Stock Decomposition Heuristic for Scheduling: A Priority Dispatch Rule Approach
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Highlighted in this article is a closed-shop scheduling heuristic which makes use of the traditional priority dispatch rule approach found in open-shop scheduling such as job-shop scheduling. Instead ...
Highlighted in this article is a closed-shop scheduling heuristic which makes use of the traditional priority dispatch rule approach found in open-shop scheduling such as job-shop scheduling. Instead of prioritizing and scheduling one job or project (or stock-order) at a time, we schedule one stock or stock-group at a time where a stock-group is a collection of individual stocks and their one or more stock-orders. These stocks can be feed-stocks, intermediate-stocks or product-stocks of which we focus on product-stocks given that most production is demand-driven. A key feature of this heuristic is our ability to compress the production network or superstructure so that only those unit-operations necessary to produce the stocks in question are included in the model thus reducing the size of the problem considerably at each iteration of the heuristic. The stock-specific network compression technique uses what we call a unit-capacity transshipment linear program to successively determine which unit-operations are redundant when making a particular stock. This heuristic is also particularly useful for those process industries that can potentially produce many product-stocks but only a fraction of these are produced within the scheduling horizon whereby the model is significantly reduced at solve time to include only those stocks that are demanded whereby redundant unit-operations are removed. An illustrative example is provided with recycle loops (i.e., stock flow-reversals) and shared units or equipment (i.e., unit flow-reversals) that demonstrates the effectiveness and efficiency of the technique.
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