Pladat: A package for process variable classification and plant data reconciliation

Abstract

Process data are used in chemical plants for the purpose of control, performance evaluation, optimization, etc.. Measurements usually have some degree of error, therefore it is necessary to adjust them through a reconciliation procedure in order to obtain a reliable process knowledge. In this work a computer package (PLADAT) is described which allows the classification of the operational variables of a complete chemical plant. The results of this procedure are used to reduce the size of the reconciliation problem. An output set assignment of the process balance equations is used to classify the measured and unmeasured variables and provide a reduced set for reconciliation. This problem is solved using a nonlinear programming technique. Previously, statistical methods are applied for the detection and elimination of gross errors, which would invalidate the reconciled results. The application of PLADAT for the instrumentation revamping of an existing ethylene plant section with 150 streams and 45 units is discussed. The minimum amount of instruments required for the determinabi1ity of all unmeasured process variables is obtained in order to develop the complete mass and energy balances. Data reconciliation results for the demethanlzing sector are provided.