A general stochastic model for intermediate storage in noncontinuous processes

Abstract

A significant role of intermediate storage in noncontinuous manufacturing systems is to decouple stages of operations. It eliminates delays and interruptions caused by the uncertainty in process operations, and increases the availability of the process. We present a stochastic model for intermediate storage in a two-stage process with multiple, nonidentical parallel units in each stage. In contrast to the existing models, the new model allows a simultaneous treatment or arbitrary types of random process disturbances such as operation (processing, cleaning, transfer, set-up etc.) time variations, unit failures and repairs, batch failures, batch size variations, etc. Using well-known results from the probability theory, we derive general analytical expressions for sizing intermediate storage to maintain the continuity of operation with a given degree of confidence. We apply these expressions to the two-stage system with only the process parameter fluctuations, and obtain specific results. For this process, we compare our model with the existing models and Monte Carlo simulation. The new model predicts much smaller storage sizes than the other models and compares very well with the simulation results.