Numerical investigation of pressure loss reduction in a power plant stack

The strengthened environmental laws require the power plants to reduce the emissions. Flue gas desulphurization and deNOx involve adding chemicals to the flow stream, thereby resulting in increased mass flow. This problem could be overcome by reducing the pressure drop in the duct work and stack combination, so that a higher flow at reduced pressure drop can be handled by the existing fans. In this study, a power plant stack model of 1:40 was investigated numerically. The pressure reduction was achieved by introduction of baffles with various orientations and turning vanes at the inlet of the stack. The flows were modeled and analyzed using commercial computational fluid dynamics (CFD) software Fluent 6.2. The numerical results were validated with the experimental data. The 30° baffle without turning vanes was found to be the optimum baffle angle in terms of the pressure loss reduction. Variation of axial velocity, swirling component and turbulence kinetic energy along the axis of the stack was analyzed to understand the mechanism of the pressure loss reduction in a power plant stack. Guidelines for further pressure loss reduction were provided based on the insight gained from the simulation results.