A trend in the chemical industry is the design of smaller flexible multiproduct plants that are located close to the markets of consumption. The motivation in building such plants lies not only in the reduction of transportation and inventory costs, but also for increasing the capability to provide a steady supply of products, and for responding more quickly to demand changes in each market. Thus, flexible multiproduct plants offer the possibility of improving the competitiveness of chemical companies. Multiproduct plants can operate in batch or continuous mode, or with a combination of the two. Typical examples of the former include plants for manufacturing pharmaceuticals, food and specialty chemicals; examples of the latter include plants for manufacturing a number of polymer products, paper mills and petroleum refineries. The main difference that arises in multiproduct plants compared to large scale dedicated continuous plants is that scheduling and production planning play a major role in the operation of these plants. Another issue is that uncertainties and fluctuations in the product demands tend to be much greater in multiproduct plants. This research deals with the development of systematic methods for the design and scheduling of various types of flexible multiproduct chemical processes that operate in the continuous mode. The work involves the development of models and solution techniques for the simultaneous design and scheduling of plants that consist of a sequence of stages and that are interconnected by intermediate inventory tanks. The basic objective is to determine optimal trade-offs arising from the selection of design variables, operating conditions, sequencing of operations, length of production cycles and inventory levels. Both rigorous and simplified models will be investigated, as well as methods for assessing and optimizing the flexibility of the designs in the face of uncertain demands.
