Lecture 13
Gas Turbine Integration
Gas Turbine Integration
Wh I t t G T bi ith Why Integrate a Gas Turbine with a
St S t P ?
Steam System or Process?
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Multiple Pressure Levels Multiple Pressure Levels Improve HRSG Performance
• Better heat recovery efficiency
• Lower stack temperature can be achieved
• Smaller stack losses in HRSG bigger power production potential
production potential
• LP steam can be used as process steam, used in stea ca be used as p ocess stea , used
steam turbine for power generation or used for
deaeration of feedwater.
How Can We Increase the Steam Generation in the HRSG?
Introduce Firing
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Firing Modes of HRSG
• Unfired HRSG
Firing Modes of HRSG
th ibl h t i th t bi h t
- uses the sensible heat in the gas turbine exhaust to raise steam
• Supplementary fired HRSG
-
Raises the temperature of the exhaust by firing fuel at the HRSG using a portion of oxygen in exhaust -Temperature limited by ducting materials - max.temperature approximately 850OC
• Fully fired HRSG
• Fully fired HRSG
-Full utilization of the excess oxygen to raise the maximum amount of steam in the HRSG
maximum amount of steam in the HRSG
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Benefits of SF
• Uses some excess oxygen in exhaust Uses some excess oxygen in exhaust
• More HP-steam for the steam cycle with high efficiency
Hi h t h t t t
• Higher steam superheat temperatures
• More flexibility in steam generation More flexibility in steam generation
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Limitations of SF
• Additional capital and operational costs
• Duct burners no solid fuels
• Firing temperature limited to 850
OC 100% SF not
same as Full Firing
Fully Fired Furnaces y
• GT exhaust used as combustion air in furnace consuming oxygen in exhaust to a practical minimum
• More steam generation than in a SF HRSG
• More steam generation than in a SF HRSG
• Lower flame temperature than in standard boiler due to less Lower flame temperature than in standard boiler due to less oxygen, therefore reduced radiative heat transfer in furnace and consequently reduced steam generation
• Modifications might be needed in boilers in retrofit
• GT size crucial as exhaust mass flow should be as close as possible to the original flue gas flow through boiler
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poss b e to t e o g a ue gas o t oug bo e
How do we size the Cogen-unit ? How do we size the Cogen unit ?
(GT HRSG) (GT + HRSG)
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G l G id li Si i
General Guidelines on Sizing
• Don't oversize the cogen-unit (rule of thumb max. 50%
of thermal peak load)
• Smaller units have a longer period of full-load operation
• Supplementary firing adds flexibility
Summary Summary
+ Short construction period and cheap natural gas makep p g the GT integration very attractive
GT i t ti id hi h d h t h t f t
+ GT integration provides high grade exhaust heat for steam generation and process heating
+ High power to heat ratio helps with plant economics - Limited capacity flexibility
High grade fuel required - High grade fuel required
- Standard frame sizes for GT
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