Geosequestration

ASSIGNMENT on GEO-SEQUESTRATION

M.Sc.(tech.) Environmental Science & Technology (CEST) RAJIV GANDHI SOUTH CAMPUS BARKACHHA MIRZAPUR BANARAS HINDU UNIVERSITY

SUPERVISED BY: VIJAYKRISHNA SIR

SUBMITTED BY: KAUSHIK KUMAR M.Sc.(tech.) 3rd SEM.

CONTENT:
1. Introduction 2. Need for Geo-sequestration 3. CO2 Capture Methods 3.1 Post combustion process 3.2 Pre combustion process 3.3 Oxy-Fuel method 4. CO2 transport 5. CO2 storage 5.1 Geological storage 5.2 Ocean Storage 5.3 Mineral storage 6. Storage capacity of Different reservoirs 7.Types of Geo-sequestration process 8. Advantages and Disadvantages 9. Conclusion 10. Reference

INTRODUCTION

:

Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. It is often referred to by its formula CO2. It is present in the Earth's atmosphere at a low concentration (0.03%) and acts as a greenhouse gas. The initial carbon dioxide in the atmosphere of the young Earth was produced by volcanic activity; this was essential for a warm and stable climate conducive to life. Now, a days volcanic releases are about 1% only of the amount of CO2, which is released by human activities.

Since the start of the Industrial Revolution, the atmospheric CO2 concentration has increased by approximately 110 µL/L or about 40%, most of it released since 1945. Burning fossil fuels such as coal and petroleum is the leading cause of increased man-made CO2; deforestation is the second major cause. Around 24,000 million tons of CO2 are released per year worldwide, equivalent to about 6,500 million tons of carbon. Various techniques have been proposed for removing excess carbon dioxide from the atmosphere in carbon dioxide sinks. A carbon dioxide sink is a carbon reservoir that is increasing in size, and is the opposite of a carbon "source". This concept of CO2 sinks has become more widely known because the Kyoto Protocol allows the use of carbon dioxide sinks as a form of carbon offset. Carbon sequestration is the term describing processes that remove carbon from the atmosphere. To help mitigate global warming, a variety of means of artificially capturing and storing carbon – as well as of enhancing natural sequestration processes – are being explored. The Global Warming Theory (GWT) predicts that increased amounts of CO2 in the atmosphere tend to enhance the greenhouse effect and thus contribute to global warming. The effect of combustion-produced carbon dioxide on climate is called the Callendar effect.

DEFINITION :
Geosequestration is the deep geological storage of carbon dioxide from major industrial sources such as: fossil fuel-fired power stations, oil and natural gas processing, cement manufacture, iron and steel manufacture and the petrochemical industries instead of allowing it to disperse in air. Geosequestration represents perhaps the only option for decreasing greenhouse gas emissions while using fossil fuels and retaining our existing energydistribution infrastructure.

General Process Description:
In a typical CO2 Capture package, 1. hot flue gas passes through the scrubber tower, where it is cooled with cooling water 2. before being fed to the absorber tower. The gas enters near the bottom of the absorber tower and flows upwards through the internal packing 3.coming into contact with the solvent, which enters near the top of the tower, as the solvent cascades down through the tower. As the flue gas rises through the tower the carbon dioxide level is progressively reduced as it is absorbed by the solvent meaning the treated gas vented from the absorber is virtually free of CO2. 4.From the bottom of the absorber tower the CO2-rich solvent is pumped through the lean-rich exchanger.

5. to pre-heat the solvent before it enters the regenerator tower. In the regenerator the solvent is heated via the reboiler 6. to reverse the absorption reaction. As the solvent cascades down through the tower, CO2 is gradually desorbed from the solvent 7. By the time the solvent reaches the bottom of the tower virtually all the absorbed CO2 has been released and the CO2-lean solvent is cooled and pumped back to the top of the absorber tower to repeat the process . 8.The desorbed CO2 exits the regenerator tower as a pure, water saturated gas from where it is cooled 9.and then passes through the reflux accumulator to remove excess water . The pure carbon dioxide product gas is then ready for direct use or further processing.

CO2 capture methods:
Capturing CO2 can be applied to large point sources, such as large fossil fuel or biomass energy facilities, major CO2 emitting industries, natural gas production, synthetic fuel plants and fossil fuel-based hydrogen production plants. Broadly, three different types of technologies exist:

1.Post-combustion:
In post-combustion, the CO2 is removed after combustion of the fossil fuel. This is the scheme that would be applied to conventional power plants. Here, carbon dioxide is captured from flue gases at power stations (in the case of coal, this is sometimes known as "clean coal"). The technology is well understood and is currently used in niche markets.

2.Pre-combustion:
The technology for pre-combustion is widely applied in fertilizer, chemical, gaseous fuel (H2, CH4), and power production. In these cases, the fossil fuel is gasified and the resulting CO2 can be captured from a relatively pure exhaust stream.

3.Chemical looping combustion(oxyfuel combustion):
An alternate method, which is under development, is the chemical looping combustion (also called “oxyfuel combustion” or simply “oxy-combustion”). Chemical looping uses a metal oxide as a solid oxygen carrier. Metal oxide particles react with a solid, liquid or gaseous fuel in a fluidized bed combustor, producing solid metal particles and a mixture of carbon dioxide and water vapor. The water vapor is condensed, leaving pure carbon dioxide, which can be sequestered. The solid metal particles are circulated to another fluidized bed where they react with air, producing heat and regenerating metal oxide particles that are recirculated to the fluidized bed combustor.

CO2 transport:
After capture, the CO2 must be transported to suitable storage sites. Those storage sites are not necessarily located in the same area as the CO2 emitting plants. Hence, transportation remains issue and pipelines, which are generally the cheapest form of transport, or ships (when no pipelines are available) are required for CO2 transportation. Note that both methods are currently used for transporting CO2 for other applications. In order for CO2 transportation to be economically viable, especially for the huge volumes produced by emitting plants, CO2 would need to be compressed and liquefied. According to the Fraunhofer Institute, the liquefaction of CO2 from atmospheric pressure to 110 bar would require 0,12 kWh per tonne of CO2.

CO2 storage:
Various forms of more or less permanent storage of CO2 isolated from the atmosphere have been conceived. These are storage in various deep geological formations (including saline formations and exhausted gas fields), ocean storage, and reaction of CO2 with metal oxides to produce stable carbonates. As of 2005, it is estimated that saline formations would offer storage capacities for approx. 50-100 years. However, tectonic movements may have significant impacts on the usability and durability of those storage sites. Also, the geographical location of some saline formations may make transportation of CO2 difficult – or even impossible.

I. Geological storage:
Also known as geo-sequestration, this method involves injecting carbon dioxide directly into underground geological formations (usually in depths of approx. 1,000–2,500 meters). Oil fields, gas fields, saline formations, and unminable coal seams have been suggested as storage sites. Here, various physical (e.g., highly impermeable cap rock) and geochemical trapping mechanisms would prevent the CO2 from escaping to the surface. CO2 is sometimes injected into declining oil fields to increase oil recovery. This option is attractive because the storage costs are offset by the sale of additional oil that is recovered. Disadvantages of old oil fields are their geographic distribution and their limited capacity. Unminable coal seams can be used to store CO2, because CO2 adsorbs to the coal surface, but the technical feasibility depends on the permeability of the coal bed. In the process it releases methane, that was previously adsorbed to the coal surface, and that may be recovered. Again the sale of the methane can be used to offset the cost of the CO2 storage. Saline formations contain highly mineralized brines, and have so far been considered of no benefit to humans. Saline aquifers have been used for storage of chemical waste in a few cases. The main advantage of saline aquifers is their large potential storage volume and their common occurrence. This will reduce the distances over which CO2 has to be transported. The major disadvantage of saline aquifers is that relatively little is known about them, compared to oilfields. To keep the cost of storage acceptable the geophysical exploration may be limited, resulting in larger uncertainty about the aquifer structure. Unlike storage in oil fields or coal beds no side product will offset the storage cost. Leakage of CO2 back into the atmosphere may be a problem in saline aquifer storage. However,

current research shows that several trapping mechanisms immobilize the CO2 underground, reducing the risk of leakage. For well-selected, designed and managed geological storage sites, IPCC estimates that CO2 could be trapped for millions of years, and the sites are likely to retain over 99% of the injected CO2 over 1,000 years.

II. Ocean storage:
Another proposed form of carbon storage is in the oceans. The following two main concepts exist: • The dissolution type injects CO2 by ship or pipeline into the water column at depths of 1,000 meters or more, and the CO2 subsequently dissolves. The lake type deposits CO2 directly onto the sea floor at depths greater than 3,000 meters, where CO2 is denser than water and is expected to form a 'lake' that would delay dissolution of CO2 into the environment. A third concept is to convert the CO2 to bicarbonates (using limestone) or hydrates.

•

The environmental effects of ocean storage are generally negative. Large concentrations of CO2 kill ocean organisms, but another problem is that dissolved CO2 would eventually equilibrate with the atmosphere, so the storage would not be permanent. Also, as part of the CO2 reacts with the water to form carbonic acid, H2CO3, the acidity of the ocean water increases. The resulting environmental effects on benthic life forms of the bathypelagic, abyssopelagic and hadopelagic zones are poorly understood. Even though life appears to be rather sparse in the deep ocean basins, energy and chemical effects in these deep basins could have far reaching implications. Much more work is needed here to define 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 on the order of 1,600 years, varying upon currents and other changing conditions. Costs for deep ocean disposal of liquid CO2 are estimated at $40-80 per ton. This figure covers the cost of sequestration at the power plant and naval transport to the disposal site. 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 impacts. An additional method of long-term ocean-based sequestration is to gather crop residue such as corn stalks or excess hay into large weighted bales of biomass and deposit it in the alluvial fan areas of the deep ocean basin. Dropping these residues in alluvial fans would cause the residues to be quickly buried in silt on the sea floor, sequestering the biomass for very long time spans. Alluvial fans exist in all of the world's oceans and seas where river deltas fall off the edge of the continental shelf such as the Mississippi alluvial fan in the Gulf of Mexico and the Nile alluvial fan in the Mediterranean Sea.

III. Mineral storage:
Mineral storage aims to trap carbon in stable minerals, and CO2 would be forever trapped. In this process, CO2 is reacted with (abundantly available) metal oxides, which produces stable carbonates. This process occurs naturally and is responsible for much of the surface limestone. However, the natural reaction is very slow and has to be enhanced by pre-treatment of the

minerals, which is very energy intensive. 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. Mineral sequestration Mineral sequestration aims to trap carbon in the form of solid carbonate salts. This process occurs slowly in nature and is responsible for the deposition and accumulation of limestone (calcium carbonate) over geologic time. Carbonic acid in groundwater slowly reacts with complex silicates to dissolve calcium, magnesium, alkalis and silica and leave a residue of clay minerals. The dissolved calcium and magnesium react with bicarbonate to precipitate calcium and magnesium carbonates, a process that organisms use to make shells. When the organisms die, their shells are deposited as sediment and eventually turn into limestone. Limestones have accumulated over billions of years of geologic time and contain much of Earth's carbon. Ongoing research aims to speed up similar reactions involving alkali carbonates One proposed reaction is that of the olivine-rich rock dunite, or its hydrated equivalent serpentinite with carbon dioxide to form the carbonate mineral magnesite, plus silica and iron oxide (magnetite). Serpentinite sequestration is favored because of the non-toxic and stable nature of magnesium carbonate. The ideal reactions involve the magnesium endmember components of the olivine (reaction 1) or serpentine (reaction 2), the latter derived from earlier olivine by hydration and silicification (reaction 3). The presence of iron in the olivine or serpentine reduces the efficiency of sequestration, since the iron components of these minerals break down to iron oxide and silica (reaction 4).

Serpentinite reactions
Reaction 1

Mg-Olivine + Carbon dioxide → Magnesite + Silica
Mg2SiO4 + 2CO2 → 2MgCO3 + SiO2 + H2O Reaction 2

Serpentine + carbon dioxide → Magnesite + silica + water
Mg3[Si2O5(OH)4] + 3CO2 → 3MgCO3 + 2SiO2 + 2H2O

Reaction 3

Mg-Olivine + Water + Silica → Serpentine
3Mg2SiO4 + 2SiO2 + 4H2O → 2Mg3[Si2O5(OH)4 Reaction 4

Fe-Olivine + Water → Magnetite + Silica + Hydrogen
3Fe2SiO4 + 2H2O → 2Fe3O4 + 3SiO2 + 2H2

CO2 re-use:
Making Jet fuel by scrubbing CO2 from the air would 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 variants exist based on potassium carbonate which can be used to create liquid fuels. Although the creation of fuel from atmospheric CO2 is not a geoengineering technique, nor does it actually function as greenhouse gas remediation, it nevertheless is potentially very useful in the creation of a low carbon economy, as transport fuels, especially aviation fuel, are currently hard to make other than by using fossil fuels. Whilst electric car technology is widely available, and can be used with renewable energy for carbon neutral driving, there are no electric jet airliners available, nor are there likely to be in the foreseeable future. Single step methods: CO2 + H2 → methanol A proven process to produce a hydrocarbon is to make methanol. Methanol is rather easily synthesised from CO2 and H2 (See Green Methanol Synthesis). Based on this fact the idea of a methanol economy was born. Single step methods: CO2 → hydrocarbons At the department of Industrial Chemistry and Engineering of Materials at the University of Messina, Italy there is a project to develop a system which works

like a fuel-cell in reverse, whereby a catalyst is used that enables sunlight to split water into hydrogen ions and oxygen gas. The ions cross a membrane where they react with the CO2 to create hydrocarbons. 2 Step methods: CO2 → CO → Hydrocarbons If CO2 is heated to 2400°C, it splits into carbon monoxide and oxygen. The Fischer-Tropsch process can then be used to convert the CO into hydrocarbons. The required temperature can be achieved by using a chamber containing a mirror to focus sunlight on the gas. There are a couple of rival teams developing such chambers, at Solarec and at Sandia National Laboratories, both based in New Mexico. According to Sandia these chambers could provide enough fuel to power 100% of domestic vehicles using 5800 km², but unlike biofuels this would not take fertile land away from crops but would be land that is not being used for anything else. James May, the British TV presenter, visited a demonstration plant in a recent programme in his 'Big Ideas' series

The worldwide capacity of potential CO2 storage reservoirs:
Ocean and land-based sites together contain an enormous capacity for storage of CO2. The world’s oceans have by far the largest capacity for carbon storage.

Sequestration option
Ocean Deep saline formations Depleted oil and gas reservoirs Coal seams Terrestrial Utilization

Worldwide capacity
1000s GtC 100s–1000s GtC 100s GtC 10s–100s GtC 10s GtC