International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Increasing Co-Generation Efficiency Its
Improvements,Operation & Maintenance
Ramananth.N.V#1 , Vijay.P*2
Mechanical department, K.L. University
Vaddeswaram, green fields, Guntur(dt), 522502, Andhra Pradesh, India
Mechanical department, K.L.University
Vaddeswaram, green fields, Guntur(dt), 522502, India
Abstract--- This document gives the information and knowledge
of importance of Co-generation system in the industries. The cogeneration or CHP system simultaneously produces both heat
energy & electricity. In this paper the prime movers are also
explained its operation and maintenance. Cogeneration was
practiced in some of the earliest installations of electrical
generation. Before central stations distributed power, industries
generating their own power used exhaust steam for process
heating. Large office and apartment buildings, hotels and stores
commonly generated their own power and used waste steam for
building heat. Types of prime movers that which are used in cogeneration (Back pressure steam turbine, extraction condensing
steam turbine) its operation & maintenance. Improvements in
increasing overall efficiency of steam turbine.
Keywords---- Co-generation, prime movers, CHP, efficiency,
baggasse, conveying energy, impulse, reaction, back pressure,
condensate, high & low pressure steam, condenser, vacuum
ejector, auxiliaries
I.
INTRODUCTION
Cogeneration is well known concept in sugar industry,
the sugar factories are already has been generating electricity
from their capacitive use, while using the steam for their
process upon the process steam consumption & prime movers.
Steam consumption can be reduced up to by using efficient
turbine with low steam consumption by using high pressure
boilers & turbines the process steam consumption can be
reduced by using double effect evaporation method at
evaporator station.
The high efficiency co-generation design not only uses
the available baggasse efficiently but also yields substantial
quantities of power for exporting to the grid, over and above
their enhances energy needs. Reduced captive steam and
power consumptions enhance baggasse availability for extra
power generation and for extending their period of operation
beyond the crushing season.
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Steam has been a popular mode of conveying
energy since the industrial revolution. Steam is used for
generating power and also used in process industries such as
sugar, paper, fertilizer, refineries, petrochemicals, chemical,
food, synthetic fiber & textile. The following characteristics of
steam make it so popular and useful to the industry:Highest
specific heat & latent heat, Highest heat transfer coefficient,
Easy to control & distribute, Cheap & inert.
In our country there is so much short fall of electricity
day by day demand of electricity is tremendous and generation
is less. Electricity is heart of industries and economy. Number
of studies carried out in India by various government
organizations has indicated the tremendous potential for
generating surplus power from sugar factories through
cogeneration system.
BENEFITS OF CO-GENERATION/CHP
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Increased efficiency of energy conversion and use
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Lower emissions, especially CO2
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Ability to use waste materials
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Large cost savings
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Opportunity to decentralize the electricity
generation.
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Promoting liberalization in energy markets
II.
STEAM TURBINE
Steam turbines are the most commonly prime mover
for co generative applications. The principle of steam turbine
involves conversion of thermal energy of high pressure
steam to kinetic energy through nozzles and then to
mechanical power through rotating blades. In the steam
turbine, the incoming high pressure steam is expanded to a
low pressure level.
The passage of steam through blades may take place
in such a manner that the pressure at the outlet side of
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
moving blade is equal to that at the inlet side. Such a turbine
is termed as Impulse turbine.
On the other hand, if the pressure of the steam at the
outlet from the moving blade is less than that at the inlet side
of the blade such a turbine is called Reaction turbine.
A.
Steam turbine co-generation system
Most common types of steam turbine Co generation
system are:
1.
Back pressure steam turbine
2.
Extraction condensing steam turbine
B.
Back pressure steam turbine
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The backpressure steam turbine has exhaust steam
pressure above atmospheric pressure and this steam is not
considered in the steam condenser but is used for process
heating in the sugar production.
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The specific steam rate of these steam turbines is
comparatively lower than the condensing turbine
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When the steam with high pressure strikes the
turbine blades or runners, rotates and makes
generator to rotate at higher speed to produce
electricity.
The controlled extraction is used for the process
which means this is used to drive the machinery in
the sugar production.
An Ejector system is used to create vacuum in the
condenser.
The outlet steam is condensed or cooled in the
condenser through the condensing process
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C. Extraction condensing steam turbine:
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When one or two exhaust steam outlets generally at
different higher pressure than atmospheric pressure
and provided to the condensing steam turbine then it
is called single or double extraction type condensing
steam turbine.
The single or double extraction system for feed water
heating improves the efficiency of the energy cycle
as the steam going to the condenser is less and the
heat loss is reduced in the condenser.
In condensate cum double extraction steam turbine
the condenser is used to cool the steam temperature
and allow it to recycle.
The steam from the inlet at high pressure and
temperature which can be reduced by passing over
these stages.
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The CONDENSING refers to the condensing system
that is attached to the unit which acts to condense
(turn back to water or condensate) the exhaust steam.
In the act of condensing, the original volume of the
exhaust steam decreases by several orders of
magnitude and since the process takes place in a
closed vessel, a steady state vacuum is created and
maintained which keeps the process cycle going.
The condenser drum has inside number of tubes in
which the cool water from the cooling water tank
flows through the tubes and the hot steam is
surrounded to the tubes.
In this process the cool water from the cooling water
tank that flows in the tubes condenses the hot steam
that which is extracted in the turbine is condensed
and is sent to the boiler for recycling.
D. Operating procedure:
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Oil system establishment
 Centrifuge in operation
 Oil sample analysis
 Oil Vapor extraction fan on
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 Auxiliary oil pump on
 Seal oil system in operation
 Gate gearing valve opened
 Jacking oil pump in operation
 Turbine on turning gear
Barring gear in operation
 Establish the lube oil system
 Ensure pressure in all bearing oil supply
line & flow is site glasses
 Ensure pressure in seal oil supply line &
flow in site glasses
 Ensure differential pressure regulator is
functioning
 DC seal & DC lube oil pumps are on auto
start mode
Turbine protection checking
 Low vacuum trip
 Axial shift high trip
 Over speed test
 Main oil level tank low trip
 Lube oil pressure low trip
 Main steam pressure low
 Generator protection
Vacuum system establishment
 Checking condenser on spring support
 Circulating water system charged
 Warm up line to land steam controller in
charge
 Vacuum pump start
Drain valves operation checking
 When vacuum achieved main MS HRH
strainer drains open
 Drain before CRH-NRV open
 HP by-pass drain open
 Drain before interceptor valve open
 Drain before LP by-pass valve open
 HP casing drain open
 Drain before extraction NRVs
HP/LP by pass in operation
Warming up operation on
Steam dumping operation on
Steam purity checking
 The purity of steam is checked by passing
pure feed water into the boiler.
 Before the passing of feed water into the
boiler the water is de-mineralized in DM
plant and adding required minerals for
maintaining purity.
Turbine ready for rolling
E. Maintenance :
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The maintenance is practiced in the following way:
a) Routine maintenance or preventive maintenance
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It is a daily maintenance of the power plant
equipments and systems to avoid breakdown.
The routine checks that are checked and recorded
are:
 Checking of oil levels
 Checking of water levels
 Checking & recording of vibrations
b) Annual maintenance
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Annual maintenance is planned for short periods of
time like 15-20 days which includes boiler cleaning,
small repairs on pressure parts, rotating equipments,
mills etc.
On turbine side bearing inspection, small
rectifications on auxiliaries, condenser tube cleaning,
hot well and de aerator cleaning, generator
inspections, hydraulic tests of various coolers etc.
c)
Capital maintenance
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Major overhaul works has been done in this stage
turbines are opened, major parts like rotor blades,
casing blades cleaning & ultrasonic tests, de
penetrate tests are carried out over the bearings,
rotor & blades.
Major repairs are carried out proper setting of
turbine clearances, alignments of rotors.
All rotating equipments are overhauled any
defective parts are replaced and re alignment of
rotor is carried out.
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III.
IMPROVING STEAM TURBINE EFFICIENCY
Steam is a major energy consumer. Optimizing
process operating conditions can considerably improve
turbine water rate, which in turn will significantly reduce
energy requirement. Various operating parameters affect
condensing and backpressure turbine steam consumption and
efficiency. The industrial sector is the largest energy
consumer, accounting for about 30 % of total energy used.
Fuel and energy prices are continuously rising.
With the present trend of energy prices and scarcity of
hydrocarbon resources
lowering energy requirement is a top priority.
Energy conservation benefits depend on the adopting
minor or major modifications and using the latest technology.
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In the large process industries, steam turbines are the main
energy consumers. Savings achieved here will be significant,
with a better return on investment than for most other
equipment.
 Turbines designed for particular operating
conditions like:
a) Steam inlet pressure
b) Steam inlet temperature &
c) Turbine exhaust pressure/
exhaust vacuum which
affects the performance of
turbines.
Variations in these parameters affects in the steam
consumption in the turbines and the turbine efficiency.
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In condensing turbines it is observed that the
exhaust vacuum of these turbines is much less than
the vacuum at the condenser.
Mainly, it is due to the higher pressure drop in the
exhaust pipeline from turbine exhaust to the
condenser.
In order to improve the vacuum at turbine exhaust
so as to reduce steam consumption in the turbine,
exhaust pipeline of these turbines can be replaced
with higher size.
5.
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4.
Effect of steam inlet pressure:
All the turbines are designed for a specified steam
inlet pressure which affects the turbine performance.
For obtaining design efficiency, steam inlet pressure
shall be maintained at a design level in the turbine.
Lower the steam inlet pressure will hampers the
turbine efficiency and steam consumption in the
turbine will increase.
At higher steam inlet pressure energy available to
run the turbine will be high, which in turn will
reduce the steam consumption in the turbine.
Effect of steam inlet temperature:
Enthalpy of steam is a function of temperature and
pressure.
At lower temperature, enthalpy will be low, work
done by the turbine will be low, turbine efficiency
will be low hence steam consumption for the
required output will be higher.
At higher steam inlet temperature, heat extraction by
the turbine will be higher and hence for the required
output, steam consumption will reduce.
Effect of exhaust pressure/vacuum:
Higher exhaust pressure/ lower vacuum, increases
the steam consumption in the turbine, keeping all
other operating parameters constant.
Exhaust pressure lower than the specified will
reduce the steam consumption and improves the
Turbine efficiency. Similarly exhaust vacuum lower
than the specified will lower the turbine efficiency
and reduces the steam consumption
Factors affect the exhaust vacuum in the condensing
turbine:
Vacuum ejector system
 Vacuum ejector system creates and maintains the
vacuum in the surface condenser by removing the
air/ inert ingress.
 Removal of air/ inert ingress is important, as
accumulation of this hampers the performance of
surface condenser, which reduces the surface
condenser vacuum.
 Motive steam condition shall be maintained as
specified. Inter-after condenser shall be cleaned in
the available opportunity, as they get choked due to
foreign material coming with cooling water.
 Flange joints shall be tightened properly to avoid
any ingress of air. Exhaust side of the turbine shall
be properly steam sealed to avoid any ingress of air.
6.
Steam
Turbine
Power
Generation
Efficiency
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Higher size of exhaust pipe:
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Increasing
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Overall efficiency of steam turbine power plant
strongly depends on turbine’s performance. Thus
any improvement slightly can increase the power
availability, decreases the component or equipment
costs.
The steam turbine efficiency ultimately depends on
its condition, relative to its design.
The evaluation of steam turbine design & operating
conditions can help increase in plants efficiency in
the following three areas:
a) Combustion to improve fuel utilization
and minimize environmental impact.
b) Heat transfer & aerodynamics to
improve turbine blade life and
performance.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
c)
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Materials to permit longer life and
higher operating temperatures.
Improvement in turbine performance has resulted
not only from developments in modern blading, but
also in the redesign of turbine sidewall contours in
high-pressure first stages, and in the reduction of
humid steam conditions in low-pressure turbine
sections that cause erosion. Such improvements
have increased turbine efficiency up to 10 %.
The turbine nozzles should be designed
aerodynamically because as the steam strikes the
blades from the nozzles forcely and there will not be
any obstacles in the path of steam. By aerodynamic
design the steam flows in the path very smoothly
and strikes the blades without any admission losses.
The turbine rotor material should withstand high
temperature and pressure so that it can bear with out
causing any disturbances in the rotation of the rotor.
A hot steam blower is places across the low pressure
stages of the turbine to add more heat in the last
stages of the turbine for better efficiency.
Lack of steam tightness of the h.p stop valve on the
supply to the turbine can lead to condensation
during shutdowns & consequent corrosion of the
report. To avoid this drawback it is advisable to
install two h.p stop valves, placed one in front of the
other with a drain open to atmosphere between the
two, to evacuate condensate due to possible leakage
of the upstream valve.
The wetness of steam 13% is the extreme limit,
beyond that the droplets of water cause serious
erosion of the blades in the last stage of the turbine.
The silica % is much less than the 0.02 PPM in the
steam that which can increase the efficiency.
IV.
I would also like to thank P.Vijay (Asst. Professor,
K.L.University) for giving me the guidance, encouragement
and for the valuable information and suggestions.
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REFERENCES
http://en.wikipedia.org/wiki/Steam_turbine
http://en.wikipedia.org/wiki/Compounding_of_stea
m_turbines
http://www.turbinesinfo.com/steam-turbineefficiency/
CONCLUSION
For the better performance of the steam turbine the operating
procedure and the maintenance can be employed effectively
and for improving the efficiency of the steam turbine the
improvements listed can be employed to attain better
efficiency based on the turbine design parameters and
capacity.
ACKNOWLEDGEMENTS
I would like to take this opportunity to express my
heartfelt thanks to our college K.L.University for giving me a
chance to come up with this paper and for the successful
completion of this paper.
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