In the course of this work the solid flow program (SOLDIST) and the main simulation program for circulating fluidized bed boilers (CFBB) have been extended, partially reprogrammed and tested. The solids flow program has been designed as a "Stand-Alone-Version" and has been extended to a "multi-air injection model". In the solids flow program, the common blocks structure (feature of the programming language Fortran 77) has been exchanged against parameter-list based variables transfer. Furthermore, the functionality of the program is checked.The current version of the simulation program allows to inject additional air to each cell of the combustion chamber. Examples where an additional mass flow of secondary air (m=5kg/s) is injected to certain cells are discussed.