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IMPACT OF COAL PROPERTIES ON POWER PLANT

1. GeneralCoal fired power station are very capital intensive ventures. Their capital cost is of the

same order as the present worth of coal consumed during the lifetime of the plant. Incountries using imported coal such as J apan life cycle fuel cost (present worth) could easily

exceed the total capital cost. The capital cost of the plant is greatly affected by the quality ofcoal and the environmental restriction. A modern coal fired power station consistence of4x700 MW unit, burning low sulphur coal, presently cost about US$ 1200 per KW to installincluding engineering and financial charges.

A similar plant, burning high sulphur coal, requiring flue gas desulphurization plant (FGD)would typically cost about US$ 1400 per KW.

Capital Cost (million US$)4 x 700 MW coal fired power plant

1. Boiler Plant US $ 11002. Coal Handling including Ship Unloading US $ 20003. Ash Collection Plant US $ 1304. Ash Plant US $ 100

Total Cost of P.P US $ 3330

5. Desulphurization Plant US $ 6206. Denitrification Plant US $ 50

Total cost wi th FGD/De-NOX US $ 4000

Operating and maintenance cost amount typically to US $ 28 per KW per year for a plantwithout FGD and approximately twice as much for a plant with FGD. Large capital savingscan be made if high quality coal can be secured for the lifetime of the power plant.

2. Coal propertiesAs naturally occuring material, coal shows a wide range of properties. For the purpose of

steam raising almost all coals can be used however different properties will requires the use

of different plant designs. In designing or operating equipment it is essential that the meanand probable range of the various coal properties are to be known and allowed for. The coalproperties that affect plant are listed on exhibit 7.

a. Calorifi c ValueCalorific value indicates the inherent quality of the coal determining the total coal volumeto be consumed at the power station for a given energy generation. Calorific valuedepends on the composition of the coal indicated by the ultimate analysis and adverselyaffected by the moisture content and ash content. Exhibit 10 compares the boiler furnacesizes for different fuels, gas, oil, coal and brown coal (lignite). It is noted that from thesefigures lower grade fuels require dramatic increase in size and consequently cost ofboiler.

b. Ash ContentAsh content has an adverse effect on power station plant and costs. An increase in ashcontent results in a direct decrease of the calorific value, requiring greater volume to behandled by the coal plant, boiler, electrostatic precipitators (ESP), and ash plantresulting in larger and expensive plant and increases operating and maintenance cost.Ash is responsible for erosion problem in boiler pressure parts and duct, resulting inadditional operating and maintenance cost and loss of availability. It has been found thaterosion in boiler is proportional velocity to the power of 3.5 (ash % x velocity

3.5).

Accordingly, during the design stage of a boiler the gas velocities are selected as afunction of the ash content in the design coal range, affecting the boiler cost.

c. Moistu re ContentMoisture not only affects directly the calorific value of coal but also the efficiency of theboiler due to the fact that the latent heat of water is lost with the flue gas. For 1%increase in moisture efficiency drops by 0.1%. A greater volume of coal is also required

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Comparison of Furnace Sizes For Dif ferent Fuels

Brown Coal

Coal Oil

Gas

1.20D

1.10W

1.25D

1.25W W

D