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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 temperaturel
Find the below link for more details: https://marcepinc.com/blog/proximate-and-ultimate-analysis-of-power-plant-coal
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