CARBON DIOXIDE CAPTURE USING SOLID SORBENTS IN A FLUIDIZED BED WITH REDUCED PRESSURE REGENERATION IN A DOWNER

The most commonly used commercial technology for post-combustion CO2 capture for existing power plants is the amine solvent scrubber. However, the energy consumption for capturing CO2 from flue gases using amine solvent technology is 15 to 30% of the power plant due to the use of steam in solvent regeneration. Hence there is a need to develop more efficient methods of removing CO2. The objective of this thesis research is to demonstrate the design of a complete loop system of dry solid sorbent technology, which consumes less energy, as an alternative CO2 capturing technology. The design of a complete riser-sorber and downer-regenerator loop system for a dry solid sorbent technology is developed using the recently developed kinetic theory based multiphase computational fluid dynamics (CFD). The complete dry solid sorbent loop system comprises of an atmospheric fluidized bed riser-sorber and a reduced pressure downer-regenerator. The proposed dry solid sorbent used in this thesis research is a dry sodium carbonate sorbent recently developed at RTI and earlier by Gidaspow and Onischak. The dry solid sorbents capture CO2 and water vapor from flue gases through chemical sorption in the sorber-riser. The captured CO2 is released from the solid sorbent along with water vapor in the reduced pressure regenerator-downer where the solid sorbent regeneration occurred. The complete dry solid sorbent loop system demonstrates the possibility of solving three main technical challenges, which are the handling of large volumetric flow rate of the flue gases, the required operating power, and the quantity of CO2 sorption. xvii A new proposed pressure-equilibrium based sorption rate model for the dry sodium carbonate sorbents is used in the simulations. The simulations of both fluidized riser-sorber and downer-regenerator were done using commercial CFD code; Fluent. The energy efficiency of the proposed dry solid sorbent loop system was studied using thermodynamic availability analysis for both an individual vessel and for the overall process for evaluating the minimum energy requirement for CO2 separation. A T-s diagram of inlet and outlet streams for both the riser-sorber and the downer-regenerator are included in the thermodynamics analysis. The results from multiphase CFD simulations showed that the heat liberated during CO2 sorption in the riser-sorber can be nearly fully recovered in form of sensible heat in the solid sorbent. The captured heat in the solid sorbents is used as the energy for CO2 desorption in the sorbent regeneration process inside the reduced pressure downerregenerator. Hence, the only parasitic power loss will be the energy needed for sorbent circulation, air-lock rotary valves, and vacuum fan. The drastic energy saving is possible due to the high solid circulation rate between sorber-riser and downer-regenerator. Additionally, the simulation results showed that the core-annular regime flow pattern in the riser-sorber can be almost completely eliminated by using multiple jet inlets and increasing solid sorbent particle size, from 75 microns manufactured by RTI to 500 micron sorbent particles. Furthermore, the large sorbent particle size allows better solid settling in the downer. The simulations also showed that a core-annular flow pattern occurred inside the downer-regenerator. However, there is no negative effect of having a core-annular regime inside the downer-regenerator.PH.D in Chemical Engineering, December 201