8.3 TECHNOLOGY

8.3 TECHNOLOGY

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RESEARCH


WES Froth Generator Absorber

By Trina Dreher, Research & Development Manager, Process Group

BCIA funds projects focussed on creating a viable and environmentally sustainable future for the brown coal industry in Australia. In this article, Process Group R&D Manager, Trina Dreher, provides a progress update on a BCIA funded carbon capture project. The WES froth generator technology enables the use of precipitating solvents and also shows the potential to significantly reduce the size of CO2 absorber columns, with implications for significant reduction in capital and operating costs for Carbon Capture and Storage (CCS) plants.



It is widely recognised that large-scale CCS is will only become a mainstream technology if significant reductions in capital and operating costs can be achieved, compared to the projected costs as currently modelled.

Moreover, these cost reductions need to be achieved across many facets of the CCS chain, as no one “silver bullet” can be expected to provide the necessary cost step change.

The commercialisation of the WES froth generator absorber represents one opportunity to address this challenge in a meaningful way. To that end, it should be characterised as an important technical development which may enable commercial implementation of CCS for CO2 mitigation.

The current state-of-the-art column internals for carbon capture consist of structured packing as well as the associated gas and liquid distributors and liquid collectors. Whilst existing state-of-the-art internals are suitable for CCS, the size of the absorbers dictated by the process performance of these internals is such that the physical equipment size (>20 metre diameter) is very much at the upper end of technical feasibility, as well constructability.

Furthermore, current internals technology is not suitable for precipitating solvents due to the scaling and blocking characteristics associated with the precipitants.

As well as realising CCS cost reductions, commercialisation of the WES froth generator technology also promises to provide the necessary technical link to allow the use of precipitating solvents for CCS processes, due to the froth generator’s ability to handle solids without blocking. This limitation is significant due to the widely held belief by many CCS solvent developers that the next generation of carbon capture solvents will be precipitating solvents.

At the heart of the WES Absorber technology is the patented Regenerative Froth Matrix packing which creates a froth matrix that continuously forms and collapses. It is this froth matrix, rather than the surface of the packing itself, that creates the surface area for mass transfer. Furthermore, the WES Absorber is enhanced by solvent pulsing phenomena that periodically increases the local liquid to gas ratio.

High speed photography of the absorber in operation displays dynamic high-frequency interaction between the gas and liquid phases. These interactions include rapidly and continuously forming droplets and bubbles, bursting bubbles and fragmenting droplets to form further micro-droplets. The transient nature of the froth ensures rapid regeneration of the liquid-gas interface. It is important to note that the WES "froth" collapses quickly so that there are no special requirements to de-foam the solvent once it exits the absorber.

The BCIA funded project has allowed considerable Computational Fluid Dynamics (CFD) modelling to be performed in order to model the fluid flow and pulsing through the WES Absorber, with the long-term aim to develop a model that can be used to scale up the WES internals.



ABOVE: WES Absorber pilot plant at GDF SUEZ Australian Energy’s Hazelwood Power Station




The models developed have been compared to high speed photography and videos of the WES Absorber, which indicates that some of the hydraulics are accurately modelled while others still require refinement. Therefore, significant work still needs to be conducted in order to accurately model the highly complex phenomena that occur within the WES Absorber.

The WES experimental program currently consists of three parts:
(i) a bench scale WES Absorber apparatus fitted with high-speed photography,
(ii) a conventional and WES Absorber laboratory plant, and
(iii) a conventional and WES Absorber industrial pilot plant.

The latter is incorporated into the CO2CRC solvent pilot plant located at GDF SUEZ Australian Energy’s Hazelwood Power Station.

Laboratory testing conducted in Maui has consisted of CO2 absorption from a synthetic flue gas with conventional solvents: MEA, sodium glycinate and potassium carbonate.

The program investigates a range of variables in order to obtain sufficient data to enable a direct comparison of the WES Absorber performance to that of a conventional absorber over a range of operating conditions.

Results for all solvents have consistently shown that the WES Absorber captures more CO2 for a given absorber height than that achieved with conventional column packing.

In addition, the WES Absorber has been operated with precipitating solvents and, in contrast to conventional packing, did not suffer from clogging or precipitant build-up. The prevention of fouling is due to the rapid interface regeneration and the highly turbulent environment created in the WES Absorber that prevents precipitates from adhering to the column internals.

In addition to laboratory experiments, pilot plant trials are being conducted with actual flue gas at the Hazelwood Power Station in order to validate the Maui laboratory results. Results from the pilot plant WES Absorber are also directly compared to a conventional absorber via the data generated by the CO2CRC.

Preliminary results achieved so far support that generated in the Maui laboratory however, further work is required in order to draw definite conclusions.

To that end, forthcoming trials will investigate the performance of the CO2CRC’s precipitating solvent and also that of a sodium glycinate solvent. It is anticipated that the results from these trials will provide invaluable information pertaining to the operating performance, theoretical model validation, and economics of the WES Absorber internals. This information will serve as a platform for the improvement of future commercial WES Absorbers to enable further development of a viable commercial product with the potential to provide a cost step change for large-scale CCS.




ABOVE: Maui lab – conventional (L) and WES (R) absorbers




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