In-Situ Capture of CO₂ in a Fluidized Bed Combustor

Increasing atmospheric concentration of CO₂ and concern over its effect on climate is a powerful driving force for the development of new advanced energy cycles incorporating CO₂ capture. This paper investigates the feasibility of CO₂ capture using the carbonation reaction of CaO “in situ” in a fluidised bed combustor, where natural gas or petroleum coke (or any other fuel with low ash content) is being burned. The sorbent can be partially regenerated for CO₂ capture by combustion of part of the fuel with O₂/CO₂ in a separate FBC. The thermodynamic limits in the proposed cycles, in terms of CO₂ capture efficiencies, are examined along with the limits imposed by the rapid decay in the sorbent activity during repeated carbonation/calcination cycles, which will be exacerbated by the presence of S. Despite these limitations, it is shown that operating windows exist where it is possible to integrate fuel combustion, CO₂ and SO₂ capture in a single dual reactor facility. The decay in activity in the sorbent appears to be the major practical limitation to this concept, but this can be compensated for by using a relatively large supply of fresh sorbent, which appears to be acceptable considering the low cost of limestone. Also, a novel concept to reactivate the spent sorbent using sonic energy is outlined here as an alternative to reduce the use of fresh limestone.