Carbon Management

CARBON SEQUESTRATION: [email protected] Introduction Carbon sequestration is the process of securely storing away CO2 originating from anthropogenic activities and sources, so that the gas does not enter into the earth s carbon cycle. Impressive examples of naturally sequestered CO2 are the coal seams, coal bed methane associated with shallow and deep coal seams, oil and gas trapped in the sedimentary traps, carbonate minerals and rocks of different geological ages. In these examples, it is the ancient geologic processes that enabled the sequestration. Research, Development, Demonstration and finally the Implementation of these CS (Carbon Sequestration) technologies will enable the nations of the world to continue with the use of fossil fuels and yet force the climate change phenomenon to abate and mitigate. Now, in the face of the threat of GHG led global warming and climate change, there are several options for abatement before us. First one, a simpler one, is the reduction of GHG emission by cutting down the dependency on the fossil fuel use. But there are not many takers for this proposal, as many of the leading countries outside of G7, like Brazil, Russia, India, and China are in the processes of marching forward to the levels of the developed nations and hence are not ready to cut the level of fossil fuel consumption at the expense of development. Perusal of Table 1 will enable one to understand the colossal size of the global carbon reservoir. Table 1 Global carbon reservoir Domain Level, GtC World oceans 39000 In Fossil fuel deposits 16000 Soils & vegetation 2500 Atmosphere 760 Current Science 2006, published an issue with a set of papers dealing with CO2 emissions and climate change from an Indian perspective and India s share of CO2 is summarised in Table 2. Table 2 Summary of v.90) GHG source & sink All energy Industrial process Agriculture Landuse/landuse change/forestry Waste Total , Gg/yr

GHG emissions, India, 1994 (in Gt): Sources and sinks (Sharma et al, 2006, CS, CO2 emission 679470 99878 n.a. 37675

CO2 removal n.a. n.a. n.a. 23533

CH4 emission 2896 2 14175 6.5

N2O emission 11.4 9 151 0.04

CO2 equivalent 743820 102710 379723 14292

n.a. 817023

23533

1003 18083

7 178

23233 1228540

* GWP indexed multipliers, CH4 =21, N2O= 310.

Another option is in place FF ( Fossil Fuels) to go for renewable sources of energy like, solar, wind, tide, nuclear, bio fuel etc. Among these, nuclear is a technology that originated in the 20th century, after the WW2 and ceased acceptability in the same century, due to the huge production coasts, risks and environmental threats and the question of disposal of spent fuel. Solar power is renewable like wind and tide, but the cost of photo-voltaic elements are still prohibitively costly preventing its acceptance across all the tiers of society and nations. Bio fuel, though quite popular in parts of the developed world, faces stiff criticism from several quarters, primarily due to its dependence on food crops like corn.

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Though large and small wind turbines have become commercially viable and hence attractive, critics allege that such large scale installations mar the scenic beauty of rural and open landscapes. So countries like Britain have erected such turbine farms in the offshore away from the visible range from the beach and sea lovers. Yet, all these alternatives have been gaining acceptance in the societies across the world. It is in this back drop that in order to save the planet and population from climate change threat, the approach of carbon capture, separation, and sequestration (CCS) gained currency in the minds of governments and among the scientific community. Before going any length about the CCS, we shall briefly examine the basic issues raised by climate change due to green house warming of the planet. .

CONSEQUENCES OF CLIMATE CHANGE World s climate is changing and will continue to change in the 21st century and beyond. Natural world and human society are affected by the changing precipitation patterns and rising temperatures. The earth s ecosystems are changing too at extraordinary rates and scales, triggering a cascade of impacts through the ecosystem like extinction of species, expansion into new areas and mingling of formerly nonoverlapping species. Anthropogenic actions are the primary cause for this climate change and the consequences, and primarily our approaches to energy, agriculture, water management, fishing, biological conservation and many other activities will transform or alter the natural systems. Manifestations of impacts of climate change are outlined in Table 3. Table 3 Effects, likelihood and possible impacts (after Gilman et al, 2007) Geophysical effect

Probability

Impacts likely to occur

Higher max. Temp., more hot days, and heat waves over nearly all landmasses

Very likely (90-99%)

Increased deaths and serious illness in older age groups & urban poor; increased heat stress in livestock & wildlife; increased risk of damage to a number of crops; increased electric cooling demand & reduced energy supply reliability.

Higher min. temp., fewer cold days, frost days and cold waves nearly over all the area.

Very likely (90-99%)

Decreased cold related morbidity & mortality; decreased risk of damage to a number of crops & increased risk to others; extended range & activity of pests & other disease vectors; reduced heating energy demand.

More intense precipitation events

Very likely (90-99%)

Increased flood, landslide, mudslide & avalanche damage; increased soil erosion; increased flood run off; increased recharge of some flood plain aquifers

Increased summer drying over most of midlatitude continental interiors & associated risk of drought.

Likely (67-90%)

Decreased crop yields, increased damage to building foundations caused by ground shrinkage; decreased water resource quantity and quality; increased risk of forest fire.

In the last 20 yr., several of the leading world governments have launched a series of studies or reviews on the nature of climate change with the help of their National Science Academies or scientific task forces to examine the ways of dealing with the consequences of climate change. On the other hand, the IPCC (of UN) utilises the voluntary efforts of thousands of scientists across the world, to synthesize the available knowledge on climate change and is subsequently subjected to intensive scrutiny and evaluation, before the final report is presented to the governments. Thus the 2007 IPCC report vouches that the earth s temperature is unequivocally on a warming trend. And the temperature rose by 0.75 o C. (1.3 o F) since 1850. Warming is not uniform in nature. Warming is rapid over the land. During the latter

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half of 20th century oceans have warmed causing melting of sea ice, bleaching of corals, species shifting their geographic ranges, rise in sea levels, and seawater holding less oxygen and carbon dioxide. Climate change also means rising sea levels due to melting of continental ice sheets, polar ice caps and mountain glaciers, as well as thermal expansion of sea water due to warmer temperatures. The global rise in sealevel is estimated at 1.7mm/yr in the 20th century. But from satellite measurements that began in 1992, the estimated rate has been 3.1mm/yr (IPCC, 2007). Higher sealevel also poses a threat to the coastal aquifers and the coastal wetland ecosystems. Manifest vulnerability of the earth s systems to climate change are indicted in Table 4. Table 4 Systems and nature of vulnerability to GCC System

Manifest vulnerability

Ecosystems

60% are degraded and most severely stressed; e.g., Aral sea, Central Asia; with past climate change ecosystems shifted to new zones; Human interference and blocking by infrastructure already stressed ecosystems do not shift locations; even a short excursion from normality can lead to collapse.

Aquatic Systems

500 million in semi arid and 200 million in arid zones; allocation and access are contentious; aquatic ecosystems and humans are affected by problems of untreated return flow entering fresh waters; agricultural intensification can lead to contamination of surface and subsurface water. By 2050 42% of population may live in countries with inadequate fresh waters stocks. Desertification due to increased drying will force 30 million to flee subSaharan Africa

Urban Systems

Only 20% of 1.6 billion lived in urban areas in 1900; today it is 50% of 6.6 billion are in urban areas; by 2050 with population of 9-10 billion vast majority of large urban centers will be in global south; climate change will aggravate all nocuous aspects of urban life in global south.

Civil systems

A brew of climate change stress and related wants of city life may disrupt civil order of population centers; may result chaotic civil life.

Tourism systems

At 10% of world business activity tourism is a driving force in the economy; warmer climate taking over temperate regions will restrict out flow of warm air seekers; Ecotourism in south American states will gradually vanish by relocation or disappearance of flora; shifting climate will affect inflow of tourists; Mediterranean can become unpleasantly hot. Nations developing tourism the stakes are especially high.

Climate change impacts the water cycle and hence transforms the pattern and rates of water availability for a variety of pursuits. Due to warming and consequent melting of Himalyan glaciers, water through put will rise in the Ganges-Brahmaputra system for a while, but it will be soon followed by a fall in water discharge and hence water availability, threatening the cities and towns in the Gangetic plain. Warmer temperature may also mean a shorter cropping season and longer drier spells leading to the food security of billions in the tropical world. Extreme events are also affected by the warmer seasons due to larger input of heat energy, which would accelerate the water cycle and seasons. Between 1950 and 2007, the aerial spread of Arctic ice shrunk by more than 50% from 11.0 Km2 to 4.1 million km2, while its thickness fell from 3.7 m to 2.5 m., a 33% decrease. It has been estimated that about 1/3 of all CO2 emitted by us is taken-up by the oceans, causing an increased acidification of water and consequent rise of pH of seawater. This rise will tend to impact the marine life. For example the corals (bleaching) and other carbonate shelled (thinner than normal shells)

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organisms will suffer due to loss of bicarbonate in the shells and/or the ability of bicarbonate to stay in solution. CAUSES OF CLIMATE CHANGE IPCC report (2007) observes that most of the climate warming in the last 50 yr. has been due to increase in emission of GHG emitted by the systems and processes related directly or indirectly to human activities. In the 19th century itself, scientists like Tyndall, Arrhenius and others established the basic physics of GHG additions causing climate change. During post industrial revolution decades, the use of fossil fuels as primary source of energy has been rapid injection the GHGs like CO2 and CH4 into the atmosphere. In 2006 per capita emission of CO2 stood at 5.5 metric tons (or a total emission of 36 Billion metric tons and the US daily average stood at 5.5 kg/person/day). As a consequence, current CO2 level is a 35% rise from 1850. Anthropogenic source of CO2 is fixed by the use of stable isotope tools CH4, a 25 times more deadly than CO2, rose by 150%, where as another GHG, i.e., N2O (nitrous oxide) nearly 300 times hazardous, increase by 20%. The hockey stick shaped curves depicting increase in the atmospheric content of these gases from the more stable levels in the last 10,000 yr. Future warming Trend Average temperature in future will certainly be warmer and its extent will depend on the human actions. Warming in 21st century will rise if we continue our dependence on fossil fuels as a vehicle of economic growth. IPCC proposes that if we continue this dependence (i.e., business as usual scenario) temperature may rise by 1.1 2.9 o C in 2100. But higher rates of rise might lead to catastrophic consequences to lifestyles, ecosystems, agriculture, and even livelihoods of vast populations (PCC, 2007). The ocean surface temperature may hit the high of .2-4oC for a B.a.U, mode, leading to high acidification of sea water, adversely affecting the sedentary animals and plants, and sea level may rise by o.6 m., The ice sheet s melting may compound the rate of sealevel rise by a factor of 2. Rise of temperature also forebodes frequent conditions of extreme heat, drought and heavy precipitation adding to the risk and frequency of incidence of droughts/floods. As climate challenge is complex and large, it calls for adoption of a bouquet of strategies and millions of workers in different parts of the world with the same goal but varying paths. ROLE OF GREEN HOUSE GASES Many gases occurring in the Earth s atmosphere act as greenhouse gases. i.e., these gases allow sunlight to enter the atmosphere freely. Some of it is re-radiated back towards space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere, to help maintain a livable environment in the planet. The greenhouse properties are actually displayed by many other natural gases (like water vapor, carbon dioxide, methane, and nitrous oxide), while others are exclusively human made (certain industrial gases). Over the years, if atmospheric concentrations of greenhouse gases remain relatively stable, the energy flux received by earth and returned to the space should be about the same leaving the temperature of the Earth s surface roughly steady or constant. Levels of several important greenhouse gases have increased by about 25 percent since large-scale industrialization began around 150 years ago. During the past 20 years, about three-quarters of anthropogenic (human-caused) emissions came from the burning of fossil fuels. Concentrations of carbon dioxide in the atmosphere are naturally regulated by numerous processes collectively known as the carbon cycle . The carbon flux between the oceans, land and atmosphere is modulated by natural processes like photosynthesis, which absorbs only like 6.2 billion tons of anthropogenic CO2 emission per year, while about 4.1 Billions tons (in terms of equivalent carbon) are added to the atmosphere annually. This imbalance results in the continued rise of atmospheric levels of GHG.

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The GHG (Green house gas) induced GW (global warming) or warming of the lower troposphere has time and again led scientists as well as finally the IPCC (International Panel on Climate Change; Chair: Dr. R.Pachauri) under auspices of the UN FCC, to caution the member governments and heads of states on the stupendous and impending threats in store for the nations and the humanity and ecosystems. But, I am tempted to believe that the consequences of GW are far more long lasting than the Global Economic melt down that hit the US in the last quarter of 08 and subsequently the other economies of the world. The Economic down turn is at least a phenomenon that can be fended by fiscal and financial measures and for which there exists a model in the depression of the 1930 s in US and of the 90 s in Japan. The GW on the other hand needs an orchestrated and scientific move by the community of nations and governments at diverse levels of GDP, rate of economic growth, and level and access to modern technologies and consequently of differing priorities.. As a result generating or designing an unanimous strategy or strategies by the community of nations, to thwart the risks and dangers of uncontrolled GW, is rather a slow and difficult process. Though the IPCC report triggered a cause for heeding to the recommendations detailed in the report, immediate action plans at policy level is yet to emerge from the state capitals. However, the IPCC report provided an impetus to re-examine both long and immediate term threats by various national science academies as well as the academia. In the US the USEPA, Oakridge National Laboratory, USDOE, such other agencies have been devoting close and keen attention to the issue of GW by periodic reviews of the scientific research related to issues leading to GW or release of GHG. Beginning with the decade of 90 s and later, the geoscience departments in the US universities and colleges have been offering undergraduate courses based on climate change/global change/climate change in the Pleistocene, to impart among the younger citizens a deep awareness on the GHG emissions and GW consequences. The publication of final IPCC report and its subsequent sharing of Nobel Peace Prize in 2007, along with the Hollywood Documentary The inconvenient Truth- by Al Gore (VP in the Clinton Presidency), further legitimized the need for more research and technology development on Climate Change (CC) by the national academies and committees as well as National Laboratories and Universities. A mission was rolled out to drive home the basics of GHG emissions, consequent GW and CC consequences to K12 level and to community leaders and members. Sources of GHG Primary source of GHG lie in the strongly coupled system of fossil fuels and energy. Level of energy production and per capita use are indicators of the economic growth as well as quality of life of the citizens of any nation. For e.g., energy-related carbon dioxide emissions represented 82 percent of total U.S. anthropogenic greenhouse gas emissions in 2006. Another greenhouse gas, methane, comes from landfills, coal mines, oil and natural gas operations, and agriculture; it represented 9 percent of total emissions. Nitrous oxide (5 percent of total emissions), is emitted through the use of nitrogen fertilizers, from burning fossil fuels and from certain industrial and waste management processes. Several human-made gases, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6), that are released as byproducts of industrial processes and through leakage, represented 2 percent of total emissions. Hydrogen and carbon are chief constituents of fossil fuels, which up on combustion yield CO2. The amount of carbon dioxide produced depends on the carbon content of the fuel; for example, for each unit of energy produced, natural gas emits about half and petroleum fuels about three-quarters of the carbon dioxide produced by coal.

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In India, 80% of electrical energy is generated by coal fired power plants. Petroleum and natural gas (he automobile and manufacturing sectors) emit equally important share of GHG. In US, fossil fuels supply 85 percent of the primary energy consumed and emit 98 percent of emissions of carbon dioxide. World carbon dioxide emissions are expected to increase by 1.8 percent annually between 2004 and 2030 (Figure 5). Much of the increase in these emissions is expected to occur in the developing world where emerging economies, such as China and India, fuel economic development with fossil energy. Emissions from the countries outside the Organization for Economic Cooperation and Development (OECD) are expected to grow above the world average at 2.6 percent annually between 2004 and 2030. In 2004, the United States produced about 22 percent of global carbon dioxide emissions from burning fossil fuels, primarily because the U.S. economy is the largest in the world and it meets 85 percent of its energy needs through burning fossil fuels. The United States is projected to lower its carbon intensity by 36 percent from 2004 to 2030. Abating the Phenomenon of CC In short, CC phenomenon is global in nature, affects humanity and posterity globally, especially the populations in poor countries. Driving force of CC is the GHG emitted by the burning of fossil fuels and the derivatives. Therefore, under the auspices of the UN (e.g., IPCC report authored by R. Pachauri, 2007) as well as under the initiatives of nations and governments, several expert working groups and task forces have been at work analyzing the CC phenomenon and its driving forces and mechanisms so that potential measures for warding off the CC could be identified, developed and demonstrated. . Such closer scientific scrutiny of CC has led to some broad realizations, foremost of which says the changes are irreversible, unless the quanta and rates of GHG emissions are reversed to some safe kevels, i.e., the pre-industrial revolution days. Several measures or schemes have been formulated for reducton of GHG emission like drastic cuts and reductions in use of fossil fuels, adopting substitutes to fossil fuels, like renewable sources of energy (e.g., wind, solar and tide), nuclear power and CCS. .

THE CARBON SEQUESTRATION For CCS to be successful, capture and separation of CO2 are the basic steps to be gone through before safe disposal at secure site for a long period of time. This program when demonstrated as a successful technology ,shall ensure the current levels of fossil fuel use as the excess CO2 is captured at the source, and injected down to the secure depths into a rock formation or transported to a secured site by a pipe line for permanent storage in terms of a few thousand years. This method is known to the scientific world as carbon capture and sequestration. The potential sequestration approaches/technologies, viz., geologic, terrestrial, biologic and oceanic are indicated in Table 5. CCS mechanisms broadly fall under the following viz. physical mechanisms, chemical mechanisms and biological mechanisms. The best examples of CCS by biological route are formation / accumulation of fossil fuels and of lime stones. Inorganic removal of CO2 from the atmospheric sources to form stable mineral phases or forms is a fitting example of chemical mechanism. Under physical mechanisms are grouped those CCS methods, wherein CO2 is pumped down into old oil wells or in depths of the ocean. A simple example of physical CCS is a landfill. Geo-engineering is the branch of technology of CCS in the ancient rocks, oil wells or aquifers. In fact, pumping CO2 down was in practice in the US since 70 s for enhanced recovery of crude from oil wells. For e.g., in the state of Texas with >10,000 CO2 wells, CO2 is delivered to the point of pumping through a very large network (= >5000 km) of pipeline.

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Table 5 Carbon Sequestration Targeted geologic formations: Oil and gas reservoirs; Unmineable coal seams (CBM), and Deep saline reservoirs- Such structures and materials are home to crude oil, natural gas, brine and CO2 over millions of years. Coincidentally CO2 emitters like power plants and others are located near geologic formations suitable for CO2 burial. CO2 injection technology has been in vogue in US for enhanced recovery of hydrocarbons. Terrestrial sequestration Methods Forest lands. Below-ground carbon and long-term management and utilization of standing stocks, understory, ground cover, and litter. Agricultural lands. Crop lands, grasslands, and range lands,with emphasis on increasing long-lived soil carbon. Biomass croplands. Long-term increases in soil carbon and value-added organic products. Deserts and degraded lands. Restoration of degraded lands offers significant benefits and carbon sequestration potential in both below-and above-ground systems. Boreal wetlands and peatlands. Management of soil carbon pools and perhaps limited conversion to forest or grassland vegetation where ecologically acceptable Biological & chemical sequestration Methods Advanced catalysts for CO2 or CO conversion; Novel solvents, sorbents, membranes and thin films for gas separation; Engineered photosynthesis systems; Non-photosynthetic mechanisms for CO2 fixation (methanogenesis and acetogenesis); Genetic manipulation of agricultural and tree to enhance CO2 sequestering potential; Advanced decarbonization systems; and Biomimetic systems

Carbon separation and concentration The single most important requirement for a CCS process is separation of pure CO2 from other impurities. In US, pure CO2 accumulates from synthetic ammonia production, calcination of limestone and production of H2. Flue gas from coal-fired power plants contains 10-12 percent CO2 by volume, while flue gas from natural gas combined cycle plants contains only 3-6 percent CO2. For effective carbon sequestration, the CO2 from all emitting sources must be separated and concentrated to at least 90% level, to be cost effective. For instance, most power plants and other large point sources use air-fired combustors, a process that exhausts CO2 diluted with nitrogen. Flue gas from coal-fired power plants contains 10-12 percent CO2 by volume, while flue gas from natural gas combined cycle plants contains only 3-6 percent CO2. For effective carbon sequestration, the CO2 in these exhaust gases must be separated and concentrated. CO2 is currently recovered from combustion exhaust by using amine absorbers and cryogenic coolers. The cost of CO2 capture using current technology, however, is on the order of $150 per ton of carbon much too high for carbon emissions reduction applications. Hence cost of electricity may go to 4 cents/kWh depending on the type of process. In US cost of carbon capture is estimated to represent three-fourths of the total cost of a carbon capture, storage, transport, and sequestration system. The most likely options currently identifiable for CO2 separation and capture include: absorption (chemical and physical), low-temperature distillation, gas separation membranes, mineralization and biomineralization Opportunities for significant cost reductions exist since very little R&D has been devoted to CO2 capture and separation technologies. Several innovative schemes have been proposed that could significantly reduce CO2 capture costs, compared to conventional processes. "One box" concepts that combine CO2 capture with reduction of criteria pollutant emissions are being explored as well. Research leading to

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solutions in revolutionary improvements in CO2 separation and capture technologies centre around new materials (e.g., physical and chemical absorbents, carbon fibber molecular sieves, polymeric membranes); micro-channel processing units with rapid kinetics; CO2 hydrate formation and separation processes and oxygen-enhanced combustion approaches. Efforts to develop retrofittable CO2 reduction and capture options for existing large point sources of CO2 emissions such as electricity generation units, petroleum refineries, and cement and lime production facilities are also considered actively.

Geologic sequestration Carbon dioxide sequestration in geologic formations is primarily focused in the oil and gas reservoirs, unmineable coal seams that are currently used only for recovery of methane (CBM), and deep saline reservoirs which are highly porous and permeable. These geological structures had stored crude oil, natural gas, brine and CO2 over millions of years. Yet another candidate is deeply buried basalt flows. More over many large emitters of CO2 like large power plants and industries are conveniently located near geologic formations that are amenable to CO2 storage. The US for that matter had been practicing the technology of injection of CO2 for enhanced oil and gas recovery (EOR) from its own oil and gas fields in the state of Texas, where nearly 5000 km of pipelines are already in place and working. The US is the world leader in enhanced oil recovery technology, using about 32 million tons of CO2 per year for this purpose. From the perspective of the sequestration program, enhanced oil recovery represents an opportunity to sequester carbon at low net cost, due to the revenues from recovered oil/gas. The scope of this EOR application is currently economically limited to point sources of CO2 emissions that are near an oil or natural gas reservoir. Further, in many cases, this scheme can enhance the recovery of hydrocarbons, providing value-added by-products that may even offset the cost of CO2 capture and sequestration. Currently, efforts are afoot, to determine the petrophysical controls or parameters of rock formations in respect of movement and trapping of CO2 as well as the physico-chemical transformations if any of the constituent minerals of the rocks which is critical to the safety and security of the underground storage and its environmental acceptability. Coal Bed Methane Coal miners often face the nightmarish problem of explosive escape of trapped methane in the coal seams occasionally resulting in fires. (Remember story of Davy s safety lamp). If the seams do occur at huge depths them mining is not the answer, instead coal gasification is. The large amounts of methanerich gas that is adsorbed onto the surface of the coal is recovered by de-pressurising the coal bed by pumping water out. Alternatively CO2 is injected into the bed. Tests have shown that the adsorption rate for CO2 to be approximately twice that of methane, giving it the potential to efficiently displace methane and remain sequestered in the bed. Though, CO2 injected recovery of coal bed methane has been demonstrated in field trials in a limited manner, much more research is warranted to understand and optimize the process. The U.S. coal reserve at an estimated at 6 trillion tons, and 90 percent of it is currently unmineable due to seam thickness, depth, and structural integrity. As several of the power plants are some what near such unminable coal seams warranting limited transport of CO2 gas before injection. Further, integration of coal bed methane with a coal-fired electricity generating system can provide an option for additional power generation with low emissions. Saline Formations Though value added products and hence cost reduction in CO2 injection is not part of sequestration of CO2 in deep saline formations, yet there are certain advantages. Firstly, the estimated carbon storage

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capacity of saline formations in the United States is large with an estimated potential of up to 500 billion tonnes of CO2 - a viable long-term solution. Secondly, most existing large CO2 point sources are within easy access to a saline formation injection point (in the US), and hence sequestration in saline formations is capable of transforming large portions of the existing U.S. energy and industrial outfits to near-zero carbon emissions via this model of low-cost carbon sequestration retrofits. But there is still more research needed to answer the safety and security concerns and environmental viability, like ensuring CO2 will not contaminate the aquifers and hence drinking water supplies or escape from the geological vaults to enter the carbon cycle. One point of support comes from the oil industry practice of use of such saline formations for injecting the brine separated from oil back into the saline formations with out much risk. Besides, US EPA has also allowed injection of some hazardous wastes down into the boreholes in saline formations and hence an extra degree of feeling of viability. In addition the Norwegian Oil Co., Statoil, is injecting a million tons per year of recovered CO2 into Utsira sand, a saline formation under the sea, an amount which is equivalent of the out put of a 150 mw coal fired power plant. Terrestrial sequestration Terrestrial carbon sequestration is defined as either the net removal of CO2 from the atmosphere or the prevention of CO2 net emissions from the terrestrial ecosystems into the atmosphere. Photosynthesising plant communities are the chief enablers or facilitators of this process. It is considered as one of the most cost effective techniques of reduction of atmospheric CO2 by one or all of the following viz., afforestation, reforestation and controlling or reducing deforestation. Vegetation and soil are the chief storage sinks of carbon. 2.0 billion tons of carbon is annually absorbed by the biosphere - i.e., roughly 1/3 of the carbon emission by anthropogenic actions. The soil and the root system of certain plants detain significant amounts of this carbon. Carbon absorbed by the global ecosystem is of the order of 2 trillion tons. An important area of research is about the development of high precision and reliable techniques of measurement of this carbon, especially in the context of carbon trading. The fundamental approaches in this respect are a) protection of ecosystems that store carbon so that such storage can be increased or maintained and b) manipulation of ecosystems like farmlands and forests, to increase carbon sequestration beyond their current levels. The ecosystems that are the most sought after in this respect are: a. Forest lands where in the focus is the below-ground carbon and long-term management and utilization of standing stocks, understory, ground cover, and litter. b. Agricultural lands Here the focal points are crop lands, grasslands, and range lands, with emphasis on increasing long-lived soil carbon. c. Biomass croplands As a complement to ongoing efforts related to biofuels, the focus is on longterm increases in soil carbon and value-added organic products. d. Deserts and degraded lands Restoration of degraded lands offers significant benefits and carbon sequestration potential in both below-and above-ground systems. e. Boreal wetlands and peatlands The emphasis here is on management of soil carbon pools and perhaps limited conversion to forest or grassland vegetation where ecologically acceptable.

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Advanced Chemical and Biological Approaches Alternatives to carbon capture and storage are recycling or reuse of CO2 from energy systems, where the goal is reduction of the cost and energy required to chemically and/or biologically convert CO2 into either commercial products that are inert or long-lived or stable solid compounds. Two promising chemical pathways are magnesium carbonate and CO2 clathrate, an ice-like material. Both provide quantum increases in volume density compared to gaseous CO2. For instance, the entire global emissions of carbon in 1990 could be contained as magnesium carbonate in a space of 10 kilometers by 10 kilometers by 150 meters. The Biological systems, incremental enhancements of carbon uptake by photosynthesis can offer a significant positive effect. An important advantage of biological systems is that they do not require pure CO2 and do not incur costs for separation, capture, and compression of CO2 gas. Further, harnessing natural, non-photosynthetic microbiological processes that are capable of converting CO2 into useful forms, like methane and acetate, could represent a technology breakthrough. In Biological systems, the areas needing closer scrutiny are advanced catalysts for CO2 or CO conversion; novel solvents, sorbents, membranes and thin films for gas separation; engineered photosynthesis systems; non-photosynthetic mechanisms for CO2 fixation (methanogenesis and acetogenesis); genetic manipulation of agricultural and tree crops to enhance CO2 sequestering potential; and advanced decarbonization systems. Ocean storage With its vast aerial coverage the ocean system is a potential candidate for carbon storage. Several concepts have emerged in this respect. a. Dissolution' or injecting CO2 from ship or pipeline into the water column at depths of 1000 m or more, to allow CO2 subsequently to dissolve. b. 'Lake' deposition of CO2 directly on the sea floor at depths of 3000 m, or more where CO2 is denser than water and is expected to form a 'lake' that would delay dissolution of CO2 into the environment. c. Convert the CO2 to bicarbonate using lime stone d .Store the CO2 in solid clathrate hydrates already available on ocean floor or growing more solid clathrate. Obviously, negative are the environmental effects of oceanic storage, and is a least understood area. Large levels of CO2 can kill organisms; yet another problem is the tendency of dissolved CO2 to eventually equilibrate with the atmosphere and hence transient nature of storage. Secondly more CO2 can acidify the ocean with all the now known consequences, and the unknown one like the adverse environmental effects on benthic forms of the bathypelagic, abyssopelagic and hadopelaghic are poorly understood.. Much work needs to be done before defining the extent of the potential problems. The time it takes water in the deeper oceans to circulate to the surface has been estimated to be in the order of 1600 years, varying upon currents and other changing conditions. Costs for deep ocean disposal of liquid CO2 are estimated at US$40 80/ton between capture and deposition. Biomass burial in regions of higher rates oceanic sedimentation is also considered as another method. The bicarbonate approach would reduce the pH effects and enhance the retention of CO2 in the ocean, but this would also increase the costs and other environmental effects.

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Mineral storage Reacting CO2 to form carbonates with naturally occurring minerals of Ca or Mg is also considered due to many potential advantages.. Most notable is the fact that carbonates have a lower energy state than CO2, which is why mineral carbonation is thermodynamically favorable and occurs naturally (e.g., the weathering of rock over geologic time periods). Secondly, the raw materials such as magnesium based minerals are abundant. Finally, such carbonates are unarguably stable and thus re-release of CO2 into the atmosphere is not an issue. However, conventional carbonation pathways are slow under ambient temperatures and pressures. The significant challenge being addressed by this effort is to identify an industrially and environmentally viable carbonation process that will allow mineral sequestration economically. In this process, CO2 is exothermically reacted with abundantly available metal oxides to produce stable carbonates.. The reaction rate can be made faster, for example by reacting at higher temperatures and/or pressures, or by pre-treatment of the minerals which require additional energy input. The IPCC estimates that a power plant equipped with CCS using mineral storage will need 60-180% more energy than a power plant without CCS. Leakage For well-selected, designed and managed geological storage sites, IPCC estimates that risks are comparable to those associated with current hydrocarbon activity. CO2 could be trapped for millions of years, and well selected storages are likely to retain over 99% of the injected CO2 over 1000 years. For ocean storage, the retention of CO2 would depend on the depth; IPCC estimates 30 85% would be retained after 500 years for depths 1000 3000 m. Mineral storage is not regarded as having any risks of leakage. The IPCC recommends that limits be set to the amount of leakage that can take place. This might rule out deep ocean storage as an option. It should also be noted that at the conditions of the deeper oceans, mixing is very low (where carbonate formation/acidification is the rate limiting step), but the formation of water-CO2 hydrates is favorable. (a kind of solid water cage that surrounds the CO2). Regarding, safety of CO2 sequestration, Norway's Sleipner gas field, the oldest plant that stores CO2 on an industrial scale, is the living example- at geosequestration program of CO2 with the most definite form of permanent geological storage of CO2. CO2 Reuse Making jet fuel by scrubbing CO2 from atmosphere will allow aviation to continue in a low carbon economy. A potentially useful way of dealing with industrial sources of CO2 is to convert it into hydrocarbons where it can be stored or reused as fuel or to make plastics. There are a number of projects investigating this possibility, currently, biofuels, represent the other potentially carbon neutral jet fuel available. Carbon dioxide scrubbing with potassium carbonate is used to create liquid fuels. Although the creation of fuel from atmospheric CO2 is potentially very useful in the creation of a low carbon economy, as transport fuels are currently hard to make without fossil fuels. Research is underway to make use of emitted CO2 to manufacture methanol and other hydrocarbons.

SUMMARY This review of CCS has brought to light several points of crucial interest to the society especially in respect of climate change and future climate trends.

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Though the adverse effect of green house gases came to be known from the early days of chemistry, the concern about climate change due to steadily rising GHG emissions came to the fore say only from the nineties. The Earth summit, the Kyoto protocol, the UNFCCC and the finally the IPCC s final report in 2007, became the wake up call for all the governments in the industrial and developing world. Carbon capture and sequestration is now considered as one of the very viable options as it can be used to mitigate and post pone the threat of climate change and at the same time without modifying or decelerating the current consumption pattern of fossil fuels. Many of the mechanisms are known in the scientific world, but designing a technology appropriate and demonstration of the same to the society is the first step. The efforts in this direction have already been launched. The terrestrial sequestration is a method to be considered for aggressive implementation in a populous nation like India where a large chunk of the population is in the BPL category and live in the villages, and follow some sort of poaching the vegetation as the surest means of energizing the cooking stove. However, as geoscientists and with the varied geology around us in India, we have a major role to play in the identification of suitable, safe and secure geological formations for carbon disposal. Acknowledgements I sincerely thank Prof. V. Radhakrishnan and the BD University administration for enabling me to be here and make a presentation on this theme. I have made use of the several internet sites for gathering information that went into this monograph. --------

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