Model-Based Optimization of Economical Grade Changes for the Borealis Borstar Polyethylene Plant

Research output: Contribution to journalArticle


Economical grade changes are considered for a Borealis Borstar polyethylene plant model, incorporating two slurry-phase reactors, one gas-phase reactor and a recycle area with three distillation columns. The model is constructed in the Modelica language and the platform is used for opti- mization. The cost function expresses the economical profit during a grade change and is formulated using on-grade intervals for seven polymer quality variables such as melt index, density and reactor split factors. Additionally, incentives to produce polymer with quality variables on grade target values, not only inside grade intervals, are added. Twelve inflows and three purge flows are used at optimization. Two grade changes are thoroughly reviewed, showing the effect of using a cost function that regards plant economy. Re- sulting trajectories can be divided into three phases with distinguishing fea- tures, and the synchronization of inflows and usage of recycle area off-gas flows are important in the grade changes.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Control Engineering
  • Chemical Engineering


  • optimization, grade change, polymer, economy
Original languageEnglish
Pages (from-to)153-166
JournalComputers & Chemical Engineering
Publication statusPublished - 2012
Publication categoryResearch

Bibliographic note

key=lar+12cace month=November project=LCCC-modeling

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