Training Session on Energy
Equipment
Cogeneration
Presentation from the
“Energy Efficiency Guide for Industry in Asia”
www.energyefficiency.asia.org
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© UNEP 2006
Training Agenda: Cogeneration
Introduction
Types of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
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Introduction
What’s a Cogeneration/CHP System?
• Generation of multiple forms of
energy in one system: heat and
power
• Defined by its “prime movers”
•
•
•
•
•
Reciprocating engines
Combustion or gas turbines,
Steam turbines
Microturbines
Fuel cells
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Introduction
Efficiency Advantage of CHP
Conventional Generation (58%
Overall Efficiency)
36 Units
(Losses)
Combined Heat & Power (85%
Overall Efficiency)
60
24
Uni
ts
 = 40%
68
100
40
34
Uni
ts
 = 85%
6 Units
(Losses)
(UNESCAP, 2004)
10 Units
(Losses)
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Introduction
Benefits of Cogeneration / CHP)
• Increased efficiency of energy conversion and
use
• Lower emissions, especially CO2
• Ability to use waste materials
• Large cost savings
• Opportunity to decentralize the electricity
generation
• Promoting liberalization in energy markets
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© UNEP 2006
Training Agenda: Cogeneration
Introduction
Types of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
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Type of Cogeneration Systems
• Steam turbine
• Gas turbine
• Reciprocating engine
• Other classifications:
- Topping cycle
- Bottoming cycle
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Type of Cogeneration Systems
Steam Turbine Cogeneration System
• Widely used in CHP applications
• Oldest prime mover technology
• Capacities: 50 kW to hundreds of MWs
• Thermodynamic cycle is the “Rankin cycle”
that uses a boiler
• Most common types
• Back pressure steam turbine
• Extraction condensing steam turbine
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Type of Cogeneration Systems
Back Pressure Steam Turbine
• Steam exits the turbine at a higher pressure
that the atmospheric
HP Steam
Boiler
Advantages:
-Simple configuration
-Low capital cost
-Low need of cooling water
-High total efficiency
Turbine
Fuel
Condensate
Process
LP
Steam
Figure: Back pressure steam turbine
Disadvantages:
-Larger steam turbine
-Electrical load and output
can not be matched
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Type of Cogeneration Systems
Extraction Condensing Steam
Turbine
HP Steam
• Steam obtained by
extraction from an
intermediate stage
• Remaining steam is
exhausted
• Relatively high
capital cost, lower
total efficiency
• Control of electrical
power independent of
thermal load
Boiler
Turbine
Fuel
LP Steam
Condensate
Process
Condenser
Figure: Extraction condensing steam turbine
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Type of Cogeneration Systems
Gas Turbine Cogeneration System
• Operate on thermodynamic “Brayton cycle”
• atmospheric air compressed, heated,
expanded
• excess power used to produce power
• Natural gas is most common fuel
• 1MW to 100 MW range
• Rapid developments in recent years
• Two types: open and closed cycle
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Type of Cogeneration Systems
Open Cycle Gas Turbine
Exhaust
Gases
• Open Brayton cycle:
atmospheric air at
increased pressure to
combustor
• Old/small units: 15:1
New/large units: 30:1
Condensate
from Process
HRSG
Steam to
Process
Combustor
Fuel
• Exhaust gas at 450600 oC
• High pressure steam
produced: can drive
steam turbine
G
Generator
Compressor
Turbine
Air
Figure: Open cycle gas turbine cogeneration
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Type of Cogeneration Systems
Closed Cycle Gas Turbine
Heat Source
• Working fluid circulates
in a closed circuit and
does not cause
corrosion or erosion
Heat Exchanger
G
Generator
• Any fuel, nuclear or
solar energy can be
used
Compressor
Turbine
Condensate
from Process
Steam to
Process
Figure: Closed Cycle Gas Turbine Cogeneration System
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Type of Cogeneration Systems
Reciprocating Engine Cogeneration
Systems
• Used as direct mechanical drives
• Many advantages:
operation,
efficiency, fuel
costs
• Used as direct
mechanical drives
• Four sources of
usable waste heat
Figure: Reciprocating engine cogeneration system
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(UNESCAP, 2000)
© UNEP 2006
Type of Cogeneration Systems
Topping Cycle
• Supplied fuel first produces power
followed by thermal energy
• Thermal energy is a by product used
for process heat or other
• Most popular method of cogeneration
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Type of Cogeneration Systems
Bottoming Cycle
• Primary fuel produces high
temperature thermal energy
• Rejected heat is used to generate
power
• Suitable for manufacturing processes
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Training Agenda: Cogeneration
Introduction
Types of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
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Assessment of Cogeneration
Systems
Performance Terms & Definitions
• Overall Plant Heat Rate (kCal/kWh):
Ms x (hs  hw)
Power Output (kW )
Ms = Mass Flow Rate of Steam (kg/hr)
hs = Enthalpy of Steam (kCal/kg)
hw = Enthalpy of Feed Water (kCal/kg)
• Overall Plant Fuel Rate (kg/kWh)
Fuel Consumption * (kg / hr )
Power Output (kW )
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Assessment of Cogeneration
Systems
Steam Turbine Performance
• Steam turbine efficiency (%):
Actual Enthalpy Drop across the Turbine (kCal / kg)
x 100
Isentropic Enthalpy drop across the Turbine (kCal / kg)
Gas Turbine Performance
• Overall gas turbine efficiency (%) (turbine
compressor):
Power Output (kW ) x 860
x 100
Fuel Input for Gas Turbine (kg / hr ) x GCV of Fuel (kCal / kg)
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Assessment of Cogeneration
Systems
Heat Recovery Steam Generator (HRSG)
Performance
• Heat recovery steam generator efficiency
(%):
M s x ( hs  hw )
[ M f x Cp (t in  t out )]  [ M aux x GCV of Fuel (kCal / kg)]
Ms = Steam Generated (kg/hr)
hs = Enthalpy of Steam (kCal/kg)
hw = Enthalpy of Feed Water (kCal/kg)
Mf = Mass flow of Flue Gas (kg/hr)
t-in = Inlet Temperature of Flue Gas (0C)
t-out = Outlet Temperature of Flue Gas (0C)
Maux = Auxiliary Fuel Consumption (kg/hr)
x 100
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© UNEP 2006
Training Agenda: Cogeneration
Introduction
Types of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
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Energy Efficiency Opportunities
Steam Turbine Cogeneration System
Steam turbine:
• Keep condenser vacuum at optimum value
• Keep steam temperature and pressure at
optimum value
• Avoid part load operation and starting &
stopping
Boiler & steam – see other chapters
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Energy Efficiency Opportunities
Gas Turbine Cogeneration System
Gas turbine – manage the following parameters:
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•
•
•
•
Gas temperature and pressure
Part load operation and starting & stopping
Temperature of hot gas and exhaust gas
Mass flow through gas turbine
Air pressure
Air compressors – see compressors chapter
Heat recovery system generator – see waste
heat recovery chapter
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© UNEP 2006
Training Session on Energy
Equipment

Cogeneration
THANK YOU
FOR YOUR ATTENTION
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© UNEP GERIAP
Disclaimer and References
• This PowerPoint training session was prepared as part of
the project “Greenhouse Gas Emission Reduction from
Industry in Asia and the Pacific” (GERIAP). While
reasonable efforts have been made to ensure that the
contents of this publication are factually correct and
properly referenced, UNEP does not accept responsibility for
the accuracy or completeness of the contents, and shall not
be liable for any loss or damage that may be occasioned
directly or indirectly through the use of, or reliance on, the
contents of this publication. © UNEP, 2006.
• The GERIAP project was funded by the Swedish
International Development Cooperation Agency (Sida)
• Full references are included in the textbook chapter that is
available on www.energyefficiencyasia.org
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© UNEP 2006