A 3-DIMENSIONAL STUDY OF CYCLONE COMBUSTORS

A study of a 100 kW scaled model of a vertical non-slagging cyclone co mbustor has been carried out, using a Dantec 5 W fibre-optic LDA syste m. This study complements a programme of work performed on 500 kW and 1.5 MW coal-fired prototype units designed for operation on kilns and furnaces. The 3-dimensionality in the combustion chamber was examined for a single inlet configuration. Both isothermal and combustion condi tions, firing on natural gas with 68% excess air, were analysed. The t angential velocity profiles followed the expected Rankine vortex form. Under isothermal conditions it was found that the tangential velocity exhibited little 3-dimensionality. Under combustion conditions they w ere found to increase in magnitude, with the maxima moving radially in wards. The axial velocity and hence secondary flows displayed greater 3-dimensional effects, and formed either two or three annuli-depending on whether the central recirculation zone was present. Temperature me asurements were also made in the combustion chamber. These profiles we re found to peak at the same radial position as the tangential velocit ies, thereby indicating that combustion was occurring in this region. Overall, under combustion conditions the 3-dimensionality of the flow reduced to the point where it was primarily axisymmetric inside the cy clone chamber. Finally the analysis of the combustion gases taken isok inetically from the chamber showed that complete combustion had occurr ed before the exhaust was reached.