Pressure
swing adsorption (PSA) experiments are carried out in a 2-column laboratory
setup using activated carbon. As feed an equimolar CO2/H2 mixture is used. Adsorption pressures of 10, 20, and 30 bar
are applied, whereas the desorption pressure and the feed temperature
are fixed at 1 bar and 25 °C, respectively. During the experiments
the temperatures at five different locations inside the columns are
measured and the composition of the product streams is analyzed by
a mass spectrometer. A one-dimensional, nonisothermal, nonequilibrium
model is used to reproduce the experiments. The model was validated
previously using breakthrough experiments, and the modifications required
to describe full PSA cycles are highlighted. It is shown that the
temperatures measured inside the columns provide an excellent possibility
for comparison of experiments and simulations, whereas the measured
concentration profiles are affected by the piping between column outlet
and MS, which has to be considered carefully.
Temperature
swing adsorption (TSA) processes are considered as
an interesting option for the capture of CO2 from flue
gases. In this work, a shortcut model is developed for a four step
cycle aimed at recovering the more retained component at high purity
from a binary mixture, e.g. CO2 from CO2/N2. The model equations, which assume local adsorption equilibrium
but take into account heat transfer kinetics, enable a direct semianalytical
solution of the cyclic steady state. For fixed temperatures of the
indirect heating and cooling fluid, interstitial velocity, and feed
composition, the remaining operating conditions can be reduced to
the high and low temperature levels achieved during the cycle, which
control the thermodynamic states defining the effective cyclic capacity.
This model is used to investigate the CO2/N2 separation by TSA on a commercial zeolitic adsorbent. Important
trends are revealed by performing a parametric analysis of the operating
conditions on the relevant quantities, that is, purity, recovery,
specific thermal energy consumption, and productivity. Optimal operating
conditions are localized within the region of feasible operating conditions
and a trade-off between productivity and specific energy consumption
is presented and discussed. Besides providing insight into TSA processes
for the recovery of the heavy component, this tool could be used for
rapid yet robust sorbent screening.
A mathematical model used to describe cyclic adsorption processes is calibrated and validated for the simulation of temperature swing adsorption (TSA) processes applied to the capture of CO 2 from a model flue gas (CO 2 /N 2 ) using zeolite 13X as sorbent material. Three types of experiments are reported in this work, all of them performed in jacketed columns packed with 13X. During these experiments, the temperature was measured at five positions along the central axis of the column, and the exit composition was measured on line by mass spectrometry. The first series of experiments were breakthrough experiments, used to characterize transport phenomena within the packed bed. The second series were heating and cooling experiments, which were used to study the heat transfer from the heating fluid in the column jacket to the bed. Lastly, cyclic TSA experiments were performed to test the model's ability to predict the cyclic steady state behavior of the column as well as the separation performance of the process.
In
this work, the adsorption of water vapor on a commercial activated
carbon is studied by means of static and dynamic measurements. To
this end, two customized setups are used, which are able to deal with
the challenges associated with adsorption measurements under humid
conditions. In the first part, the equilibrium of water vapor on activated
carbon during adsorption and desorption at 45 °C is characterized.
The equilibrium adsorbed amount of water vapor exhibits a pronounced
hysteresis loop, requiring the use of an isotherm model with hysteresis
to describe the data. In the second part, fixed-bed experiments for
both adsorption and desorption conditions at three feed velocities
are presented. These dynamic experiments are described by a nonisothermal
detailed column model, which considers the linear driving force model
for mass transfer and axial dispersion. Heat and mass transfer coefficients
are estimated so as to describe the fixed-bed experiments. The results
from the static and dynamic measurements are shown to be consistent
with each other for both adsorption and desorption conditions, provided
the hysteretic behavior of the adsorption equilibrium is considered.
Finally, it is shown that the use of an average value for the mass
transfer coefficient results in good agreement between experiment
and simulation, and the improvement due to a more complex model is
minimal.
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