Chemical solvents using amines are the most likely technologies to be deployed in the near future to capture CO2 from industrial flue gases. The advantage of these solvents is related to the fact that they have excellent effectiveness and efficiency to absorb CO2 in the flue gas from fossil fuel power plants operating with low partial pressures. In addition, these solvents can be regenerated and injected back into the process to capture more CO2. For the acceptance and deployment of this process, the technology should be optimised for efficiency, cost and environmental consequences.
Operating the power plants with this technology can certainly reduce the atmospheric emissions of CO2. However, different degradation products will be produced as results of the following three degradation pathways of the MEA solvent:
Thermal degradation that mainly occurs in the stripper due to carbamate polymerization at temperatures higher than 100 oC ;
Oxidative degradation initiated by the presence of O2, SO2, NO2 and other impurities present in the flue gas
The degradation products produced during the solvent degradation may produce new pollutants which could be emitted to the atmosphere when the CO2 lean flue gas is released. Some of these new pollutants may have different effects on human health and the environment when compared with those emitted from operating traditional power generation facilities.
The proponents of PCC demonstration projects in Europe note that there are knowledge gaps in the information needed to carry out proper environmental impact assessments for future commercial deployment of PCC processes (Shao and Stangeland, 2009),The report here, assesses the gaps in the knowledge using the ASPEN Plus process simulation approach and available public domain information in order to inform a robust environmental impact assessment process.
Nitrosamines and nitramines are two species of special concern due to their potential health risks. These species are formed under selected conditions where NOx and amines can undergo some complex chemical reactions. Clearly, this issue must be addressed with some urgency in the context of the Australian PCC demonstration projects since the Australian coal-fired power plants are not equipped with the de-SOx and de-NOx equipments as required statutorily in Europe and USA. These and other degradation products may escape the PCC plants both in the gaseous state due to their vapour pressures and as droplets due to physical entrainment in the CO2 lean flue gas. It is therefore crucial that the formation of degradation products of amine solvents and their likely atmospheric emission be determined in a pro-active manner for development of emission guidelines or protocols for vendors looking to provide PCC-solutions.
This study employs Aspen-Plus process simulator to estimate the atmospheric emissions of a base case 30 % w/w aqueous MEA solvent and its degradation products.