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.

The values above describe the density of the coal substance or lump material. For storage, delivery and truck-body calculations, bulk density is more important: because of voids between the pieces, 1 m³ of hard coal usually weighs less than a solid cube without voids. 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, but the value depends on the coal grade, moisture and ash content. For dry ash-free mass, about 30.5 - 36.8 MJ/kg is commonly quoted; in working condition, with moisture and ash present, the actual calorific value can be noticeably lower. The composition of hard coal depends on the place where the deposits formed and includes a number of complex components:

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, ash content and material moisture.