Hard coal (bituminous coal): properties, grades and applications / Articles

Hard coal (bituminous coal) is a solid combustible mineral, a sedimentary rock of plant origin formed as a result of long-term metamorphism of ancient peat bogs. It is one of the most important types of energy and technological raw materials, which for centuries has ensured the development of industry, power engineering and metallurgy. Hard coal occupies an intermediate position between young lignite (brown coal) and the most metamorphosed anthracite, possessing a high carbon content (75–92%), relatively low moisture (12–15%) and a high calorific value, which makes it a universal fuel and valuable chemical feedstock.

Chemical Nature and Physicochemical Properties

Hard coal is a complex heterogeneous mixture of high-molecular organic compounds and mineral impurities. The organic mass of coal consists of carbon, hydrogen, oxygen, nitrogen and organic sulfur. The mineral part is represented by clay minerals, quartz, carbonates, iron sulfides (pyrite) and other compounds that form ash during combustion.

The key physicochemical characteristics of hard coal determine its industrial value:

Calorific value: 30.5–36.8 MJ/kg, significantly higher than lignite but lower than anthracite.
Carbon content: 75–92% depending on the degree of metamorphism.
Moisture content: 12–15%, which must be taken into account during transportation and combustion.
Ash content: 5–25% (average 15–18%), depending on the occurrence conditions and beneficiation quality.
Volatile matter yield (Vdaf): 8–40% and above, which determines the behavior of coal when heated and its suitability for coking.
Caking and coking ability: the ability of coal, when heated without air access, to pass into a plastic state and form strong coke — the most important technological property for metallurgy.

Classification, Grades and Standards

In Russia and CIS countries, the classification of hard coals is regulated by GOST 25543-88 (and the updated GOST R 70207-2022) "Brown coals, hard coals and anthracites. Classification according to genetic and technological parameters". Coals are divided into types (brown, hard, anthracite), classes (by vitrinite reflectance), categories, types and subtypes. For practical application, the division of hard coals into technological grades is of the greatest importance:

D (long-flame) — used in power engineering and for the production of semi-coke.
DG (long-flame gas) — used in power engineering and the chemical industry.
G (gas) — used for coking and energy purposes.
GZh (gas fat) and Zh (fat) — valuable raw materials for coking.
KZh (coking fat), K (coking) and KO (coking lean) — the main grades for the production of metallurgical coke.
KS (coking weakly caking) and TS (lean caking) — used in blends for coking and power engineering.
SS (weakly caking) and T (lean) — energy and technological grades.

In international practice, the classification by coal rank is used, where hard coal corresponds to bituminous coal with a carbon content of 45% to 86% and a high calorific value.

In addition to grades, coal is classified by lump size: P (plate, >100 mm), K (large, 50–100 mm), O (nut, 25–50 mm), M (small, 13–25 mm), S (seed, 6–13 mm), Sh (slack, 0–6 mm) and R (run-of-mine, without size restrictions).

Mining and Beneficiation Technology

Hard coal mining is carried out by two main methods: open-pit (surface) and underground (shaft). The open-pit method is used for shallow seams and provides high productivity using powerful mining equipment — draglines, bucket-wheel excavators and heavy dump trucks. The underground method is used for deep seams (up to 1.5 km) and is the only alternative for mining particularly valuable coking coals and anthracites.

The mined coal is typically subjected to beneficiation — the process of removing mineral impurities (rock) to increase the calorific value and reduce ash content. The main beneficiation methods include gravity (heavy-media separators, jigging), flotation, magnetic and electrical methods, as well as dry pneumatic separation for fine coal classes. Beneficiation allows a concentrate with an ash content of 5–10% to be obtained and reduces harmful emissions during combustion.

Applications

Power engineering. The largest area of hard coal consumption. Coal is burned at thermal power plants (TPPs) to produce steam that drives turbines. Energy grades (D, DG, G, SS, T) with certain calorific value, ash content and volatile matter yield are used for these purposes.

Metallurgy and coking. Coking coals of grades G, GZh, Zh, K, KO are raw materials for the production of metallurgical coke — a reducing agent and fuel for blast furnaces. Coking is carried out in coke oven batteries at a temperature of 1000–1100 °C without air access. Coal coke is indispensable in ferrous metallurgy.

Chemical industry. During the coking and semi-coking of coal, valuable chemical products are formed: coal tar, benzene, ammonia, hydrogen sulfide and coke oven gas. From tar, dyes, medicines, plastics and other organic synthesis products are obtained.

Other applications. Hard coal is used in the production of cement, lime and brick (as fuel for firing), as household fuel for heating residential buildings, and as a raw material for the production of artificial graphite, activated carbons and carbon fibers.

Safety and Storage

Hard coal is fire-hazardous: it is prone to spontaneous combustion during storage in large stockpiles due to oxidative processes. During storage, ventilation must be ensured, stockpile height limited and temperature controlled. Coal dust is explosive, so strict dust suppression rules apply at coal enterprises. When working with coal (especially dust), respirators and safety goggles must be used, as prolonged inhalation of coal dust can cause pneumoconiosis (anthracosis). Coal storage is carried out on open areas with hard surfacing or in closed warehouses protected from atmospheric precipitation.

Market and Trends

The global hard coal market remains one of the largest commodity markets for energy carriers, despite the global decarbonization trend. The largest producers are China, India, Indonesia, the USA, Australia and Russia. In Russia, hard coal occupies a significant share in the fuel and energy balance and exports: according to Rosstat, at the beginning of 2024, coal mining was carried out by 179 enterprises, of which 127 carried out open-pit mining and 52 — underground mining.

Key industry trends are: the transition to cleaner combustion technologies (ultra-supercritical steam parameters, CCS — carbon capture and storage technologies), growing demand for coking coals in the Asia-Pacific region (India, China), and the modernization of beneficiation capacities to improve concentrate quality and reduce ash content. Producers with access to high-quality coking coal reserves and modern beneficiation complexes occupy stable competitive positions.

Conclusion

Hard coal remains a fundamental energy and technological raw material, providing power engineering, metallurgy and the chemical industry. Understanding the grade composition according to GOST 25543-88, the differences between thermal and coking coals, mining and beneficiation technologies is the basis for competent material selection and the organization of efficient supplies. Selecting the coal grade for specific technological tasks and organizing logistics requires an individual approach taking into account ash content, sulfur content, volatile matter yield and caking ability.