CYCLONE APEX

Research project P 14739 Cyclone Apex Gernot STAUDINGER 09.10.2000 The cyclone as a dust precipitator is well known. While the respective literature is extensive, it is by no means complete. The lower part of the cylone called Apex where dust exits to the bunker - has long been considered to affect seperation efficiency. Nevertheles it has received little attention so far. Proposals exits for optimal design of the Apex, however the rules for calculation of separation efficiency do not differentiate between the different Apex geometries used in practice. The relationship between pressure drop and the different Apex-geometries is largely ignored. It is becoming increasingly clear that repeatedly proposed optimal geometry with an upward pointing cone below or in the Apex is far from being optimal in all situations, and that simpler and more common Apex- geomentries give significantly better seperation and different pressure drop of the cyclone. The aim of the project proposed here is to understand the gas flow and the separation mechanism in and below the Apex and then to derive practical advice concerning the design of optimal Apex geometries under certain boundary conditions. This is achieved by measuring gas velocity and by CFD simulation of the gas flow. The separation of small particles is thought to be influenced by agglomeration, To check for this, pictures of particles (or agglomerates) which descend in the Apex will be made with a CCD camera, equipped with a long distance microscope. A powerful laser will be used to produce a sheet of light. By using various types of dust material, the influence of dust type on agglomeration behaviour can also be examined. At the end of the experimental phase. three of the tested cyclones will be scaled to match the conditions of the high temperature and pressure test plant of TU Braunschweig. They will be tested in a two month campaign.

The cyclone can separate particles (solid or liquid) from a continuous, fluid phase. This is brought about by the centrifugal force which acts on the particles in the rotating fluid. At common cyclones the fluid- (in our case air-) outlet is at the top, whereas the particles (in our case dust) leave the cyclone at the conical bottom, called apex. The configuration of the apex was repeatedly mentioned as having an effect on separation efficiency, but it has not been subject of a systematic investigation so far. In this research project five different configurations of the dust outlet were tested at one and the same cyclone at identical operating conditions and significant differences in separation efficiency and pressure loss were found. One "new" configuration, which was not treated in literature so far proved to be advantageous if compared to the traditional configurations. The advantage is, that a cyclone, equipped with this new apex can precipitate more fine particles than a cyclone with a traditional apex configuration. To elucidate the mechanisms behind the different separation efficiencies, extensive mathematical simulations and measurements with LDA and PDA were undertaken. It was found that already a very low solids loading changes the flow pattern in the cyclone. Consequently a CFD- Simulation of the flow of the pure fluid phase cannot give insight into the real fluid flow in a cyclone, if particles are present. Above this the existence of agglomerates could be proven, however the size of these agglomerates and the number of elementary particles is not yet known, but subject for further research.