Combustion at programmed temperature in a thermobalance is a common test for the rapid assessment of coal combustibility. In this study two series of blends (low rank/medium rank coal-AB and low rank /petroleum coke-AC) with the low rank coal in three different proportions (1/4, 2/4 and 3/4) have been tested.Ministry of Education (Ministerio de Educación), Project PSE2-2005. Consejo Superior de Investigaciones Científicas, CSICCNPq, Project 2005BR00054. CNPq, Project CNPq/CSIC 491127/2005-7.Peer reviewed