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Release : 2014
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Kind : eBook
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Book Synopsis Models and Solution Methods for Chemical Production Scheduling by :
Download or read book Models and Solution Methods for Chemical Production Scheduling written by . This book was released on 2014. Available in PDF, EPUB and Kindle. Book excerpt: Chemical production scheduling optimization has the potential to reduce operating cost, increase profits, and improve efficiency. These optimization problems often formulated as mixed integer programming models which, despite advances in computer hardware and optimization software, remain hard to solve. We first formulate a more general model and then develop several solution methods to speed up the computational times. We show that the production environment can be defined by material handling constraints and formulate a general model that is valid for all production environments. We develop new formulations for processes with changeovers and compare their relative tightness and present computational results for several example problems. In the first solution method, customer orders are propagated backwards through the network to find the minimum amount of material each task must process, providing a lower bound on the number of times each task must run. We extend these methods to the general model. This method is most effective for cost minimization and can lead to a 2-3 order-of-magnitude improvement in computational time. The next method reduces the size of the model by using different time grids for each task, unit, material, and utility. We prove that this formulation will have the same optimal solution as a single-grid formulation. This method is most effective for makespan. The third method uses a parallel batch-and-bound algorithm. The scheduling problem is divided into subproblems by branching on the number of times each task runs. Each of these subproblems is solved in parallel by a separate core and may be divided further. Many difficult problems can be solved to optimality with this method. The final method is the simplest and most effective. Many equivalent schedules can be formed by simply shifting tasks in units with idle time earlier or later. These schedules have the same number of batches and similar objectives. Introducing a new integer variable representing the number of batches of each task allows the solver to branch on this variable to find truly different schedules quickly. This method is the most effective with over 2, 3, or 4 orders-of-magnitude improvements for makespan, profit, and cost optimization respectively.
