The calcium looping cycle for large-scale CO2 capture

The reversible reaction between CaO and CO₂ is an extremely promising method of removing CO₂ from the exhaust of a power station, generating a pure stream of CO₂ ready for geological sequestration. The technology has attracted a great deal of attention recently, owing to a number of its advantages: the relatively small efficiency penalty which it imposes upon a power station (estimated at 6–8 percentage points, including compression of the CO₂); its potential use in large-scale circulating fluidised beds (a mature technology, as opposed to the vastly upscaled solvent scrubbing towers which would be required for amine scrubbing); its excellent opportunity for integration with cement manufacture (potentially decarbonising both industries) and its extremely cheap sorbent (crushed limestone).     

Expert opinions on carbon dioxide capture and storage—A framing of uncertainties and possibilities

There are many uncertainties and knowledge gaps regarding the development of carbon dioxide capture and storage (CCS)—e.g., when it comes to costs, life-cycle effects, storage capacity and permanence. In spite of these uncertainties and barriers, the CCS research community is generally very optimistic regarding CCS’ development. The discrepancy between the uncertainties and the optimism is the point of departure in this study, which is based on interviews with 24 CCS experts. The aim is to analyse experts’ framings of CCS with focus on two key aspects: (i) the function and potential of CCS and (ii) uncertainties. The optimism among the CCS experts is tentatively explained. The interpretative flexibility of CCS is claimed to be an essential explanation for the optimism. CCS is promoted from a wide variety of perspectives, e.g., solidarity and peace, bridge to a sustainable energy system, sustaining the modern lifestyle and compatibility with the fossil fuel lock-in. Awareness of the uncertainties and potential over-optimism is warranted within policy and decision making as they often rely on scientific forecasts and experts’ judgements.     

Implications of generator siting for CO2 pipeline infrastructure

The location of a new electric power generation system with carbon capture and sequestration (CCS) affects the profitability of the facility and determines the amount of infrastructure required to connect the plant to the larger world. Using a probabilistic analysis, we examine where a profit-maximizing power producer would locate a new generator with carbon capture in relation to a fuel source, electric load, and CO₂ sequestration site. Based on models of costs for transmission lines, CO₂ pipelines, and fuel transportation, we find that it is always preferable to locate a CCS power facility nearest the electric load, reducing the losses and costs of bulk electricity transmission. This result suggests that a power system with significant amounts of CCS requires a very large CO₂ pipeline infrastructure.     

European CO2 prices and carbon capture investments

We assess the option to install a carbon capture and storage (CCS) unit in a coal-fired power plant operating in a carbon-constrained environment. We consider two sources of risk, namely the price of emission allowance and the price of the electricity output. First we analyse the performance of the EU market for CO₂ emission allowances. Specifically, we focus on the contracts maturing in the Kyoto Protocol's first commitment period (2008 to 2012) and calibrate the underlying parameters of the allowance price process. Then we refer to the Spanish wholesale electricity market and calibrate the parameters of the electricity price process.We use a two-dimensional binomial lattice to derive the optimal investment rule. In particular, we obtain the trigger allowance prices above which it is optimal to install the capture unit immediately. We further analyse the effect of changes in several variables on these critical prices, among them allowance price volatility and a hypothetical government subsidy.We conclude that, at current permit prices, immediate installation does not seem justified from a financial point of view. This need not be the case, though, if carbon market parameters change dramatically, carbon capture technology undergoes significant improvements, and/or a specific governmental policy to promote these units is adopted.     

A review of physical modelling and numerical simulation of long-term geological storage of CO2

Numerical simulations are essential to the understanding of the long-term geological storage of CO₂. Physical modelling of geological storage of CO₂ has been based on Darcy’s law, together with the equations of conservation of mass and energy. Modelling and simulations can be used to predict where CO₂ is likely to flow, to interpret the volume and spatial distribution of CO₂ under storage conditions, and to optimise injection operations. The state of the art of physical modelling and numerical simulation of CO₂ dispersion is briefly reviewed in this paper, which calls for more accurate and more efficient modelling approaches. A systematic evaluation of the numerical methods used and a comparison between the streamline based methods and the grid based methods would be valuable. Multi-scale modelling may prove to be of great value in predicting the long-term geological storage of CO₂, while highly accurate numerical methods such as high-order schemes may be employed in numerical simulations of CO₂ dispersion for local transport calculations.     

Conceptual study of distributed CO2 capture and the sustainable carbon economy

Capture of carbon dioxide from distributed sources is often neglected as a viable solution to the global problem of CO₂ emissions management. Small scale power plants, including those applicable to the transportation sector, can be designed to capture their CO₂ exhaust stream, provided it is not heavily diluted with air. Liquefaction of carbon dioxide allows the captured CO₂ to be stored densely, with a minimal energetic penalty and space requirement, until it can be permanently sequestered. In this short-term solution, the energetic penalty for CO₂ capture can be further offset by exploiting novel energy conversion processes involving regeneration of the reaction product stream – a simple strategy that is not exploited in conventional systems. More importantly, in the long-term, as the renewable energy infrastructure is built up, the collected CO₂ can be recycled into synthetic carbon-based liquid fuels which act as energy carriers in the sustainable carbon economy.     

Tackling CO2 reduction in India through use of CO2 capture and storage (CCS): Prospects and challenges

CO₂ capture and storage (CCS) is not currently a priority for the Government of India (GOI) because, whilst a signatory to the UNFCCC and Kyoto Protocol, there are no existing greenhouse gas emission reduction targets and most commentators do not envisage compulsory targets for India in the post-2012 phase. The overwhelming priority for the GOI is to sustain a high level of economic growth (8%+) and provision of secure, reliable energy (especially electricity) is one of the widely recognised bottlenecks in maintaining a high growth rate. In such a supply-starved context, it is not easy to envisage adoption of CCS—which increases overall generation capacity and demand for coal without increasing actual electricity supply—as being acceptable. Anything which increases costs—even slightly—is very unlikely to happen, unless it is fully paid for by the international community. The majority viewpoint of the industry and GOI interviewees towards CCS appears to be that it is a frontier technology, which needs to be developed further in the Annex-1 countries to bring down the cost through RD&D and deployment. More RD&D is required to assess in further detail the potential for CO₂ storage in geological reservoirs in India and the international community has an important role to play in cultivating such research.     

A study of the methanation of carbon dioxide on Ni/Al2O3 catalysts at atmospheric pressure

The hydrogenation of carbon dioxide producing methane and CO has been investigated over Ni/Al₂O₃ catalysts. The as prepared catalysts have been characterized by XRD and Temperature Programmed Reduction. Spent catalysts have been characterized by XRD and Field Emission SEM. Catalytic activity needs the presence of Ni metal particles which may form in situ if the Ni loading is higher than that needed to cover the alumina surface with a complete monolayer. If Ni content is lower, pre-reduction is needed. Catalysts containing very small Ni particles obtained by reducing moderate loading materials are very selective to methane without CO formation. The larger the Ni particles, due to higher Ni loadings, the higher the CO production. Cubic Ni metal particles are found in the spent catalysts mostly without carbon whiskers. The data suggest that fast methanation occurs at the expense of CO intermediate on the corners of nanoparticles interacting with alumina, likely with a “via oxygenate” mechanism.     

The Ni/ZrO2 catalyst and the methanation of CO and CO2

The Ni/ZrO₂ catalyst is one of the most active systems for the methanation of CO to be employed in the hydrogen purification for PEMFC. This contribution aims to study the effect of ZrO₂ on the methanation of CO and CO₂. The catalytic behavior of Ni/ZrO₂, Ni/SiO₂, a physical mixture comprising Ni and ZrO_2, and a double-bed reactor were evaluated. The TPD of CO and CO₂, TPSR and the cyclohexane dehydrogenation reaction were carried out to describe the catalysts and the reactions. The high activity of Ni/ZrO₂ catalyst toward the methanation of CO is related to the presence of active sites on the ZrO₂ surface. The methanation of CO occurs on ZrO₂ due to its ability to adsorb CO and also because of the hydrogen spillover phenomenon. Apparently, the effect of ZrO₂ is less relevant for the methanation of CO₂. Ni/ZrO₂ is a very promising system for the purification of hydrogen.     

Opportunities for low-cost CO2 storage demonstration projects in China

Several CO₂ storage demonstration projects are needed in a variety of geological formations worldwide to prove the viability of CO₂ capture and storage as a major option for climate change mitigation. China has several low-cost CO₂ sources at sites that produce NH₃ from coal via gasification. At these plants, CO₂ generated in excess of the amount needed for other purposes (e.g., urea synthesis) is vented as a relatively pure stream. These CO₂ sources would potentially be economically interesting candidates for storage demonstration projects if there are suitable storage sites nearby.     

Reservoir simulation of CO2 sequestration pilot in Frio brine formation,USA Gulf Coast

Reservoir simulation studies were performed to investigate compositional effects between aquifer fluid (brine) and injected supercritical CO₂ during the sequestration process in the Frio brine formation. Accurate data calibrations of CO₂ solubility and density, as well as brine density and viscosity, were performed. Hysteresis relative permeability was taken into consideration to account for the effect of trapped gas in the aquifer. In addition, real aquifer data obtained from the test site were used in order to characterize the Frio aquifer.     

Anthropogenic emissions of CO2 and CH4 in an urban environment

Regular observations of atmospheric mixing-ratios of carbon dioxide and methane in the urban atmosphere, combined with analyses of their carbon-isotope composition (δ¹³C, δ¹⁴C), provide a powerful tool for assessing both the source strength and source partitioning of those gases, as well as their changes with respect to time. Intense surface fluxes of CO₂ and CH₄, associated with anthropogenic activities result in elevated levels of these gases in the local atmosphere as well as in modifications of their carbon-isotope compositions. Regular measurements of concentration and carbon-isotope composition of atmospheric CO₂, carried out in Krakow over the past two decades, were extended to the period 1995–2000 and also to atmospheric mixing-ratios of CH₄ and its carbon-isotope composition. Radiocarbon concentrations (δ¹⁴C) in atmospheric CO₂ recorded at Krakow are systematically lower than the regional background levels. This effect stems from the addition of ¹⁴C-free CO₂ into the local atmosphere, originating from the burning of fossil fuels. The fossil-fuel component in the local budget of atmospheric carbon calculated using a three-component mixing model decreased from ca. 27.5 ppm in 1989 to ca. 10 ppm in 1994. The seasonal fluctuations of this component (winter–summer) are of similar magnitude. A gradually decreasing difference between the ¹⁴CO₂ content in the local atmosphere and the regional background observed after 1991 is attributed to the reduced consumption of ¹⁴C-free fuels, mostly coal, in southern Poland and the Krakow municipal area. The linear regression of δ¹³C values of methane plotted versus reciprocal concentration, performed for the data available for Krakow sampling site, yields the average δ¹³C signature of the local source of methane as being equal to −54.2‰. This value agrees very well with the measured isotope signature of natural gas being used in Krakow (−54.4±0.6‰) and points to leakages in the distribution network of this gas as the main anthropogenic source of CH₄ in the local atmosphere.     

CO2 sequestration in Ontario, Canada. Part II: cost estimation

As the Kyoto target set for Canada is to reduce GHG emission by 6% of the 1990 level by 2008–2012, several options are being considered to achieve this target. One of the possible options in Ontario is geological sequestration of captured CO₂ in saline aquifers, where CO₂ is expected to be stored for long geological periods, from 100 to several thousand years depending on the size, property and location of the reservoir. The preferred concept is to inject CO₂ into a porous and permeable reservoir covered with a cap rock located at least 800 m beneath the earth's surface where CO₂ can be stored under supercritical conditions. This paper evaluates the capital and operating cost for CO₂ sequestration in southwestern Ontario from a 500 MW coal fired power plant. The main focus is on the cost of sequestration (CO₂ transport and injection), and thus, the cost of capturing and pressurizing the CO₂ from the plant flue gas is not considered here.

A significant amount of capital investment is necessary to transfer CO₂ from a 500 MW fossil fuel power plant to the injection location and to store it underground. Major components of the cost include: cost of pipeline, cost of drilling injection wells and installing platforms, since the more plausible injection area is under Lake Erie. Many uncertainties are associated with cost estimation; several are identified and their impacts are considered in this paper. The estimated cost of sequestration of 14,000 ton/day of CO₂ at approximately 110 bar in southwestern Ontario is between 7.5 and 14 US$/ton of CO₂ stored.     

Carbon dioxide (CO2) storage and sequestration of land cover in the Leyte Geothermal Reservation

This study estimated the existing stored carbon (C) and rate of sequestration by vegetation that can potentially serve as a sink for the carbon dioxide emitted from eight geothermal plants in Leyte Geothermal Reservation, Philippines. For the 20,438 ha watershed in the vicinity of the power project, the total C storage is 3.84 Mt C (14.10 Mt CO₂) while C sequestration based on biomass change was 47.35 kt C (173.77 kt CO₂). Relative to power plant emission, the C stored in the reserve is equivalent to more than 22 years of CO₂ emission. Annual C sequestration is 27% of CO₂ emission per year. For the next 25 years, two scenarios were projected. Under Scenario I (“Business as Usual”), the forest reserve will be able to store and sequester more than 32 years of CO₂ emission from the power plants. Under Scenario II (“Accelerated Reforestation”), the reserve will be able to store and sequester about 34 years of CO₂ emission.In addition, the rate of C sequestration based on biomass change in vegetation was recorded to assess the optimum land use that can absorb the carbon dioxide emitted by the power project. These are as follows: tree plantations (10.09 tC/ha/yr)>coconut (4.78 tC/ha/yr)>brushland (4.29 tC/ha/yr)>natural forest (0.92 tC/ha/yr).In terms of cost, the power project operator is spending P1.22 per t CO₂ (P4.4 or US$0.12 per tC) for every year of C storage and sequestration. For 25 years, the total cost is P30.40 per tCO₂ (P111.5 or US$2.94 per tC) which is comparable to the cost of C offset in other tropical countries.     

Characterization of water gas shift reaction in association with carbon dioxide sequestration

The characteristics of a water gas shift reaction (WGSR) in association with carbon dioxide sequestration under the effects of a high-temperature catalyst (HTC) and a low-temperature catalyst (LTC) are studied experimentally. With the condition of fixed residence time (0.1 s) for the reactants in the catalyst bed, it is found that the reaction behaviors with the HTC are inherently different from those with the LTC. Specifically, for the WGSR with the HTC, the reaction can be divided into a rapid growth regime, a progressive growth regime and a slow growth regime with increasing reaction temperature or steam/CO ratio. With regard to the WGSR with the LTC, three different regimes are also exhibited; however, they consist of a rapid growth regime, a progressive decay regime and a growth-frozen regime. According to the aforementioned characteristics, proper or better operation conditions using the HTC and the LTC for the application of fuel cells are suggested. When the product gas passes through a Ca(OH)₂ solution, the obtained results reveal that CO₂ removal efficiency increases with increasing solution concentration or steam/CO ratio for both the HTC and the LTC used in the WGSR.     

Photoreduction of carbon dioxide with H2 and H2O over TiO2 and ZrO2 in a circulated photocatalytic reactor

The photocatalytic reduction of carbon dioxide (CO₂) was studied in a self-designed circulated photocatalytic reaction system under titanium dioxide (TiO₂, Degussa P-25) and zirconium oxide (ZrO₂) photocatalysts and reductants at room temperature and constant pressure. The wavelengths of incident ultraviolet (UV) light for the photocatalysis of TiO₂ and ZrO₂ were 365 and 254 nm, respectively. Experimental results indicated that the highest yield of the photoreduction of CO₂ were obtained using TiO₂ with H₂+H₂O and ZrO₂ with H₂. Photoreduction of CO₂ over TiO₂ with H₂+H₂O formed CH₄, CO, and C₂H₆ with the yield of 8.21, 0.28, and 0.20 μmol/g, respectively, while the photoreduction of CO₂ over ZrO₂ with H₂ formed CO at a yield of 1.24 μmol/g. The detected reaction products supported the proposition of two reaction pathways for the photoreduction of CO₂ over TiO₂ and ZrO₂ with H₂ and H₂O, respectively. Additionally, a one-site Langmuir-Hinshewood (L-H) kinetic model was successfully applied to simulate the photoreduction rate of CO₂.     

Expulsive force in the development of CO2 sequestration: application of SC-CO2 jet in oil and gas extraction

With the rapid development of global economy, an increasing amount of attention has been paid to the emission of greenhouse gases, especially CO₂. In recent years, dominated by the governments around the world, several significant projects of CO₂ sequestration have been conducted. However, due to the huge investment and poor economic effects, the sustainability of those projects is not satisfactory. Supercritical CO₂ (SC-CO₂) has prominent advantages in well drilling, fracturing, displacement, storage, plug and scale removal within tubing and casing, which could bring considerable economic benefits along with CO₂ sequestration. In this paper, based on physicochemical properties of SC-CO₂ fluid, a detailed analysis of technical advantages of SC-CO₂ applied in oil and gas development is illustrated. Furthermore, the implementation processes of SC-CO₂ are also proposed. For the first time, a recycling process is presented in which oil and gas are extracted and the CO₂ generated could be restored underground, thus an integrated technology system is formed. Considering the recent interests in the development of enhancing hydrocarbon recoveries and CO₂ sequestration, this approach provides a promising technique that can achieve these two goals simultaneously.     

Accounting for behavioral effects of increases in the carbon dioxide (CO2) tax in revenue estimation in Sweden

In this paper we describe how behavioral responses of carbon dioxide (CO₂) tax increases are accounted for in tax revenue estimation in Sweden. The rationale for developing a method for this is a mix between that a CO₂ tax is a primary climate policy tool aiming to reduce CO₂ emissions and that the CO₂ tax generates sizable tax revenues.     

Toward integrated energy and materials policies? A case study on CO2 reduction in the Netherlands

Energy and material flows are closely related. The materials system is of major significance from a national energy and CO₂ point of view. Integrated energy and materials studies can show significant new policy options for energy savings and CO₂ emission reduction through materials system improvements, shown in a case study on long-term CO₂ emission reduction in the Netherlands. An integrated energy and materials system MARKAL model is used for this analysis. The results show that, on one hand, CO₂ emission reduction costs are significantly reduced in the integrated approach and, on the other hand, the materials system is significantly influenced by CO₂ emission reduction. Consideration of dynamic interactions results in better understanding of future developments in both energy and materials systems.     

Cost and performance of fossil fuel power plants with CO2 capture and storage

CO₂ capture and storage (CCS) is receiving considerable attention as a potential greenhouse gas (GHG) mitigation option for fossil fuel power plants. Cost and performance estimates for CCS are critical factors in energy and policy analysis. CCS cost studies necessarily employ a host of technical and economic assumptions that can dramatically affect results. Thus, particular studies often are of limited value to analysts, researchers, and industry personnel seeking results for alternative cases. In this paper, we use a generalized modeling tool to estimate and compare the emissions, efficiency, resource requirements and current costs of fossil fuel power plants with CCS on a systematic basis. This plant-level analysis explores a broader range of key assumptions than found in recent studies we reviewed for three major plant types: pulverized coal (PC) plants, natural gas combined cycle (NGCC) plants, and integrated gasification combined cycle (IGCC) systems using coal. In particular, we examine the effects of recent increases in capital costs and natural gas prices, as well as effects of differential plant utilization rates, IGCC financing and operating assumptions, variations in plant size, and differences in fuel quality, including bituminous, sub-bituminous and lignite coals. Our results show higher power plant and CCS costs than prior studies as a consequence of recent escalations in capital and operating costs. The broader range of cases also reveals differences not previously reported in the relative costs of PC, NGCC and IGCC plants with and without CCS. While CCS can significantly reduce power plant emissions of CO₂ (typically by 85–90%), the impacts of CCS energy requirements on plant-level resource requirements and multi-media environmental emissions also are found to be significant, with increases of approximately 15–30% for current CCS systems. To characterize such impacts, an alternative definition of the “energy penalty” is proposed in lieu of the prevailing use of this term.