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An Experimental Investigation Of Optimum Conditions For Continuous Two-Stage Reclaiming Of MEA Solvent Inventories From Commercial Plants

Pokora, Marcin; Joel, Lucas; Ibrahim, Aisha; Lucquiaud, Mathieu; Michailos, Stavros; Gibbins, Jon

Authors

Marcin Pokora

Lucas Joel

Aisha Ibrahim

Mathieu Lucquiaud

Jon Gibbins



Abstract

This paper describes a series of tests to investigate the optimum conditions for continuous two-stage reclaiming of used monoethanolamine (MEA) solvent from an operating commercial plant, plus process modelling to assess the impact of fully integrated reclaimer operation on the overall energy requirements of a complete capture system. While modelling the reclaiming process itself can give useful semi-quantitative insights, the extreme complexity of the range of impurities present in real processes means that representative small-scale testing is required to confirm trends with the reliability needed to inform commercial equipment configurations and operating procedures.Although a generic solvent, MEA, is being used, which allows full disclosure of all results, much of the information and insights are expected to apply to any amine solvent formulation where thermal reclaiming achieves good separation between solvent components and impurities.
The key performance requirement for any reclaiming system is to remove all added or formed impurities from an operating amine capture system and indefinitely maintain the circulating solvent at an acceptable purity level. The two-stage system proposed for this purpose is shown in Figure 1. The first stage is operated by venting into the stripper to return heat to the system as water vapour as well as reclaimed MEA and therefore would operate either at stripper pressure or at a lower pressure with mechanical vapour compression. The second stage would vent into the absorber and operate at either atmospheric pressure or at reduced pressure using a vacuum pump. For both stages, the use of added equipment to achieve reduced operating pressures represents a trade-off between amine recovery, energy requirements and capital and maintenance costs, which the test data and process modelling will help to inform.
The objective for the first reclaiming stage is to recover as much of the reclaiming thermal energy input as possible to help regenerate further solvent, while also giving satisfactory amine recovery and impurity rejection overall. It will run continuously with the unwanted residue leaving in a relatively dilute, and hence free flowing, ‘blowdown’ stream, mixed with some of the incoming MEA and water. The impact of variable real impurity levels (based on used solvent from a commercial capture plant), the ratio between the ‘blowdown’ to the second stage and water addition on operating temperature, MEA recovery and volatile impurity returns will be reported for a maximum stripper pressure of 2.4 bara (20 psig) and lower pressures requiring vapour recompression.
The second reclaiming stage is intended to maximise amine recovery while also not using excessive energy and not returning an excessively high proportion of the more volatile impurities. Caustic is also added in this stage to release heat-stable salts, with the amount based on sample testing. Operation is in batch mode, involving three stages:
a) A filling/concentration stage where the inflowing first-stage blowdown (plus added water and any caustic) is heated, and vapour is collected until a characteristic temperature (The value of which is a key finding from the test programme) is reached where thermal degradation and unwanted volatile carryover become excessive.
b) An MEA recovery stage where first-stage blowdown input is stopped (two second-stage reclaimers may be used to allow continuous first-stage operation) and only water is added; the temperature will fall in this stage eventually reaching a plateau, indicating the MEA recovery stage completion, although the trade-offs between maximising MEA recovery and unwanted volatile residue recycling must be considered.
c) A concentration stage where (mainly) water is removed to the point where a flowing residue can still be obtained, in order to minimise the volume of waste while maintaining residue handleability; again, unwanted component evaporation must also be evaluated.
MEA recovery is measured using gas chromatography. In the test system used the vapour is condensed and collected, allowing a complete MEA balance to be made. The heterogeneous and complex residues and evaporates are characterised using thermogravimetric analysis (TGA), which can assess the entirety of the sample, plus mass spectrometry. TGA is a method that may be suitable for routine industrial use.
Data from tests on both reclaimer stages are included in the overall system modelling to estimate impacts on energy requirements as a function, mainly, of impurity levels and water addition. Modelling has been carried out using the CCSI toolkit Aspen Plus V12.1.
This work is expected to inform the operation of existing reclaimers and be the basis for the design of future commercial fully integrated MEA reclaiming systems.

Citation

Pokora, M., Joel, L., Ibrahim, A., Lucquiaud, M., Michailos, S., & Gibbins, J. (2024, October). An Experimental Investigation Of Optimum Conditions For Continuous Two-Stage Reclaiming Of MEA Solvent Inventories From Commercial Plants. Presented at 17th Greenhouse Gas Control Technologies Conference (GHGT-17), Calgary, Canada

Presentation Conference Type Conference Paper (published)
Conference Name 17th Greenhouse Gas Control Technologies Conference (GHGT-17)
Start Date Oct 20, 2024
End Date Oct 24, 2024
Acceptance Date Dec 20, 2024
Online Publication Date Dec 20, 2024
Deposit Date Mar 18, 2025
Publicly Available Date Mar 31, 2025
Journal SSRN
Print ISSN 1556-5068
Peer Reviewed Peer Reviewed
DOI https://doi.org/10.2139/ssrn.5064077
Keywords Amine post-combustion capture; Solvent management; Reclaiming; Thermal reclaiming; Carbon capture; MEA; Monoethanolamine
Public URL https://hull-repository.worktribe.com/output/5085217