Design criteria for multicyclones in a limited space

Multicyclones for gas-solids separation consist of many parallel cyclone cells within a common housing having a common solids hopper. They are preferably used for high-efficiency separation of a gas-solids flow. Principally increasing the number of cyclone cells and decreasing their size improves the efficiency of a multicyclone without changing the flow cross-section of the device and its pressure drop. The prerequisite for that is however that gas and solids can be equally distributed among all cyclone cells and bypass flows through the solids discharge openings from one cyclone cell to the other can be avoided.In many cases, multicyclones use standard reverse flow cyclone cells with an axial inlet, also called swirl tubes. Alternatively, multicyclones can be made from uniflow cyclone cells. Deviating from swirl tubes uniflow cyclones have gas and particles passing through them in only one direction exiting at the same end of the device which makes them much more compact than swirl tubes. In recent years comprehensive experimental and theoretical studies of uniflow cyclones have strongly improved their understanding and led to approved design criteria and calculation methods similar to those which have already been achieved for standard reverse flow cyclones. In the present investigation well-proven calculation programs have been applied to compare multiclones based on swirl tube cells with those based on uniflow cyclone cells regarding their efficiency to separate a specified gas-solids feed at a given pressure drop. The investigation has been performed by varying the available space for the dedusting device, the number of cyclone cells, the cyclone pressure drop, the particle size distribution of the feed and the particle density. The results indicate that, under the considered operation conditions, a uniflow multiclone is more efficient than its swirl tube counterpart if space is limited onto about the volume needed by the uniflow multiclone for its optimum performance and the available pressure drop is low. Furthermore, the results show, that regardless of any limitation on volume or pressure drop the efficiencies of both multiclone types approach each other with increasing cell number, pressure drop and particle size, as well as particle density of the solids feed.