Note: Descriptions are shown in the official language in which they were submitted.
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INTEGRATED MULTI-FUNCTIONAL PIPELINE SYSTEM FOR DELIVERY OF
CHILLED MIXTURES OF NATURAL GAS AND CHILLED MIXTURES OF
NATURAL GAS AND NGLS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefits of US Provisional Patent
Application
Serial No. 62/210,286 filed August 26, 2015, and US Provisional Patent
Application Serial No. 62/342,688, filed May 27, 2016, the content of each of
which
is incorporated herein by reference in its entirety. This invention is also
related to
US Patent 6,217,626 and US Patent 6,201,163, the content of each of which is
incorporated herein by reference in its entirety.
FIELD
[0002] Embodiments herein relate to high pressure pipeline systems used for
delivery of chilled natural gas mixtures to a terminus for subsequent
downstream
applications such as in LNG, Separation/fractionation facilities and mobile
trans-
shipment. More particularly, the new method delivers a chilled product
directly
from the pipeline providing most, if not all of the chilling energy
requirement to
meet downstream specification of temperature and pressure for subsequent
applications. In support of the processing function the packing
characteristics of
delivered product under pre-chilled conditions permit the upstream pipeline
section
to be utilized for containment of stored buffer volumes as suits the flow
demands
of the processing facilities.
BACKGROUND
[0003] Traditionally natural gas and/or mixtures of natural gas and NGLs
(Products) have been transported by pipelines to deliver such products at the
terminus of such pipelines as dictated by the pressure and temperature needs
of
downstream applications such as separation /fractionation, LNG production and
trans-shipment.
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[0004] Chilling of Products is often required for said downstream
applications. The
traditional approach is to accept some chilling using small available pressure
differentials at the destination, typically providing a low degree of Joule-
Thompson
effect chilling typically to the range of -10 F degrees to -25 F degrees. The
bulk of
further process chilling of these Products is then achieved by external means
at
significant energy consumption.
[0005] There remains a need for more cost effective chilling to meet
downstream
process demands.
SUMMARY
[0006] The methods herein provide significantly more cost effective chilling
and
increased pressure energy recovery, thereby reducing/eliminating the need for
costly external chilling to meet downstream process demands depending on the
application. In particular the method reduces much of the pre-chilling
infrastructure
involved with LNG processing.
[0007] Further, methodologies disclosed herein, integrated with the needs of
the
downstream process, delivers these Products for subsequent processing using
the
greater pressure differential available from an elevated pipeline maximum
operating pressure (MOP). The higher reductions in pressure and temperature
exceeding those of traditional segregated pipeline/process systems are
achieved
through a turbo expander or similar Joule-Thompson (J-T) device at the
terminus
of the pipeline. The above steps substantially increase the benefits of the
chilling
stage to the range of about -60 F degrees to about -100 F degrees.
[0008] As well, considerable recovery of the last stage pipeline pressure
energy
now becomes available as electrical/or shaft power where the J-T device is
coupled with generation/mechanical linkage.
[0009] Herein, Applicant applies methods for manipulation of gas transport
and
delivery parameters that result in significant increases in the mass rate of
product
delivered for a given pipeline. Reductions in capital expense and energy
required
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for both transport and chilling, and savings in trans-shipment infrastructure
and
expense.
[0010] The customary handover of prior Rich Gas mixtures between project
design groups for pipeline and process aspects primarily imposes and results
in a
gradual drop in configured pipeline flowing pressure to a level just above the
minimum receipt specified for the downstream process. The process design group
then dictates control, compressing, heating or energy intensive chilling of
the
Product for further treatment. This invariably involves considerable loss and
replacement of available energy from a high pressure pipeline. The new
methodologies disclosed herein bridge that gap by providing first stage
process
conditioning for chilling requirements, more efficiently using inherent
properties of
the current product delivered directly from the pipeline. Control and location
of this
pre-chilling can be under the pipeline or process operational jurisdiction and
ownership.
[0011] In conventional systems, delivery pressure differential may result
in a
small temperatures drop with the majority of process chilling being achieved
by
external means heat exchange methodologies, such methodologies requiring
outside energy to chill the Products.
[0012] Herein, Applicant enhances delivery conditions for heretofore
untapped
opportunities for internally-generated chilling Products that is significantly
more
cost effective than the prior external-generated chilling of Products. The
traditional
approach having modest delivery pressures and differentials would at most
result
in chilling during pressure letdown in a range of -10 F degrees to -25 F
degrees,
the balance to Product conditions being chilled through known exchange
methodologies.
[0013] This new art extends the boundary conditions of pipeline pressure,
temperature and NGL constituents of existing technologies for the
transportation
and optional storage of North. American Spec natural gas mixtures or rich
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mixtures of natural gas/NGLs, (Products), in a pipeline system for delivery of
chilled Products for downstream applications.
[0014] The delivery of "internally" chilled Products at the terminus of the
higher
pressure section of the pipeline system significantly reduces capital and
operating
costs compared to traditional methods of "externally" chilling these Products
using
auxiliary processing infrastructure.
[0015] The installation of a high lift compressor station with an increase
of the
Maximum Allowable Operating Pressure (MAOP) of pipeline section(s) of natural
gas delivery system primarily provided the optimal environment for
refrigeration
pressure differential by Joule-Thompson chilling of the pipeline contents.
[0016] The new system provides an integrated multi-functional pipeline
derived
system, for the reduction in energy for both transport and downstream
processing
of the aforementioned Products by making available a larger deltaP pressure
reduction than that normally associated with traditional process
considerations.
This includes, at the terminus of the last stage high pressure pipeline
section, a
turbo expander or similar device which reduces pressure and "internally"
chills the
outflowing Products through the Joule-Thompson effect of their constituent
properties. This system can also be retrofitted to existing pipeline systems
for
certain applications. Recovery of pipeline pressure energy for power
generation
can also be harnessed if a turbo expander or similar device used for pressure
reduction is then employed to generate electricity or shaft power. Process
energy/heat transfer normally acquired from "external" sources can then be
largely
displaced by this form of recovered upstream energy missing in traditional
segregation of pipeline and process disciplines.
[0017] Additionally, the NGL content carried in such mixtures in a single
pipeline eliminates the need for a separate pipeline, or other means for
transportation of multiple product streams to markets. Coupled with higher
pressure operation the effects of enhanced NGL content results in a reduction
in
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diameter of the pipeline by at least one standard size over that for an
equivalent
flow of Spec natural gas.
[0018] The economy of scale of a single facility to process the Rich Gas
mixtures at the market place reduces capital and operating costs compared to
numerous smaller field facilities.
[0019] Delivery of outlet Products can be set to prescribed temperature and
Pressure dependent on downstream application. Substantial overall reduction in
energy consumption and associated CO2 emissions is thereby achieved through
integrated pipeline/processing applications.
[0020] The method described herein, integrated with the needs of a variety
of
downstream processes, delivers these Products for subsequent processing using
the greater pressure differential available from an elevated pipeline maximum
operating pressure (MOP) and adjustments to the conveyed mixtures. Higher
reductions in pressure and temperature are achieved through a turbo expander
or
similar Joule-Thompson (J-T) device at the terminus of the pipeline, those
reductions exceeding those of traditional segregated pipeline/process systems
As
disclosed herein, the pressure differentials employed substantially increase
the
benefits of the J-T chilling stage in the range of -60 F degrees to -100 F
degrees.
[0021] As well, in another embodiment, considerable recovery of last-stage
pipeline pressure energy is available as electrical/or shaft power when a J-T
device with generation/mechanical linkage is used to achieve the J-T chilling.
[0022] Without limitation, the new method provides significantly more cost
effective chilling and increased pressure energy recovery, and thereby
reduces/eliminates the need for costly external chilling to meet the
downstream
process demands depending on the application.
[0023] In EMBODIMENTS FOR PROCESSING: Applicant controls the pipeline
compression cycles, to heretofore higher pressure differentials, and
concurrently
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provides destination storage at new higher pressures. This enables a J-T
effect
for significant, if not all, process chilling of the product from the storage
at the
destination. This also enables delivery of a chilled gaseous product at
commercial
densities for transshipment in lighter lower pressure containment vessels.
[0024] According to one aspect of this disclosure, at final recompression
or
storage pressures of about 4500 psig to about 3200 psig are attained. At the
aforementioned range of pressures, the Joule Thompson chilling effect that
accompanies gas expansion becomes effective.
[0025] The available pressure differential from Applicant's high pressure
pipeline containment conditions, let down to destination process levels, far
exceeds those of traditional gas process steps. In respect of these higher
pressure differentials for both Standard Spec Gas and NGL enhanced mixtures
Applicant has determined that temperature reductions down to -100 F or colder
are available for the described mixtures.
[0026] These mixtures are to be specified free of water and CO2
constituents
that would otherwise be susceptible to hydrate and freezing issues at these
extreme conditions.
[0027] CHILLING EMBODIMENTS FROM JOULE THOMPSON EFFECT:
Energy efficiency is enhanced due in part to the ability to drop the pressure
of
these enhanced mixtures from their high pressure containment levels to
destination pressures, thereby. The heretofore unavailable processing pressure
differentials efficiently utilize the high refrigerant properties (latent heat
of
vaporization) from the high levels of constituent NGLs in the Flow-stream as
the
pressure is permitted to drop to process levels further differentiates this
system
from other pipeline systems and downstream stream process configurations.
[0028] The customary handover of prior Rich Gas mixtures between project
design groups for pipeline and process aspects primarily imposes and results
in a
gradual drop in configured pipeline flowing pressure to a level just above the
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minimum receipt specified for the downstream process. The process design group
then dictates control, compressing, heating or chilling of the Product for
further
treatment. This invariably involves considerable loss and replacement of
available
energy from a high pressure pipeline. The new methodologies disclosed herein
bridges that gap by providing first stage process conditioning for chilling
requirements, more efficiently using inherent properties of the current
product
delivered directly from the pipeline.
[0029] The J-T effect, caused by forcing the stored gas mixture through the
resistance of a J-T valve, chills the gas in an adiabatic manner. This gives a
high
degree of cooling of the delivered gas without work being added to or done by
the
system. In other embodiments, using a turbo expander at the point of
installation
of the J-T valve recovers a large part of this pressure energy in the form of
generation of electricity or shaft power at the delivery point while the
chilling takes
place. This power recovery can be substantial, having values in the order of
5,000
to 10,000 kW pre BCF/d of flow on a large installation. The recovered power
can
be used directly for upstream recompression or more generally for electrical
generation exported to the grid or for other process use.
[0030] These preconditioned temperature reductions are particularly attractive
to
lessening the heavy energy load for LNG processing where final stage
temperatures are reduced to the region of -260F. Where demonstrated economies
of scale must be shown for the viability of these megaprojects to occur, the
less
intense capital expenditure on reduced size of chilling plant and availability
of
recovered pipeline compressive energy from this invention warrants
consideration.
[0031] Conventional natural gas compressive characteristics and pipeline
delivery conditions require high pressure storage for good levels of
volumetric
retention. High pressures demand thick walled vessels, resulting in expensive
pressure containment in the context of trans-shipment ships or vessels. In the
case of a trans-shipment vessel, without limiting further applications, the
resulting
increased densities of the current Rich Gas mixtures can be contained at lower
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pressures than previously possible: more so when chilled, they can be shipped
in
less expensive, lighter wall containers. Herein, the current chilled product
can be
stored at lower pressures of about 1300 psig and yet match the transport
volume
of Standard Transmission specification gas shipped under the much higher
pressures at 1800 psig plus levels. The improvement in the gas to steel mass
to
volume ratio of Rich Gas mixes relative to Standard Specification gas storage
is of
the order of 50%. This effective reduced use of steel containment can amount
to
tens of millions of dollar savings in a marine vessel designed for 20,000 tons
of
Rich Gas capacity, and further add to the economic distance over which such a
vessel can deliver its cargo.
[0032] IN HYDRAULIC FLOW EMBODIMENTS: Higher pressure pipeline
operating conditions are provided for transmission of Rich Gas mixtures with
elevated levels of Natural Gas Liquids (NGL) constituents, either inherent in
the
mixture or achieved by additive or subtractive means, which create additional
reductions in the Z factor values over those available in the prior art. In
embodiments, higher pressure transmission pipelines with enhanced Rich Gas
mixtures can be configured to operate for most efficient general transmission
at
upper or of MOP operating pressures of over about 2250 psig and in further
embodiments between MOP of about 2250 to about 2850 psig. Recompression
can occur at about 1500 psig or at recompression thresholds of between about
1500 to about 1900 psig to attain the hydraulic and compressive power benefits
from optimum compressibility Z values and enables reduction in pipe diameters
by
at least one standard size over those for prior lower pressure designs for
reduced
capital cost.
[0033] Various methods of conditioning natural gas mixtures are applied in
a
pipeline for implementing lower compressibility (Z) factors such that the
resulting
mixture also exhibits internal chilling behavior during its transport and
storage
within the pipeline infrastructure. This mixture is formulated by additive or
subtractive processing of the natural gas and NGL constituents. Operational
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conditions where these effects occur are between a storage pressure of about
3500 psig reduced in pressure to 800 psig and 120F and -120F respectively. The
low temperature range is reserved for the lightest mixtures not exhibiting
liquid fall
out. Further, a pipeline carrying lean North American Spec Gas or NGL Rich
Gas,
that is project specific in volume, by virtue of its entire length and cross
sectional
area and pipe layout, used for product flow, high pressure storage, and de-
pressuring the contents, which operates within the limits of a storage
pressure of
about 4500 psig reduced down to a low pressure of about 350 psig according to
end use for a chilled delivered product.
[0034] As NGL constituents are transported in a single pipeline system,
mixed
with the natural gas component, the NGLs are transported for a fraction of the
cost
of building separate pipelines and handling infrastructure. Flowing Rich
Mixtures
also reduce the complexity of field plants to handle NGLs, and also at the
delivery
point where economies of scale can be obtained from a single
separation/process
facility built at that site.
[0035] As an example, comparison of an embodiment of the current pipeline
system, compared to an installation-based the technology set forth in the
earlier
US patent 6,217,626, limited to an MOP of about 2150 psig, shows a 35%
increase in flow of its Rich Gas per unit of compressive horsepower over the
lower
pressure industry configurations that were the norm at the time of its
construction.
Herein, implementing a MOP that is raised incrementally to about 2250 psig and
flowing a product of more dense NGL-enhanced Rich Gas mixture the new
configuration can deliver approximately 12% more volume of the Product per
unit
of compressive horsepower, all without risk of liquid falling out of the
gaseous
phase.
[0036] Accordingly, world scale delivery and processing of NGL constituents
of
the order of 100,000 bbl/day per 1.0 BCF/day of the utility gas component can
be
conveyed in this single system.
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[0037] STORAGE EMBODIMENTS OF ENHANCED RICH GAS: Herein,
operational control is improved by implementing an intermediate storage
capability
without liquid fallout. As stated earlier, the ability to provide interim
storage
permits continued upstream or downstream operations despite process disruption
at opposing ends of the process. Storage density is a function of the low Z
factor
particularly for an enhanced Rich Gas mixture held under high pressure
conditions
at ambient flowing temperatures.
[0038] Optional storage conditions exist within the pipeline system given
the
high packing densities of the claimed mixtures. This feature is enabled by the
provision of an ultra-high pressure accumulator section of the pipeline
generally
located immediately upstream of the terminus of the pipeline. Storage
configurations within the pipeline system become an optional function of
project-
specific needs, and can be provided in the form of a number of parallel loops
of
pipe of predetermined diameters, or a single section of larger diameter.
[0039] Conventional natural gas compressive characteristics and pipeline
delivery
conditions require high pressure storage for good levels of volumetric
retention.
High pressures demand thick walled vessels, resulting in expensive pressure
containment in the context of trans-shipment ships or vessels.
[0040] In the case of a trans-shipment vessel, without limiting further
applications,
the resulting increased densities of the current Standard Spec Gas and Rich
Gas
mixtures under lowered temperatures can more effectively be contained at lower
pressures than previously possible: The mixtures can be shipped in less
expensive, lighter wall containers. Herein, the Rich Gas chilled products can
be
stored at 1300 psig and match the transport volume of Standard Transmission
specification gas shipped under the much higher pressures at 1800 psig plus
levels. The improvement in the gas to steel mass to volume ratio particularly
of
Rich Gas mixes relative to Standard Specification gas storage is of the order
of
50%. This effective reduced use of steel containment can amount to tens of
millions of dollar savings in a marine vessel designed for 20,000 tons of Rich
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capacity, and further add to the economic distance over which such a vessel
can
deliver its cargo.
[0041] EMBODIMENTS OF ENERGY INTENSITY: High pressure cycles in the
transmission system and the selection of the NGL constituents allow for the
inclusion of Rich Gas mixtures with an upper value of MW of about 23.2 adapted
to an appropriately designed pipeline. Energy levels of the order of about
1500
BTU/ft3 for the higher heating value (HHV) of the delivered Rich Gas mixtures
can
result. This favourably compares to the HHV value of 1050 BTU/ft3 for a
typical
North American Standard Transmission specification gas delivered in today's
pipeline network.
[0042] EMBODIMENTS REGARDING DOWNSTREAM PROCESSING, the
delivered gas can now be customized to both optimal temperature and pressures
of specified downstream process applications such as LNG, separation and
fractionation facilities. When provided as described above, the internally
generated chilling can replace first stage or even second stage process
chilling
trains of the prior art. The energy of the high pressure pipeline section
results in
coupled with the high degree of "internal" chilling. Harnessing the behavior
of the
refrigeration properties of the flowing products within a pipeline adds a new
dimension to energy savings in the processing of natural gas mixtures. The
customary requirement for refrigeration of process products of natural gas
mixtures that has been normally provided externally from energy intensive
infrastructure can now be minimized or eliminated with the integration of high
pressure pipeline and process design. This can be built into the design of new
projects or installed as a retrofit to existing infrastructure.
[0043] Coupled with increased demands for lowered emissions per unit of
compression and increased energy delivery per mass of pipe installed,
embodiments herein now enable industry to further meet societal demands for
increased energy delivery and efficiency with reduced CO2 emissions for both
Rich Gas and Standard Transmission Spec Gas.
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[0044] Extending the benefits of high pressure internal chilling to even
the
lesser NGL content of Standard Spec natural gas mixes enables even these
mixtures to require substantially less process energy when subjected to
chilled
storage or LNG production.
[0045] The customary requirement for refrigeration of process products that
has been normally provided externally from energy intensive infrastructure
that
can now be minimized or eliminated with the integration of pipeline, process
design, and/or as a retrofit to existing infrastructure.
[0046] Historically pipelines and downstream facilities such as gas
processing
and LNG facilities have been treated as independent functions, and have been
designed, constructed and managed as separate unrelated functions in the
hydrocarbon energy infrastructure space with very little understanding or
appreciation for the operational relationships of their respective functions
Herein
Applicant has determined that significant efficiencies can be achieved by
considering the capability and needs of both the pipeline and downstream
functions. A new integrated method for delivery and transport of chilled gas
product to downstream applications has been developed.
[0047] In summary, in a pipeline gas transmission system, the last
compressor
station, for storage or preparatory for chilling, is used to increase pressure
prior to
conditioning of the product by chilling of the gas through a J-T device, the
chilling
optionally conducted through a downstream turbo-expander for generation of
recovery power for other applications. Storage pressure created by this last
compressor is customized and designed for a specific downstream application.
One can a pressure environment to enable sufficient chilling for the
separation and
fractionation of NGL's from natural gas for processing facility applications
Depending on the gas mixture, one can provide a significant portion of the
chilling
for LNG applications thereby reducing, by the equivalent level, capital and
operating costs comparable to conventional systems. One can retrofit existing
pipeline systems for existing gas processes and LNG facility applications.
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Recovered power from the J-T device can be used for additional power needs,
fractionation or sold to the electric grid system.
[0048] Herein, Applicant has advanced the known pipeline systems by
providing a method of accelerating the onset of lower compressibility (Z)
factors in
natural gas pipelines, implementing broader pressure, temperature, and range
of
constituents within Rich Gas mixtures for yielding a new array of
transportation
benefits including: a wider band of low flow resistance in pipelines over
prior art
otherwise restricted by lower maximum operating pressures; increases in
storage
densities resulting from these lowered Z factors; and an ability to take
advantage
of high levels of NGLs within the new gas mixtures and their behavior within
the
broader pipeline pressure differentials (sitting within 3500 psig and 900
psig), The
pipeline differentials that result enable effective use of the J-T effect for
"internal"
chilling to occur from within the product transported by the pipeline, without
a need
for added external energy,.
[0049] This internal chilling matches or exceeds that of conventionally
provided
by costly and external chilling via heat exchangers and industrial
refrigerants
commonly used in the downstream gas processing industry, applied to products
below 800 psig and 1300 psig plant design thresholds. These industrial
refrigerants in the prior art here are frequently non-hydrocarbon in nature
and
increasingly being avoided or withdrawn from the market in recognition of
their
severe and negative environmental impact.
[0050] Applicant delivers a pre-chilled product by pipeline that alleviates
this
energy and environmental demand on the industry. Further, when provided via
turbo expander, Applicant's system recovers pipeline energy otherwise lost in
the
custody transfer between segregated pipeline and end process disciplines.
[0051] In conclusion, this disclosure sets forth a method of accelerating
the
onset of, and access to, lower compressibility (Z) factors in natural gas
pipelines
such that flow resistance and storage density are improved. The properties of
the
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Rich Gas mixtures and higher operating/storage pressures involved are such
that
internal chilling within the transported medium can then take place through
the
Joule-Thompson effect, making a lower pressure delivery of a Rich Gas Product
direct from the pipeline. The subsequent delivery of a chilled product using
recovered pipeline energy can replace a substantial amount of chilling
otherwise
externally created for many downstream applications
[0052] Design developments incorporated herein permit simplified operations
within a broader pressure range of low compressibility factor (Z) operation to
take
place. Pre-conditioning processing in the field is simplified, mainline
compressor
stations can incorporate single units. Operating pressures now broaden between
2500 psig through the best efficiency point around 2100 psig to the
recompression
point of about 1300 psig or about 1450 psig, depending on gas mixture.
[0053] On a project specific basis there is nothing to preclude design and
construction of all sections of the pipeline to a high MOP of about 3500 psig
for
realizing hydraulic, storage and chilling benefits throughout its length.
[0054] Reduced capital expenditure, compression infrastructure and
operating
costs emerge from this less energy and emissions-intensive Rich Gas
transmission, chilling and containment system. The need and environmental
impact of multiple pipelines, rail and trucking movements for gas and NGL
transport is eliminated or takes place through seamless integration of new
process
plant and retrofitting of existing infrastructure to meet future demands on
the
industry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] In the following description, reference is made to the accompanying
drawings:
[0056] Figure 1 is a schematic of one embodiment of a pipeline system
disclosed
herein with expanded storage staging section and transshipment facilities to
precondition flow for downstream processing and facilities for loading land,
marine
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or air vessels. As a multiplicity of gas mixtures can be implemented,
embodiments
of storage and transmission behavior is simply provided herein using two
component mixtures of methane with each of the primary NGLs of ethane,
propane, and butane.
[0057] Figure 1A shows a pressure trace at corresponding points of flow in
Fig.
1, against the backdrop of the phase envelope of the transmitted gas-based on
a
re-injected ethane-rich gas mixture from natural gas produced in Alaska;
[0058] Figure 1B shows a temperature trace at corresponding points of flow
in
Figs. 1 and 1A;
[0059] Figure 1C illustrates the pressure temperature trace of the gas flow
in
the pipeline relative to the phase envelope of the flow mixture. Three staging
steps
are covered from the normal pipeline section flow between compressor stations,
to
the high pressure storage containment, to the delivery pressure drop with
chilling
specified for Product delivery.
[0060] Figure 2A illustrates the compressibility factors of typical
transmission
specification gas mixture having an S.G. =0.6, a catenary trace for Z Factor
values
for selective temperatures is shown and a typical Z Factor at 75F at
transmission
pressures of 1500 psig;
[0061] Figure 2B illustrates the compressibility factors of typical of an
example
Rich Gas mixture, a catenary trace for Z Factor values for selective
temperatures.
The path traced by gas flow in the current pipeline staging sections at high
to low
pressures is shown as A-B-C;
[0062] Figures 3 through 5 illustrate the chilling abilities available for
downstream deliveries for three progressively richer gas mixtures containing a
blend of constituents Cl, C2, C3 ... C6+. The mixtures are distinguished by
HHV
(high heat Values) in USBTU/ft3 units given in the title block of each of the
Figures .. We have full property behaviour reports including Phase
Envelopesthe
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charts illustrating the temperature drop for a rich gas mixture reduced in
pressure
for a variety of pressure ranges between about 1750 psig down to 600 psig, and
3500 psig down to about 600 psig.
[0063] Figures 6A through 8C illustrate the storage aspects attainable
within
the pipeline system simplified as 2-component Rich Gas mixes, and quantified
as
ratios of Mass-of-Gas to Mass-of-Containment Steel
[0064] Figure 6A illustrates storage characteristics of pipe containment
ethane-
based rich gas mixtures showing regions of optimal net volume ratio of ethane-
based mixtures compared to CNG volume ratios under same storage conditions,
wherein comparable mass of gas to mass of containment steel pipe ratios are
listed;
[0065] Figure 6B illustrates gas storage characteristics of ethane-based
rich
gas, with tabulated data of concentration of ethane for densest mixture under
stated conditions of temperature and pressure, wherein resulting maximum
volume ratio of mixture under stated conditions of temperature and pressure
exceeds those of Standard Transmission specification mixture, and lower
storage
pressures reflect with lower m/m mass ratio for containment;
[0066] Figure 6C further illustrates regions and limitations of the ethane-
based
rich gas of Fig. 6B for illustrating preferred VA/ and M/M ratios over those
of
standard transmission gas and limitations where rich gas mixtures could stray
into
the liquid phase;
[0067] Figure 7A shows storage characteristics of pipe containment propane-
based rich gas mixtures, showing regions and limitations for optimal net
volume
ratio of propane-based mixtures compared to CNG volume ratios under same
storage conditions, where comparable mass of gas to mass of containment steel
pipe ratios are listed;
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[0068] Figure 7B illustrates gas storage characteristics of propane-based
rich
gas, with tabulated data of concentration of propane for densest mixture under
stated conditions of temperature and pressure, wherein resulting maximum
volume ratio of mixture under stated conditions of temperature and pressure
exceeds those of Standard Transmission specification mixture, and lower
storage
pressures reflect with lower m/m mass ratio for containment;
[0069] Figure 7C further illustrates regions and limitations of the propane-
based
rich gas of Fig. 7B for illustrating preferred VA/ and M/M ratios over those
of
standard transmission gas and limitations where rich gas mixtures could stray
into
the liquid phase;
[0070] Figure 8A shows storage characteristics of pipe containment butane-
based rich gas mixtures, showing regions and limitations for optimal net
volume
ratio of butane-based mixtures compared to CNG volume ratios under same
storage conditions, wherein comparable mass of gas to mass of containment
steel
pipe ratios are listed;
[0071] Figure 8B illustrates gas storage characteristics of propane-based
rich
gas, with tabulated data of concentration of butane for densest mixture under
stated conditions of temperature and pressure, wherein resulting maximum
volume ratio of mixture under stated conditions of temperature and pressure
exceeds those of Standard Transmission specification mixture, and lower
storage
pressures reflect with lower m/m mass ratio for containment;
[0072] Figure 8C further illustrates regions and limitations of the butane-
based
rich gas of Fig. 8B for illustrating preferred VA/ and M/M ratios over those
of
standard transmission gas and limitations where rich gas mixtures could stray
into
the liquid phase;
[0073] Figures series 6 illustrate the internal chilling aspects now
available from
contained gas behavior under the claimed operating and storage conditions for
the
pipeline. For the most part the Joule Thompson effect kicks in at a pressure
of
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3200 psig. Higher pressures generally occur from operational storage
considerations and can be further utilized downstream of the pipeline.
[0074] Figure 9A shows a comparison between a conventional pipeline system
and the transmission system of Fig. 1; illustrating benefits in deliverable
heat
value, reduction in pipe mass, compression power, fuel and CO2 emissions;
[0075] Figure 9B shows a selection of values of the heat of vaporization of
outgoing CFC refrigerants and those similar values of NGLs operating from an
initial temperature of 80 F; and
[0076] Fig. 9C is a schematic illustrating the replacement of a first stage
propane section of a cascaded propane-ethylene-methane process for LNG
production, external chilling at the first stage of an LNG plant being
replaced by an
internally chilled mixture emerging from the pipeline. The Rich Gas pipeline
flow is
separated into an NGL stream and a lean gas feedstock for the LNG process.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0077] Having reference to Figs. 1, 1A, and 1B, embodiments of the
operation
of a multifunctional high pressure Rich Gas pipeline system 100. As shown in
schematic form in Fig. 1, the system 100 is illustrated for moving a product
of
mixtures of natural gas and NGLs through a series of compression/recompression
cycles 112 from a source 110 to a destination 126.
[0078] In Figs. 1A and 1B, pressure and temperature traces respectively are
shown for the operating scenario of Fig. 1A, that transmits and stores the
natural
gas mixture in the dense phase mode, and are arranged to correspond with the
steps of system 100. The operating scenario is overlaid on the backdrop of the
phase envelope of the gas being transmitted and stored according to Fig. 1.
[0079] In Figs. 1A, 1B, reference characters "A", "B", "C", "Cx", "D", "E"
and "F"
are matched to the component locations shown in Fig. 1.
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[0080] In Fig. 1 the pipeline system 100 comprises several transmission
staging sections, including a transmission or pipeline staging section 102 for
moving rich gas from the source 112 to the destination 126, a storage staging
section 104 for storing the transmitted rich gas at or near the destination,
and a
trans-shipment staging section 106 having necessary facilities for delivering
rich
gas to downstream applications. In each staging section 102, 104, 106, NGLs or
make up methane gas may be injected into the pipeline 112 or storage pipes at
points m/118 for adjusting the rich gas therein.
[0081] The pipeline transmission staging section 102 comprises one or more
pipelines 112 for moving natural gas mixture, and one or more compressors 114
for recompression of the natural gas mixture at each section to a higher
pressure.
Thus, the pipeline staging section 102 transmits natural gas mixture within
desired
pressure and temperature ranges.
[0082] In embodiments, the natural gas mixture is a Standard Gas mixture
Rich
Gas mixture, formulated by additive or subtractive processing, and comprising:
from 40% to 98% by molar volume (mol volume) of methane, from trace to 35%
by mol volume of ethane, from trace to 22% by mol volume of propane, from
trace
to 9% by mol volume of butane, and trace elements of C5+ (i.e., C5, C6, ...)
hydrocarbons not exceeding 0.25% by mol volume; and the total of (a) to (e)
being
100%, and such mixture being completely gaseous or dense phase (supercritical)
with no liquid phase at the temperature and pressure of operation.
[0083] The pipeline extends from the source to the destination, through a
series
of recompression cycles. One or more, or all of recompressions raise the Rich
Gas to a maximum operating pressure (MOP), having a Rich Gas mixture adjusted
to avoid liquid fallout. The re-compression pressure is raised of over about
2250
psig and in further embodiments between MOP of about 2250 to about 2850 psig.
As energy and pressure is lost over the 100 or more kilometer transmission
between compressor stations, recompression can occur at about 1500 psig or at
recompression thresholds of between about 1500 to about 1900 psig to attain
the
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described hydraulic and compressive power benefits from optimum
compressibility
Z values. Further, as the volumetric efficiency of the Rich Gas mixture is
improved, one can reduce in pipe diameters by at least one standard size over
those for prior lower pressure designs for reduced capital cost whilst moving
the
same mass of Rich Gas.
[0084] In this embodiment, and in greater detail, the pipeline staging
section
102 operates with a maximum operating pressure (MOP) of 2500 psig and
recompression at 1300 psig, utilizing a range of low compressibility factors Z
range, Point A to Point B to Point C of Fig. 2B, and at temperatures between
about
50 F and about 120 F.
[0085] Transmission pipeline compressors are shown as "C" types. In the final
Storage/Delivery pipe section 104 the pressure is lifted through stepped
compressors "Cx" from 1300 psig to 3000 psig storage to provide the head for
de-
compression (D-E). This drop in pressure at the exit of the storage section
reduces the storage temperature via Joule¨Thompson effect on the flowing
products to -45F as shown here. Depending on the gas mixtures and pressure
drop, much lower temperatures in accordance with downstream Application can be
provided.
[0086] The above described arrangement of transportation management and
the use of above described rich gas mixture provide a synergy in pipeline
operations resulting in an option to use smaller pipe diameters for same
transmission capability and while reducing compressive power needed for Rich
Gas pipelines.
[0087] Further, the final pressure and temperature conditioning of the
natural
gas, departing the Turbo Expander into pipeline section 106 at the
destination,
results in large savings in both capital and operational costs to produce the
delivered product in a form that eliminates the need for the first stage
chilling of the
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certain downstream applications. Overall, the capital costs of such pipeline
systems are reduced over conventional natural gas transportation systems.
[0088] The higher transmission efficiency and thus the lower cost of the
pipeline system disclosed herein is obtained by transmitting natural gas
mixtures,
such as the rich gas mixture disclosed herein, at desired pressure and
temperature ranges to achieve a lower compressibility factor (Z) substantially
throughout during transmission.
[0089] With reference to FIG 1C the Phase Envelope for a Rich NGL-laden Alaska
gas mixture is noted alongside the pipeline pressure/temperature trace. The
trace
C-D is representative of pipeline section flow, the trace D to E is the high
pressure
lift to storage, and E to F is the drop of pressure and temperature through a
simple
Joule-Thompson valve to a condition suited to gas separation or chilled
Compressed Natural Gas (CNG) storage. The phase remains gaseous without
liquid fall out throughout the transmission of the Product to Downstream
Applications.
[0090] With reference to Figs. 2A and 2B, compressibility factor (Z)
comparative characteristics of typical Standard Transmission specification gas
mixtures and Rich Gas mixtures are represented. Properties of typical Standard
Transmission gas of MW = 17.4 are shown on Fig. 2A. Characteristics of the
Rich
Gas mixture and the compressibility factors thereof are represented by a gas
of
MW = 20.3 as shown in Fig. 2B.
[0091] Both the pipeline hydraulics and net storage densities are improved
by
incorporating a lower Z value in the system design by virtue of the NGL
constituents in the gas mixture. The process disclosed herein takes advantage
of
the accumulated effects of stored density and pipeline hydraulics to elevate
the
transmission economics to another level. A typical MOP of a pipeline carrying
Standard Transmission specification gas mixture at about 1450 psig at 75 F
(see
point S of Fig. 2A) with a Z value of about 0.79.
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[0092] Whereas prior teaching advocated running Rich Gas mixture pipelines
between 2100 psia and 1300 psia (left of Point B to Point C of Fig. 2B),
Applicant
has discovered that advances in steel toughness to counter crack propagation
now permits the use of higher pressures, enabling operations in the region
found
on the right portion of the low Z value inflexion from point B on the catenary
curve
of Fig. 2B. Now a pipeline carrying above described rich gas mixture can run
between 2500 psia (Point A of Fig. 2B) through the low Z value spot at 2100
psia
(Point B of Fig. 2B), and even lower down to a pressure of about 1300 psia to
1500 psia in the region about Point C of Fig. 2B before recompression. The
higher
MOP achieving hydraulic benefits also is advantageous towards stepping the
Rich
Gas storage upwards towards levels shown in Figs. 4 and 5 to attain the
internal
or self chilling advantages of Rich Gas mixtures. Optimally designed, the
operation
of the rich gas pipeline at the new higher MOP towards Point A of Fig. 2B can
result in a 12% increase in flow for less power per unit of gas over the
performance of the earlier high pressure designs with an MOP at Point B of
Fig.
2B.
[0093] Now a pipeline carrying above described rich gas mixture can run
between 2500 psia, Point A, through the prior known low Z value at 2100 psia
at
Point B, and even lower down to a pressure of about 1300 psia to 1500 psia in
the
region of Point C before recompression.
[0094] The recompression point depends on station spacing and pipe diameter
relative to pipeline flow rate. This wider recompression pressure cycle, or
wider
operating pressure range, also permits longer distances between compressor
stations for reduced capital expenditure.
[0095] Optimally designed, the operation of the rich gas pipeline at the
new
higher MOP towards Point A can result in a 12% increase in flow for less power
per unit of gas over the performance of the earlier designs with a MOP at
Point B.
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[0096] In an embodiment, by recompressing at about 1300 to about 1450 psia,
at about Point C, Applicant found new operating efficiencies that outweigh the
required increase in pipe wall thickness demanded by the higher MOP. Compared
to conventional pipeline systems, the average Z value drops from 0.705 to
0.682,
and the compressor station spacing increases by 15%, easily removing one
complete compressor station from the infrastructure of a typical 1000 mile
long-
distance pipeline. For example, conventional spacing of one station per 100
miles
might be increased to one station per 120 miles, further reducing capital cost
and
complexity.
STORAGE FOR COMPRESSOR OUTAGE SITUATIONS:
[0097] Referring to Figs. 1, 1A and 1B, in an embodiment, compaction of the
natural gas mixture in the standard-diameter pipeline sections 112 between
compressor stations 114 acts as a line pack accumulator 122. The amount of gas
stored in the accumulator portion(s) 104 permits a correctly designed dense
phase
pipeline to operate at normal flow for several days in the event of a station
outage
before the new steady state, lower flow conditions dictated by the outage set
in
place. This now enables the pipeline staging section 102 to be designed with a
slight catch up overage in the horsepower available at each compressor station
114, which allows the system 100 to operate for this repair interval without
the
need for standby compressors at these stations 114. There is adequate time to
repair breakdowns or even replace a compressor 114 or cartridges during this
interval before the long term lower flow steady state conditions occur. Given
the
high reliability of modern compressor systems today this is a statistically
low risk
advantage to the operation of Rich Gas pipeline designs. This further reduces
material and capital investment in each station of a dense phase pipeline
system.
[0098] With reference to Fig. 1C the performance characteristics of the
high
pressure accumulator performance is illustrated against the backdrop of the
Phase
Envelope for a Rich NGL laden Alaska gas mixture, noted alongside the pipeline
pressure/temperature trace. The trace C-D (176-174) is representative of
pipeline
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section flow, the trace D to E (174-178) is the high pressure lift to storage,
and E
to F (178-180) is the drop of pressure and temperature through a simple Joule-
Thompson valve to a condition suited to gas separation or chilled Compressed
Natural Gas (CNG) storage. The operating conditions lie in the Dense
Phase/Supercritical zone above and to the right of the Critical Point of the
Gas,
point 170. For accumulation, compression is shown from point 174 to point 178
at
about 3250 psig where the mixture can be held under conditions of high
density.
[0099] The phase remains gaseous without liquid fall out throughout the
transmission of the Product to Downstream Applications.
[0100] Point 176 marks the Maximum Operating Pressure (MOP) to which the
gas is compressed in a mainline segment to 2500 psig. The pressure and
temperature drop as the Product flows along the segment to the point of Re-
Compression at point 174, 1750 psig. For normal flow from segment to segment,
the gas would be compressed back to MOP level at 2500 psig and the cycle begin
again.
[0101] However, for illustration the compression here is taken from point
174 to
point 178 at 3250 psig, representing the containment condition in a high
pressure
storage stage of the pipeline where the mixture can be held under conditions
of
high density. The storage volume for the product would be dependent on the
project-specific pipe volume made available here. From point 178 to point 180
the
Product is seen to drop rapidly in pressure towards 1200 psig. This flow takes
place in a J-T device such as a turbo expander, and temperature is noted to
chill,
in one embodiment, from 90F to 1OF as a result of the Joule-Thompson effect on
the flowing medium, which is now available for delivery. These delivery
conditions
avail themselves for a selection of downstream applications. Far lower
temperatures can be experienced for specific process needs by adjustment of
inlet
pressure and outlet pressure across the J-T device.
STORAGE FOR DELIVERY DEMAND:
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[0102] The accumulator or storage staging section 104, usually located at
the
destination, comprises one or more storage pipes 122, and a Joule-Thomson (J-
T)
expander 132 (described later) for transmitting rich gas from the storage
pipes to
the trans-shipment staging section 106. A high, and last stage, pressure
booster
compressor station 116 can be located between staging sections 102 and 104 and
has a high head capability to lift the pressure up from above described,
normal
operating pressures to a desired elevated storage pressure in the storage
pipes
122.
[0103] In some embodiments each of the storage pipes 122 is a pipe having a
longer section length and a larger diameter ("A" to "B" of Fig. 1B) to provide
required storage volume. Further, compared to the pipelines 112, the storage
pipe(s) 122 operate at a higher pressure to act as an accumulator for storage
purposes. The high storage pressure, set at the upper level of where the Joule
Thomson (J-T) effect is activated in the transmitted gas mixture, also
provides the
differential from the high pressure (at the storage pipes 122) to low pressure
(after
passing through the J-T expander 132), which is required to obtain the
internal gas
chilling in the trans-shipment staging section 106 via the J-T cooling effect
(described later).
[0104] In one embodiment, the Rich Gas mixture disclosed herein may be
contained in the storage pipes 122 at pressures between about 3250 psig and
about 3500 psig, depending on liquid fallout limits of the particular gas
mixture,
and preferably at ambient/ground temperatures. About 110 F has been noted in
modeling summer operations where limitations of air cooling and residence
times
in the pipeline have not proved to be prohibitive to in-pipe storage. In
temperate
zone winter conditions about 75 F or lower is the norm for flow emerging from
storage. This lower temperature is the basis for J-T chilling summarized for
Standard Specification and Rich Gas mixes in Figs. 3, 4 and 5.
[0105] An optional temperature trimming system is incorporated within or
downstream of the storage compressors to condition the gas flow to optimal
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temperature or density conditions for process applications downstream of the
invention. Where the pipeline is specifically designed to handle expansion,
stress
and material behavior, an operating condition, upper temperature limit of 150
F is
specified to maintain flow in gaseous state when the pipeline is installed in
cold
environments having high heat losses along the sectional length(s).
STORAGE WHERE OTHER FACILITIES ARE UNAVAILABLE:
[0106] Such an accumulator storage system takes advantage of the available
conventional pipeline installation equipment, techniques and inspection and
quality
control aspects implemented for the pipelines 112 in the pipeline staging
section
102. For example, three (3) parallel 36" pipes can be used as the storage
pipes
122 between the last compressor station 116 and the trans-shipment staging
section 106. As a result, excessive costs or lack of onsite storage or caverns
are
no longer prohibitive at the destination or shipping point of the system 100.
Thus,
the storage staging section 104 ahead of the shipping point can now
incorporate a
large volume by means of pipes 122. Alternatively, the pipes 112 may be a mix
of
pipes of different lengths and/or diameters for holding this strategically
determined
volume.
[0107] The increased diameter(s)/cross-section(s) or combined
diameter(s)/cross-section(s) of the storage pipes 122 in the storage staging
section 104 further reduce the hydraulic pressure loss that may be experienced
by
the conventional pipeline system during normal operating conditions.
STORAGE ENERGY CHILLING AND TRANSPOSITION:
[0108] As shown in Fig. 1, for trans-shipment, the natural gas mixture in
the
storage pipes 122 first passes through the molecular sieve/J-T expander 132
coupled downstream of the high pressure accumulator 122 to reduce the pressure
thereof and to chill the natural gas mixture.
[0109] The J-T expander 132 reduces adiabaticaly the pressure of the natural
gas
mixture, or in one embodiment the rich gas mixture, from the high storage
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pressure (about 3250 to 3500 psig) to approximately 1300 psig. Such a pressure
drop at the J-T expander 132 results in J-T cooling to the natural gas mixture
passing therethrough for trans-shipment at optimal conditions illustrated in
Figs.
6A, 7A and 8A.
[0110] Using the energy in the high pressure accumulated Rich Gas mixture,
the J-T expander acts as an internal chiller that, dependent on the
destination
demands, may be all the chilling that is required. The J-T expander 132 may be
any gas expander and ancillary equipment suitable for reducing the pressure of
the natural gas mixture and for chilling the natural gas mixture using the
Joule¨
Thomson effect (i.e., internal, or self-chilling). For example, in one
embodiment,
the J-T expander 132 is a pressure reduction valve; in another embodiment and
more efficiently, the J-T expander 132 is an energy recovering turbo expander.
As
is known in the art, the Joule-Thomson effect refers to the phenomenon that,
with
no heat exchange with the environment, the temperature of a gas changes when
it
is forced through a flow restrictor.
[0111] In one embodiment, the J-T expander 132 uses the J-T effect to chill
the
natural gas mixture to a low temperature suitable for trans-shipment without
liquid
fallout, e.g., in some embodiments to between about -20 F and about -30 F for
Rich Gas Mixtures, or in other embodiments to between about -10 F and about -
80 F for Standard Specification Gas. Whereas carbon steels are generally
limited
in service to -55 F, utilizing these lower temperatures is dependent upon the
materials of construction with lower limits such as nickel steels, aluminum
and
stainless steel.
[0112] With reference to Figs. 3, 4 and 5, rich gas mixtures at standard
temperature 75F will drop in temperature, when reduced in pressure from about
1750 to about 1200 psig to about 30F, and when dropped from about 3500 psig to
about 1200 psig, to about -30F. The maximum temperature drop achieved flattens
out for storage pressures of over about 3,000 psig, higher and higher starting
pressures resulting in very little change in final temperate.
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ENERGY RECOVERY AS ELECTRICAL GENERATION:
[0113] In another embodiment where a turbo-expander is used for polytropic
expansionõ lower temperatures are achievable along with energy conservation
by recovering energy through generation of electricity or mechanical power
from
its output shaft.
[0114] Recovered power from the turbo expander and chilled fluid emerging
from the pipeline system present a more efficient means of providing external
and
downstream energy needs. The generated power can also exported off site.
[0115] Chilling to downstream processing production is provided more
efficiently from pipeline compression. Given the additional External Chilling
requirements for compression, heat transfer, fouling interface, and re-
condensing
the internal chilling availability from this invention will eliminate over
half the
expected energy load. In an embodiment, over a range of temperatures between
110 F and - 40F, internal chilling exhibits a nominal overall efficiency of
general
order of 28% compared to external chilling showing a general order of 12%
overall
efficiency.
DOWNSTREAM OPTIONS:
[0116] Alternative pre-chilled feed stock can be provided from header 134
shown in Fig.1 for a variety of process/transportation technologies that can
benefit
from reductions in chilled front end energy needs and lowered CO2 emissions
when coupled with the pipeline system 100 in this manner. Typical but not
exhaustive technologies applicable as downstream destinations for pre-chilled
flow
include separation and fractionation 142, CNG processing 144, NGL processing
feedstock 146, first stage liquefied natural gas (LNG) processing 148, and
compressed LNG for emerging market 150.
[0117] While located adjacent a terminus in one embodiment for J-T cooling,
as
shown in Fig. 1, the storage staging section 104 and the trans-shipment
staging
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section 106 may be alternatively located at other locations such as
intermediate
locations or spur-lines anywhere along the pipeline 112.
[0118] In an alternative embodiment the storage pipes 122 can operate at a
high pressure up to 4500 psig for increasing process storage density. At such
high
pressures the J-T effect on the contained Products is minimal, an external
trimming cooler system is coupled to the J-T expander to reduce the discharged
natural gas mixture to optimal temperature for colder temperature downstream
applications.
[0119] In alternative embodiments, traditional Standard Transmission
specification gas mixture may be transmitted in the disclosed high-pressure
pipeline system 100. For example, in one embodiment, Standard Transmission
specification gases may be transmitted in the high-pressure pipelines 112
operating between an MOP of about 2750 psig and recompression at 1650 psig or
1700 psig for transmitting the Standard Transmission specification gases at a
low
Z factor for improved gas transmission efficiency.
[0120] In an alternative embodiment, an external trimming cooler system can
also be coupled to the J-T expander 132 to reduce the discharged natural gas
mixture to optimal temperature or density conditions for alternate specified
downstream applications.
INFLUENCE OF GAS CONSTITUENTS CARRIED BY PIPELINE:
[0121] Given the multiplicity of combinations of affective NGL constituent
combinations possible in Rich Gas mixtures it is convenient to illustrate the
benefits and limitations of mixtures against Standard Transmission
specification
gas mixtures, modeled as straight methane (Cl), and the Rich Gas modeled as 2-
part mixtures of methane and each of one of the three common and principal NGL
constituents of ethane (C2), propane (C3), and butane (C4) and modelling
Standard Transmission specification gas as simple methane. Figs. 6A, 7A and 8A
show comparative values for the volumetric compression of the methane
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constituent in progressively richer mixes against Standard Transmission
specification mixtures under the same conditions. Areas of best performance
are
shown as side-by-side graphs. As a commercial measure, one compares the
mass of gas mixture to containment steel to show the effectiveness of this
mode of
storage.
[0122] In the following, the benefits of the disclosed two-component Rich
Gas
mixtures are described with reference to Figs. 6A to 8C. Figs. 6A to 6C show
the
benefit of a Rich Gas mixture having ethane (C2) added as the compression
constituent. Figs. 7A to 7C show the benefit of a Rich Gas mixture having
propane (C3) added and Figs. 8A to 8C show the benefit of Rich gas mixture
having butane (C4) added as the compression constituent..
[0123] In the graphs of Figs. 6A,7A and 8A, characteristics of Rich Mixes
are
shown in italic notation are where points of maximum content of methane (Cl)
occur at 2 Phase or Liquid States. Reduction in mol% of Cl at these points
will
change state to Gas phase and still yield higher values of VA/ and M/M than
for
Std Specification Gas under same Temperature and Pressure conditions ¨ higher
values will vary according to other constituents in real mixes.
[0124] In the Fig. 6A chart, performance for storage of the gaseous Rich Gas
mixture (for the NGL constituent represented by ethane (C2), measured against
the Standard Transmission specification mixture, appears in the 1100 to 1400
psig
range of pressures at temperatures in the -30 F to -20 F window, balancing
increased compressed volume ratio against mass ratio.
[0125] At a pressure of 1200 psig at temperatures of -40 F and -30 F the v/v
ratio
of the two mixtures show useful increases of the order of 35% for the Rich Gas
over the Standard Transmission specification mixture.
[0126] There is a clear distinction between the two gas types in the
comparative
mass ratio plots. The useful value of 247 VA/ for the net volumetric ratio of
Rich
Gas at 1200 psig and -20 F yields a lb/lb gas to containment material mass
ratio of
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0.40 exceeding the 0.22 number for CNG (from Standard Transmission
specification gas mixture) under the same conditions. The mass ratio of the
containment system for methane constituent in the Rich Gas is virtually
doubled
here over that for CNG when stored in this manner for onward
transportation/storage in containment vessels, resulting in significant
capital cost
savings.
[0127] Fig. 7A shows the benefits in storage of Rich Gas mixtures (for the NGL
constituent represented by propane (C3) over standard Standard Transmission
specification / CNG mixes. The Rich Gas is modeled as a two component propane
/ methane mix, and net VA/ ratios are for the solo methane component, to make
a
comparison to the CNG case under the same storage conditions. Rich Gas mixture
benefits are shown as mass of gas to mass of containment steel ratios on a
lb/lb
basis, especially important when high tonnage of materials are involved in
storage
vessels.
[0128] For propane rich constituents the best compressive performances for
storage of the gaseous Rich Gas mixture measured against the Standard
Transmission specification mixture appear in the 900 to 1400 psig range of
pressures at temperatures in the -30 F to -20 F window suited to steel
containment.
[0129] At a pressure of 1200 psig at temperatures of -30 F and -20 F the v/v
ratio
of the optimal mixtures show useful increases of the order of 69 to 60% for
the
Rich Gas. At colder temperatures, and higher pressures it is evident that
instabilities of liquid formation and fallout is to be avoided for richer
mixtures.
[0130] There is a clear distinction between the two gas types in the
comparative
mass ratio plots. The useful value of 250 for the volumetric ratio of Rich Gas
at
1200 psig and -20 F yields a lb/lb gas to containment material mass ratio of
0.38
exceeding the 0.22 number for CNG under the same conditions. The mass ratio of
the required containment system is reduced to 2/3 here when Rich Gas is stored
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for transportation. Conversely similar containment performance of Standard
Transmission specification mixture would call for that product to be stored at
1400
to 1800 psig at a temperature of -40 F with a corresponding increase in wall
thickness of the steel
[0131] Fig. 8A shows the benefits in storage of Rich Gas mixtures (using C4)
over
standard CNG transmission mixtures. The rich gas is modeled as a two
component butane / methane mixture, and net VA/ ratios are for the methane
component only to make a comparison to the CNG case under the same storage
conditions. Rich gas mixure benefits are shown as mass of gas to mass of
containment steel ratios on a lb/lb basis, especially important when high
tonnage
of materials are involved in storage vessels.
[0132] Best compressive performances for storage of the gaseous Rich Gas
mixture measured against the Standard Transmission specification mixture
appear
in the 900 to 1200 psig range of pressures at temperatures in the -30 F to -20
F
window suited to steel containment.
[0133] At a pressure of 1200 psig at temperatures of -30 F and -20 F the v/v
ratio
of the two mixtures show useful increases of the order of to 45% for the Rich
Gas
over Standard Transmission specification mixture. At colder temperatures, and
higher pressures it is evident that instabilities of liquid formation and
fallout is to be
avoided for richer mixtures.
[0134] There is a clear distinction between the two gas types in the
comparative
mass ratio plots. The useful value of 229 for the volumetric ratio of Rich Gas
at
1200 psig and -20 F yields a lb/lb gas to containment material mass ratio of
0.37
exceeding the 0.22 number for CNG under the same conditions. The mass ratio of
the containment system is less than 2/3 here when Rich Gas is stored for
transportation. Conversely similar containment performance of Standard
Transmission specification mixture would call for that product to be stored at
1400
to 1800 psig at a temperature of -40 F.
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[0135] With reference to the graphs of Figs. 6C,7C and 8C, each graph
illustrates gas property trends for primary NGL constituents. Each graph
illustrates
the maximum gas storage values of rich gas-vs-std specification gas for gases
enriched with ethane, propane and butane respectively. Of the rich mix gases,
higher m/m values are shown in grey tone and are subject to moderate reduction
in peak NGL concentration to avoid two-phase or liquid state storage
conditions.
The Y-axis represents V/V, being (Volume of Natural Gas at Std. Conditions) /
(Volume of Natural Gas at Storage Conditions). The corresponding Y-axis M/M =
Gross Mass of Contained Mixture/Mass of steel in Containment System. Further,
for the volume ratios V/V, the contained natural gas in Rich Gas Mix is net
value of
natural gas component within the Mix.
[0136] Performance for storage of the gaseous Rich Gas mixture (for the NGL
constituent represented by ethane (C2), measured against the Standard
Transmission specification mixture, appears in the 1100 to 1400 psig range of
pressures at temperatures in the -30 F to -20 F window, balancing increased
compressed volume ratio against mass ratio.
[0137] At a pressure of 1200 psig at temperatures of -40 F and -30 F the
v/v
ratio of the two mixtures show useful increases of the order of 35% for the
Rich
Gas over the Standard Transmission specification mixture.
[0138] There is a clear distinction between the two gas types in the
comparative mass ratio plots. The useful value of 247 V/V for the net
volumetric
ratio of Rich Gas at 1200 psig and -20 F yields a lb/lb gas to containment
material
mass ratio of 0.40 exceeding the 0.22 number for CNG (from Standard
Transmission specification gas mixture) under the same conditions. The mass
ratio of the containment system for methane constituent in the Rich Gas is
virtually
doubled here over that for CNG when stored in this manner for onward
transportation/storage in containment vessels, resulting in significant
capital cost
savings.
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[0139] Fig. 6B shows tables for the derivation of graphics used in Fig. 6A.
In
particular the ratio of m/m mass ratio numbers for Rich Gas mixtures alongside
those for the standard gas/CNG mixture, should be noted as confirming industry
teaching with one caveat ¨ this being that for Rich Gas mixtures, the various
states of storage can be achieved from the dense phase state by controlled
pressure and temperature reduction from the pipeline without the need for the
more complex compression and cooling infrastructure common to single phase
CNG storage configurations. Rich Gas mixtures offer 50% or better Mass Ratio
figures for storage of the methane constituent (essentially Standard
Transmission
specification gas) under selected conditions of storage than is attainable
from
Standard Transmission Specification mixtures under these moderate levels of
pressure and temperature.
[0140] Fig. 6C shows clearly where Rich Gas mixtures are superior to
Standard
Transmission specification mixtures under storage conditions and where the
technology must respect the onset of undesirable liquid phase above certain
concentrations of the NGL constituent.
[0141] Fig. 7A shows the benefits in storage of Rich Gas mixtures (for the
NGL
constituent represented by propane (C3) over Standard Transmission
specification
/ CNG mixes. The Rich Gas is modeled as a two component propane / methane
mix, and net VA/ ratios are for the solo methane component, to make a
comparison to the CNG case under the same storage conditions.
[0142] In Fig. 7B Rich Gas mixture benefits are shown as mass of gas to
mass
of containment steel ratios on a lb/lb basis, especially important when high
tonnage of materials are involved in storage vessels.
[0143] Best compressive performances for storage of the gaseous Rich Gas
mixture measured against the Standard Transmission specification mixture
appear
in the 900 to 1400 psig range of pressures at temperatures in the -30 F to -20
F
window suited to steel containment.
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[0144] At a pressure of 1200 psig at temperatures of -30 F and -20 F the
v/v
ratio of the optimal mixtures show useful increases of the order of 69 to 60%
for
the Rich Gas. At colder temperatures, and higher pressures it is evident that
instabilities of liquid formation and fallout is to be avoided for richer
mixtures.
[0145] There is a clear distinction between the two gas types in the
comparative mass ratio plots. The useful value of 250 for the volumetric ratio
of
Rich Gas at 1200 psig and -20 F yields a lb/lb gas to containment material
mass
ratio of 0.38 exceeding the 0.22 number for CNG under the same conditions. The
mass ratio of the required containment system is reduced to 2/3 here when Rich
Gas is stored for transportation. Conversely similar containment performance
of
Standard Transmission specification mixture would call for that product to be
stored at 1400 to 1800 psig at a temperature of -40 F with a corresponding
increase in wall thickness of the steel
[0146] Fig. 7C shows clearly where Rich Gas mixtures are superior to
Standard
Transmission specification mixtures under storage conditions and where the
technology must respect the onset of the liquid phase.
[0147] Fig. 8A shows the benefits in storage of Rich Gas mixtures using
butane
(C4) over standard CNG transmission mixtures.
[0148] In Fig. 8B Rich gas mixure benefits are shown as mass of gas to mass
of containment steel ratios on a lb/lb basis, especially important when high
tonnage of materials are involved in storage vessels.
[0149] Best compressive performances for storage of the gaseous Rich Gas
mixture measured against the Standard Transmission specification mixture
appear
in the 900 to 1200 psig range of pressures at temperatures in the -30 F to -20
F
window suited to steel containment.
[0150] At a pressure of 1200 psig at temperatures of -30 F and -20 F the
v/v
ratio of the two mixtures show useful increases of the order of to 45% for the
Rich
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Gas over Standard Transmission specification mixture. At colder temperatures,
and higher pressures it is evident that instabilities of liquid formation and
fallout is
to be avoided for richer mixtures.
[0151] There is a clear distinction between the two gas types in the
comparative mass ratio plots. The useful value of 229 for the volumetric ratio
of
Rich Gas at 1200 psig and -20 F yields a lb/lb gas to containment material
mass
ratio of 0.37 exceeding the 0.22 number for CNG under the same conditions. The
mass ratio of the containment system is less than 2/3 here when Rich Gas is
stored for transportation. Conversely similar containment performance of
Standard
Transmission specification mixture would call for that product to be stored at
1400
to 1800 psig at a temperature of -40 F.
[0152] Fig. 8C shows clearly where Rich Gas mixtures are superior to
Standard
Transmission specification gas/CNG mixtures under these storage conditions and
where the technology must respect the onset of undesirable liquid phase.
[0153] Fig. 9A shows a comparison between a conventional pipeline system
and the high pressure transmission system 200 disclosed herein. As shown, the
conventional pipeline system (column 102) is operated at a pressure of about
1440 psig, transmitting a Standard Transmission gas mixture with Molecular
Weight (MW) of 16.75. On the other hand, the high pressure transmission system
200 (column 202) is operated at a pressure of about 2250 psig, transmitting a
rich
gas mixture with Molecular Weight (MW) of 19.93.
[0154] Based on an upper limit of inlet flow of one billion ft3/day, and
operating
at an MOP of 1440 psig, for 1000 miles of transmission, the conventional
pipeline
system requires a mass of steel of about 463,913 US tons, and the Rich Gas
high
pressure pipeline of smaller diameter, system 200, requires a mass of steel of
about 499,799 US tons. Although the design of the Rich Gas system 200 requires
fractionally more mass of steel, it achieves higher daily heat value delivery
per US
ton steel (2.411 million BTU/US Ton Steel vs. 2.217 million BTU/US Ton Steel).
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The smaller diameter of system 200 is not restricted to the comparative inlet
flow
rate of 1.0 billion ft3/day used here for comparative purposes and can achieve
a
still higher daily heat value delivery per US ton steel. In system 201, which
is
essentially system 200 subjected to a higher flow rate and velocity
restrictions, the
delivered heat value ratio is seen to increase by the order of +30%, depending
a
higher flow rate and velocity limitations). See system 201.
[0155] Further, Fig. 9A also shows that the compressor stations of system 200
also require less power than those of the conventional system 100 to deliver
the
set volume of gas at the rate of 1.0 bcf/d. The move to a higher flow rate of
system
300 shows a prorated increase in overall compressor power and CO2 emissions
over that of the lower pressure system 100.
[0156] Fig. 9B shows a selection of values of the enthalpies of
vaporization of
CFC refrigerants for external chilling and those of NGLs operating from an
initial
temperature of 80 F. It will be noted that the efficacy of NGLs are comparable
alongside the more typical R21 CFC refrigerant, which is amongst those being
withdrawn from the market out of environmental concerns of damage to the ozone
layer of the atmosphere. Given the chilling ability of constituent
hydrocarbons in a
Rich Gas mixture, and the elevated levels of storage , the opportunity exist
here
for those skilled in the art to design the delivery of chilled product as the
gas exits
the pipeline beyond those promised for Standard Specification gas mixtures. In
other contexts where less emphasis is placed on storage and hydraulics a
system
could be designed to achieve greater temperature reductions for Standard
Specification gas mixtures, in particular the retrofit of existing LNG
systems.
[0157] Fig. 9C shows the replacement of the first stage propane section of
a
cascaded propane-ethylene-methane process for LNG production. The cold gas is
first used to provide maximum temperature differential to the LNG process
prior to
becoming feedstock for an NGL separation plant. Methane and residual ethane
from this separation plant is then introduced back as feedstock into the LNG
process.
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[0158] The gas stream leaves the pipeline/storage system via the turbo
expander 132 that both chills the gas as its pressure drops and generates
shaft
power that can be converted into electricity W. The flowrate is monitored at a
custody transfer point C. An opportunity exists here downstream of custody
transfer to ship an optional side-stream C-R-G of compressed Chilled Rich Gas
to
an export point ahead of LNG processing. An opportunity here also exists for
an
auxiliary process chilling flow C-V of product to be withdrawn.
[0159] The main pipeline delivery flow destined for the LNG plant passes
into
the first stage chiller LNG1 at point D where all or most of the chilling
normally
supplied by a propane refrigeration plant is replaced by the pipeline outflow.
This
unit chills the LNG plant feedstock passing through the heat exchanger from
point
H to point K.
[0160] From Point E the flow goes to Point F where it enters a separation
tower
SP1 where NGL liquids are extracted (departing the tower at Point J) leaving
behind a lean gas stream of mostly methane and some ethane that forms the
basis of the LNG feedstock. This product flows from point G to the inlet of
the first
stage chiller LNG 1 at point H. It will generally not require any intermediate
processing with correct operation of the separation tower SP1 that is ideally
specified as an absorbent process.
[0161] From chiller LNG1 the LNG feedstock enters a second stage chilling
process LNG 2 at Point L. This chiller uses a refrigerant such as ethylene
outside
of the temperature range and scope of this invention onroute to the LNG
production of the plant.
[0162] The separation unit SP1 has a loop for regeneration of adsorbent
fluid
through a process skid RG1. The previously mentioned chilled side-stream of
pipeline outflow of cold rich gas CV is used in the chiller section of this
skid. The
chilling stream enters the RG1 unit at W, leaving at X to rejoin intercept at
point V
and reunite with the mainstream flow EF emerging from the Chiller LNG 1.
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[0163] This disclosure discusses a method of accelerating the onset of, and
access to, lower compressibility (Z) factors in natural gas pipelines covering
embodiments of broader pressure, temperature, and constituents within Rich Gas
mixtures yielding a new array of transportation benefits. A wider band of low
flow
resistance in pipelines over that in the prior art which restricted by lower
maximum
operating pressures. Storage density is improved. The properties of the Rich
Gas
mixtures and higher operating/storage pressures involved are such that
internal
chilling within the transported medium can then take place through the Joule-
Thompson effect and making a chilled, lower pressure delivery of product
direct
from the pipeline.
[0164] The subsequent delivery of a chilled product using recovered
pipeline
energy can replace a substantial amount of chilling otherwise externally
created
for many downstream applications.
[0165] The ability to take advantage of high levels of NGLs within the new
gas
mixtures and their behavior within the broader pipeline pressure differentials
(sitting within 3500 psig and 900 psig) for this invention enables the Joule-
Thompson effect of "internal" chilling to occur within the product transported
by the
pipeline. This chilling matches or exceeds that of external chilling via heat
exchangers commonly found in the downstream gas processing industry to be
working below 800 psig and 1300 psig plant design thresholds. These industrial
refrigerants here are frequently non-hydrocarbon in nature and increasingly
being
withdrawn from the market in the interests of their more severe environmental
impact.
[0166] Having a pre-chilled product delivered by the pipeline will
alleviate this
demand on the industry, and when provided via turbo expander recover pipeline
energy often lost in the custody transfer between segregated pipeline and
process
disciplines.
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[0167] Design developments incorporated herein permit simplified operations
within a broader pressure range of low compressibility factor (Z) operation to
take
place. Pre-conditioning processing in the field is simplified, mainline
compressor
stations can incorporate single units. Operating pressures now broaden between
2500 psig through the best efficiency point around 2100 psig to the
recompression
point about 1300 psig or about 1450 psig, depending on gas mixture.
[0168] On a project specific basis there is nothing to preclude design and
construction of all sections of the pipeline to a high MOP of 3500 psig
encompassing hydraulic, storage and chilling benefits claimed by this
invention
throughout its length.
[0169] Reduced capital expenditure, compression infrastructure and
operating
costs emerge from this less energy and emissions intensive Rich Gas
transmission, chilling and containment system. The need and environmental
impact of multiple pipelines, rail and trucking movements for gas and NGL
transport is eliminated or takes place through seamless integration of new
process
plant and retrofitting of existing infrastructure to meet future demands on
the
industry.
[0170] As a result and enabled herein, embodiments include a method of
bringing about the chilling of Natural Gas and Natural Gas/NGL mixtures
delivered
from a pipeline system such that the resulting mixture also exhibits internal
chilling
behavior during its transport, storage, and withdrawal from the system that is
associated with behavior properties of the constituents of the conveyed
product.
Such mixtures can be formulated by additive or subtractive processing of the
natural gas and NGL constituents. Operational conditions where these effects
occur can be between 3500 psig and 500 psig and 120F and -120F. The low
temperature range being reserved for the lightest mixtures not exhibiting
liquid fall
out.
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[0171] The method replaces or reduces the need for externally provided
chilling
traditionally applied in downstream processing of the delivered products.
Notwithstanding the types of process here include but are not limited to pre
chilling
for LNG production, chilling for separation and fractionation, and chilling
for
enhanced storage of CNG.
[0172] In another aspect, a method of high pressure pipeline transmission
and
systems of storage for Natural Gas mixtures and Natural Gas/NGL enhanced
mixtures is provided, the mixtures formulated with the objective of lowering
compressibility (Z) factors under Maximum Operating conditions (MOP) between
above about 2150 psig and up to about 4500 psig. Such mixtures can be
formulated by additive or subtractive processing of the natural gas and NGL
constituents.
[0173] In an example of the range of effective gas mixtures applicable
comprise: from 40% to 98% by mol volume of methane, from trace to 35% by mol
volume of ethane; from trace to 22% by mol volume of propane; from trace to 9%
by mol volume of butane; residual amounts of N2 not exceeding 2% by mol
volume; trace elements of C5+ (ie C5, C6 ...) hydrocarbons not exceeding 0.25%
of mol volume; and the total being 100%, wherein the operating conditions of
the
mixture is completely gaseous or in the supercritical-dense phases with no
liquid
phase.
[0174] Notwithstanding, the mol% of any of the Light Hydrocarbons (ethane,
propane, butane) given here can also lie within the 0 to specified minimum
(:)/0 mol
range as shown, where the stand alone (:)/0 mol of remaining Light
Hydrocarbons is
sufficient to bring about the reduction in Z factor value and dense phase
flow/storage behavior and/or chilling effects.
[0175] Such stand alone values are 6% for ethane, 1.5% for propane and 0.5%
for butanes for Rich Gas mixtures : and 2% for ethane,1% for propane and 0.25%
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for butanes in the 2500 psig or higher pressure Standard Transmission
specification mixtures.
[0176] Turning to the storage aspect, a high pressure staged section of the
pipeline, that is project specific in volume by virtue of length and cross
sectional
area, can be used for high pressure storage, product flow and de-pressuring of
the
pipeline contents, which operates within the limits of 3500 psig and 800 psig
according to end use for the delivered product. Such as system can also be
operated within the limits of 4500 psig and 800 psig according to end use for
the
delivered product.
[0177] Regarding the internal chilled through Joule Thompson effect, a
pressure and temperature reducing device such as a J-T valve or Turbo Expander
is located at the exit points of the pipe sections that will bring about the
refrigeration effect within the transmitted gas mixture subjected to the
pressure
drop. Preferably a turbo expander system is employed that permits shaft or
electrical recovery of pipeline energy from the high pressure storage. Despite
the
chilled effects achieved using embodiments described herein, and where
internal
chilling is insufficient, an optional temperature trimming system incorporated
within
or downstream of the storage compressors to condition the gas flow to optimal
temperature or density conditions for process applications downstream of the
invention.
[0178] In embodiments where the pipeline is specifically designed to handle
expansion, stress and material behavior, an upper temperature limit of 150F is
claimed for operating conditions to maintain flow in gaseous state when the
pipeline is installed in cold environments with high heat losses along the
sectional
length(s).
[0179] A pipeline can be configured to carry lean North American Spec Gas
or
NGL Rich Gas, that is project specific in volume, by virtue of its entire
length and
cross sectional area and pipe layout, used for product flow, high pressure
storage,
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and de-pressuring the contents, which operates within the limits of 4500 psig
and
350 psig according to end use for a chilled delivered product.
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