OPTIMIZATION OFCONVENTIONAL THERMAL & IGCC POWER PLANT FOR GREEN MEGA POWERDr. V K Sethi & J K ChandrashekarDr. V K Sethi & J K Chandrashekar Director AdviserDirector Adviser University Institute of Technology RGTU Bhopal
AGENDA FOR THE ENERGY GENERATION SECTOR:
Increased use of Advanced Fossil Fuel Technology.
Promote CCT in countries where coal is main stay fuel for Power Generation.
Reduce Atmospheric Pollution from Energy Generating Systems.
Enhance productivity through Advanced Fossil Fuel Technology.
Adoption of Renewable Energy Technologies in Rural Sector
WORLD SUMMIT ON SUSTAINABLE DEVELOPMENT
INDIAN POWER SECTOR JOINS TERA CLUB BY 2010
POWER GENERATION BY UTILITIES TODAY 1,47,965 MW …600 Billion kWh per annum TARGETTED CAPACITY ADDITION BY XI PLAN END
Central 46,500 MW State & IPP 41,800 MW NCES 10,700 MW Nuclear 6,400 MW Total 105,400 MW
BY 2012 WE NEED TO GENERATE ANNULLY …Over 1000 Billion kWh
THUS WE WILL BE A TRILLION or TERA kWhTERA kWh (Unit)GENERATING POWER SECTOR BY 2012
Tera-watt Challenge for synergy in Energy & Environment
A terawatt Challenge of 2012 for India To give over one billion people in India the minimum Electrical
Energy they need by 2012, we need to generate over 0.2 terra watt (oil equivalent to over 3 million barrels of oil per day) and 1 TW by 2040,primarily through Advanced fossil fuel technologies like CCTs for limiting GHG emission levels
By 2020 our mix of generation would have the Peak in Thermal, certainly it would be the Green Thermal Power:
Thermal 326,000MW Renewable & Hydro 104,000 MW Nuclear 20,000 MW Total 450,000 MW
POWER SCENARIO IN INDIA
Installed capacity in Utilities as on April 07 …1,
47, 965 MW Thermal Installed Capacity…93,726 MW (Coal 77,648 MW, Gas 14,876 MW, Diesel 1202 MW + Others- cogen
etc.)
Hydro Power …36,877 MW Nuclear Power … 4120 MW Renewable Energy Sources …13,242 MW Electric Demand…..7-8% growth Peak & Energy Shortage…..16.7% & 12.1% Capacity Addition in 11th Plan……80,020 MW
INDIANINDIAN POWER SECTOR - TOWARDS POWER SECTOR - TOWARDS SUSTAINABLE POWER DEVELOPMENTSUSTAINABLE POWER DEVELOPMENT
Total Installed Capacity … 1,47,965 MW Thermal Generation … over 66 % Although no GHG reduction targets for India
but taken steps through adoption of Renewable Energy Technologies,Combined cycles, Co-generation, Coal beneficiation,Plant Performance optimization
Under Kyoto Protocol; Clean Development Mechanism (CDM) conceived to reduce cost of GHG mitigation, while promoting sustainable development as per Framework Convention on Climate change (FCCC)
Prime Clean Coal Technology OptionsPrime Clean Coal Technology Options
Supercritical Power Plants Integrated Gasification
Combined Cycle (IGCC) Power Plants Circulating Fluidized Bed Combustion (CFBC) Power
Plants
GREEN ENERGY TECHNOLOGIES – PRIMARILY THE CLEAN COAL TECHNOLOGIES
ZERO EMISSION TECHNOLOGIES FOR TRANSPORT, POWER PLANTS & INDUSTRIAL SECTOR
AFFORDABLE RENEWABLE ENERGY TECHNOLOGIES
ENERGY EFFICIENCY
CDM OPPORTUNITIES IN ENERGY SECTOR
FRONTALS IN ENERGY & ENVIRONMENT
OPTIMISATION OF
A CONVENTIONAL THERMAL POWER
PLANT
Efficiency Improvement OpportunitiesAverage 1.5% increase in effeciency of Thermal Power Plants inIndia could result in: CO2 reduction: 4.5% per annum (over 10 Millon Ton/ annum) Coal savings: 9 Million tons per annum Coal savings worth Rs. 630 Crore Higher productivity from same resources; equvalent to
capacity addition. Lower generation cost per KWh.
ENERGY CONSERVATION IN THERMAL POWER STATION
1
% MWHeat input to boiler 100 1428Boiler losses 9.5 137Steam & feed range radiation losses 0.5 7Condenser loss 52.5 750TG set Elec. & Mech. Losses 1.5 20Works Auxiliaries 1 14Generator output 35 500
ENERGY BALANCE OF 500 MW PLANT UNIT
ENERGY CONSERVATION IN THERMAL POWER STATION
2
Basic Rankine Cycle 41.40%Cycle with superheat 45.80%Cycle with reheat 47.50%Cycle with superheat and feedheating 52.00%Cycle with reheating and feedbeating 53.20%Carnot Cycle 52.10%
EFFICIENCY OF VARIOUS IDEAL CYCLES
ENERGY CONSERVATION IN THERMAL POWER STATION
3
4
5
6
7
8
9
10
ENERGY CONSERVATION IN THERMAL POWER STATION
ENERGY EFFICIENT MEASURESDURING OPERATION
Factors during operation - Turbo-Generator:
(1) Controlling the throttle losses.
(2) Optimising condenser performance.
(3) Optimising feed heaters performance.
(4) Optimising auxiliaries consumption.
(5) Reduction in make-up water consumption.
11
Optimization of Prime Performance Functions- Heat Rate & Boiler
Efficiency Heat Rate – The Heat supplied to Steam in Boiler for producing one kWh
MATHEMATICAL MODELING
The mathematical models for the plant performance can be
divided into two main categories 1. Basic Models: These consist of
(a) Steam table model.(b) Combustion model –total approach to combustion of PF.(c) Wet steam expansion model.(d) Boiler heat transfer model for radiation and other unaccountable losses
2. Specific models Boiler accountable losses based on fuel characteristics. Mill operation window. Unburnt Carbon Turbine heat rate. Cylinder efficiency. Condenser performance. Feed heaters. Overall unit heat rate model.
TURBINE HEAT RATE MODEL
The system chosen for the purpose of modeling and subsequent optimization is a
210 MW unit with cycle diagram given in figure 1. This is an information flow
diagram showing temperatures, pressures and flows at critical locations and a
control volume to determine the net energy exchange between the boiler and the
turbine.
Turbine heat rate objective function with reference to above figure is,
Where mass flows are simulated as functions of pressures and temperatures as
given below
KWAKW
hhMhhMhhMTHR fwhsgscrhrhrfwmsms
)()()(
Main, reheat and extraction flows: As functions of Operating paprameters
5.0
1
113250
cr
cr
ms
msms V
P
V
PM
1167 )( glexexmshr MMMMM
27319410
7
77
ex
exex
t
PM
273
362056
66
ex
exex
t
PM
Leak offs from HP turbine in reference to figure 2 are:
gligli
glicrgligli VP
PPKM
22
11
Where Kgli = 8.8766, 75.137, 106, 776 77.6, 4235.0 for i=1, 2, 3, 4 & 5
respectively.
Pcr = Cold reheat line pressures and Curtis wheel pressure at each
value of i for leak offs from both sides of turbine.
Gland steam flow
Turbine heat rate objective function is given on right side of the scheme ‘NPHR’,
given at Figure 3. It gives objective function for turbine heat rate NTHR considering
effect of various operating parameters as well as the associated condenser vacuum
system. Steam properties are drawn from various subroutines and the two-phase
enthalpy through subroutine EXHAL.
An increase in boiler excess air increases steam outlet temperature, as most of the
super heaters are convective type and requires larger spray input for temperature
control, ultimately affecting the turbine heat rate. This is known as two ways
coupling as shown in figure -3. The results of two-way coupling are given at fig. 4 in
which Plant Heat Rate is plotted against boiler excess air and particle size of
pulverized fuel.
2734
46896
2733
3111034
2732
21839
2731
158019
gst
gsP
gst
gsP
gst
gsP
gst
gsPgsM
OPTIMIZING BOILER EFFICIENCY:
A heat balance diagram of 210 MW, boiler shown in Fig.5 is used to estimate the
various boiler losses. While other boiler losses could be determined using standard
ASME PTC- 4.1 Formulations, the combustion losses and the un-burnt carbon loss
could be modeled using probabilistic approach. The probability that a particle would
remain un-burnt depends on the difference between combustion and particle
residence time. This probabilistic approach yields following empirical relation for a
PC boiler for Un-burnt carbon loss
Un-burnt carbon loss per kg of coal= cCVA
E
D
100
)(103008.0
28
Or,
Un-burnt carbon loss per kg of coal= cc CVU
Where:
D: particles diameter in meters
E: Excess air percentage
A: Ash percentage
CVc: Calorific value of Carbon.
Incomplete combustion loss= )()(2
cc UCCVCOCO
CO
Using above models and ASME test code formulations for other losses the boiler efficiency
is determined for different values of excess air and particle diameter.
The boiler efficiency variation with excess air for particle sizes ranging from 80 to 200µ is
plotted in figures 6. It is seen that the excess air considerably affects the boiler efficiency.
The excess air needed to attain maximum boiler efficiency increases with increase in
particle size of the pulverized fuel, with peak at 20 percent excess air for particles of 80µ
size and 50 percent for particles of 200µ size. Fig. 7 for Combustion loss shows that the
unburnt carbon loss drastically increases at low excess air values below 20 percent. The
optimum excess air at a particle diameter is given by:
This formulation has a useful practical value in operation of modern pulverized
fuel fired boilers as depicted at Fig. 8 drawn for particle size variation from 80 to 200
microns and gas outlet temperature variation from 140 to 155 degree Celsius.
229.272.3443.6 DDoptE
INTEGRATED OPTIMIZATION
A computer programme was run for the 210 MW unit as shown schematically in
Figure 9 using specifically designed software ‘ULTMAT’. In this program both Turbine and
Boiler are independently optimized and then through an overriding program for two way
coupling a correction is provided. Some of the results of the program are summarized in
the following Table:
Excess Air for minimum Plant Heat Rate (PHR) at
various back pressures in milli bar (mb) of the
Condenser
Average Particle
Size in Microns
(u)
Excess air for
Optimum Boiler
Efficiency
94.3 mb 130 mb 150 mb
200 u 51.0 % 24.8 % 23.97 % 23.18 %
150 u 24.0 % 21.0 % 20.12 % 19.85 %
80 u 20.2 % 15.0 % 14.77 % 14.35 %
It is seen that the coupling between boiler and turbine becomes more complex with
firing of large size PF particles and at deteriorated backpressures.
The scheme is considered useful in online and on-time performance Monitoring and
Analysis of a Thermal Unit.
REFERENCES
1. Sharma, P.B., Sethi, V.K. "A Technique for computerized Thermal Power Plant Performance Monitoring", Jr. Irrigation and Power, Min. of Energy, India, pp. 417-428, July 1984.
2. Sethi, V.K. Sharma, P.B. and Gupta, SK " A mathematical Model of turbine
heat rate for a Thermal power Plant ", Jr. IEEE, pp. 1257-61, Dec. 1983.
3. Sethi, V.K., Sharma, P.B. and Gupta, SK "Effects of Condenser Performance
on Turbine Heat Rate of a Thermal Power Plant", Jr. of Thermal Engg. Vol. 4, No.2, pp. 46, 1985.
4. Sethi V.K. and Sharma, P.B. "A Model for combustion Losses in a
pulverized fuel fired power plant boiler"; Proc. I. Mech.E. (London), Vol. 202, No. A4.
5. Sethi V.K. and Sharma, P.B. "Computer Aided Optimization of Turbine Heat
Rate of a Thermal Power Plant", Trans. ASME. "Jr. of Energy Resources", 1984.
6. Sethi V. K. “Performance Monitoring and Testing - Some Newer Techniques”, Jl. CEA, December 1997.
IGCC (Integrated Gasification Combined Cycle)
The IGCC process is a two-stage combustion with cleanup between the stages.
The first stage employs the gasifier where partial oxidation of the solid/liquid fuel occurs by limiting the oxidant supply.
The second stage utilizes the gas turbine combustor to complete the combustion thus optimizing the gas turbine/combined cycle (GT/CC) technology with various gasification systems.
IGCC (Integrated Gasification Combined Cycle)
The Syn-Gas produced by the Gasifiers however, needs to be cleaned to remove the particulate, as well as wash away sulphur compounds and NOx compounds before it is used in the Gas Turbine.
It is the Integration of the entire system components, which is extremely important in an IGCC Plant.
Various sub-systems of an IGCC Plant thus are:i) Gasification Plantii) Power Blockiii) Gas Clean-up System
EFFICIENCY IMPROVEMENT FORECASTCONVENTIONAL Vs IGCC
60
55
50
45
40
35
301990 1995 2000 2005 2010
Year of commercial use
Net
The
rma
l Effi
cie
ncy
(%)
Ceramic gasturbine
566 Co 600 Co623 Co
1300 Co 1500 Co
540 Co
650 Co1184 Co
IGCC (15 C Amb)
IGCC (Indian Condition)
Super Critical PC Power Plant (15 C Amb.)o
Super Critical PC Power Plant (Indian Condition)o
Sub Critical PC Power Plant (Indian Condition)
Gasifier
Raw Gas Cooler
CombustionChamber
Comp. Turb.
Alternator
Air
COAL
Ash
Exhaust Gases
Condenser
WHB
Alternator
ST
Air
Fuel
Steam
Gas Clean Up
Booster
Steam
IGCCIGCC
Steam to Super Heater
Cyclone
FurnaceCoal FeedHopper
Ash Cooler
Back-Pass
ESP
ExternalHeat-Exchanger
HP Air
Circulating Fluidized Bed BoilerCirculating Fluidized Bed Boiler
Coal Gasification
Combustion Process: Excess Air Gasification Process: Partial Combustion of
coal with the controlled oxygen supply (generally 20 to 70% of the amount of O2
theoretically required for complete combustion)
C + 1/2 O2 gasification CO
C + H2O gasification CO + H2
EXPECTED IMPROVEMENTS OF IGCC POWER PLANT EFFICIENCY
Flexibility to accept a wide range of fuels IGCC technology has been proven for a variety of
fuels, particularly heavy oils, heavy oil residues, pet-cokes, and bituminous coals in different parts of the globe. In fact the same gasifiers can handle different types of fuels.
Environment Friendly Technology IGCC is an environmentally benign technology. The
emission levels in terms of NOx, SOx and particulate from an IGCC plant have been demonstrated to be much lower when compared to the emission levels from a conventional PC fired steam plant. In fact, no additional equipment is required to meet the environment standards.
Lower Heat Rates & Increased Output The heat rate of plants based on IGCC
technology are projected to be around 2100 kcal/kWh compared to 2500 kcal/kWh for the conventional PC fired plants
Gas Clean-up System
The typical steps for Gas Clean-up System aim at particulate removal, sulfur removal and NOx removal. This is achieved as follows:
• Particulate Removal: Combination of Cyclone Filters & Ceramic candle Filters
• SOx & NOx removal: Combination of steam/water washing and removing the sulfur compounds for recovery of sulfur as a salable product. Hot Gas Clean-Up technology is currently under demonstration phase. Wet scrubbing technology, though with a lower efficiency, still remains the preferred option for gas clean-up systems in IGCC.
• Sulfur from the hot fuel gas is captured by reducing it to H2S, COS, CS2 etc. The current sulfur removal
systems employ zinc based regenerative sorbents (zinc ferrite, zinc titanate etc.) Such zinc based sorbents have been demonstrated at temperatures up to 650 0C.
• Sulfur is also removed by addition of limestone in the gasifier. This is commonly adopted in air-blown fluidized bed gasifiers.
• In fact, in the case of Air Blown Gasifiers, sulfur is captured in the gasifier bed itself (above 90%) because of addition of limestone. The sulfur captured in the bed is removed with ash.
Sulfur Removal
sys = con x { gt ( 1- sc ) (1 – Hbp) + sc } x gen
Where: sys = overall efficiency of the IGCC system
con = fuel conversion efficiency
gt = Gas turbine cycle efficiency
sc = steam cycle efficiency
Hbp = heat by-pass ratio (0< Hbp<1)
gen = generator efficiency
Overall Efficiency of IGCC System
The optimization of overall efficiency of IGCC System sys requires following factors to be
maximized or minimized:
Fuel Conversion Efficiency as high as possible.
Heat by-pass ratio as low as possible. Generator Efficiency as high as possible
Green Energy Technology Center has been set up to focus on following areas:
- Clean Coal Technology & CDM
- Bio-fuels and bio-diesel
- Renewable Energy devices (hybrid) targeted to produce 1 MW Power for the campus
- Energy Conservation & Management
- CO2 Sequestration & CO2 capture technologies
.
RGTU INITIATIVESRGTU INITIATIVES
Coal is going to remain our main stay in Power Scenario. A synergy between Energy & Environment is need of the
day as over 56% GHG Emission is from Energy Generating Systems, for which:Accelerated growth of Power generation should be
coupled with Environmental concern through adoption of Clean Coal Technologies
Renewable Energy Technologies need a fillip particularly for Rural Sector
Heat Rate Optimization & Energy Conservation measures will go a long way in reducing Demand : Supply Gap
IGCC is going to remain the prime CCT of the third Millennium for Indian Power Sector
Summary
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