Dust Outlet Research Articles

Investigation of the flow pattern in different dust outlet geometries of a gas cyclone by laser Doppler anemometry

The separation process in a gas cyclone can be divided in three determining steps: (1) the movement of the particles in the cyclone chamber towards the cyclone wall due to centrifugal force, (2) agglomeration of particles at the wall and in the dust bin and (3) separation of the particles and/or agglomerates in the bin. For many years the dust outlet has been considered to be very important for the separation process. However, the actual geometry of the dust outlet was rarely investigated. Tests performed by the authors prove that different dust outlet geometries have significantly different separation efficiencies.Laser Doppler anemometry measurements in a cyclone equipped with three different dust outlet geometries show that both the gas flow in the dust outlet and the gas flow within the lower part of the cyclone change. By examining the different flows within the different dust outlet geometries the influence of the geometry on the separation efficiency can be explained. The best dust outlet of a cyclone is a downcomer tube, due to the “additional” separation process which takes place within it.

The Dust Outlet of a Gas Cyclone and Its Effects on Separation Efficiency

So far, the effect of the dust outlet geometry on the separation process in gas cyclones has rarely been investigated. In this work, extensive tests have shown that by changing the dust outlet geometry separation efficiency can be improved significantly due to a change of the flow pattern in the lower part of the cyclone.

The Dust Outlet of a Gas Cyclone and Its Effects on Separation Efficiency

The Dust Outlet of a Gas Cyclone and Its Effects on Separation Efficiency

Investigations into Cyclone Dust Collectors

The paper describes experimental investigations made in the mechanical engineering laboratory at Delft, in the field of cyclone separators. These investigations aimed first at determining the most efficient shape of a cyclone, by measuring the effect of a variation of each of its principal dimensions on the efficiency; as a result, a very efficient cyclone shape was developed. The influence of the position of a cyclone on the efficiency was examined, and a new type of cyclone with curved axis, horizontal gas exhaust, and vertical downward dust outlet was constructed. The flow of gas and dust inside a cyclone was examined. The static pressure and the three components of the gas velocity at different points in a cyclone were measured with a globe-Pitot tube. In a cyclone exhausting to atmosphere, a core of low pressure extends over the entire height of the cyclone. Inside this core the flow is very turbulent and unsteady, so that the gas velocities cannot be measured exactly; outside, the pressure is high throughout the remainder of the cyclone. With the exception of the turbulent area in the centre, the total velocity of the gas deviates only slightly from the tangential component V t, which increases as the distance from the centre of the cyclone diminishes. The vertical component V h is directed downwards along the cyclone walls and carries the dust particles to the bunker, and the radial velocity V r is directed towards the centre in the greater part of the cyclone; but in the very turbulent centre, V r is directed outwards and V h upwards. From these measurements a simple cyclone theory was developed, enabling the approximate calculation of the size of the largest dust particles that may escape a cyclone. The effect of a variation in the quantity of gas on the efficiency was determined; this effect was small for a well-constructed cyclone. Efficiencies are given for different sizes of similar shaped cyclones and for various sizes of dust particles. These data enable the selection of a cyclone collector suitable for a particular kind of dust, and the choice of cyclone dimensions for a given efficiency. A method of measuring the dust content of a gas-flow, by means of a small cyclone, is described.