Using CFD to Model Coal Roping Phenomenon in Coal Transport Systems

Coal roping is a well-known phenomenon occurring in pneumatic transport of pulverized coal. In coal roping the majority of the coal is concentrated in a small portion of the transport piping cross section. This region of concentrated solid flow is created by a number of factors. For example, as the two phase flow of air and coal travels through an elbow or turn in the coal transport piping the centrifugal forces exerted on the coal concentrate the coal on the outside edge of the elbow. After the coal rope is formed these particles will tend to travel together. Coal roping upstream of a coal distributor (bifuractor) can create a significant imbalance in coal loading between in the split between the two branches. This can result in unbalance coal loading between burners and ununiform coal injection in plant burners. This can significantly impact plant performance and increase NOx production. This paper examines how CFD model can be used to understand common creation and breakup mechanisms of coal roping.