Abstract
A study was carried out to investigate the CO2 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: 0.1MPa, 0.5MPa, and 1.0MPa. 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 CO2transport and storage, and an analysis has been provided to give an assessment of the potential benefits associated with such an option using process software.
Highlights
Current technologies for capturing CO2 are based on absorption by means of liquid solvents, which are expensive and have serious drawbacks in terms of the energy requirements vs. solvent regeneration percentage (Feron and Hendriks, 2005)
The performance of a Ca looping system could potentially be improved by means of a pressurised system operating at 850–900 ◦C, which is typical of fluidised bed combustion conditions, and so far this has only been explored using a pressurised thermogravimetric analyser (PTGA) (Chen et al, 2010)
The carbonation conversion of calcined sorbent decreases as the pressure is increased during calcination
Summary
Current technologies for capturing CO2 are based on absorption by means of liquid solvents, which are expensive and have serious drawbacks in terms of the energy requirements vs. solvent regeneration percentage (Feron and Hendriks, 2005). Process intensification is a potential advantage of pressurised calcination It might offer potential in terms of “smoother” operation at high pressures with smaller bubbles and higher dense phase voidage in the fluidised bed reactor (FBR), leading to better contact between particles and the gas and enhanced heat and mass transfer, when using higher oxygen levels in the calciner (SanchezBiezma, 2014) with the goal of reducing the size of the calciner. To explore the potential of this approach an experimental study was carried out on the performance of limestone in a cycle which included pressurised calcination This was supplemented by a UniSim process simulation to evaluate the change in required compression energy with the calciner operating at different pressures. The simulation looks at all critical elements of the plant and includes an estimate of the air separation unit (ASU) energy consumption given the oxygen flowrate and delivery pressure required for the calciner using a correlation from literature (Fu and Gundersen, 2012) and the same pressures used for the test regime, namely 0.1, 0.5 and 1.0 MPa
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