Improving copper matte grade control in a concentrate flash furnace

Abstract

The copper matte grade (CMG) variation in a flash furnace depends on bath temperature, phase levels, ratio of oxygen to sulfur, iron and copper content on the feed, and tonnage ratio of silica flux and feed, among others. The CMG is obtained from laboratory analysis of samples taken when the matte is tapped out from the furnace. Then the CMG is known with a time delay of 1–2 hours, almost every one hour. Since feed characteristics usually change during this period, any feedback control of CMG cannot reduce enough the grade variability. On the other hand, it was shown that main disturbances are coming with the composite feed tonnage and composition, being the powder tonnage control system the main contribution. A new calibration system was proposed and implemented. During an evaluation period of 60 days, it was found that the standard deviation of the CMG was reduced in 25%. This improvement can be explained considering two effects. First, the stabilization of the total feed tonnage that affect the mass balance in the furnace. Second, even when the powder tonnage is only 7% of the total tonnage, its special chemical composition contributed to increase the copper content in the matte. The stabilization of the furnace operation also improved the phase separation, as well as reduced the variance of the gas SO2 composition and flow rate. The operators took advantage of this reduced variability to increase the fusion rate and thus the mean generated gas flow rate in the furnace, without violating the plant constraints.One important conclusion is that this result will permit to increase the average value of CMG, when the development of the virtual sensor of feed composition is completed and when this estimation becomes part of a FF-FB control.