U.S. patent application number 15/607653 was filed with the patent office on 2018-11-29 for integrated multi-functional pipeline system for delivery of chilled mixtures of natural gas and chilled mixtures of natural gas and ngls.
The applicant listed for this patent is JL ENERGY TRANSPORTATION INC.. Invention is credited to John LAGADIN, Ian MORRIS.
Application Number | 20180340730 15/607653 |
Document ID | / |
Family ID | 64401070 |
Filed Date | 2018-11-29 |
United States Patent
Application |
20180340730 |
Kind Code |
A1 |
LAGADIN; John ; et
al. |
November 29, 2018 |
INTEGRATED MULTI-FUNCTIONAL PIPELINE SYSTEM FOR DELIVERY OF CHILLED
MIXTURES OF NATURAL GAS AND CHILLED MIXTURES OF NATURAL GAS AND
NGLS
Abstract
Herein pipeline pressure, temperature and NGL constituents are
manipulated for the transportation and optional storage in a
pipeline system of natural gas mixtures or rich mixtures for
delivery of chilled Products for downstream applications. Pressure
reduction from a last compression section delivers internally
chilled Products for reduced capital and operating costs. A high
lift compressor station before the pipeline terminus provides
pressure differential for Joule-Thompson chilling of the pipeline
contents. The chilling step can be retrofitted to existing pipeline
systems, and the chilling steep can include a turbo expander or the
like for recovery of pipeline pressure energy for power generation.
For like throughout, with this higher pressure operation, the
effects of enhanced NGL content results in a reduction in diameter
of the pipeline by at least one standard size. Substantial overall
reduction in energy consumption and associated CO2 emissions is
thereby achieved through integrated pipeline/processing
applications.
Inventors: |
LAGADIN; John; (Calgary,
CA) ; MORRIS; Ian; (Okotoks, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JL ENERGY TRANSPORTATION INC. |
Calgary |
|
CA |
|
|
Family ID: |
64401070 |
Appl. No.: |
15/607653 |
Filed: |
May 29, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 2230/30 20130101;
F17D 1/08 20130101; F25J 1/0035 20130101; F25J 1/0022 20130101;
F25J 1/0205 20130101; F25J 1/0082 20130101; F25J 1/0237 20130101;
F25J 1/0052 20130101; F25J 1/0085 20130101; F25J 2210/06 20130101;
F25J 1/0254 20130101; F25J 1/0232 20130101; F17D 3/01 20130101;
F25J 2220/64 20130101 |
International
Class: |
F25J 1/02 20060101
F25J001/02; F25J 1/00 20060101 F25J001/00 |
Claims
1. A terminus for a natural gas pipeline comprising: a high
pressure storage section of the pipeline for storing rich gas
mixtures remaining supercritical in the pressure range of between
about 2500 and about 4500 psig; and a Joule-Thompson (J-T) device
for reducing the pressure of the stored rich gas mixture to form a
chilled product without liquid fallout.
2. The pipeline terminus of claim 1, wherein the pressure range is
between about 2500-3250 at ambient conditions
3. The pipeline terminus of claim 1, wherein the cooled product is
reduced in pressure to the range of about 1200 to 800 psig.
4. The pipeline terminus of claim 1, wherein the J-T device is a
valve or a turbo expander.
5. The pipeline terminus of claim 1, wherein the J-T device is
coupled to a shaft for energy recovery therefrom.
6. The pipeline terminus of claim 1, the rich gas mixtures
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.
7. The pipeline terminus of claim 6, wherein a single component of
one of more of the light hydrocarbons of ethane, propane, or butane
is at its lowest range, while a standalone % 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.
8. The pipeline terminus of claim 7, wherein such standalone % mol
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% for
butanes in the 2500 psig or higher pressure Standard Transmission
specification mixtures.
9. The pipeline terminus of claim 7, wherein chilled product is
delivered for LNG production, separation and fractionation, or for
enhanced storage of CNG.
10. A high pressure natural gas pipeline comprising: one or more
transmission staging sections for moving rich gas from a source to
a destination with recompression to pressures of above about 2150
psig; a high pressure storage section of the pipeline adjacent the
destination for storing rich gas mixtures remaining supercritical
in the pressure range of between about 2500 and about 4500 psig;
and a Joule-Thompson device for reducing the pressure of the stored
rich gas mixture to form a chilled product without liquid
fallout.
11. The pipeline of claim 10, wherein the cooled product is reduced
in pressure to the range of about 1200 to 800 psig.
12. The pipeline of claim 10, wherein the J-T device are located at
an exit points one or more of the transmission staging
sections.
13. The pipeline of claim 10, wherein the J-T device is a turbo
expander system have a shaft coupled for electrical recovery of
pipeline energy from the high pressure storage section.
14. The pipeline of claim 10, wherein the rich gas mixtures
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.
15. The pipeline terminus of claim 14, wherein a single component
of one of more of the light hydrocarbons of ethane, propane, or
butane is at its lowest range, while a standalone % 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.
16. The pipeline terminus of claim 15, wherein such standalone %
mol 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% for
butanes in the 2500 psig or higher pressure Standard Transmission
specification mixtures.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefits of U.S. Provisional
Patent Application Ser. No. 62/210,286 filed Aug. 26, 2015, and
U.S. Provisional Patent Application Ser. 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 U.S.
Pat. No. 6,217,626 and U.S. Pat. No. 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.
[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 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 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 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 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 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 -260 F.
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 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 conditions where these effects occur are between a
storage pressure of about 3500 psig reduced in pressure to 800 psig
and 120 F and -120 F 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 U.S. Pat. No. 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.
[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 Gas 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.
[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. 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 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] FIG. 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 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] FIG. 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] FIG. 1B shows a temperature trace at corresponding points of
flow in FIGS. 1 and 1A;
[0059] FIG. 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] FIG. 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 75 F at transmission pressures of
1500 psig;
[0061] FIG. 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] FIGS. 3 through 5 illustrate the chilling abilities
available for downstream deliveries for three progressively richer
gas mixtures containing a blend of constituents C1, 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 Envelopes the
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] FIGS. 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] FIG. 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] FIG. 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] FIG. 6C further illustrates regions and limitations of the
ethane-based rich gas of FIG. 6B for illustrating preferred V/V and
M/M ratios over those of standard transmission gas and limitations
where rich gas mixtures could stray into the liquid phase;
[0067] FIG. 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;
[0068] FIG. 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] FIG. 7C further illustrates regions and limitations of the
propane-based rich gas of FIG. 7B for illustrating preferred V/V
and M/M ratios over those of standard transmission gas and
limitations where rich gas mixtures could stray into the liquid
phase;
[0070] FIG. 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] FIG. 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] FIG. 8C further illustrates regions and limitations of the
butane-based rich gas of FIG. 8B for illustrating preferred V/V 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 3200 psig.
Higher pressures generally occur from operational storage
considerations and can be further utilized downstream of the
pipeline.
[0074] FIG. 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] FIG. 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.degree. 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.
[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 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.degree. F.
and about 120.degree. 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
-45 F 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
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.degree. F. (see point S of FIG. 2A) with a Z value of about
0.79.
[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.
[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 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 90 F to 10 F 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:
[0102] The accumulator or storage staging section 104, usually
located at the destination, comprises one or more storage pipes
122, and a Joule-Thompson (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
Thompson (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.degree. 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.degree. 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 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.degree. 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 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-Thompson 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-Thompson 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.degree. F. and about -30.degree. F. for Rich Gas
Mixtures, or in other embodiments to between about -10.degree. F.
and about -80.degree. F. for Standard Specification Gas. Whereas
carbon steels are generally limited in service to -55.degree. 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 75 F will drop in temperature, when reduced in
pressure from about 1750 to about 1200 psig to about 30 F, and when
dropped from about 3500 psig to about 1200 psig, to about -30 F.
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.
Energy Recovery as Electrical Generation:
[0113] In another embodiment where a turbo-expander is used for
polytropic expansion, 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 -40 F, 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 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 (C1), 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 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 (C1) occur at 2 Phase or Liquid States.
Reduction in mol % of C1 at these points will change state to Gas
phase and still yield higher values of V/V 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.degree. F. to -20.degree. F. window,
balancing increased compressed volume ratio against mass ratio.
[0125] At a pressure of 1200 psig at temperatures of -40.degree. F.
and -30.degree. 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 V/V for
the net volumetric ratio of Rich Gas at 1200 psig and -20.degree.
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.
[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 V/V 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.degree. F. to -20.degree. F. window suited to steel
containment.
[0129] At a pressure of 1200 psig at temperatures of -30.degree. F.
and -20.degree. 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.degree. 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.degree. 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 V/V
ratios are for the methane component only 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.
[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.degree. F. to -20.degree. F.
window suited to steel containment.
[0133] At a pressure of 1200 psig at temperatures of -30.degree. F.
and -20.degree. 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.degree. 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.degree. F.
[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.degree. F. to -20.degree. F. window, balancing increased
compressed volume ratio against mass ratio.
[0137] At a pressure of 1200 psig at temperatures of -40.degree. F.
and -30.degree. 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.degree.
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.
[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 V/V 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.degree. F. to -20.degree. F.
window suited to steel containment.
[0144] At a pressure of 1200 psig at temperatures of -30.degree. F.
and -20.degree. 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.degree. 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.degree. 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 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.
[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.degree. F. to -20.degree. F.
window suited to steel containment.
[0150] At a pressure of 1200 psig at temperatures of -30.degree. F.
and -20.degree. 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.
[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.degree. 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.degree. 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). 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.degree. 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.
[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.
[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.
[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 120 F and -120 F. The low temperature
range being reserved for the lightest mixtures not exhibiting
liquid fall out.
[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 % mol range as shown, where the stand alone % 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% 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 150 F 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, 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.
* * * * *