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Optimized on-line process control of bleaching operations with OptCab
Linköping University, Department of Mathematics, Optimization . Linköping University, The Institute of Technology.
Billerud AB, Skärblacka, Sweden.
Department of Finance and MAnagement Science, Norwegion School of Economics and Business Administration, Bergen, Norway.
2007 (English)In: Norges Handelshoeyskole. Institutt for Foretaksoekonomi. Discussion Paper, ISSN 1500-4066Article, review/survey (Refereed) Published
Abstract [en]

To produce pulp for paper production or as market pulp is a complicated on-line process with many integrated stages that impact the final quality. In the bleaching plant which is at the end of pulp production, the main objective is to increase pulp brightness within specified limits. Here chemical treatments are applied in sequential stages to achieve the right brightness while striving to maintain the pulp strength as unaffected as possible. The raw material, i.e. pulp logs and wood chips from saw mills, differ in quality and properties. Due to this, it is important to continuously update the amount of chemicals added to the pulp in real-time. This is typically done by experienced operators. In this paper, we describe an on-line optimization based decision support system called OptCab that controls the bleaching process at Billerud AB's paper mill in Skärblacka. The solution approach is based on two phases. In phase one, we establish approximations of each of the processes based on process data collected on-line. These approximations are found by solving a set of constrained least square problems and are updated every 15 minutes. In phase two, we formulate an overall nonlinear control problem that links all stages together and aims to minimize the cost of chemicals. This is solved on-line every five minutes. The system has been in operation during the last three years providing a 10% reduction in the use of chemicals. Additional benefits include a more stable brightness quality.

Place, publisher, year, edition, pages
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-85523OAI: diva2:571200

This is a working paper.

Available from: 2012-11-21 Created: 2012-11-21 Last updated: 2012-11-22
In thesis
1. Application of operations research in operative planning in the forest industry
Open this publication in new window or tab >>Application of operations research in operative planning in the forest industry
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this thesis is the use of Operations Research for pplications in the forest industry. Optimization models and methods have been developed for problems in the forest supply chain and they have been integrated in decision support systems. The problems considered in this thesis are operative with a planning horizon of less than a month. Short solution times for the methods and the feasibility of the models used are important aspects. The body of this thesis consists of eight research papers where six of them consider operative problems and follows the forest supply chain. The industrial applications include routing of forwarders, routing of logging trucks, a process control problem, and roll cutting problems. The other two papers consider an operative planning problem in the home care sector. They are spin offs from one of the other projects in this thesis. In these applications both linear and nonlinear problems occur.

The forwarding problem is to decide routes for forwarders to pick up the small piles of logs the harvesters have left in the harvest areas. The forwarders then put the logs adjacent to forest roads. The logging truck problem is to decide routes for logging trucks to pick up the piles created by the forwarders and transport them to demand points, for example pulp or paper mills. The process control problem appear in the bleaching stage of a pulp mill where the control variables are the bleaching chemical charges. The cost of bleaching chemicals is minimized while a finishing brightness within target values is ensured. Mainly two roll cutting problems are studied. One is to minimize the number of cutting patterns and one is to minimize the number of reels when defects in the papper reels are considered. The solution methods developed for the forwarding problem have also been applied to a routing problem which appears in staff planning for home care operations.

The different DSS developed and implemented have been tested and several are in daily industrial use. In each of the papers, we have developed robust OR models and quick and effective OR methods. The savings from using the systems vary but are typically in the range 5-20%.

Place, publisher, year, edition, pages
Matematiska institutionen, 2007. 31 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1104
operative planning, routing, forestry, modelling, Decision Support System, optimization, OR in practice
National Category
Computational Mathematics
urn:nbn:se:liu:diva-8806 (URN)978-91-85831-91-3 (ISBN)
Public defence
2007-05-30, C3, Hus C, Campus Valla, Linköpings Universitet, Linköping, 10:10 (English)
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2012-11-22

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