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Proximate and Ultimate Analysis of Power Plant Coal

Added: (Sat Nov 04 2017)

Pressbox (Press Release) - The proximate analysis determines only the Fix carbon, Volatile matter. The ultimate analysis is useful in determining required air for combustion for power plants coal.
Different coal sources have different constituents in the coal.
Even coal from the same mine at different seams has got different constituents.
Every constituent has got different impact on coal combustion as such it is very important to know them in detail

There are two different methods of doing above
Proximate coal analysis
Ultimate coal analysis

Proximate coal analysis
The proximate analysis determines only the Fix carbon, Volatile matter, Moisture and Ash percentage in the coal sample given for analysis.
To carry out proximate analysis very simple apparatus are required
Measurement of moisture:
Moisture is carried out by placing a weighted powder sample of raw power plant coal of size minus 200 microns in an uncovered crucible and it is placed in the oven at 108 plus minus 2-degree centigrade.
The sample is cooled to room temperature and weighed again. The loss of weight represents moisture.
Measurement of the volatile matter:
Determination of volatile matter is carried out by taking a weighed fresh sample of coal and is placed in the covered crucible and is heated in the furnace at 900 plus minus 15-degree centigrade.
The sample is cooled and weighed.
The loss of weight represents Moisture+ Volatile matter
Remainder is coke (Fix carbon + Ash)
Measurement of Carbon and Ash:
The cover from the crucible of test carried out to determine volatile matter is to be removed and the crucible is to be heated over bushel burner until all carbon is burnt.
The residue is weighed which is Ash.
100 ( Moisture + Volatile matter + Ash)= Fix carbon
Fix carbon is mostly consist of carbon but also contains some hydrogen, oxygen, sulfur, nitrogen
Volatile matters are methane, hydrocarbons, carbon monoxide, hydrogen and incombustible gases like CO2 and N2. Thus volatile matter is an index of gaseous fuels present in coal
Typical proximate coal analysis of Indian coal
Constituents Indian coal
Moisture 6
Ash 38
Volatile matter 21
Fix carbon 35
The significance of various parameters of proximate coal analysis:
Fix carbon:
Fix carbon acts as a main heat generator during burning.
Fix carbon gives a rough estimate of heating value of coal
Volatile matter:
Volatile matter also contributes to the heating value of coal
Increase in percentage of volatile matter in coal proportionately increases flame length and helps in easier ignition of coal
Sets of minimum limit of furnace height and volume
Influences secondary oil support
Ash:
Ash is an impurity which will not burn
Ash content is important in design of furnace grate, combustion volume, pollution control equipment (ESP) and Ash handling plant
Ash increases transportation, handling, storage cost
Ash affects combustion efficiency and boiler efficiency
Ash causes clinkering and slagging problems in boiler
Moisture :
Moisture increases transportation, handling, storage cost
Moisture decreases the heat content per kg of power plant coal
Moisture increases heat loss due to evaporation and superheating of vapor
Moisture helps in binding the fines
Moisture helps in radiation heat transfer

Ultimate coal analysis
The ultimate analysis indicates the various elemental chemical constituents in coal such as carbon, hydrogen, oxygen, sulfur, nitrogen etc.
The ultimate analysis is useful in determining the quantity of air required for combustion and volume and composition of combustion gases. This information is required for calculation of flame temperature and flue gas duct design

Typical ultimate coal analysis of Indian coal
Parameter Indian coal
Moisture 6
Ash 38
Carbon 41
Hydrogen 3.35
Nitrogen 1.25
Sulphur 0.4
Oxygen 10
Effect of sulfur content:
Affects clinkering and slagging tendencies
Corrodes chimney and other equipment
Limits flue gas exit temperature
Proximate and ultimate analysis of coal


There are four basic terms of analysis as below:
As received basis
Air dry basis
Dry basis
Dry and ash free basis
As received means as it has come
Air dry basis means 100 Surface moisture
Dry basis means 100 (Surface moisture + Inherent moisture)
Dry and ash free basis means 100 - (surface moisture + inherent moisture + Ash)
The calorific value of thermal coal:
The calorific value of power plant coal is the amount of potential energy in coal that can be converted into actual heating ability.
Calorific value of coal can be determined either by calculation from chemical analysis or by burning a sample in calorimeter
Calculation of CV of coal based on proximate analysis gives very rough estimate of calorific value of coal but is used for deciding the grade of coal and formula adopted by Coal India is as below:
Useful heat value of coal = 8900 (M + Ash)
Ultimate analysis gives fairly correct calorific value of coal and formula to be used is as below
GCV of coal in Kcal/Kg = (355 x C + 1148 x H + 95 x S 145 X O) / 4.1868
C, H, S, O are % figures obtained in the ultimate analysis of coal.
Caloric value obtained by calorimeter is the only correct value and gives GCV
There are two heating values of coal as below
GCV = Gross calorific value = High Heating value = HHV
NCV = Net calorific value = Low Heating value = LHV
In any fuel of power plant coal containing hydrogen calorific value found by calorimeter is higher than that obtainable under most working conditions in power plant boiler practice by an amount equal to the latent heat of vaporization of water
There is no absolute measure of LHV but is calculated by following formula
LHV in Kcal/Kg = HHV 50.6 H 5.85 M 0.191 O
H, M, O are % figures obtained from ultimate analysis of coal
HHV is only considered in boiler practice.

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