Abstract:
This thesis has addressed several gaps in the knowledge with regards to the
calcium looping cycle for carbon dioxide capture, including identification of engineering
challenges associated with the scale-up of the technology to pilot scale and
beyond; assessment of changes in sorbent morphology during the pilot scale
capture process; and partitioning of elemental impurities in the limestone
between the solid and gaseous phase during the carbon dioxide capture process.
Hydrodynamic investigations identified the optimum superficial velocities
required for the reactor in order to optimise solids entrainment and flux, and to
minimise gas bypassing. Estimations made in determining how particle attrition
would affect minimum fluidisation velocity confirmed a decrease of
approximately 0.09m/s for every 5 % reduction in particle size. Amendments
made to the exhaust diameter and position, and the loop seals, improved the
pressure balance of the system thus enhancing solids transfer.
Reactor and process modifications, including modification of carbonator
temperature, and maintenance of temperature above 420°C in standpipes
resulted in improved carbon dioxide capture %. Increasing bed inventory had a positive
effect of carbon dioxide capture % due to an increased Ca looping ratio. Steam addition
also benefitted the carbonation process, due to improved sorbent morphology
and therefore carbon dioxide diffusion into the sorbent. Sulfur dioxide was considered to have a
detrimental effect on carbon dioxide capture due to pore pluggage, although burner-
derived steam had a positive effect in maintaining capture %.
Gaseous elemental emissions from the process were low for all elements, but
concentrations of elements in the solid sorbent phase were influenced by bed
inventory, implying that filtering systems may be required in industry for the
large masses of sorbent required. Concentrations of elements in the sorbent
were identified to be below levels typical of cement, with the exception of Ni,
implying that there is potential for spent sorbent to be used in the cement
industry with adequate mitigation measures in place.
