Technology development for low CO₂

Background and project purpose?
From theory and simulation work it was well understood that there were efficiency losses in solvent-based CO₂ capture processes when shifting from treating relatively concentrated flue gas streams (e.g. from coal-fired boilers, waste incinerators, cement kilns, etc.) to more dilute streams (CCGT, smelter industry, etc.). In addition, the influence of solvent degradation (ageing) was suspected to cause minor chemical changes in the solvent that potentially could reduce capture efficiency and perhaps more pronounced for dilute streams.
Thus, the purpose of the project was to quantify the above effects by applying a combination of pilot plant testing and more fundamental laboratory trials and characterization.

What was the project objective?
The objective of the project was to investigate and improve the carbon capture solvent for flue gases with low CO₂ content. In particular to determine if specific solvent degradation products impacted carbon capture ability in flue gases with low CO₂ content.

What has the project done in terms of activities?
A pilot plant test campaign was conducted with ACC’s mobile test unit at predominantly low CO₂ concentrations (2.5 – 5 %-vol) to investigate CO₂ capture performance for dilute flue gas sources.
The test campaign was conducted on solvent that had been “aged” in a previous test campaign, hence the contents of degradation products were representative to that of industrially operating carbon capture plants. Different test runs were conducted to deduce the impact of flue gas CO₂ concentration on the carbon capture rate and energy efficiency.
Secondly a series of laboratory tests were conducted to determine if the presence of certain degradation products impacted the CO₂ solubility, absorption rate and physical properties of the solvent. Amongst others by using advanced solvent characterization methods such as NMR and Raman spectroscopy.

What has the project achieved? Did the project achieve its objective?
800 hours of pilot plant operation with 37 different operating points were achieved. The pilot campaign demonstrated that achieving 85-95% CO₂ capture rates were possible with the low CO₂ concentrations tested. The energy requirement for carbon capture increased significantly as expected as the CO₂ concentration of the flue gas decreased. For CO₂ concentrations above 5%-vol, the specific energy requirement for CO₂ capture was not very sensitive to the applied carbon capture rate, whereas a more distinctive influence of the carbon capture rate was observed below 5%-vol CO₂. Considering the obtained results, the pilot plant activity achieved its objectives on quantifying the process performance at low CO₂ flue gas conditions.
The more fundamental laboratory investigations were also executed as planned. The laboratory tests did not reveal significant influence of the presence of degradation products on the CO₂ solubility or absorption rate when comparing fresh samples with aged samples from the pilot plant trial. No substantial change in physical properties could be detected nor did the speciation of CO₂ change between fresh and degraded samples. However, some uncertainty remained on the experimental results and whether the laboratory absorption rate tests were fully representative of industrial absorption columns.
In addition, the laboratory tests also demonstrated that the more abundant degradation products could be partially regenerated under certain conditions, which indicates a possibility for improving solvent consumption rates in industrial plants.
All in all the project has achieved its main objectives in demonstrating the feasibility of CO₂ capture on dilute CO₂ streams. Also, no fundamental showstoppers were revealed in terms of change in solvent chemistry at low CO₂ concentrations.

Future plans?
The project has provided significant data and insight into the performance of an amine-based carbon capture process for flue gases with low CO₂ concentrations. The results will assist ACC in designing and providing carbon capture solutions for industries with relatively dilute CO₂ streams.