In this work, a CFD numerical study of co-firing coal and cynara in a 350 MWe utility boiler is presented. The most influent operational factors related to the biomass feeding conditions such as biomass mean particle size, level of substitution of coal by biomass and feeding location in the furnace, are analyzed, determining their influence in the combustion process. Validation of the simulations is performed using measurements gathered at the plant. Results from the study show interesting conclusions for their implementation in the power plant, suggesting recommendable limits in the maximum biomass substitution level and particle size in order to keep a reasonable boiler efficiency, and pointing out the outstanding influence of the biomass injection location discussing thermal and fluid-dynamic implications and the possibility of introducing retrofitted or specific biomass burners. (C) 2009 Elsevier B.V. All rights reserved.