CAPTURE OF CO_2 WITH CAO IN A PILOT FLUIDIZED BED CARBONATOR EXPERIMENTAL RESULTS AND REACTOR MODEL

摘要

Calcium oxide particles can absorb CO_2 at high temperatures ( > 600℃) to form CaCO_3, which can be regenerated back to CaO and pure CO_2 in a calciner. We are investigating this chemical loop to develop more energy-efficient post-combustion systems. In this work we present the results of pilot-scale tests of one of the key units for the process: the high-temperature fluidized bed absorber. Fluidized beds of calcined limestone are shown to be very effective absorbers of CO_2 from a typical flue gas at atmospheric pressure, as long as there is a sufficient fraction ( > 5%) of CaO in the bed material reacting in the fast-carbonation regime. The experimental results with different limestones, and after several cycles of carbonation-calcination, are very encouraging. They are interpreted with a well-established fluid bed reactor model (the Kunii-Levenspiel model) that allows an extrapolation of the results to conditions beyond those tested in the pilot rig. These include a special case for in-situ CO_2 capture in fluidized bed combustion at low temperatures that can be of interest for highly reactive fuels like biomass; this is discussed to some extent in this work.