A new concept for separating yeast from beer has been developed at Alfa Laval in Tumba. The yeast is now continuously fed out from the separator instead of discharged when too much yeast have collected in the separator. The concept makes it possible to save beer which otherwise would have been wasted at discharges. For the concept to be profitable, the density of out yeast must be high enough even though the inlet density is steadily declining, and at the same time have good separation efficiency.
In this study a control strategy has been developed for this high speed centrifugal separation process. Through experimental studies a mathematical model of the separation process could be made. This model was then used for a MPC-controller where the density was controlled by controlling the flows of the process. An implementation of the control strategy was carried out in the process laboratory in Tumba.
The separation was assumed to be good as long as the mass inow was relatively low and the pressure levels were steady. With the MPC-controller it was possible to maintain the density over the set limit in laboratory experiments. It is also shown that a multivariable controller has benefits compared to a single variable controller. Controlling the separation efficiency is deemed possible and is the next step.
Author: Svensson, Anders