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Abstract
Approximately one third of all CO2 emissions due to human activity come from fossil fuels used for generating electricity, with each power plant capable of emitting several million tones of CO2 annually. A variety of other industrial processes also emit large amounts of CO2 from each plant, for example oil refineries, cement works, and iron and steel production. These emissions could be reduced substantially, without major changes to the basic process, by capturing and storing the CO2. Other sources of emissions, such as transport and domestic buildings, cannot be tackled in the same way because of the large number of small sources of CO2.
Carbon capture and storage (CCS) is an approach to minimize global warming by capturing carbon dioxide (CO2) from large point sources such as fossil fuel power plants and storing it instead of releasing it into the atmosphere CCS applied to a modern conventional power plant could reduce CO2 emissions to the atmosphere by approximately 80-90% compared to a plant without CCS.
1. INTRODUCTION
Carbon dioxide (CO2) is a greenhouse gas that occurs naturally in the atmosphere. Human activities are increasing the concentration of CO2 in the atmosphere thus contributing to Earth’s global warming. CO2 is emitted when fuel is burnt – be it in large power plants, in car engines, or in heating systems. It can also be emitted by some other industrial processes, for instance when resources are extracted and processed, or when forests are burnt.Currently, 30 Gt per year of CO2 is emitted due to human activities.The increase in concentration of carbon in the past two hundred years is shown in the Fig 1.1
Fig 1.1 Increase in concentration of CO2 in past two centuries
Fig 1.2 Increase in global temperature in past 200 years.
One possible option for reducing CO2 is to store it underground. This technique is called Carbon dioxide Capture and Storage (CCS).
In Carbon capture and storage (CCS), carbon dioxide (CO2) is capured from large point sources (A point source of pollution is a single identifiable localized source of air, water, thermal, noise or light pollution).such as fossil fuel power plants and storing it instead of releasing it into the atmosphere. Although CO2 has been injected into geological formations for various purposes, the long term storage of CO2 is a relatively untried.
CCS applied to a modern conventional power plant could reduce CO2 emissions to the atmosphere by approximately 80-90% compared to a plant without CCS.
Fig 1.3 Power plants with and with out CCS.
The section2 presents the general framework for the assessment together with a brief overview of CCS systems. Section 3 then describes the major sources of CO2, a step needed to assess the feasibility of CCS on a global scale. Technological options for CO2 capture are then discussed in Section 4, while Section 5 focuses on methods of CO2 transport. Following this, each of the storage options is addressed on section 6. Section 6.1 focuses on geological storage, Section 6.2 on ocean storage, and Section 6.3 on mineral carbonation of CO2 section 7 discus the risk of CO2 leakage, The overall costs and economic potential of CCS are then discussed in Section 8, followed by the conclusion in Section 9.
2. CARBON DIOXIDE CAPTURE AND STORAGE
One technique that could limit CO2 emissions from human activities into the atmosphere is Carbon dioxide Capture and Storage (CCS). It involves collecting, at its source, the CO2 that is produced by power plants or industrial facilities and storing it away for a long time in underground layers, in the oceans, or in other materials
The process involves three main steps:
1. capturing CO2, at its source, by separating it from other gases produced by an industrial process
2. transporting the captured CO2 to a suitable storage location (typically in compressed form)
3. storing the CO2 away from the atmosphere for a long period of time, for instance in underground geological formations, in the deep ocean, or within certain mineral compounds.
Fig 2.1 The three main components of the CCS process
Fig 2.2 The Esbjerg Power Station, a CO2 capture site in Denmark
3. THE CHARACTERISTICS OF CCS
Capture of CO2 can be applied to large point sources. The CO2 would then be compressed and transported for storage in geological formations, in the ocean, in mineral carbonates2, or for use in industrial processes. Large point sources of CO2 include large fossil fuel or biomass energy facilities, major CO2-emitting industries, natural gas production, synthetic fuel plants and fossil fuel-based hydrogen production plants (see Table 3.1).
Potential technical storage methods are: geological storage (in geological formations, such as oil and gas fields, unminable coal beds and deep saline formations3), ocean storage (direct release into the ocean water column or onto the deep seafloor) and industrial fixation of CO2 into inorganic carbonates. This report also discusses industrial uses of CO2, but this is not expected to contribute much to the reduction of CO2emissions.
Table 3.1. Profile by process or industrial activity of worldwide large stationary CO2 sources with emissions of more than 0.1 million tonnes of CO2 (MtCO2) per year.
4. SOURCES OF CO2 EMISSIONS SUITABLE FOR CAPTURE AND STORAGE
Several factors determine whether carbon dioxide capture is a viable option for a particular emission source:
• The size of the emission source,
• Whether it is stationary or mobile,
• How near it is to potential storage sites, and
• How concentrated its co2 emissions are.
Carbon dioxide could be captured from a large stationary emission sources such as a power plants or industrial facilities that produce large amounts of carbon dioxide. If such facilities are located near potential storage sites, for example suitable geological formations, they are possible candidates for the early implementation of CO2 capture and storage (CCS).
Small or mobile emission sources in homes, businesses or transportation are not being considered at this stage because they are not suitable for capture and storage.