{"id":532,"date":"2008-03-30T04:32:45","date_gmt":"2008-03-30T09:32:45","guid":{"rendered":"http:\/\/www.realclimate.org\/index.php\/archives\/2008\/03\/air-capture\/"},"modified":"2009-06-10T20:55:09","modified_gmt":"2009-06-11T01:55:09","slug":"air-capture","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2008\/03\/air-capture\/","title":{"rendered":"Air Capture Captura de Aire<\/lang_sp>"},"content":{"rendered":"
\n

Guest Commentary by Frank Zeman<\/a><\/small><\/p>\n

[This is one of an occasional series on the science of mitigation\/adaptation\/geo-engineering that we hope to continue. Since this isn’t our core expertise, we’d especially appreciate balanced contributions from other scientists.]<\/it><\/small><\/p>\n

One of the central challenges of controlling anthropogenic climate change is developing technologies that deal with emissions from small, dispersed sources such as automobiles and residential houses. Capturing these emissions is more difficult as they are too small to support infrastructure, such as pipelines, and may be mobile, as with cars. For these reasons, proposed solutions, such as switching to using hydrogen or electricity as a fuel, rely on the carbon-free generation of electricity or hydrogen. That implies that the fuel must be made either by renewable generation (wind, solar, geothermal etc.), nuclear or by facilities that capture the carbon dioxide and store it (CCS).<\/p>\n

There is however an alternative that gets some occasional attention: Air Capture (for instance, here<\/a> or here<\/a>). The idea would be to let people emit the carbon dioxide at the source but then capture it directly from the atmosphere at a separate facility. <\/p>\n

Par Frank Zeman<\/a>, traducido por Angela Carosio<\/small><\/lang_sp>
\n<\/p>\n

The removal of carbon dioxide directly from the atmosphere is a natural phenomenon that occurs in the surface ocean or during photosynthesis. Ocean absorption is a result of both the higher concentration of CO2<\/sub> in the atmosphere and the alkaline nature of seawater (Note that this absorption that is leading to the \u201cother\u201d CO2<\/sub> problem<\/a>, ocean acidification – which may prove detrimental to coral reefs and other organisms that use carbonate). Land-based air capture is an effort to enhance this mechanism at an industrial scale so that CO2<\/sub> can be removed from the atmosphere under controlled conditions. Given that it is performed under controlled conditions, we can use more alkaline solutions to improve the rate of capture without adversely affecting the biosphere. <\/p>\n

Industrial air capture is based on the absorption of CO2<\/sub> using alkali earth metals such as sodium or potassium. The process is a variant of the Kraft Process<\/a> used in most pulp and paper mills and as such, benefits from a long industrial history. The CO2<\/sub> is absorbed into solution, transferred to lime via a process called causticization and released in a kiln. With some modifications to the existing processes, mainly an oxygen-fired kiln, the end result is a concentrated stream of CO2<\/sub> ready for storage or use in fuels. An alternative to this thermo-chemical process is an electrical one in which an electrical voltage is applied across the carbonate solution to release the CO2<\/sub>. While simpler, the electrical process consumes more energy as it splits water at the same time. It also depends on electricity and so unless the electricity is renewable or nuclear, will result in the storage of more CO2<\/sub> than the chemical process. <\/p>\n

If the technology is well established and, aside from the oxygen combustion of lime, dates back over 50 years, what stops it from being used and what might change in the future?<\/p>\n

The main barrier is the efficiency of the energy requirements during the reducing process. Air capture requires energy to move the air, manufacture the absorbing solutions and solids as well as to produce the oxygen, fuel and make up chemicals. All of these items will result in additional CO2<\/sub> emissions, which reduce the efficiency and therefore the benefits. The second important consideration, and maybe the dominant one, is cost. Air capture has to be more economical than the proposed alternatives (hydrogen, electricity, renewables, greater efficiency etc.). It should be stated clearly that air capture is not a viable alternative to capture at large, point source emitters such as power plants since it will always be more efficient to capture and store carbon dioxide from more concentrated streams. So while there are any non-CCS fossil fuel plants, Air Capture is a non-starter. <\/p>\n

But recent suugestions have re-thought air capture as a thermal<\/em> process. The early incarnations of air capture used electricity as the energy source and therefore depended on carbon-free sources. A thermal Air Capture system uses heat that can be generated on-site, reducing the inefficiencies associated with producing electricity, but of course it still needs a source of (carbon-free) heat. Notably, this implies that air capture could reduce greenhouse gas emissions independently of developments in the power generation or transportation sector. Preliminary experimentation has shown that causticization can occur at ambient temperatures and that conventional vacuum filtration is sufficient to avoid large evaporation penalties. These developments reduce the total energy required for the process by about half compared to the conventional method and thereby reduce the amount of CO2<\/sub> that would need to be sent to storage.<\/p>\n

However, the cost of air capture is still basically unknown. Estimates have varied wildly and real numbers will only come from pilot projects over the next few years. In some sense, that puts this technology on par with the hydrogen economy with expansion potentially starting sometime after 2015. For now there are far easier (efficiency) and cheaper (power plants) ways of reducing emissions of CO2<\/sub> and so air capture is not a replacement for other efforts to reduce emissions. But in the long run, all carbon sources will require mitigation – including the transportation sector – and at that time air capture could be the most cost effective option for some sources. It is not any kind of panacea though.<\/p>\n


\n(Este es solo uno de una serie ocasional de Ciencia de la Mitigaci\u00f3n \/Adaptaci\u00f3n\/Geoingenier\u00eda que esperamos poder continuar. Debido a que no somos expertos en \u00e9ste rubro, apreciamos opiniones equilibradas de otros cient\u00edficos)<\/small><\/p>\n

Uno de los desaf\u00edos m\u00e1s importantes de controlar los cambios clim\u00e1ticos causados por el hombre es tratar el tema de las emisiones de fuentes peque\u00f1as y dispersas, como los autom\u00f3viles y las casas residenciales. La captura de estas emisiones es muy dif\u00edcil ya que son demasiado peque\u00f1as para soportar infraestructura como por ejemplo, ca\u00f1er\u00eda, y son m\u00f3viles, como por ejemplo, los autom\u00f3viles. Por estas razones, las soluciones alternativas propuestas, como usar hidr\u00f3geno o electricidad como combustible, se apoyan en generar electricidad o hidr\u00f3geno libre de di\u00f3xido de carbono. Esto implica que el combustible debe ser producido por medio de energ\u00eda renovable (viento, solar, geotermal, etc.), nuclear o en facilidades que puedan capturar el CO2 emitido y almacenarlo (CCS).<\/p>\n

Hay, sin embargo, una alternativa que ocasionalmente llama la atenci\u00f3n, la Captura de Aire. (Por ejemplo: aqui<\/a> o aqui<\/a>). La idea es dejar que se emita CO2 en la fuente pero capturarlo directamente de la atm\u00f3sfera en un lugar separado.<\/p>\n

La remoci\u00f3n de di\u00f3xido de carbono directamente de la atm\u00f3sfera es un fen\u00f3meno natural que ocurre en la superficie del oc\u00e9ano durante la fotos\u00edntesis. La absorci\u00f3n oce\u00e1nica de CO2 es el resultado de una alta concentraci\u00f3n de CO2 en la atm\u00f3sfera y la naturaleza alcalina del agua marina. N\u00f3tese que esta absorci\u00f3n conduce a otro problema, el de la acidificaci\u00f3n del oc\u00e9ano<\/a>, que podr\u00eda ser nocivo para los arrecifes de corales y otros organismos que usan carbonatos. La captura de aire con base terrestre est\u00e1 dise\u00f1ada para incrementar dicha absorci\u00f3n bajo condiciones controlables. Dado que el proceso se realiza bajo condiciones controladas, se pueden usar mas soluciones alcalinas para mejorar el ritmo de captura sin afectar adversamente la bi\u00f3sfera.<\/p>\n

La captura de aire industrial est\u00e1 basada en la absorci\u00f3n de di\u00f3xido de carbono usando metales terrestres alcalinos como el sodio y el potasio. Este proceso es una variante del proceso llamado Kraft<\/a> usado en el procesamiento de pulpa y papel, y como tal, se ve beneficiado por una larga trayectoria industrial. El CO2 es absorbido en una soluci\u00f3n, luego transferido a cal mediante un proceso llamado caustificaci\u00f3n, y luego liberado en un horno. Con algunas modificaciones al proceso existente, principalmente un horno con llamas de ox\u00edgeno, el resultado final es un flujo de CO2 listo para almacenar o para usar en combustibles. Otra alternativa a este proceso termoqu\u00edmico es un proceso el\u00e9ctrico en donde un voltaje el\u00e9ctrico es aplicado a una soluci\u00f3n carbonatada para que libere el CO2. Si bien esta \u00faltima soluci\u00f3n es m\u00e1s sencilla, el proceso el\u00e9ctrico consume mucha m\u00e1s energ\u00eda ya que divide agua al mismo tiempo. Tambi\u00e9n depende de la electricidad, y, a menos que la electricidad sea renovable o nuclear, ser\u00eda necesario almacenar m\u00e1s CO2 que con el proceso qu\u00edmico.<\/p>\n

Si la tecnolog\u00eda est\u00e1 bien establecida y, aparte de la combusti\u00f3n de oxigeno de la cal, data de 50 a\u00f1os atr\u00e1s, \u00bfqu\u00e9 es lo que nos impide usarla y que podr\u00eda cambiar en el futuro?<\/p>\n

La principal barrera es la eficiencia de los requerimientos energ\u00e9ticos durante el proceso de reducci\u00f3n. El proceso de captura de aire requiere energ\u00eda para mover el aire, para la elaboraci\u00f3n de las soluciones absorbentes y los s\u00f3lidos as\u00ed como tambi\u00e9n para producir el ox\u00edgeno, combustible y la composici\u00f3n de productos qu\u00edmicos. Todos estos procesos dar\u00e1n como resultado emisiones adicionales de CO2, lo que reduce la eficiencia y, consecuentemente, los beneficios. La segunda consideraci\u00f3n importante, y quiz\u00e1s dominante, son los costos. La captura de aire debe ser m\u00e1s econ\u00f3mica que las alternativas propuestas (hidr\u00f3geno, electricidad, energ\u00edas renovables, mayor eficiencia, etc.). Se debe dejar bien en claro que la captura de aire no es una alternativa viable para superficies extensas, y apunta m\u00e1s vale a fuentes de emisiones como las centrales de energ\u00eda, ya que siempre ser\u00e1 mucho m\u00e1s eficiente capturar y almacenar di\u00f3xido de carbono de flujos concentrados. De modo que, mientras no haya ninguna planta procesadora de combustibles f\u00f3siles con CCS, la captura de aire resulta imposible.<\/p>\n

Pero, recientemente se ha re pensado en la captura de aire como un proceso termal. Las primeras manifestaciones de captura de aire usaban electricidad como fuente de energ\u00eda y, por lo tanto, depend\u00edan de fuentes libres de di\u00f3xido de carbono. En un sistema de captura de aire termal se usa el calor que puede ser generado in situ, reduciendo de esta manera las ineficiencias asociadas con la producci\u00f3n de electricidad, pero, por supuesto, todav\u00eda se necesita una fuente de calor libre de di\u00f3xido de carbono. Esto implica, notablemente, que la captura de aire podr\u00eda reducir las emisiones de gases de invernadero independientemente del desarrollo en los sectores de generaci\u00f3n de energ\u00eda y de transporte. Experimentos preliminares han demostrado que el proceso de caustificaci\u00f3n pude ocurrir a temperatura ambiente, y que el filtrado convencional al vac\u00edo es suficiente para evitar penalidades por evaporaci\u00f3n a gran escala. Estos desarrollos reducen el requerimiento energ\u00e9tico necesario para el proceso a la mitad, comparado con los m\u00e9todos convencionales, reduciendo, de este modo, la cantidad de CO2 que se necesitar\u00eda almacenar.<\/p>\n

Sin embargo, se desconoce a\u00fan el costo de la captura de aire. Las estimaciones var\u00edan enormemente y solo se podr\u00e1n obtener valores reales de proyectos piloto en los pr\u00f3ximos a\u00f1os. En cierto sentido, esto pone a dicha tecnolog\u00eda a la par con la econom\u00eda de hidr\u00f3geno para potencialmente empezar a partir del a\u00f1o 2015. Por el momento hay maneras m\u00e1s sencillas (eficientes) y econ\u00f3micas (plantas de energ\u00eda), de reducir las emisiones de CO2 y, por consiguiente, la captura de aire no reemplaza otros esfuerzos por reducir las emisiones. Sin embargo, todas las fuentes de carbono deber\u00e1n ser mitigadas a largo plazo, incluyendo el sector del transporte. Para ese entonces, la captura de aire podr\u00eda ser la opci\u00f3n m\u00e1s rentable para algunas fuentes. De todos modos, no es ninguna panacea.
\n<\/lang_sp><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

Guest Commentary by Frank Zeman [This is one of an occasional series on the science of mitigation\/adaptation\/geo-engineering that we hope to continue. Since this isn’t our core expertise, we’d especially appreciate balanced contributions from other scientists.] One of the central challenges of controlling anthropogenic climate change is developing technologies that deal with emissions from small, […]<\/p>\n","protected":false},"author":12,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[1,3],"tags":[],"class_list":{"0":"post-532","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-climate-science","7":"category-greenhouse-gases","8":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/532","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/comments?post=532"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/532\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=532"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=532"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=532"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}