Artificial storage
Contenido
Para la fijación artificial del carbono (es decir, sin utilizar el ciclo natural del carbono), primero debe ser capturado y luego almacenado por diferentes medios.
Las plantas de purificación de gas natural deben eliminar el dióxido de carbono para evitar que el hielo carbónico obstruya los camiones cisterna o para impedir que las concentraciones de CO superen el 3% como máximo permitido en la distribución de gas natural.
Además, una de las tecnologías más prometedoras para el almacenamiento de carbono es el almacenaje de CO que proviene de las centrales eléctricas (en el caso del carbón, se conoce como "carbón limpio"). Normalmente, una central eléctrica de reciente producción de 1000 megavatios, de combustión de carbón, emite aproximadamente 6 millones de toneladas de CO al año. El desarrollo de la captura de carbono en las plantas existentes equivale a un aumento de los costos de producción de energía muy elevado. Además, una planta de carbón de 1000 MW, requiere el almacenamiento de 50 millones de barriles de CO al año.
Los costes de producción de la electricidad se han reducido cuando la tecnología de gasificación del carbón se ha utilizado en las instalaciones nuevas, aunque los costes de la electricidad han sido entre un 10 y un 12% más elevados que la producida por la quema de carbono fósil.
El transporte de dióxido de carbono ha de cumplir normas de seguridad severas, ya que es letal en concentraciones superiores al 10%, como lo demuestra la trágica desgasificación del lago Nyos.
Está en estudio el diseño de barcos de transporte de dióxido de carbono según el mismo principio que los barcos de transporte de GNL.
carbon capture
Currently, CO absorption is done on a large scale through the use of amino solvents, especially with monoethanolamine (2-aminoethanol, IUPAC nomenclature). Other techniques being explored include rapid temperature/pressure absorption, gas separation and cryogenics.
In coal-fired power plants, the main alternative to amine-based CO absorption is coal gasification and oxygen-fuel combustion. Gasification produces a primary gas, consisting of hydrogen and carbon monoxide, which is burned to produce carbon dioxide. Oxygen-fuel combustion burns coal with oxygen instead of air, producing only easily separable CO and water vapor. However, this combustion produces extreme temperatures and materials that can withstand this temperature have yet to be created.
Another long-term option is capturing carbon from the air using hydroxides. The air is literally stripped of all its CO2. This idea is an alternative to non-fossil fuels for the transport sectors (car, truck, public transport...).
A test carried out in a 420 megawatt power plant of the Elsam company in Esbjerg (Denmark) was carried out on March 15, 2006,[18] within the framework of the European project Castor piloted by the French Petroleum Institute (IFP), which brings together around thirty scientific and industrial partners. The post-combustion process should make it possible to reach half the cost of CO capture, reducing it from 20 to 30 euros per ton.
Its cost in four years (2004-2008) is 16 million euros, of which 8.5 million are financed by the European Union. Castor is intended to validate technologies for large industrial units - power plants, steel, cement, etc. - whose activity generates 10% of European CO emissions, so that this technique is in line with the European price of CO emission permits (€27 per ton).
Afterburner Capture
Emissions from power plants consist of less than 20% carbon dioxide. Therefore, before burying it underground, it must be captured: it is afterburning capture. In contact with an acid gas (such as CO), an aqueous solution of 2-aminoethanol forms a salt at room temperature. The solution is then transported to a closed environment where it is heated to about 120°, which, according to Le Châtelier's principle, releases the (pure) CO and the aqueous 2-aminoethanol solution is regenerated.
The oceans
Direct injection of carbon into the ocean is another type of carbon sequestration option. In this method, CO is injected into deep water, to form a "lake" of liquid CO trapped by the pressure exerted at depth. Experiments carried out between 350 and 3600 meters indicate that liquid CO reacts to pressure by solidifying into methane hydrate, which dissolves little by little in the surrounding waters. The imprisonment is therefore only temporary.
This technique has harmful consequences for the environment. CO reacts with water to form carbonic acid HCO. The biological balance of the seabed, little known, will probably be affected. The effects on benthic life forms in pelagic areas are unknown. From a political point of view, it is doubtful that carbon storage in or under the oceans is in line with the London Convention for the Prevention of Marine Pollution. [1].
Another method of ocean sequestration is the long-term collection of crop residues (such as wheat stalks or hay) into large bales of biomass and their deposition in the "alluvial fan" areas of deep ocean basins. Submerging these residues in alluvial deposits will have the effect of burying them at the bottom of the ocean, capturing the biomass for a very significant time. Alluvial deposits exist in all oceans and seas of the world. world where river deltas penetrate the continental shelf, such as the Mississippi alluvial deposit in the Gulf of Mexico and the Nile deposit in the Mediterranean.
Specific use of algae
The City of Libourne has plans to equip one of its car parks with CO-absorbing lamps. They would be equipped with a tank containing algae. These, placed near a light source, absorb carbon dioxide and emit oxygen.[19].
Selection of adapted organisms can give significant returns. It is estimated that a device of this type, with a volume of 1.5 m³, could absorb up to one ton of CO.
The Castor project includes the study of four places for the geological storage of CO: The Casablanca oil reserve located along the northeast coast of Spain, the Atzbach-Schwanenstadt natural gas deposit (Austria), the Snøhvit aquifer (Norway) and the K12B natural gas field exploited by Gaz de France in the Netherlands, in which it is necessary to ensure tightness. Other similar projects are being carried out around the world.
According to the BRGM")[20] 20 million tons of carbon dioxide each year will be stored in saline aquifers. Saline aquifers are formed by groundwater that is too salty to be used. Their capacity is estimated between 400 to 10 billion tons. The gas must be injected to a depth of at least 800 meters and under 800 bar of pressure at a temperature of 40 degrees in a "supercritical" form in equilibrium with their environment.
Geological storage
This technique uses the injection of carbon dioxide directly into underground geological formations. Oil fields and saline aquifers are ideal storage sites. Caves and ancient mines commonly used to store natural gas are not used due to lack of storage security.
CO is injected into declining oil fields for more than 30 years to increase the rate of oil recovery. This option is attractive because the cost of storage is offset by the sale of additional oil that has been generated. Other benefits of this technique come from the use of existing infrastructure and geophysical and geological studies carried out by oil exploration. All oil fields have a geological barrier that prevents the release of gaseous fluids (such as CO) in the future.
The disadvantages of oil fields lie in their geographical distribution and limited capacity.