This study presents the development of a model for a chemical batch plant which is used in the integration of energy demanding unit operations, energy conversion systems and waste management during process design. If energy conversion and waste management systems are only considered as “slaves to the production plant”, this can lead to oversizing of installations or alternatively to problems with peak loads and generally to operating with low efficiency due to variations of operating conditions from initial design conditions. The latter scenario has a high importance in the case of a batch plant, where the product portfolio can change quickly leading to changes in utility requirements both quantitatively and qualitatively. In order to avoid the problems mentioned above and to look for a global optimum from financial and environmental point of view, an integrated design of the chemical production, the energy conversion and the waste management system must be achieved.

For this purpose, models for energy conversion systems and waste treatments based on real-life applications should be built to predict the energy consumption/production and the emissions as a function of process demands. Initially, a monoproduct plant has been chosen to represent the simplest case for the modeling of utility consumption (steam, brine, water, electricity). The Bottom-Up approach (Bieler et al 2004) was applied to calculate the energy consumption of a whole building with the help of process data and results were compared with the real consumption. Direct measurements of unit operations were performed to develop empirical parametric models of thermal losses and heat exchange efficiencies were calculated. These values will be useful during tasks scheduling in order to choose the most appropriate equipment for operation depending on their energy requirement.

Then, the energy profiles that are predicted by the models will serve as data for the design of a heat exchanger network specially built for batch processes in order to estimate the potential heat recoveries by applying direct heat exchange or by using an energy storage structure. The overall result has to be assessed with financial and environmental indicators in order for Pareto optimal alternatives to be identified. Only such an approach will ensure that an improvement of one part of the process is actually beneficial for the overall system and therefore it has to be undertaken.

Reference

1. Bieler PS, Fischer U, Hungerbuhler K. 2004. Modeling the Energy Consumption of Chemical Batch Plants: Bottom-Up Approach. Ind. Eng. Chem. Res. 43:7785-95