Global warming is the rise in the average temperature of Earth's atmosphere and
oceans since the late 19th century, and its projected continuation. Since the
early 20th century, Earth's mean surface temperature has increased by about 0.8 °C (1.4 °F), with
about two-thirds of the increase occurring since 1980. Warming of the climate system is primarily caused by increasing concentrations of greenhouse gases produced by human
activities such as deforestation and the burning of fossil fuels. Where we will burn the hydrocarbons and produce CO2
methane etc. The cause of temperature rise due to GHG is described in figure
below.
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| Fig: GHG effect |
An increase in global temperature will cause sea levels to rise and will change the
amount and pattern of precipitation, as well
as cause a probable expansion of subtropical deserts. Now a days we can see the effect of climate change mainly in
japan and other mountainous countries as like Nepal there are so many
landslides and flood problem due to high intensity rainfall on short time. Also
in Nepal the snow line is shifting up and the perennial rivers are going to
draught that directly hit to the agriculture and hydropower generation also the
ecosystem will be in disorder. The change of average temperature during 10
years (2000-2009) is shown in figure.
Fig: temperature change on earth Fig: GHG emission by country
Emissions of
GHG are mainly due to the burning of fuels and other activities like that so
its concentration is high in developed countries like USA, China, Brazil etc.
above figure shows about the total GHG emission by the country.
This graph shows
for the constant atmospheric condition we have to reduce the carbondioxide
emission drastically. We cannot reduce energy consumption on that way that will
adverse the economic growth and sustainibility, hence we have to find out the
different mechanisms to reduce the emission of GHG into the atmosphere. There
are some methods to store CO2 in to the ground after separating from
the purification plants of oil.
Carbon capture and storage (CCS)
One of the options that can be used to combat climate change
is to capture CO2 produced
by power generation and industrial processes and store it deep underground, a
process known as Carbon Dioxide Capture and Storage (CCS). CCS involves
capturing the CO2 produced
by the burning of hydrocarbons (e.g. coal and natural gas) before it enters the
atmosphere, and storing it in deep underground. The main components of CCS are:
capture (separation from the gas stream) at a power plant or an industrial
source, compression and transport via pipeline and injection of fluids (at the
pressures associated with CCS injection, CO2 is a fluid rather than a gas) into an
underground storage formation through a well.Following fig shows the
mechanism of CCS.
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Capturing of CO2
Capturing
of the CO2 from its sources is the first step in CCS. It is possible
to capture from the atmosphere also but it will not be the feasible from
economic point of view. Mainly there are three primary methods to capture the
CO2. Post combustion, Pre combustion and Oxy-fuel combustion.This
following schematic diagram shows the processes.
In
post-combustion capture the CO2 is removed after the combustion process,
it is directly separated from the flue gas, after power generation has taken
place. This means that little modification is needed to the industrial
equipment, as the capture plant is bolted to the end of the process.
CO2 is
captured prior to the burning of fossil fuels in pre-combustion capture. One of
the advantages of capturing the CO2 before burning is that the technique
separates hydrogen from the fuel/gas. Hydrogen is a ‘clean’ fuel, producing
only water when burned, and can be used itself as a fuel. A downside to
pre-combustion capture is that it requires a relatively large amount of
modification to the power plant, and is therefore harder to retrofit (that is
fit capture machinery to existing power plants). The scheme is generally
applied to new fossil fuel burning power plants, rather than converting
existing plants.
In
the oxy-fuel combustion process the fossil fuel is burned in an environment of
almost pure oxygen rather than air, which means the resulting flue gas, is made
up of mainly CO2and water. The technique is promising, but the initial air
separation step requires a lot of energy.The benefit of this process is that
the CO2 contains far fewer other substances, and therefore requires much
less processing to remove impurities before it is stored. Oxy-fuel combustion
is at a relatively early stage of development, although there are now a small
number of large scale demonstrations ongoing around the world.
Transportation
It
is not necessary to be the captured area is just above the storage geology so
if it is different then Captured CO2 has to take from captured
station to storage area by using pipeline or vehicle which will be efficient
and viable. Captured CO2 will be in liquid form hence we have to
consider the safety for the environment.
Storage
For the storage of CO2 mainly we use
internal part of the earth it will help the recovery of the oil pores after its
drawing. There are three types of storage systems oil and gas reservoirs, deep
saline formations and unminable coal beds. This figure explain about the
storage of CO2 . There are some risks of releasing of stored CO2
due to some geological fractures but these are very rare case.
Effect of CCS on global warming.
This
CCS method contribute the 80-90 percent carbon dioxide emitted from the oil
industries will store at deep ground hence thousands of tons per day will go to
store without emitted on atmosphere. It will provide control over CO2
and reduce the increase of GHG that will cause slow down of rate of adverse
effects by climate change. Some statistics of CO2 injection is
presenting below.
Hence
we can see the CCS is very effective method to store carbon dioxide. But we
have to research on the other way to convert CO2 and use in life of
human that will give the stability for long term.
