THE BEHAVIOR OF MINERAL MATTER DURING COMBUSTION OF SPANISH SUBBITUMINOUS AND BROWN COALS

Combustion experiments up to 1400-degrees-C were carried out with subb ituminous coals from the Teruel power station, the Teruel Mining Distr ict, the Santa Eulalia coal deposit and with lignite from the As Ponte s power station in Spain. The characterisations of the occurrence and distribution of inorganic matter and its transformation during combust ion of these coals were carried out by means of X-ray diffraction and optical and electron microscopy. The combustion experiments show that the inorganic transformations during the combustion of all the coals s tudied vary depending on the sulphur and calcium contents. The sulphur , iron and calcium contents govern the quality of anhydrite crystallis ation (which takes place between 600 and 900-degrees-C. Furthermore, t he high calcium oxide content produces the fouling of the combustion w astes at relatively low temperatures (1200-degrees-C), prevents the oc currence of mullite and magnetite in the ashes and leads to the crysta llisation of anorthite and esseneite during the cooling. The compariso n of the inorganic phases of fly ashes and slags from the Teruel power station with those of the experimental wastes shows that the inorgani c transformations during coal combustion in the power station can be p redicted by means of laboratory furnace experiments provided that the residence time in the flame and the effect of the cooling and evacuati on controls of gases and particles from the power station are taken in consideration.