Overview
Separation accuracy in a coal preparation plant is set by density. The suspension density in a heavy-medium cyclone is the cut point — when it drifts from setpoint, clean-coal yield and ash move with it. Downstream, slime-water concentration drives flocculant dosing, thickener load and filter-press throughput; coal-water slurry preparation and pipeline transport are likewise concentration-controlled.
Typical challenges
- Magnetite-loaded medium is highly abrasive and needs closed-loop density control
- At medium and high solids, slime water is too dark for optical methods (dilute overflow and circulating water are still usually measured by turbidity)
- Entrained gas and coarse particles wear or block insertion-style meters
- Some lines cannot be shut down for tapping, so a non-invasive option is required
Recommended solutions
| Measuring point | Principle | Model |
|---|---|---|
| Correct medium (correct-medium pump discharge; medium inlet of gravity-fed cyclones) | Ultrasonic acoustic impedance; run alongside the existing gauge before closing the loop on it | PS7000 |
| Thickener feed (50–100 g/L, often part-full) | Ultrasonic acoustic impedance, sensor on the lower side wall | PS7000 |
| Thickener underflow / filter-press feed (above 200 g/L) | Ultrasonic acoustic impedance | PS7000 |
| Flotation feed (typically 50–120 g/L) | Ultrasonic acoustic impedance, on the full line after the feed pump and upstream of reagent addition | PS7000 |
| Slime-water line (metal, unlined, no tapping allowed) | Ultrasonic attenuation, clamp-on; coupling and live-slurry feasibility test first, which also sets the lowest usable concentration | PS7010 |
| Coal-water slurry preparation (one coal blend, low-pressure section) | Ultrasonic acoustic impedance, calibrated per coal blend, for trend control rather than as a lab substitute; Coriolis on small bores or a bypass | PS7000 / PS7200 |
Selection notes
At medium and high solids, coal and slime water are too dark for optical methods. Correct-medium density feeds the separation loop directly, so run the new meter alongside the existing gauge and agree the offset before switching over. Thickener feed is a small-signal point — about 0.4 kg/m³ per g/L — so agree temperature compensation and the sampling basis up front; feed lines often run part-full, so the sensor goes on the side wall below the lowest operating level. Fine clays and flocs build up on anything that projects into the flow, which is why insertion forks are a poor fit on thickener feed and underflow. Where a line cannot be tapped, unlined metal pipe can take a clamp-on attenuation meter (PS7010); confirm OD, wall thickness and material first — the signal crosses the wall twice, and rubber-lined pipe usually cannot be penetrated.
