A stochastic model for performance analysis of pharmaceutical high purity water systems

The operating performance of high purity water systems such as pharmaceutical Deionized and Water for Injection (DI/WFI) distribution systems can be difficult to analyse due to the highly variable demand that is drawn from these systems; a situation compounded by schedule and demand volume uncertainties. This work presents a stochastic model to simulate volume and schedule uncertainties of industrial size DI/WFI systems. The model utilises discrete-event simulation combined with the Monte Carlo method to calculate the demand profile of the distribution system and a continuous simulation to compute the variation of the level in the storage tank. It is shown that the model may be used to predict if an existing DI/WFI systems is capable of delivering water for a new process, for which historical data is lacking. The model is programmed in Excel 2003 and is available for download [1] as open software.