The document outlines the coal sampling and analysis procedure according to Indian standards. It describes how to collect representative coal samples from shipments in increments and prepare them for analysis. The main steps of proximate analysis are then explained to determine the moisture content, ash content, volatile matter, and fixed carbon of the coal samples on both an air dried and equilibrated basis. Commercial coal grades are assigned based on the useful heat value calculated from these analyses.

1. COAL SAMPLING PROCEDURE
AND ANALYSIS OF COAL
COAL : Non renewable fossil solid fuel formed by a series of natural geochemical process from
the plant remains accumulated together with other sediments.
COAL SAMPLING & SAMPLE PREPARATION
The BIS specification No. 1S-436 (Part-I, Section-I) 1964 and IS:436 (Part-II) 1965
describes the method of sampling and sub sampling of the coal/coke so as to achieve a
representative sample as homogenous as possible for laboratory in 212 micron size.
COAL SAMPLING
Indian standard Institute has laid down some specific sampling procedure which is
obligatory to both the supplier and consumer otherwise both the parties may mutually adopt
some methods on the basis of the ISI specification of sampling.
For each consignment of 250 tonne one sample is recommended. After receipt of coal rack in
TPS, placement report is filled in which wagon numbers and name of the colliery is mentioned.
(2) The standard practice is to collect about 350kg samples for 250 tonnes of coal received
in increments.
(3) 25% of total wagons received should be selected from coal sampling Random Table.
R A N D O M T A B L E
8 1 7 4 6 7 9 5 7 0 5 6 5 1 5 4 5 0 5 3
6 1 3 7 4 2 6 2 9 3 9 6 3 4 1 8 2 2 8 9
5 2 0 7 1 6 2 9 3 9 0 4 7 1 1 4 7 6 7 8
4 3 0 8 7 7 2 5 7 2 4 9 8 6 0 3 8 3 4 5
6 5 3 2 2 7 4 0 6 3 5 7 9 7 8 4 8 2 8 7
2 1 5 8 1 1 2 3 8 0 1 0 3 0 0 1 1 0 0 4 4
3 1 9 0 5 5 8 8 1 3 3 6 2 4 9 1 1 9 6 4
7 3 9 8 2 0 0 5 6 8 4 6 6 9 8 5 9 4 5 9
3 3 1 5 3 5 2 6 7 9 9 2 3 8 1 2 4 1 1 7
7 5 6 6 9 9 0 9 0 6 4 7 4 8 6 0 2 8 0 2
(4) About 5 Kg of sample are collected each from four corners and centre from every
selected wagon by digging 0.5 Mtr. Depth.
(5) The bulk of 350 Kg sample so collected are well mixed and reduced either by mechanical
sample dividers or by hand methods using shovel by coning and quartering etc.
(6) The gross sample is reduced to 50 Kg in stages. The 50 Kg mass is crushed to ?” size
and again reduced by coming and quartering in stages to get a final sample of about
2 Kg. This sample is further reduced by coning and quartering till 1 Kg of sample is
obtained.
(7) 1 Kg of sample is finally powdered (72 mesh) in Raymond will for analysis.
(8) Out of 1 Kg, pulverized fine powdered sample (72 mesh). Two packets of 250 gm
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2. samples are prepared one is referee sample and other is for analysis.
PROXIMATE ANALYSIS :
Proximate analysis which comprises determination of moisture, ash, volatile matter and
fixed carbon expressed in terms of weight percentage. This gives quick and valuable information
regarding commercial classification and determination of suitability for a particular Industrial
use.
PROXIMATE ANALYSIS OF COAL
A) Determination of moisture on air dried basis :-
1) Take about 1.5 gms. Of air dried sample in a weighing dish and spread the coal in a
uniformly thin layer.
2) Put the weighing dish in hot air oven.
3) Heat at temp. of 1080 C + 20 C until there is no further loss in mass. This normally takes
about 1.5 to 3 hrs.
4) Express the loss in mass as a % of the total moisture of sample.
100 (M2 - M3)
5) M % (Air dried basis) = —————————
(M2 - M1)
M1 = Mass in gms. Of empty weighing dish plus lid.
M2 = Mass in gms. Of weighing dish with lid plus coal.
M3 = Mass in gms. Of weighing dish with lid plus dry coal.
B) Determination of ash on air dried basis :-
1) Weigh a clean dry empty crucible and lid.
2) Weigh accurately about 1.0 gm. Of laboratory sample and spread the coal uniformly in
the crucible.
3) Insert the uncovered crucible into the muffle furnace at room temperature.
4) Raise the temp. to 5000 C in 30 minutes and 8150 + 100 C in further 30 to 60 minutes
and maintain at this temp. for 60 minutes. Cover the crucible with lid and remove from
the muffle furnace and allow to cool for 10 minutes and finally take in a Desicator.
Weigh the mass of ash by difference.
100 (M3 - M1)
5) Ash % = —————————
(On Air dried basis) (M2 - M1)
M1 = Mass in gms. of empty weighing crucible plus lid.
M2 = Mass in gms. of weighing crucible with lid plus coal.
M3 = Mass in gms. of weighing crucible with lid plus Ash.
UHV Kcal/Kg = 8900 - 138 (M% + Ash %)
C) % Volatile matter (Vm) :
Weigh silica crucible + 1 gm sample with lid heated at 9100 C in furnace for 7 Minutes.
Then calculate,
% Vm as loss in difference calculated in % - Moisture% = % Volatile matter.
D) Determination of Moisture on Equilibrated Basis :
(At 400 C & 600 C R.H.)
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3. 1) Take 4 to 5 gms. coal sample in a clean conical flask/beaker 100 ml. Cap.
2) Pour 20 ml D.M. Water.
3) Heat this mixture on heating pad/Electrical heater, gently Boil it 10 to 15 minutes.
4) Cool the mixture 10 to 15 minutes & filter all the material in next conical flask and
pressing the contain in between filter papers.
5) Take about 1.5 gms. of wet coal in dish and spread it uniform layer.
6) Prepare the H2 SO4 acid having Sp. Gr. 1.280 and transfer it in desiccator. The quantity
of H2 SO4 (Sp. Gr. 1.280) may be 300 ml. to 400 ml. in one desiccator.
7) Put the above petridesh without cover in the desiccator.
8) Close the desiccator & put this desiccator in a humidity oven at 400 C for 72 hrs.
9) Very next day break up the coal lumps & make fine powder & again put in the above
stated oven. Total timing for keeping the desiccator is 72 Hrs. Or till the change
in mass does not exceed the 0.001 gms.
E) After 72 Hrs. analyze the moisture percentage by as usual procedure as stated in air
dry basis & Calculate into percentage.
NOTE :Only Moisture is actually tested on equilibrated basis. All other air dried
values are then converted into equilibrated basis, by calculations as follows
:
100 - M2(Eq. M%)
Equilibrated Ash % = ————————————— X A% of air dry basis.
100 - M1 (Air dried M%)
100 - M2(Eq. M%)
Equilibrated V.M.% = —————————————— X VM% of air dry basis.
100 - M1 (Air dried M%)
Equilibrated F.C.% = 100-[Total of M% + Ash% + VM%]
Equilibrated UHV Kcal/kg = 8900 - 138 (M% + ash%)
COMMERCIAL GRADES OF COAL FOR BILLING CALCULATED
ON THE BASIS OF UHV (USEFUL HEAT VALUE)
GRADE UHV (Kcal/Kg)
A
B
C
D
E
F
G
Un / Graded
> = 6200
5601 - 6200
4941 - 5600
4201 – 4940
3361 – 4200
2401 – 3360
1301 – 2400
< 1300
Equilibrated UHV Kcal/kg = 8900 - 138 (M% + Ash %)
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