Sort coal by picking out stone and brassy pyrite by hand where it comes off the face, then screen it through rough grates into lump, medium and fines, and send lump coal to stoves and fines to the forge or to briquettes. Reject any coal that is heavy for its size or banded with stone, because it will deliver ash instead of heat.
Part of Coal Surface Mining
Hand-picking, size grading and quality rejection of mined coal, with the intended use of each size.
Size Decides Where Each Coal Burns Best
The parent article states the working rule: lump coal (fist-size and larger) burns best in stoves, and fines are better for forge work or briquetting. Lump leaves gaps for air to pass through a fuel bed. Fines pack and choke the draught in a stove, but in a forge the blast pushes air through them and they burn well.
| Grade | Rough size | Use |
|---|---|---|
| Lump | Fist-size and larger | Stoves, household heating |
| Medium | Walnut to egg | Cooking stoves, small grates |
| Fines | Smaller, with dust | Forge, briquettes, mixed with lump |
The size cuts are a choice, not a standard; fix them to your own grates and stoves.
Method
Step 1: Pick at the face. Pull out stone, clay and shale as the coal comes out. A piece that is heavy for its size, or shows stone layers, is rejected (parent article).
Step 2: Screen. Build two grates of parallel bars or woven poles at different spacings in a sloped frame. Throw coal onto the upper grate; large lumps roll off, the next size drops through to the second grate and the fines drop through both. A sample set of bar spacings can be 50 mm and 20 mm, adjusted to what your stoves take.
Step 3: Check sulphur. Pick out brassy specks and nodules of pyrite; they raise sulphur in the smoke and corrode flues.
Step 4: Test a batch for ash. Weigh and burn a sample as described in the coal quality article. Grade batches by ash, not just by size.
Step 5: Store each grade separately. Keep fines away from the lump pile; fines restrict air flow and promote heating in storage.
Common Mistakes
- Mixing grades in the stove. Fines among lump clog the air gaps.
- Dry screening in a closed shed. It fills the air with fine dust.
- Keeping the stone “just in case”. Heavy waste costs transport and ash handling.
Safety
Screening is a dust job
Working a grate raises respirable dust. Dampen the coal, work in the open and upwind, and wear the best respirator you have (Dust & Respiratory Protection). Do not dry sweep.
What’s Next
- Learn next: Washing — separating the rock picking cannot reach
- Combine with: Storage & Weather Protection — keeping each grade