Applying CFD for Design of Gas Conditioning Towers With Swirling Flow

The aim of the present study is to investigate the gas flow distribution within a Gas Conditioning Tower (GCT) used for cooling hot flue gases by means of atomized water injection. Special focus is placed on developing a design that prevents wall flow separation in the evaporation zone as well as in the tower in general. In due cause a special swirler design is presented introducing the swirling type of flow in the tower (swirl no. in the range of 0.2 to 1.0). The GCT geometry studied includes inlet ducting, swirl generator unit, conical diffuser section and tower section. The swirler is a totally new design while the inlet ducts and conical diffusers studied are modifications of the traditional design. The three-dimensional flow distribution within the GCT is calculated by standard Computational Fluid Dynamical (CFD) tools giving high resolution of the calculation domain. The presented results include intensive validation studies of the swirling flow introduced by the swirler and practical applications. The validation case shows that medium mesh resolution, second order upwind difference scheme and the high Reynolds number form of the standard k-ε turbulence model with the law of the wall representation offer a good compromise between accuracy, required number of computational cells, computer time and agreement with experimental data. Studies of practical applications include design flexibility in general, optimization of gas distribution and sensitivity to water droplet size. Depending on the actual parameter in play, the results clearly demonstrate, that the newly developed design reflects the needs of an acceptable gas distribution in GCTs and that the design can be used in other flue gas process units including large opening angle diffusers. Also, the study indicates that the swirl number is a good measure of optimum operation.