Buyer guide — Quality
Coal quality specifications explained
A coal certificate is a dense page of numbers. This guide explains what each parameter means commercially, and which ones actually matter for your plant.
Calorific value (CV)
Energy per unit mass, quoted in kcal/kg or MJ/kg, and reported gross as received (GAR), air dried (ADB) or net as received (NAR). Always confirm the basis — the same coal can be quoted 400 kcal/kg apart on different bases.
Ash
Non-combustible residue. High ash means more disposal, more abrasion and lower effective CV. Ash fusion temperature matters more than ash percentage in kilns prone to clinkering.
Sulphur
Drives SO₂ emissions and corrosion. Zimbabwean thermal grades typically test at or below 1.0%, and coking grades at or below 0.8%.
Moisture and volatile matter
Total moisture reduces delivered energy and you pay freight on water. Volatile matter drives ignition behaviour and flame length — critical for kiln burners and coke making.
Sizing
Grate and stoker plants need consistent sizing and low fines. Fluidised bed and pulverised systems prefer fines. Ordering the wrong fraction is the single most common buyer error.
Typical export specifications
| Grade | CV (kcal/kg) | Sulphur | Ash | Moisture | Sizing |
|---|---|---|---|---|---|
| Thermal RB1 | 6,000 | ≤ 1.0% | ≤ 15% | ≤ 8% | 0–50 mm |
| Thermal RB3 | 5,500 | ≤ 1.0% | ≤ 20% | ≤ 10% | 0–50 mm |
| Washed peas / nuts | 6,200 | ≤ 0.9% | ≤ 12% | ≤ 7% | 5–25 mm / 25–50 mm |
| Metallurgical (coking) | 7,200 | ≤ 0.8% | ≤ 10% | ≤ 6% | 0–50 mm |
| Foundry / blast coke | 6,800 | ≤ 0.9% | ≤ 12% | ≤ 5% | 20–80 mm |
| Coal fines / duff | 5,200 | ≤ 1.1% | ≤ 22% | ≤ 12% | 0–5 mm |
Frequently asked questions
- What does GAR mean on a coal certificate?
- Gross calorific value as received — measured on the coal in its delivered condition, including moisture.
- Which specification matters most?
- It depends on your plant. Grate boilers care about sizing and clinkering; kilns care about volatile matter and ash fusion; smelters care about ash and sulphur.
Related — Buyer guides
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