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Abstract

Approximately one third of all CO 2 emissions due to human activity come from

fossil fuels used for generating electricity, with each power plant capable of emittingseveral million tones of CO 2 annually. A variety of other industrial processes also emit

large amounts of CO 2 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 CO 2. 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 CO 2.

Carbon capture and storage (CCS) is an approach to minimize global warming

by capturing carbon dioxide (CO 2) 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 CO 2 emissions to the atmosphere by

approximately 80-90% compared to a plant without CCS.

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1. INTRODUCTION

Carbon dioxide (CO 2) is a greenhouse gas that occurs naturally in the atmosphere .Human activities are increasing the concentration of CO 2 in the atmosphere thuscontributing to Earths global warming. CO 2 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 whenforests are burnt.Currently, 30 Gt per year of CO 2 is emitted due to human activities.Theincrease 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.

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One possible option for reducing CO 2 is to store it underground. This technique iscalled Carbon dioxide Capture and Storage (CCS).

In Carbon capture and storage (CCS), carbon dioxide (CO 2) 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 itinstead of releasing it into the atmosphere. Although CO 2 has been injected intogeological formations for various purposes, the long term storage of CO 2 is a relativelyuntried.

CCS applied to a modern conventional power plant could reduce CO 2 emissions tothe 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 CO 2, a stepneeded to assess the feasibility of CCS on a global scale. Technological options for CO 2 capture are then discussed in Section 4, while Section 5 focuses on methods of CO 2 transport. Following this, each of the storage options is addressed on section 6. Section6.1 focuses on geological storage, Section 6.2 on ocean storage, and Section 6.3 onmineral carbonation of CO 2 section 7 discus the risk of CO 2 leakage, The overall costsand economic potential of CCS are then discussed in Section 8, followed by theconclusion in Section 9.

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2. CARBON DIOXIDE CAPTURE AND STORAGE

One technique that could limit CO 2 emissions from human activities into theatmosphere is Carbon dioxide Capture and Storage (CCS). It involves collecting, at itssource, the CO 2 that is produced by power plants or industrial facilities and storing it awayfor a long time in underground layers, in the oceans, or in other materials

The process involves three main steps:

1. capturing CO 2, at its source, by separating it from other gases produced by anindustrial process

2. transporting the captured CO 2 to a suitable storage location (typically incompressed form)

3. storing the CO 2 away from the atmosphere for a long period of time, for instancein underground geological formations, in the deep ocean, or within certain mineralcompounds .

Fig 2.1 The three main components of the CCS process

Fig 2.2 The Esbjerg Power Station, a CO 2 capture site in Denmark

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3. THE CHARACTERISTICS OF CCS

Capture of CO2 can be applied to large point sources. The CO2 would then becompressed and transported for storage in geological formations, in the ocean, in mineralcarbonates2, or for use in industrial processes. Large point sources of CO2 include largefossil fuel or biomass energy facilities, major CO2-emitting industries, natural gas

production, synthetic fuel plants and fossil fuel-based hydrogen production plants (seeTable 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), oceanstorage (direct release into the ocean water column or onto the deep seafloor) andindustrial fixation of CO2 into inorganic carbonates. This report also discusses industrialuses 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 CO 2 sourceswith emissions of more than 0.1 million tonnes of CO 2 (MtCO 2) per year.

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4. SOURCES OF CO 2 EMISSIONS SUITABLE FOR CAPTURE ANDSTORAGE

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 co 2 emissions are.

Carbon dioxide could be captured from a large stationary emission sources such asa power plants or industrial facilities that produce large amounts of carbon dioxide. If such facilities are located near potential storage sites, for example suitable geologicalformations, they are possible candidates for the early implementation of CO 2 capture andstorage (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.

Fig 4.1 The Gibson coal power plant, a good example of a large stationary source.

Process Number of sources Emissions (MtCO 2 yr -1)

Fossil fuels Power 4,942 10,539

Cement production 1,175 932Refineries 638 798Iron and steel industry 269 646Petrochemical industry 470 379Oil and gas processing N/A 50Other sources 90 33BiomassBioethanol and bioenergy 303 91

Total 7,887 13,466

Table 4.1 Profile by process or industrial activity of worldwide large stationary CO 2 sourceswith emissions of more than 0.1 MtCO 2 per year.

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In 2000, close to 60% of the CO 2 emissions due to the use of fossil fuels were produced by large stationary emission sources, such as power plants and oil and gasextraction or processing industries (see Table 3.1).

Four major clusters of emissions from such stationary emission sources are: theMidwest and eastern USA, the northwestern part of Europe, the eastern coast of Chinaand the Indian subcontinent (see Figure 4.2).

Fig 4.2 Global Distribution of large CO2 sources

Many stationary emission sources lie either directly above, or within reasonable distance

(less than 300km) from areas with potential for geological storage (see Fig 4.2 & Fig 4.3)

Fig 4.3 Possible storage sites

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5. CO 2 CAPTURE

The purpose of CO 2 capture is to produce a concentrated stream of CO 2 at high pressure that can readily be transported to a storage site. Although, in principle, the entiregas stream containing low concentrations of CO 2 could be transported and injectedunderground, energy costs and other associated costs generally make this approachimpractical. It is therefore necessary to produce a nearly pure CO 2 stream for transportand storage. Applications separating CO 2 in large industrial plants, including natural gastreatment plants and ammonia production facilities, are already in operation today.Currently, CO 2 is typically removed to purify other industrial gas streams. Removal has

been used for storage purposes in only a few cases; in most cases, the CO 2 is emitted tothe atmosphere . Capture processes also have been used to obtain commercially usefulamounts of CO 2 from flue gas streams generated by the combustion of coal or natural gas.However, there have been no applications of CO 2 capture at large (e.g., 500 MW) power

plants.

Three systems are available for power plants: post-combustion, pre-combustion, andoxy fuel combustion systems. The captured CO 2 must then be purified and compressedfor transport and storage.

Fig 5.1 CO2 capture process.

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5.1 Post-Combustion Systems

This system separate CO 2 from the flue gases produced by the combustion of the primary fuel in air. These systems normally use a liquid solvent to capture the smallfraction of CO 2 (typically 315% by volume) present in a flue gas stream in which themain constituent is nitrogen (from air). For a modern pulverized coal (PC) power plant or a natural gas combined cycle (NGCC) power plant, current post-combustion capturesystems would typically employ an organic solvent such as monoethanolamine (MEA).

Fig 5.2 Gas turbine combine cycle with post-combustion

5.2 Pre-Combustion Systems

In this process the primary fuel in a reactor with steam and air or oxygen to produce amixture consisting mainly of carbon monoxide and hydrogen (synthesis gas).Additional hydrogen, together with CO 2, is produced by reacting the carbon monoxidewith steam in a second reactor (a shift reactor). The resulting mixture of hydrogen andCO 2 can then be separated into a CO 2 gas stream, and a stream of hydrogen. If the CO 2 isstored, the hydrogen is a carbon-free energy carrier that can be combusted to generate

power and/or heat. Although it is costly than post-combustion systems, the highconcentrations of CO 2 produced by the shift reactor (typically 15 to 60% by volume on adry basis) and the high pressures often encountered in these applications are morefavorable for CO 2 separation.

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Fig 5.3 Pre-combustion capture of CO 2

5.3 Oxyfuel Combustion Systems

This system use oxygen instead of air for combustion of the primary fuel to produce a flue gas that is mainly water vapour and CO 2. This results in a flue gas withhigh CO 2 concentrations (greater than 80% by volume). The water vapour is thenremoved by cooling and compressing the gas stream. Oxyfuel combustion requires theupstream separation of oxygen from air, with a purity of 9599% oxygen assumed inmost current designs. Further treatment of the flue gas may be needed to remove air

pollutants and non- condensed gases (such as nitrogen) from the flue gas before the CO 2 is sent to storage. As a method of CO 2 capture in boilers, oxyfuel combustion systems arein the demonstration phase. Oxyfuel systems are also being studied in gas turbine

Current post-combustion and pre-combustion systems for power plants could capture

8595% of the CO 2 that is produced. Higher capture efficiencies are possible, althoughseparation devices become considerably larger, more energy intensive and more costly.Capture and compression need roughly 1040% more energy than the equivalent plantwithout capture, depending on the type of system. Due to the associated CO 2 emissions,the net amount of CO 2 captured is approximately 8090%. Oxyfuel combustion systemsare, in principle, able to capture nearly all of the CO 2 produced. However, the need for additional gas treatment systems to remove pollutants such as sulphur and nitrogen oxideslowers the level of CO 2 captured to slightly more than 90%.

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6. CO 2 TRANSPORTATION

After capture, the CO 2 must be transported to suitable storage sites. Today Pipelinesoperate as a mature market technology and are the most common method for transportingCO 2. Gaseous CO 2 is typically compressed to a pressure above 8 MPa in order to avoidtwo-phase flow regimes and increase the density of the CO 2, thereby making it easier andless costly to transport. CO 2 also can be transported as a liquid in ships, road or railtankers that carry CO2 in insulated tanks at a temperature well below ambient, and atmuch lower pressures.

The first long-distance CO 2 pipeline came into operation in the early 1970s. In theUnited States, over 2,500 km of pipeline transports more than 40 Mt CO 2 per year fromnatural and anthropogenic sources, and it is mainly used for EOR. These pipelines operatein the dense phase mode (in which there is a continuous progression from gas to liquid,without a distinct phase change), and at ambient temperature and high pressure. In mostof these pipelines, the flow is driven by compressors at the upstream end, although some

pipelines have intermediate (booster) compressor stations.

In some situations or locations, transport of CO 2 by ship may be economically moreattractive, particularly when the CO 2 has to be moved over large distances or overseas.Liquefied petroleum gases (LPG, principally propane and butane) are transported on alarge commercial scale by marine tankers. CO 2 can be transported by ship in much thesame way (typically at 0.7 MPa pressure), but this currently takes place on a small scale

because of limited demand. The properties of liquefied CO 2 are similar to those of LPG,

and the technology could be scaled up to large CO 2 carriers if a demand for such systemswere to materialize.

Road and rail tankers also are technically feasible options. These systems transportCO 2 at a temperature of -20C and at 2 MPa pressure. However, they are uneconomicalcompared to pipelines and ships, except on a very small scale, and are unlikely to berelevant to large-scale CCS.

Fig 6.1 An LPG tanker-CO 2 can be transported in the similar way.

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7. CO 2 STORAGE (SEQUESTRATION)

Various forms have been conceived for permanent storage of CO 2. These formsinclude gaseous storage in various deep geological formations (including salineformations and exhausted gas fields), liquid storage in the ocean, and solid storage byreaction of CO 2 with metal oxides to produce stable carbonates .

7.1 Geological Storage.

Also known as geo-sequestration, this method involves injecting carbon dioxide,directly into underground geological formations. Geological formations are currentlyconsidered the most promising sequestration sites, and these are estimated to have astorage capacity of at least 2000 Gt CO 2 (currently, 30 Gt per year of CO2 is emitted dueto human activities). Oil fields , gas fields , saline formations, unminable coal seams , andsaline-filled basalt formations have been suggested as storage sites. Various physical(e.g., highly impermeable caprock) and geochemical trapping mechanisms would preventthe CO 2 from escaping to the surface. CO 2 is sometimes injected into declining oil fieldsto increase oil recovery ( enhanced oil recovery ).CO 2 storage in hydrocarbon reservoirs or deep saline formations is generally expected to take place at depths below 800 m, wherethe ambient pressures and temperatures will usually result in CO 2 being in a liquid or supercritical state. Under these conditions, the density of CO 2 will range from 50 to 80%of the density of water. This is close to the density of some crude oils, resulting in

buoyant forces that tend to drive CO 2 upwards. Fig7.1.1 shows some of the methods usedin geological storage.

This option is attractive because the storage costs may be partly offset by the sale of additional oil that is recovered

Unminable coal seams can be used to store CO 2 because CO 2 adsorbs to the surfaceof coal. However, the technical feasibility depends on the permeability of the coal bed. Inthe process of absorption the coal releases previously absorbed methane, and the methanecan be recovered ( enhanced coal bed methane recovery ). The sale of the methane can

be used to offset a portion of the cost of the CO 2 storage.

Saline formations contain highly mineralized brines, and have so far been considered

of no benefit to humans. Saline aquifers have been used for storage of chemical waste in afew cases. The main advantage of saline aquifers is their large potential storage volumeand their common occurrence. This will reduce the distances over which CO 2 has to betransported. The major disadvantage of saline aquifers is that relatively little is knownabout them, compared to oil fields.

For well-selected, designed and managed geological storage sites, IPCC estimatesthat CO 2 could be trapped for millions of years, and the sites are likely to retain over 99%of the injected CO 2 over 1,000 years.

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Fig 7.1.1 Geological storage options.

Reservoir type

Lower estimate of storage capacity (GtCO 2)

Upper estimate of storage capacity (GtCO 2)

Oil and gas fields 675 a 900 a

Unminable coalseams (ECBM)

3-15 200

Deep saline

formations

1,000 Uncertain, but

possibly 104

Table 7.1.1 Storage capacity for several geological storage options.

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8. METHODOLOGICAL FRAMEWORK FOR CO2 CAPTURE AND STORAGESYSTEMS

8.1 Greenhouse Gas Inventories

The two main options for including CCS in national greenhouse gas inventories have been identified and analysed using the current methodological framework for total chainfrom capture to storage (geological and ocean storage). These options are: Sourcereduction: To evaluate the CCS systems as mitigation options to reduce emissions to theatmosphere;

Figure 8. 1 Simplified flow diagram of possible CO 2 emission sources during CCS

Sink enhancement: To evaluate the CCS systems using an analogy with the treatmentmade to CO2 removals by sinks in the sector Land Use, Land-Use Change and Forestry.A balance is made of the CO2 emissions and removals to obtain the net emission or removal. In this option, removals by sinks are related to CO2 storage. In both options,estimation methodologies could be developed to cover most of the emissions in the CCSsystem (see Figure 9.1), and reporting could use the current framework for preparation of national greenhouse gas inventories. In the first option, reduced emissions could bereported in the category where capture takes place. For instance, capture in power plantscould be reported using lower emission factors than for plants without CCS. But thiscould reduce transparency of reporting and make review of the overall impact onemissions more difficult, especially if the capture process and emissions fromtransportation and storage are not linked. This would be emphasized where transportationand storage includes captured CO2 from many sources, or when these take place acrossnational borders. An alternative would be to track CO2 flows through the entire captureand storage system making transparent how much CO2 was produced, how much wasemitted to the atmosphere at each process stage, and how much CO2 was transferred tostorage.

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The second option is to report the impact of the CCS system as a sink. For instance,reporting of capture in power plants would not alter the emissions from the combustion

process but the stored amount of CO2 would be reported as a removal in the inventory.Application of the second option would require adoption of new definitions not availablein the UNFCCC or in the current methodological framework for the preparation of inventories. UNFCCC (1992) defines a sink as any process, activity or mechanism whichremoves a greenhouse gas, an aerosol, or a precursor of a greenhouse gas from theatmosphere. Although removal was not included explicitly in the UNFCCC definitions,it appears associated with the sink concept. CCS11 systems do not meet the UNFCCCdefinition for a sink, but given that the definition was agreed without having CCS systemsin mind, it is likely that this obstacle could be solved (Torvanger et al., 200 ). Generalissues of relevance to CCS systems include system boundaries (sectoral, spatial andtemporal) and these will vary in importance with the specific system and phases of thesystem. The basic methodological approaches for system components, together with thestatus of the methods and availability of data for these are discussed below. Mineralcarbonation and industrial use of CO2 are addressed separately.

8.2 Ocean Storage

A potential CO 2 storage option is to inject captured CO 2 directly into thedeep ocean (at depths greater than 1,000 m), where most of it would be isolated from theatmosphere for centuries. This can be achieved by transporting CO 2 via pipelines or shipsto an ocean storage site, where it is injected into the water column of the ocean or at thesea floor. The dissolved and dispersed CO 2 would subsequently become part of the globalcarbon cycle . Fig 8.2 shows some of the main methods that could be employed. Oceanstorage has not yet been deployed or demonstrated at a pilot scale, and is still in theresearch phase. However, there have been small- scale field experiments and 25 years of theoretical, laboratory and modeling studies of intentional ocean storage of CO 2.

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Fig 8.2 Ocean storage methods.

CO2 injection, however, can harm marine organisms near the injection point. It isfurthermore expected that injecting large amounts would gradually affect the wholeocean. Because of its environmental implications, CO2 storage in oceans is generally nolonger considered as an acceptable option

8.3 Mineral Storage

Through chemical reactions with some naturally occurring minerals, CO 2 isconverted into a solid form through a process called mineral carbonation and storedvirtually permanently. This is a process which occurs naturally, although very slowly.

These chemical reactions can be accelerated and used industrially to artificially storeCO 2 in minerals. However, the large amounts of energy and mined minerals neededmakes this option less cost effective.

Earthen Oxide Percent of Crust Carbonate Enthalpy change(kJ/mol)

SiO 2 59.71

Al2O3 15.41

CaO 4.90 CaCO 3 -179

MgO 4.36 MgCO 3 -117

Na 2O 3.55 Na 2CO 3

FeO 3.52 FeCO 3

K 2O 2.80 K 2CO 3

Fe2O3 2.63 FeCO 3

21.76 All Carbonates

Table 8.1 Principal metal oxides of Earth's Crust . Theoretically up to 22% of thismineral mass is able to form carbonates .

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9. RISK OF LEAKAGE

The risks due to leakage from storage of CO 2 in geological reservoirs fall into two broad categories: global risks and local risks. Global risks involve the release of CO 2 thatmay contribute significantly to climate change if some fraction leaks from the storageformation to the atmosphere . In addition, if CO 2 leaks out of a storage formation, localhazards may exist for humans, ecosystems and groundwater . These are the local risks.

Fig 9.1 Geological leakage routes

10 THE CURRENT STATUS OF CCS TECHNOLOGY

There are different types of CO2 capture systems: postcombustion, pre-combustionand oxyfuel combustion. The concentration of CO2 in the gas stream, the pressure of thegas stream and the fuel type (solid or gas) are important factors in selecting the capturesystem. Post-combustion capture of CO2 in power plants is economically feasible under specific conditions5. It is used to capture CO2 from part of the flue gases from a number of existing power plants. Separation of CO2 in the natural gas processing industry, whichuses similar technology, operates in a mature market6.

The technology required for pre-combustion capture is widely applied in fertilizer

manufacturing and in hydrogen production. Although the initial fuel conversion steps of pre-combustion are more elaborate and costly, the higher concentrations of CO2 in the

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gas stream and the higher pressure make the separation easier. Oxyfuel combustion is inthe demonstration phase7 and uses high purity oxygen.

This results in high CO2 concentrations in the gas stream and, hence, in easier separation of CO2 and in increased energy requirements in the separation of oxygen fromair.

Pipelines are preferred for transporting large amounts of CO2 for distances up toaround 1,000 km. For amounts smaller than a few million tones of CO2 per year or for larger distances overseas, the use of ships, where applicable, could be economically moreattractive. Pipeline transport of CO2 operates as a mature market technology (in the USA,over 2,500 km of pipelines transport more than 40 MtCO2 per year). In most gas

pipelines, compressors at the upstream end drive the flow, but some pipelines needintermediate compressor stations.

Dry CO2 is not corrosive to pipelines, even if the CO2 contains contaminants. Wherethe CO2 contains moisture, it is removed from the CO2 stream to prevent corrosion andto avoid the costs of constructing pipelines of corrosion-

Figure 10.1 Schematic representations of capture systems.

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11. THE LOCAL HEALTH, SAFETY AND ENVIRONMENT RISKS OF CCS

The local risks24 associated with CO2 pipeline transport could be similar to or lower than those posed by hydrocarbon pipelines already in operation. For existing CO2

pipelines, mostly in areas of low population density, accident numbers reported per kilometre pipeline are very low and are comparable to those for hydrocarbon pipelines. Asudden and large release of CO2 would pose immediate dangers to human life and health,if there were exposure to concentrations of CO2 greater than 710% by volume in air.Pipeline transport of CO2 through populated areas requires attention to route selection,overpressure protection, leak detection and other design factors. No major obstacles to

pipeline design for CCS are foreseen.

With appropriate site selection based on available subsurface information, amonitoring programme to detect problems, a regulatory system and the appropriate use of remediation methods to stop or control CO2 releases if they arise, the local health, safetyand environment risks of geological storage would be comparable to the risks of currentactivities such as natural gas storage, EOR and deep underground disposal of acid gas.

Natural CO2 reservoirs contribute to the understanding of the behaviour of CO2underground. Features of storage sites with a low probability of leakage include highlyimpermeable caprocks, geological stability, absence of leakage paths and effectivetrapping mechanisms. There are two different types of leakage scenarios: (1) abruptleakage, through injection well failure or leakage up an abandoned well, and (2) gradualleakage, through undetected faults, fractures or wells. Impacts of elevated CO2concentrations in the shallow subsurface could include lethal effects on plants and subsoilanimals and the contamination of groundwater. High fluxes in conjunction with stableatmospheric conditions could lead to local high CO2 concentrations in the air that couldharm animals or people. Pressure build-up caused by CO2 injection could trigger smallseismic events.

12. THE LEGAL AND REGULATORY ISSUES FOR IMPLEMENTING COSTORAGE

1. Some regulations for operations in the subsurface do exist that may be relevant or,in some cases, directly applicable to geological storage, but few countries have specifically developed legal or regulatory frameworks for long-term CO2 storage.Existing laws and regulations regarding inter alia mining, oil and gas operations, pollutioncontrol, waste disposal, drinking water, treatment of high-pressure gases and subsurface

property rights may be relevant to geological CO2 storage. Long-term liability issuesassociated with the leakage of CO2 to the atmosphere and local environmental impactsare generally unresolved. Some States take on longterm responsibility in situationscomparable to CO2 storage, such as underground mining operations.

2. No formal interpretations so far have been agreed upon with respect to whether or

under what conditions CO2 injection into the geological sub-seabed or the ocean iscompatible. There are currently several treaties (notably the London26 and OSPAR27

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Conventions) that potentially apply to the injection of CO2 into the geological sub-seabedor the ocean. All of these treaties have been drafted without specific considerationof CO2 storage.

13. THE IMPLICATIONS OF CCS FOR EMISSION INVENTORIES ANDACCOUNTING

The current IPCC Guidelines2 do not include methods specific to estimatingemissions associated with CCS. The general guidance provided by the IPCC can beapplied to CCS. A few countries currently do so, in combination with their nationalmethods for estimating emissions. The IPCC guidelines themselves do not yet providespecific methods for estimating emissions associated with CCS. These are expected to be

provided in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Specificmethods may be required for the net capture and storage of CO2, physical leakage,fugitive emissions and negative emissions associated with biomass applications of CCSsystems .

The few current CCS projects all involve geological storage, and there is thereforelimited experience with the monitoring, verification and reporting of actual physicalleakage rates and associated uncertainties. Several techniques are available or under development for monitoring and verification of CO2 emissions from CCS, but these varyin applicability, site specificity, detection limits and uncertainties.

CO2 might be captured in one country and stored in another with differentcommitments. Issues associated with accounting for cross-border storage are not uniqueto CCS. Rules and methods for accounting may have to be adjusted accordingly. Possible

physical leakage from a storage site in the future would have to be accounted.

14 THE GAPS IN KNOWLEDGE

There are gaps in currently available knowledge regarding some aspects of CCS.Increasing knowledge and experience would reduce uncertainties and thus facilitatedecision-making with respect to the deployment of CCS for climate change mitigation.

15 APPROACHES AND TECHNOLOGIES FOR MONITORING

ENVIRONMENTAL EFFECTSTechniques now being used for field experiments could be used to monitor some near

field consequences of direct CO2 injection. For example, researchers (Barry et al., 2004,2005; Carman et al., 2004; Thistle et al., 2005) have been developing experimental meansfor observing the consequences of elevated CO2 on organisms in the deep ocean.However, such experiments and studies typically look for evidence of acute toxicity in anarrow range of species (Sato, 2004; Caulfield et al., 1997; Adams et al., 1997; Tamburriet al., 2000). Sub-lethal effects have been studied by Kurihara et al. (2004). Processstudies, surveys of biogeochemical tracers, and ocean bottom studies could be used to

evaluate changes in ecosystem structure and dynamics both before and after an injection.It is less clear how best to monitor the health of broad reaches of the ocean interior

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Ongoing long-term surveys of biogeochemical tracers and deep-sea biota could help todetect long-term changes in deep-sea ecology.

16 ENVIRONMENTAL IMPACTS, RISKS, AND RISK MANAGEMENT

Overall, there is limited knowledge of deep-sea population and community structureand of deep-sea ecological interactions. Thus the sensitivities of deep ocean ecosystemsto intentional carbon storage and the effects on possibly unidentified goods and servicesthat they may provide remain largely unknown. Most ocean storage proposals seek tominimize the volume of water with high CO2 concentrations either by diluting the CO2 ina large volume of water or by isolating the CO2 in a small volume (e.g., in CO2 lakes).

Nevertheless, if deployed widely, CO2 injection strategies ultimately will produce largevolumes of water with somewhat elevated CO2 concentrations (Figure 6.15). Becauselarge amounts of relatively pure CO2 have never been introduced to the deep ocean in acontrolled experiment, conclusions about environmental risk must be based primarily onlaboratory and small-scale in-situ experiments and extrapolation from these experimentsusing conceptual and mathematical models. Natural analogues (Box 6.5) can be relevant,

but differ significantly from proposed ocean engineering projects. Compared to thesurface, most of the deep sea is stable and varies little in its physiochemical factors over time. The process of evolutionary selection has probably eliminated individuals apt toendure environmental perturbation. As a result, deep-sea organisms may be moresensitive to environmental disturbance than their shallow water cousins (Shirayama,1997). Ocean storage would occur deep in the ocean where there is virtually no light and

photosynthesizing organisms are lacking, thus the following discussion primarilyaddresses CO2 effects on heterotrophic organisms, mostly animals. The diverse fauna thatlives in the waters and sediments of the deep ocean can be affected by ocean CO2storage, leading to change in ecosystem composition and functioning. Thus, the effects of CO2 need to be identified at the level of both the individual (physiological) and theecosystem.

Introduction of CO2 into the ocean either directly into sea water or as a lake on thesea floor would result in changes in dissolved CO2 near to and down current from adischarge point. Dissolving CO2 in sea water increases the partial pressure of CO2(pCO2, expressed as a ppm fraction of atmospheric pressure, equivalent to atm), causesdecreased pH (more acidic) and decreased CO3 2 concentrations (less saturated). Thiscan lead to dissolution of CaCO3 in sediments or in shells of organisms. Bicarbonate(HCO3 ) is then produced from carbonate (CO3 2). The spatial extent of the waters

with increased CO2 content and decreased pH will depend on the amount of CO2released and the technology and approach used to introduce that CO2 into the ocean.Table shows the amount of sea water needed to dilute each tonne of CO2 to a specified.pH reduction. Further dilution would reduce the fraction of ocean at one .pHPhotosynthesis produces organic matter in the ocean almost exclusively in the upper 200m where there is both light and nutrients (e.g., PO4, NO3, NH4 +, Fe). Photosynthesisforms the base of a marine food chain that recycles much of the carbon and nutrients inthe upper ocean. Some of this organic matter ultimately sinks to the deep ocean as

particles and some of it is mixed into the deep ocean as dissolved organic matter. The fluxof organic matter from the surface ocean provides most of the energy and nutrients tosupport the heterotrophic ecosystems of the deep ocean (Gage and Tyler, 1991). With the

exception of the oxygen minimum zone and near volcanic CO2 vents, most organismsliving in the deep ocean live in low and more or less constant CO2 levels.8th Semester Dept. of Mechanical Engineering GNDEC Bidar

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table : Relationships between . p H, changes in p CO 2 , and dissolved inorganic carbonconcentration calculated for mean deep-sea conditions.

17. COST OF CO2 CAPTURE AND STOREGE OPERATIONS

CCS applied to a modern conventional power plant could reduce CO 2 emissions tothe atmosphere by approximately 80-90% compared to a plant without CCS. Capturingand compressing CO 2 requires much energy and would increase the fuel needs of a coal-fired plant with CCS by about 25%. These and other system costs are estimated toincrease the cost of energy from a new power plant with CCS by 21-91%.

Naturalgas combinedcycle

Pulverized coal

Integratedgasification combinedcycle

Without capture(reference plant)

0.03 - 0.05 0.04 -0.05

0.04 - 0.06

With captureand geological storage

0.04 - 0.08 0.06 -0.10

0.06 - 0.09

With captureand Enhanced oil

recovery

0.04 - 0.07 0.05 -0.08

0.04 - 0.08

Table 17.1 Costs of energy with and without CCS (2002 US$ per kWh )

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18 THE FUTURE OF CO 2 CAPTURE AND STORAGE

CO2 capture and storage is technologically feasible and could play a significantrole in reducing greenhouse gas emissions over the course of this century. Butmany issues still need to be resolved before it can be deployed on a large scale.

Full-scale projects in the electricity sector are needed to build knowledge andexperience. More studies are required to analyse and reduce the costs and toevaluate the suitability of potential geological storage sites. Also, pilot scaleexperiments on mineral carbonation are needed.

An adequate legal and regulatory environment also needs to be created, and barriers to deployment in developing countries need to be addressed.

If knowledge gaps are filled and various conditions are met, CO2 capture and

storage systems could be deployed on a large scale within a few decades, as longas policies substantially limiting greenhouse gas emissions are put into place.

The scientific consensus views carbon capture and storage as one of the importantoptions for reducing CO2 emissions. If it were deployed, the cost of stabilizing theconcentration of greenhouse gases in the atmosphere would be reduced by 30% or more.

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19 CONCLUSION

Large reductions in emissions of CO 2 to the atmosphere are likely to be neededto avoid major climate change. Capture and storage ofCO 2, in combination with other CO 2 abatement techniques, could enable these large reductions to be achieved with leastimpact on the global energy infrastructure and the economy. Capture and storage is

particularly well suited to use in central power generation and many energy-intensiveindustrial processes. CO 2 capture and storage technology also provides a means of introducing hydrogen as an energy carrier for distributed and mobile energy users.

For power stations, the cost of capture and storage is about $50/t ofCO 2 avoided.

This compares favorably with the cost of many other options considered for achievinglarge reductions in emissions. Use of this technique would allow continued provision of large-scale energy supplies using the established energy infrastructure. There isconsiderable scope for new ideas to reduce energy consumption and costs of CO 2 captureand storage which would accelerate the development and introduction of this technology

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REFERENCES

1. Department of Trade and Industry (UK), Gasification of Solid and Liquid Fuelsfor Power Generation, report TSR 008, Dec. 1998

2. Department of Trade and Industry (UK), Supercritical Steam Cycles for Power Generation Applications, report TSR 009, Jan. 1999

3. Durie R, Paulson C, Smith A and Williams D, Proceedings of the 5thInternationalConference on Greenhouse Gas Control Technologies, CSIRO(Australia)

publications, 2000

4. Eliasson B, Riemer P W F and Wokaun A (editors), Greenhouse Gas ControlTechnologies, Proceedings of the 4th International Conference, Elsevier ScienceLtd., Oxford 1999

5. Herzog H, Eliasson B and Kaarstad O, Capturing Greenhouse Gases, ScientificAmerican, Feb. 2000 , 54-61

6. Intergovernmental Panel on Climate Change (IPCC), Climate Change 1995 -TheScience of Climate Change, Cambridge University Press, 1996

7. International Energy Agency, Key World Energy Statistics, 1999 edition.IEAGreenhouse Gas R&D Programme, Transport &Environmental Aspects of Carbon

Dioxide Sequestration, 1995 , ISBN 1 898373 22 18. IEA Greenhouse Gas R&D Programme, Abatement of Methane Emissions,

June1998 , ISBN 1 898 373 16 7

9. IEA Greenhouse Gas R&D Programme, Ocean Storage of CO2, Feb. 1999 , ISBN1 898 373 25 6

10. IEA Greenhouse Gas R&D Programme, The Reduction of Greenhouse GasEmissions from the Cement Industry, report PH3/7, May 1999

11. IEA Greenhouse Gas R&D Programme, The Reduction of Greenhouse GasEmissions from the Oil Refining and Petrochemical Industry, report PH3/8, June1999

12. www.ipcc.ch

13. www.Greenfacts.org

14. www.ieagreen.org.uk

8th Semester Dept. of Mechanical Engineering GNDEC Bidar