Flue gas carbon dioxide capture

Physical sorbents for carbon dioxide separation and removal were extensively studied by industrial gas companies. Zeolite 13X, activated alumina, and their improved versions are typically used for removing carbon dioxide and moisture from air in either a TSA or a PSA process. The sorption temperatures for these applications are usually close to ambient temperature. There are a few studies on adsorption of carbon dioxide at high temperatures. The carbon dioxide adsorption isotherms on two commercial sorbents hydrotalcite-like compounds, EXM911 and activated alumina made by LaRoche Industries, are displayed in Fig. 8.F23,i24] shown in Fig. 8, LaRoche activated alumina has a higher carbon dioxide capacity than the EXM911 at 300° C. However, the adsorption capacities on both sorbents are too low for any practical applications in carbon dioxide sorption at high temperature. Conventional physical sorbents are basically not effective for carbon dioxide capture at flue gas temperature (> 400°C). There is a need to develop effective sorbents that can adsorb carbon dioxide at flue gas temperature to significantly reduce the gas volume to be treated for carbon sequestration. 

Lu W, ScuHey JP, Yuan D, Krishna R, Wei Z, Zhou H-C (2012) Polyamine-tethered porous polymer networks for carbon dioxide capture from flue gas. Angew Chem Int Ed 51 7480-7484... 

Reynolds, S., Ebner, AD. and Ritter, J.A. (2006) Carbon dioxide capture from flue gas by pressure swing adsorption at high temperature using a K-promoted HTlc - Effects of mass transfer on the process performance. Environmental Progress, 25 (4), 334-342. 

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.

Nelson, T.O., P.D. Box, D.A. Green, and R.P. Gupta, Carbon Dioxide Recovery from Power Plant Flue Gas using Supported Carbonate Sorbents in a Thermal Swing Process, Sixth Annual Conference on Carbon Capture and Sequestration, Pittsburgh, PA, May 2007. 

Like natural gas, the producer gas from coal is a clean fuel. Additionally, it is a rich source of chemicals. Coal-derived gas can also be recombined into liquid fuels, including high-grade transportation fuels, and a range of petrochemicals that serve as feedstock workhorses in the chemicals and refining industries. In contrast to conventional combustion, carbon dioxide exits a coal gasifier in a concentrated stream rather than diluted in a high volume of flue gas. This allows the carbon dioxide to be captured more effectively and then used... 

Compared to conventional combustion, carbon dioxide exits a coal gasifier in a concentrated stream instead of a diluted flue gas. This allows the carbon dioxide to be captured more easily and used for commercial purposes or sequestered. 

The idea here is to capture carbon dioxide from power plants and then inject it into natural gas hydrate reservoirs assumed to contain primarily methane hydrate. Thus one achieves the simultaneous sequestration of carbon dioxide with the production of natural gas. Lee et al. (2003) presented laboratory data that showed the replacement of methane molecules by C02. Yoon et al. (2004) and Ota et al. (2005) confirmed these laboratory findings. Park et al. (2006a) used a CO2/N2 mixture containing 20 mol % carbon dioxide (flue gas) instead of pure C02 and noticed that the methane recoveiy increased from 64 to 85 %. A similar idea for sequestering captured C02 is to use it as cushion gas for natural gas storage in reservoirs (Oldenburg, 2003). 

As was mentioned earlier, it is probably wise to separate the carbon dioxide from the flue gas and inject only a C02-rich stream. This is the so-call "capture" part of the carbon capture and storage. 

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. 

Figure 1. QAFAC methanol plant with an example of process integration, where CO2 from the flue gas from the reformer is captured and fed to the methanol reactor, CDR refers to Carbon Dioxide Recovery [11],...

McDonald TM, Lee WR, Mason JA et ai (2012) Capture of carbon dioxide from air and flue gas in the alkylamine-appended metal-oiganic framework mmen-Mg2(dobpdc). J Am Chem... 

D. R. Paul, Y. P. Yampol skii, Gas Separation Membranes, Boca Raton, CRC Press (1994). C. E. Powell, G. G. Qiao, Polymeric CO2/N2 gas separation membranes for the capture of carbon dioxide from power plant flue gases, J. Membr. ScL, 279, 1 9 (2006). 

Schach, M., Schneider, R., Schramm, H. and Repke, J. (2010) Techno-economic analysis of postcombustion processes for the capture of carbon dioxide from power plant flue gas. Industrial and Engineering Chemistry Research, 49 (5), 2363-2370. 

Industrially important absorption processes are for example the removal of sour gases (CO2, H2S) from natural gas or synthesis gas, the removal of carbon dioxide in chemical plants such as ethylene oxide plants, the removal of SO2 from flue gas, or the absorption of CO2 in power plants (carbon capture and storage (CCS)), and so on. One has to distinguish physical and chemical absorption... 

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