Optimal design of buffers in plants with recycling

Buffer tanks are commonly employed to dampen the effect of disturbances in chemical processes. In order to minimize the number and size of tanks, the buffers should be designed to mainly handle disturbances that cannot be effectively handled by a feedback control system. In this paper we consider optimal design of buffers in plants with recycle of material and/or energy. Such recycling is becoming common in process plants, and typically increases the disturbance sensitivity significantly, and hence the potential need for buffers. We show that the location of the buffer is a crucial decision in recycle systems, and derive simple model-based tools that can be used to determine both the optimal size and location of buffers in recycle systems.