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40 Technical Summary Figure TS.10. Material fluxes and process steps associated with the mineral carbonation of silicate rocks or industrial residues (Courtesy ECN). energy required would be 30 to 50% of the capture plant output. Considering the additional energy requirements for the capture of CO 2 , a CCS system with mineral carbonation would require 60 to 180% more energy input per kilowatthour than a reference electricity plant without capture or mineral carbonation. These energy requirements raise the cost per tonne of CO 2 avoided for the overall system significantly (see Section 8). The best case studied so far is the wet carbonation of natural silicate olivine. The estimated cost of this process is approximately 50–100 US$/tCO 2 net mineralized (in addition to CO 2 capture and transport costs, but taking into account the additional energy requirements). The mineral carbonation process would require 1.6 to 3.7 tonnes of silicates per tonne of CO 2 to be mined, and produce 2.6 to 4.7 tonnes of materials to be disposed per tonne of CO 2 stored as carbonates. This would therefore be a large operation, with an environmental impact similar to that of current large-scale surface mining operations. Serpentine also often contains chrysotile, a natural form of asbestos. Its presence therefore demands monitoring and mitigation measures of the kind available in the mining industry. On the other hand, the products of mineral carbonation are chrysotilefree, since this is the most reactive component of the rock and therefore the first substance converted to carbonates. A number of issues still need to be clarified before any estimates of the storage potential of mineral carbonation can be given. The issues include assessments of the technical feasibility and corresponding energy requirements at large scales, but also the fraction of silicate reserves that can be technically and economically exploited for CO 2 storage. The environmental impact of mining, waste disposal and product storage could also limit potential. The extent to which mineral carbonation may be used cannot be determined at this time, since it depends on the unknown amount of silicate reserves that can be technically exploited, and environmental issuessuch as those noted above. Industrial uses Industrial uses of CO 2 include chemical and biological processes where CO 2 is a reactant, such as those used in urea and methanol production, as well as various technological applications that use CO 2 directly, for example in the horticulture industry, refrigeration, food packaging, welding,
Technical Summary 41 beverages and fire extinguishers. Currently, CO 2 is used at a rate of approximately 120 MtCO 2 per year (30 MtC yr -1 ) worldwide, excluding use for EOR (discussed in Section 5). Most (two thirds of the total) is used to produce urea, which is used in the manufacture of fertilizers and other products. Some of the CO 2 is extracted from natural wells, and some originates from industrial sources – mainly high-concentration sources such as ammonia and hydrogen production plants – that capture CO 2 as part of the production process. Industrial uses of CO 2 can, in principle, contribute to keeping CO 2 out of the atmosphere by storing it in the “carbon chemical pool” (i.e., the stock of carbon-bearing manufactured products). However, as a measure for mitigating climate change, this option is meaningful only if the quantity and duration of CO 2 stored are significant, and if there is a real net reduction of CO 2 emissions. The typical lifetime of most of the CO 2 currently used by industrial processes has storage times of only days to months. The stored carbon is then degraded to CO 2 and again emitted to the atmosphere. Such short time scales do not contribute meaningfully to climate change mitigation. In addition, the total industrial use figure of 120 MtCO 2 yr -1 is small compared to emissions from major anthropogenic sources (see Table TS.2). While some industrial processes store a small proportion of CO 2 (totalling roughly 20 MtCO 2 yr -1 ) for up to several decades, the total amount of long-term (century-scale) storage is presently in the order of 1 MtCO 2 yr -1 or less, with no prospects for major increases. Another important question is whether industrial uses of CO 2 can result in an overall net reduction of CO 2 emissions by substitution for other industrial processes or products. This can be evaluated correctly only by considering proper system boundaries for the energy and material balances of the CO 2 utilization processes, and by carrying out a detailed life-cycle analysis of the proposed use of CO 2 . The literature in this area is limited but it shows that precise figures are difficult to estimate and that in many cases industrial uses could lead to an increase in overall emissions rather than a net reduction. In view of the low fraction of CO 2 retained, the small volumes used and the possibility that substitution may lead to increases in CO 2 emissions, it can be concluded that the contribution of industrial uses of captured CO 2 to climate change mitigation is expected to be small. 8. Costs and economic potential The stringency of future requirements for the control of greenhouse gas emissions and the expected costs of CCS systems will determine, to a large extent, the future deployment of CCS technologies relative to other greenhouse gas mitigation options. This section first summarizes the overall cost of CCS for the main options and process applications considered in previous sections. As used in this summary and the report, “costs” refer only to market prices but do not include external costs such as environmental damages and broader societal costs that may be associated with the use of CCS. To date, little has been done to assess and quantify such external costs. Finally CCS is examined in the context of alternative options for global greenhouse gas reductions. Cost of CCS systems As noted earlier, there is still relatively little experience with the combination of CO 2 capture, transport and storage in a fully integrated CCS system. And while some CCS components are already deployed in mature markets for certain industrial applications, CCS has still not been used in large-scale power plants (the application with most potential). The literature reports a fairly wide range of costs for CCS components (see Sections 3–7). The range is due primarily to the variability of site-specific factors, especially the design, operating and financing characteristics of the power plants or industrial facilities in which CCS is used; the type and costs of fuel used; the required distances, terrains and quantities involved in CO 2 transport; and the type and characteristics of the CO 2 storage. In addition, uncertainty still remains about the performance and cost of current and future CCS technology components and integrated systems. The literature reflects a widely-held belief, however, that the cost of building and operating CO 2 capture systems will decline over time as a result of learning-by-doing (from technology deployment) and sustained R&D. Historical evidence also suggests that costs for first-of-a-kind capture plants could exceed current estimates before costs subsequently decline. In most CCS systems, the cost of capture (including compression) is the largest cost component. Costs of electricity and fuel vary considerably from country to country, and these factors also influence the economic viability of CCS options. Table TS.9 summarizes the costs of CO 2 capture, transport and storage reported in Sections 3 to 7. Monitoring costs are also reflected. In Table TS.10, the component costs are combined to show the total costs of CCS and electricity generation for three power systems with pipeline transport and two geological storage options. For the plants with geological storage and no EOR credit, the cost of CCS ranges from 0.02–0.05 US$/kWh for PC plants and 0.01–0.03 US$/kWh for NGCC plants (both employing post-combustion capture). For IGCC plants (using pre-combustion capture), the CCS cost ranges from 0.01–0.03 US$/kWh relative to a similar plant without CCS. For all electricity systems, the cost of CCS can be reduced by about 0.01–0.02 US$/kWh when using EOR with CO 2 storage because the EOR revenues partly compensate for the CCS costs. The largest cost reductions are seen for coalbased plants, which capture the largest amounts of CO 2 . In a few cases, the low end of the CCS cost range can be negative,
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