Computational fluid dynamic (CFD) tool has been applied to investigate the erosion of duct walls and that of tubers (10 x 10 aligned tube bank in the duct) near side walls, which is caused by coal ash particle impaction. The flow field is obtained by using direct numerical simulation (DNS) method. The coupling between tubes and flows are made through the immersed boundary technique. Particles are tracked by using Lagrangian approach and further coupled with gas phase. Four coal ash particles are considered 6.2, 20, 80, and 200 mu m. In the end, the erosion of the duct walls and that of the tubes near side walls has been well predicted and characterized. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 66-78, 2010