Upcoming Meetings & Conferences

Spain

21st Symposium: Turbomachinery Measuring

22-23 March - 2012

United Kingdom

Conference on Thermal Energy Management

26 March - 2012

United Kingdom

The Energy Institute training course

27-29 March - 2012

United Kingdom

20th PIN Meeting

2 May - 2012

Turkey

6th International Conference: Thermal Engineering

22-25 May - 2011

Switzerland

8th ECI International Conference

3-7 June - 2012

Turkey

Sustainable Energy In Buildings

14-20 October - 2012

Carbon Capture and Process Intensification

One of Professor Colin Ramshaw's many papers on process intensification, in particular using centrifugal forces, was that published in Heat Recovery Systems & CHP in 1993 - see the reference [1] later. It was here that there were early hints of using rotating systems to intensify CO2 removal from gas streams.

More recently [2] Colin and co-workers at Cranfield University have written a paper on post-combustion CO2 capture based upon absorption, and a more precise discussion on the use of rotation to enhance carbon capture was given there. The Abstract of the paper is reproduced here, followed by a short extract relating specifically to the CO2 absorption possibilities.

Global concentration of CO2 in the atmosphere is increasing rapidly. CO2 emissions have an impact on global climate change. Effective CO2 emission abatement strategies such as Carbon Capture and Storage (CCS) are required to combat this trend. There are three major approaches for CCS: post-combustion capture, pre-combustion capture and oxyfuel process. Post-combustion capture offers some advantages as existing combustion technologies can still be used without radical changes on them. This makes post-combustion capture easier to implement as a retrofit option (to existing power plants) compared to the other two approaches. Therefore, post-combustion capture is probably the first technology that will be deployed. This paper aims to provide a state-of-the-art assessment of the research work carried out so far in post-combustion capture with chemical absorption. The technology will be introduced first, followed by required preparation of flue gas from power plants to use this technology. The important research programmes worldwide and the experimental studies based on pilot plants will be reviewed. This is followed by an overview of various studies based on modelling and simulation. Then the focus is turned to review development of different solvents and process intensification. Based on these, we try to predict challenges and potential new developments from different aspects such as new solvents, pilot plants, process heat integration (to improve efficiency), modelling and simulation, process intensification and government policy impact.

[1] Ramshaw, C. The opportunities for exploiting centrifugal fields. Heat Recovery Systems & CHP Vol. 13, No. 6, pp. 493-513, 1993
[2] M. Wang, A. Lawal, P. Stephenson, J. Sidders, C. Ramshaw. Post-combustion CO2 capture with chemical absorption: A state-of-the-art review. Chemical Engineering Research and Design, 89 (2011) 1609–1624

A recent laboratory study in China of CO2 absorption has shown that the height of transfer unit (HTU) for an 8 cm diameter RPB was 1–4 cm, at modest rotational speed of less than 1000 rpm. The inlet CO2 concentration was 1% mole fraction of CO2–N2 mixture and NaOH (0.2 kmol/m3) was the absorbent. This compares with the 10–60 cm of conventional packed beds for similar ratings. In a more recent study by Cheng and Tan (2009) using high voidage packed beds, similar findings were reported with amine solutions. These studies indicate that process intensification technology has the potential to reduce the size of CO2 capture plants and reduce both the capital and operating costs.

The standard concentration of the MEA solution used for carbon capture in conventional equipment is 30 wt%. This is largely determined by the need to limit solution viscosity and the corrosion potential with carbon steel construction. However, recent work by Jassim et al. (2009) using a RPB and stronger solutions, has shown that much more efficient absorption can be achieved despite the higher solution viscosity. This effect is probably due to the accelerated chemical kinetics associated with MEA solution concentrations in the range 50–100 wt%. A further advantage of this approach is that the CO2 loading/m3 of solvent solution is much higher, thereby resulting in lower liquid flows between the absorber and stripper.

In order to overcome corrosion problems, the rotating stripper (including reboiler) would have to be fabricated in stainless steel. However, this would not present too much of a cost penalty in view of the small size of the unit compared to the carbon steel conventional columns.

Jassim, M.S., Rochelle, G., Eimer, D., Ramshaw, C., 2009. Carbon dioxide absorption and desorption in aqueous monoethanolamine solutions in a rotating packed bed. Ind. Eng. Chem. Res. 46, 2823–2833.

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