• Comparative study of time-based and activity-based production scheduling

      Das, B.P.; Shah, N.; Chung, Paul Wai Hing; Huang, Wei (University of Pannonia (Hungary), 2000)
      In this paper the principles behind the Time-based and Activity-based approaches to production scheduling are briefly explained. Based on a typical scheduling problem relating to chemicals processing sectors, two schedules using the two different approaches are generated for the purpose of comparison. The first schedule is generated using gBSS, which is a Time-based scheduling software package, which uses mathematical optimisation techniques. The second schedule is produced using BPS, which is a constraint-based scheduler following the principle of the Activity-based approach. A comparison is made between the two schedules considering three different aspects: (1) User input requirements to the problem (2) Quality of the schedule produced (3) Solution statistics. Interestingly, the two schedules produced by the two different approaches are slightly different, although both of them satisfied the product delivery requirements
    • A constraint approach for rescheduling batch processing plants including pipeless plants

      Huang, Wei; Chung, Paul Wai Hing; Loughborough University (Elsevier, 2003)
      In the process industries batch plants are attracting attentions because of their suitability for producing small-volume, high-value added commodity chemicals. Pipeless plants have also been developed and built to increase plant flexibility. Unexpected events, such as the failure of a processing unit, sometimes happen during operations. To avoid risk and to utilise the remaining resource, it is important to reschedule the production operation quickly. The constraint model in BPS has been extended to include constraints for rescheduling. These additional constraints are described in this paper and a case study is used to demonstrate the feasibility of the approach.
    • 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 multistage multiproduct chemical batch plants using a constraint-based approach

      Huang, Wei; Chung, Paul Wai Hing; Loughborough University (Elsevier, 1999)
      Multistage multiproduct chemical batch plants provide great flexibility but the task of scheduling them to meet product demands can be challenging. A typical scheduling problem involves the allocation of resources over time. A constraint-based approach to solve this kind of scheduling problems is considered. The essential feature of this approach is that it does not require elaborate mathematical formulae, but it requires a problem to be stated in terms of constraints. A general constraint model was created to represent a common class of chemical batch plants and a scheduling system was produced based on this model. A user can simply input the information of production requirements through a user interface and, if necessary, modify the constraints related to the specific problem and a viable schedule is created automatically.
    • Scheduling of pipeless batch plants using constraint satisfaction techniques

      Huang, Wei; Chung, Paul Wai Hing; Loughborough University (Elsevier, 2000)
      Process industries need to be able to adapt to the fast changing market in order to meet consumer demands. Pipeless batch plants are being developed and implemented to improve flexibility to meet this requirement. However, their efficiency greatly depends on the generation of feasible production schedules. This paper proposes a general constraint model to solve this kind of scheduling problem for pipeless batch plants. In this model, constraints on resource allocation, activity precedence, time bound and safety issues are considered. A computer system, BPS, based on the constraint model and the search algorithm used in BPS are also presented. A case study is described to demonstrate the applicability of the proposed approach.