Modelling of the Initial Part of a Smoke Plume from a Four-Flue Stack at a Thermal Power Station

Abstract

Multiflue stacks are finding ever increasing application at thermal power stations (TPS) in recent years. Until the present time, the opinion has prevailed that multiflue stacks at the same emission parameters offer lower floating-up height of flue gases than single-flue stacks do. Hence, they must be higher or be provided with devices making a single flume, such as common hoods, or due to a concentric slope of the outlet section of the stack flues. However, the research tools used up until now had poorer capabilities as compared to those implemented in the ANSYS Fluent software package. The process of combining jets outflowing from individual flues of a four-flue stack is studied and analyzed using the ANSYS Fluent package. Much attention is given to the selection of a proper turbulence model and its verification against generally accepted theoretical and experimental data. This revealed the effect of rapprochement of the jets’ axis from individual parallel flues similar to the Coanda effect. Comparison of the characteristics of cross sections in a combined plume from a four-flue stack and a plume from a single-flue stack having the same outflow parameters and the distance from the stack mouth, as well as using them as initial data for calculating the trajectory of the smoke plume, showed a good agreement of these trajectories. Selection of a turbulence model and a calculation scheme suitable for the considered conditions is rather complicated, as it is determined not only by physical and geometric parameters but also by the required model accuracy and available computer and time resources. Solutions are presented that are obtained using the ANSYS Fluent package in analyzing jet flows with a scale of approximately 100 m, and a procedure for selecting a turbulence model for a nonisothermal jet is described.