(546h) Systematic Analysis, Diagnosis and Optimal Operation of an Industrial Hydrogenation System

Hydrogenation is a frequently used process in the chemical industry. In this project, we study an industrial hydrogenation system employed in phenylene diamine production. There are three sections in this system, consisting of:(1) hydrogenation reaction & catalyst sedimentation, (2) catalyst filtration, and (3) solvent regeneration. It is a typical chemical process consisting of reaction, separation, and recycle. Due to increasing demand for the product, the hydrogenation system has been expanded and reformed several times, resulting in a quite complex process flowsheet with hybrid connections. Seven parallel hydrogenation reaction & catalyst sedimentation subsystems, which are connected serially to the filtration and regeneration subsystems, have been added. The unreacted material and catalysts are recycled through complex recycle schemes. Moreover, as the operation of some of the separation steps involve vapor-liquid-solid phases, these steps are operated in batch mode. In other words, it is a hybrid process with both continuous and batch production, where use of computer-aided monitoring and analysis technique would be highly desirable.

To achieve safe, reliable and efficient operation of the hydrogenation system, a systematic analysis, diagnosis and optimal operation is of great importance. In this project, a systematic computer-aided model and data-based technique consisting of three steps, is developed. First, a reference point is established. That is, the process actual "operating" process flow-diagram is established and process data are collected, analyzed and reconciled, based on available measurements. Second, a diagnosis of the operational problems is made through reconciled plant data and validated process simulations, identifying thereby, process hot-spots. These process hot-spots indicate, for example, processing steps that are sensitive to disturbances, have inefficient operation in terms of energy and/or waste, and, are difficult to maintain at their desired specifications. The diagnosis-analysis helps to establish targets for process alternatives as well as the requirements of a monitoring system. Third, process-operational alternatives that match the established targets to overcome the hot-spots are generated and evaluated through a monitoring system simultaneously developed to monitor and control the operational set-points. With the developed methods and tools, the process operation becomes transparent as it enables good understanding of the key operational variables and parameters that affect the process; the deviations of mass and energy balance, if any, from the desired operation; and process optimization–control measures that are employed through off-line what-if analysis. The development of the monitoring system and its application to an industrial hydrogenation system will be presented.