The paper presents the results of the experimental research conducted on an industrial scale and directed at stabilizing the process of the thermal destruction of biomass in the form of animal post-slaughter waste and dead animals. During the realization of the combustion process with the participation of oxygen from 6 to 17% the interaction between such gas products of the process of thermal destruction as SO2 and HCl was analyzed. The results of the experiment clearly indicate that the concentration of SO2 in flue gas is dependent on the participation of O-2 in the process of combustion. Hydroxyapatites in the high temperature atmosphere were decomposed, among others, to CaO and P2O5. Particles of CaO, in largely oxidizing atmosphere, carried in the stream of exhaust gases bonded SO2. When the participation of O-2 oscillates around 16 to 17%, the concentration of SO2 is close to zero. However, at the same time there are no clear premises concerning the influence that the participation of O-2 has on the concentration of HCl. The results in the form of the dependence HCl -> f(O-2) only suggest that the concentration of HCl in outlet gases decreases for large participation of oxygen of more than 13%. (C) 2013 Elsevier B.V. All rights reserved.