Maria Teresa Moreira Rodrigues

Reactive scheduling approach for multipurpose chemical batch plants

Abstract In this paper a reactive scheduling technique for multipurpose plants is presented. A Mixed Integer Linear Problem (MILP) formulation is used based on the State Task Network (STN) representation of Kondili et. al. (1993). In order to obtain short response times a rolling horizon is utilized, which is reasonable as far as it is considered a reactive context where perturbations in the future are expected. To bring into consideration time constraints outside the rolling horizon a lookahead characteristic is introduced.

Short-term planning and scheduling in multipurpose batch chemical plants: a multi-level approach

Abstract This paper deals with short-term planning/scheduling problems when the product demands are driven by customer orders. This type of problem is, in general difficult to be solved, once the orders are subject to changes in short periods. In this paper is proposed a multi-level decomposition procedure, containing at least two levels. At the planning level, demands are adjusted, a raw material delivery plan is defined and a capacity analysis is performed. Therefore, time windows for each operation are defined. At the scheduling level, an MILP model is developed. In order to reduce scheduling problem dimension, it is performed an analysis of equipment contention profile, enabling to model only situations where a decision variable is requested.

Scheduling heuristics based on tasks time windows for APS systems

Abstract Advanced Planning and Scheduling systems (APS) are intensively utilized in the industry, namely because they allow generating and analyzing planning scenarios very quickly. They are not well suited for make-to-order situations since due dates are not considered hard constraints to be fulfilled. Processing time windows allow to take into account due dates in the development of APS enhanced heuristics.

Optimization of water removal in the press section of a paper machine

An optimization problem regarding water removal in the press section of a paper machine is considered in this work. The proposed model tries to minimize a cost function comprising the replacement of the felts in the press section, the cost of energy to operate the press and the cost of energy in the drying section, while satisfying the constraints of water mass balance in the process. The model is classified as a mixed-integer nonlinear program (MINLP) in which the most important decisions are: a) the sequence of paper to produce or when to produce the paper; b) the need to exchange the felts; and c) when to exchange the felts. Numerical examples are presented to illustrate the performance of the model.

SEQUENTIAL APPROACH TO PRODUCTION PLANNING IN MULTISITE ENVIRONMENTS

Abstract A sequential planning approach is proposed for make-to-order situations that tries to emulate the practitioners approach. It deals sequentially with assignment of sites and transportation, completion time, exact timing and detailed sites planning, allowing negotiation among sites in terms of runtime required for each site.

Constraint Propagation Tools in Multipurpose Batch Plants Short Term Planning

Abstract Constraint propagation tools, used in scheduling problems, are utilized in a short term planning problem in a batch plant to obtain a planning frame in the form of batches processing time windows and equipment units loading. An extended propagation mechanism is proposed to deal with storage constraints.

A Mathematical Model for Water Removal in the Press Section of a Paper Manufacture Industry

Abstract A production optimization problem concerned with the water removal in the press section in a paper machine is considered in the present paper. The proposed model seeks to determine the planning of production of paper in order to minimize a cost function that consists of replacement of the felts in the press section, cost of energy to operate the press and cost of energy in the drying section. The proposed model corresponds a mixed-integer nonlinear programming (MINLP) where the most important decisions in the paper machine are: a) the sequence of paper to produce, or when to produce the paper, b) the need to exchange the felts, and c) when to exchange the felts. Numerical examples are presented to illustrate the performance of the model. This work was developed considering a real case with data from a Brazilian paper plant.

A holistic framework for supply chain management

Abstract A new approach to Supply Chain Management (SCM) is proposed that considers different structures conceived as module components of a holistic framework. In this way, decision support is supplied at different levels and for different functionality. Thus, the system may be also used for multi-objective assistance to decision making, while systematically considering the time and other intrinsic constraints associated to the structure of the supply chain. This approach is applicable to the different supply chain layers, from the individual single sites to the global Supply Chain optimisation, including multi-site (single company) competitive strategic decisions, or the independent management of a similar objective (i.e. benefits, client satisfaction, etc.) for different companies.

A time-windows approach for enhancing the capabilities of batch scheduling systems: An application to simulated annealing search

Simulated Annealing (SA) is utilized for a short term scheduling problem where batches have to be scheduled inside processing time windows obtained in a planning phase. It is well known that SA, when used for solving a short-term scheduling problem, can generate a large quantity of infeasible candidates in heavily constrained situations, since it is difficult to filter out infeasible candidates based only in their structure, basically an ordering relation between the tasks. It is shown that tools from Constrained Based Search scheduling techniques can be utilized to implement a filtering procedure for the problem, determining which interchanges lead to feasible situations.

Time windows for short term planning in multipurpose batch plants

Abstract A planning approach is presented for short term mode of operation in multipurpose batch plants. Planning output is given in the form of processing time windows for intermediate products. Time windows are established from the time profile demand of final products and raw materials availability plan input by the user. Equipment units capacity analysis is used to assure a feasible situation and an acceptable plant loading.