By Aaron Wagner,2014-07-30 19:10
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    Emilio Muñoz, Eva Díaz, Salvador Ordóñez, Aurelio Vega

    University of Oviedo, Oviedo, Spain


    The increasing atmospheric CO2 concentration, mainly caused by fossil fuel

    combustion, have become an important concern for global warming because the atmospheric

    CO2 concentrations increased significantly in the last century and rises continuously at a

    faster rate. Carbon dioxide is produced in large quantities by many important industries such

    as fossil-fuel-fired power plants, steel production, chemical and petrochemical manufacturing,

    cement production, and natural gas purification. The reasons for the CO2

    removal are

    traditionally technical and economical concerns. Carbon dioxide present in natural gas will

    reduce the heating value of the gas and as an acid component it has the potential to cause

    corrosion in pipes and process equipment and also to cause catalyst poisoning in ammonia

    synthesis (1). In the past decades, CO2 removal from flue gas streams started

    as a

    potentially economic source of CO2, mainly for enhanced oil recovery

    operations. Moreover,

    CO2 was also produced for other industrial applications such as carbonation of brine, welding

    as an inert gas, food and beverage carbonation, dry ice, urea production, and soda ash

    industry (2). However, environmental concerns, such as the global climate change, are now

    focused as one of the most important and challenging environmental issues facing the world

    community, and have motivated intensive research on CO2 capture and


    Carbon dioxide as one of the greenhouse gases (GHG) is currently responsible for over 60 %

of the enhanced greenhouse effect, methane (CH4) contributes 20 %, and the

    remaining 20

    % is caused by nitrous oxide (N2O), a number of industrial gases, and ozone. Scientific

    evidence now strongly suggests that increased levels of GHG may lead to higher

    temperature, and cause climate change on a global scale. Various climate models estimate

    that the global average temperature may rise by about 1.4 5.8 ºC by the year

    2100 (3).

    The standard method to removal CO2 break down the whole system into its

    component parts: capture, transport, and storage. The capture and ulterior storage in a

    geologic reservoir is, nowadays, the technique more useful to reduce the CO2


    in the atmosphere. However, the total amount of antrophogenic carbon dioxide that is

    captured is lower than 19 Mt/year. The reason is because the capture is only possible for

    large stationary sources of CO2, like power plants or cement fabrics. The large stationary

    sources produce around 60 % of the total carbon dioxide, which is 14 Gt CO2/year.

    Below, each of these components is defined:

     Capture, is the production of a CO2 stream that is ready for transport and

    storage. CO2

    from large industrial sources is usually part of a stream composed of several gases. In

    general, the CO2 is separated as a fairly pure stream (90-99% pure) and then compressed to over 100 atm. While power plants are the largest single source of CO2

    (over a third of all CO2 emissions), other industrial operations (e.g., ammonia plants,

    refineries, natural gas processing) also provide attractive targets. In most cases,

    capture (including compression) is by far the largest cost component (typically 80% of

    the costs for power plants) (4), Table 1.

     Transport is moving CO2 from the capture site to the storage site. For moving large

    amounts of CO2, pipeline transport is almost always the preferred mode. Small amounts of CO2 can be transported via truck, while tanker ships are being


    for some circumstances.

     Storage is comprised of injecting CO2 into a reservoir. Monitoring and

    verification fall

    under this component.

    Some processes (e.g. acid gas processing, hydrogen and ammonia production)

    produce point sources of highly concentrated or pure CO2. The process

    already includes CO2

    separation therefore these sources typically only require compression and dehydration for

    CO2 capture and therefore the capture cost is relatively low (4-8 ?/t CO2).

    However, these

    sources are typically dispersed and small scale with the total current worldwide, estimated to

    be around 120 Mt/year. The power sector represents the largest opportunity for capture and

    storage. In the power sector, capture using existing technologies such as post-combustion

    amine systems have a current costs in the range of 32-48?/t CO2, avoided for

    new build

    projects using pulverised coal or natural gas combined cycle generation (2,6). Integrated

    gasification combined cycle (IGCC), an emerging coal or coke-based technology for power

    generation offers the lowest cost of capture for power at 12-20?/t CO2 as the

    CO2 stream is

already concentrated (7).

    Thus, it is evident that the fact of obtaining an economically technique to capture the

    cabon dioxide is of prime concern.

    Types of techniques for capture of CO2