Note: Descriptions are shown in the official language in which they were submitted.
1
A METHOD TO PRODUCE PLNG AND CCNG AT STRADDLE PLANTS
FIELD
[0001] This relates to a method for producing PLNG (Pressurized Liquid Natural
Gas) and
CCNG (Cold Compressed Natural Gas). The method was developed with straddle
plants in
mind, but has broader application.
BACKGROUND
[0002] Canadian Patent Application 2,813,260 (Lourenco et al) entitled
"Producing LNG
at Straddle Plants using a NG high pressure stream" describes a process
addition to straddle
plants which are used to capture and recover natural gas liquids (NGL's) from
gas
transmission pipelines. The described process allows these plants to be
retrofitted to also
produce Liquefied Natural Gas (LNG).
[0003] There will hereinafter be described an alternative to the method
described in the
2,813,260 patent application to also produce PLNG and CCNG. The method can be
used
wherever pressurized gas flows and supporting infrastructure exists to deal
with the process
streams, such as at straddle plants.
SUMMARY
[0004] According to an aspect, there is provided a method to produce
Pressurized Liquid
Natural Gas (PLNG) and Cold Compressed Natural Gas (CCNG), comprising passing
a
dewatered natural gas stream at pressures of between 450 psig and 1200 psig
through one or
more heat exchangers to pre-cool the natural gas stream, passing the pre-
cooled natural gas
stream through a gas column where natural gas liquid fractions and natural gas
fractions are
separated, passing the pre-cooled natural gas fractions at pressures of
between 450 psig and
1200 psig through one or more heat exchangers to further cool the natural gas
fractions,
passing the further cooled natural gas fractions at pressures of between 450
psig and 1200
psig through a gas expansion apparatus where pressure of the natural gas
fractions is lowered
to a pressure of less than 300 psig, and passing the natural gas fractions at
a pressure of less
than 300 psig through a separator where they are separated into a PLNG stream
and a
gaseous stream at a pressure of less than 300 psig.
Date Regue/Date Received 2022-12-02
CA 02881949 2015-02-12
2
[0005] According to another aspect, this process may be a retro-fit to
existing straddle plants.
[0006] According to an aspect, there is provided a method to produce PLNG
where a high
pressure, pre-treated, pre-cooled natural gas stream from a straddle plant is
routed to a gas
expansion apparatus, the PLNG section comprising providing heat exchangers on
a high
pressure, pre-treated, pre-cooled natural gas PLNG feed line to a gas
expansion apparatus,
providing a gas liquid separator downstream of the expansion apparatus, and
providing a
pressure reducing device for the separated gaseous stream into the straddle
plant fractionator.
[0007] According to another aspect, the gas expansion apparatus may be a JT
valve or a gas
expander turbine.
[0008] According to another aspect, further cooling may be provide by the
vapour fraction of
the expanded gas.
[0009] According to another aspect, the gaseous stream from the PLNG separator
may be
returned to the straddle plant fractionator.
[0010] According to another aspect, the gas to be liquefied may be pressurized
liquid natural
gas (PLNG).
[0011] According to an aspect, there is provided a method to produce CCNG
where a high
pressure, pre-treated, pre-cooled natural gas stream from a straddle plant is
routed to a gas
expansion apparatus.
[0012] According to an aspect, there is provided a straddle plant CCNG
section, comprising a
gas expansion apparatus, a feed line feeding gas to the gas expansion
apparatus, a CCNG
receiver to separate the vapour and liquid fractions, and a liquids return
line to the straddle
plant fractionator.
[0013] According to another aspect, the liquefied gas production plant may
include a PLNG
line to storage.
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[0014] According to another aspect, the CCNG liquid fraction may be routed to
the straddle
plant fractionator for NGL's recovery.
.. [0015] According to an aspect, there is provided a method to produce
Pressurized Liquid
Natural Gas (PLNG), the method comprising the steps of passing a dewatered
natural gas
stream at pressures of between 450 psig and 1200 psig through a first phase
separator to
obtain a natural gas liquid fraction and a natural gas fraction, the separated
natural gas
fractions being at a pressure of between 450 psig and 1200 psig, passing at
least a portion of
.. the natural gas fraction through a gas expansion apparatus to reduce the
pressure of the
natural gas fractions to less than 300 psig, and passing the pressure-reduced
natural gas
fraction through a second phase separator to obtain at least one of a PLNG
stream and a
CCNG stream at a pressure of less than 300 psig.
[0016] According to another aspect, the dewatered natural gas stream may be a
natural gas
stream in a straddle plant.
[0017] According to another aspect, the method may further comprise the step
of passing a
natural gas stream through a dewaterer and a heat exchanger to cool the
natural gas stream
.. prior to obtaining the dewatered natural gas stream.
[0018] According to another aspect, the method may further comprise the step
of cooling at
least a portion of the separated natural gas fraction in one or more heat
exchangers.
[0019] According to another aspect, the method may further comprise the step
of collecting
each of the at least one of the PLNG stream and the CCNG stream separately in
a storage
vessel.
[0020] According to another aspect, the gas expansion apparatus may comprise a
JT valve or
a gas expander turbine.
[0021] According to another aspect, at least a portion of an output of the
first or the second
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phase separator may be used to cool the natural gas stream.
[0022] According to another aspect, at least a portion of the output of the
second phase
separator may be used to cool a fractionator of the saddle plant.
[0023] There is provided a method to produce also PLNG and CCNG at straddle
plants. A
first step involves passing a dewatered natural gas stream at pressures of
between 400 psig
and 1200 psig, through one or more heat exchangers to pre-cool the natural gas
stream. A
second step involves passing the dewatered and pre-cooled natural gas stream
through a gas
separator where natural gas liquids and gaseous fractions are separated. A
third step involves
passing a portion of the gaseous fraction at pressures of between 400 psig and
1200 psig
through one or more heat exchangers for further cooling. A fourth step
involves passing the
cooled gaseous fraction at pressures of between 400 psig and 1200 psig through
a gas
expansion apparatus where the gas pressure is lowered to pressures less than
300 psig. A fifth
step involves passing the expanded gas into a separator where the expanded gas
is separated
into a PLNG stream and a gaseous stream at pressures less than 300 psig.
[0024] Where there is a high pressure stream of natural gas (i.e. at pressures
in a range of 400
psig to 1200 psig) that can be tapped, the above method can operate without
external power
inputs, resulting in substantial savings in both capital and operating costs.
[0025] The input temperature of a high pressure stream of natural gas is
relatively constant.
This means that once steady state is achieved, the ratio of cold gas vapour is
constant relative
to a flow rate of the natural gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] These and other features will become more apparent from the following
description in
which reference is made to the appended drawings, the drawings are for the
purpose of
illustration only and are not intended to in any way limit the scope of the
invention to the
particular embodiment or embodiments shown, wherein:
FIG. 1 labelled as PRIOR ART is a schematic diagram of a typical straddle
plant
CA 02881949 2015-02-12
equipped with a gas pre-treatment, heat exchangers (cold box), an expander-
compressor and a
main compressor for re-compression to gas transmission pipeline.
FIG. 2 is a schematic diagram of a typical straddle plant with the addition of
a PLNG
production unit facility equipped with heat exchangers, an expander, a
separator, a JT valve
5 and associated process instrumentation controls.
FIG. 3 is a schematic diagram of a typical straddle plant with the addition of
a PLNG
production unit facility equipped with a JT valve in lieu of an expander.
FIG. 4 is a schematic diagram of a typical straddle plant with the addition of
a PLNG
production unit facility with an alternate flow path to the PLNG production
facility.
FIG. 5 is a schematic diagram of a typical straddle plant with the addition of
PLNG
and CCNG production unit facilities equipped with a IT valve and an expander.
FIG. 6 is a schematic diagram of a typical straddle plant with the addition of
PLNG
and CCNG production unit facilities equipped with IT valves in lieu of an
expander.
FIG. 7 is a schematic diagram of a typical straddle plant with the addition of
PLNG
and CCNG production unit facilities with an alternate flow path to the
production facilities.
FIG. 8 is a schematic diagram of a typical straddle plant with addition of
PLNG and
CCNG production unit facilities and a pump back to the fractionation column.
FIG. 9 is a schematic diagram of a typical straddle plant with addition of
PLNG and
CCNG production unit facilities that are not connected to the fractionation
column.
FIG. 10 is a schematic diagram of a typical straddle plant with addition of a
CCNG
= production unit facility.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0027] A straddle plant is a natural gas processing plant constructed near a
transmission
pipeline downstream from the fields where the natural gas in the pipeline has
been
produced, also called an "on-line" plant. The straddle plant removes natural
gas liquids,
the C21' gas fractions, from the transmission natural gas stream. This is done
by first pre-
treating the gas stream, pre-cooling it and then reducing the transmission gas
high pressure
stream in a range of 400 to 1200 psig, typically about 1000 psig, through a
gas expander
to pressures typically about 275 psig, to cool, condense and separate the C2+
gas fractions
in a distillation column. The bottoms of the distillation column exit the
plant as the
CA 02881949 2015-02-12
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recovered natural gas liquids (NGL's). The distillation column overhead
stream, primarily
C2- gas fractions, are pre-heated in a countercurrent heat exchange by the
straddle plant
pre-treated feed gas stream and re-compressed in two steps back to the same
transmission
pipeline gas pressure. The major operating cost of these straddle plants are
the re-
compression costs. The re-compression is typically done in two steps. The
first step is
done through a booster compressor, which typically is a direct drive
compressor connected
to the gas expander, the energy recovered by expanding the gas from the
transmission gas
pipeline high pressure is directly used to compress the distillation gas
overhead stream
from distillation column pressure to an intermediate gas pressure. The main re-
compressor then compresses this intermediate gas pressure to transmission gas
pipeline
pressure. The economics of a straddle plant are based on the quantities and
revenues of
natural gas liquids (C2- gas fractions) produced against the re-compression
and
maintenance costs.
[0028] In Canadian Patent ApplicAion 2,813,260 (Lourenco et al) entitled
"Producing
LNG at Straddle Plants using a NG high pressure stream" the objective was to
produce
LNG by diverting a portion of a pre-treated and pre-cooled high pressure
natural gas,
cooling it further, treating it for carbon dioxide removal, followed by
further cooling and
expansion to low pressures to produce LNG at -160 C. The objective of this new
process
is to produce PLNG and CCNG, the process differs from the above LNG process
since it
does not require the removal of carbon dioxide. The key point of PLNG
technology is that
it condenses and stores at pressures between 150 and 300 psig corresponding to
a
temperature range of approximately -100 to -120 C. At these higher
temperatures, the
solubility of carbon dioxide in PLNG increases up to 2 mol%, thus eliminating
the need
for carbon dioxide treatment as in the production of LNG which requires a
minimum
carbon dioxide concentration of 50 ppm to avoid carbon dioxide freeze-out and
process
pluggage. This is an important feature since carbon dioxide treatment requires
the use of
molecular sieves which are capital intensive and contribute significantly to
the operating
costs of a LNG plant. Therefore, in terms of capital and operating costs the
production of
PLNG provide a more economical alternative to the use of natural gas in lieu
of LNG
where applicable.
CA 02881949 2015-02-12
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[0029] The main feature of CCNG is its density when compared to CNG
(Compressed
Natural Gas). The density of natural gas is best achieved by controlled
cooling and
pressure. A Straddle Plant is an ideal location to produce CCNG since its
normal
operating process conditions allows for a simple retrofit to route a portion
of the pre-
cooled, high pressure gas stream, to a controlled CCNG production unit.
Allowing CCNG
to be produced at Straddle Plants, on demand, at a client's required density.
This retrofit
will allow existing Straddle Plants to generate a new product commodity and
associated
new revenues.
[0030] Referring to FIG. 1, a pressurized pipeline natural gas stream 1 is
routed to a straddle
plant through valve 2. Valve 38, allows the transmission gas pipeline to
bypass the straddle
plant. High pressure gas stream 3 enters the straddle plant and is first pre-
treated in unit 4 to
remove the water content. The de-watered stream 5 is then routed to cold box 6
where it is
pre-cooled in coil 7 by counter current gas streams is series, first by gas
coil 24, then gas coil
31 and finally gas coil 21. The high pressure, pre-cooled gas stream 8 enters
separator 9
where the liquids and gaseous frac-ions are separated. The liquid fraction is
routed through
stream 18 to expansion valve 19, where the pressure is reduced to column 26
operating
pressure, this pressure expansion generates more coolth energy and the now
expanded and
cooler gas is routed through stream 20 to coil 21 in the cold box, pre-cooling
the high pressure
gas stream in coil 7. The now warmer stream 22 enters distillation column 26
for
fractionation and NGL recovery. The gaseous fraction exits separator 9,
through stream 10
which divides into two streams, 11 and 14. Stream 11 enters expander
compressor 12 where
the high pressure gas is expanded to column 26 operating pressure, generating
torque in shaft
A, which drives booster compressor 33, and the colder gas stream exits the
expander-
compressor 12 through stream 13 into column 26 for NGL's recovery. The gaseous
stream
14 is routed through heat exchanger 29 for further cooling. The colder high
pressure stream
15 is flows through expansion valve 16, where the high pressure gas is
expanded to column
26 operating pressure and the cooler expanded gas enters column 26 through
stream 17 as a
reflux stream to control column 26 overhead operating temperature. The control
of column
overhead 26 operating temperature determines the recovery of NGL's from the
feed gas
stream. The distillation column bottoms temperature is controlled by reboiler
stream 23,
which obtains heat through coil 24 and returns it through stream 25 to the
bottom section of
CA 02881949 2015-02-12
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distillation column 26. The control of column 26 bottoms operating temperature
determines
the quality of the NGL's recovered. The recovered NGL's exit column 26 bottoms
through
line 27. The stripped gas exits column 26 through stream 28 and is pre-heated
in heat
exchanger 29, the warmer stripped gas enters the cold box through coil 31 for
further pre-
heating. The warmer gas stream 32 enters booster compressor 33 which is
connected through
shaft A to the expander 12, thus recovering the mechanical work produced by
the expander
and boosting stream 32 pressure to stream 34. The boosted pressure stream 34
enters main
compressor 35, where the pressure is increased to transmission pipeline
pressure and routed
through stream 36, through straddle plant block valve 37 and into pipeline gas
distribution
stream 39.
[0031] The above described process in FIG. 1 is the operation of a traditional
straddle plant,
there are various straddle plant modes of operation to improve the recovery of
the NGL's, in
all cases its objective is to produce NGL's.
[0032] Referring to FIG. 2, the difference from FIG. 1, is the addition of a
PLNG production
section to a conventional straddlL plant which as described above produces
NGL's. A
pressurized pipeline natural gas stream 1 is routed to a straddle plant
through valve 2. Valve
38, allows the transmission gas pipeline to bypass the straddle plant. High
pressure gas
stream 3 enters the straddle plant and is first pre-treated in unit 4 to
remove the water content.
The de-watered stream 5 is then routed to cold box 6 where it is pre-cooled in
coil 7 by
counter current gas streams is series, first by gas coil 24, then gas coil 31
and finally gas coil
21. The high pressure, pre-cooled gas stream 8 enters separator 9 where the
liquids and
gaseous fractions are separated. The liquid fraction is routed through stream
18 to expansion
valve 19, where the pressure is reduced to column 26 operating pressure, this
pressure
expansion generates more coolth and the now expanded and cooler gas is routed
through
stream 20 to coil 21 in the cold box, pre-cooling the high pressure gas stream
in coil 7. The
now warmer stream 22 enters distillation column 26 for fractionation and NGL
recovery. The
gaseous fraction exits separator 9, through stream 10 divides into two
streams; 11 and 14.
Stream 11 enters expander-compressor 12 where the high pressure gas is
expanded to column
26 pressure, generating torque in shaft A, which drives booster compressor 33
and, the colder
gas stream exits expander-compressor 12 through stream 13 into column 26 for
NGL's
CA 02881949 2015-02-12
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recovery. Stream 14 is routed through heat exchanger 29 where it is further
cooled, the colder
stream 15 is split into two streams; 40 and 41. Stream 41 is expanded through
valve 16 to
distillation column 26 operating pressure as a reflux stream to control
distillation column
overhead temperature of stream 28. The control of column 26 overhead operating
temperature determines the recovery of NGL's from the feed gas stream. The
distillation
column bottoms temperature is controlled by reboiler stream 23, which obtains
heat through
coil 24 and returns it through stream 25 to the bottom section of distillation
column 26. The
control of column 26 bottoms operating temperature determines the quality of
the NGL's
recovered. The recovered NGL's exit column 26 bottoms through line 27. The
stripped gas
exits column 26 through stream 28 and is pre-heated in heat exchanger 29, the
warmer
stripped gas stream 30, enters the cold box 6 through coil 31 for further pre-
heating. The
warmer gas stream 32 enters booster compressor 33 which is connected through
shaft A to the
expander 12, thus recovering the mechanical work produced by the expander and
boosting
stream 32 pressure to stream 34. The boosted pressure stream 34 enters main
compressor 35,
where the pressure is increased to transmission pipeline pressure and routed
through stream
36, through straddle plant block valve 37 and into pipeline gas distribution
stream 39.
[0033] The high pressure gaseous stream 40 is the PLNG section feed stream, it
is routed
through heat exchanger 42 where it is further cooled by gaseous stream 47, the
colder stream
43 enters expander-generator 44, where and is expanded to separator 46
operating pressure,
the expanded stream 45 enters separator 46, where the liquid fraction PLNG is
separated from
the its gaseous fraction. The gaseous stream 47 exits separator 46 and enters
heat exchanger
42 where it gives up some of its coolth to stream 40, the warmer stream 48
flows through
pressure control valve 49 into column 26. The pressure control valve 49
controls separator 46
operating pressure. The produced PLNG stream 51 is routed to storage.
[0034] The teachings described herein permit straddle plants to produce PLNG
in addition
to NGL's by adding a PLNG skid to an existing straddle plant. The benefit of
producing
PLNG versus LNG is the elimination of a carbon dioxide treatment unit which is
a pre-
requisite to produce LNG. A straddle plant is an ideal plant to retrofit and
produce PLNG
in addition to NGL's, it has the front end and back end infrastructure to
easily incorporate
a PLNG production skid using standard operating equipment. The novelty of the
proposed
CA 02881949 2015-02-12
teachings is in the integration of a process to produce PLNG into an existing
straddle
plant. The production of PLNG provides an alternative to LNG as a natural gas
supply in a
liquid form at lower operating and capital costs. By adding a PLNG skid to an
existing
straddle plant, it simplifies the process and reduces capital, maintenance and
operations
5 costs. In the preferred method, a pre-treated, pre-cooled high pressure
natural gas stream
is further cooled in a counter-current second heat exchanger with the produced
very cold
gaseous stream and then expanded through a gas expander. The gas expander
produces
torque and therefore shaft power that can be converted into mechanical
compression power or
electricity. In the preferred application the shaft power is used for
electricity. The
10 expanded gas is separated into a gaseous and a PLNG stream. The gaseous
stream is first
routed to a heat exchanger where it further cools the pre-treated, pre-cooled
high pressure
gas stream and then discharged into a distillation column. This gaseous flow
stream
controls the separator pressure. The liquid stream, PLNG is routed to storage.
Using these
teachings, a straddle plant may improve its economics by also producing PLNG
in
.. addition to NGLs.
[0035] A main feature of this method is the flexibility of the process to meet
various
operating conditions since the ratio of PLNG production is proportional to the
cold gaseous
stream generated and returned to the distillation column. The method also
provides for a
significant savings in energy when compared to other PLNG processes since the
process uses
existing straddle plant infra-structure. The teachings can be used in any
straddle plant size.
Variations:
[0036] It should be noted that the motive force generated by the expanders can
be
.. connected to a gas compressor to boost gas pressure versus a power
generator that
produces electricity as proposed.
[0037] Referring to FIG. 3, the main difference from FIG. 2 and 3, is the use
of a JT
expansion valve 52 in lieu of an expander-generator. The use of a JT valve
versus an
expander-generator is an alternative mode of PLNG production at a lower
capital cost but
resulting in a lower production of PLNG.
CA 02881949 2015-02-12
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[0038] Referring to FIG. 4, the main difference from FIG. 2, and 3, is the
temperature of the
stream to the PLNG skid is upstream of heat exchanger 29. This stream is
warmer and hence
the production of PLNG for this mode of operation will be less than in FIG. 2
and 3.
[0039] Referring to FIG. 5, the difference from FIG. 2, 3 and 4 is the
production of Cold
Compressed Natural Gas (CCNG) in addition to production of PLNG. The main
feature of
CCNG is its density when compared to CNG (Compressed Natural Gas). The density
of
natural gas is best achieved by controlling both; cooling and pressure. A
Straddle Plant is
an ideal location to also produce CCNG since its normal operating process
conditions
allows for a simple retrofit to route a portion of the pre-cooled, high
pressure gas stream,
to a controlled CCNG production unit. Allowing CCNG to be produced at Straddle
Plants,
on demand, at a client's required density.
[0040] This retrofit referring to FIG. 5, is an addition of a CCNG production
section to a
conventional straddle plant which as described previously produce NGL's. A
pressurized
pipeline natural gas stream 1 is routed to a straddle plant through valve 2.
Valve 38, allows
the transmission gas pipeline to bypass the straddle plant. High pressure gas
stream 3 enters
the straddle plant and is first pre-treated in unit 4 to remove the water
content. The de-
watered stream 5 is then routed to cold box 6 where it is pre-cooled in coil 7
by counter
current gas streams is series, first by gas coil 24, then gas coil 31 and
finally gas coil 21. The
high pressure, pre-cooled gas stream 8 enters separator 9 where the liquids
and gaseous
fractions are separated. The liquid fraction is routed through stream 18 to
expansion valve 19,
where the pressure is reduced to column 26 operating pressure, this pressure
expansion
generates more coolth and the now expanded and cooler gas is routed through
stream 20 to
coil 21 in the cold box, pre-cooling the high pressure gas stream in coil 7.
The now warmer
stream 22 enters distillation column 26 for fractionation and NGL recovery.
The gaseous
fraction exits separator 9, through stream 10 divides into two streams; 11 and
14. Stream 11
enters expander-compressor 12 where the cold high pressure gas is expanded to
column 26
pressure, generating torque in shaft A, which drives booster compressor 33
and, the colder gas
stream exits expander-compressor 12 through stream 13 into column 26 for NGL's
fractionation and recovery. Stream 14 is routed through heat exchanger 29
where it is further
cooled, the colder stream 15 is split into two streams; 54 and 41. Stream 41
is expanded
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through valve 16 to distillation column 26 operating pressure as a reflux
stream to control
distillation column overhead temperature of stream 28. The control of column
26 overhead
operating temperature determines the recovery of NGL's from the feed gas
stream. The
distillation column bottoms temperature is controlled by reboiler stream 23,
which obtains
heat through coil 24 and returns it through stream 25 to the bottom section of
distillation
column 26. The control of column 26 bottoms operating temperature determines
the quality
of the NGL's recovered. The recovered NGL's exit column 26 bottoms through
line 27. The
stripped gas exits column 26 through stream 28 and is pre-heated in heat
exchanger 29, the
warmer stripped gas stream 30, enters the cold box 6 through coil 31 for
further pre-heating.
The warmer gas stream 32 enters booster compressor 33 which is connected
through shaft A
to the expander 12, thus recovering the mechanical work produced by the
expander and
boosting stream 32 pressure to stream 34. The boosted pressure stream 34
enters main
compressor 35, where the pressure is increased to transmission pipeline
pressure and routed
through stream 36, through straddle plant block valve 37 and into pipeline gas
distribution
stream 39.
[0041] The high pressure gaseous stream 54 is the CCNG section feed stream, it
is routed
through expander-generator 55, where and is expanded to separator 57 operating
pressure, the
expanded stream 56 enters separator 57, where the liquid fraction PLNG is
separated from its
gaseous fraction, CCNG. The gaseous stream 63 exits separator 57 and is routed
to CCNG
storage. The PLNG fraction exits Separator 57 through stream 58 and is
splitted into streams
59 and 60. Stream 59, is an optional PLNG production stream, routed to PLNG
storage.
Stream 60 is further expanded through valve 61 and routed as a reflux stream
62 into
fractionation column 26.
[0042] The CCNG process configuration as described in FIG.5 provides an option
for a
Straddle Plant to produce CCNG and PLNG in addition to its current mode of
operation
that produces just NGL's. The availability of CCNG and PLNG provides new
markets for
the use of natural gas.
[0043] Referring to FIG. 6, the main difference from FIG. 5, is the use of a
JT expansion
valve 64 in lieu of an expander-generator. The use of a JT valve versus an
expander-
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generator is an alternative mode of CCNG production at a lower capital cost
but resulting in a
lower production of CCNG.
[0044] Referring to FIG. 7, the main difference from FIG. 5, is the high
pressure gaseous
stream 65 to the CCNG section feed stream. This routing before heat exchanger
29, prevents
changing heat exchanger 29 sizing, since no additional cooling load is
required, albeit
producing a less denser CCNG stream than in FIG.5.
[0045] Referring to FIG. 8, a pump 66 is used to return condensed liquids in
line 60 from
separator 57 to column 26. As line 62 conveys a liquid to column 26, the
pressure in line 58
and 60 may be less than the pressure of column 26. As such the production of
CCNG and
PLNG may not be limited by the pressure of column 26. In other words, the
pressure of.
separator 57 may be less than the pressure in column 26, which allows for
greater flexibility
in the pressure and temperature characteristics of the produced CCNG and PLNG.
[0046] Referring to FIG. 9, the example process has a CCNG stream 63 and a
PLNG stream
59, but does not have a return flow to column 26 as in the other examples.
While the return
flow may be used to increase the efficiency of column 26 in some
circumstances, the entire
flow along line 65 may be used to produce CCNG or PLNG, the composition of
which will be
controlled by the temperature and pressure within separator 57.
[0047] Referring to FIG. 10, the example process is used to produce a CCNG
stream 63 only,
with any liquids separated in separator 57 is returned to column 26.
[0048] It will be understood that the examples shown in FIG. 2 ¨ 10 are non-
limiting
examples, and that the various features and options discussed and depicted may
be combined
in other combinations than those depicted where practical. For example,
certain examples
may be modified to only produce CCNG instead of both CCNG and PLNG; certain
examples
may be modified to only produce PLNG; JT valves and expanders may be
alternately used
depending on the circumstances; the point at which the feed stream used to
produce CCNG
and/or PLNG is taken may be selected based on the preferences of the user; and
there may or
may not be a return stream to column 26. Other modifications and combinations
of features
will be apparent to those skilled in the art. While not shown, the CCNR and/or
PLNG may be
CA 02881949 2015-02-12
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collected in a separate storage vessel that is separate from the normal, or
prior art, operation of
the straddle plant.
[0049] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
.. [0050] The scope of the claims should not be limited by the preferred
embodiments set forth
in the examples, but should be given a broad purposive interpretation
consistent with the
description as a whole.
