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

THANK YOUTHANK YOU