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What Is a Multicyclone?
A multicyclone is a dust pre-separator built from many small axial-entry cyclone tubes arranged in parallel between an upper clean-gas plenum and a common ash hopper. MDSJ Process — DUCON manufactures multicyclones for hot flue gas where a downstream bag filter or electrostatic precipitator needs protection from coarse dust, sparks and embers.
- Working principle: Dirty gas enters each tube through 8 fixed guide vanes set at 40°. The vanes create a downward vortex; dust is thrown to the tube wall and slides into the hopper, while clean gas leaves upward through a Ø120 mm vortex finder into the plenum.
- Tube sizes: Ø150 mm for fine ash and high efficiency; Ø230 and Ø320 mm for heavy dust loads and coarse particles. The Ø150 element is 1,200 mm long with a 600 mm cylindrical separation zone, a 400 mm cone and a Ø50 mm dust outlet.
- Materials: Tubes and vanes in grey cast iron EN-GJL-250 (GG25), 8 mm wall including wear allowance, so no separate lining is needed. S355JR steel tubes are an alternative. The casing is welded, gas-tight steel with external stiffeners.
- Ash discharge: Pyramidal hopper with a minimum 60° wall angle, flanged outlet and rotary valve for continuous discharge.
Pressure Drop and Efficiency
Pressure drop rises with the square of tube velocity. Higher velocity gives a smaller cut size and higher efficiency. A low pressure drop means more tubes and a larger casing. Typical values are 5–20 mbar and 80–95% efficiency on boiler ash, depending on particle size distribution. In a 100,000 m³/h biomass and sewage sludge boiler duty with d50 52 µm, 132 elements at 11.9 m/s gave 8–9.6 mbar and about 83%; 96 elements at 16.4 m/s gave 15–18 mbar and about 92%.
Role in the Gas Cleaning Line
An outlet of 0.5–1.2 g/Nm³ is above most emission limits. The multicyclone is therefore a pre-separator: it lowers the dust load and removes sparks and glowing particles before a bag filter or electrostatic precipitator brings the gas to the limit value. It has no moving parts; maintenance covers vane and tube wear checks through access doors and hopper sealing.
