Conventional　simulations　of　dense　particle　flows　in　complex　geometries　usually　involve　the　use　of　glued　particles　to　approximate　geometric　surface.　This　study　is　concerned　with　the　development　of　a　robust　and　accurate　algorithm　for　detecting　the　interaction　between　a　spherical　particle　and　an　arbitrarily　complex　geometric　surface　in　the　framework　of　soft-sphere　discrete　element　model　(DEM)　without　introducing　any　assumptions.　Numerical　experiments　specially　designed　to　validate　the　algorithm　shows　that　the　new　algorithm　can　accurately　predict　the　contact　state　of　a　particle　with　a　complex　geometric　surface.　Based　on　the　proposed　algorithm,　a　new　solver　for　simulation　of　dense　particle　flows　is　developed　and　implemented　into　an　open　source　computational　fluid　dynamics　(CFD)　software　package　OpenFOAM.　The　solver　is　firstly　employed　to　simulate　hydrodynamics　in　a　bubble　fluidized　bed.　Numerical　results　show　that　a　3D　simulation　can　predict　the　bubble　size　better　than　a　2D　simulation.　Subsequently,　gas-solid　hydrodynamics　in　an　immersed　tube　fluidized　bed　is　simulated.　Results　show　that　bubble　coalescence　and　breakup　behavior　around　the　immersed　tubes　are　well　captured　by　the　numerical　model.　In　addition,　seven　different　particle　flow　patterns　around　the　immersed　tubes　are　identified　based　on　the　numerical　results　obtained.　(C)　2011　Elsevier　Ltd.　All　rights　reserved.