Coal Qualities
Definition
Measures the energy content of coal, typically expressed in megajoules per kilogram (MJ/kg) or British thermal units (BTU).
Summary
A higher calorific value means more energy output per kilogram of coal. Anthracite has the highest calorific value (around 30 MJ/kg), making it ideal for high-energy applications such as steel production and electricity generation. Bituminous coal also has a high calorific value, suited for similar uses.
Definition
Indicates the percentage of carbon remaining after volatile components are removed, reflecting coal’s combustibility and energy potential.
Summary
Higher fixed carbon content enhances burning efficiency. Anthracite, with up to 97% fixed carbon, burns cleaner and longer, while bituminous coal, ranging from 45-86% fixed carbon, is versatile for both power and industrial applications.
Definition
The amount of water in coal is usually shown as a percentage.
Summary
Lower moisture levels improve burning efficiency, as less energy is spent on evaporation. Anthracite and bituminous coal have low moisture (about 2-8%), enhancing their efficiency, while lignite has high moisture (up to 70%), making it less suitable for high-efficiency applications.
Definition
The mineral residue left after coal combustion.
Summary
Lower ash content is preferred, as higher ash reduces energy output and increases disposal costs. Anthracite typically has low ash content, while some domestic power-grade coals may contain up to 30% ash, which is suitable for boiler use but less desirable for export.
Definition
Measures the sulfur percentage in coal.
Summary
Lower sulfur content is preferred to meet environmental standards, as sulfur emissions contribute to pollutants like sulfur dioxide (SO₂). Anthracite has minimal sulfur, resulting in cleaner combustion, while bituminous coal has moderate sulfur levels, often requiring emissions control.
Definition
Compounds in coal that vaporize when heated, such as methane and other hydrocarbons.
Summary
High volatile matter improves coal’s ignition but may reduce combustion cleanliness. Bituminous coal, with moderate to high volatile content, ignites easily for power generation, while anthracite’s low volatile matter supports a slower, smokeless burn, making it ideal for heating.
Market Applications
Electricity Generation
Metallurgical Applications
Heating and Industrial Uses
Mining Methods: Bord and Pillar Mining
The bord-and-pillar method is a widely used technique in South African underground coal mining, particularly for seams between 1 and 5 meters thick. This approach involves creating “boards” (horizontal passages) while leaving “pillars” of unmined coal in place to support the roof, forming a stable grid structure. It effectively balances resource extraction with ground stability, making it ideal for shallow to moderate-depth coal seams.
- Grid Layout
- Pillar Dimensions
- Roof Support
Effective ventilation is essential to maintain air quality and reduce gas hazards in bord-and-pillar mining:
- Air Circulation
- Monitoring
- Computerized ventilation modelling
In bord-and-pillar mining, coal is extracted using either Drill and Blast or Continuous Miner (CM) methods, chosen based on factors like project size, seam conditions, and cost.