Rastogi, Fluor, New Delhi, India
Global demand for crude oil,
natural gas, coal and other fossil fuels is continuously increasing in various
industries and petrochemical plants. While the use of renewables, improved
energy efficiency and electric vehicles are areas of focus, oil and
natural gas will continue to be in demand for petrochemicals and fueling
transportation by land, sea and air. Greater fossil fuel consumption
means more carbon dioxide (CO2) emissions. CO2 is the
primary greenhouse gas (GHG) and its rising levels cause extreme climate events
like temperature rise and shift in rainfall/snow patterns. This article
addresses the various available technologies used for capturing carbon, reducing
CO2 emissions and utilizing the captured carbon for monetization. The
article also addresses barriers in deploying carbon capture, utilization and
storage (CCUS) technologies in various industries.
CCUS is the process of capturing CO2
formed during power generation and industrial processes and preventing it from being
emitted into the atmosphere. Captured CO2 is then further processed
and either permanently stored thousands of feet below the surface or
transported to other businesses to produce products (e.g., synthetic fuels, building
materials, urea, carbonated drinks) or used for enhanced oil recovery. CCUS
technologies have significant potential to reduce CO2 emissions from
new and existing coal- and gas-fired power plants, petrochemical complexes,
refineries and other industrial processes. CCUS technologies play an important
role in reducing the carbon intensity of industrial operations to meet the net-zero
emissions ambitions of the Paris agreement by 2050. CCUS involves three major
steps: capture, processing and transport, and storage or utilization (FIG. 1). Various technologies can be used to
capture CO2 at the source.
Post-combustion carbon capture.
This is the most common technology used in petrochemical facilities, power
generation plants and other industries to capture CO2 from exhaust
gases created by burning fossil fuels. These include pressure swing adsorption
(PSA), amine absorption and cryogenic separation technologies for CO2 separation.
Amine-based absorption is the most common technology used for post-combustion
capture. Generally, exhaust gases bring in contact with a liquid solvent,
typically an aqueous amine solution. The amine selectively absorbs the CO2,
capturing more than 90% and preventing nitrogen and oxygen from being released
into the atmosphere. A CO2-rich amine is regenerated by stripping
the CO2 out of the liquid with steam, enabling the lean amine
to be recycled to the absorber while producing a concentrated CO2 stream.
The captured CO2 is then compressed and cooled in liquid form.
Pre-combustion carbon capture.
This technology is mostly used in industrial processes and involves removing CO2
from fossil fuels before combustion. It is based on gasification processes
where a feedstock (e.g., coal) is partially oxidized in steam and oxygen/air
under high temperature and pressure to form synthetic gas (syngas). Syngas is a
mixture of hydrogen (H2), carbon monoxide (CO), CO2 and smaller
gaseous components, such as methane. The syngas is further processed to convert
CO and water to H2 and CO2. The CO2 is then
captured, and the H2-rich fuel is combusted.
combustion. This process combusts fossil fuel in a nearly pure oxygen
environment, as opposed to air. Oxy-fuel combustion generates flue gas with
very high CO2 and water vapor concentrations. Low-temperature
dehydration and desulfurization processes can easily produce a high-purity CO2
stream from this flue gas.1
carbon capture. Work is underway to develop mobile carbon capture and
storage (CCS) technologies for the transport sector. The prototype developed by
Aramco can capture 40% CO2 from the exhaust of a heavy-duty truck.2
This CO2 is stored in onboard tanks where the gas can be unloaded at
fuel stations and then sent to a central location for re-use or sequestration.
Once fully developed, this technology can be deployed to marine vessels,
heavy-duty trucks and other mobile applications to capture the CO2
at its source.
Processing and transport. Captured
CO2 contains water vapors that must be removed due to the risk of
corrosion and hydrate formation. The level of accepted water content after
dehydration of CO2 depends on the use of the captured CO2.
Several different gas dehydration methods are available. The simplest
dehydration methods are cooling, water condensing and gas/water separation.
Other methods are dehydration by absorption (for large scale), adsorption (for
low water levels) or using membranes (for low flow). The most traditional
method for large-scale dehydration is absorption into triethylene glycol (TEG).
The water from captured CO2 is removed by absorption into TEG,
followed by desorption (FIG.
CO2 is then transported in three states: gas, liquid and
solid. Commercial-scale transport uses tanks, pipelines and ships for
gaseous and liquid CO2. Gas at atmospheric pressure occupies such a
large volume that extensive facilities are needed. The gas must be compressed,
and compressed gas is transported by pipeline. Volume can be further reduced by
liquefaction and solidification. Solidification requires much more energy than
other options and is inferior from a cost and energy viewpoint; therefore, it
is not preferred.
Utilization and storage. Captured
CO2 can be put to productive use in enhanced oil recovery (EOR) and
the manufacture of syngas and building materials or be stored in underground
geologic formations. In EOR, CO2 is injected to extract deep oil and
gases from developed oil and gas reservoirs. These reservoirs offer geologic
storage potential and economic opportunity. Revenue from selling captured CO2
to EOR operators could help to meet the cost of capture technology at
power plants and industrial facilities.
is also used as feedstock in manufacturing various products; however, this is
not a permanent solution. These products, when degraded, will release CO2 back
into the atmosphere. However, using CO2 to make syngas can help meet
energy demand and reduce fossil fuel consumption.
IN CCUS DEPLOYEMENT
High capital cost. The
most significant barrier to the development of CCUS technologies is the high
equipment and energy cost needed for the capture and compression phases.
Capturing the CO2 decreases a plant’s efficiency and increases water
use. Any additional costs posed by these (and other) factors can make a CCUS
project financially nonviable. Additional research and development are required
to optimize CCUS technology to reduce the overall cost of implementing a CCUS
Transportation challenges. In
addition to the high costs of capture technology, transporting captured CO2
is also very costly. Significant energy is required to compress CO2
for transporting it via pipeline or ship. Moreover, the compressors, onsite storage
and pipelines themselves are expensive. Additionally, captured CO2 must
be processed to remove impurities (including water), which can cause damage to
pipelines and lead to leaks and explosions as the compressed fluid rapidly
expands into a gas. Such processing facilities add further costs to CCUS
Takeaway. CCUS deployment is
viewed as the most practical decarbonization method in petrochemical facilities,
power generation plants and other industries. It can address global climate
issues by reducing GHG emissions and contributing to the 2050 net-zero
emissions goal. To accelerate CCUS deployment, local regulations and policies
must be in place to enforce the carbon capture project at power generation
plants, industrial facilities and petrochemical complexes. Governments should also
incentivize CCUS projects and other businesses using captured CO2. HP
ANUJ RASTOGI is a
mechanical engineer with Fluor Daniel India Private Ltd., New Delhi and has
been with the company for 12 yr. He has more than 17 yr of packaged equipment
experience and earned a BE in mechanical engineering.