Carbon Sequestration - Internal

Carbon sequestration is the processes of removing carbon from the atmosphere in order to help mitigate global warming. Sequestration is a new technology and a variety of ways of artificially capturing and storing carbon are being explored. Research is on-going of also enhancing natural sequestration processes.

NATURAL SEQUESTRATION also known as carbon sinks:

LAND: Vegetation and soils are widely recognized as carbon storage sinks. The global biosphere absorbs roughly 2 billion tons of carbon annually, an amount equal to roughly one third of all global carbon emissions from human activity. Significant amounts of this carbon remains stored in the roots of certain plants and in the soil. In fact, the inventory of carbon stored in the global ecosystem equals rougly 1,000 years worth of annual absorption, or 2 trillion tons of carbon. Check out Deforestation issues for more.

OCEANS: CO2 is soluble in ocean water, and through natural processes the oceans both absorb and emit huge amounts of CO2 into the atmosphere. In fact, the amount of carbon stored in the ocean dwarfs the carbon stored in terrestrial ecosystems.

ROCK: Carbon dioxide sequestration in geologic formations includes oil and gas reservoirs, unmineable coal seams, and deep saline reservoirs. These are structures that have stored crude oil, natural gas, brine and CO2 over millions of years.

Before carbon dioxide (CO2) gas can be sequestered it must be captured as a relatively pure gas. CO2 is routinely separated and captured as a by-product from industrial processes such as synthetic ammonia production, H2 production, and limestone calcination. Large point sources of CO2 emissions include electricity generation units, petroleum refineries, and cement and lime production facilities.

Most power plants and other large point sources use air-fired combustors, a process that exhausts CO2 diluted with nitrogen. Flue gas from coal-fired power plants contains 10-12 percent CO2 by volume, while flue gas from natural gas combined cycle plants contains only 3-6 percent CO2. For effective carbon sequestration, the CO2 in these exhaust gases must be separated and concentrated.

CO2 is currently recovered from combustion exhaust by using amine absorbers and cryogenic coolers.

Research into new capture and sequestration techniques has identified the following options for CO2 separation and capture:

Absorption (chemical and physical)
Adsorption (physical and chemical)
Low-temperature distillation
Gas separation membranes
Mineralization and biomineralization

Examples of sequestration: The Norwegian oil company, Statoil, is injecting approximately one million tonnes per year of recovered CO2 into the Utsira Sand, a saline formation under the sea associated with the Sleipner West Heimdel gas reservoir. The amount being sequestered is equivalent to the output of a 150-megawatt coal-fired power plant.

Environmental Practice at Work Publishing Company Ltd.