Modelling and CFD simulation of a fluidized bed process for the capture of C02 from fossil fuel combustion sources

• Main Author: Molaei Chalchooghi, Mazaher
• Other Authors: Pericleous, Kyriacos; Patel, Mayur
• Published: University of Greenwich 2013
• Subjects: 532; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616541

Fossil fuels provide the main source of energy for power generation in existing power plants. A mitigation option to reduce carbon dioxide (CO2) emission from existing power plants with fossil fuel combustion is the sequestration of carbon dioxide and storage in geological formations, in the ocean or for use in industrial processes. CO2 capture from combustion exhaust gases by mineral carbonation using a fluidised bed is studied in this project. CFD modelling has been used to study the efficiency of CO2 capture in a fluidized bed reactor containing a solid sorbent Calcium Oxide (CaO). This present work seeks to maximize CO2 conversion by a systematic modification of the flow domain. In particular, it is intended to use a convergent-divergent geometry to control the velocity of particles in the reaction domain thereby keeping the particles in the domain as long as possible. This is expected to improve the performance of the system as more time is allowed for any remaining CO2 to react with CaO and then be removed in the calcination stage. Further the effect of other key parameters such as particle size, CO2 concentration of flue gas and mass loading of solid sorbent have also been investigated. A Lagrangian/Eulerian scheme has been developed for this purpose, which uses a particle tracking model to describe CaO particle trajectories and mass, momentum and energy exchange with the carrier gas, entering the reactor in a typical flue gas composition. A steady-state condition is assumed, with each trajectory representing a parcel of particles of a given mass and diameter. The number of particles entering the fluidised bed is kept constant, and the fluidization velocity is chosen so that particles remain in the reactor. As the carbonation progresses, heavier well-reacted particles are collected at the bottom of the reactor. In the case of a non-uniform size distribution, fine particles would escape from the top of the reactor; in order to keep such particles within the domain the geometry was modified to increase the residence time of particles and to obtain maximum conversion. CO2 reduction of the order of 90% was achieved in a single pass, with a mass loading of 2.5 times of equivalent solid sorbent to CO2 in gas.