Stabilizing Duct-Flow to Reduce Power Consumption of ID Fans on the Site of Taichung No. 10 Power Plant

Abstract

The power of fans at a coal-fired power plant is necessary to bring air to the furnace, transport pulverized coal, and removing the products of combustion in the flus gases. The highly turbulent flow in the flue-gas duct system downstream the Induced Draft (ID) fans usually caused the power consumption increased of the electric auxiliary-power systems in a coal-fired power plant. The excessive pressure drop through the flue-gas duct, caused by the highly turbulent flow in it, was reduced by modifying the turning vanes and adding splitters in the flue-gas duct system. Modifications are effective to reduce power consumption of the electric auxiliary-power systems. The analysis showed that the excessive pressure drop of the flue duct is caused by the local eddy which is resulted from the non-uniform flow with regions of a secondary flow. The gas flow in duct system is complicated, due to the duct diffuser and presence of several curved solid boundaries make the gas flow highly turbulent. In addition, the inadequate design in a mixing flow device caused turbulence to be enlarged. The effects in flow turbulent diffusion and local instability caused by the curved flow lead to the secondary flow and the non-uniform flow in the duct, which are able to cause a pressure drop increased. Measurements were taken by inserting a special designed pitot-tube into the duct to acquire gas velocity fields. Simulation of turbulent gas flow distribution in duct system is attempted through computational fluid dynamics analysis using ANSYS CFX software. Numerical flow modeling with physical boundary conditions was used to be a modified design and an analysis tool for improving the flue gas distribution in the duct. These modifications can include added turning vanes and flow splitters. Numerical modeling has advantages over physical modeling in that actual geometric scale and measured gas velocity fields are used. Advantages over a field data based study include the ability to quickly analyze a optimal design without actually modifying vanes in advance, and the availability of significantly more data with which to interpret the results. The modification of the turning vanes and splitters added in the flue-gas duct system on Taichung no. 10 Power Plant for the reduction of turbulence, which in turn, reduced the duct pressure drop.