Post-combustion Carbon Capture - Toward the Integration of Cooling Crystallization into Ammonia-based Processes
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Date
2020
Publication Type
Doctoral Thesis
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yes
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Abstract
The Chilled Ammonia Process (CAP) enables the separation of CO2
from concentrated and stationary CO2 emission sources. In particular,
this process can be used to treat large-scale power plants’ flue gas, thus
reducing the carbon dioxide concentration of the stream sent to stack.
More recently, the development of an advanced CAP configuration in
which a fraction of the absorbed CO2 is precipitated in the form of an
inorganic salt via cooling crystallization, allowed for an increase of the
CO2 capture efficiency as well as for a reduction of the overall plant’s
energy consumption.
This novel process, referred as the controlled solid formation-Chilled
Ammonia Process (CSF-CAP), produces solids in a closed-loop system
described in the following and uses them as a carbon carrier. At first, the
ammonium bicarbonate is crystallized from the CO2-loaded solution
exiting the absorption unit and partially separated from the mother
liquor by means of hydro-cyclones, thus obtaining a concentrated slurry
at a reduced mass flow-rate. Then, the slurry is sent to the regeneration
section where the solid phase is completely dissolved before to entering
the desorption unit where the solvent regeneration cycle is completed.
Assessing the feasibility of integrating continuous crystallization into
a CO2 capture plant framework necessarily requires the analysis of
thermodynamic and kinetics limitations of the system. This thesis seeks
to serve as a template for the design and optimization of a continuous
solid handling section integrated with the CSF-CAP and by doing so it
tackles several engineering challenges related to the process. At first,
the use of a bottom-up approach has allowed to achieve a solid understanding
of the system thermodynamics as well as of the ammonium
bicarbonate solid formation kinetics via a combined experimental and
modeling strategy. Then, the knowledge gathered on these fundamental
aspects of the system has been used in a rate-based mathematical model
that accounts for heat and mass transfer limitations during continuous crystallization.
Finally, this thesis shows that the first principle mathematical framework
developed, combined with the experimental solid-liquid equilibria data
of the CO2-NH3-H2O system, represents a powerful tool for the analysis
of the system’s behavior and for the optimization of the overall
process performance.
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Examiner : Mazzotti, Marco
Examiner : Gazzani, Matteo
Examiner : Menegatti, Stefano
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ETH Zurich
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Subject
Carbon capture and sequestration (CCS); CRYSTALLIZATION AND CRYSTALLIZERS (PROCESS ENGINEERING); IR spectroscopy; Process optimisation
Organisational unit
03484 - Mazzotti, Marco (emeritus) / Mazzotti, Marco (emeritus)