Post-combustion calcium looping process with a highly stable sorbent activity by recarbonation

Abstract

This paper presents a novel sorbent regeneration technique for post-combustion calcium looping CO₂ capture systems. The advantage of this technique is that it can drastically reduce the consumption of limestone in the plant without affecting its efficiency and without the need for additional reagents. The method is based on the re-carbonation of carbonated particles circulating from the carbonator using pure CO₂ obtained from the gas stream generated in the calciner. The aim is to maintain the CO₂ carrying capacity of the sorbent close to optimum values for CaL post-combustion systems (around 0.2). This is achieved by placing a small regeneration reactor between the carbonator and the calciner. This reactor increases slightly the conversion of CaO to carbonate so that it exceeds the so-called maximum CO₂ carrying capacity of the sorbent. This increase compensates for the loss of CO₂ carrying capacity that the solids undergo in the next calcination–carbonation cycle. Two series of experiments carried out in a thermogravimetric analyzer over 100 cycles of carbonation–recarbonation–calcination show that the inclusion of this recarbonation step is responsible for an increase in the residual CO₂ carrying capacity from 0.07 to 0.16. A conceptual design of the resulting capture system shows that a limestone make-up flow designed specifically for a CO₂ capture system can approach zero, when the solid sorbents purged from the CaL system are re-used to desulfurize the flue gas in the existing power plant.