Dynamic Simulation of a Sugar House for Discrete Time Control

GUILLERMO A. DURAND; DENNIS BONNÉ; STEN BAY JØRGENSEN

Helsinborg (Dinamarca)

Congreso; CAPEC Annual Meeting 2002; 2002

Computer Aided Process-Product Engineering Center - Technical University of Denmark

The production of beet sugar the process is carried out in several houses. One of the most important is the sugarhouse. The purpose of the sugarhouse is to separate and crystallize the sugar from the thick juice obtained in previous stages. Sugar factories in various countries differ considerably with respect to conditions for factory operation and the level of technological development, but in most countries the separation processes are done in continuous and batch units. The batch units are located between continuous operations, if the processing capabilities of the upstream and downstream units do not match those of the batch stage(s) then accumulation problems may arise. The most common solution is to use more than one batch unit and schedule their operation to make the overall production of the batch process as similar as possible to that of the upstream and downstream continuous stages. The scheduling also has to be planned considering the optimization of the operation in order to reach the maximum utilization of the total process plant, constrained by the batch stage sizes. The scheduling basically consists of a series of decisions of whether to start or not to start a specified batch unit at a determined moment. Besides, as in most of modern factories, the utilities -specially heating medium (steam) and vacuum- are shared by more than one house, and disturbances in one house may make the operating conditions for the sugarhouse to fluctuate. This creates a special problem for the optimization: the constraints vary in time. The scheduling has to consider this aspect as well. For these kind of optimization problems, with many and complicated relations between the different running units, it is no possible to come up with suitable equations for a one-step solution. When this happens, the integrated modeling/optimization approach is well suited to solve the problem. In this approach, the optimization algorithm propose some operation conditions, these conditions are applied to a model of the sugarhouse, in order to test the performance of the process under those conditions. The optimization algorithm looks for the optimal operating conditions comparing the results of tests under different settings, and choosing the better ones. As it can be seen, this approach can be very time-consuming, so, it is very important for the model to be fast in the obtaining of results, and for the optimization algorithm to be effective in the search of the optimal operating conditions. The goal of this project is to obtain such model, and applied it to a discrete-time, dynamic programming schedule optimization algorithm already developed last year.