Cyclone separator

A cyclone separator removes particulate from a gas stream by centrifugal force: gas enters tangentially at the top of a vertical cylinder, spirals downward, and exits axially at the top through an inner pipe (vortex finder); heavier particles are thrown outward to the wall, slide down the conical bottom, and discharge through the dipleg below.

Where cyclones are used

CFB boiler primary separators - large-diameter, high-temperature
Cement preheater cyclones - multi-stage gas-to-meal heat exchange
Pre-cleaners ahead of baghouses and ESPs - knock out coarse dust to reduce downstream load
Process gas separation in chemical and refining duty

Cyclone fouling

Wall build-up - dust accretes on the wall and gradually narrows the gas path; flow re-organises and efficiency drops
Dipleg pluggage - separated material backs up in the dipleg, eventually re-entraining
Vortex finder fouling - alters internal swirl pattern

Cleaning

Sonic horns installed on the cyclone shell or dipleg keep wall deposits from consolidating. On cement preheater cyclones particularly, sonic horns are the standard preventive against the coatings that form under alternative-fuel firing.

Separation mechanism

A cyclone forces gas to rotate. Particles with enough inertia move toward the wall, lose momentum and fall into the cone and dipleg, while cleaned gas exits through the vortex finder. Efficiency improves with particle size, particle density and inlet velocity, but higher velocity also increases pressure drop and erosion.

Cyclones are robust because they have no filter media and few moving parts. Their limitation is fine particulate. Very small particles follow the gas stream and are better handled by ESPs, baghouses or scrubbers downstream.

Design and operating issues

Key design features include inlet shape, barrel diameter, cone angle, vortex finder depth, dipleg seal and wear protection. Small geometry changes can alter the internal vortex. Erosion at the inlet or cone can reduce efficiency and create holes that admit false air.

Failure modes include wall build-up, dipleg pluggage, vortex-finder wear, refractory failure, gas bypass and re-entrainment from an overfilled hopper. Operators infer cyclone health from pressure drop, outlet dust loading, hopper discharge, temperature profile and inspection of wear patterns.

Acoustic-cleaning context

Sonic horns can help where cyclone performance is limited by sticky wall deposits or dipleg bridging. They are not a substitute for correct cyclone sizing or for downstream fine-particle control. In cement, CFB and biomass applications, acoustic cleaning is most useful at the cone, dipleg and hopper interface, where a small blockage can quickly become a process upset.

Field checks

Cyclone performance is judged from pressure drop, inlet velocity, solids loading, outlet dust, underflow discharge and wear pattern. If pressure drop falls, the cyclone may be bypassing, eroded or starved of flow. If pressure drop rises, the inlet, cone, vortex finder or dipleg may be fouled. Good diagnosis needs both gas-side and solids-side checks because a plugged discharge can ruin separation even when the inlet geometry is intact.

Maintenance teams inspect refractory or wear liners, inlet scrolls, vortex finders, cone tips, diplegs, rotary valves and expansion joints. Abrasive service can thin steel or remove liners, while sticky dust can narrow the cone until the separation pattern collapses. Acoustic cleaning is useful for dry build-up on cyclone walls, cones and dipleg entries when the deposit is not strongly sintered. It is not a substitute for correct inlet velocity, gas distribution, wear protection or a reliable solids discharge path.

Particle size is the hidden variable. A cyclone that performs well on coarse ash may pass fine fume even when it is mechanically perfect. If upstream combustion, milling or material handling creates more fines, the outlet loading can rise without any visible cyclone fault. Testing should therefore include dust size distribution as well as mass concentration.