Advances in Thermal Power Plants

7/30/2019 Advances in Thermal Power Plants

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Emerging Strategies andTechnologies for Development of

Thermal Power Dr S. K. Mohapatra

Senior Professor & DOAADepartment of Mechanical engineeringThapar University, Patiala


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Energy from Fossil Fuel

Supply of electricity commenced in 1880 atDarjeeling with the commissioning of a small130 kW hydro-electric power plant.

First thermal power station of one MW capacitywas installed in 1899 at Calcutta.

Installed capacity at the time of independencewas 1352 MW having 15 MW unit size.

Present installed capacity is 1,40,000 MW outof which thermal capacity is approximately90,000 MW.


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Future Projections

Projected demand for electricity in India atthe end of XI plan will be 235000 MW withthe share of coal at 54%.

Power generation by natural gas isexpected to be 22030 MW forming 9.5%of the total generation.


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Status of Power Generation in India

The ratio of hydro-thermal mix which was 51:49in 1962-63 has come down to 25:75.

From environment point of view, there has been

a significant improvement in particulateemission level (98% with combined cyclonecum ESP).

NO 2 level of most of the recent power stations is400 ppm.

SO 2 level is taken care of by installation of tallstacks of 220 metres for 200/250 MW units.


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Emerging Strategies

Fuel Supply Scenarios Switchover to or blending with imported coals Beneficiated coals Washery rejects Coal/lignite water slurry fuels Lignite

Biomass fuels for co-firing with coals Refinery residue


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Switchover to or blending withimported coals

Coal is being imported by many utilitiesparticularly in Western and Southern Indiato meet coal deficits.

Burning blends in PF boilers may produceundesirable consequences. Theperformance of a blend should be

assessed fully from the view point of slagging, fouling, NOx and SOx etc.


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Beneficiated Coal

Reducing ash content to 32% bybeneficiation, the cost of transportation for 18 million tons of coal will reduce by Rs.1000 crores.

Investment made on coal beneficiation islikely to form only 2.5 to 3% of total cost

of a power plant and payback period oninvestment is 4 to 5 years.


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Beneficiated Coal

Ministry of Environment & Forest GOI hasenacted a law recently that power plantswhich are away from the coal mine by1000 km and above and located near urban and sensitive areas shall use onlywashed coals with ash content of 32 2%

from June 2005 onwards.


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Beneficiated Coal

Apart from higher efficiency, reduced oilconsumption and increased life of power components are also the other benefits.

The investment made in coalbeneficiation plants are likely to form only2.5 to 3% of total cost of a power plant

and the payback period on investment is4 to 5 years.


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Washery Rejects

In coking coal washeries the allowableash content is only 17 to 18% and hencethe reject content and their GCV arehigher.

India has 20 coking coal washeries and islikely to add another 15 or 20.

These washeries will produce rejectshaving 60% ash and 1800 kcals/kg C.V.


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Coal/lignite Water Slurry Fuels

These fuels are formulated to consist of 66 to 71% coal, 1-2% additives andremaining water.

Attractive aspects of CWS are that it canbe stored, transported and burnt like thatof liquid fuels.

Technology of coal water slurrypreparation, transportation andcombustion is an established fact.


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Coal/lignite water slurry fuels

It is a Technology Waiting on the Wingsready to take off any time necessaryeither due to increasing price of oil or availability of CWS at a cost cheaper thanoil.

Utilities may find it advantageous from the

view point of consistent fuel quality, lower NOx, SOx, particulate and trace metalemissions as well as lower ash disposalproblems at power plant sites.


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Coal/lignite water slurry fuels

In Indian context co-firing CWS along with coalpulverised and stoker fired boilers to the tune of 20% capacity is likely to be the beginning.

Since low rank sub-bituminous coals andlignites form about half of the worlds solid fuelreserves, it is only a question of time that hotwater dried low rank coal based slurry

preparation units become commercial.


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Lignites

Neyveli, Jayakondam, Srimushnam andMannergudi together in T.N. have about 25billion tons of lignite.

Though pulverised lignite firing systems areconstrained by heating values, sulphur contentand ash slagging, few pulverised lignite firedboilers of 250 MW are anticipated.

For lignites which have low ash fusioncharacteristic FBC/CFBC is better suited somany CFBC boilers are likely to be installed.


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Bio-mass fuels for co-firing

Biomass CombustionWorldwide, interest in using biomass for energy is increasing because of: Political benefits: e.g. reduced

dependency on imported oil Employment creation: biomass fuels

create up to 20 times more employmentthan coal and oil.


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Biomass Combustion

Environmental benefits such as mitigationof greenhouse gas emissions, reductionof acid rain, and soil improvement.

Already around 12% of the global energyrequired is generated by combustion of biomass fuels, which vary from wood to

animal by-products and black liquor.


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Refinery waste fuels

Vacuum residue CV of vacuum residue is around 10,000 kcal/kg and it is

in solid state at room temp.

Flowability of vacuum residue is as good as that of other fuels oils if adequate temperatures are maintained in thestorage tanks and in conveying lines.

IOC is planning to put up power projects based onrefinery residue fuels at five locations; Haryana, Baroda,Gujarat, M.P. and Orissa.


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Table1:Typical characteristics of refinery residue

344003785038250LHV (kJ/kg)

0.280.130.04 Ash0.020.78-Oxygen

2.040.680.31Nitrogen

5.914.906.20Sulphur 3.348.919.65Hydrogen

88.4184.683.8Carbon

Pet coke AsphaltVacuumresidue

Parameters


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Refinery waste fuels

Petroleum Coke The residual coke is low in volatiles and rich in

Va, Fe, Ni, Sulphur. Its reactivity is between

bituminous coal and anthracite and closer tobituminous coal. RPL is putting up a 250 MW plant with CFBC

technology at Jamnagar that will be consuming1.2 mt/annum of petcoke.

About 10 million tons of petcoke are likely to beavailable in the near future with the newrefineries by RPL, IPCL, HPCL, BPCL andESSAR generating petcoke.


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Petroleum coke

It has almost double the calorific value of coal.

RPL is proposing to many power plants tofire blend of petcoke and coal in PF firedboilers, blend optimised so that boiler performance and pollution levels are not

affected.


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Emerging Trends

Fluidised Bed Boilers In fluidised bed, combustible particles are

burned in a self-mixing suspension of gasand solid bed material (usually silica sandand dolomite) in which air for combustionenters from below. Depending upon

fluidisation velocity, bubbling andcirculating fluidised bed combustionsystems can be distinguished.


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Fluidised Bed Boilers

Advantages The smooth, liquid like flow of particles

allows continuous, automaticallycontrolled operation with ease of handling.

Rapid mixing of solids leads to nearlyisothermal conditions throughout thecombustor; hence the operation can becontrolled easily and reliably.


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Fluidised Bed Boilers

Heat and mass transfer rates betweengas and particles are high whencompared with other modes of contacting.

Since bed temperature is kept normallybelow 1000 0C, little atmospheric nitrogenis converted to NOx.

Low-grade fuels such as high ash coaland biomass can be used in the system.


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FBC is a method of burning fuels in abed of heated

particlessuspended in a gasflow.

Main Components: Distributor Plenum Bed of particles

FLUIDIZED BED COMBUSTION


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A Circulating Fluidised Bed


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CFB: Next Option

It can handle a wide range of fuels suchas coal, waste coal, anthracite, lignite,petroleum coke and agricultural waste.

Material handling and feeding systemshould be properly designed to meetthese fuel variations.

In CFBC the elutriated particles arecollected by the solids separators andcirculated back into the furnace.


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PFBC: Future Option

As AFBC and CFBC power plants are based onRankine cycle, their overall plant efficiency issame as that of PC plant.

PFBC combined cycle operation facilitates thehigh pressure combustion gases to run a gasturbine in a Brayton cycle and the high pressuresteam to operate a steam turbine in the

Rankine cycle with overall plant efficiency in therange of 39-43% in addition to better SO 2 control and smaller plant size because of higher operating pressure.


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PFBC

The first demonstration plant of capacityof 130 MW has been operating inStockholm, Sweden since 1996.

Another demonstration plant of 80 MWcapacity is operating in Escatron, Spainusing 36% ash lignite.

Recently a 350 MW PFBC power plant isplanned in Japan and another is in order in USA.


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PFBC


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Emerging Strategies

Supercritical cycles At live steam conditions of 600 0C and 300 bar with

double reheating will help in reducing CO 2emissions

by 20% and increasing plant efficiency by 2-3%. Present power station steam parameters is540 0C/180 bar and single reheat.

Focus is on for developing further the existing hightemp. resistant materials for production of rotors,casings &chests, pipes and headers capable of operating with inlet steam temp. up to 593 0C.


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Supercritical Cycles

Supercritical units are known to havefaster starting times, suitable for dailystart up/shutdown operation, faster load

changes, and better efficiency. Unit sizes of 750-800 MW could be

adopted for this technology for

economical considerations.


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Emerging Strategies

Integrated gasification cycle power plants IGCC is another promising technology which involve

conversion of coal into gas under pressure that canbe fed into gas turbine to generate electricity incombined cycle mode.

The combined cycle operation of using gas turbineand steam turbine results in an overall plantefficiency between 39-45% and emission of

particulate matter, NOx and SOx is also lower. A 250 MW IGCC power plant is being set up at Dadri

(U.P.) recently.


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IGCC


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Emerging Strategies

Integrated Solar Combined Cycle Our country is gifted with vast potential to

generate electric power from solar energy.

Direct solar insolation values of over 8kWh/m 2/day of over 10 months in a year areavailable in the Thar desert stretching over Rajasthan.

Even if 1% of it is used to install solar collectors,it can generate about 6000 MW of electricpower.


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Integrated Solar Combined Cycle

A power plant running purely on solar heat inputwill not have appreciable PLF and will have alow conversion efficiency.

The integrated solar combined cycle integratesnon-conventional solar power generation withconventional combined cycle power generation.

It consists of a gas turbine, steam turbine and

elaborate system of solar heat collectors.


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As much as 6-8% savings in fuel arepossible with this kind of plant operatingat 80% PLF on annual basis.

For a 140 MW ISCC plant solar contribution would be of the order of 35MW and would save liquid fuel to the tune

of 10,300 tons per annum and in theprocess also reduces emission of CO 2 by64,000 tons per annum.


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Clearance has been given to an 140 MWISCC power demonstration project (to belocated in Rajasthan) which would be the

first of its kind in the world. Future plants on this technology may

prove to be commercially viable besides

environmentally friendly mode of power generation.


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Carbon Dioxide Sequestration

It is a by which carbon dioxide is removedfrom the atmosphere and storedindefinitely.

The first step in sequestration is carbondioxide capture. Numerous schemes arepossible, some commercially available at

present, but all with a significant cost.


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Geological Sequestration

Carbon dioxide can be pumped intounderground coal, oil and gas fields andinto saline aquifers. There is significant

evidence to suggest that thesetechniques can reliably retainsequestered carbon dioxide. It is hoped

that studying these natural systems willgive insight into how long termsequestration can be achieved.


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Geological Sequestration

A by-product of coal and oil sequestrationis enhanced methane production. Thismethane can be recovered and the value

of the methane used to offsetsequestration costs. The amount of methane is approximately half that of

carbon dioxide sequestered. Some pilot plants are under way in Australia and the US.


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Ocean Sequestration

The ocean is a primary component of thenatural carbon cycle, acting as a reservoir to balance atmospheric carbon dioxide

levels. It is thought that by deep oceanrelease of carbon dioxide the amount of carbon dioxide held can be significantly

increased. Studies are underway todetermine retention times.


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Mineral and BiologicalSequestration

One method of overcoming the gradualleakage of carbon dioxide back into theatmosphere is to chemically combine it

with naturally occurring minerals such asmagnesium silicate.

The process happens naturally over long

timescales but research suggests thatsignificantly faster conversion rates arepossible.


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Conclusions

In the coming decade coal fired power stationswill be continued to be built because of considerations of security of supply and tosupport indigenous coal production.

Many coastal based power plants may switchover to imported coal.

Many lignite fired CFBC boilers of 250 MW

range are likely to be installed. A few boilers may start firing slurry fuels.


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Conclusions

A number of fluidised bed boilers using coal washeryrejects will be installed near coal washeries.

A number of FBC boilers will come up with agriwaste. Refurbishment of old power plants through upgrading

and repowering will become an important activity inpower sector.

CFBC boilers with super critical steam conditions alsowould be developed.

Repowering of old plants with gas/oil based IGCC alsois a potential candidate.

Integrated solar cycles may also come up. More research activities in carbon dioxide sequestration

will be taken up.


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THANK YOU


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Advances in Thermal Power Plants