Improving distillation modelling in a dynamic process simulator
Seppänen, Tuuli (2016)
Seppänen, Tuuli
2016
Automaatiotekniikan koulutusohjelma
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2016-08-17
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201608034377
https://urn.fi/URN:NBN:fi:tty-201608034377
Tiivistelmä
The need of maximizing the economic benefits of a distillation unit often requires operating close to its capacity limits. The limits of an operating column depend on the internal vapor and liquid flows and their physical properties. In this thesis, distillation modelling in a dynamic process simulator was improved to consider internal phenomena in a distillation column i.e. tray hydraulics.
The structure of the original distillation model was first reconsidered. In the developed model, separate flash separators were used to represent an active area and a downcomer of a tray. The hydraulic phenomena included in the model were jet flooding, downcomer backup flooding, downcomer choke flooding and weeping. Downcomer backup flooding occurred in the model automatically due to the model structure and configuration. To represent the other hydraulic phenomena in the model, correlations were used. These correlations were rationalized based on the literature study. For determining the limit values, at which each phenomenon begins, and maximum jet flooding and downcomer choke flooding occurs in a specific distillation column, Koch-Glitsch’s KG-TOWER software was utilized.
The developed distillation model was first implemented in the dynamic process simulator with fixed pressure, and jet flooding, downcomer choke flooding and weeping occurring only on one tray. The liquid flow rates, pressures and levels of the tanks were also calculated manually with a spreadsheet, and simulation results were compared to those to verify the accuracy of the simulation model. After ensuring the reasonable function of the correlations, the calculation of the correlations was implemented in the simulator code by programming. For more extensive examination, the model was implemented in a distillation game model. The function of the model was studied by varying the reboiler duty, feed rate and reflux rate.
The simulation results showed that some oscillation occurs easily both in flooding and in weeping. To ensure the stability in all situations, the model configuration needs further examination. All the hydraulic phenomena did, however, occur in the model according to implemented calculation as assumed.
The structure of the original distillation model was first reconsidered. In the developed model, separate flash separators were used to represent an active area and a downcomer of a tray. The hydraulic phenomena included in the model were jet flooding, downcomer backup flooding, downcomer choke flooding and weeping. Downcomer backup flooding occurred in the model automatically due to the model structure and configuration. To represent the other hydraulic phenomena in the model, correlations were used. These correlations were rationalized based on the literature study. For determining the limit values, at which each phenomenon begins, and maximum jet flooding and downcomer choke flooding occurs in a specific distillation column, Koch-Glitsch’s KG-TOWER software was utilized.
The developed distillation model was first implemented in the dynamic process simulator with fixed pressure, and jet flooding, downcomer choke flooding and weeping occurring only on one tray. The liquid flow rates, pressures and levels of the tanks were also calculated manually with a spreadsheet, and simulation results were compared to those to verify the accuracy of the simulation model. After ensuring the reasonable function of the correlations, the calculation of the correlations was implemented in the simulator code by programming. For more extensive examination, the model was implemented in a distillation game model. The function of the model was studied by varying the reboiler duty, feed rate and reflux rate.
The simulation results showed that some oscillation occurs easily both in flooding and in weeping. To ensure the stability in all situations, the model configuration needs further examination. All the hydraulic phenomena did, however, occur in the model according to implemented calculation as assumed.