An S-graph is a graphical and theoretical approach to efficiently solving batch process scheduling problems in chemical plants.[1][2] S-graph is especially developed for the problems with non-intermediate storage (NIS) policy, which often appears in chemical productions, but it is also capable to solve problems with unlimited intermediate storage (UIS) policy.[2]
Overview
S-graph representation has the advantage of exploiting problem-specific knowledge to develop efficient scheduling algorithms.[2] There are products, and a set of tassk, which have to be performed to produce a product. There are dependencies between the tasks, and every task has a set of equipments, that can perform the task. Different processing times can be set for the same task in different equipments. It is also possible to have more equipment units from the same type, or define changeover times between two task in one equipment.
There are two types of the scheduling problems:
The number of batches to produce is set, and we try to minimize the makespan (processing time).
Every product has a revenue, and a time horizon is set. The objective is to maximize the revenue in this fixed time horizon. S-graph framework also contains combinatoricalgorithms to solve both of these problems.
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