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" Does not include monitoring costs.

b Includes offshore transportation costs; range represents 100-500 km distance offshore and 3000 m depth.

c Unlike geological and ocean storage, mineral carbonation requires significant energy inputs equivalent to approximately 40% of the power plant output.

" Does not include monitoring costs.

b Includes offshore transportation costs; range represents 100-500 km distance offshore and 3000 m depth.

c Unlike geological and ocean storage, mineral carbonation requires significant energy inputs equivalent to approximately 40% of the power plant output.

8.2.3.2 Ocean storage4

The cost of ocean storage is a function of the distance offshore and injection depth. Cost components include offshore transportation and injection of the CO2. Various schemes for ocean storage have been considered. They include:

• tankers to transport low temperature (-55 to -50oC), high pressure (0.6-0.7 MPa) liquid CO2 to a platform, from where it could be released through a vertical pipe to a depth of 3000m;

• carrier ships to transport liquid CO2, with injection through a towed pipe from a moving dispenser ship;

• undersea pipelines to transport CO2 to an injection site.

Table 8.2 provides a summary of costs for transport distances of 100-500 km offshore and an injection depth of 3000 m.

Chapter 6 also discusses the option of carbonate neutralization, where flue-gas CO2 is reacted with seawater and crushed limestone. The resulting mixture is then released into the upper ocean. The cost of this process has not been adequately addressed in the literature and therefore the possible cost of employing this process is not addressed here.

8.2.3.3 Storage via mineral carbonation5 Mineral carbonation is still in its R&D phase, so costs are uncertain. They include conventional mining and chemical processing. Mining costs include ore extraction, crushing and grinding, mine reclamation and the disposal of tailings and carbonates. These are conventional mining operations and several studies have produced cost estimates of 10 US$/tCO2 (36 US$/tC) or less. Since these estimates are based on similar mature and efficient operations, this implies that there is a strong lower limit on the cost of mineral storage. Carbonation costs include chemical activation and carbonation. Translating today's laboratory implementations into industrial practice yields rough cost estimates of about 50-100 US$/tCO2 stored

4 This section is based on material presented in Section 6.9. The reader is referred to that section for a more detailed analysis and literature references.

5 This section is based on material presented in Section 7.2. The reader is referred to that section for a more detailed analysis and literature references.

(180-370 US$/tC). Costs and energy penalties (30-50% of the power plant output) are dominated by the activation of the ore necessary to accelerate the carbonation reaction. For mineral storage to become practical, additional research must reduce the cost of the carbonation step by a factor of three to four and eliminate a significant portion of the energy penalty by, for example, harnessing as much as possible the heat of carbonation.

8.2.4 Integrated sys tems

The component costs given in this section provide a basis for the calculation of integrated system costs. However, the cost of mitigating CO2 emissions cannot be calculated simply by summing up the component costs for capture, transport and storage in units of 'US$/tCO2'. This is because the amount of

Reference Plant

Plant with CCS

CO2 avoided

CO2 captured

C02 produced (kg/kWh)

Figure 8.2 CO2 capture and storage from power plants. The increased CO2 production resulting from loss in overall efficiency of power plants due to the additional energy required for capture, transport and storage, and any leakage from transport result in a larger amount of 'CO2 produced per unit of product'(lower bar) relative to the reference plant (upper bar) without capture

Box 8.1 Defining avoided costs for a fossil fuel power plant

In general, the capture, transport, and storage of CO2 require energy inputs. For a power plant, this means that amount of fuel input (and therefore CO2 emissions) increases per unit of net power output. As a result, the amount of CO2 produced per unit of product (e.g., a kWh of electricity) is greater for the power plant with CCS than the reference plant, as shown in Figure 8.2 To determine the CO2 reductions one can attribute to CCS, one needs to compare CO2 emissions of the plant with capture to those of the reference plant without capture. These are the avoided emissions. Unless the energy requirements for capture and storage are zero, the amount of CO2 avoided is always less than the amount of CO2 captured. The cost in US$/tonne avoided is therefore greater than the cost in US$/tonne captured.

CO2 captured will be different from the amount of atmospheric CO2 emissions 'avoided' during the production of a given amount of a useful product (e.g., a kilowatt-hour of electricity or a kilogram of H2). So any cost expressed per tonne of CO2 should be clearly defined in terms of its basis, e.g., either a captured basis or an avoided basis (see Box 8.1). Mitigation cost is best represented as avoided cost. Table 8.3 presents ranges for total avoided costs for CO2 capture, transport, and storage from four types of sources.

The mitigation costs (US$/tCO2 avoided) reported in Table 8.3 are context-specific and depend very much on what is chosen as a reference plant. In Table 8.3, the reference plant is a power plant of the same type as the power plant with CCS. The mitigation costs here therefore represent the incremental cost of capturing and storing CO2 from a particular type of plant.

In some situations, it can be useful to calculate a cost of CO, avoided based on a reference plant that is different from the CCS plant (e.g., a PC or IGCC plant with CCS using an NGCC reference plant). In Table 8.4, the reference plant represents the least-cost plant that would 'normally' be built at a particular location in the absence of a carbon constraint. In many regions today, this would be either a PC plant or an NGCC plant.

A CO2 mitigation cost also can be defined for a collection of plants, such as a national energy system, subject to a given level of CO2 abatement. In this case the plant-level product costs presented in this section would be used as the basic inputs to energy-economic models that are widely used for policy analysis and for the quantification of overall mitigation strategies and costs for CO2 abatement. Section 8.3 discusses the nature of these models and presents illustrative model results, including the cost of CCS, its economic potential, and its relationship to other mitigation options.

Table 8.3a Range of total costs for CO2 capture, transport, and geological storage based on current technology for new power plants.
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