Hydrocarbon Processing - August 2022 - 31

Refining Technology
timated product slate, energy use and CO2
emissions. Parameters are varied to bring
out the major factors that impact CO2
emissions. CO2
emissions are presented
as per barrel (bbl) of crude processed to
eliminate the impact of refinery capacity.
For this article, the default data and constants
in PRELIM are used for estimates.
PRELIM does give the option to modify
these defaults values with data available
for specific design.
The input parameters that are varied
are: crude quality; refinery configuration;
cogeneration, included or not; source of
electricity; and upstream emissions for
NG, included or excluded. This covers
a wide range of existing refineries and
captures the variations in CO2
emissions
both at an aggregate level and specific to
the source.
Discussion of
modelling results.
/bbl
From TABLE 2, CO2 emissions range between
30 kg CO2/bbl and 90 kg CO2
of crude processed. Major findings are
summarized below:
1. For the same crude (Cases
2-4), moving from a mediumconversion
to deep-conversion
refinery with a coker increases
CO2
emissions by ~40%.
Processing the same crude in
deep conversion with a residue
hydrocracker further increases
emissions by ~20%.
2. For a refinery with the same
configuration (a deep conversion
with coker), processing heavier
crude (Cases 3 and 5) increases
CO2
emissions by ~25%.
3. The difference in CO2
emissions
between a deep-conversion
refinery with a residue
hydrocracker vs. one with a coker
is 50% (Cases 5 and 6).
4. For the same crude and refinery
configuration, the decrease
in CO2
emissions by switching
from a natural gas combinedcycle
(NGCC) power plant,
or cogeneration based on NG,
to a low-carbon power source
is ~8% (Cases 5, 7 and 8).
5. For the same crude and refinery
configuration, the decrease in
CO2
a coal-fired power plant source
to a low-carbon power source
is ~14% (Cases 9 and 11).
emissions in switching from
6. Upstream NG emissions can
account for ~10% of the total
estimated CO2
emissions
(Cases 6 and 10).
7. Process heating accounts for
30%-65% of the total CO2
emissions. This share is higher for
refineries processing lighter crudes.
8. H2 production from the SMR can
account for 15%-60% of the total
estimated CO2
emissions. This
share is much higher for refineries
with residue hydrocracking.
9. An FCCU accounts for 6%-12%
of CO2
highest single source after process
heating and H2
emissions and is the next
production.
These conclusions are based on per/
bbl basis and, therefore, crude capacity
is not a factor. However, depending on
crude quality and refinery configuration,
the product slates can differ. An alternate
perspective of looking at refinery CO2
emissions is by allocating the CO2
to the
products. This perspective can then be
utilized in estimating the carbon intensity
of fuel products. This aspect is not discussed
in this paper. PRELIM estimates
are based on calculations and equations
available in literature, and it allows expert
input to correct for design when used for
a specific site.
CO2
REDUCTION OPTIONS
Refinery configuration, crude selection
and product slate are determined based
on economics. Results presented and discussed
in the previous section indicate the
possibility of reducing CO2
saved as a result. Similarly, for
. This approach
emissions by
processing a lighter crude. This will be
feasible if the additional cost of lighter
crude is compensated by being eligible for
trading CO2
new refineries in the planning stage, CO2
emissions can be included in internal rate
of return (IRR) calculations by assigning
a price to the emitted CO2
will penalize configurations with higher
CO2
emissions. These options are not further
elaborated here since the focus is on
existing refineries and on deeper reductions
than offered by crude switching or
change in configuration.
Another option for refineries is to
source electricity from a low-carbon
source. For refineries operating with electricity
sourced from coal-fired plants, this
provides substantial (~14%) CO2
reductions.
For refineries operating with cogeneration
utilizing NGCC, the benefits
are lower (~8%). This option requires a
review of the overall refinery steam and
power balance and investigating the conversion
of some of the steam-driven equipment
to electric drives to decrease CO2
To achieve deeper reduction in CO2
.
emissions, refineries must reduce emissions
from three sources: process heating,
H2
production and FCC catalyst
from these areas are pre-comregeneration.
Three main approaches to
reduce CO2
bustion, post-combustion and oxy-fuel
combustion.
Post-combustion systems separate
CO2 from the flue gases produced by the
combustion of the primary fuel with air.
Pre-combustion systems process the primary
fuel in a reactor with steam and air
or oxygen to produce a mixture of carbon
monoxide (CO), CO2
gas). Additional H2
and H2 (synthesis
, together with CO2
and CO2
- and a H2
,
is produced by reacting the CO with
steam in a second reactor (shift reactor).
The resulting mixture of H2
then be separated into a CO2
rich stream. The CO2
the syngas or carbon-free H2
can
-
is captured, and
can be combusted
to generate power and/or heat, or
utilized for synthesizing chemicals.
Oxy-fuel combustion systems use
oxygen rather than air for combustion
of the primary fuel to produce a flue
gas that is mainly water vapor and CO2
.
This results in a flue gas with high CO2
concentrations (> 80 vol%). The water
vapor is then removed by cooling and
compressing the gas stream. While all
three are technically feasible, considering
the need for an air separation unit,
extensive oxygen piping, retrofit of flue
gas recycle, sealing of furnaces, etc., the
option of oxy-fuel firing is not considered
in this article. The other two options are
discussed in detail in the subsequent sections
for each type of emissions source.
CO2
reduction from refinery heaters.
CO2 emissions attributed to process heaters
are spatially distributed across the
refinery. TABLE 3 presents typical sourcewise
emissions for a deep-conversion
coking refinery processing 100,000 bpd.
Flue gases from these furnaces have
high volumetric flowrates, are at atmospheric
pressure and have low CO2
tial pressure. Despite the low CO2
parpartial
pressure, certain amines-such as
monoethanolamine (MEA) and other
Hydrocarbon Processing | AUGUST 2022 31
Hydrocarbon Processing - August 2022

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