Discrete event simulation in the design, layout and scheduling of pipeless batch plants

A way forward in multi-product manufacturing is the emerging technology of ''pipeless plants". The basic idea of a pipeless plant is to move the process vessel between fixed stations for mixing, separation and other activities. The elimination of pipework for the transfer of material offers great flexibility for change, and allows a company to respond quickly to market demands and technological advances. As well as reduced downtime for product changeovers, and the ability to introduce new products without too much modification, other benefits include reduced product loss, ease of cleaning, and reduced inventories (Just-In-Time processing). Little research has been found on the safe design of pipeless plants, which can be split into three aspects: process, computer-control, and schedule. This paper is focused on the subject of scheduling. Although little published literature is available, papers on the subject have worked on the premise that a correctly working schedule would overcome the safety issues. However, scheduling is usually concerned with optimum product output, and is not adequate from a safety perspective, as demonstrated in this paper. Layout and scheduling have to be considered simultaneously in the design of a pipeless plant, and a method of analysing the interaction between the two is required. This paper illustrates the value of discrete event simulation (DES) both as a design tool and as a hazard identification tool, by taking a published schedule and simulating it using ARENA Simulation Software. Several issues are raised such as where vessels start from and where they finish, and the rules that they must follow on each leg of their journey. As well as revealing potential problems, discrete event simulation enables the designer to propose alternatives, and explore them. The result of which should be an optimum schedule, both in terms of output and safety, for a proposed layout.