detailed programme - SIMS - Scandinavian Simulation Society

Keyword: CO2 capture, Stripping column, Dynamic modeling
Abstract: Post combustion CO2 capturing holds an important position in the area
of carbon capture and sequestration (CCS). Research is operating in this area
ranging from experimental work to modeling work. Dynamic models are
interesting since these describe the plant operation during variations, up-stream
or
down-stream.
A dynamic model of a stripping column of a CO2 capture plant has been
developed. The stripping column model is equipped with a tower model,
condenser model together with a reflux drum and a re-boiler model. The model
has been validated against pilot plant data found in the literature for steady state
predictions.
The non-equilibrium stage rate based modelling is used to describe the stripping
tower, and it is discretized into a number of control volumes. Each volume in the
discretization consists of a bulk liquid phase, a bulk vapour phase and an
interface with a liquid and a vapour film. The bulk phases in a control volume are
considered as continuous stirred tanks (CST). The specie and the energy
conservation equations are applied for each of the bulk phases. Reactions are
included, except for the vapour phase. The set of liquid phase reactions and
reaction kinetics are taken from the thermodynamic models and the kinematic
data available in literature. The Kent-Eisenberg model is used as the
thermodynamic model to calculate the reaction equilibrium.
Velocity inside the stripping tower has been taken to be constant, while the
pressure drop is distributed linearly among each control volume along the tower.
Mass and energy conservation at the interface is considered assuming that CO2,
H2O and MEA are the only species which transfers across the interface. The
specie transfer rates are calculated according to the driving force which is given
by the difference between the actual and equilibrium specie partial pressures. An
enhancement factor is used to introduce the influence of the reactions on mass
transfer.
The condenser is modelled using flash calculations, a constant pressure and
constant temperature flash (P-T flash), to compute the details of the vapour and
the liquid phases. The liquid leaving the condenser is the feed to the reflux drum
and the reflux flow is manipulated to control the liquid level inside the drum.
Overall mass balance and specie balance are applied to find the liquid level and
the composition of the liquid.
The re-boiler is modelled as a flash drum. A P-T flash with a constant vapour to
feed fraction (V/F) is used to compute the compositions of the liquid and the
vapour leaving the re-boiler. A simple energy balance is performed to calculate
the re-boiler duty.
Sensitivity of the model for the combination of the correlations in use, reactions
in use and the transfer of the minor species are analyzed.
Dynamic model predictions will be presented.
Authors: Sanoja Jayarathna, Achini Weerasooriya, Bernt Lie, Morten Melaaen.
Organization: Telemark University College.