Uneven solids distribution causes wear-out problem in Cyclones in Parallel

 

Introduction

There are two common reasons for choosing to install more than one cyclone in parallel.

1. One device handling the whole gas stream would become too large for practical purposes.

2.  One large cyclone could not achieve the required separation efficiency.

Cyclones in parallel offer engineers a practical way to increase the collection efficiency without increasing pressure loss by splitting up the solid-laden process stream over two or more identical cyclones and operating them in parallel.

Parallel arrangements of cyclones can be modeled using the same model equations as for single units. The solids-bearing gas stream is simply divided evenly between the parallel-working units.

Overriding concern when designing cyclones in parallel

When designing parallel cyclones, the overriding concern is that the gas and solids be distributed evenly among identical units, and consequently, each will theoretically have the same pressure drop.

One way of achieving this is to design and arrange the cyclones such that,

1. each individual unit experiences the same total pressure (dynamic and static) at the inlet and,
2. the gas exiting each gas outlet pipe experiences the same flow resistance.

These two criteria normally can be met by rendering both the inlet and overflow piping as symmetrical as possible. But, with the on-site space limitation, this is not always guaranteed.

Wear problem on cyclones in parallel

At some point in the upstream piping the incoming, dust-laden gas flow will usually encounter a bend which will tend to segregate the incoming solids to its outer wall (see the pictures below). This can lead to solids maldistribution in the inlet piping and, in turn, hopper ‘crossflow’ if the cyclones share the same hopper. For this reason, bends should be located well ahead of any parallel bank of cyclones – preferably 10 pipe diameters or its equivalent, or a drop-out box can be put into use ahead of the cyclone bank to separate big particles and re-mix the dust laden gas flow.

The two pictures below are example of solids maldistribution caused by a bend just ahead of the inlet manifold of the cyclone bank. The solids maldistribution was revealed by the wear-out problem on the first cyclone unit.

The first picture shows the first cyclone of the quad suffers the worst wear-out on the inlet scroll and the lower part of the cone because of solids maldistribution caused by the bend just ahead of the cyclone inlet manifold.

Patches on the inlet scroll and lower cone of a quad-cyclone

The second picture below was taken half a year later after the first picture above was taken. The wear-out problem on the lower cone became worse and worse and the customer had to finally block it off.

one unit was blocked off because of wear-out

The more solids a cyclone unit receives, the lower the pressure loss it will have. And consequently, it will take more gas flow, which causes a higher inlet velocity, making  the unit wear out quickly, as shown in the example above.

 

Cyclone services by Airvate that you can afford

Whether you are sizing a cyclone or using one now, if you need any services listed below, feel free to contact Airvate at info@airvate.com.

1. Existing cyclones in parallel don’t work as expected.
2. Want to solve the uneven solids distribution problem in applications of dual-cyclone, quad-cyclone, or multi-barrel cyclone; with this issue, one or two cyclone barrels get more dust, and consequently, it causes wear-out in their inlet section and cone bottom more quickly than on others.
3.  Existing cyclones in series don’t work as expected.
4.  Have to change dimensions of inlet, gas outlet, and/or dust outlet, and want to know how the changes affect cyclone performance.
5. Need a new cyclone that has to meet the specified requirement.
6.  Need a new cyclone with the best available performance in a limited space.
7. Want to avoid or reduce the wear-out or blockage that always happens to your cyclone.
8. Want to reuse an existing cyclone and know its performance in a new process.
9. Want to optimize the performance of an existing low-efficiency cyclone.
10. The existing cyclone collection efficiency is too high for the process and you want to lower it.
11. The existing cyclone has either too high or too low of a pressure drop
12. Want to optimize the performance or solve any problem of the combo of an existing cyclone (as a pre-cleaner) and a baghouse.