Different approaches for the production control of a pulp mill

Abstract

Three approaches to carry out the pulp mill production control calculations are discussed. These approaches are a simulation method, a hierarchical optimization algorithm and a network flow algorithm.In the simulation approach a general program package for the production control calculations was developed. The scheduling is based on a simulation model and some simple logical rules for production scheduling. It proceeds iteratively from a given production schedule to a production schedule that satisfies all the system constraints.The production schedules of both the pulp lines of the mill and the chemical recovery cycle can be calculated using Tamura’s time delay algorithm. This algorithm was modified so that the specific features of the problem can be taken into account. These include the compensation of planned shut-downs, identification of infeasible situations, etc.The use of standard linear programming algorithms to production control calculations is restricted by the fact that they need a considerable amount of core memory. However, for some special cases network flow algorithms that can solve LP-problems have been developed. In this connection Ford-Fulkerson out-of-kilter algorithm is considered.The applicability of these approaches was compared using simulations with UNIVAC 1100/20-computer of the University of Oulu. In the simulations the preselected simulation period of 48 hours was divided into intervals of 8 hours. Several kinds of test runs that correspond problems in the real plant environment were carried out.