The design and implementation of shutdown logic in batch control application is often done in Hold and Abort Handlers of unit phases. This is evident because most of operating characteristics and interaction between unit equipments are observed and controlled by unit phases, but this approach requires significant amount of programming for Hold and Abort Handlers; most of which can be identified as redundant. A general purpose Unit Shutdown strategy discussed in this paper will demonstrate benefits of distributed shutdown handling.
Four main elements of unit shutdown strategy are:
Unit Shutdown Control Module using sequential control function of DCS has already been implemented at Ely Lilly Pharmaceutical facility in Puerto Rico in 2005. Unit shutdown strategy, integrating above four shutdown strategy elements, which would result in increased reliability, code optimization, solving control logic deadlocks for shared equipment and batch reporting function requirement is incepted in this paper.