A framework for the environmental, health and safety hazard assessment for amine-based post combustion CO2 capture

Journal article, 2017

Given the environmental concerns driving process developments and considering the size and scale of potential application of post combustion capture (PCC), it is important to fully understand process hazards. In this work we present an environmental, health and safety (EHS) hazard assessment framework for screening and comparing amine based PCC options. A multi-criteria assessment compares the performance of 7 m Monoethanolamine (MEA), 4 m Diethanolamine (DEA), 10 m Diglycolamine (DGA), 8 m Piperazine (PZ) and a blend of 7 m Methyldiethanolamine (MDEA) with 2 m PZ under a set of different process conditions. The EHS assessment takes into account varying circulating volumes, process conditions and potential for solvent degradation. The EHS assessment is also compared with operating costs and life cycle assessment (LCA) metrics. The EHS assessment is carried out on two levels. The first is less data intensive and provides a unified score that can be used to compare and screen process alternatives, while the second level studies the contribution of individual degradation products to different EHS hazard categories in detail. Results of the parametric study show that lean loading is an influential factor in determining first level EHS scores, process costs and environmental impacts and a trade-off is observed between EHS and LCA scores for some of the solvents. In the second level EHS assessment, the parent amine heavily influences most mass dependent hazard categories such as the fire/explosion, acute toxicity and air mediated effects category. Heat stable salts affect the solid waste category. Most degradation products are considered corrosive or irritant and therefore feature strongly in that category in addition to the parent amine. The second level EHS assessment is complemented with workplace exposure analysis to ensure the compliance with workplace threshold limits. Nitrosamines stand out for acute and chronic toxicity effects and are therefore used as an example to demonstrate the workplace exposure. Workplace amines and nitrosamine concentrations are estimated to assess long and potential short term worker exposure as a result of gas leakages and spills respectively. Indoor ventilation rates are inadequate to keep workplace amine and nitrosamine concentrations below the recommended guidelines. To reduce short term exposure effects, a steady state liquid nitrosamine concentration lower than 13.7 mM is required. The results of the parametric study show that changing process conditions can lower nitrosamine concentrations, but can also shift the contribution of the parent amine and degradation products of the other hazard categories and affect LCA metrics. The sensitivity of the EHS and LCA results to model assumptions and conditions are tested by varying inlet NOx, expected aerosols and solvent degradation levels. Low NOx levels in the flue gas are required for PZ and MDEA-PZ systems to meet the nitrosamine concentration thresholds for environmental and health concerns. This study also highlights the need to consider hazard effects during early process design phases, identifies degradation related data gaps and critical process parameters towards more environmentally benign PCC design.