Cogeneration and its basics for energy management

Cogeneration, also known as Combined Heat and Power (CHP), is a highly efficient energy production process that simultaneously generates electricity and useful thermal energy (such as steam or hot water) from a single fuel source. This integrated approach to energy production maximizes overall energy efficiency and reduces greenhouse gas emissions compared to separate generation of electricity and thermal energy.

1. COGENERATION
By
Er. T. AYISHA NAZIBA, Dr. D. RAMESH, Dr. S. PUGALENDHI

2. Cogenerationisthesimultaneousproductionofpower
andheat,withaviewtothepracticalapplicationofboth
products.
•A way of local energy production
• Heat is main product, electricity by-product
• Uses heat that is lost otherwise
• Way to use energy more efficiently
• Different area’s of application
• Different technologies
COGENERATION

3. ADVANTAGE OF COGEN POWER
Most techno-commercial viable projects with short
pay back
Cost of power production is very cheap compare to that
of purchase power
Dependability and reliability with quality of power
Quick return on investments
Restore ecological imbalance
Ability to use biomass and organic matters like wood,
grass, agro wastes and also MSW
Availability of power between November to May when
hydelpower availability less
Provides economical and timely solution of power
problems

4. 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
COGENERATION SYSTEM
•Steam turbine
•Gas turbine
•Reciprocating engine
•Other classifications
-Topping cycle
-Bottoming cycle

5. BENEFITS OF COGENERATION
•Improve energy efficiency
•Reduce use of fossil fuel and reduce emission of CO
2
•Increased efficiency of energy conversion and use
Also,
•Reduce cost of energy
•If heat fits demand, cheapest way of electricity
production
•Improve security of supply
•Use of organic waste as fuel
•Position on energy market
•Opportunity to decentralize the electricity generation
•Conserve natural resources
•Support grid infrastructure
–Fewer T&D constraints
–Defer costly grid upgrades
–Price stability

6. 6
EFFICIENCY ADVANTAGE OF CHP

7. 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

8. •Steamexitstheturbineatahigherpressureorequalto
theatmosphericpressure
•After the steam exits the turbine, it is fed to the load
where it releases heat and is condensed. The condensate
then returns to the system
BACK PRESSURE STEAM TURBINE
COGENERATION SYSTEM
Fuel
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 output can not be
matched
Boiler
Turbine
Process
HP Steam
Condensate LP
Steam

9. •Remaining steam is
exhausted to the pressure of
the condenser
•Relatively high capital cost,
lower total efficiency
•Control of electrical power
independent of thermal load
EXTRACTION CONDENSING STEAM
TURBINE COGENERATION SYSTEM
Boiler
Turbine
Process
HP Steam
LP Steam
Condensate
Condenser
Fuel
EXTRACTION CONDENSING STEAM
TURBINE
•The steam for the thermal load is obtained through
extraction from one or more intermediate stages at
appropriate pressure and temperature

10. •Operateonthermodynamic“Braytoncycle”
•Atmosphericaircompressed,heated,expanded
•Excesspowerusedtoproducepower
•Naturalgasismostcommonfuel
•1MWto100MWrange
•Rapiddevelopmentsinrecentyears
•Twotypes:openandclosedcycle
GAS TURBINE COGENERATION SYSTEM

11. •Open Brayton cycle: atmospheric air at increased pressure
to combustor
OPEN CYCLE GAS TURBINE
COGENERATION SYSTEM
Air
G
Compressor
Turbine
HRSG
Combustor
Fuel
Generator
Exhaust
Gases
Condensate
from Process
Steam to
Process•Old/small units: 15:1
New/large units: 30:1
•Exhaust gas at 450-600
o
C
•High pressure steam
produced: can drive steam
turbine
OPEN CYCLE GAS TURBINE
COGENERATION SYTEM

12. •Working fluid circulates in a
closed circuit and does not
cause corrosion or erosion
•Any fuel, nuclear or solar
energy can be used
CLOSED CYCLE GAS TURBINE
COGENERATION SYSTEM
Heat Source
G
Compressor
Turbine
Generator
Condensate
from Process
Steam to
Process
Heat Exchanger
CLOSED CYCLE GAS TURBINE
COGENERATION SYSTEM

13. •Used as direct mechanical drives
•Many advantages: operation, efficiency, fuel costs
•Used as direct mechanical drives
•Four sources of usable waste heat
RECIPROCATING ENGINE COGENERATION
SYSTEMS
RECIPROCATING ENGINE COGENERATION SYSTEM

14. 14
•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
TOPPING CYCLE COGENERATION SYSTEM

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•Primaryfuelproduceshightemperaturethermal
energy
•Rejectedheatisusedtogeneratepower
•Suitableformanufacturingprocesses
BOTTOMING CYCLE COGENERATION SYSTEMS

16. ASSESSMENT OF COGENERATION SYSTEMS
•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)
Performanceterms and definitions)(
)(
kWOutputPower
hwhsxMs  )(
)/(*
kWOutputPower
hrkgnConsumptioFuel

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•Steam turbine efficiency (%)
Steam turbine performance
Gas turbine performance
•Overall gas turbine efficiency (%) (turbine
compressor)100
)/(
)/(
x
kgkCalTurbinetheacrossdropEnthalpyIsentropic
kgkCalTurbinetheacrossDropEnthalpyActual 100
)/()/(
860)(
x
kgkCalFuelofGCVxhrkgTurbineGasforInputFuel
xkWOutputPower
ASSESSMENT OF COGENERATION SYSTEMS

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•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 (
0
C)
t-out= Outlet Temperature of Flue Gas (
0
C)
Maux= Auxiliary Fuel Consumption (kg/hr)
Heat Recovery Steam Generator (HRSG) Performance100
)]/([)]([
)(
x
kgkCalFuelofGCVxMttCpxM
hhxM
auxoutinf
wss


ASSESSMENT OF COGENERATION SYSTEMS

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ENERGY EFFICIENCY OPPORTUNITIES
•Keep condenser vacuum at optimum value
•Keep steam temperature and pressure at
optimum value
•Avoid part load operation and starting and
stopping
Steam Turbine Cogeneration System

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Gas Turbine Cogeneration System
•Gas temperature and pressure
•Part load operation and starting & stopping
•Temperature of hot gas and exhaust gas
•Mass flow through gas turbine
•Air pressure
ENERGY EFFICIENCY OPPORTUNITIES

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• Depends very much on tariff system
• Heat-avoided cost of separate heat production
Electricity
•Less purchase (kWh)
•Sale of surplus electricity
•Peak shaving (kWe)
• Carbon credits (future)
ECONOMIC VALUE OF COGENERATION

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COGENERATION IN SUGAR MILLS

23. BOILER
ALTERNATORTURBINE
To process
To process
Fuel
Air
TO
POWER
SUPPLY
CONDENSER
TO
COOLING
TOWER
COGENERATION PLANT LAYOUT
Feed water
PRDS

24. KCP Boiler
70 TPH, 43.4ata
& 400ºC
TBW Boiler
70 TPH, 67ata &
485ºC
COMPARISON
Prevailing System Proposed System
Multi fuel Boiler
105ata, 525º C, 88%
GEC Turbine
SIEMENS Turbine
C
C
11 KV BUS
C
C
GEC Turbine
SIEMENS Turbine

25. Actual Thermal Efficiency of existing power plant on date
Heat value of KPC boiler ≈ 767 Kcal/kg (from steam table)
(at 43.4 ata and 400ºC)
Then net heat value of KPC boiler ≈ 767 –105 ≈ 662 Kcal/kg.
Thermal efficiency of KPC boiler = η
th= (Net heat value * Total Steam generation) / (CV of
the bagasse * total bagasse consumption)
η
th = (662 * 122759) / (2277 * 61672)
= 57.99% ≈ 58% ( against 69% of design)
Heat value of TBW boiler = 807.7 Kcal/kg (From steam table)
(at 67 ata and 485ºC)
Then net heat value of TBW boiler ≈ 807.7 –105 ≈ 702.7 Kcal/kg
GCV of coal = (CV of coal * total coal consumption) / Total fuel consumption
= (5500 * 4622) / 56213 = 452.22 Kcal/kg
GCV of Bagasse = (CV of bagasse * total bagasse consumption) / Total fuel consumption
= (2277 * 51591) / 56213 = 2089.77 Kcal/kg
Then net GCV = 452.22 + 2089.77 = 2542 Kcal/kg

26. Then net heat gain = heat gain * steam required for cane * efficiency of Topping TG set
= 13.8 * 125*10
3
* 0.9
= 1552.5 Kcal/kg
Total power generation = 1552.5/860 = 1.8 MW
Transfer rate = 1800 * 24 * 330 * 1.96 = 2.79 crore
Thermal efficiency of TBW boiler = ηth = (Net heat value * Total Steam generation) /
(Net GCV * total fuel consumption)
= (702.7 * 129399) * 100 / (2542 * 56213)
ηth = 63% (against 71.75% of design)
Average thermal efficiency of KPC & TBW boiler = (58+63) / 2 = 60.5%
Expected direct efficiency of multifuel boiler = 84%
Then fuel saving = 84 –60.5 = 23.5%
Cost of fuel saving = Actual cane crushed * % of fuel caned * % fuel save
for 02-03 = 729598 * 0.3 * 0.235
= Rs. 51436.65
Then total saving of bagasse = 51437 * 500
= Rs. 2,57,815
= 2.57 crore

27. Net gain in power = 2.79 crore
Net gain in fuel save = 2.57 crore
Then total gain = 2.79+2.57 = 5.36 crore
Heat value of AFBC boiler = 821.5 Kcal/kg (from steam table)
(at 515º C and 105 kg/cm
2
)
Then net heat gain = 821.5 –807.7
= 13.8 Kcal/kg
From data
Budgeted crane crushed/year = 775000 M.T
Actual crane crushed/year = 72598.401 M.T
No. of crop days = 170 days
% Steam required for crane = 48%
% of bagasse in cane = 30%
Then steam required for cane/hr. = (budgeted cane crushed * %steam reqd. for cane) /
(No. of days * 24)
= (775000 * 0.48) / (170*24)
= 91.176 tph
≈ 100 tph
For maximum efficiency
steam required for cane/hr = 100/0.80 = 125 tph

28. STEPS FOR SAVINGS
Savingofbagassebyadoptinghightechnologyhigh
pressureboilers
Reductionofmoistureinbagasse50to45%by
improvingmillingtechnique
Reductioninprocesssteamconsumptionsinevaporator
andprimemoversBLTFFevaporators
Reductioninlivesteamconsumptionbyusingmulti
stagereactionturbines
ReductioninoverconsumptionsofpowerTCHusing
newtechniqueofvariabledrivesandhighefficient
auxiliaries
Improvecrushingratebyhavingqualitypower

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