Analysis of low temperature carbon dioxide capture in a supersonic nozzle

Abstract

Most energy scenarios suggest carbon capture and storage (CCS) from power generation might contribute to achieve the carbon emissions reduction necessary to stabilize the long-term global average atmospheric temperature. Low temperature CO2 capture represents a novel alternative to the state-of-the-art monoethanolamine (MEA) post-combustion technology. The separation process aims to reduce the flue gas temperature from the ambient temperature to a low temperature range necessary to freeze the CO2.The potential reduction in overall energy consumption and the simplicity of the separation system compared to MEA suggest that the low temperature CO2 capture concept might be a cost-effective technology necessary to be further analyzed. However, designing a low temperature carbon capture system involves complex challenges including solid formation and handling, heat transfer at low temperatures and process integration. In this investigation a supersonic Laval nozzle has been modeled in one dimension to analyze the nozzle flow behavior with particle formation. Specifically this study seeks to understand and predict the desublimation of carbon dioxide present in the flow. The primary objective is the basic design of a converging diverging nozzle capable to desublimate carbon dioxide from low concentration flue gases by at least 50% for a range of inlet flow conditions and properties. The inlet conditions are limited to 5% CO2 by mol of flue gas present in the flow. The second objective is the optimization of the nozzle pressure recovery system. A preliminary analysis of the various processes that take place in the nozzle has been performed and the governing equations have been implemented into a coupled 1D set of differential equations. Based on the 1D model a design tool has been developed that allows for the prediction of the main flow parameters throughout the nozzle. The predictions have been verified by comparison with experiments available in the open literature. A design of experiments, varying several input parameters, has been designed to perform a sensitivity analysis of the 1D model necessary for the subsequent optimization. The optimized system desublimates 95% of the initial gaseous carbon dioxide while 40% of the inlet pressure is recovered in the diffuser. The particle size obtained is around 80μm which enables separation due to centrifugal forces. The swirl model, as well as boundary layer corrections and viscosity losses have not been taken into account in this preliminary design and a complete 3D CFD analysis has been recommended for further investigation.