14/15 Semester 4
Plant Utility System
(TKK-2210)
Instructor: Rama Oktavian
Email: rama.oktavian86@gmail.com
Office Hr.: M-F 13-15
Training Agenda: Cogeneration
Introduction
Types of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
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© UNEP 2006
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 “Rankine
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
Boiler
Turbine
Fuel
LP Steam
Condensate
Process
• Relatively high
capital cost, lower
total efficiency
• Control of electrical
power independent of
thermal load
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
13System
Figure: Closed Cycle Gas Turbine Cogeneration
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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
(UNESCAP, 2000)
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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
Topping Cycle
Bahan bakar
Siklus termodinamika
produksi kerja
G
Energi termal
Bahan baku
PABRIK
Produk
Panas terbuang
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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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Type of Cogeneration Systems
Bottoming Cycle
Bahan bakar
Bahan baku
PABRIK
Produk
Energi termal sisa
Siklus termodinamika
produksi kerja
Panas terbuang
G
Listrik
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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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© UNEP 2006
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
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Energy Efficiency Opportunities
Gas Turbine Cogeneration System
Gas turbine – manage the following parameters:
•
•
•
•
•
Gas temperature and pressure
Part load operation and starting & stopping
Temperature of hot gas and exhaust gas
Mass flow through gas turbine
Air pressure
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