An off-line computer simulation for controlling the repulp section in a plant

Abstract

An off-line computer simulation program is proposed to control a repulping section of a plant that has previously been controlled solely by an operator. The off-line computer program can be used as a tool by the operator to improve the control of repulping a certain material before leaching commences. Controlling the repulping section is of special importance, especially to processes employing unit operations after the repulping section with fast reaction kinetics. The fast reaction kinetics make it essential to control the conditions of the incoming pulp to the leaching vessel. The simulation uses dynamic mass balance equations to simulate the physical properties of the system. It then solves the set of differential equations with an iteration procedure that uses the fourth order Runge-Kutta(RK) procedure and the Golden Section Search(GSS) optimisation procedure, thus obtaining optimum settings so that the desired conditions in the process could be maintained or reached as quickly as possible. The simulation was tested on a plant and indicated that considerable improvement in the stability of the operation could be achieved. Two calculation methods were also investigated for the mathematical models, i.e. the Runge-Kutta procedure mentioned above and the Laplace transform solution. Comparing the two methods it was evident that the Laplacian solution was not as accurate as the Runge-Kutta solution due to the inherent linearisation step employed. This was especially evident for large deviations from the desired conditions.