Smoldering in porous media is a very complex situation that happens in situations where a reactive part of the porous material is oxidized using heat content without flaming. A three-dimensional numerical tool for the simulation of smoldering in fixed beds of solid fuels is presented in this paper. The description is based on the microscale equations, in a detailed discretized image of the porous medium. A set of 3D simulations demonstrates the ability of the model to handle a variety of situations, and to provide detailed local information. The cases treated here are clearly orientated to standard experimental cases.