Viscosity model uncertainties in an ash stabilization batch mixing process

Recycling wood ash from burnt wood (back to the forest grounds) is of great ecological importance. However, the ash cannot be recycled directly after combustion. There are several reasons for this, one being the volatility of wood ashes. Mixing ash/dolomite/water in order to obtain granular material is one method to stabilize wood ashes. The main problem is predicting the quantity of water to be added, since the necessary amount varies with the wood ash quality. One possible solution is to measure the mixture viscosity and study whether this parameter can be used to control the amount of added water In this paper, the viscosity is estimated in the batch mixing process by measuring the normalized effective power P-e(t), that represents the rate of useful work being performed by the three-phase asynchronous machine used for the stirrer drive. The coherence function is used in order to detect any non-linear relationship between the input-output data - the variable water flow and the normalized effective power P-e(t). It is shown that measuring P-e(t) is extraordinary well suited for future control of the amount of added water. First and second stage experiments are carried through in order to obtain a model of the viscosity dynamics.