Influence of inter-particle collisions and agglomeration on cyclone performance and collection efficiency

For further improving the understanding of particle separation in gas cyclones including the effect of agglomeration, numerical calculations based on the coupled Euler/Lagrange approach were conducted using an open source CFD code. The gas phase was simulated by LES (large eddy simulations) combined with a dynamic Smagorinsky sub-grid-scale (SGS) model for resolving the highly anisotropic turbulence structure. Two-way coupling (i.e., the influence of the particles on the fluid flow field) was accounted for in the momentum equations as well as in the SGS turbulence. Solid particle agglomeration was modelled on the basis of the stochastic inter-particle collision model.(1) In that respect, it is also important to consider the effect of particle dispersion by SGS turbulence and wall roughness in particle-wall collisions,(2) which eventually will also modify inter-particle collisions and agglomeration. For describing the agglomeration phenomenon, two different approaches were tested. The first one, the so-called sphere model, considers that the agglomerate diameter is calculated from the sum of the volume of the involved primary particles (volume equivalent diameter). In the second approach, the agglomeration history model(3) allows the calculation of the agglomerate porosity, which is used to calculate a more suitable hydrodynamic diameter and, therefore, allows a better prediction of the motion of newly formed agglomerates. The effect of inter-particle collision and agglomeration on the performance of a cyclone was analyzed in a hypothetical study considering a high efficiency Stairmand cyclone.