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1
Combined Heat and
Power
Combustion Turbines and Co-generation
Lecture 12
Combustion Turbines
and
Combined Heat and Power (CHP) Systems
See B. K. Hodge, Chapter 5 and Chapter 11.
ISBN: 978-0-470-14250-9
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Combustion Turbines
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http://me.queensu.ca/courses/MECH230/notes/
Gas/Combustion Turbine Power Plants
Gas Turbine Power Plants are lighter and more compact than vapor power plants.
The favorable power-output-to- weight ratio for gas turbines make them suitable
for transportation. Air-standard Brayton Cycle
Air-standard Brayton Cycle
Regenerative Gas Turbines
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Regenerative Gas Turbines
table_05_02
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LM 2500 Gas Turbine (GE Energy)
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table_05_04
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Cogeneration Defined
Cogeneration is the
simultaneous generation
of two or more types of
energy from a single fuel
source
Process
Combined Heat and Power
• When combustion engines are used only for
generating electricity, most of the usable energy
from fuel combustion is lost in the form of heat -
resulting in systems that are only 20 - 30%
efficient.
• Generating systems can be made greater than
70% efficient by recovering and using waste
heat from the combustion process - this strategy
is more commonly known as "Cogeneration" or
"Combined Heat and Power."
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Useful Energy From Conventional
Electric Generation
Useful Energy From Cogeneration
Typical cogeneration reaches efficiencies of
75%, while conventional electricity generation
operates at efficiencies around 33%
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Attractive Load Profile for Cogeneration
The following
diagram illustrates
how use of
Combined Heat &
Power can increase
efficiency:
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Combined Cycle Co-generation System
Combined Cycle GT
Compressor Turbine
Combustor
Inlet Air
Gas Turbine
GS
Heat Recovery
Boiler
Steam Turbine
Feed Pump
Steam
Condenser
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Start here Monday
12
DHC Cogeneration
Compressor Turbine
Combustor
Inlet Air
Heat Recovery
Boiler
Feed Pump
Building
Loads
MIT Campus System Layout
Boiler 3 Boiler 4 Boiler 5 HRSG
GS
Generator
Steam System
To Chilling
Plant
To MIT
Campus
Combustion Turbine
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Typical Cycle
Efficiencies
0%
10%
20%
30%
40%
50%
60%
70%
80%
Simple GT Rankine CCGT DHC GT
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fig_11_05
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*******CGT & HRSG Diagram
Combustion Turbine
Dual Fuel
Supplementary Firing
CO
Catalyst
Bed GS
22 MW(e)
21 kg/s Steam
1000 degree exhaust
EV Dual-Cone Combustor
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Emission Control Techniques
• Water injection to
reduce flame
temperature
• Bypass air for
temperature air
control
• Pilot fuel ratio
variation
• CO oxidation in
exhaust
Water Tube Boilers
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Combined Cycle Heat Balance Oct 23
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Temperature
Profile in
Heat
Recovery
Boiler
Steam Turbine Assisted Co-generation
(allows better matching of heat and electricity loads)
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CGT & HRSG Diagram
Combustion Turbine
Dual Fuel
Supplementary Firing
CO
Catalyst
Bed GS
22 MW(e)
21 kg/s Steam
1000 degree exhaust
fig_11_04
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PINCH POINT ANALYSIS
PINCH POINT
PINCH POINT ANALYSIS
PINCH POINT
200 kg/s
Superheated
Steam
Sub-cooled
Liquid
Saturated
Steam
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32.45 kg/s
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PINCH POINT
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Other Types of Co-generation
Heat and Power
•Fuel Cell
•Micro Gas Turbine
•IC Engine
• Fuel Cell
• Micro Gas Turbine
• IC Engine
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******Diesel Engine Co-gen
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fig_11_13
Thermal Cooling Technologies
Traditional Conventional
Vapour-Compression
(non-thermal
Common Types of Thermal Air Conditioning
•Absorption Chillers
•Adsorption Chillers
•Desiccant Dehumidifiers/Evaporative Coolers
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Absorption Chiller
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http://www.cogeneration.net/absorption_chillers.htm
http://en.wikipedia.org/wiki/Chiller#How_adsorption_technology_works
Absorption Chiller Refrigeration Cycle
The basic cooling cycle is the same for the absorption and electric chillers. Both systems use a low-
temperature liquid refrigerant that absorbs heat from the water to be cooled and converts to a vapour phase (in
the evaporator section). The refrigerant vapours are then compressed to a higher pressure (by a compressor or
a generator), converted back into a liquid by rejecting heat to the external surroundings (in the condenser
section), and then expanded to a low- pressure mixture of liquid and vapour (in the expander section) that goes
back to the evaporator section and the cycle is repeated.
The basic difference between the electric chillers and absorption chillers is that an electric chiller
uses an electric motor for operating a compressor used for raising the pressure of refrigerant vapors and an
absorption chiller uses heat for compressing refrigerant vapours to a high-pressure. The rejected heat from the
power-generation equipment (e.g. turbines, microturbines, and engines) may be used with an absorption chiller
to provide the cooling in a CHP system.
The basic absorption cycle employs two fluids, the absorbate or refrigerant, and the absorbent. The
most commonly fluids are water as the refrigerant and lithium bromide as the absorbent. These fluids are
separated and recombined in the absorption cycle. In the absorption cycle the low-pressure refrigerant vapour
is absorbed into the absorbent releasing a large amount of heat. The liquid refrigerant/absorbent solution is
pumped to a high-operating pressure generator using significantly less electricity than that for compressing the
refrigerant for an electric chiller. Heat is added at the high-pressure generator from a gas burner, steam, hot
water or hot gases. The added heat causes the refrigerant to desorb from the absorbent and vaporize. The
vapours flow to a condenser, where heat is rejected and condense to a high-pressure liquid. The liquid is then
throttled though an expansion valve to the lower pressure in the evaporator where it evaporates by absorbing
heat and provides useful cooling. The remaining liquid absorbent, in the generator passes through a valve,
where its pressure is reduced, and then is recombined with the low-pressure refrigerant vapours returning from
the evaporator so the cycle can be repeated.
Absorption chillers are used to generate cold water (44°F) that is circulated to air handlers in the
distribution system for air conditioning.
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