| 1. |
- Andersson, Niklas, et al.
(författare)
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Calibration of a polyethylene plant for grade change optimisations
- 2011
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Ingår i: 21ST European Symposium on Computer Aided Process Engineering. - 1570-7946. - 9780444538956 ; 29, s. 673-677
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Konferensbidrag (refereegranskat)abstract
- A polyethylene plant model coded in Modelica and based on a nonlinear MPC model currently used at Borealis AB is considered for calibration. A case study of model calibration at steady-state for four different operating points are analysed, both when looking at one operating point separately, but also to calibrate several simultaneously. Both model parameters and reactor inputs are calibrated for true plant measurement data. To solve the parameter estimation problem, the JModelica.org platform is used, offering tools to express and solve calibration problems. Calibration was obtained with narrow confidence intervals and shows a potential to improve the model accuracy by changing the parameter values. The results will be used for dynamic optimisations of grade changes.
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| 2. |
- Andersson, Niklas, et al.
(författare)
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Parameter Selection in the Parameter Estimation of Grade Transitions in a Polyethylene Plant
- 2015
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Ingår i: Studies in Engineering and Technology. - : Redfame Publishing. - 2330-2038 .- 2330-2046. ; 3:1, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- A polyethylene plant at Borealis AB is modelled in the Modelica language and considered for parameter estimations at grade transitions. Parameters have been estimated for both the steady-state and the dynamic case using the JModelica.org platform, which offers tools for steady-state parameter estimation and supports simulation with parameter sensitivies. The model contains 31 candidate parameters, giving a huge amount of possible parameter combinations. The best parameter sets have been chosen using a parameter-selection algorithm that identified parameter sets with poor numerical properties. The parameter-selection algorithm reduces the number of parameter sets that is necessary to explore. The steady-state differs from the dynamic case with respect to parameter selection. Validations of the parameter estimations in the dynamic case show a significant reduction in an objective value used to evaluate the quality of the solution from that of the nominal reference, where the nominal parameter values are used.
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| 3. |
- Larsson, Per-Ola, et al.
(författare)
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Economic Cost Function Design and Grade Change Optimization for a Gas Phase Polyethylene Reactor
- 2011
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Konferensbidrag (refereegranskat)abstract
- Gas phase polyethylene reactors are able to produce several different grades of polymer. Adapting to market conditions requires grade transitions, associated with costs in terms of raw material and temporary production of lower priced off-specification products. In this paper, both stationary production and dynamic grade transitions are optimized to maximize profit, i.e., economic process optimization. A cost function for transitions that utilizes product quality variable intervals, specifying premium priced products, and that also gives incentives to produce products having quality variables on target, i.e., equal to a defined grade, is designed. A previously published reactor model is extended with quality variable models and several grade transitions are optimized and shown.
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| 4. |
- Larsson, Per-Ola, et al.
(författare)
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Model-Based Optimization of Economical Grade Changes for the Borealis Borstar Polyethylene Plant
- 2012
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Ingår i: Computers & Chemical Engineering. - : Elsevier BV. - 1873-4375 .- 0098-1354. ; 46, s. 153-166
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Tidskriftsartikel (refereegranskat)abstract
- 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 JModelica.org 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.
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| 5. |
- Larsson, Per-Ola, et al.
(författare)
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Modelica Based Grade Change Optimization for a Polyethylene Reactor
- 2010
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Konferensbidrag (refereegranskat)abstract
- This paper presents a dynamic optimization procedure of grade changes of polyethylene production. The optimization is built upon a novel modular Modelica library containing e.g., non-linear DAE models for polyethylene reactors based on models currently used in nonlinear MPC of industrial reactors at Borealis AB. Using Optimica, which extends the Modelica language with constructs for optimization problems, and JModelica.org, a novel framework to translate such optimization problems into NLP problems, grade transition ptimization problems can be solved. The solution procedure and a transition xample with optimal inputs and outputs are given in the paper showing promising results.
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| 6. |
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| 7. |
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| 8. |
- Larsson, Per-Ola, et al.
(författare)
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Modeling and Optimization of Grade Changes for Multistage Polyethylene Reactors
- 2011
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Konferensbidrag (refereegranskat)abstract
- Grade changes in polyethylene reactors, i.e., changes of operating conditions, are performed on a regular basis to adapt to market demands. In this paper, a dynamic optimization procedure is presented built upon the Modelica language extended with Optimica constructs for formulation of optimization problems. A Modelica library for the Borstar R multistage polyethylene reactors at Borealis AB, consisting of two slurry and one gas phase reactor, has been constructed. Using JModelica.org, a framework to translate dynamic optimization problems to NLP problems, optimal grade transitions between grades currently used at Borealis AB, can be calculated. Optimal inflows and grade key variables are shown.
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| 9. |
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