Chemical Absorption by Aqueous Solutions of Ammonia

Carbon capture is proposed as a viable way of exploiting the fossil resources for power plants and industrial processes. The post-combustion capture by chemical absorption in amine aqueous solutions has been in use in chemical and petrochemical areas for decades. As an alternative, the absorption in aqueous ammonia has received great attention recently. The carbon capture by aqueous ammonia is based on the conventional absorption-regeneration scheme applied to the ternary system CO2-NH3-H2O. It can be implemented in a chilled and a cooled process, depending upon the temperatures in the absorber and, hence, the precipitation of salts. The process simulation can be conducted in two manners: the equilibrium and the rate-based approaches. The specific heat duty is as low as 3.0, for the cooled process, and 2.2 MJ/kgCO2, for the chilled one. Moreover, the index SPECCA is as low as 2.6, for the cooled, and 2.9 MJ/kgCO2, for the chilled one. The overall energy performances from the simulations in the rate-based approach, compared against those in the equilibrium approach, results only slightly penalized. From an economic perspective, the carbon capture via chemical absorption by aqueous ammonia is a feasible retrofitting solution, yielding for the chilled process a cost of electricity of 82.4 €/MWhe and of avoided CO2 of 38.6 €/tCO2.