Proximate analysis of coal indicates the percentage by weight of the fixed carbon, volatiles matter, Ash and moisture content in coal.
Significance of various parameters in proximate analysis of coal:
It is the solid fuel left in the furnace after volatile matter is distilled off. It gives a rough estimate of heating value of coal.
Volatile matters are the methane, hydrocarbons, hydrogen and incombustible gases like carbon dioxide and nitrogen found in coal. Typical range of volatile matter is 20 to 35 %.
It is an impurity that will not burn. Typical range of ash is 5 to 40%.
It decreases the heat content per kg of coal. Typical range of moisture is 0.5 to 10%.
Typical range of sulphur is 0.5 to 0.8%.
Procedure – Proximate Analysis of Coal by ASTM Method on Air Dry Basis (ADB)
1. Determination of Total Moisture (TM)
- Air drying cabinet – Capable of maintain a constant and uniform temperature of 40°C.
- Non-Corrodible or S.S Tray of approx. 1000 sq.cm in area and 5 cm in depth.
- Weighing vessel and oven capable of maintain 107 ±3°C.
STAGE 1A (Air Drying)
- Take the weight of the moisture free empty dry tray.
- Take about 4 kg of 4.75mm coal samples and spread it uniformly in the tray.
- Allow the samples in the tray to air dry at atmospheric temperature in a well-ventilated place free from dust.
- Leaves the samples for air drying, mix or stir from time to time being careful not to lose any coal particles till weight loss is less than 0.1%/h.
- Record the weight of the tray + sample after air drying.
STAGE 1B (Air Drying Cabinet)
- After determination of 1A weight loss crush the whole sample upto 2.36mm. Weight 1 kg of 2.36mm sample in tray, spread it uniformly.
- Allow the sample in the tray to dry in an air-drying cabinet with temperature not more than 40°C.
- Allow the sample in the air drying cabinet Mix or stir from time to time being careful not to lose and coal particles till weight loss is less than 0.1%/h.
- Record the weight of the tray + sample after air drying cabinet.
STAGE II (Residual Moisture)
- Heat the empty dish at 107 ±3°C and weigh after colling.
- Pass the air dried sample through 250 micron sieve.
- Spread about 1 gm of 250 micron sample uniformly in the dish.
- Place the uncover dish in the hot air oven at 107 ±3°C for 1 hr.
- Remove the dish from the oven, allow it to cool in desiccator and weigh.
- Record the weight of dish + sample after drying.
Calculation of Total Moisture (TM)
M’ = [R(100-ADL’)/100]+ADL’
TM = [M’(100-ADL)/100]+ADL
TM = Total Moisture
R = Residual Moisture
ADL’ = Moisture in crushed laboratory sample in Stage 1A
ADL = Air dry loss (Stage 1B)
2. Determination of Volatile Matter
- Crucible and lid – Cylindrical crucible with a well-fitting lid both of fused silica and of other suitable ceramic material or platinum.
- Stand – On which the crucible is placed in the muffle furnace to achieve the appropriate rate of heating.
- Muffle Furnace – Capable of maintaining a zone of constant and uniform temperature of 950 ±20°C.
- The final prepared (250 micron) sample is air dried.
- Heat the empty V.M Crucible with lid at 950 ±20°C for 7 minutes and weigh after cooling. Let the weight of empty crucible + lid be M1 gm.
- Take 1gm sample and spread it uniformly in the crucible. Let the weight of the sample+ crucible + lid be M2 gm.
- Place the sample with crucible and lid in the muffle furnace. Heat it for exactly 7 minutes at a temperature of 950 ±20°C.
- Remove the crucible. Then cool it in a metal plate. Let the weight of the sample+ crucible+ lid be M3 gm.
Calculation of Volatile Matter
VM % on ADB = 100 * (M2-M3)/(M2-M1)-M0
M0 = % of moisture in the sample on air dry basis (Inherent Moisture).
3. Determination of Ash Content
- Muffle Furnace
- Silica Dish
- The final prepared sample (250 micron) is air dried.
- Weigh a clean, dry empty dish. Let its weight be M1 gm.
- Weigh approximately 1 gm of the sample and distribute the same to the dish and weigh. Let the weight of the dish + sample be M2 gm.
- Then insert the dish into the muffle furnace at room temperature, and then raise the temp to 450°C – 500°C in 1 hour and then furnace to heat coal sample so that the final temperature of 750°C±15°C is reached by the end of second hour maintain the temperature for another 2 hrs.
- Then remove the dish from the furnace and then allow it to cool, Let the weight of the dish+ash be M3 gm.
% Ash on ADB = 100*(M3-M1)/(M2-M1)
4. Determination of Gross Calorific Value (GCV) By Bomb Calorimeter
Bomb calorimeter, Crucible, Ignition Circuit, Pressure regulator and pressure gauge, Benzoic acid, Oxygen (30 atmospheric), Distilled water, Cotton thread/ Fuse wire (Ni/Cr).
- Switch on the instrument, maintain room temp at approximately 25 degree Celsius.
- Clean the sampler holder and bomb then put 1-2 ml distilled water.
- Connect firing wire across the terminals of the bombs.
- Weigh 1 gm sample (air dried) into previously cleaned and dry crucible.
- Place the crucible along with sample in the holder and arrange the ends of firing wire touch the sample.
- Place the sample holder into the bomb and the bomb lid and air pressure screws are tightly screwed.
- The bomb is filled with oxygen to 30 atmospheric pressure.
- Put 2 litre water in the bucket and place in the jacket.
- The bomb is lowered in the bucket with help of tongue.
- Connect the electrode and close the cover.
- Press start.
- ID Code: Type the sample ID of the sample as received
Weight of sample: Type the weight of the sample taken in gm.
- The temperature after pre fire should be raised, it is not increasing then discards the sample and proceed new one.
- The result of GCV will be displayed after 8 minutes.
- Remove the bomb, release the pressure and dismantle the bomb.
- After analysis of all parameters of proximate analysis and GCV the results are entered in daily log sheet and the final result are entered in to the ISS/ICTMS portal with sample ID. The decoded sample ID is then downloaded in excel & reported accordingly.
5. Determination of Sulphur Content
Preparation of Test Sample
Sample shall be pulverized to pass 212/250 micron.
- Nickle Crucible
- Muffle furnace 800±25°C
Reagents and solutions
- Eschka mixture
- HCL (1:1)
- BaCl2 (10%)
- Methyl Orange Indicator
- AgNo3 (1%)
- Filter Paper – 41 &42
- Weight 1 gm coal sample+3 gm Eschka mixture in nickel crucible and cover with about 1 gm of eschka mixture.
- Place the crucible in cold muffle furnace & raise the temperature to 800±25°C.
- Hold the crucible in furnace at 800±25°C for 1.30 hrs.
- Extract the material with 100ml hot water(distilled water) & digest it for 30 min in hot plate with continue stirring.
- Filter through whatman 41 and wash the residue with hot water.
- Make the filtrate amounting 250 ml. Add 1-2 drops of methy red indicator in filtre until colour of indicator changes.
- Add conc HCL (1:1) and then add 1 ml of HCL in excss.
- Boil and Add 10ml BaCl2 solution from pipette while stirring constantly.
- Continue boiling for 15min and allow to stand for at least 2 hrs.
- Filter through whatman 42 paper, wash with hot distilled water until 1 drop of AgNO3 (1%) solution produced no more than a slight opalescence.
- Place the wet filter paper containing the precipitate of BaSO4 in nickle crucible, ignited at 800±25°C for 15 minutes.
- Weight BaSO4
- Carry out a blank determination under the same conditions but omitting the material.
% of Sulphur by weight = (A-B)*C*32/233*100
A= Weight in gram of BaSO4 in sample
B= Weight in gram of BaSO4 in blank.
C= Weight in gram sample taken.
6. Determination of Fixed Carbon
% of Fixed Carbon = 100-% of Total Moisture -% of Volatile Matter – % of Ash Content