Transcript TPE
UNIT I
STEAM GENERATORS
Types and classification Fire tube – Water tube
Low Pressure – High pressure Stationary – Mobile
Power generation – Processing Coal fired – Oil and
gas fired Vertical – Inclined – Horizontal
Fire
tube boilers
Cochran
Cornish
Lancashire
Marine
Locomotive
Water
Tube Boilers
Simple vertical boiler
Babcock Wilcox
Stirling
1.
2.
3.
4.
5.
6.
7.
8.
Safety valve
Pressure gauge
Water level indicator
Steam stop valve
Fusible plug
Manholes, handholes
Blow off cock
Feed pump
Superheater
Economiser
Steam
water separator
Air preheater
Performance
To
testing
find
Equivalent evaporation
Boiler efficiency
Losses
Heat balance sheet
Factor
of evaporation
h-hf /2257
E = total heat required to evaporate feed
water from and at 100oC
E= me(h-hf)/2257, where me is mass of steam
actualy produced in kg/kg of fuel or like
units
Efficiency of boiler = ms (h-hf)/mf.C
Capacity
required, pressure and temperature
of steam
Base load or peak load
Place of erection of boiler
Fuel and water available (Quality and
quantity)
Probable permanency of the station
Losses
due to unburnt coal
Losses due to moisture present in coal
Losses due to sulphur like elements
Heat lost in flue gases
Radiation heat loss
Fire Tube boiler
Water Tube Boiler
Low pressure boiler p<80 bar
High pressure boiler p>80 bar
Shell must be present
Shell need not be there
Forced circulation very difficult
Forced circulation makes the heat transfer
more effective
Explosion risk less
Explosion risk more
Transportation and Erection difficult
Transportation and Erection easy
Fixed capacity
Capacity can be increased by increasing
the pressure
Scale formation and thus less heat Forced circulation and less or no scale
transfer
formation
Lancashire bolier, Cochran boiler
Babcock and Wilcox boiler
STEAM NOZZLES
A convergent nozzle
Steam out
A convergent – divergent nozzle
A divergent nozzle
In
steam turbines to increase velocity of
steam
In steam injectors to pump water into the
boiler
In processing plants for drying the chemicals
etc
Isentropic
expansion
1/2
C2 = [2(h1-h2)]
m/s
where C2 is the exit velocity,
h1 and h2 are the enthalpy of steam at inlet of
the nozzle and at the exit of the nozzle
respectively (in J)
Effect of friction
•To increase dryness fraction of the steam
•To reduce the total heat drop and thus reduce the exit velocity of the
steam coming out of the nozzle
STEAM TURBINES
Rotary
machine to convert heat energy of
steam in to shaft work
Impulse turbine and reaction turbine
Used in power plants
First reaction turbine is hero engine
Single stage – multistage
Governing is needed to control the speed visà-vis load
ROTARY
Balancing and
lubrication easy
Less vibration
Less linkages
Does not Need
flywheel
Used in power plant
Less losses
Costly
Steam TURBINE
RECIPROCATORY
Balancing and
lubrication difficult
More vibration
More linkages
Need flywheel
Used in only small
engines
More losses
cheap
STEAM ENGINE
Works on impulse principle
Small in size
More losses
More power per stage
Nozzle present
Symmetric blades
Does not need pressure
tight casing
Flow only through nozzle
Cheap
DeLaval turbine
Impulse TURBINE
Works on reaction
principle
Big in size
Less power per stage
No nozzles only guide
blades
Aerofoil blades
Air tight casing needed
Flow through the entire
annular space
Costly
Parson turbine
Reaction turbine
I C ENGINES
A
reciprocating device that converts heat
energy into shaft work
As per thermodynamic cycle
Otto cycle
Diesel cycle
Dual Cycle
As
per Stroke
Two stroke
Four stroke
Vertical
engines
Horizontal ingines
Incline engines
Inline engines
Radial engines
V-engines
Opposed cylinder engines
Single cylinder
Multi cylinder engines
Automobiles
Agricultural
equipments
Power generation
Earth movers
Marine applications
Rail locomotives
To Cool the IC engine
To lubricate the moving parts of an IC Engine
To inject diesel into the
combustion chamber at very
high pressure for atomisation
Pushing
out the burnt gases out of the
cylinder before taking the fresh charge is
called as scavenging.
In 4-stroke engine scavenging takes place in
exhaust stroke.
If scavenging is poor, then power produced
will be reduced
Supplying
more air during the inlet or suction
stroke by pressure is called supercharging.
This is done to improve volumetric efficiency
This increases the net power produced by
the engine.
Supercharging is carried out by turbocharger,
which is driven by the exhaust gas from the
engine
In
SI engine ignition takes place before the
TDC of the piston due to certain
circumstances (like preignition). This is
called as detonation.
Isooctane has zero detonation characteristics
and any fuel is measured in octane rating.
Due
to the combustion, different wave fronts
are formed inside the cylinder and the
wavefronts compress the already compressed
fuel. This increases the temperature and the
compressed but yet to be ignited fuel burns
and opposes the wave front thus producing
knocking
Knocking is measured in Cetane rating
To find the power and performance
characteristics, the performance tests such as
brake power test, Morse test are conducted
Indicated power (IP) is the power produced
inside the cylinder – measured by indicator
IP = pLANk/60 (Watt)
Brake power (BP) is the power obtained in a
dynamometer outside the flywheel shaft
BP = 2πNT/60 (Watt)
Friction power = indicated power – Brake power
Air
standard efficiency
Indicated thermal efficiency
Brake thermal efficiency
Mechanical efficiency
Volumetric efficiency
Heat
carried out by exhaust gases
Heat carried out by cooling fluid
Heat lost due to friction power
Unaccountable losses
SI ENGINE
CI ENGINE
Compression ratio 1:8
Compression ratio 1:22
Petrol fuel
Diesel fuel
Spark ignition
Compression ignition
Carburetor
Fuel injector
Need current for ignition
Does not need current
More air std efficiency
Less air std efficiency
Lighter cylinder
Heavier cylinder
Less heat and vibration
Vibration and heat more
Lighter flywheel
Heavier flywheel
Cooling, balancing and
lubrication easy
Cooling, balancing and
lubrication difficult
One power stroke in one
revolution
Lighter flywheel
Suitable for small engines
Lubrication difficult
High specific power
High speed
More pollution, scavenging
difficult
Starting easy
Special design for piston
No valves only ports
High specific fuel consumption
Low volumetric efficiency
One power stroke in TWO
revolutions
Heavier flywheel
Suitable for heavy engines
Lubrication easy
Low specific power
Low speed
Less pollution, separate
exhaust stroke
Starting difficult
Simple design for piston
valves present
Low specific fuel consumption
High volumetric efficiency
GAS TURBINES
A
rotary device, (a prime mover) transforms
heat energy of gases into mechanical work or
shaft work
An external combustion engine
Works on Brayton thermodynamic cycle (or
reverese Joule’s cycle)
Used in airplanes, turbochargers and power
generation
Two types of gas turbines are
Open cycle
Closed cycle
Processes
1-2 Isentropic compression
2-3 Constant pressure heat addition
3-4 Isentropic expansion (power process)
4-1 constant pressure heat rejection
Fue
l
Gas
Turbine
Starti
ng
motor
Generato
r
Air
Compressor
Exhaust gases
Atmospheric air
Open
cycle
Mixing type
combustion chamber
Air and gas as
medium
Aviation fuel as fuel
Relatively cheap
High specific power
Used in airplanes
Power cannot be
increased
Closed
cycle
Non-mixing type
Helium or liquid
sodium medium
Any low quality fuel
Costly
Low specific power
Power plants
Power can be
increased by
increasing the
pressure ratio
Gas turbine
Rotary device
High speed prime
mover
Aviation fuel as fuel
Less balancing
Difficult to start
Used in airplanes
Lubrication easy
No flywheel
Governing difficult
IC Engine
Reciprocating device
Low speed
Petrol, diesel as fuel
Complicated
balancing
Easy to start
Automobiles, Power
plants
Lubrication difficult
Flywheel must
Governing easy
Net Power Produced =
Work done by Turbine – Work
done on compressor
W = Wt – Wc
Work ratio = W /Wt
Efficiency of the Turbine
system
= (Qs – Qr) /Qs
= [(T3-T2) – (T4-T1)] / (T3 –
T2)
=
1 – (1 / rp (γ-1)/ γ)
Intercooling
Reheating
Regeneration
Combination
of the above