Separation performance of new type of multi-stage axial cyclone used as demister in power plant emission system

This paper presents an investigation of the performance of a multi-stage axial flow cyclone used as a demister in power plants to reduce pollution emissions. Four axial cyclones with different structural parameters were studied by numerical simulation and verification experiments. A numerical model of a two-phase flow in the cyclone separator was established and the separation efficiency and pressure loss of cyclone separators were simulated by employing the Reynolds stress model (RSM) for turbulence modeling. A test rig was constructed and the diameter distributions of droplets at the inlet and outlet of the separator were measured by a Malvern laser particle size analyzer to verify the simulation model. The results indicated that a multi-stage swirler can improve the tangential velocity to strengthen the gas swirling in the cyclone body effectively, thereby improving the separation efficiency of the cyclone. The effects of the multi-stage swirler on the flow field were analyzed, for a better understanding of the mechanisms of the flow field in the separation region for improved performance. The tangential velocities of cyclones Sep-C and Sep-B were found to be 1.5 to 2 times higher than that of the single-stage cyclone Sep-O, although the separation efficiency of Sep-C was reduced significantly when the velocity was greater than 7.9 m/s. Based on the results of this study, cyclone Sep-B was considered to be the best performing axial-flow cyclone within the acceptable pressure drop range and was proposed as a demister in power plant.