Modelling of wood-chip refining processes

At present, due to the complexity of the wood chip refining processes, there are no suitable physical or parametric models available which can be used when studying different control strategies. It is shown that the process, which consists of two serially linked refiners, can be modelled as two multiple input, single output systems. To each refiner the dynamics from the chip flow to the motor load and from dilution water to the motor load are examined. It is shown that the pressure cannot be ignored in the model and that the motor load of the first refiner can be used as an input when modelling the second refiner. This indicates the possibility to use the load for feed forward control. The time stability of the models found was examined. The survey showed a small change in the model characteristics, but the ability to simulate the motor toads was not significantly reduced.