Results of entrained flow carbonator/ calciner tests - D12.2

This document reports the progress to date in the investigation of reactor components in integrated Calcium Looping systems designed to use entrained bed reactors for the step of CO2 capture by carbonation (Romano et al. 2013), (Spinelli et al. 2016), after the generation of a sufficient flow of active CaO by calcination of a Ca-rich raw material.

New experimental work in a thermogravimetric analyser has been carried out, at the limits of detection of this equipment, in an attempt to elucidate the role of belite formation during fast calcination of different raw meals as this parallel reaction was found to deactivate the calcined material towards CO2 capture (see MS12.2). The new tests have revealed great differences in behaviour among raw meals depending on the level of aggregation of Ca and Si elements. CO2 activities towards CO2 as low as 0.1 have been measured for a marl-type raw meal after a first calcination of the material in less than 1 minute, in rich CO2 and H2O(v) atmospheres at just over 900ºC. In contrast, other raw meals containing mixed CaCO3 grains in the micrometre scale are able to sustain activities of CaO towards CO2 over 0.6 (i.e. very similar those of parent limestones).

On the other hand, in order to carry out CO2 capture test with gas/solid contact times in the range of those expected in entrained reactor systems, a new retrofit has been completed of the 30 kWth Calcium looping pilot used earlier for the CFBC test (see D12.1). Many challenges related to the feeding of a continuous flow of calcined powdered solids to the system, or with the operation of gas/solid contact under differential conditions, have been found and partially solved. Tests with different activity material have been carried out, measuring experimental conversion of gas (CO2 concentration profiles) for gas/solid contact times between 0.5-6 seconds. Results follow trends that can be interpreted with a simple plug flow reactor model when changing solid flow rates, gas flow rates (residence time of gas and solids in the reactor) and CO2 concentration at the inlet of the reactor. These results should allow for a suitable tuning of kinetic expressions for the carbonation reaction (in progress for MS12.5) expected to support the reactor design of the “integrated CaL” process.