Study On The Formation Mechanism And The Ferrite Eutectoid Process Of The Slag Lumps In Shell Gasifier

In order to reveal the formation mechanism and the ferrite eutectoid process of the slag lumps in Shell gasifier, chemical composition, mineral composition, surface morphology and micro-chemical composition of slags, which came from the industrial device, were analysed by XRF, XRD and SEM-EDX. Yunnan coal with high S content was selected to simulate the ferrite eutectoid process of slags in different atmosphere mixed with CO and N2at high temperature. XRD and K value method were used to quantitative analysis about mineral evolution process of simulation slag samples in different atmosphere mixed with CO and N2. Surface morphology and micro-chemical composition of simulation slag samples were analyzed emphatically by SEM-EDX and multi-point test method, and the trend of main atoms percentage in microcell with the increasing of Fe atom percentage were probed. The results showed that,1) The formation process of slag lumps in Shell gasifier were dominated by the migration and transformation of iron-bearing minerals and calcium-bearing minerals in coal. When the gasifier was during unstable operation condition, iron-bearing minerals and calcium-bearing minerals happened obvious migration and enrichment phenomenon. It made some slags with low Fe and high Ca content, and some slags high Fe and low Ca content. The first kind of slags formed eutectic mixture known as anorthite. These slags had absorption and liquation property, which made slags grow bigger, and were apt to crystallize at low temperature, which made the density of slag increased and the hardness strengthen. The second of slags were apt to form structure of (Fe-S-O)melt, which had strong ability to absorb and adhere small slags, so that made slags grow bigger rapidly and finally evolved into a lot of iron-bearing minerals named troilite and a small amount of iron. These slags were apt to crystallize at low temperature that made the density of slags increased and the hardness strengthen. Therefore, slag-bloking accidents with the ferrite eutectoid phenomemon were more harmful.2) The ferrite eutectoid process of simulation slag samples was bound up with fusion and adhesion phenomenon at lower temperature and the migration and enrichment of Fe and sulfur enrichment phenomenon at high temperature. Its influence factors were the concentration of CO in reaction atmosphere, the reaction temperature and the relative content of Fe element and S element. In the atmosphere of low CO concentration, the ferrite eutectoid phenomenon didn't occur. Only when the concentration of CO was up to certain value, the ferrite eutectoid phenomenon would occur. The temperature of ferrite eutectoid phenomenon could reduce in high concentration of CO, but the content of iron was't proportional to the concentration of CO. Only when the temperature reached a certain value, the ferrite eutectoid phenomenon would happen. Only when the content of Fe enriching up to a certain value, rich-sulfur phenomenon would happen and formed intermediate product (Fe-S-O). The content of S element with the increasing of the Fe content showed "M" type during the whole ferrite eutectoid process, and the ratio of S atom and Fe atom was less than or equal to1.Figure [51] table [26] reference [74]...