3 benefites of cfb boiler over pc-fired boiler

8/10/2019 3 Benefites of Cfb Boiler Over Pc-fired Boiler

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3 Benefits Of CFB-Boiler over PC- fired Boiler

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Benefits OfCFB-Boiler over PC- fired Boiler

CFBC, although nearly 20 year old is a mature technology with more than

400 CFB boilers are in operation world wide ranging from 5MW(e)-

300MW(e) and unto 600MW(e) supercritical CFB boiler is under

contraction stage.

Moreover CFB boiler have potential to replace pulverized coal fired boiler

completely in near future. And we have number of reasons in support of

CFB boiler Over PC-fired boiler.They are: -

3.1 Potential To Burn High Ash Coal:

And we all know that Indian coal contains large percentage of ash (upto

60%, even more). Most of PC-fired boilers are designed to handle upto 50-

55% of ash (maximum). But CFB boiler can burn upto 75% of ash coal

efficiently.

Conclusion:So in order to utilize our low-grade coal (upto 75%), we must

have to employ CFB boiler in current scenario


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Start- Up Comparison Of boilers: PC Vs CFB

Type of Start up CFB PC

Cold 6 7hrs 9 10 hrs

Warm(PC after 8 hrs, CFB after48 hrs)

3 hrs 5 6 hrs

Hot(PC after 2 hrs, CFB after12 hrs)

2 hrs 5 6 hrs

So, as seen above, start up time of CFB is lesser in different type of start up

than PC-fired boiler.

Conclusion: Due to low start up time CFB Boilers are able to save time and

energy. Hence more economical also.

3.2 Multi Fuel Flexibility:

PC boilers can hardly burns low-grade coal of C, D, E and F-Grade of

C.V ranging from 5000 Kcal/Kg to 3000 Kcal/Kg.

But CFB boiler can handle wide range of fuel with low heating values (1500

Kcal/Kg), and high moisture content (upto 60%).

The main reason that CFB boiler is capable of using various fuels and

low-grade fuel mixes is due to large amount of heat stored in circula-ting

bed material and ash at high temperature.

List of fuels that can be burn in CFB boiler:

Coal & Brown Coal

Anthracite

High Ash Coal Wood & Wood Waste

Petroleum Coke

Paper Waste

Plastics

Agricultural Waste

Bark


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Gases

Differing Sludge

Residual & Waste Oil

Oil Shale

Classified Residues

Conclusion: Acceptance of wider range of fuels makes CFB boiler more

fuel economical.

3.3 Reduced Pulverizing Cost & Mills Performance:

CFB-Boiler PC-Fired Boiler Benefits Of CFB

Fuel Size: 6-12 mm < 75 microns Grinding Cost

Reduces

Disadvantages of PC- fired boiler coal mils over CFB boiler coal mills-

Requires frequent maintenance

Power consumption is more

Affected more by foreign particles

High capital cost

Conclusion:Low O&M cost.

3.4 Lower Operating Temperature:

Furnace temperature of CFB boiler is 800-900 Degree Celsius.

Furnace temperature of CFB boiler is 1100-1400 Degree Celsius

Conclusion: This leads to reduction in material cost, O&M cost also

reduces.

3.5 Low Auxiliary Fuel Support :

CFB-Boiler PC-Fired Boiler Benefits Of CFB

Auxiliary Fuel Support upto 20-30% upto 60% Less oil or gas

(Oil & Gas) consumption


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In CFB boiler oil is only needed for cold start-up and operation below 25%

Whereas, PC-fired boiler requires auxiliary fuel support upto 40-60% MCR .

Conclusion: Reduces auxiliary fuel cost and operation cost too.

3.6 Low Flue Gas Velocity:

Erosion is the main cause of higher maintenance in CFB boiler ,due to high

solid loading in flue gas.

CFB boilers have lesser f.g. Velocity compare to PC-boiler.

In CFB- boiler:

F.G. Velocity at superheater=8m/s

In PC- boiler:F.G. velocity at superheater=10-12m/s

Conclusion: Low f.g. Velocity reduces the maintenance cost and also

increases the life cycle of TPS.

3.7 High Heat Transfer Coefficient:

Even though CFB boiler is designed for relatively lower f.g. Velocities, the

heat transfers coeff. Of CFB furnace is nearly double that of PC fired.

3.8 For Same Environmental Performance CFBC Is VeryEconomical:

Emission CFB-Boiler PC-Fired Boiler World Bank Req

SOx (ppm)


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compared with 870 to 1,200C (1,600 to 2,200F) for SNCR. The most

commonly used catalysts are a vanadium/titanium formulation (V2O5

stabilized in a TiO2base) and zeolite materials. The figures below illustrate

hot- and cold-side SCR systems

Average Cost of SCR Unit : US$ 110/kw

For 210MW Unit: (210000KW * 110)= US$23100000= Rs.100 Crore

C) SNCR (Selective Non-Catalytic Reduction) System

NOx emissions in the flue gas are converted into elemental

nitrogen and water by injecting a nitrogen-based chemical reagent,most commonly urea (CH2CONH2) or ammonia (NH3; either

anhydrous or aqueous). The chemical reactions, in a simplified form,

are as follows:

SNCR technologies can reduce NOx emissions by 35 to 50percent without significant impacts on unit performance.

2NO + CH2CONH2+ O2 2N2+ CO2+ 2H2O

NOx + NH3+ O2+ H2O + (H2) N2+ H2O


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Average Cost of SNCR Unit : US$ 20/kw

For 210MW Unit: (210000KW * 20)= US$4200000= Rs.18 Crore

Conclusion: There is no need of such costly system of SCR/SNCR

In CFB boiler because its operating furnace temperature

is low as compare to PC boiler hence Nox formation is very

negligible.

Also for SOx reduction highly costly FGD system is

required in PC boiler but in CFB boiler SOx can reducedin a cost effective manner by just injecting lime stone

in furnace.

3.9 High Combustion Efficiency:

Even though combustion temperature of CFB is low but the fuel resident

time is higher than PC boiler (a single particle can be circulated to 10-50

times depending upon the size of particle)

Conclusion: Combustion efficiency is upto 99% is possible, almost

comparable to PC boiler.

3.10 Repowering:

Repowering means conversion of older PC-boiler into CFB boiler, that can

fit into the existing support steel and also using the other existing

components like:

Boiler Drum Downcomer

Risers

Steel Support

Coal Bunkers

Existing Steel Support

Fans etc.


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Size comparison of PC boiler firing lignite and bituminous coal and its repoweringCFB boiler.

Above figure shows how the new unit fits within the existing bay when

the only required modification to the building is a height increase. The fore-

to-aft footprint of this unit as compared to the Tychy unit is reduced by two

means: a) placing part of the superheater in the vertical downpass, thus

reducing the depth of the horizontal pass, and b) utilizing available space for

the air heater at the side of the downpass .

Main objective of repowering :

1.To increase MW output to rated capacity

2.To reduce O&M cost

3.To use poor quality of domestic fuel

4.To extend the existing plant life.


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Conclusion:The main objective of repowering is to replace existing PC

fired boiler, economically and environmentally acceptable

manner. Many PC boilers have already been repowered

successfully in many countries like USA, China, Ukraine etc.

In India this approach is also under development stage of

some older PC boiler.

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3 benefites of cfb boiler over pc-fired boiler

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