Use of steel slag for CO2 capture under realistic calcium-looping conditions

Abstract

In this study, CaO derived from steel slag pretreated with diluted acetic acid has been tested as a dry sorbent for CO₂ capture under realistic Ca-Looping (CaL) conditions, which necessarily implies calcination under high CO₂ partial pressure and fast transitions between carbonation and calcination stages. The multicycle capture performance of the sorbent has been investigated by varying the precalcination time, carbonation/calcination residence times and with the introduction of a recarbonation stage. Results show that the sorbent can be regenerated in very short residence times at 900 °C under high CO₂ partial pressure, thus reducing the calciner temperature by about 30–50 °C when compared to limestone. Although the introduction of a recarbonation stage to reactivate the sorbent, as suggested in previous studies for limestone, results in a slightly enhanced capture capacity, the sorbent performance can be significantly improved if the main role of the solid-state diffusion-controlled carbonation is not dismissed. Thus, a notable enhancement of the capture capacity is achieved when the carbonation residence time is prolonged beyond just a few minutes, which suggests a critical effect of solids residence time in the carbonator on the CO₂ capture efficiency of the CaL process when integrated into a power plant.