Carbon capture post-combustion

Keywords Carbon dioxide, post-combustion, carbon capture, conversion, utilization... 

Carbon dioxide capture and storage is especially studied in connection with electricity generation, where different technology routes - post-combustion capture, pre-combustion capture and oxyfuel combustion - are under research and development. Carbon dioxide capture is also crucial in connection with hydrogen production... 

Post-combustion carbon capture equipment can be added to existing power plants, but this is very expensive. In the United States several such projects have been abandoned (in Illinois, Florida, West Virginia, Ohio, Minnesota, and Washington State). Storing the carbon dioxide underground requires very unique soil and rock formations to prevent leakage or ground-water pollution. 

In the carbon capture world there are two approaches to capturing the carbon dioxide 1. post-combustion and 2. pre-combustion.The post-combustion approach is to take the COz from the combustion process, purify it, and then inject it. In the pre-combustion approach, the carbon is removed from the fuel before combustion. These two approaches are discussed in the following sections. 

Eimer, D. Post-combustion C02 separation technology summary. In Carbon Dioxide Capture for Storage in Deep Geological Formations—Results from the C02 Capture Project. Capture and Separation of Carbon Dioxide from Combustion Sources (ed. D.C. Thomas), Vol. 1. Amsterdam Elsevier, p. 91-97, 2005. 

Pre-combustion capture is when the carbon dioxide is separated from the hydrogen before it is combusted in a gas turbine. Post-combustion capture is the more usual process where the fuel is burnt first and the carbon dioxide is extracted from the exhaust gas. See Section 3.2, Chapter 3. 

All three major processes - post-combustion capture, oxy-fuel combustion, pre-combustion capture - require a step that, variously, involves the separation of carbon dioxide, oxygen or hydrogen from a bulk gas stream (flue gas, air or syngas, respectively). These separations can be accomplished by means of physical/chemical solvents, membranes, solid sorbents or cryogenic processes. 

Because of the growing importance of carbon dioxide sequestration, there is currently a lively debate as to whether future coal-fired power stations should be conventional pulverized fuel, oxy-fuel or gasification designs. This is by no means a straightforward choice and involves considerations of overall fuel efficiency, engineering complexity and capital and operating costs. In addition, there are many types of coal (anthracite, bituminous coal, brown coal) with possibly dissimilar impurity contents, each of which may dictate a different plant design. The jury is still out on whether future coal-fired power stations will employ post-combustion or pre-combustion capture of carbon dioxide this is a crucial issue to decide as the plants have a life of 40—50 years. 

Bounaceur R., Lape N., Roizard D., Vafiieres C., Favre E. 2006. Membrane processes for post-combustion carbon dioxide capture A parametric study. Energy 31 2556-2570. 

Noble RD. Achieving a 10,000 GPU permeance for post-combustion carbon capture with RTIL-based membranes, DOE NETL CO2 Capture Technology Meeting, Pittsburg, PA, 2011. 

Merkel TC, Lin H, Wei XT, Baker R. Power plant post-combustion carbon dioxide capture An opportunity for membranes. J Membr Sci 2010 359(1-2) 126-139. 

Favre, E., R. Bounaceur, and R. Denis, A hybrid process combining oxygen enriched air combustion and membrane separation for post-combustion carbon dioxide capture. Separation and Purification Technology, 2009. 68(1) 30-36. 

Favre, E., Svendsen, H.F. 2012. Membrane contactors for intensified post-combustion carbon dioxide capture by gas-liquid absorption processes. /. Membr. Sci. 407-408 1-7. 

Post-combustion capture involves separating the carbon dioxide from other exhaust gases after combustion of the fossil fuel. Post-combustion capture systems are similar to those that already remove pollutants such as particulates, sulfur oxides, and nitrogen oxides from many power plants. 

In summary, porous carbon-based materials for CO2 capture have experienced rapid development in the last several decades and will continue to blossom. The requirements of CO2 captures vary a lot depending on different processes, namely post-combustion (low pressure, predominantly CO2/N2 separation), pre-combustion (high pressure, predominantly CO2/H2 separation) capture and natural gas sweetening (predominantly CO2/CH4 separation). Thus, various kinds of new carbon materials with defined textural properties as well as tailored surface chemistry have been synthesized for a specific CO2 capture process. Another advantage lies... 

Abu-Zahra, M.R.M., Schneiders, L.H.J., Niederer, J.P.M. et al. (2007b) CO2 capture from power plants, part i. a parametric study of the technical performance based on monoethanolamine. International Journal of Greenhouse Gas Control, 1(1), 37 6. Merkel, T.C., Lin, H., Wei, X. and Baker, R. (2010) Power plant post-combustion carbon dioxide capture An opportunity for membranes. Journal of Membrane Science, 359(1-2), 126-139. 

Figure 2.8 Example of carbon dioxide separation from power plant flue gas using a two-step membrane process with two options for managing the permeate from the second membrane step. In Option 1 purple double-dotted lines), air is used directly in the burner while a vacuum pump creates partial pressure driving force in the second membrane step with return of the second step permeate to front of membrane process. In Option 2 blue dashed lines), the combustion air is used as a countercurrent permeate sweep gas in the second membrane step. Adapted from Figs. 11 and 12 in Merkel TC, Lin H, Wei X, Baker R. Power plant post-combustion carbon dioxide capture an opportunity for membranes. J Membr Sci 2010 359(1—2) 126—139.

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