Carbon Dioxide Capture for Geological Sequestration - The Issues and Decision Parameters for T&T's Petrochemical and Power Generation CO2 Sources

Abstract

Since there is a growing emphasis on Carbon Dioxide (CO2) sequestration as a carbon management strategy coupled with the acceptance that geological sequestration is perhaps one of the most promising carbon management techniques, the need to capture CO2 at sources in a cost effective and safe manner is gaining widespread attention. This is justified as CO2 capture is often one of the more expensive components of any geological sequestration capture, transportation and storage chain. As such, much emphasis is currently being placed in the advancement of processes such as increasing capture efficiency and reducing capture cost which are demonstrated by the many pilot plants being built worldwide. Carbon capture essentially produces a concentrated stream of CO2 at high pressure, rendering it to be readily transported to appropriate storage sites. Although theoretically the entire gas can be transported using the various transportation modes, the cost associated with doing this often deems this option impractical. Extracting the CO2 in a more concentrated form and elevating it to the required high pressure is therefore an important component of the Carbon Capture and Storage (CCS) chain. For Trinidad and Tobago (T&T), post combustion capture is most desirous as the targeted CO2 sources emanate from existing plants. This is so because physical space at these plants is limited and does not readily allow for precombustion technologies. While oxyfuel combustion may be applicable to some of the existing plants, since the sources being evaluated in this paper are related emissions from Ammonia Synthesis and Power Generation, the concentration of CO2 in these streams is either already high and commensurate with that of oxyfuel carbon capture (as it the case with Ammonia) or the plants cannot be easily retrofitted for oxyfuel capture (as with the Power Generation). Interestingly, most of T&T’s emissions (over 50%) emanate from the petrochemical sector and in particular from Ammonia production processes. There are eleven (11) Ammonia plants in T&T which contributes to the nation being the number one exporter of this commodity globally. During the synthesis of Ammonia, a relatively pure stream of CO2 is produced in the process typically consisting of over 90% CO2 with some mostly water vapour as the other impurity. One can therefore argue that to an extent the CO2 is already captured. Further purification of the CO2 stream via water vapour, oxygen separation and pressurization is all that is needed for engagement in CCS projects. This paper investigates CO2 capture from Ammonia Plants and compares it with CO2 capture from Power Plants in TT Ammonia and Power). These simulations were then used as the primary tool to estimate CO2 capture cost for T&T from Ammonia synthesis and Power Generation. Of particular interest for T&T, this study illustrates an estimate of the costs for capturing up to 8 Mt/yr of CO2. It is expected that this information can be critical in evaluating the overall CCS economics for T&T and can contribute towards a suitable pilot project.