The Austrian utility company EVN AG is investigating possibilities to substitute part of the hard coal used in their Durnrohr power station by biomass pyrolysis gas produced in an upstream rotary kiln at relatively low temperatures of <= 600 C degrees. A major advantage of the low temperature is the retention of alkalis and halogenes in the coke. The aim of the present work was to set up a working thermo-chemical computer model in order to calculate the possible effects that this co-firing may have on corrosion phenomena in the boiler. The work was carried out using the software packages FactSage (R) and SimuSage (R). A model was successfully developed and validated using data from laboratory analyses as well as from the power station and a biomass pyrolysis test facility set up next to the plant. The results of the calculations show that the gas produced in the rotary kiln at the planned scale very likely does not pose any potential threat to the power plant. (C) 2010 Elsevier B.V. All rights reserved.