Nyhet | 2014-08-08 | 15:13

Modelling amine solvent degradation and reclamation in pilot scale post-combustion CO2 capture

Gustav Sandborgh, Chemical Engineering, Royal Institute of Technology (KTH).

Abstract

Post-combustion carbon capture (PCC) using amine solvents is the most mature carbon capture technology. It will be essential in preventing further anthropogenic CO2 emissions from fossil fuelled power stations, as the transition is made toward renewable energy sources. The most prevalent issue with the technology is solvent management. All amine solvents display some tendency to degrade, leading to a loss of solvent and several issues with the efficiency of the process itself.

Following a literature review, three primary pathways of degradation were identified: thermal, oxidative and acid-base. At the pilot scale, oxidative degradation is dominant. Caused by irreversible reactions between flue gas oxygen and solvent, it mainly leads to the formation of heat stable salt compounds (HSS). These compounds are also formed in reactions between the solvent and flue gas impurities such as SO2. Utilizing experimental data acquired at the CCPilot100+ PCC pilot plant, a kinetic power-law model predicting the formation of HSS, with an absolute average deviation (AAD) of 19%, was developed.

r_HSS=3.29∙〖10〗^13 [〖SO〗_2 ]^1.67 [O_2 ]^1.85

PCC processes include a reclaimer system. Reclaimers attempt to remove HSS and other degradation products from the solvent. In this project, three reclaimer techniques were investigated: distillation, ion exchange and electrodialysis. A material balance was setup for each reclaimer system, which included the predictive kinetic model. This material balance was consequently used to predict the lowest concentrations of HSS each type of reclaimer could theoretically achieve in three realistic operational scenarios.

Judging by four criteria (i.e. achieved HSS concentration in the solvent, necessary fresh solvent additions, size of reclaimer waste stream and caustic additions), the simulations demonstrated a slight advantage in using a distillation-based technique during operating conditions where the formation of HSS is accelerated, which has been typical for pilot scale PCC plants. However, from both a qualitative and quantitative standpoint, there is not one particular technique that offers a significant advantage over the others. The best alternative for one operational scenario will not necessarily be the best alternative for other ones. Pilot plant experience also clearly demonstrate that all three techniques need to be further adapted for PCC applications.

Keywords
post-combustion carbon capture; pilot plant; amine; degradation; reclamation; kinetics; modelling; process simulation

Thesis grade: A