Specific weight of hard coal and its features
Coal deposits form in the depths of the Earth. This happens through the accumulation of plant residues that undergo decomposition and the pressure of rock layers. The most suitable environment for the occurrence of this mineral is swampy peatland formed by shifts of tectonic plates. Hard coal undergoes significant chemical changes in its structure: it becomes enriched with carbon and loses moisture, oxygen and volatile substances. Mineral impurities in coal are represented by coal-forming substances and mineral neoformations. They take the form of fine dispersion, small crystals, thin interlayers, lenses and concretions. As a result of complex processes, a solid black combustible rock is formed.
Hard coal has a number of physical features:
- solid;
- dense;
- mechanically strong;
- the ability of gelified and lipoid components, when heated, to turn into a plastic mass and form a porous coke material.
| Coal type | Specific weight (g/cm³) |
| Humic | 1.4 - 1.5 |
| Gulitolite brown coal | 1.6 - 1.8 |
| Anthracite | 1.25 - 1.27 |
According to the data above, the weight of 1 m³ of hard coal ranges from 1200 kg/m³ to 1500 kg/m³. Hard coal is suitable for industrial use when its ash content is not higher than 30%.
The most important criterion for this mineral is its calorific value. Hard coal has high heat output: wet ash-free mass releases about 23.8 MJ/kg, or 5700 kcal/kg. The composition of hard coal depends on the place where the deposits formed and includes a number of complex components:
| Substance | Carbon | Hydrogen | Oxygen | Sulfur | Nitrogen | Volatile substances | Water | Ash |
| Mass fraction, % | 75 - 95 | 1.5 - 5.7 | 1.5 - 15 | 0.5 - 4 | >1.5 | 2 - 45 | 4 - 14 | 2 - 45 |
The content of the components mentioned above varies depending on the grade of hard coal. Mineral impurities are dangerous during combustion, and some compounds have harmful carcinogenic properties.
Applications of hard coal
Hard coal is widely used in many areas of production:
- electric power generation;
- heavy metallurgical industry (coke);
- chemical industry;
- production of structural materials;
- hydrogenation (aromatic products);
- fuel energy sector (synthetic, gaseous and liquid fuel);
- production of nitrogen-enriched fertilizers;
- manufacture of wax and plastics.
Calculations of hard coal volume and mass
Due to the extensive use of this mineral, there is a justified need to know the bulk weight of hard coal. The specific weight of hard coal is divided into two types:
- specific weight of hard coal with natural ash content;
- specific weight of ash-free mass.
For industrial purposes, this division is extremely important when calculating the need for the fuel component.
The specific weight of hard coal has the following calculation formula:
Specific weight of hard coal = weight of solid particles ⁄ volume of solid particles
Specific weight can change depending on the type of coal rock. Calculations of its changes are shown in the table.
Frequently Asked Questions
Can the density of hard coal be used for precise calculations?
The density and weight values for hard coal in this article are reference values. They are suitable for preliminary estimates, but design, construction, production and other critical calculations should be checked against standards, material datasheets or measurement results.
Why can the actual weight of hard coal differ from the table?
The actual weight of hard coal depends on composition, moisture, temperature, porosity, fraction size, material grade and measurement conditions. Because of this, real values may differ from the average table data.
How do you calculate the mass of hard coal from density?
For an approximate calculation, use the formula: mass = density × volume. If the density of hard coal is given in kg/m³ and the volume is in m³, the result will be in kilograms.