Multi Cyclones

Multi Cyclones

WHY ARE MULTI-CYCLONES NECESSARY?

Because particulate matter is detrimental to human health, multi-cyclones are necessary to remove entrained particles from a gas stream before the stream is discharged to the environment through a chimney stack.

Particles that are smaller than 10 µm in size and especially particles that are smaller than 2.5 µm in size (called PM10 and PM2.5 respectively) are the most harmful to human health. PM10 is sufficiently small to become embedded deep in the respiratory system, and PM2.5 can enter directly into the blood stream by passing through the respiratory system.

From an environmental perspective, particles that are entrained in the atmosphere contribute to smog. Smaller particles remain entrained in the atmosphere for many months. This is why it is necessary to remove these particles from the gas stream before the stream is discharged into the environment.

HOW DOES A CYCLONE WORK?

A gas stream that contains particulate matter enters a cyclone tangentially, which causes the gas to spin downwards flinging the particles to the side of the cyclone and releasing them at the bottom or apex of the cyclone when the gas reverses its direction. The bottom of the cyclone is sealed which forces the gas to change direction and spiral back up the centre of the cyclone. This is called a vertical reverse-flow cyclone, and is the most common type.

The efficiency of cyclones increases with decreasing cyclone diameter. In order to treat large quantities of gas with a high efficiency it is most effective to group numerous cyclones with small diameters together. This unit is then called a multi-cyclone.

HOW DOES A MULTI-CYCLONE WORK?

A multi-cyclone is comprised of many individual cyclones that each use the principles of centrifugal force and inertia to separate particulate matter from a gas stream. Often the particulate laden gas enters each individual cyclone within a multi-cyclone through inlet guide vanes, instead of the tangential entry shown in the diagram above. The guide vanes cause the gas to spiral downwards to the apex of each cyclone.

As a result of centrifugal force, the particles in the gas move radially towards the outer walls and then slide downward towards the apex where they are collected. Near the apex, the clean gas reverses its downward spiral and moves upwards in a second, smaller spiral before it exits from the top of each cyclone. When the gas changes direction, the inertia of the particles keeps them moving downwards, out of the cyclone and into the collection area. This process is shown in the picture beneath and in the video that follows:

A multi-cyclone is comprised of many individual cyclones that each use the principles of centrifugal force and inertia to separate particulate matter from a gas stream. Often the particulate laden gas enters each individual cyclone within a multi-cyclone through inlet guide vanes, instead of the tangential entry shown in the diagram above. The guide vanes cause the gas to spiral downwards to the apex of each cyclone.

As a result of centrifugal force, the particles in the gas move radially towards the outer walls and then slide downward towards the apex where they are collected. Near the apex, the clean gas reverses its downward spiral and moves upwards in a second, smaller spiral before it exits from the top of each cyclone. When the gas changes direction, the inertia of the particles keeps them moving downwards, out of the cyclone and into the collection area.