Hydrocarbon Processing - June 2022 - GP-21

LNG
Decarbonize LNG liquefaction with
pre-combustion CO2
D. VESKOVIC, J. BEARD, M. ROBERTS and D. GRAHAM,
Air Products and Chemicals Inc., Allentown, Pennsylvania
In recent years, lifecycle greenhouse
gas (GHG) emissions studies of the natural
gas industry have drawn attention to
the significant environmental impact of
liquefied natural gas (LNG). Not only is
carbon dioxide (CO2
) released when natural
gas is burned at the end user, but the
processes of extracting, treating, liquefying,
shipping and regasifying the natural
gas all contribute to the total emissions
of using natural gas as fuel. With natural
gas representing a rising fraction of the
world's total energy consumption, the
importance of reducing these emissions
will continue to grow in the future.
Emissions from end users occur across
many different geographic locations,
from large-scale power generation facilities
to individual homes. For many of
these users, capturing and sequestering
the CO2
associated with their emissions
is challenging for various reasons (economics,
lack of sequestration infrastructure,
etc.). Conversely, LNG liquefaction
facilities present a unique opportunity to
capture GHG emissions, as they provide
a single location where a significant portion
of emissions is concentrated.
For both retrofits to existing plants
and for new-build plants, pre-combustion
CO2
capture can significantly reduce the
overall carbon footprint of LNG. This
article examines how a proprietary approach
to implementing and integrating
pre-combustion capture with an LNG
liquefaction facility can reduce the overall
CO2
by more than 97%. This approach comprises
the following three main steps:
1. Producing hydrogen (H2
) fuel
from natural gas or other fuel gases
within the liquefaction facility
2. Removing CO2 from the syngas
generated during H2
production
3. Using the H2
as the primary fuel
in the plant's gas turbines.
The details of this configuration are
flexible and can be adjusted to serve individual
project needs.1-5
Methods to reduce CO2
emissions.
CO2 emissions at an LNG liquefaction
facility can be categorized into three primary
sources:
1. CO2
vented during upstream
pretreatment to remove acid gases
2. CO2 released in the flue gas from
gas turbines used to power the
liquefaction process
3. CO2 released in the generation
of power for the remainder
of the facility.
to reduce the CO2
Two broad approaches can be utilized
emissions from these
sources. One approach is to reduce the
amount of CO2
improving efficiency. The second is to
capture and sequester the CO2
and the CO2
created during power generation.
A combination of both approaches is
necessary to achieve a high degree of overall
emissions reduction.
Capturing and sequestering the CO2
in
the feed is already possible with well-proven
technologies. A typical acid gas removal
unit (AGRU) for LNG already separates
CO2
amine-based absorption process. Although
many facilities today reject that CO2
mosphere, some already possess the capability
to capture CO2
emissions from a liquefaction facility
sequester it. The use of this approach can
reduce the total CO2
found in the feed.
also reduce CO2
from the natural gas feed using an
to atremoved
this way and
emissions from an
LNG facility by up to 30%, depending on
the amount of CO2
Improvements to plant efficiency can
emissions. Although
many LNG facilities use simple-cycle industrial
gas turbines, newer facilities have
made use of aeroderivative gas turbines
generated, primarily by
in the feed
capture technology
or combined-cycle arrangements to improve
power efficiency. With improved
power efficiency, less fuel is required to
generate the same power available for liquefaction.
This results in lower emissions
for the same LNG production. The use
of aeroderivative turbines can potentially
reduce the CO2
emissions of a facility by
approximately 14% over equivalent industrial
gas turbines, while a combinedcycle
arrangement can reduce CO2
emissions by approximately 25% over a
simple-cycle arrangement.
While these existing methods can significantly
reduce the amount of CO2
released
from a facility, they cannot address
all the CO2
plant's gas turbines. To capture the remaining
CO2
Flue gas CO2
released in the flue gas from a
, a different approach is required.
reduction via pre- or
emissions
post-combustion capture. Two potential
approaches to reduce CO2
from methane-burning gas turbines are
post-combustion capture and pre-combustion
capture.
With post-combustion capture, shown
in FIG. 1, air and methane-rich fuel are fed
to the gas turbine and CO2
moved from the flue gas by a CO2
system. In this configuration, CO2
is directly recapture
is
available
at low partial pressure (near-atmospheric
pressure with single digit mol%
of CO2
) and high temperature. These
conditions make it challenging to design
a cost-effective recovery system that captures
most of the CO2
. Furthermore, in
retrofit applications, the lack of plot space
close to the gas turbines can be problematic.
The low pressure and high volume of
flue gas may be impractical to transport to
a distant CO2
recovery unit.
Conversely, pre-combustion capture,
shown in FIG. 2, captures CO2
from streams
at higher pressure and with higher fractions
Gas Processing & LNG | MAY/JUNE 2022 21
Hydrocarbon Processing - June 2022

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