INVESTIGATION OF THE HIGH-TEMPERATURE BEHAVIOR OF EXCLUDED SIDERITE GRAINS DURING PULVERIZED FUEL COMBUSTION

An investigation of the behavior of excluded siderite samples derived from both pure mineral species and by density separation of pulverized coal samples was conducted at combustion temperatures of 1100 and 160 0 degrees C. Analysis of quenched combustion residues collected from t he combustion gases under oxidizing conditions was obtained via scanni ng electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray fluorescence (XRF) spectroscopy. The FeO-MgO-CaO ternary ph ase diagram was used to predict the behavior of excluded siderite grai ns under combustion conditions and indicated that the siderite is unli kely to form sticky or completely melted particles at 1600 degrees C u nless MgO < 5wt %, CaO < 37.5 wt % and (MnO + FeOn) > 60wt %. The exte nt of melting observed for collected particles having different compos itions agreed with this prediction. By comparison with published work for excluded pyrite particles, residues from excluded siderite particl es are found to be sticky at higher temperatures (1380 degrees C compa red to similar to 1080 degrees C for pyrite), and will generate less f ines as fume or by fragmentation. Slagging indices based on iron in as h for coals containing pyrite will therefore not apply to coals contai ning siderite.