The topic of global warming as a result of increased atmospheric CO2 concentration is arguably the most important environmental issue that the world faces today. It is a global problem that will need to be solved on a global level. The link between anthropogenic emissions of CO2 with increased atmospheric CO2 levels and, in turn, with increased global temperatures has been well established and accepted by the world. International organizations such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC) have been formed to address this issue. Three options are being explored to stabilize atmospheric levels of greenhouse gases (GHGs) and global temperatures without severely and negatively impacting standard of living: (1) increasing energy efficiency, (2) switching to less carbon-intensive sources of energy, and (3) carbon sequestration. To be successful, all three options must be used in concert. The third option is the subject of this review. Specifically, this review will cover the capture and geologic sequestration of CO2 generated from large point sources, namely fossil-fuel-fired power gasification plants. Sequestration of CO2 in geological formations is necessary to meet the President's Global Climate Change Initiative target of an 18% reduction in GHG intensity by 2012. Further, the best strategy to stabilize the atmospheric concentration of CO2 results from a multifaceted approach where sequestration of CO2 into geological formations is combined with increased efficiency in electric power generation and utilization, increased conservation, increased use of lower carbon-intensity fuels, and increased use of nuclear energy and renewables. This review covers the separation and capture of CO2 from both flue gas and fuel gas using wet scrubbing technologies, dry regenerable sorbents, membranes, cryogenics, pressure and temperature swing adsorption, and other advanced concepts. Existing commercial CO2 capture facilities at electric power-generating stations based on the use of monoethanolamine are described, as is the Rectisol process used by Dakota Gasification to separate and capture CO2 from a coal gasifier. Two technologies for storage of the captured CO2 are reviewed--sequestration in deep unmineable coalbeds with concomitant recovery of CH4 and sequestration in deep saline aquifers. Key issues for both of these techniques include estimating the potential storage capacity, the storage integrity, and the physical and chemical processes that are initiated by injecting CO2 underground. Recent studies using computer modeling as well as laboratory and field experimentation are presented here. In addition, several projects have been initiated in which CO2 is injected into a deep coal seam or saline aquifer. The current status of several such projects is discussed. Included is a commercial-scale project in which a million tons of CO2 are injected annually into an aquifer under the North Sea in Norway. The review makes the case that this can all be accomplished safely with off-the-shelf technologies. However, substantial research and development must be performed to reduce the cost, decrease the risks, and increase the safety of sequestration technologies. This review also includes discussion of possible problems related to deep injection of CO2. There are safety concerns that need to be addressed because of the possibilities of leakage to the surface and induced seismic activity. These issues are presented along with a case study of a similar incident in the past. It is clear that monitoring and verification of storage will be a crucial part of all geological sequestration practices so that such problems may be avoided. Available techniques include direct measurement of CO2 and CH4 surface soil fluxes, the use of chemical tracers, and underground 4-D seismic monitoring. Ten new hypotheses were formulated to describe what happens when CO2 is pumped into a coal seam. These hypotheses provide significant insight into the fundamental chemical, physical, and thermodynamic phenomena that occur during coal seam sequestration of CO2.

Separation and Capture of CO2 from Large Stationary Sources and Sequestration in Geological Formations—Coalbeds and Deep Saline Aquifers

Kinetics of carbon dioxide sorption on potassium-doped lithium zirconate

Driven by the need to develop technologies for converting CO2, an extraordinary array of chemical looping based process concepts has been proposed and researched over the past 15 years. This review aims at providing first a historical context of the molecule CO2, which sits at the center of these developments. Then, different types of chemical looping related to CO2 are addressed, with attention to process concepts, looping materials, and reactor configurations. Herein, focus lies on the direct conversion of carbon dioxide into carbon monoxide, a process deemed to have economic potential.

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110th Anniversary : carbon dioxide and chemical looping : current research trends

Potassium-doped lithium zirconate (Li2ZrO3) sorbents with similar crystallite but different aggregate sizes were prepared by a solid-state reaction method from mixtures of Li2CO3, K2CO3, and ZrO2 of different particle sizes Carbon dioxide sorption rate on the prepared Li2ZrO3 sorbents increases with decreasing sorbent aggregate size It is the size of the aggregate, not the crystallite, of Li2ZrO3 that controls the sorption rate Temperature effect on CO2 sorption is complex, depending on both kinetic and thermodynamic factors A mathematical model based on the double-shell sorption mechanism was established for CO2 sorption kinetics and it can fit experimental data quite well Above 500°C, the rate-limiting step of CO2 sorption is the diffusion of oxygen ions through the ZrO2 shell formed during the carbonation reaction Oxygen ion conductivities in the ZrO2 shell were obtained by regression of the experimental CO2 uptake curves with the model and are consistent with the literature data

K. Nakagawa

Papers

High Temperature CO2 Absorption Using Lithium Zirconate Powder