Process safety is paramount in the secure and viable operation of any chemical process plant. Many techniques and methodologies have been defined over the years to undertake steps that will ensure a safe operating environment at a chemical facility. However, until now, process simulation has found very little or no use in safety-related studies. This article introduces a systematic framework based on Extended Hazop (that is, Hazop supported by disturbance simulation related to process malfunctions.) The Extended Hazop differs from standard Hazop in documenting results, classification of frequency and consequences of process deviations, and application of a risk potential matrix (Hazop decision matrix). In this article, the Extended Hazop method is explained. Application of this method will be demonstrated in a separate article. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2007

Methodology for the generation and evaluation of safety system alternatives based on extended Hazop

In order to achieve optimal energy-saving, load-dependent operation of rectification columns, development and implementation of model-based control concepts are necessary. This paper reports on the design and step-by-step testing of a state observer for the estimation of two state variables which cannot be measured directly, namely the vapour rate and the location of mass transfer zone (temperature front) in the stripping section of a production column. The procedure is described, and the relevant simulation and operation results are presented and discussed. Initial experience, gained when the concept was put into practical operation, is reported.

Design and analysis of a state observer for the temperature front of a retification column

Simulation and experimental analysis of operational failures in a distillation column

Experimental studies were made with the help of laboratory-scale distillation column. Concentration and temperature profiles were obtained at the steady-state operating point, and transition behaviour was observed after specific changes were made to relevant process variables. These results were compared with results obtained by means of simulation calculations. The mathematical model is explained in detail, as is the study method employed. The aim of this study was to obtain experimental verification of steady-state and dynamic calculation methods. It was found that the simulation results agreed closely with those obtained experimentally. The experimental findings thus confirmed the accuracy of the model and its underlying assumptions.

Experimental and theoretical studies of the steady-state and dynamic behaviour of packed columns

Untersuchungen zur stochastischen Online Optimierung kontinuierlicher Destillationsprozesse unter Unsicherheiten

For the simulation of steady- and non-steady-state behaiour of separation columns, a simulation program was developed and employed for the calculation and optimization of methanol-water separation. The demand for increasingly higher purities and energy-saving optimization of plants results in complex column configurations and thus in complex control schemes. The number of possible control schemes was reduced on the basis of heuristic rules. By simulating the process, the optimum control and manipulative variables and measuring points were determined from the reduced number of control concepts. A control scheme was introduced. The model was verified by simulation of the dynamic behaviour of the process. The investigation included the effects of computing technique, time interval, model reduction and tray hold-up on the results. Thus, various effects and interactions were verified theoretically with respect to the robustness of the model. This was followed by a simulation of the non-ontrolled and controlled column. By implementing the controllers in the existing column program, the computer can predict the control parameters. These parameters were checked and corrected when the metahnol-ater column was put in operation. In the start-up phase, major problems were caused by the sensitivity and failure rate of density, throughput and pump measuring sensors. Feed impurities were another source of problems. Operation with high product purities is possible, with a side stream to discharge impurities.

Werner Witt

Papers

Dynamics of distillation with high product purities

Simulation of operational failures in two-phase semibatch processes

Erhöhung der Prozeßsicherheit durch Untersuchung potentieller Betriebsstörungen mittels dynamischer Simulation am Beispiel des Ethoxylierungsprozesses