Hydrocarbon Processing - June 2022 - 75

Carbon Capture/CO2
Pathway 4: CCUS technology. Another
pathway to decarbonization is through
CCUS. This technology plays a key role
in decarbonizing H2
produced by steam
methane reforming (SMR) to produce
blue H2
. Carbon capture is also key to
capturing CO2 in processes (such as natural
gas, ethylene oxide, ethanol and H2
production) that produce streams of high
CO2
is instrumental in reducing CO2
concentration. Additionally, CCUS
emissions
in the hard-to-decarbonize steel
and concrete industries.
The oil and gas industry is a leader in
developing and deploying CCUS technology.
In 2020, global anthropogenic
(human-made) CO2
gigatons, with only 40 megatons (0.12%)
being captured.30
captured 70% of the CO2
emissions totaled 34
Oil and gas operations
emitted. The
oil and gas industry has the capability to
implement CCUS on a large scale. Depending
on the success of implementing
the other decarbonization pathways, the
International Energy Agency (IEA) estimates
that CCUS may be needed to capture
as much as 7.6 gigatons/yr of CO2
to
meet 2050 global net-zero goals.
In the U.S., the 45Q tax credit provides
an incentive to install CCUS at $35/t
for CO2
(EOR) and at $50/t for CO2
into storage. These incentives are not large
enough for capturing CO2
in diluted CO2
used
streams. Depending on oil prices, drillers
may pay $20/t-$30/t for CO2
in EOR. CO2 capture cost ranges from
$30/t-$40/t for streams with high CO2
concentrations and can cost $60/t-$90/t
for CO2
gas, where CO2
The cost to capture CO2
captured from fired heater flue
content is only 8%-10%.
in naturalgas-fired
power generation ranges from
$60/t-$90/t. Adding carbon capture
and storage (CCS) to a combined-cycle
power plant derates net power output by
12%-15%. Derating is the result of the
heat required to regenerate CO2
solvent (2 Gj/t CO2
absorber
). Note that 2 Gj/t CO2
) and power for CO2
is roughly
There
capused
in examples) and capturing
CO2
gas contains 8%-9% CO2
in a fired heater stack. Flue
, 70%
Flue gas low CO2
compression (200 kWh electricity/t
CO2
equivalent to 1 t steam/1 t CO2.31,d
are three primary methods of CO2
ture from combustion:
* Post-combustion: This method
includes burning fuel (CH4
is
Heat input to reformer
Fuel CH4 or H2
Reformer firebox
60% CO2 capture with just unit A
90% capture with unit A and B or one large unit B
Alternative is unit A and use product H2 to fuel firebox
if burned H2 in firebox, then get 100% recovery
but reduced H2 production
Firebox flue gas
CO2 capture " B "
FIG. 6. Three methods to capture CO2 from combustion.
Hydrocarbon Processing | JUNE 2022 75
Firebox CO2 40% recovery
with no unit A and larger unit B can get 90% recovery
CO2, H2
Fuel HC4
Steam H2O
Reformer (SMR)/shift
reactor
Tail gas to fuel
Pre-combustion
capture " A "
PSA
CO2, H2
H2
used for enhanced oil recovery
that goes
Fuel CH4
Oxygen from ASU
O2
CH4 + 2 O2 = CO2 + 2 H2O
Air separation unit
Reaction CO2 60% recovery
H2O, N2 and no CO2
Flue gas
Boiler
Air N2, O2
2 H2 + O2 = 2 H2O
Pre-combustion capture
SMR reaction CH4 + 2 H2O = CO2 + 4 H2
Boiler
Fuel CH4
Air N2, O2
Boiler
CH4 +2 O2 = CO2 +2 H2O
Oxy-firing for capture
Flue gas
CO2 compressor
CO2, H2O and no N2
H2O
CO2
nitrogen, 18% water and 2%-3%
oxygen at atmospheric pressure.
Note: A gas turbine's exhaust
without duct burner firing
contains only 3%-5% CO2
removed from flue gas
Mitigation
* Oxy-firing system: This system
involves burning CH4
fuel with
. Postcombustion
capture uses chemical
solvents, such as hindered amines.
Net CO2
capture is about 90% of the actual
CO2
captured, since absorber
solvent regeneration and CO2
compression have a CO2
Post-combustion capture
Flue gas
CCS
CO2, H2O, and N2
Amine capture
PSA
H2O
N2
CO2
footprint
that reduces the actual CO2
removed from the atmosphere.
oxygen (supplied from an air
separation unit) in a fired heater.
Flue gas contains CO2
but no nitrogen. No CO2
and water
capture
unit is required. Compressing flue
gas removes water to produce a
pure CO2
stream. Personnel must
seal leaks in the convection section
to keep it from sucking in air, which
will add nitrogen in the flue gas,
leading to the captured CO2
being
off specifications.
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