Modelling of pulp flow rate with variable consistency

Pulp and paper mills can be seen as big pumping plants, where mass is pumpe d front one step to another. The proper operation of the process in its dif ferent stages does not allow large deviations from given operation conditio ns, which makes it essential to monitor and control the flow rate and the c onsistency of the pulp. A structure is suggested for the modelling of pulp flow rate, and possibilities for using the pump-valve system as a flow mete r are examined. The overall model structure consists of a Wiener model for pressure difference, a non-linear dynamic valve model, and a static mapping for flow rate. A full-scale pilot plant of pulp flow through a valve in a pipeline is used for experimentation. Linear dynamics and non-linearities d ue to the pump, valve and the pulp consistency are identified based on onli ne measurements obtained from calibration tests. The results show that a si mple model could be identified which, together with a valve model, call be further applied for the purposes of accurate flow control.