Determining the Gross Calorific Value in Coal

Coal, as it is commonly known, is a solid fossil hydrocarbon fuel material. The gross calorific value of coal is frequently used when determining the total calorific value for a specific amount of coal for fuel value purposes or when establishing the rank of classification of the coal material. The sulfur value and gross calorific value of the coal material is also suitable for determining if the coal material complies to regulatory requirements for industrial fuel use or not.

Sample Requirements

Sample Preparation

A representative, even sample is needed (-60 Mesh).

Standard Method

The standard technique used is ASTM D5865.

Accessories

The following accessories are required for this analysis:

  • 774-204 nickel crucibles
  • 776-978 glass scoop
  • Tweezers
  • 502-461 cotton thread fuse

Calibration Sample

The samples for calibration are LECO 774-208 benzoic acid pellets, or benzoic acid pellets made from NIST 39j.

Method Parameters

The method parameters are:

  • Method - TruSpeed®
  • Standard Mode - ASTM D5865

Thermochemical Corrections

Table 1. shows the thermochemical corrections performed.

Titrant Energy Value 0.0039683 BTU/ml
Sulfur Correction 3.861 BTU/lb
Calculation Mode TruSpeed
Analysis Time 5.0 Minutes
Equilibrate Time 1.5 Minutes
Main Time 2.8 Minutes
Stir Speed 13.0

System Parameters – Database

Table 2. shows the system parameters.

Fuse Type Cotton
Fuse Length 10 cm
Fuse Combustion Heat 0.006255562 BTU/cm
Significant Digits 5
Result Units BTU/lb
Sleep Timeout 300 minutes
Water Temperature 25°C
Auto Increment Sample Name Disable
Alarm Yes

Experimental Procedure

The experimental procedure involves preparing the instrument as recommended in the operator's instruction manual, then the TruSpeed technique is chosen for testing. The unit needs to be next conditioned by testing LECO 774-208 benzoic acid pellet.

Calibration involves weighing ~1.0 g benzoic acid pellet into a 774-204 crucible, entering mass and sample identification into the AC600 software and then placing the crucible with the onto the crucible holder of the combustion vessel.

A single cotton thread fuse is then tied to the electrode wire and one end of the fuse is positioned below the sample. The combustion vessel needs to be cautiously closed and then seal the closure ring. Oxygen is then pressurized in the vessel. The vessel is then vessel in a distilled water container to ensure there are no leaks.

The combustion vessel is next placed on the electrode connectors of the loading mechanism. Analysis can be initiated by pressing the green analyze button to start testing. On completion of analysis, the loading machinery will lift.

The vessel is then removed and depressurized. After depressurizing is completed, clean out the inside of the combustion vessel with distilled water and pour the washings into a clean beaker. One to two drops of indicator is added and titrated with sodium carbonate till the endpoint is achieved.

The titrated amount is filled in milliliters into the nitrogen correction column of the AC600 software. For at least five times, steps 4a through 4n is repeatedly performed and the instrument is thus calibrated.

Sample analysis involves measuring ~0.80 g of a coal sample, entering mass and sample identification into the AC600 software and the crucible holding the sample is placed on to the crucible holder of the combustion vessel.

A separate cotton thread fused to the electrode wire is tied and put one end of the fuse on top of the sample. Steps 4e through 4n are repeated for the sample analysis. Steps 5a through 5e are repeated for all coal samples.

Typical Results

Typical results are shown in Table 3:

Coal A 0.8004 14048
Low Volatile 0.8017 14064
Bituminous 0.8031 14054
  0.8063 14056
  0.8003 14043
  X = 14053
  s = 8
Coal C 0.8012 12983
High Volatile C 0.8032 12969
Bituminous 0.8038 12976
  0.8040 12974
  0.8071 12974
  X = 12975
  s = 5
Coal B 0.8046 13769
High Volatile A 0.8091 13774
Bituminous 0.8047 13766
  0.8004 13754
  0.8007 13768
  X = 13766
  s = 7

 

This information has been sourced, reviewed and adapted from materials provided by LECO Corporation.

For more information on this source, please visit LECO Corporation.

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