CO2 storage in geological media: Role, means, status and barriers to deployment

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

Energy is a vital input for social and economic development of any nation. With increasing agricultural and industrial activities in the country, the demand for energy is also increasing. Formulation of an energy model will help in the proper allocation of widely available renewable energy sources such as solar, wind, bioenergy and small hydropower in meeting the future energy demand in India. During the last decade several new concepts of energy planning and management such as decentralized planning, energy conservation through improved technologies, waste recycling, integrated energy planning, introduction of renewable energy sources and energy forecasting have emerged. In this paper an attempt has been made to understand and review the various emerging issues related to the energy modeling. The different types of models such as energy planning models, energy supply–demand models, forecasting models, renewable energy models, emission reduction models, optimization models have been reviewed and presented. Also, models based on neural network and fuzzy theory have been reviewed and discussed. The review paper on energy modeling will help the energy planners, researchers and policy makers widely.

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A review of energy models

Rotor flux observers can provide an attractive means for achieving direct field oriented control of induction machines. This paper presents a physics-based design methodology and uses it to evaluate open-loop observers and to develop a new closed-loop flux observer. It is shown that the new flux observer is a straightforward structure with properties that combine the best features of known methods. A distinction is made between observers, which use only integration and feedback summation operations, and those estimation methods requiring approximate differentiation which are, in essence, "cancellation" methods. Furthermore, a clear distinction is made between accuracy and dynamic robustness of the observer. This distinction is important because the accuracy of flux observers for induction machines is inherently parameter sensitive, whereas robustness of observers, in a controls sense, is not parameter sensitive. Moreover, it is shown how flux observers can provide robust field oriented control because the flux angle is substantially more correct than the flux magnitude. A distinctive form of frequency response function (FRF) analysis similar to that used in classical control engineering is demonstrated to be a useful and insightful tool even though flux observers are multiple-input, multiple-output systems. Finally, the limits of such flux observers are experimentally evaluated. >

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A physically insightful approach to the design and accuracy assessment of flux observers for field oriented induction machine drives

A speed estimation method for an induction machine and its application to a flux observer-based field orientation (FOFO) control system proposed previously is presented. The motor speed is estimated on the basis of the difference between two flux estimators. The convergence of the method is analyzed, and a novel pole assignment method is proposed. The speed estimator is applied to the FOFO controller. The system has been implemented using a DSP, and some laboratory experiments showing that the speed-sensorless FOFO operates with enough stability and has a strong robustness to rotor resistance variation are reported. >

Speed sensorless field orientation control of the induction machine

The role of CO2 removal and disposal

A study on economic measures for CO2 reduction in Japan

A Novel Induction Machine Flux Observer and its Application to a High Performance AC Drive System

Time to realization: Evaluation of CO2 capture technology R&Ds by GERT (Graphical Evaluation and Review Technique) analyses

Current emission scenarios that allow keeping the global temperature increase below 2 °C or even 1.5 °C—as foreseen by the Paris Agreement—are based on very optimistic assumptions, including enormous volumes of carbon dioxide removal (CDR). A closer look at the globally most important emission sectors—power, transport and industry—shows manifold barriers for very ambitious mitigation. A new policy guideline called “Net Zero CO2 Emissions without relying on massive CDR” and promotion of technological research, in addition to economic incentives and other policy measures, would help to overcome the often simplistic demands for positive modelling results and refocus climate policy on tackling the enormous barriers in key emitting sectors. Such an approach is more aligned with the Paris Agreement’s bottom-up logic and therefore more appropriate to make the transformational project of global decarbonization a success.

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Yoichi Kaya

Papers

The role of CO2 removal and disposal

A study on economic measures for CO2 reduction in Japan

A Novel Induction Machine Flux Observer and its Application to a High Performance AC Drive System

Time to realization: Evaluation of CO2 capture technology R&Ds by GERT (Graphical Evaluation and Review Technique) analyses

Towards net zero CO 2 emissions without relying on massive carbon dioxide removal