Development and demonstration of a new non-equilibrium rate-based process model for the hot potassium carbonate process.
Date
2009
Authors
Ooi, Su Ming Pamela
Editors
Advisors
O'Neill, Brian K.
Colby, Christopher Brett
King, Keith Douglas
Colby, Christopher Brett
King, Keith Douglas
Journal Title
Journal ISSN
Volume Title
Type:
Thesis
Citation
Statement of Responsibility
Conference Name
Abstract
Chemical absorption and desorption processes are two fundamental operations in the process
industry. Due to the rate-controlled nature of these processes, classical equilibrium stage models are
usually inadequate for describing the behaviour of chemical absorption and desorption processes. A
more effective modelling method is the non-equilibrium rate-based approach, which considers the
effects of the various driving forces across the vapour-liquid interface.
In this thesis, a new non-equilibrium rate-based model for chemical absorption and desorption is
developed and applied to the hot potassium carbonate process CO₂ Removal Trains at the Santos
Moomba Processing Facility. The rate-based process models incorporate rigorous thermodynamic
and mass transfer relations for the system and detailed hydrodynamic calculations for the column
internals. The enhancement factor approach was used to represent the effects of the chemical
reactions.
The non-equilibrium rate-based CO₂ Removal Train process models were implemented in the Aspen
Custom Modeler® simulation environment, which enabled rigorous thermodynamic and physical
property calculations via the Aspen Properties® software. Literature data were used to determine the
parameters for the Aspen Properties® property models and to develop empirical correlations when the
default Aspen Properties® models were inadequate. Preliminary simulations indicated the need for
adjustments to the absorber column models, and a sensitivity analysis identified the effective
interfacial area as a suitable model parameter for adjustment. Following the application of adjustment
factors to the absorber column models, the CO₂ Removal Train process models were successfully
validated against steady-state plant data.
The success of the Aspen Custom Modeler® process models demonstrated the suitability of the non-equilibrium
rate-based approach for modelling the hot potassium carbonate process. Unfortunately,
the hot potassium carbonate process could not be modelled as such in HYSYS®, Santos’s preferred
simulation environment, due to the absence of electrolyte components and property models and the
limitations of the HYSYS® column operations in accommodating chemical reactions and non-equilibrium
column behaviour. While importation of the Aspen Custom Modeler® process models into
HYSYS® was possible, it was considered impractical due to the significant associated computation
time.
To overcome this problem, a novel approach involving the HYSYS® column stage efficiencies and
hypothetical HYSYS® components was developed. Stage efficiency correlations, relating various
operating parameters to the column performance, were derived from parametric studies performed in
Aspen Custom Modeler®. Preliminary simulations indicated that the efficiency correlations were only
necessary for the absorber columns; the regenerator columns were adequately represented by the
default equilibrium stage models. Hypothetical components were created for the hot potassium
carbonate system and the standard Peng-Robinson property package model in HYSYS® was modified to include tabular physical property models to accommodate the hot potassium carbonate
system. Relevant model parameters were determined from literature data. As for the Aspen Custom
Modeler® process models, the HYSYS® CO₂ Removal Train process models were successfully
validated against steady-state plant data.
To demonstrate a potential application of the HYSYS® process models, dynamic simulations of the
two most dissimilarly configured trains, CO₂ Removal Trains #1 and #7, were performed. Simple first-order
plus dead time (FOPDT) process transfer function models, relating the key process variables,
were derived to develop a diagonal control structure for each CO₂ Removal Train. The FOPDT model
is the standard process engineering approximation to higher order systems, and it effectively
described most of the process response curves for the two CO₂ Removal Trains. Although a few
response curves were distinctly underdamped, the quality of the validating data for the CO₂ Removal
Trains did not justify the use of more complex models than the FOPDT model.
While diagonal control structures are a well established form of control for multivariable systems, their
application to the hot potassium carbonate process has not been documented in literature. Using a
number of controllability analysis methods, the two CO₂ Removal Trains were found to share the same
optimal diagonal control structure, which suggested that the identified control scheme was
independent of the CO₂ Removal Train configurations. The optimal diagonal control structure was
tested in dynamic simulations using the MATLAB® numerical computing environment and was found
to provide effective control. This finding confirmed the results of the controllability analyses and
demonstrated how the HYSYS® process model could be used to facilitate the development of a
control strategy for the Moomba CO₂ Removal Trains.
In conclusion, this work addressed the development of a new non-equilibrium rate-based model for the
hot potassium carbonate process and its application to the Moomba CO₂ Removal Trains. Further
work is recommended to extend the model validity over a wider range of operating conditions and to
expand the dynamic HYSYS® simulations to incorporate the diagonal control structures and/or more
complex control schemes.
School/Discipline
School of Chemical Engineering
Dissertation Note
Thesis (Ph.D.) - University of Adelaide, School of Chemical Engineering, 2009
Provenance
2 volume set.
Vol. 1 Text -- Vol. 2 Appendices
This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exception. If you are the author of this thesis and do not wish it to be made publicly available or If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exception. If you are the author of this thesis and do not wish it to be made publicly available or If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals