An introduction to the concept of roving pumps in the synthesis of multipurpose batch plants

Abstract

Multipurpose batch chemical plants are commonly used to produce valuable, high quality products in low volumes. A series of discrete and independently operated tasks allow for flexible production in order to adapt to rapid market fluctuations. Batch plants commonly require pumping equipment in order to transfer liquid material between processing units and storage vessels. However, previous mathematical formulations that address short-term scheduling and synthesis of multipurpose batch plants have largely omitted the importance and impact of the pumping equipment on the batch plant. Presented in this dissertation is a novel technique to flexibly allocate pumps throughout a batch plant, so called roving pumps. The nature of batch processes allows for the allocation of pumps to different units and tasks depending on pump availability. A Mixed Integer Linear Program mathematical formulation is presented to determine the optimal number and allocation of pumps within the batch plant while simultaneously synthesizing the plant and optimizing the batch production schedule. Also addressed in this dissertation are the material transfer times associated with variable batch sizes during production. By optimally allocating pumps to processing units, this formulation has shown a significant decrease in the number of pumps required within a batch plant, thereby improving the utilization of available equipment. It is shown by way of an example that it is possible to decrease the number of pumps required for operation from eleven to three pumps, while another example identified a decrease in the number of pumps required from seven to two. The formulation was also applied to two case studies, where it was shown that it is possible to reduce the number of pumps required from 17 to 4 and from 19 to 5 for each case, respectively. By using fewer pieces of equipment more frequently, equipment degradation due to nonuse can be reduced and equipment utilization can be maximized. It is, therefore, possible to significantly reduce capital cost investment and maintenance costs by implementing the formulation while still achieving or improving on existing throughputs.