Method for Determining the Calorific Value of Solid Combustibles

Method for Determining the Calorific Value of Solid Combustibles

Solid combustibles refer to solid substances that can ignite upon contact with fire, heat sources, impact, or friction. They cover a wide variety of types, ranging from daily necessities to industrial raw materials, such as wood, paper, and textiles.

Key Characteristics

Flammability: Easy to ignite rapidly upon contact with fire sources, with fast flame spread.

Hazard: Combustion may produce toxic substances, and fire extinguishing can be difficult (e.g., metal powders may intensify reactions when exposed to water).

Diversity: Including self-reactive substances, stable explosives, etc.

Common Types：

Natural Solids: Wood, peat, lignite, bituminous coal, anthracite, oil shale, etc.

Processed Solids: Charcoal, coke, briquettes, coal balls, etc.

Special Solids: Solid alcohol, solid rocket fuel, etc.

Experimental Objectives：

1.Determine Calorific Value: Accurately measure the heat released during the complete combustion of solid combustibles (e.g., wood, coal) using equipment such as oxygen bomb calorimeters. This is a core indicator for evaluating fuel quality.

2.Master Experimental Techniques: Learn the operating procedures of oxygen bomb calorimeters, including key steps such as oxygen charging, ignition, and temperature measurement. Understand the difference between combustion heat and calorific value, and identify error sources requiring correction in the experiment (e.g., combustion of ignition wire, heat absorption by the instrument).

3.Understand Instrument Principles: Familiarize with the structure of oxygen bomb calorimeters (e.g., bomb cylinder, temperature sensor, stirrer); master the heat capacity calibration method and calibrate the instrument using standard substances such as benzoic acid.

Experimental Samples and Instruments

Experimental Samples: Solid combustibles

Experimental Instruments: SH500 Calorimeter, compliant with GB/T 384

Experimental Procedures

1.Instrument Preparation and Calibration：

Oxygen Bomb Calorimeter Inspection: Ensure the inner wall of the oxygen bomb is clean and free of residues; check whether the ignition wire (nichrome wire) is intact and the electrodes are in good contact.

Heat Capacity Calibration: Use benzoic acid (standard calorific value: 26450 J/g) as the calibration substance. Weigh 0.5~1.0 g (accurate to 0.0001 g) and place it in the oxygen bomb crucible. Add 10 mL of distilled water into the oxygen bomb, fill it with oxygen to a pressure of 2.6~3.3 MPa, and let it stand for 5 minutes to exhaust air. Place the oxygen bomb in the inner cylinder of the calorimeter, add 2000 g of distilled water (temperature difference with the ambient temperature ≤ 1℃), start stirring and temperature collection. Power on for ignition, record the water temperature change, and calculate the heat capacity (C). Repeat the operation 3 times and take the average value; the deviation of heat capacity shall be ≤ 0.5%.

2.Sample Preparation

Solid Sample Treatment: Grind the solid combustible (e.g., coal, biomass pellets) to a particle size of < 0.2 mm to ensure uniformity; weigh 0.5~1.0 g of the sample (accurate to 0.0001 g) and place it in a dry crucible.

Moisture Control: If the sample contains moisture, dry it at 105℃ to constant weight to avoid the impact of moisture evaporation on calorific value calculation.

Oxygen Bomb Charging and Ignition

3.Oxygen Charging Operation: Place the sample crucible into the oxygen bomb, add 10 mL of distilled water (to dissolve combustion products), install the ignition wire and make it contact the sample. Fill the oxygen bomb with oxygen to a pressure of 2.8~3.0 MPa, and let it stand for 5 minutes to exhaust air, ensuring no air residue is left.

Ignition and Combustion: Place the oxygen bomb in the inner cylinder of the calorimeter, add 2000 g of distilled water, start stirring and temperature collection. Power on for ignition, record the water temperature change (initial period, main period, final period), and capture the maximum temperature point during the main period. After combustion, check that there is no unburned residue in the oxygen bomb; otherwise, the test must be repeated.

Experimental Results

This experiment strictly complies with the GB/T 384-2025 standard. The measured net calorific value of the coal sample is 17,780.83 J/g (4247.6 kcal/kg), with good repeatability and reliable data.