Una de las estrategias propuestas para combatir el cambio climático, en lo referente al aumento de la concentración de dióxido de carbono en la atmósfera, consiste sencillamente en eliminarlo de la misma. Pero un nuevo estudio sugiere que esta solución no es económica ni práctica.
Antes de que la actividad industrial comenzara a arrojar a la atmósfera dióxido de carbono, a partir de la mitad del siglo XVIIII, la concentración de este gas en la atmósfera era alrededor de 280 partes por millón (ppm). Hoy día excede las 390 ppm y sigue aumentando a razón de 2 ppm por año. Algunos científicos han sugerido que en vez de reducir las emisiones de gases de efecto invernadero cambiando a fuentes neutras desde el punto de vista del carbono: eólicas, solares o nucleares, y dejando que la vegetación y los océanos absorban gradualmente el dióxido de carbono, la humanidad podría disminuir esas concentraciones más rápidamente, eliminando de forma activa el dióxido de carbono del aire.
Para ello se podrían dejar enormes depósitos abiertos conteniendo una disolución de hidróxido sódico, o potásico, o aminas. O bien se podría forzar a que el aire cargado de CO2 burbujeara a través de dichos depósitos. De esa manera, el gas quedaría fijado como carbonato. Al calentar esos compuestos se liberaría de nuevo el dióxido de carbono inyectándolo en el subsuelo debajo de rocas impermeables, igual que están los depósitos naturales de crudo o de gas natural. Estas estrategias conforman lo que se ha llamado Geoingeniería, con la cual algunos científicos esperan detener el calentamiento global.
Estudios anteriores cifraban el gasto en unos cuantos cientos de euros por tonelada métrica de dióxido de carbono, de manera que los 33.500 millones de toneladas generadas por la actividad industrial podrían eliminarse con cerca de 10 billones de dólares, un coste tremendo pero económicamente viable. No obstante, un nuevo estudio publicado online por Kurt House y colaboradores , en los Proceedings of the National Academy of Sciences sugiere que el coste por tonelada sería mucho más caro, cerca de 1100 dólares por tonelada.
Eso significa que se gastarían al menos 33 billones de dólares solo para mantener los niveles actuales, pero uno vez capturado debría gastarse energía para comprimirlo en forma líquida y almacenarlo. Y excepto que la energía empleada en estos procesos no produzca ella misma CO2, el resultado neto sería aumentar la concentración de dicho gas y no disminuirla.
Según otros expertos como Robert Socolow, físico de la Universidad de Princeton, está claro que a día de hoy “el proceso sería caro y que aún no se sabe cómo llevarlo a cabo a bajo coste, pero hay trabajo por hacer para reducir los costes de forma significativa”
David Keith, físico de la Universidad de Harvard y presidente de una compañía que desarrolla dicha tecnología, opina que hay mucha incertidumbre asociada con las técnicas empleadas por House y colaboradores, con lo que el coste por tonelada podría oscilar entre 100 y varios miles de dólares. Añade que “en este momento, la captura de carbono es un solo un concepto../... Para saber lo que cuesta, alguien tendría que hacerlo”.
House y sus colegas opinan que a corto plazo es mejor dejar de emitir CO2 en primer lugar. Entre ahora y 2050 , se podrían capturar las emisiones de carbono utilizando técnicas tales como eliminándolo antes de que deje las chimeneas con un coste de menos de 300 dólares por tonelada. Pero la mejor manera, sugieren muchos, es sencillamente encontrar fuentes de energía más ecológicas.
Since a buildup of humanmade carbon dioxide is causing the planet to warm, why not just suck this greenhouse gas straight out of the atmosphere? That's one strategy scientists have proposed to combat climate change. But a new analysis suggests that the approach may be neither economical nor practical.
Before widespread industrial activity began spewing CO2 into the air in the mid-1700s, atmospheric concentrations of the gas were around 280 parts per million (ppm). They now exceed 390 ppm and are growing rapidly, about 2 ppm per year. Rather than reducing emissions of the greenhouse gas by shifting to carbon-neutral sources of energy—wind, solar, and nuclear power, for example—and then letting vegetation and the oceans gradually absorb CO2 in the long term, humans could lower concentrations more rapidly by actively pulling CO2 from the air, some scientists have suggested.
In such a scheme, researchers would leave large vats out in the open, filled with solutions of sodium hydroxide, potassium hydroxide, or chemicals called amines. Or, the CO2-laden air could be forcefully bubbled through such reservoirs. When CO2 in the air reacts with these solutions, it becomes trapped in carbonate-rich compounds. Scientists can later heat these compounds and release the CO2 and dispose of it, typically by injecting it into deep geologic formations beneath impermeable rock, such as natural reservoirs of oil and natural gas. This strategy and many similar others, are part of a suite of ideas, dubbed Geoengineering, in which scientists hope to use technology to curb global warming.
Previous studies have hinted that capturing CO2 directly from the air could cost a few hundred dollars per metric ton of CO2 so it would total cost $10 trillion to completely counteract the estimated 33.5 billion tons of CO2 emissions generated by humans—a tremendous cost, yet one that is still economically viable. But Kurt House and his colleagues suggest online in the Proceedings of the National Academy of Sciences that the cost per ton of CO2 may actually be much more expensive, around $1100 per ton.
That's a total price tag of at least $33 trillion just to hold atmospheric concentrations of CO2 steady Then, once the gas is captured, even more energy must be expended to compress the gas into a liquid and then dispose of it. And unless the energy needed to drive these processes are carbon-neutral—that is, unless they produce no CO2 emissions of their own—the net result might add CO2 to the atmosphere, not reduce it.
Other experts, such as Robert Socolow, a physicist at Princeton University, say that “this [carbon-capture] process would be expensive now…./… we don't know how to do this at low cost, but there's work that can be done that might reduce costs significantly”
David Keith, a physicist at Harvard University and president of a start-up company developing such technology, says that the there is a lot of uncertainty associated with the analytical techniques used by House and his colleagues so the costs per ton could range anywhere from several thousand dollars to as low as $100. He adds that, "at this point, carbon capture [from ambient air] is a very conceptual environment…/…To really know what it costs, someone actually has to build it."
House and his colleagues note that for the near future, it's probably better to avoid releasing CO2 into the atmosphere in the first place. Between now and 2050, they say, carbon emissions can be captured—using more-developed techniques such as scrubbing the gas before it ever leaves the smokestack, for instance—for less than $300 per ton. But the best approach, many suggest, is simply to find greener sources of energy.
Tomado de/Taken from Science
Resumen de la publicación/Abstract of the paper
Economic and energetic analysis of capturing CO2 from ambient air Kurt Zenz House, Antonio C. Baclig, Manya Ranjan, Ernst A. van Nierop, Jennifer Wilcox and Howard J. Herzog
Published online before print December 5, 2011, doi: 10.1073/pnas.1012253108
Abstract
Capturing carbon dioxide from the atmosphere (“air capture”) in an industrial process has been proposed as an option for stabilizing global CO2 concentrations. Published analyses suggest these air capture systems may cost a few hundred dollars per tonne of CO2, making it cost competitive with mainstream CO2 mitigation options like renewable energy, nuclear power, and carbon dioxide capture and storage from large CO2 emitting point sources. We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing CO2 from the air are likely to have been underestimated. Specifically, our analysis of existing gas separation systems suggests that, unless air capture significantly outperforms these systems, it is likely to require more than 400 kJ of work per mole of CO2, requiring it to be powered by CO2-neutral power sources in order to be CO2 negative. We estimate that total system costs of an air capture system will be on the order of $1,000 per tonne of CO2, based on experience with as-built large-scale trace gas removal system
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