(596g) Energy Improvement in VCM Plant Through Process Redesign and Pinch Technology
Pinch Technology for Heat Exchanger Networks (HEN) is in wide use now, not only for grassroot designs but also in retrofits of existing facilities for capacity enhancement and energy efficiency improvements. Limitation in use of the Grand Composite Curves (GCC), cross-pinch heat transfer regulations and subsequent optimization techniques are their disregard or disconnect from the process side. A standard chemical plant is fairly complex in its process-process interactions and it is here where greater optimization potential rests. Thus newer techniques of optimization based on integrated GCC are being utilized, with pinch analysis being applied across distillation columns, water and refrigeration networks and even Reactor schemes.
In this case study for well known technology of Vinyl Chloride Monomer, we present the effectiveness of process based pinch. The requirements of quench cooling in many chemical processing will always appear as cross-pinch heat transfer in most HEN pinch studies, but this practice is borne out of necessity, e.g. to avoid fouling and polymerization of desired product through excessive residence time over heat exchange surfaces. Such scenarios are best optimized by cost-benefit relationships, i.e. Will the energy recovery be feasible enough to accommodate the equipment down-time required for frequent cleaning? Concept of operational changes and then pinch analysis is also evaluated, which shows the positive influence of such approach on energy optimization. By introducing changes in operational philosophy of distillation columns, steam savings of 30 ton/hr are possible, in a plant where the net import is 70 ton/hr. Further savings of 5-10 ton/hr are possible through process heat recovery. If heat is recovered instead of quenching, an additional 20 ton/hr of steam can be generated. Thus the whole Unit can become nearly self-sufficient in steam generation.