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A study was carried out to investigate the CO 2 capture performance of limestone under atmospheric carbonations following pressurised calcination. A series of tests was carried out to study the role of pressurised calcination using a fluidised bed reactor. In this investigation, calcination of limestone particles was carried out at three levels of pressure: 0.1 MPa, 0.5 MPa, and 1.0 MPa. After calcination, the capture performance of the calcined sorbent was tested at atmospheric pressure. As expected, the results indicate that the carbonation conversion of calcined sorbent decreases as the pressure is increased during calcination. Pressurised calcination requires higher temperatures and causes an increase in sorbent sintering, albeit that it would have the advantage of reducing equipment size as well as the compression energy necessary for CO 2 transport and storage, and an analysis has been provided to give an assessment of the potential benefits associated with such an option using process software. [ABSTRACT FROM AUTHOR]

Steam can be used to lower calcination temperatures or to provide the process heat for calcination in a Ca-looping cycle because it can be removed from the CO 2 stream by simple condensation. Here, the performance of limestone for CO 2 removal from flue gases, calcined in the presence of steam, has been investigated. Three steam concentrations (28%, 48% and 78%) were used to investigate the effect of high-temperature steam in the calciner. For comparison, the effects of steam were compared to similar levels of N 2 as the primary diluent. Subsequent to calcination at elevated steam levels, the performance of the calcined sorbent was tested during carbonation with two levels of steam (6% and 20%) typical for flue gases from fossil fuel power plants. This allowed the effects of steam in carbonation to be investigated as well. As this study focused on CO 2 capture from flue gases produced by existing power plants (using Ca-looping as a post-combustion process), the corresponding industrial conditions were simulated for the carbonation atmosphere. Steam addition in the calciner was found to be more effective in improving capture than steam addition in the carbonator, with CO 2 capture capacity being increased with increasing steam levels in the calciner. [ABSTRACT FROM AUTHOR]

High temperature CO 2 and SO 2 sequential capture in a bubbling fluidised bed was investigated using a natural limestone and synthetic composite pellets. Calcination was conducted under oxy-combustion conditions, while carbonation and sulphation occurred in an air-combustion atmosphere. The goal of sequential capture of CO 2 /SO 2 is to desulphurise the flue gas first, followed by cyclic carbonation and calcination. Here, fresh sorbent is first used in the cyclic calcination/carbonation process and then the spent sorbent is sent for sulphation. The pellet carrying capacity is 0.29 g CO 2 /g sorbents for the first cycle, while that of natural limestone is about 0.45 g CO 2 /g sorbents. The carrying capacity first fell and then finally plateaued around 0.10 and 0.12 g CO 2 /g sorbents for limestone and pellets respectively. The SO 2 carrying capacity for limestone and pellets after 20 cycles of CO 2 capture was 0.17 and 0.22 g SO 2 /g sorbents respectively. This indicates that the sorbent spent in CO 2 capture can be effectively reused for SO 2 removal. Abrasion was observed to be the main mode of attrition, but some agglomeration was also found with increasing number of cycles and this may be a concern in the use of Ca-based sorbent for CO 2 or SO 2 fluidised bed capture. • Sequential capture of carbon and sulphur was investigated with a natural and synthetic limestone pellets. • Pellets performed better cyclic activity over a large number of cycles. • Experienced some weak agglomeration which can be destroyed by gently shaking or stirring. • Intensified attrition created cracks on the surface of limestone, however smoother surface on the pellets. [ABSTRACT FROM AUTHOR]