• Integrating routing and scheduling for pipeless plants in different layouts

      Huang, Wei; Chung, Paul Wai Hing; University of Luton; Loughborough University (Elsevier, 2005)
      Pipeless batch plants are built to provide the ability to adapt to fast market changes. The scheduling of pipeless plants adds new challenges to the scheduling of conventional batch plants. This is because of the requirement to consider the allocation of resources and also the plant layout so that vessels can move from one processing station to another without conflict. This research investigates the integrated problem of scheduling and routing in pipeless plants and develops a constraint-based methodology suitable for different layouts. During the scheduling process, besides time and resource allocation, a planner is also called to find possible routes to move vessels from one processing station to the next proposed station. Each of the dynamically generated routes is immediately check for feasible track allocation so that any infeasible route is discarded as soon as possible to save computational time. A typical scheduling problem and results are described in detail to show how this integrated approach works.
    • Scheduling of batch plants: constraint-based approach and performance investigation

      Huang, Wei; Chen, Bo; University of Luton; University of Warwick (Elsevier, 2007)
      Batch processing plants are attractive due to their suitability for the manufacturing of small-volume, high-value added products. Scheduling batch plants by using computer-aided systems is important for improving the plant productivity, since it harmonizes the entire plant operation efficiently to achieve production goals. However, the current scheduling approaches for batch plants are inadequate. This research develops a constraint-based model and system for batch-process scheduling and investigates their performance. The proposed constraint model analyses and brings together many scheduling constraints, adds new constraints and categorizes them according to their functionality. A computer scheduling system, Batch Processing Scheduler, is developed in C++ to apply the model. A number of examples have been devised to study the performance of our constraint-based approach. It is found that the approach can schedule complex plants and solve large-size problems by finding feasible solutions satisfying all imposed constraints, which include some hard ones such as those of finite wait time. It is also identified that the first feasible solution can be found very quickly, but much more time, even exponentially more, is required to find the optimal solution particularly for complex and large-size problems. Feasibility and limitations of the proposed methodology are demonstrated by the results.