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Understanding the ignition behaviour of coal is of utmost importance for the design of boilers and control of the combustion process. In recent years there has been an increasing utilisation of coal blends for combustion, but information on the possible interactive effects during ignition of the individual components is scarce. In this work the ignition behaviour of a series of coal blends, made up from three coals of different rank, sub-bituminous, high volatile and low volatile bituminous, was studied. To this end a thermogravimetric analyser linked to a mass spectrometer for evolved gas analysis was used. Different ignition behaviour was observed for the coals studied; the sub-bituminous and low volatile bituminous coals ignited heterogeneously, while homogeneous ignition occurred for the high volatile bituminous coal. In the case of blends of the low and high volatile bituminous coals, different mechanisms of ignition were observed depending on the blends composition. Peer reviewed

An experimental study to determine the temperature and mechanism of coal ignition was carried out by using an entrained flow reactor (EFR) at relatively high coal feed rates (0.5 g min−1). Seven coals ranging in rank from subbituminous to semianthracite, were tested and the evolved gases (O2, CO, CO2, NO) were measured continuously. The ignition temperature was evaluated from the gas evolution profiles, and it was found to be inversely correlated to the reactivity of the coal, as reflected by the increasing values of the ignition temperature in the sequence: subbituminous, high volatile bituminous, low volatile bituminous and semianthracite coals. The mechanism of ignition varied from a heterogeneous mechanism for subbituminous, low volatile bituminous and semianthracite coals, to a homogeneous mechanism for high volatile bituminous coals. A thermogravimetric analyser (TGA) was also used to evaluate coal ignition behaviour. Both methods, TGA and EFR, were in agreement as regards the mechanism of coal ignition. From the SEM micrographs of the coal particles retrieved from the cyclone, it was possible to observe the external appearance of the particles before, during and after ignition. The micrographs confirmed the mechanism deduced from the gas profiles. Work carried out with the financial support of FONDECYT, Project 2010113 and MECESUP UCO0108 (Chile) which provided a mobility grant. Peer reviewed

5 pages, 8 figures.-- Printed version published Sep 2007.-- Issue title: "The 6th European Conference on Coal Research and its Applications". Ignition tests were carried out on blends of three coals of different rank – subbituminous, high volatile and low volatile bituminous – in two entrained flow reactors. The ignition temperatures were determined from the gas evolution profiles (CO, CO2, NO, O2), while the mechanism of ignition was elucidated from these profiles and corroborated by high-speed video recording. Under the experimental conditions of high carbon loading, clear interactive effects were observed for all the blends. Ignition of the lower rank coals (subbituminous, high volatile bituminous) enhanced the ignition of the higher rank coal (low volatile bituminous) in the blends. The ignition temperatures of the blends of the low rank coals (subbituminous–high volatile bituminous) were additive. However, for the rest of the blends the ignition temperatures were always closer to the lower rank coal in the blend. Work carried out with the financial support of FONDECYT, Project 2010113 and MECESUP UCO0108 (Chile) which provided a mobility grant. Peer reviewed