Accelerating Net Zero
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ACCELERATING NET ZERO
ACCELERATING NET ZERO
Role
of CCUS in
Net Zero
Transition
Prof. Rajnish Kumar
Department of Chemical Engineering,
IIT Madras
hile role of renewables, solar, wind, hydro/waves,
hydrogen etc. including nuclear would ensure a cleaner
future. Current energy need, and proposed GDP growth
in many parts of the world could not be achieved without
ensuring implementation of CCUS. In general, people
around the world are aware of the effect of rising CO2 in the atmosphere
and resulting global warming. Prime challenge for the scientific
community is to educate people that the scale at which CCUS has to be
implemented has no parallel in the history of human kind. Significant
effort is required to identify a solution which is not only economical but
also sustainable at the scale it has to be delivered.
In 2023, not a single electricity producing commercial plant around the
world has been able to demonstrate CCUS in its entirety.
CCUS is essentially a three-step process, the first step is to capture the
carbon dioxide at its source;
1. Point source capture (or separation) of CO2 from its associated
gases (mostly N2, as the other toxic gases which are at a much lower
concentration has already been captured) from industries like steel
manufacturing, cement manufacturing, electricity production etc.
For CO2 capture the most mature process is use of mono-ethanol amine
(MEA, or a derivative of this molecule) for CO2 capture. An alternate route
which uses solid adsorbent/absorbent like, carbon nanotubes (CNT), metal
organic framework (MoF) etc. has not been proven at this scale. Some
Innovative solutions also exists (hydrates, ionic liquids etc.) which are being
tested at lab/pilot scale. If one talks about the most mature process which
utilizes a chemical solvent (like MEA) to capture CO2 from its associated
gases, the biggest challenge is in recycling and regeneration of MEA,
assuming that the corrosion issues could be handled appropriately. Some
of the major concerns are regeneration cost, loss of active material during
regeneration, and significantly large losses of water from cooling towers
and other operations. If one talks about CNT, and MoF like materials for
CO2 capture, corrosion is not an issue, however, generation of such
material itself at such a scale is a big challenge. MEA based processes are
being implemented for demonstration around the world, with a typical cost
of USD 30-50 per ton of CO2 captured. This only captures the process cost
of CO2 capture from using MEA based solvent. However, if one looks at the
raw material (i.e. MEA itself) it has its own CO2 footprint. MEA is produced
from reacting ammonia and ethylene oxide, thus, production of these two
chemicals should also be decarbonised and the cost of the same should
appropriately be added in the overall CO2 capture cost.
Direct air capture (DAC) is a technology which many believes is a way
to go, the proponent of this approach takes a futuristic view. It is argued
that producing fossil fuels and capturing CO2 from its utilization is an
endless trap, rather one should stop using fossil fuels all together! This
approach ensures no anthropogenic CO2 emission into the atmosphere (at
least not from use of fossil fuel). Sometime in future when there is no CO2
emission from point source, DAC would ensure that all the CO2 which has
been emitted by humans (so far) could be captured directly from air, and
its concentration could be brought down to 350-400 PPM level. However,
capture of PPM level CO2 from a gas stream is not going to be trivial, and
this process could be prohibitively expensive, current cost is close to 200
USD per ton for captured CO2. Further, the material/chemical required to
capture PPM level CO2 (from air) is currently quiet immature, and actual
cost of the process will not be evident unless one does a proper life cycle
analysis of this approach.
The second step in CCUS involves utilization of captured CO2.
Here one has to realise that an electricity production plant or a cement
manufacturing unit produces tonnes of CO2 every day!
2. Transporting the captured, relatively purer CO2 (which comes
from step 1) to the utilisation site where CO2 could be processed (with a
hydrogen rich source, or H2) and converted to a liquid chemicals. Some of
the typical chemicals are methanol, dimethyl ether, formic acid, aviation
fuels etc.
However, if one looks
at the raw material
(i.e. MEA itself) it has
its own CO2 footprint.
MEA is produced from
reacting ammonia
and ethylene oxide,
thus, production of
these two chemicals
should also be
decarbonised and
the cost of the same
should appropriately
be added in the overall
CO2 capture cost
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