Coal is a heterogeneous solid mixture and there is nature in grade what is different started from lignite, sub bituminous, and anthracite. By virtue of matter content flies (volatile matter) and level of temperature calorie yielded by coal is divided to to become 9 main class. In commerce is recognized term Hard Coal and brown of Coal. Hard Coal is coal type yielding calorie gross more than 5700 kcal/kg and divided :
a.Matter content flies (volatile matter) until 33 %, including class 1-5.
b.Matter content flies (volatile matter) bigger 33 %, including class 6-9.
Hard coal is coal type with higher level calorie result compared to bituminous/sub bituminous and lignite (brown of coal).
Type coal character anthracite :
+ Black and hardly gleams and compact
+ Very caloric value height, very carbon content height.
+ Very few water content.
+ Very few ash content.
+ Very few sulfur content.
Type coal character bituminous/sub bituminous :
+ Black and gleams, less compact.
+ High caloric value, relative carbon content of height.
+ Water content a few.
+ Ash content a few.
+ Sulfuric content a few.
Lignite type coal character (brown of coal) :
+ Black and very fragile.
+ Low caloric value, carbon content a few.
+ High water content.
+ Ash content many.
+ Sulfuric content many.
Visible coal characters with analysis as follows :
a. Analysis Proximate, consisted of :
1. Moist (moisture) which in the form of free moist (free moisture), wafting moist (inherent moisture), Total moist (total moisture).
2. Ash content (ash)
3. Carbon (Fixed carbon)
4. Matter flies (volatile matter
b. Analysis Ultimate, consisted of element analysis C, H, O, N, Sulfur, P and Cl.
c. Caloric value, there is 2 kinds of caloric value that is :
1. Caloric value net (net calorific value or low heating value), that is combustion caloric value where all water (H2O) calculated in a state of presentation of gas.
2. Gross caloric value (grosses calorific value or high heating value), that is combustion caloric value where all water (H2O) calculated in a state of liquid existence. This caloric value expressed in cal/gram, Btu/lb or MJ/kg.
d. Sulfuric total
Sulfuric or brimstone in coal can be met as pyrite mineral, marchasite, calcium organic sulfate or brimstone which at the time of combustion will turn into SO2.
e. Dusty analysis
Dusty happened at coal firing will form oxides as follows : SiO2, Al2O3, Fe2O3, TiO2, Mn3O4, CAO, Magnesia, Na2O, K2O. This ash especially would in mixed solid with klinker (at cement industry) and will influence quality of cement.
f. Grind Index (Hard grove Index)
Be a number which show can easy or not of coal is grind to become powder fuel. More and smallest the number is more and more situation firm of the coal. The price of hard grove index for Indonesia coal ranges from 35-60.
g. The bearing coal character with volatile matter
As according to in character, coal generally is divided to 4 kinds :
1. Anthracite, contains a few volatiles matter
2. Bituminous, contains volatile medium matter
3. Lignite, contains many volatiles matter
4. Peat
Sources : Batubara and Gambut, Ir. Sukandarrumidi, MSc, Ph.D. Gajah Mada University Press