnace and forces the
exhaust gas up the stack.
• Almost all induced draught furnaces operate
with a slightly negative pressure.
31

• Mechanical forced draught is provided by
means of a fan forcing air into the
combustion chamber.
• Air is often passed through an air heater;
which, as the name suggests, heats the air
going into the furnace in order to increase
the overall efficiency of the boiler.
• Dampers are used to control the quantity of
air admitted to the furnace. Forced draught
furnaces usually have a positive pressure.
32

• Balanced draught is obtained through use of
both induced and forced draught.
• This is more common with larger boilers
where the flue gases have to travel a long
distance through many boiler passes.
• The induced draught fan works in
conjunction with the forced draught fan
allowing the furnace pressure to be
maintained slightly below atmospheric.
33

• The method of firing industrial steam boiler is
such that, the system may be easily handled
and also, operation and maintenance should
be minimum. There are mainly two methods
of firing steam boiler with coal as fuel. One is
solid fuel firing boiler other is pulverized fuel
firing
34

• There are two general types of boilers: ''fire-
tube'' and ''water-tube''. Boilers are classified
as "high-pressure" or "low-pressure" and
"steam boiler" or "hot water boiler." Boilers
that operate higher than 15 psig are called
"high-pressure" boilers.
35

• Pulverised firing is achieved by powdering the
fuel into minute particles (in microns)bymeans
of pulversing mills
• Mills are of hammerType, Beater type or ball
Mills. In each case Fuel is crashed or
powdered and fed into the Boilers.
• Pulversied fuel will get total contact with fire
and firing will be total
36

37

Fluidised bed Combustion Boiler
38

• Subcritical – up to 705 degrees Fahrenheit (374°C)
and 3,208 psi (the critical point of water)
• Supercritical – up to the 1,000–1,050 degrees
Fahrenheit range (538–565°C); turbine speed
increases dramatically, requires advanced materials
• Ultra-supercritical – up to 1,400 degrees Fahrenheit
and pressure levels of 5,000 psi. (760°C; additional
innovations, not specified, would allow even more
efficiency)
39

Super CriticalBoiler
40

SFEE Steady Flow Energy Equation
SFEE for Boiler , h4 + Q 1 = h1
Q 1 = h1 - h4
SFEE for Turbine h 1 = WT + h2
SFEE for Condenser h 2 = Q2 + h3
SFEE for Pump h 3 + WP= h4 41

Efficiency of Rankine Cycle
= W (Net) = (WT–WP)/Q1
Q1
Heat rate = Q1/(WT–WP)
Heat transfer to water in Steam Generator in 3 regimes :
1. Water heated in Economizer using sensible heat in
liquid phase from state 4 to state 5
2. In Evaporator, there is a phase change as water into
steam from state 5 to state 6 by absorbing latent heat
3. Saturated vapor at state 6 is further heated at const.
pressure in super heater to state 1
42

• As the Live steam pressure increases , the
latent heat decreases , heat absorbed in the
evaporator decreases and the fraction heat
absorbed in the super heater increases.
• In High pressure Boilers, more than 40 % of
total heat absorbed in super Heaters.
• In Boilers operating above critical pressure
there is no Evaporator (Boiler Drum). There is
a transition zone where all the liquid on being
heated suddenly flashes into vapor.
43

• Liquid leaving the pump (Boiler Feed Pump –
BFP) > Turbine Inlet Pressure
• Steam generator pressure > Turbine Inlet
pressure
• Too small pinch point temp difference causes
increase in surface area, large expensive more
efficient
• Large pinch point temp difference decrease in
surface area, inexpensive but with a reduced
efficiency
44

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50

Effects of Super Heat
• Increase in the Super heat
at constant pressure
increases the mean temp.
of heat addition , hence the
Cycle efficiency increases.
• Increase in super heat, the
expansion line of steam in
the turbine shifts to the
right, as a result the quality
of steam of turbine exhaust
improves ie. Dryness
fraction improves which
increases the performance
of Turbine.
1.Instead of T1 if the steam is further
super heated to T1’ – heat addition (T1’-
t1) & work done increased by 2-1-1’-2’
2. More over the expansion line 1-2 is
shifted to right side as 1’-2’ , hence the
dryness fraction of steam at Turb.
Exhaust improves , hence the
performance of turbine.
51

Effects of Inlet Pressure
• Due to increase in pressure to p2,
ideal expansion line of steam shifts
to left and the moisture content of
steam at exhaust stage of turbine
increases because x6< x2
• Steam with high moisture content
will erode the edges of last stage
blades.
• Hence the maximum moisture
content in the steam should not
exceed 12% or the quality of steam
should not falll below 88 %.
Max. temp. of stem is fixed on
metallurgical considerations.. It is
called metallurgical limit.
When the steam inlet pr. Increases
from p1 to p2, the mean temp. of heat
addition increases since Tm1
between stage 7 and 5 is higher than
stage 1 and 4, but inlet pr. Increases
to p2 from p1. 52

Effects of Reheat
In order to limit the quality of steam
at Turbine exhaust above 0.88,
reheating of steam has to be
adopted.
All the steam after partial expansion
is brought back to Boiler , reheated
by combustion gases and then fed
back to turbine for further expansion
53

• In the reheat cycle the
expansion of steam from
initial state 1 to the
condenser is carried out in
one or more steps
depending upon the
number of reheats used.
• In the first step, the steam
expands in HP turbine into
some intermediate
pressure (process 1-2 S).
• Steam is reheated to super
heater temp. of HP turbine
inlet at const. pressure
(process 2 S -3)
and the remaining expansion of
steam is carried out in LP Turbine
(process 3-4 S).
• Had pressure p1 has been
without reheat the cycle would
be 1- 4’S - 5 -6Swith lot of
moisture at turb. Exhaust. Having
steam quality of x4’s.. With the use
of reheat . The area under 2s -3- 4S
-4’S is added , net out put
increases since (h 3 -h4S ) is greater
than
• (h 2s -h4’S ). Reheating also
improves the quality of steam at
turb. exhaust from x 4’s to x 4s
54

55

Effects of Regeneration
• Increases the Cycle Efficiency
• Reduces heat rate and thus operating cost.
• Increases Steam flow rate (Bigger Boiler)
• Reduces the flow to condenser (Small
Condenser)
• Size of turbine small
• If there is no change of Boiler output, Turbine
output drops.
56

DEAERATOR
• Deaeration is the
mechanical removal of
dissolved gases from the
boiler feedwater. There are
three principles that must
be met in the design of any
deaerator. ... The incoming
feedwater must be heated
to the full saturation
temperature,
corresponding to the steam
pressure maintained inside
the deaerator .
57

• A deaerator is a device that is widely used for the removal of
oxygen and other dissolved gases from the feedwater to
steam-generating boilers. In particular, dissolved oxygen in
boiler feedwater will cause serious corrosion damage in
steam systems by attaching to the walls of metal piping and
other metallic equipment and forming oxides (rust). Dissolved
carbon dioxide combines with water to form carbonic acid
that causes further corrosion. Most deaerators are designed
to remove oxygen down to levels of 7 ppb by weight
(0.005 cm³/L) or less as well as essentially eliminating carbon
dioxide.
• cylindrical vessel which serves as both the deaeration section
and the storage tank for boiler feedwater.
58

• There are two basic types of deaerators, the Termochimica spray&tray-type
and the Stork spray-type:[2][3][4][5][6]
• The Termochimica spray&tray-type (also called the cascade-type) includes a
vertical or horizontal domed deaeration section mounted on top of a
horizontal cylindrical vessel which serves as the deaerated boiler feedwater
storage tank.
• The Stork spray-type consists only of a horizontal (or vertical)
• Deaerator Working Principle
• Water is heated close to saturation temperature with a minimum pressure
drop and minimum vent. This ensures the best thermal operating efficiency.
Deaeration is done by spraying the boiler feedwater over multiple layers of
trays designed to provide large contact area between the liquid surface and
deaeration steam. This scrubbing steam is fed from the bottom of the
deaerator. When it makes contact with boiler feedwater, it heats up to
saturation temperature and dissolved gases are released from the
feedwater through the vent valve. The treated water falls to the storage
tank below the deaerator.
59

Spray &Tray type Deaerator
• The typical spray&tray-type
deaerator in Figure has a vertical
domed deaeration section mounted
above a horizontal boiler feedwater
storage vessel.
• Boiler feedwater enters the vertical
deaeration section through spray
valves above the perforated trays
and then flows downward through
the perforations.
• Low-pressure deaeration steam
enters below the perforated trays
and flows upward through the
perforations.
60

• Combined action of spray valves & trays guarantees very
high performance (as confirmed by HEI std ) because of
longer contact time between steam and water. Some
designs use various types of packed bed, rather than
perforated trays, to provide good contact and mixing
between the steam and the boiler feed water.
• The steam strips the dissolved gas from the boiler feedwater
and exits via the vent valve at the top of the domed section.
• The vent line usually includes a valve and just enough steam
is allowed to escape with the vented gases to provide a
small visible telltale plume of steam.
61

• The deaerated water flows down into the horizontal storage
vessel from where it is pumped to the steam generating
boiler system. Low-pressure heating steam, which enters the
horizontal vessel through a sparger pipe in the bottom of
the vessel, is provided to keep the stored boiler feedwater
warm. External insulation of the vessel is typically provided
to minimize heat loss
• Main functions of Deaerator are
1. Removes dissolved gases thro deaeration
2. Stores water in between Condenser and BoilerDrum
3. It preheats feed water
To provide positive suction to Boiler Feed pump ,deaerators
are placed at a higher elevation
62

Stork Spray-type deaerator
• The typical spray-type
deaerator is a horizontal
vessel which has a
preheating section (E) and a
deaeration section (F).
• The two sections are
separated by a baffle (C).
Low-pressure steam enters
the vessel through a sparger
in the bottom of the vessel.
• The boiler feedwater is
sprayed into section (E)
where it is preheated by the
rising steam from the
sparger. S.PALANIVEL ASSOCIATE PROF./MECH
63

Stork Spray-type deaerator
• The purpose of the feedwater spray nozzle (A) and the
preheat section is to heat the boiler feedwater to its
saturation temperature to facilitate stripping out the
dissolved gases in the following deaeration section.
• The preheated feedwater then flows into the deaeration
section (F), where it is deaerated by the steam rising from the
sparger system. The gases stripped out of the water exit via
the vent at the top of the vessel
• the air vent line usually includes a valve and just enough
steam is allowed to escape with the vented gases to provide a
small and visible telltale plume of steam.
• The deaerated boiler feedwater is pumped from the bottom
of the vessel to the steam generating boiler system by Boiler
feed pumps
64

Feed water Treatment
• Ammonia and hydrazine are use in LP dosing.where it was
dosed in low pressure side before BFP or in dearator. ... where
Ammonia used for boosting PH in condensate(feed water). feed
water has to alkalized to PH of 9 or little high(high alkalized
solution causes caustic corrosion), to reduce oxidation and to
support the formation of a stable layer of Magnetite on water
side surface of boiler, protecting metal from further corrosion.
NH3(aq) + H2O(1) > NH4 + 2 H2O
• where Hydrazine is used as scavenging oxygen in condensate to
avoid corrosion, so we de-oxydised by using hydrazine.
N2H4 + O2 > N2 + H2O
• It also helpful as it was react with Fe2O3 in the boiler water to
form a passive magnitude film on the boiler surface preventing
form the corrosion.
65

• Tri sodium phosphate is used as HP dosing it was dosed in
boiler drum
• Tri sodium phosphate is used as PH booster and help react
with salts like Mg++ or Ca++ form the sludge in boiler drum
it was removed by Continue Blow Down(CBD).
• Tri sodium phosphate was most effective at 270c to 340c
only. other wise it cause Phosphate hide out. That’s why
Phosphate doing is done at Boiler drum
• Na3PO4 + H2O > Na2HPO4 + NaOH
• Na3PO4 + 3 CaSO4 > 3NaSO4 + Ca3(PO4)2
• Na3PO4 + 3MgSO4 > 3NaSO4 +Mg3(PO4)2
66

Condenser
• A surface condenser is a
commonly used term for a
water-cooled shell and
tube heat exchanger
installed on the exhaust
steam from a steam
turbine in thermal power
stations. These condensers
are heat exchangers which
convert steam from its
gaseous to its liquid state
at a pressure below
atmospheric pressure.
67

Condenser
• A tank or reservoir in which
hot water is collected before
being recirculated, especially
condensed steam about to be
returned to a boiler. Origin of
hot well.
• Cooling water called
circulating water taken either
from sea or cooling tower
basin made thro tubes thro
inlet manifold and hot water
after condensing steam gets
collected at the outlet
manifold of Condenser,
sent back to sea or Cooling
Towers for further cooling
• Cooling water is pumped
into condenser from Cooling
water basin or from sea
• Where cooling water is in
short supply, an air-cooled
condenser is often used. An
air-cooled condenser is
however, significantly more
expensive and cannot achieve
as low a steam turbine
exhaust pressure (and
temperature) as a water-
cooled surface condenser.S.PALANIVEL ASSOCIATE PROF./MECH
68

Condenser
• By condensing the exhaust
steam of a turbine at a
pressure below
atmospheric pressure, the
steam pressure drop
between the inlet and
exhaust of the turbine is
increased, which increases
the amount of heat
available for conversion to
mechanical power. Most of
the heat liberated due to
condensation of the
exhaust steam is carried
away
• by the cooling medium
(water or air) used by the
surface condenser
69

• SHELL
• The shell is the condenser's outermost body and contains the heat
exchanger tubes. The shell is fabricated from carbon steel plates
and is stiffened as needed to provide rigidity for the shell. When
required by the selected design, intermediate plates are installed
to serve as baffle plates that provide the desired flow path of the
condensing steam. The plates also provide support that help
prevent sagging of long tube lengths.
• At the bottom of the shell, where the condensate collects, an
outlet is installed. In some designs, a sump (often referred to as
the hotwell) is provided. Condensate is pumped from the outlet or
the hotwell for reuse as boiler feedwater.
• For most water-cooled surface condensers, the shell is under
vacuum during normal operating conditions.
70

Condenser
• Tube Sheets
• At each end of the shell, a sheet of sufficient thickness usually
made of stainless steel is provided, with holes for the tubes to be
inserted and rolled. The inlet end of each tube is also bellmouthed
for streamlined entry of water. This is to avoid eddies at the inlet
of each tube giving rise to erosion, and to reduce flow friction.
Some makers also recommend plastic inserts at the entry of tubes
to avoid eddies eroding the inlet end. In smaller units some
manufacturers use ferrules to seal the tube ends instead of rolling.
To take care of length wise expansion of tubes some designs have
expansion joint between the shell and the tube sheet allowing the
latter to move longitudinally. In smaller units some sag is given to
the tubes to take care of tube expansion with both end water
boxes fixed rigidly to the shell.
71

Condenser
• Condenser Tubes
• Generally the tubes are made of stainless steel, copper alloys such as
brass or bronze, cupro nickel, or titanium depending on several selection
criteria. The use of copper bearing alloys such as brass or cupro nickel is
rare in new plants, due to environmental concerns of toxic copper
alloys. Also depending on the steam cycle water treatment for the
boiler, it may be desirable to avoid tube materials containing copper.
Titanium condenser tubes are usually the best technical choice, however
the use of titanium condenser tubes has been virtually eliminated by the
sharp increases in the costs for this material. The tube lengths range to
about 85 ft (26 m) for modern power plants, depending on the size of
the condenser. The size chosen is based on transportability from the
manufacturers’ site and ease of erection at the installation site. The
outer diameter of condenser tubes typically ranges from 3/4 inch to 1-
1/4 inch, based on condenser cooling water friction considerations and
overall condenser size.
72

Condenser
• The tube sheet at each end with tube ends rolled, for each end of the
condenser is closed by a fabricated box cover known as a waterbox, with
flanged connection to the tube sheet or condenser shell. The waterbox
is usually provided with man holes on hinged covers to allow inspection
and cleaning.
• These waterboxes on inlet side will also have flanged connections for
cooling water inlet butterfly valves, small vent pipe with hand valve for
air venting at higher level, and hand operated drain valve at bottom to
drain the waterbox for maintenance. Similarly on the outlet waterbox
the cooling water connection will have large flanges, butterfly valves,
vent connection also at higher level and drain connections at lower
level. Similarly thermometer pockets are located at inlet and outlet
pipes for local measurements of cooling water temperature.
• In smaller units, some manufacturers make the condenser shell as well
as waterboxes of cast iron.
73

74

EFFICIENCIES IN A STEAM POWER PLANT
• A STEAM POWER PLANT IS A BULK ENERGY CONVERTER
FROM FUEL TO ELECTRICITY
• OVERALL EFFI. = ȠOA= POWER AT GEN. TERMINAL
RATE OF ENERGY RELEASE OF FUEL
= MWe X 103
(w
f = FUEL RATE
w
fX C.V. C.V.= CALORIFIC VALUE)
EFFICI. OF BOILER = ȠBr = RATE OF ENERGY ABSORPTION BY WATER TO FORM STEAM
RATE OF BY ENERGY RELEASE FUEL
= wS (h1 - h4 ) (w
s = STEAM RATE)
w
fX C.V
EFFICI. OF CYCLE = ȠCY = (h1 - h2 ) (PUMP WORK HAS BEEN NEGLECTED)
(h1 - h4 )
EFFICI. OF TURBINE = ȠTUR.mech. = BRAKE OUTPUT OF TURBINE = BRAKE OUTPUT 75

EFFICI. OF GENERATOR = ȠGEN.. = ELEC. OUTPUT AT GENERATOR= MWe X 103
BRAKE OUTPUT OF TURBINE BRAKEOUTPUT IN K.We
ȠOA = ȠBr X ȠCYX ȠTUR.mechX ȠGEN
=wS (h1 - h4 ) X wS (h1 - h2 ) X BRAKE OUTPUT X MWe X 103
w
fX C.V wS (h1 - h4 ) wS (h1 - h2 ) BRAKE OUTPUT
ȠOA = MWe X 103
= ȠBr X ȠCYX ȠTUR.mechX ȠGEN
w
fX C.V.
ȠAUX. = Net Power Transmitted by Generator
Gross Power produced by Plant
ȠOA = ȠBr X ȠCYX ȠTUR.mechX ȠGEN X ȠAUX.
= 0.92 x 0.44x 0.95x 0.93x0.95 = 0.34
76

• Only 34 % of the energy in fuel is converted to
electricity and 66% of the energy is lost.
• Maximum loss of energy takes place in the
condenser where heat is rejected to cooling
water.
• Parameter readily reflects fuel economy is the
heat rate, which is inversely proportional to
efficiency. Lower the heat rate means unit is
operating with better efficiency.
77

Heat rates
• Net cycle heat rate = rate of heat addition to cycle =Q1/ W net
net cycle work output
Gross cycle he at rate = rate of heat addition = Q1/ WT
Turbine output
Net Station heat rate = rate of heat addition to boiler (Q1 )
net station output
Gross Station heat rate = rate of heat addition to boiler (Q1 )
gross generation output
Net station output = Gross generation (Total power generation )
– Auxiliaries consumption
78

Co-Generation Plant
• Paper mills, Textile mills, Chemical factories
require STEAM for heating
• Saturated Steam at the DESIRED TEMP. used
for heating.
• Apart from process heat, factory need power
to drive machines, lighting etc.
• By modifying initial steam pressure and
EXHAUST pressure, possible to generate
power & make available required steam for
process work
79

• Process heater replacing Condenser
• Exhaust press. of the Turbine is the saturation
pressure corresponding to temp. desired in
the process heater. Such Turbine is called Back
Pressure Turbine.
• Plant producing both elec. Power and process
heat simultaneously is called as Cogeneration
Plant.
• Process Steam is basic need, power is
produced incidentally as a by-product, the
cycle is called a by- product power cycle.
80

• WT = Turbine output in kW.
• QH = Process heat reqd, in kJ/h
• wS = Steam flow rate in kg/h
• WT x 3600 = wS (h1 - h2)
• QH = wS (h2 - h3 )
• QH = WT x 3600 x (h2 - h3 ) kJ/h
(h1 - h2 )
Q1 is the total energy input as heat, WT is shaft work
converted into elec. Balance energy
Q1 – WT is utilized as process heat.
Cogeneration Plant Effi. ȠCO = WT + QH 81S.PALANIVEL ASSOCIATE PROF./MECH ENGG

• Co generation is beneficial if the efficiency of
the cogeneration plant is greater than of
separate generation.
• Back pressure Turbines are small w.r.t. power
output because exhaust steam density high
• They are single cylinder , it is cheaper in cost
per MW compared to condensing sets of same
power.
• They are used in process, petro chemical,
desalination of sea water, domestic heating,
for driving compressors and Feed Pumps.

• A steam power plant with inlet steam to H.P. turbine
at 90 bar and 500 deg. C and condensation at 40 deg.
C produces 500 MW. It has one stage of reheat
optimally placed which raises the steam temp. back
to 500 deg C One closed feed water heater with
drains cascaded back to the Condenser receives bled
steam at the reheat pressure, and the remaining
steam is reheated and then expanded in L.P. turbine.
The H.P. and L.P. turbines have isentropic efficiencies
of 92 % and 90 % respectively. The isentropic
efficiency of Pump is 75 %. Calculate a) the mass flow
rate of steam at turbine inlet in kg/s b) the cycle effi.
And c) cycle work ratio. Use TTD = - 1.6 deg.C

• Inlet Steam press. & temp. = 90 bar, 500⁰C
• Condenser Temp = 40 ⁰C : RH Temp = 500⁰C
• Isent. Effi. HPT = 92 %, LPT=90% Pump=75%
• TTD = - 1.6⁰C
Assume RH press= 20 % of HPTPr.= 0.2x90=18bar
h1 for 90 bar & 500 ⁰C =3386. 8 kJ/kg
s1 for 90 bar & 500 ⁰C =6.660 kJ/kg = s2S
h2Sfor 18 bar & 250 ⁰C = 2911 kJ/kg
h3 for 18 bar & 500 ⁰C =3469. 8 kJ/kg
s for 18 bar & 500 ⁰C = 7.4825 kJ/kg = s 84S.PALANIVEL ASSOCIATE PROF./MECH ENGG

s4S = sf+ x4s sfg (ref. S for 40 ⁰C)
x4s= 7.4825 – 0.572 = 0.8991
7.686
h4s = 167.5+ 0.8991 x 2406.9 = 2331.54 kJ/kg
h5 = 167.5 ( ref. hf for 40 ⁰C)
h7 = 884.5 kJ/kg ( ref. h7 for 18 bar)
WPs = vdp = 0.001008 x 90 x10 = 9.072 kJ/kgƪ
H6s = 176.64 kJ/kg
h1 - h2 = ȠHPT (h1 - h2s ) =0.92 (3386.8 -2911)
= 437.736 : h2= h1- 437.736=3386.8- 437.736=2949.06

h4= 3469.8 – 1024.434 = 2445.366 kJ/kg
WP = ȠP (h6- h5) = 9.072
h6- h5 = 9.072/0.75 = 12.1 kJ/kg
h6=12.1+167.57 = 179.67 kJ/kg
Tsat at 18 bar = 207.1⁰C
T9 = 207.1 +1.6 = 208.7 ⁰C : h9 = 875 +(22.7x3.7/5)=891.8
1(h9- h6 ) = m(h2- h7 ) : m = 891.8 – 179.67 = 712.13
2949.06- 884.5 2064.56
= 0.3449 kg.
WT = (h1- h2)+ (1-m) (h3- h4)=437.736 +0.6551x 1024.434
= 1108.8427 kJ/kg 86

Wnet = WT - WP = 1108.8427- 12.1 = 1096.7427
wS = MWx 103
/ Wnet = 500x1000/ 1096.7427
= 455.895 kg/s
Q1= (h1– h9)+ (1-m) (h3– h2)
= (3386.8 - 891.8)+0.6551 (3469. 8 -2949.06)
= 2495 + 341.137 =2836.137 kJ/kg
Ƞcy = Wnet /Q1 = 1096.7427/ 2836.137=0.3867=38.67 %
Work ratio = Wnet /WT = 1096.7427/ 1108.8427=0.989
87

• An ideal steam power plant operates between 70 bar, 550 ⁰C
and 0.075 bar. It has seven feed water heaters. Find the
optimum pressure and temperature at which the heaters
operate
TB= Saturation temp at 70 bar = 285.9 ⁰C
TC = Saturation temp at 0.075 bar = 40.3 ⁰C
Temp. rise /heater = (285.9-40.3)/(7+1)=30.7 ⁰C
Heater 1: t1 = 285.9- 30.7 =255.2⁰C: p1=43.246 bar
Heater 2: t2 = 255.2- 30.7 =224.5⁰C: p2=25.318 bar
Heater 3: t3 = 224.5 - 30.7 =193.8⁰C: p3=13.67 bar
Heater 4: t4 = 193.8- 30.7 =163.1⁰C: p4=6.714 bar
Heater 5: t5 = 163.1- 30.7 =132.4⁰C: p5= 2.906 bar
Heater 6: t6 = 132.4- 30.7 =101.7⁰C: p6= 1.08 bar
Heater 7: t7 = 101.7- 30.7 =71⁰C: p7=0.32535 bar 88S.PALANIVEL ASSOCIATE PROF./MECH ENGG

• A Textile factory requires 10 t/h of steam for process
heating at 3 bar saturated and 1000 kW of power,
for which a back pressure turbine of 70 % internal
efficiency is to be used. Find the steam condition
required at the inlet of turbine.
If w = mass flow rate of steam
W((h1 - h2s) = 1000 kW ;
(h1 - h2) =1000x3600/10,000 = 360 kJ/kg
For 3 bar h2 =2724.7 kJ/kg : h1 = 2724.7+360= 3084.7
h1 - h2s = 360/0.7= 514.286 kJ/kg
h2s = 3084.7 -514.286 = 2570.414 = hf + x2s x2163.2
=561.47 + x2s x2163.2 : x2s =0.9287 89

s2s =1.6718+ 0.9287 (6.9919-1.6718)=6.6125 kJ/kg = s1
Corresponding h1 = 3085.3 kJ/kg and s1 =6.6125
From Mollier diagram
P1= 37.3 bar and t1 =344 ⁰C
90

• In a steam power plant the efficiencies of
Boiler is 90%, Turbine (mechanical) is 94 %,
Generator is 96% and it consumes 6 % power
consumption, overall efficiency of the plant is
34%,findout the losses in Condenser
• ȠOA = ȠBr X ȠCYX ȠTUR.mechX ȠGEN X ȠAUX.
• ȠAUX. = 1 – 0.06 =0.94
• ȠCY= ȠOA / ȠBr X ȠTUR.mechX ȠGEN X ȠAUX
• ==0.34/.9x.94x.96x.94 =0.4275
• Loss in Condenser= 100 - 42.75 = 57.25%S.PALANIVEL ASSOCIATE PROF./MECH
91

• A steam power station uses the following cycle: Steam at
,Condenser at 0.1 bar, Using the Mollier chart and assuming
ideal processes, find the (a) Quality at turbine exhaust, (b)
cycle effieciency, (c) steam rate.
• From Mollier diagram
• h1= 3465 kJ/Kg,
• h2s 3065 kJ/Kg
• h3 = 3565 kJ/Kg
• h4s= 2300 kJ/Kg :x4s =0.88
• W p=vΔp =10-3
x 150 x 102
=15 kJ/Kg
• h6s = 206.83 kJ/Kg
92

• Q1 = (h1—h6s) + (h3-h2s)
= (3465-206.83)+(3565-3065)
= 3758.17kJ/Kg
WT = (h1-h2s) +(h3-h4s)
= (3465 – 3065) + (3565 – 2300) = 1650kJ/Kg
ȠCY = Wnet/ Q1 = 1650/3758.17 =0.439 say 44%
Steam rate =3600/WT = 3600/1650 = 2.18 Kg/Kwh
93

Unit1 COALBASEDPOWER PLANTS

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Unit1 COALBASEDPOWER PLANTS