(524d) 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.