Helene Lidestam

Use of Lagrangian decomposition in supply chain planning

The integrated planning of transportation of raw material, production and distribution of products of the supply chain for a large pulp company is studied. The planning period is one year and a number of time periods are considered. The tactical decisions included in the model regard transportation of raw materials from harvest areas to pulp mills, production mix and contents at pulp mills, distribution of pulp products from mills to customers either via terminals or directly, and the selection of potential orders and their levels at customers. A mixed integer linear programming model for the supply chain problem is developed. The main solution method in this paper is a Lagrangian heuristic method based on Lagrangian decomposition. The heuristic divides the problem into two subproblems representing different physical stages in the supply chain, each including several time periods. The advantage of the proposed solution approach is that it generates feasible solutions of high quality in short time. A number of cases based on real data is analysed.

Hierarchical scheduling and utility disturbance management in the process industry

The integration of scheduling and control in the process industry is a topic that has been frequently discussed during the recent years, but many challenges remain in order to achieve integrated solutions that can be implemented for large-scale industrial sites. In this paper we consider production control under disturbances in the supply of utilities at integrated sites together with the integration towards production scheduling. Utilities, such as steam and cooling water, are often shared between the production areas of a site, which enables formulation of an optimization problem for determining the optimal supply of utilities to each area at the occurrence of a disturbance. Optimization in two timescales is suggested to handle the scheduling and disturbance management problems in a hierarchical fashion. The suggested structure has been discussed with companies within the chemical process industry. A simple example is provided to show how the structure may be used.

Environmental evaluation of public procurement for bus transports

Purpose – The process of choosing the best part in the public procurement of bus transports is easier if the demands of the qualifications are well specified and detailed. On the other hand, detailed contracts will lead to limitations and could force the entrepreneurs to use uneconomical, but most of all, less environmentally friendly alternatives. The effects of using less specified contracts in order to achieve more environmentally friendly bus traffic have been tested and evaluated by optimization models. The paper aims to discuss these issues.Design/methodology/approach – A mathematical model with binary variables is developed to evaluate the environmental effects of more optimized bus sizes. Computational results from a bus service provider are reported. Different scenarios have been tested in order to evaluate the environmental effects of less detailed contracts.Findings – The results of the mathematical model indicate that all parts involved in the public procurement process, the public authority, ...

Factors reflecting bids in procurement of bus transports

Purpose – To facilitate the choice of the winning bid in the public procurement of bus transports in Sweden and to make sure that the winning bid has the qualities that are requested, the placed demands are very detailed. On the other hand, the detailed demands will lead to limitations and could force the operator to use less environmentally friendly alternatives. The purpose of this paper is to identify factors regarding the buses and their properties that are commonly used in the public procurement process and analyze their level of details.Design/methodology/approach – The method is to collect and study foundations from the process of public procurement of bus transport for three years in Sweden.Findings – The result shows the most common and relevant aspects regarding the buses and their properties that have been requested and taken into consideration when creating the final contracts. Most of the demands regarding the factors were also described in very great detail.Research limitations/implications ...

Supply Chain Modeling for a Process Industry

Process industries of today differ from other industries in many aspects. The purpose of this paper is to consider these special properties of process industries when developing a mathematical model that can be used as a decision support tool for the supply chain planning for a chemical process industry in Sweden. A mixed-integer linear programming model is developed, and solutions to the model present how the products will be transported between the different sites of the company, the levels of the inventories, the setups and purchases from the external suppliers and also the production rates. The mathematical model takes many special properties regarding process industries into account. By using the results from the model and test different scenarios, the model can be used as an important support tool when making decisions. The decision support tool can for example be used in the companys budget process and thereby improve the chances of future profits increases.

Hierarchical Production Scheduling - A Case Study at Perstorp

Planning and scheduling are functions that have large economic impact in the chemical process industry. For integrated sites with many interconnected production areas, obtaining production schedules that respect all production-related constraints is a complex task. One important issue is the constraints due to disturbances in utilities, such as steam and cooling water. These are often site-wide disturbances that may make it impossible to maintain desired production rates in several production areas at a site. In this study, scheduling at two levels of the functional hierarchy at a site of a world lead chemical industry, Perstorp, is handled. The activities are denoted production scheduling (PS) and detailed production scheduling (DPS). Real data of incoming orders and utility disturbances are used to produce a production schedule and detailed production schedule for one month. The PS and DPS problems are formulated as optimization problems, where production-related constraints such as production rate constraints, inventory limitations, and start-up costs are included. The objective functions of the PS and DPS problems are formulated to reflect the importance of different issues at the site. The procedure aims to show how the hierarchical optimization framework may be used to provide decision support for how to operate the production at a site in order to maximize profit while minimizing the effects of site-wide disturbances.