A Mathematical Programming Approach for Integrated Design of Scheduling/Heat-Recovery/Water-Reuse Network in Batch Plants
Date Issued
2009
Date
2009
Author(s)
Chang, Chia-Yuan
Abstract
This dissertation aims to develop an integrated mathematical formulation to solve the scheduling, heat-integration and water-reuse problems. The framework is divided into two modules: one is batch scheduling incorporated with heat recovery, whereas the other one is batch water-reuse network. The later is mainly used to work in coordination with the scheduling module. However, it can also be used individually. A continuous time formulation, which is more competitive in efficiency than traditional discrete one, is adopted as the time representation in designing each subsystem. Both short-term and periodic operation modes are considered to cover most of the production scenarios.iscussions are elaborated from a novel framework of Resource-Task Network (RTN) proposed by Castro et al. To extend the capability of scheduling toward simultaneous scheduling and direct heat-recovery, a generalized mathematical formulation is firstly proposed by introducing new parameters and a set of new binary variables in managing heat-integration. In comparison with literature examples, the new model is proven competitive with its flexibility and without the loss of compromising with efficiency.hen, a new water-reuse framework is proposed with the same continuous time concept in general scheduling model. This new formulation contains water-reuse and storage facilities for multi contaminant environment. Both single and periodic operation modes are also derived in correspondence with the scheduling model. The water-reuse module is connectable with scheduling module via the decision binary variables. However, they are regarded as predefined parameters if the water-reuse module works alone. Therefore, in the two basic scenarios of water minimization, no binary variable is required; therefore, the model is formulated in NLP, which is very competitive with the result reported in literatures.n overall model is carried out thereafter by simply combining the scheduling with water-reuse module proposed previously. However, the computational issue in handling large scaled MINLP is inevitable. Instead of global optimum, an acceptable solution might be more attractive in reasonable computation time. Since the priority in scheduling is usually higher than that in water-reuse network, a hierarchical two-step solving procedure is proposed. In the first stage, the water-reuse module is converted into a ''convex hull'' MILP model and then combined with the scheduling module. The resulting relaxed model is MILP and could be easily solved to obtain the decision binary variable in scheduling. In the second step, the overall model is solved with the fixed production schedule. Therefore, only a NLP, which is easier to solve than the original MINLP, must be solved. Several enhancements are carried out in the linearization of water-reuse module to narrow the difference between the original and relaxed model. Two examples are demonstrated to verify the performance of the solving procedure.
Subjects
Batch process
Scheduling
Heat Integration
Water-reuse Network
Mixed-integer linear programming (MILP)
Mixed-integer nonlinear programming (MINLP)
Type
thesis
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