| The thesis is partly based on the practice in Baogang Group and systematicallystudied the quality of the four kinds of fine iron ores, thermal conditions of grate-kiln,suitable iron ore proportion and process optimization of the grate-kiln. Importantindexesincluding pelletizing ability, falling strength of green ball, compression strengthof green ball, preheated ball and fired pellet, mineraogical phase of preheated and firedball have all been thoroughly examined. Moreover, another study was also performedtoclarify the effects of roasting time and temperature on interconnected crystal withreference to the practical situation in Baogang Group. Finally, a series of orthogonal testwere carried out to find out the best ore proportion and production condition in terms ofthe strength of preheated ball. The tests were performed by fixing the bulk materialproportion as40%according to practical situation while adjusting the relative contents offine Barun ore and coarse Barun ore. Thereby, the appropriate conditions for pelletizationwere clarified. After that, the suitable ore proportion and optimization of grate-kiln weredecided by analyzing the mineraogical phase of preheated and fired ball withsimultaneous incorporation of theoretical knowledge.The study shows that:For pelletizing ability, fine Barun ore>regrinding ore>coarseBarun ore> Bulk materials;For preheated ball strength, fine Barun ore>regrindingore>Bulk materials>coarse Barun ore;For fired ball strength, fine Barun ore>Bulkmaterials>regrinding ore>coarse Barun ore.The study also reveals that when roastingtemperature is low, the extension of roasting time has a strong influence on the bondstrength of pellet. As the roasting temperature rises, the influence gradually decreases.The reason lies in the fact that under high temperature condition, the interconnectedcrystal of hematite has become so strong that the extension of roasting time could nothave an appreciable effect one it. On the other hand, liquid phase becomes more as theroasting time is prolonged. The optimum process varies with ore proportion. However,the best preheating temperature is invariably1000degrees while the rotation rate isalmost1.5m/min. All these indicate that in practical operation, the preheatingtemperature should be increased, rotation rate should be lowered down, adding more fine Barun ore and restricting the coarseBarun ore to increase the compression strength of thepreheated ball. The appropriate pelletizing parameters are that moisture of green ball7.5-8.0%, bentonite addition1.5-2.0%, and0.75%binder addition. |
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