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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.