Mathematical modeling of zinc concentrate roasting in a fluidized bed

Abstract

The paper aims to stabilize the roasting of zinc sulfide concentrates in fluidized-bed furnaces using oxygen- enriched air. The balance between the given excess air blast (on average 20%) and the amount of loaded charge is achieved by selecting an appropriate number of evaporative cooling elements in the fluidized-bed furnace. Through the evaluation of scientific and technical information, as well as literature sources on the research topic, data were collected on the effects produced by an oxygen excess in the blast on the quality of sulfide concentrate roasting and by a blast volume on the state of the fluidized bed. In addition, statistical data for the study were obtained by analyzing the operation of fluidized-bed furnaces at Electrozinc. As part of the study, the heat balance in roasting was determined, taking into account the following technical characteristics of fluidized-bed furnaces used for roasting zinc sulfide concentrates: fluidized- bed level, number of nozzles, furnace diameter, diameter in the bed zone, hearth thickness, and the total weight of the furnace. Relying on the operation analysis of fluidized-bed furnaces, a method was proposed to regulate the oxygen supply depending on the amount of loaded charge. The oxygen supply is regulated in order to ensure a stable excess of oxygen in the blast without causing any significant changes in the blast volume and, consequently, to maximize the sulfur removal from the charge. A decrease in the excess air blast below 15% was found to significantly degrade the quality of the resulting cinder and dust, while an increase of over 20% reduced the SO2 content in the exhaust gases with no noticeable improvement in the quality of cinder. Therefore, the proposed method for regulating the oxygen supply to the furnace can improve the techno-economic performance of zinc sulfide concentrate roasting in fluidized-bed furnaces.