Hydrocarbon Processing - August 2021 - GP-12

SPECIAL FOCUS: SMALL-SCALE LNG
mixed-refrigerant processes and 25% below
dual nitrogen expander processes.
To offer an overall optimized and integrated
design, various feed gas scenarios
have been developed, namely:
* Pipeline gas at pressure and
containing low levels of impurities
* Low-pressure biogas or coal seam
gas containing high amounts of CO2
* Low-pressure flare gas containing
low levels of heavier hydrocarbons.
Optimized integration between the
feed gas preparation and the liquefaction
sections of the LNG plant is important
to ensure high methane recovery and
the lowest lifecycle operating cost for the
overall facility.
FIG. 2b
indicates typical feed preparation
arrangements for a range of feed gas
scenarios and how they can be integrated
with the liquefaction section. It is necessary
to remove CO2
, water vapor and
aromatics (benzene) to prevent freezing
in the liquefier.
Scheme for high-pressure natural gas
CO2
Natural gas
CO2 removal
(amine wash)
Scheme for low-pressure biogas, coal seam gas
Molsieve dryer
Compression
Biogas
Coal seam gas
Water wash,
VOC + siloxane
removal
Water
Scheme for low-pressure hydrocarbon gas (flare gas)
Compression
CO2 removal,
sulfur removal
Flare gas
Water
FIG. 2. Three feed gas scenarios.
1
Business
case
alignment
session
2
Process
value
engineering
session
3
Class of
plant
overview
4
Class of
plant
detailed
checklists
FIG. 3. Lean design process and concept.
12 JULY/AUGUST 2021 | GasProcessingNews.com
5
Design
margin
review
6
High impact
systems
and
equipment
analysis
7
Opportunity
follow-up
and
governance
CO2, H2S +
Organic S
Molsieve dryer
Membrane
separation
CO2-rich
fuel gas
Low-pressure
recycle gas
Liquefaction
LNG
Molsieve dryer
BTX removal
Liquefaction
LNG
The CO2
in natural gases, usually
less than 5%, is conventionally removed
by washing with amine. The gas is then
dried with a molecular sieve. With high
CO2
gas, an arrangement of CO2
membranes, followed by final CO2
removal
and drying with molecular sieves,
may be more suitable.
Aromatics in pipeline gas, typically
below 100 mol ppm, are removed with
molecular sieves or other sorbents. High
concentrations of aromatics in the feed
gas may be condensed, together with
C5
+, in the liquefaction section by an
appropriate configuration of the warm
expander circuit running through EXP1,
with significant CAPEX savings over
conventional NGL removal.
Project/product development and
implementation. To develop a best-inclass,
standardized and modular design,c
innovative work processes have been apfeeds
such as biogas and coal seam
removal by
plied, including:
* Structured lean design and
development workshops with the
entire design team, resulting in
a capital-efficient design
* A proprietary, four-step project
execution work processd
followed, comprising:
was
° Step 1: Identify factors that
influence modularization
° Step 2: Determine degree of
modularization and preassembly
° Step 3: Develop optimized layout
° Step 4: Develop modular support
documentation.
Applying the aforementioned processes
resulted in a design allowing 80%
of the labor to be moved offsite compared
to a traditional stickbuilt execution, as
well as the ability to design one and build
many plants.
The following sections provide more
information on the concepts of lean design,
standardization and modularization.
Lean design. Lean design principles
were followed to develop a design that is
the lowest lifecycle cost and provides the
most competitive offering. This is illustrated
in FIG. 3.
Standardization. To offer a costcompetitive
product, standardization was
considered essential to reduce capital cost
and the overall project schedule, as well as
to reduce the lifecycle cost of the plants.
Applying standardization supports the
" design one, build many " philosophy and
typically results in capital cost savings of
10%-20%, as illustrated in FIG. 4.
Modularization. The use of modIntegrated
heavies
removal
BTX,
C5
+
Liquefaction
LNG
ules reduces onsite construction labor
hours and allows for scalable, adaptable,
plug-and-play units, as well as easy integration
with existing systems. An added
advantage is that the compact footprint
optimizes the use of space. A compact
modular solution also reduces capital cost
due to improved labor productivity and
reduced bulk material quantities.
Principles of modularization have
been specified during plant development,
including module definitions and basic
layouts. A structured, four-step work process
was applied in developing optimal
modular layouts, with the aim of reducing
the overall plot area and key quantities.
The basic principle was to allow modularization
to drive the layout, as opposed to
the layout driving modularization.
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Hydrocarbon Processing - August 2021

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