The particle dynamics in a 40 MW biomass (wet wood chips) fired furnace was investigated using numerical calculations of the Navier-Stokes equations, energy and species transport equations, as well as particle tracking equations. Calculations of the particles' spatial distribution and residence time in the furnace and the momentum of emitting particles at the outlet were performed. The trace of particles near the furnace walls was predicted, so that the impact of particles on the furnace walls was identified. The swirling flow introduced by the uppermost four jets led the particles to a helical motion in the furnace. Some particles were found to hit the walls and others slip along the walls. The air curtain, introduced by two groups of secondary air jets opposite to each other in the middle height of the furnace, induced another recirculation motion, which could trap the particles so that the particles had longer residence time inside the furnace. Parameter studies showed that by changing the air supply configuration at the air curtain, the residence time of particles could be prolonged by as much as 16%. These results provide options for the design of biomass furnaces and for optimal industrial operations.