In growing bulk crystals from the melt, impurities contained in silicon feedstock, generated due to the melt-to-crucible contact and transported by the gas flow from graphite elements strongly affect the efficiency of mono and multicrystalline silicon solar cells. The present paper is aimed at developing an advanced coupled chemical model accounting for such phenomena as oxygen and nitrogen solution at crucible wall, oxygen and carbon transport through the melt free surface, formation of Si3N4-, Si2N2O- and SiC-particles in the melt, mass transport of Si, CO- and Si-species in argon carrier gas and, finally, formation of parasitic deposits on the furnace units. The model is verified by simulation of DS and Cz Si-crystal growth. It is shown that the computational results agree well with available experimental data, and the model can be used for optimization of Cz and DS processes. (C) 2013 Published by Elsevier B.V.