Nitrogen and sulphur chemistry in pressurised flue gas systems: A comparison of modelling and experiments

Abstract

The nitrogen and sulphur chemistry is more significant during compression of flue gases than they are under atmospheric conditions. This fact became apparent during the development of oxy-fuel power plant technology to capture carbon dioxide (CO2). In the oxy-fuel power plant, the CO2-rich flue gas stream is compressed to enable efficient transport and storage. During this process, NOx and SOx are removed as acids in the condensed water. However, the chemistry of these steps is not understood well enough to allow for control and design of the process.In the present work, the gas- and liquid-phase chemistry of NOx and SOx at elevated pressures were evaluated by comparing a state-of-the-art reaction mechanism to the results of experimental investigations. The model used confirms previous observations of substantial absorption of NOx and SOx and subsequent formation of acids in pressurised flue gas systems. The results of the modelling show that the oxidation of NO into NO2 governs the absorption of NOx. The complex chemistry of the liquid phase, which includes reactions between HNO2, H2SO3, and possibly H2SO4, is critical for the rate of absorption of NOx and SOx from the gas to the liquid phase. This process is heavily dependent upon the pH level. The modelling suggests that N2O is formed as a stable product through the liquid-phase reactions.