In order to solve the diffusion equations with numerical methods the PDEs must be discretized to a system of algebraic equations. We use the box integration method (BM) for the discretization of the diffusion equation. Similarly to the Finite Difference (FD) method the differential operators are replaced by differences, but BM can be applied to any grid which fulfill the Delaunay criterion. As the main task of this thesis was to develop and implement a general purpose diffusion simulator using the box-integration method, we will focus on the discretization of the general diffusion equation using the BM in the next sections.