Services
Services
■■ Liquefied■Natural■Gas
■■ Gas■Compressor■Stations
■■ Off■Loading■Gas■and■LNG
■■ Normal■and■Floating■LNG■Terminals
Gas and LNGConsulting Services
8
2 Gas and LNG
3Gas and LNG
Natural Gas
Natural gas is a hydrocarbon gas mixture,
which consists primary of methane and a
fraction heavier hydrocarbons as well as im-
purities like water and carbon dioxide. Natu-
ral gas is widely used as an important energy
source for many applications including hea-
ting, electricity generation, industrial power
generation and as a fuel for vehicles. Gas is
often found in the near vicinity of oil, but also
together with oil in deep underground natu-
ral rock formations.
In order to use natural gas as a power source,
it is processed to clean the gas and remove
impurities to meet the requirements of the
end user.
Dynaflow Research Group (DRG) has perfor-
med a large number of static and dynamic
calculations related to the structural integrity
of gas pipeline systems, and their supporting
installations and equipment. Dynamic flow
calculations play a major role in solving vibra-
tion and pulsation problems.
Liquefied Natural Gas (LNG)
On account of its low density, it is not straight-
forward to store natural gas or transport the
gas by road. Additionally, transporting natu-
ral gas across the oceans is highly impracti-
cal. Furthermore, the existing gas pipeline
network is already close to capacity such that
a significant number of new pipelines are re-
quired to fulfill the need for gas in the near
future.
“LNG has become an impor-tant part of modern energy transportation”
Cooling natural gas to about -160 degrees
Celsius at atmospheric pressure results in
the condensation of the gas into liquid form,
DRG■provides■consulting■services■and■engineering■solutions■for■Liquefied■Natural■Gas■(LNG)■systems
Liquefied Natural Gas
4 Gas and LNG
known as Liquefied Natural Gas (LNG). LNG
is natural gas that has been temporarily con-
verted into a liquid for the ease of storage
and transport. The volume of LNG is about
1/600th of the equivalent volume of natural
gas in the gaseous state.
While LNG is reasonably costly to produce,
recent technologies are considerably redu-
cing the costs to liquify the natural gas and
regasify the LNG. Natural gas is converted
into a liquid at a liquefaction plant (LNG ex-
port terminal), after which it is used for trans-
porting the natural gas to the markets. Here,
the LNG is regasified (LNG import terminal)
and distributed as pipeline natural gas.
Rapid phase transition explosion
The very low operating temperature around
-160 degrees Celsius means that it is extre-
mely important to remove water and car-
bon dioxide and other components that will
freeze under the low temperature necessary
for LNG storage and transport. One of the
major risks of LNG is a rapid phase transition
explosion (RPT), which occurs when cold LNG
comes into contact with water.
Transport and regasification of LNG
LNG production and transportation requi-
res an important infrastructure consisting of
one or more LNG trains, each of which is an
independent unit for gas liquefaction. Sub-
sequently, the LNG is loaded onto ships and
delivered to a regasification terminal, where
the LNG is reconverted into gas. The regasi-
fication terminals are usually connected to
a storage and pipeline distribution network
to distribute the natural gas to the local dis-
tribution companies or independent power
plants (IPPs).
LNG terminals
Liquefied natural gas is used to transport na-
tural gas over long distances, often by sea. In
most cases, LNG terminals are purpose-built
ports used exclusively to export or import
LNG, an example of which is the Gate termi-
nal in Rotterdam harbour.
The LNG is stored in large insulated tanks.
Although very efficient insulation is applied,
heat does inevitably leak into the LNG. In-
evitably, heat leakage will warm and vapou-
rise the LNG. LNG boils at -160°C when at
atmospheric pressure. By boiling the liquid
natural gas evaporates and becomes natural
gas. The process of evaporation (phase chan-
5Gas and LNG
ge) takes a large amount of energy from the
liquid. This amount is called the heat of eva-
poration and makes evaporation an efficient
cooling mechanism. By letting gas escape the
LNG-tank is kept at atmospheric pressure
and therefore the liquid in the tank is always
kept at -160°C. Any heat that leaks in causes
evaporation of the liquid which cools the
remaining liquid. The combination of high
quality insulation and cooling by evaporation
causes only a relatively small amount of boil-
off is necessary to maintain the temperature,
called auto-refrigeration. The boil-off gas re-
sulting from on-shore LNG storage tanks is
usually compressed and fed to natural gas
pipeline networks. Some LNG carriers use
boil-off gas for fuel.
Dynaflow Research Group
Dynaflow Research Group (DRG) has a broad
experience in providing assistance to the de-
sign and verification of natural gas and LNG
terminals, supporting equipment and corres-
ponding transportation lines. The considered
systems include:
■ Design of LNG and Gas storage tanks,
■ Gas compressor stations, including coo-
ler banks, filters and compressors,
■ Coolwater and firewater systems of Ter-
minals, primarily GRE piping,
■ LNG terminals and floating platforms,
■ Off-loading of natural gas (jetty),
■ High and low pressure vessels contai-
ning gas, LNG and other type of fluids.
Practical engineering solutions are provided
to these complex piping systems and the at-
tached equipment. Examples of these analy-
sis types are pulsation or acoustic analyses,
mechanical response studies, structural
(thermal and stress) analysis (FEA) and detai-
led flow calculations (CFD).
Transient flow software packages are often
used to simulate and analyse surge, water
hammer, pulsations and transient accous-
tical behaviour of liquid and gas piping sys-
tems. As a result of a pulsation analysis, the
magnitude of the unbalanced forces are cal-
culated for each pipe section, and these can
be used in a mechanical response analysis.
Such a mechanical response analysis will be
performed by means of a pipe stress soft-
ware package with dynamic capabilities, such
as CAESAR II, PipePlus or FE/Pipe.
DRG provides solutions which are able to
comply with a range of industry standard Co-
des such as ASME, DIN, NEN, AD Markblat-
ter, API 618, API 674 codes and VDI 3842.
6 Gas and LNG
7Gas and LNG
Gas compressor stations
A gas compressor station enables the trans-
portation process of natural gas from one lo-
cation to another. While transporting natural
gas through a gas pipeline, the gas needs to
be constantly re-pressurized at certain dis-
tance intervals.
The location of the compressor station heavi-
ly depends on the type of terrain but also on
the number of gas wells in the vicinity of the
compressor station. A large numer of gas
wells and frequent elevation changes will re-
quire more compressor stations.
The gas in compressor stations is normally
pressurized by special turbines, motors and
engines. As the name implies, the compres-
sor station compresses the natural gas, this is
needed for the gas to be transported through
the pipeline.
Additional compressor stations are needed
Design■and■installation■of■gas■compressor■stati-ons■require■complex■engineering■solutions
Gas Compressor Stations
due to the pressure loss that the moving gas
experiences along a pipeline route, typically
every 70 to 150 kilometers. The size of the
station and the number of compressors va-
ries, based on the diameter of the pipe and
the volume of gas to be moved. Nevertheless,
the basic components of each compressor
station are similar.
Centrifugal and reciprocating com-pressors
When the natural gas has reached the com-
pressor station, it is compressed by a com-
pressor powered by either a turbine, electric
motor or internal combustion engine. Tur-
bine compressors are fueled by using a small
portion of the energy from the gas they com-
press. The turbine itself serves to operate
a centrifugal compressor, which contains a
type of fan that compresses and pumps the
natural gas through the pipeline. Some com-
8 Gas and LNG
pressor stations are operated by using an
electric motor to power the centrifugal com-
pressor. This type of compression does not
require the use of any of the natural gas from
the pipe, however it does require a reliable
source of electricity.
Reciprocating natural gas engines are also
used to power some compressor stations.
The advantage of reciprocating compressors
is that the volume of gas pushed through the
pipeline can be adjusted incrementally to
meet small changes in customer demand.
Mechanical Integrity Analysis
Any structure has a number of mechanical
resonance (natural) frequencies. If these
frequencies coincide with those of external
excitations, for example those due to pumps
or the fluid flow within a pipe, then any small
pipe deflection caused by the excitation me-
chanism at these frequencies, could be am-
plified and result in resonant vibrations in the
mechanical structure.
These mechanical vibrations, if persistent,
could result in problems due to Low Cycle
Fatigue or High Cycle Fatigue. The fatigue ca-
pabilities of your piping structure or pressure
vessel can be assessed by means of dedica-
ted Finite Element Analysis (FEA) software,
keeping in mind Code compliance with rele-
vant Codes such as ASME, DIN, NEN and EN.
Pulsations and Mechanical Res-ponse
Reciprocating compressors produce pulsati-
ons in the suction and discharge piping that
can be damaging to the piping and to the
equipment itself. The pulsations can lead to
potential fatigue failure, undesirable vibrati-
ons, reduced efficiency or errors in flow mea-
surement results.
“By optimizing gas compres-sor stations gas transporta-tion benefits are increased”
Also, pulsations in the piping system might
result in cyclic stresses and fatigue problems.
A pulsation analysis is most often performed
either in the design phase or as a result of
a failure in the field. Field problems usually
require inspecting and numerous measure-
ments taken by an expert to help identify the
exact nature of the pulsation.
A “Design Phase” analysis is typically compli-
cated since it requires that the analyst makes
sure that all the possible and relevant sce-
narios are defined and that the worst-case
9Gas and LNG
scenario is simulated. All potential excitation
frequencies and gas conditions must be in-
vestigated, and all the applicable rules of API
618 must be satisfied. Furthermore, climate
and local ambient air changes may result in
variations in the speed of sound of up to 15%.
Typically, a variety of gas and ambient condi-
tions as well as critical load cases will be ana-
lyzed. The worst of these cases will then be
used for the mechanical response analysis.
A pulsation analysis is often performed in
conjunction with a mechanical response ana-
lysis using dedicated pipe stress software.
Here both stress analysis software and BOS-
pulse can be used to check the mechanical
shaking forces and the API 618 allowables to
ensure smooth compressor operation.
The API allowable acoustic level is specified
on a per frequency basis and so each fre-
quency contribution to the pulsation must
be evaluated separately. BOSpulse applies
a time history approach and automatically
decomposes the calculated pressure pul-
sations to produce an API 618 pulsation
compliance report for all sections of the pi-
ping system. Alternatively, a separate har-
monic analysis for each compressor loading
component can be performed if desired.
As a result of the pulsation analysis, for each
pipe section, the magnitude of the unbalan-
ced forces are calculated and used in the
mechanical response analysis. This mecha-
nical analysis is performed by means of a
pipe stress software package with dynamic
capabilities, such as CAESAR II, PipePlus or
FE/Pipe.
Gas Liquid Separation
As the pipeline enters the compressor sta-
tion, the natural gas passes through scrub-
bers, strainers filters or separators. These
different types of equipment are all designed
to remove any free liquids or dirt particles
from the gas before it enters the compressor.
In order to study and optimize the liquid se-
paration from the gas full three-dimensional
multi-phase flow fields can be obtained. For
complex and sensitive systems, it can be ne-
cessary to investigate the three-dimensional
flow field. This can be obtained by perfor-
ming a full Computational Fluid Dynamics
(CFD) analysis.
10 Gas and LNG
11Gas and LNG
Pressure surges in off-loading
At LNG terminals, the liquefied gas is off-
loaded from the LNG ship by means of jetty
constructions. The off-loading lines running
from these jetties up to the storage tanks can
be up to several kilometers in length.
An example of a steel off-loading line is a
system with a diameter of 1000mm which
connected a storage tank with a loading arm
upon the jetty. The design flow rate reached
a maximum of 2000 ton/hr. The analysis of a
number of anticipated transient update sce-
narios was required.
Three transient upset scenarios were simula-
ted and investigated in depth:
■ The rapid closure of the control valve in
the loading arm. The valve was an emer-
gency valve which closed to prevent the
spoil of LNG if the ship, from which LNG,
is being unloaded, moves too far from
DRG■provides■consulting■services■and■engineering■solutions■for■off-loading■gas■and■LNG
Off Loading Gas & LNG
the jetty
■ The emergency trip of the pump on-
board of the ship
■ The closure of the valve, located just
upstream of the storage tank, when the
LNG in the tank reaches its maximum
liquid level
A transient one-dimensional fluid model of
the pipeline was produced in BOSfluids to si-
mulate and analyze the transient upset con-
ditions. From the transient flow model, un-
balanced forces were extracted, and applied
in a dynamic mechanical time-history ana-
lysis using CAESAR II. The dynamic stresses,
displacements and support reactions caused
by the various upset conditions were calcula-
ted and assessed. Subsequently, the dynamic
pipe stresses were assessed according to the
ASME B31.3 code.
In steady operation (no transient valve or
pump actions), it was observed that vapor
12 Gas and LNG
pressure level was reached at the top of the
siphon immed-iately upstream of the LNG
storage tank for low liquid levels in the tank.
Due to the low pressures at the top of the
siphon, a large vapor filled sect ion was crea-
ted at the top of the siphon. During transient
conditions the cavitation caused by the vapor
condensing downstream of the siphon led to
significant unbalanced forces in the piping.
The results indicated that the occurence of
the use of a low tank nozzle would prevent
this cavitation and also eliminate the associa-
ted unbalanced forces.
Cavitation and column separation
Closure of a safety valve or the tripping of the
pump will stop the LNG flow in a relatively
short period. As a result, low pressures can
be created in the loading arms and immedi-
ately downstream of the loading arms and in
pipe bridges.
These low pressures can reach vapor pres-
sure levels and as result column separation
would occur. Under most circumstances the
flow decelerates and reverses. This couses
the cavity to collapse which is accompanied
with large pressure spikes.
The transient flow simulations performed
using BOSfluids® for the off-loading line, sho-
wed that indeed large pressure waves were
generated. These had a peak value of up to
30 barg, and travelled through the line some
time (about 30 seconds) after the start of the
most critical transient scenario. The pressure
wave was seen to be caused by the collapse
cavity in between the liquid columns.
The dynamic mechanical analysis showed
that the pressure wave generated large un-
balanced forces for a very short duration of
time, which would causes pipe stresses im-
mediately downstream of the loading arm
that were in excess of those permitted under
the ASME B31.3 code for occasional loading.
Large displacements were also predicted in
these critical locations. Therefore, additional
pipe supports were recommended in the cri-
tical parts of the line.
Dynamic pipe stresses
Due to the large displacements and stresses
seen on the off loading line, a dynamic pipe
stress analysis was also required. However,
for the critical locations, it was not feasible
to reduce the displacements through the in-
troduction of further restraints on account of
the flexibility and strength of the pipe brid-
ges.
13Gas and LNG
The mechanical response modes were identi-
fied and were excited as a result of the unba-
lanced loads obtained.
The calculated dynamic stress levels were
used to determine which sections of the off-
loading line were likely to suffer fatigue is-
sues.
Through modifying the pipe supporting wit-
hin the system, it was possible to change the
frequencies of the mechanical response, and
thereby eliminate the fatigue problem.
BOSfluids®
For years, piping engineers have laboured
with simple hand calculations, or user-un-
friendly software products when in need of
a simple tool to analyse the impact of pulsati-
ons upon their piping system.
BOSfluids® has been built specifically to ad-
dress the needs of the piping engineer, who
requires details of the dynamic forces acting
on a piping system.
BOSfluids® is an interactive computer simula-
tion package that is able to model the steady
state and transient flow in liquid or gas car-
rying piping systems. It has been developed
in-house by Dynaflow Research Group and
has been extensively used on projects for
our clients. BOSfluids® has been commerci-
ally available since 1998.
“By reducing pressure surges, the system integrity and safety can be drastically improved”
14 Gas and LNG
15Gas and LNG
LNG Terminals
Liquefied natural gas is used to transport na-
tural gas over long distances, often by sea. In
most cases, LNG terminals are purpose-built
ports used exclusively to export or import
LNG, an example of which is the Gate termi-
nal in Rotterdam harbour.
Before or after liquefied natural gas (LNG) is
transported over long distances, the LNG is
stored in large insulated tanks. Although very
efficient insulation is applied, heat does inevi-
tably leak into the LNG.
LNG terminals involve large installations, of-
ten forming purpose-built ports to exclusi-
vely export or import LNG, such as the Gate
terminal in Rotterdam harbour. Consequent-
ly, the design and verification of gas and LNG
terminals requires the assessment of the
mechanical integrity of a wide variety of sup-
porting equipment and connected transpor-
A■recent■trend■in■the■design■of■LNG■terminals■are■floating■LNG■terminals
tation lines. The considered systems include
but are not limited to:
■ Design of LNG and Gas storage tanks
■ Gas compressor stations, including coo-
ler banks, filters and compressors
■ Coolwater and firewater systems of Ter-
minals, primarily GRE piping
■ LNG terminals and floating platforms
■ Off-loading of natural gas (jetty)
■ High and low pressure vessels contai-
ning gas, LNG and other type of fluids
“Structural integrity of LNG terminals is important for safety and the environment”
Engineering solutions are provided to these
complex piping systems and the attached
equipment. Examples of these analysis types
are pulsation or acoustic analyses, mechani-
cal response studies, structural (thermal and
stress) analysis (FEA) and detailed flow calcu-
Normal and FloatingLNG Terminals
16 Gas and LNG
lations (CFD).
Case: LNG terminal design calcula-tions
For a new regasification LNG plant with tre-
atment facilities design verifications have
been performed. Sea water required for the
LNG vaporizing duty of the terminal was to
be shared with the sea water requirements
of the neighbouring power station located
in the same industrial area. Existing sea wa-
ter intakes, facilities (sea water filtration and
pumping) were used to supply sea water to
both the power station and the LNG terminal.
A dedicated line was to be routed to the LNG
terminal to supply sea water to the booster
pumps. From the LNG vaporizers, sea wa-
ter is to be fed back to the main sea water
lines to the power station. As cold seawater
was beneficial for operating the power plant
condensers, the seawater requirements of
the power plant and the LNG terminal could
be adequately integrated as seawater used
for vaporizing LNG is actually cooled. DRG
has performed an extensive mechanical res-
ponse analysis for this LNG terminal.
Structural integrity of lines
Static and dynamic stress analysis of suppor-
ting systems at LNG terminals, for instance in
plant piping, or the cooling, fire and dump
lines is critical. Often, the lines are fabricated
of steel or using Glassfiber Reinforced Epoxy
(GRE) to deal with corrosive and erosive en-
vironments.
The piping of the considered systems can be
above ground or buried and includes several
connections to above ground equipment.
System routing and pipe properties used for
the analysis are based on data provided by
the suppliers. The resulting pipe stresses are
assessed for their conformance with the ISO
14692 code for GRE lines or the applicable
ASME code, such as B31.3, for steel lines.
Surge analysis
The time-dependent unbalanced loads
caused by the transient flow of a pump failu-
re, pump start-up and subsequent failure can
be applied on a dynamic time-history stress
model are calculated.
With these unbalanced loads a mechanical
response analysis over a wide range of ope-
rating conditions can be executed. The re-
sulting maximum dynamic stresses are com-
bined with the static operational stresses and
assessed according to the applicable design
code.
17Gas and LNG
FLNG compressor modules
A floating production, storage and off-
loading(FPSO) unit is a floating vessel used
by the offshore oil and gas industry for the
processing of hydrocarbons and the storage
of oil. An FPSO vessel is designed to receive
hydrocarbons produced from nearby plat-
forms or subsea production facilities, process
them, and store oil until it can be offloaded
onto a tanker or, less frequently, transported
through a pipeline.
The relatively large bore suction and dischar-
ge piping connected to the natural gas com-
pressor onboard a floating LNG platform
may be exposed to extreme load conditions.
In addition to the normal thermal and pres-
sure design loads also loads due to large
wind velocities as a result of storm fields pas-
sing by having to be accommodated by the
pipework this may result in large compressor
nozzle loads. As a result of the ocean waves
the FLNG compressor module is also subject
to rocking motions.
The rocking motions impose accelerations
on the piping. For this type of piping the pipe
material stress is hardly ever governing for
the design. The allowable compressor nozzle
loads (API 617) are in general ruling. A piping
support arrangement will be designed to ac-
commodate the external loads due to wind
and barge movements and minimize the
resulting compressor nozzle loads. Gener-
ally this requirement conflicts with a piping
support arrangement designed to minimize
nozzle loads resulting from thermal expan-
sion.
DRG has been involved with the analysis of
various compressor piping layouts for the
feasibility of reconciliation of these con-
flicting requirements on a FLNG Terminal.
The target for such an analysis is to keep the
nozzle loads under all load conditions within
a safety margin that conforms with API 617.
Source: Hoegh
18 Gas and LNG
19Gas and LNG
DRG■provides■consulting■services■and■engineering■solutions■for■flow■and■mechanical■problems■rela-ted■to■Gas■and■LNG■systems
What can we do for you?
What can we do for you?
The engineers at Dynaflow Research Group
(DRG) have a thorough understanding of the
necessary fundamental physics related to
natural gas and LNG. We have a broad expe-
rience in providing assistance to the design
and verification of gas and LNG terminals,
supporting equipment and corresponding
transportation lines. The considered systems
include:
■ Design of LNG and Gas storage tanks
■ Gas compressor stations, including coo-
ler banks, filters and compressors
■ Coolwater and firewater systems of Ter-
minals, primarily GRE piping
■ LNG terminals and floating platforms
■ Off-loading of natural gas (jetty)
■ High and low pressure vessels contai-
ning gas, LNG and other type of fluids
A thorough understanding of the problem is
of crucial importance in order to assist you
in optimizing your process, to increase your
profit and the safety of your system. There-
fore, we believe we are well-positioned to
tackle your challenges related to your LNG
terminal or floating production platform.
Our consulting services are related to pulsati-
on or acoustic analysis, mechanical response
studies, structural (thermal and stress) analy-
sis (FEA) and detailed flow calculations (CFD).
Communication
To us communication with our clients during
a project is of upmost importance. For each
project the client is updated regularly with
the progress of our work, and we liaise with
the client to ensure the best information is
available with which to conduct the analyses.
20 Gas and LNG
“Dynaflow■Research■Group■(DRG)■is■a■world■wide■well■respected■consultant.■We■help■our■clients■to■solve■their■most■complex■and■critical■technical■issues”■
Dynaflow Reseach Group
Consulting services
We provide engineering consulting services in all
aspects of design and analysis for the Petro- che-
mical industry. Our work often requires a multi-
disciplinary approach where we combine exper-
tise in fluid flow behaviour, dynamic oscillations,
FEM and stress analysis with sophisticated analy-
sis software to predict system performances.
Training
DRG offers a wide range of training courses such
as software training, fiberglass training, dyna-
mics and stress training. Most of these training
courses are offered on a regular basis during
the year. We also develop customised training
programs with our customers fit to their specific
needs.
Products
DRG has been developing software for many
years, which has resulted in several commercially
available software packages such as BOSfluids®,
BOSpulse®, Jive and Hades. We also provide tech-
nical consulting services, and develop numerical
software that can be used in computer simulati-
ons and other types of scientific computations.
Research
DRG conducts research on different aspects of
pipe-system design and pressure vessels. Most
of this research is done in close collaboration
with Paulin Research Group and their Houston
test facilities (www.paulin.com). Dynaflow Re-
search Group provides support to clients with
their R&D to help them continuously improve
their products.
21Gas and LNG
Topic specific brochures:
• Consulting Service Series• Software Product Series• Training Series
Visit our website www.dynaflow.com or send an e-mail to [email protected]
Houtsingel 95 2719 EB Zoetermeer The NetherlandsReg nr. 27320315
T F E W
+31 79 361 5150+31 79 361 [email protected]
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