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Cyclones

large cyclone

CFW manufactures bespoke cyclones tailored to specific applications. We have developed and installed many cyclone units built to customer specifications. Our comprehensive design and fabrication facilities and support for services enables us to provide reliable, durable equipment.

Cyclones are used for a wide variety of air pollution control applications and are also used as a separation device. Dry cyclones are typically used to recover dry powder or dust where air concentrations of dust are high (for example as a primary dust collection device in rotary dryers). Their low energy costs and maintenance requirements make them an ideal method of removing larger particles: they are about 90% efficient for particles larger than 5 µm and somewhat effective for particles of 2-3 µm. Pressure drops vary widely. Particulates are more efficiently removed than with spray towers, but less efficiently than with venturi scrubbers. A typical application for cyclone filters is sawdust removal in a saw mill. Where smaller particles must be collected, they should be supplemented by additional scrubbers or filters.

The performance of a cyclone depends on many factors. The most important variables that increase collection efficiency are:

  • Higher particle sizes and densities
  • Higher air velocities in the cyclone
  • Small cyclone diameters
  • Longer gas residence times (residence time increases with cyclone length)

While the open construction of cyclones makes them resistant to plugging, and therefore easier to maintain, the spray nozzles can become plugged and the sides of the chamber can be damaged by erosion from abrasive particulates or by corrosion. Designs with easily accessible nozzles can reduce the difficulty of nozzle cleaning, while the sides of the chamber should be constructed from robust, abrasion-resistant materials.

The rotating action of a dryer, blasting from a sand blasting booth, or vaporization from cooking can entrain particles in air streams. The gas containing the particles enters the cyclonic separation chamber tangentially and the particles are concentrated along the walls of the device by the corkscrew motion of the gas stream, where they are collected.

In the case of wet cyclones, liquid is sprayed into the chamber so that the particles are caught in droplets and washed out. Wet cyclone designs include irrigated cyclones, where the gas enters the chamber through the top and changes direction back upwards, and cyclonic spray scrubbers, where the air proceeds from the bottom to the top. These cyclones are also used to control very soluble pollutant gases, but they are less efficient for this purpose than for removing particulates. The same high gas velocity that makes them relatively efficient for removing particulates compared to spray towers also reduces the contact time of the liquid with the gases.

Cyclones can also be classified according to their diameter. The diameter of wider cyclones may vary from about 30 cm to more than 4 m. These models are generally used to remove coarse nuisance dusts and larger particles. Typical pressure drops during operation are lower than for multicyclones.

Smaller, narrower cyclones are often grouped in multi-cyclone collectors which often act on airstreams with moderate or large particulate loads and can either stand on their own or act as pre-collectors for electrostatic or fabric-type dust collectors.

Standard cyclones do not handle sticky particulates well and custom solutions may be needed. The material tends to build up on the sides of the cyclone. Stringy substances can also build up on the inlet vanes of multi-cyclones, which prevents the establishment of proper cyclonic airflow patterns, severely reducing collection efficiency.

Individual narrow-diameter cyclones remove particulates more efficiently. However, the tangential high air velocities achieved in these cyclones result in fast-moving particles that are very abrasive. This means that erosion problems can be worse for smaller cyclones. Larger particles are more abrasive. These cyclones are also not able to handle large air volumes. Multi-cyclones usually have relatively high pressure drops.

Cyclones can protect fans and other equipment from abrasive dusts, improve working environments and prevent the loss of valuable powders that can be reused or sold as a product.