Ammonia-based post combustion - The techno-economics of controlling ammonia emissions

An important process consideration in ammonia-based, post-combustion CO2 capture is the volatility of ammonia. Consequently, there is a need to adopt control measures to minimize the emission (the slip) of ammonia from such processes. This work evaluates techno-economic aspects of methods to reduce the ammonia slip. The emission of ammonia is required to be below 10 ppm while the ammonia slip from the absorber in an ammonia-based process may exceed 10%. The ammonia control methods that are evaluated in this work are staged absorption, ammonia abatement cycle, chilled absorption and acid wash. The control methods are also evaluated with respect to local conditions, such as cooling water temperature and flue gas CO2 concentration. Rate- and equilibrium-based thermodynamic modelling forms the basis for the evaluation process. A simplified economic estimation method is used to evaluate the utility cost of ammonia control designs under different operating conditions. The economic estimation shows that for the best case conditions the utility cost are as low as 1.5€/tCO2. However, the cost of the ammonia control may be more than tenfold when the available cooling water temperature is increased (>5°) or when the flue gas CO2 concentration is decreased (<15 vol%). Thus, the cost of the slip control measures narrows the range of process conditions at which ammonia-based, post combustion capture is an economically feasible option.