At a glance
Coal crusher selection balances feed top size, product top size, coal hardness, moisture, acceptable fines generation, and required capacity. Roll crushers and sizers minimize fines; hammer mills produce finer products at the cost of higher fines generation. The right choice depends on the duty.
Crusher types in coal service
Four crusher families cover most coal crushing duties. Single- and double-roll crushers reduce coal by compression between rotating rolls; they produce minimal fines and are preferred for soft coal. Sizers use twin counter-rotating shafts with tooth-like picks; they handle sticky, wet coal well and are widely used at pit-tops and run-of-mine handling. Hammer mills reduce coal by impact in a high-speed rotor with swinging hammers; they produce a finer product with more fines, and are used in coal preparation and power plant coal handling. Impact crushers (horizontal-shaft impactors) sit between hammer mills and roll crushers in fines generation.
Selection criteria
Five factors dominate selection: feed top size (limits the crusher inlet); product top size (sets reduction ratio and crusher type); coal hardness measured by Hardgrove Grindability Index (sets wear rate and energy consumption); moisture content (affects sticky-coal handling); and capacity (sets crusher size). Acceptable fines generation is the 'soft' factor that often shifts the choice between otherwise-equivalent options.
Roll crushers and sizers
Use these for run-of-mine and pit-top crushing where you want to minimize fines. Roll crushers handle dry-to-moderate moisture coal. Sizers handle wet, sticky coal better than any other type because the picks self-clean as the shafts rotate. Capacity is set by roll/shaft diameter and length.
Hammer mills
Use these in preparation plants and power plant coal handling where a finer product is required. Wear part replacement is more frequent than with roll crushers; protection against tramp metal is essential. Hammer mills are sensitive to wet coal — they tend to plug if moisture is too high.
Two-stage versus single-stage crushing
For high reduction ratios (e.g. ROM at 1,500 mm to product at 25 mm), two-stage crushing is usually preferred. The first stage handles large lumps at moderate reduction; the second stage handles a sized feed and can be optimized for product quality. Single-stage crushing is simpler but produces more fines because the crusher operates near its reduction-ratio limit.