Experimental and numerical study of the pulverised-fuel distribution in the mill-duct system of the Loy Yang B lignite fuelled power station

The boiler efficiency of a Lignite fuelled power station can be significantly affected by the distribution of the coal within the boiler furnace. The mill-duct systems are designed to allow sufficient resident time for the raw Lignite to dry. The raw Lignite, which contains approximately 66% water, is conveyed by post combustion hot off-take gases and delivered to the furnace with an appropriate distribution to ensure when mixed with sufficient oxygen, complete combustion occurs. The mill-duct systems for a lignite fuelled boiler are generally very complex and as such, are not yet fully understood. The distributions of the coal and gas mixture within these complicated mill ducts have been investigated experimentally and numerically to better understand the flow patterns. Isokinetic sampling of the gas and coal was undertaken within the lower, intermediate and upper legs of a mill-duct system downstream of the grinding mill under standard operating load at the Loy Yang B power station in the Latrobe Valley, Australia. CFD modelling using an Eulerian/Lagrangian approach, due to the low solids-to-gas ratio, was used to achieve good agreement with the experimental data. The gas–coal mixture must travel through a series of bends before entering the furnace and a bias of coal flow toward the outer wall of the upper and lower legs was noted downstream of the bend at the trifurcation for the mill-duct legs. The slightly different geometry configuration of the intermediate resulted in a more homogenous coal and gas flow but a significantly lower coal loading than the upper and lower legs.