Study of the Effect of Stripping Components in Absorption Processes for CO2-Removal From Power Plant Flue Gases

One possibility for removal of CO₂ in conventional coal-fired power plants is the so-called Post-Combustion-Capture process. In this process CO₂ is separated from the power plant flue gas by absorption. Amongst others aqueous amine solutions are considered as one possible solvent for absorption. Advantageous of the Post-Combustion-Capture process is the fact that existing power plants could be retrofitted. A disadvantage however is the additional energy consumption occurring when regenerating the solvent in the desorber. For regeneration steam is taken from the turbines of the power plant. This reduces the overall efficiency of the power plant significantly.

Adding an organic component, which is almost immiscible with water, could have a positive effect on the regeneration of the solvent and therefore also on the overall efficiency of the power plant. By adding this organic component a miscibility gap is formed in the desorber and subsequently the boiling temperature decreases, an effect also known from steam distillation. As the temperature in the desorber is lower, the pressure of the required steam for regenerating the solvent can also be lower.

In this work the influence of the miscibility gap on the absorption process is examined. Therefore, a model for a three phase equilibrium was developed. Based on this model for phase equilibrium a multistage column model, representing the desorber, was designed. With this model and another model for the absorber, both implemented in MATLAB, the overall absorption process can be simulated.

First results show that depending on the choice of the organic component the boiling temperature of the reboiler can be significantly lowered. The effect on the overall performance of power plant including CO₂ separation was then estimated by a simple exergetic analysis. The considered process options showed about the same performance in this estimation. Therefore, a more detailed evaluation including a power plant simulation model is planned for the near future. Furthermore, other amines and amine strength will be subject of further optimizations.