9 gas turbine- cogeneration_3
TRANSCRIPT
7/28/2019 9 Gas Turbine- Cogeneration_3
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Dr. Walid Abdelghaffar
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
CogenerationCogeneration
IntroductionTypes of cogeneration systems
Assessment of cogeneration systemsEnergy efficiency opportunities
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Background
Cogeneration first appeared in Europe
and in the U.S.A. during the early partsof the 20th century.
In addition to decreased fuelconsumption, cogeneration results in a
decrease of pollutant emissions.
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
What is Cogeneration?
Cogeneration is on-site generation andutilisation of energy in different forms
simultaneously by utilising fuel energy atoptimum efficiency in a cost-effective andenvironmentally responsible way.
Cogeneration systems are of severaltypes and almost all types primarilygenerate electricity along with making the
best practical use of the heat, which is aninevitable by-product.
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
The most prevalent example of cogeneration is the generation of electric
power and heat. The heat may be used for generating
steam, hot water, or for cooling through
absorption chillers. In a broad sense, the system, that
produces useful energy in several forms by
utilising the energy in the fuel such thatoverall efficiency of the system is veryhigh, can be classified as Cogeneration
System or as a Total Energy System.
What is Cogeneration?
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
What is Cogeneration?
Conventional utility power plants utilise the highpotential energy available in the fuels at the endof combustion process to generate electricpower.
However, substantial portion of the low-endresidual energy goes to waste by rejection to
cooling tower and in the form of hightemperature flue gases.
On the other hand, a cogeneration process
utilises first the high-end potential energy togenerate electric power and then capitalises onthe low-end residual energy to work for heatingprocess, equipment or such similar use.
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
IntroductionIntroduction
• Increased efficiency of energy conversion anduse
• Lower emissions, especially CO2
• Ability to use waste materials• Large cost savings
• Opportunity to decentralize the electricity
generation
• Promoting liberalization in energy markets
Benefits of Cogeneration / CHP)
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
CogenerationCogeneration
IntroductionTypes of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
•Steam turbine
•Gas turbine
•Reciprocating engine
•Other classifications:
- Topping cycle- Bottoming cycle
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
• 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
Steam Turbine Cogeneration System
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
• Steam exits the turbine at a higher pressure
that the atmospheric
Back Pressure Steam Turbine
Fuel
Figure: Back pressure steam turbine
Advantages:
-Simple configuration-Low capital cost-Low need of cooling water-High total efficiency
Disadvantages:-Larger steam turbine-Electrical load and outputcan not be matched
Boiler Turbine
Process
HP Steam
Condensate LP
Steam
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
• Steam obtained byextraction from anintermediate stage
• Remaining steam is
exhausted
• Relatively high capitalcost, lower totalefficiency
• Control of electricalpower independent of thermal load
Extraction Condensing Steam
Turbine
Boiler Turbine
Process
HP Steam
LP SteamCondensate
Condenser
Fuel
Figure: Extraction condensing steam turbine
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
• 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
Gas Turbine Cogeneration System
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Typical Heat-to-Power Ratios for EnergyIntensive Industries
1.92.51.5Paper
1.22.50.8Food
23.00.8Fertilizer
2.02.51.5Pharmaceuticals
3.14.51.1Breweries
AverageMaximumMinimumIndustry
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Gas turbine based cogeneration system
This type of system works on the basic principle of Bryton cycle of thermodynamics.
Air drawn from the atmosphere is compressed and
mixed in a predetermined proportion with the fuel in acombustor, in which the combustion takes place. The flue gases with a very high temperature from the
combustor are expanded through a gas turbine, whichdrives electric generator and air compressor.
A portion of mechanical power is used for compressionof the combustion air: the balance is converted intoelectric power.
The exhaust flue gases from the gas turbine,
typically at a high temperature of 480-540 C, acts asa heat source from which the heat is recovered inthe form of steam or hot air for any desiredindustrial application.
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Gas turbine based cogeneration system
Industrial gas turbine based power plants installed togenerate only electric power operate at the thermalefficiency of 25-35% only depending of type and size of gas turbine.
Aero derivative gas turbines operate at marginal higherefficiency than the conventional industrial heavy-dutymachines.
With recovery of heat in exhaust flue gases in a waste
heat recovery boiler (WHRB) or heat recovery steamgenerator (HRSG) to generate the steam, overall plantefficiency of around 85-90% is easily achieved.
As an alternative, the heat of exhaust flue gases can
also be diverted to heat exchanger to generate hot wateror hot air (District Heating purpose in foreign countries)instead of generating steam. The Figure shows aschematic of Gas Turbine based cogeneration system.
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Gas turbine based cogeneration systemwith supplementary fired WHRB
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Gas turbine based cogeneration system
Compared to steam turbine based cogeneration system,the gas turbine based cogeneration system is ideal for thechemical process industries where the demand of steam is
relatively high and fairly constant in comparison to that of steam.
Gas turbine based cogeneration system gives a better
performance with clean fuels like natural gas, or non-ashbearing or low ash bearing liquid hydrocarbon fuels likeNaphtha, High speed Process Consumer diesel, etc. Though high ash bearing hydrocarbon based fuels like fueloil, crude oil or residual fuel oil can also be fired in the gasturbines, but with some inherent problems like frequentcleaning of gas turbine, more maintenance and spares,etc.
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
•Open Brayton cycle:
atmospheric air atincreased pressure tocombustor
Open Cycle Gas Turbine
Air
G
Compressor Turbine
HRSG
Combustor
Fuel
Generator
Exhaust
Gases
Condensatefrom Process
Steam to
Process
•Old/small units: 15:1
New/large units: 30:1
•Exhaust gas at 450-
600 oC
•High pressure steamproduced: can drivesteam turbine
Figure: Open cycle gas turbine cogeneration
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
•Working fluid circulates ina closed circuit and doesnot cause corrosion or
erosion•Any fuel, nuclear or solar
energy can be used
Closed Cycle Gas Turbine
Heat Source
G
Compressor Turbine
Generator
Condensate
from Process
Steam to
Process
Heat Exchanger
Figure: Closed Cycle Gas Turbine Cogeneration System
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
•Used as direct mechanical drives
Reciprocating Engine Cogeneration
Systems
Figure: Reciprocating engine cogeneration system (UNESCAP, 2000)
•Many advantages:operation,
efficiency, fuelcosts
•Used as directmechanical drives
•Four sources of usable waste heat
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType of Cogeneration Systems
• Supplied fuel first produces powerfollowed by thermal energy
• Thermal energy is a by product used forprocess heat or other
• Most popular method of cogeneration
Topping Cycle
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Type of Cogeneration SystemsType 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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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
IntroductionTypes of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
CogenerationCogeneration
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Assessment of Cogenerationssessment o ogenerat on
SystemsSystems
• Overall Plant Heat Rate (kCal/kWh):
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)
Performance Terms & Definitions
)(
)(
kW Output Power
hwhs x Ms −
)(
)/(*
kW Output Power
hr kgnConsumptioFuel
A f C it t
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Assessment of Cogenerationssessment o ogenerat on
SystemsSystems
• Steam turbine efficiency (%):
Steam Turbine Performance
Gas Turbine Performance
• Overall gas turbine efficiency (%) (turbine
compressor):
100)/(
)/( x
kgkCalTurbinetheacrossdrop Enthalpy Isentropic
kgkCalTurbinetheacross Drop Enthalpy Actual
100)/()/(
860)( x
kgkCalFuelof GCV xhr kgTurbineGas for Input Fuel
xkW Output Power
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Assessment of Cogeneration Assessment of Cogeneration
SystemsSystems
• Heat recovery steam generator efficiency(%):
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)
Heat Recovery Steam Generator (HRSG)
Performance
100)]/([)]([
)( x
kgkCalFuelof GCV x M t t Cp x M
hh x M
auxout in f
wss
+−
−
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
CogenerationCogeneration
IntroductionTypes of cogeneration systems
Assessment of cogeneration systems
Energy efficiency opportunities
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Dr. Walid AbdelghaffarThermal Equipment/Cogeneration
Energy Efficiency OpportunitiesEnergy 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