CARBON

1. Carbon Sequestration

3. Carbon Sequestration
 Also known as “carbon capture and storage”.
 More than 33 billion tons of carbon emissions (annual worldwide).
 According to the Intergovernmental Panel on Climate Change,
nations may need to remove between 100 billion and 1 trillion
tonnes of carbon dioxide from the atmosphere this century to avert
the worst effects of climate change, far more than can be absorbed
by simply planting more trees.
 Carbon sequestration is the long-term storage of carbon in
plants, soils, geologic formations, and the ocean.
 Carbon sequestration occurs both naturally and as a result of
anthropogenic activities.

4. Methods of CS
Methods:
Natural Carbon Sequestration:
It is the process by which nature has achieved a balance of carbon dioxide in
our atmosphere suitable for sustaining life.Animals expel carbon dioxide, as
do plants during the night.
Nature provided trees, the oceans, earth and the animals themselves as
carbon sinks, or sponges. All organic life on this planet is carbon based and
when plants and animals die, much of the carbon goes back into the ground
where it has little impact on contributing to global warming.
Artificial Carbon Sequestration:
Number of processes whereby carbon emissions are captured at the
point of production (e.g. Factory Chimneys) and then buried.
ocean sequestration whereby carbon dioxide is injected deep into the
ocean, forming lakes of CO2. In theory, the CO2 will stay down deep due to
the pressure and temperature of the surrounding water, gradually dissolving into
that water over time.
Another example is geological sequestration where the carbon dioxide
is pumped into underground chambers such as old oil reservoirs,
aquifers and coal seams that are unable to be mined.

5. Types of CS
1.Terrestrial Carbon Sequestration:
 The process through which CO2 from the atmosphere is absorbed
naturally through photosynthesis & stored as carbon in biomass &
soils.
 Tropical deforestation is responsible for 20% of world’s annual CO2
emissions.
 Ways to reduce greenhouse gases:
- Avoiding emissions by maintaining existing carbon storage in trees and
soils.
- Increasing carbon storage by tree planting or conversion from
conventional to conservation tillage practices on agricultural lands.

6. Types of CS
1. Terrestrial Carbon Sequestration:
 Carbon seq. rates differ based on the species of tree, type of soil,
regional climate, topography & management practice.
 Carbon accumulation eventually reaches saturation point where
additional sequestration is no longer possible (when trees reach
maturity, or when the organic matter in soils builds back up to
original levels before losses occurred).
 After saturation, the trees or agricultural practices still need to be
sustained to maintain the accumulated carbon and prevent
subsequent losses of carbon back to the atmosphere.

8. Types of CS
2. Geological Carbon Sequestration:
 Geologic Storage involves capturing anthropogenic CO2 before it
enters the atmosphere and injecting it into underground formations.
 Once CO2 is injected deep underground (typically more than 800
meters) it is trapped in minute pores or spaces in the rock structure.
 Impermeable cap rocks above the storage zones act as seals to
ensure the safe storage of CO2.
 Oil fields, gas fields, saline formations, unminable coal seams, and
saline-filled basalt formations have been suggested as storage sites.
 CO2 is sometimes injected into declining oil fields to increase oil
recovery (enhanced oil recovery).
 This option is attractive because the storage costs are offset by the
sale of additional oil that is recovered.

9. Types of CS
2. Geological Carbon Sequestration:

10. Types of CS
2. Geological Carbon Sequestration:

11. CO2 Capture Technologies
• Pre-combustion: In these cases, the fossil fuel is partially oxidized, for instance
in a gasifier. The CO from the resulting syngas (CO and H2) reacts with added
steam (H2O) and is shifted into CO2 and H2. The resulting CO2 can be captured
from a relatively pure exhaust stream. The H2 can be used as fuel; the CO2 is
removed before combustion. The technology for pre-combustion is widely applied
in fertilizer, chemical, gaseous fuel (H2, CH4), and power production.
Gasification:
 Convertion of biomass or fossil fuel based carbonaceous materials into gases,
like CO, H2, and CO2.
 This is achieved by reacting the feedstock material at high temperatures (typically
>700°C), without combustion, via controlling the amount
of oxygen and/or steam present in the reaction.
 The resulting gas mixture is called syngas or producer gas (CO and H2) and is
itself a fuel due to the flammability of the H2 and CO of which the gas is largely
composed.

12. CO2 Capture Technologies
• Post-combustion: capturing CO2 from flue gas generated after combusting a
C –based fuel such as coal or natural gas. In conventional fossil fuel power
plants, coal or natural gas is burned with air to generated heat energy which is
converted to electricity.
• Oxyfuel combustion: pure oxygen, instead of air, is used for combustion to
obtain high concentration of CO2. To control the temperature of furnance flame,
part of cooled flue gas is required to recirculate. At last the flue gas consist
mainly CO2 and water vapour. The latter of which is condensed through
cooling.The result is an almost pure CO2 stream.
• Chemical looping combustion: A metal oxide is used as an oxygen carrier
instead of using pure oxygen directly for the combustion as in the case of
oxyfuel combustion. During the process the metal oxide is reduced to metal
while the fuel is being oxidized to CO2 and water.

13. CO2 SeparationTechnologies
The main CO2 separation technologies that can be applied to isolate the CO2
from the fuel gas stream prior to transportation.
 Absorption: A liquid sorbent is used to separate the CO2 from the flue gas.
The sorbent can be regenerated through a stripping or regenerative process by
heating and/or depressurization. Ex.: Alkyl amines
 Adsorption: In contrast to absorption processes which use a liquid
absorbent, a solid sorbent is used to bind the CO2 on its surfaces. Large
specific surface area, high selectivity and higher generation ability are the main
criteria for sorbent selection. Ex.: Silica gel, zeolite, graphite etc
 Membrane separation: Membranes can be used to allow only CO2 to pass
through, while excluding other components of the flue gas.

14. CO2 SeparationTechnologies
 Hydrate-based separation: Hydrate-based CO2 separation is a new
technology by which the exhaust gas containing CO2 is exposed to
water under high pressure forming hydrates. The CO2 in the exhaust
gas is selectively engaged in the cages of hydrate and is separated from
other gases.
 Cryogenic distillation: Cryogenic distillation is a gas separation
process using distillation at very low temperature and high pressure,
which is similar to other conventional distillation processes except that
it is used to separate components of gaseous instead of liquid.

15. Types of CS
3. Oceanic Carbon Sequestration:
• Carbon sequestration by direct injection into the deep ocean involves the
capture, separation, transport, and injection of CO2 from land or tankers.
• 1/3 of CO2 emitted a year already enters the ocean.
•

16. Types of CS
3. Oceanic Carbon Sequestration:
Two main concepts exists;
• The 'dissolution' type injects CO2 by ship or pipeline into the water column at
depths of 1000 m or more, and the CO2 subsequently dissolves.
• The 'lake' type deposits CO2 directly onto the sea floor at depths greater than
3000 m, where CO2 is denser than water and is expected to form a 'lake' that
would delay dissolution of CO2 into the environment.
• This can be done in two ways- enhancing productivity of ocean biological
systems through Iron fertilization, and injecting CO2 into the deep ocean.
• The dumping of iron stimulates phytoplankton production, which in turn leads
to enhanced photosynthesis from these microorganisms, helping in
CO2 absorption.

17. Potential of Artificial Carbon Sequestration
• Faster Sequestration:
 Natural sequestration is a slow process compared to artificial
sequestration.Thus it can complement natural sequestering to achieve
goals which are necessary to fight climate change.
 Increase in Productivity:
 Enhanced agricultural yield and better oil recovery as a result of stored
carbon in underground chambers such as old oil reservoirs, aquifers
and coal seams.
 Employment Generation:
 This new and emerging field is attracting private players and venture
capitalists, which in turn can help in employment generation.

18. Challenges of Artificial Carbon Sequestration
 Lack of technology:
◦ A growing number of corporations are pouring money into so-called engineered
carbon removal techniques.
◦ However, these technologies are at a nascent stage and need an overhaul to be
exploited.
 High Cost:
◦ Carbon removal technologies remain too expensive for widespread use.
◦ Artificial carbon sequestration is costly, energy intensive, relatively
untested and has no other side benefits.
 Environmental Concerns:
◦ Carbon dioxide may be stored deep underground. Reservoir design faults, rock
fissures, and tectonic processes may act to release the gas stored into the ocean
or atmosphere leading to unintended consequences such as ocean
acidification etc.

19. Thank you