We propose design specifications and operating conditions for an absorber in an ammonia-based, post-combustion carbon capture process. We used a rate-based multistage column model to simulate a baseline-case scenario involving an absorber installed at a large-scale CO2 emission source. The goal was to exploit the chemistry of the NH3-CO2-H2O system to evaluate the performance of the absorber with respect to carbon capture, ammonia slip, and the height of the absorber. Thus, we identified as the two important prerequisites for absorber design: (1) that staged absorption is used and (2) that the rich CO2 loading does not exceed 0.5.