Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
RECOVERY OF HELIUM FROM NITROGEN-RICH STREAMS
BACKGROUND
[0001] This disclosure relates to the recovery of helium from nitrogen-rich
gas. This has
particular application in the recovery of helium from nitrogen-rich natural
gas from an underground
source.
[0002] US5167125A discloses a process for recovering light gases such as
hydrogen, neon and
helium, from gas stream containing higher boiling components such as nitrogen
and C1_2
hydrocarbons. According to the embodiment depicted in Fig. 1 of US5167125A, a
stream 100 of
feed gas is cooled by indirect heat exchange and the cooled feed gas 110 is
reduced in pressure
across valve 112 and fed to a distillation column 102 where it is separated
into bottoms liquid
depleted in light gas(es), and overhead vapor enriched in light gas(es). The
bottoms liquid is
reboiled using the feed gas in reboiler 108 to provide vapor for the column.
Nitrogen in the
overhead vapor is condensed in the overhead condenser 116 by indirect heat
exchange against a
stream 104 of bottoms liquid that is expanded across valve 122, and the
resultant liquid nitrogen is
recycled to the column as reflux 120. A stream 118 of impure helium gas is
removed from
condenser 16.
BRIEF SUMMARY
[0003] It is an objective to provide an improved process for recovering helium
from nitrogen-rich
gases comprising helium, particularly nitrogen-rich natural gas from
underground sources.
[0004] It is an objective of preferred embodiments to reduce the overall power
required to recover
helium from such gases. Helium may be recovered at a higher pressure than in
prior proceses and
with reduced loss.
[0005] It is also an objective of preferred embodiments to reduce the capital
and operating costs
of apparatus for recovering helium from such gases.
[0006] According to a first aspect, there is provided a process for recovering
helium from a
nitrogen-rich feed gas comprising helium. The process comprises cooling a
pressurized nitrogen-
rich feed gas comprising helium to produce cooled feed; and separating said
feed in a first
distillation column operating at an elevated operating pressure to produce
helium-enriched
overhead vapor and nitrogen-enriched bottoms liquid. The process is
characterized in that the feed
to the first distillation column is at least partially condensed; and that the
cooling of the feed gas is
achieved by indirect heat exchange against at least a first bottoms liquid at
a first elevated
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Date Recue/Date Received 2020-08-07
pressure and a second bottoms liquid at a second elevated pressure that is
different from the first
elevated pressure.
[0007] According to a second aspect, there is provided apparatus for
recovering helium from a
nitrogen-rich feed gas comprising helium, said apparatus comprising:
a distillation column for operation at an elevated operating pressure to
separate at least
partially condensed feed gas into helium-enriched overhead vapor and nitrogen-
enriched
bottoms liquid;
an overhead condenser for partially condensing the helium-enriched overhead
vapor by
indirect heat exchange to produce helium-enriched vapor as product and liquid
for reflux in
the column;
a first heat exchange system for cooling feed gas by indirect heat exchange
with a first
nitrogen-enriched bottoms liquid to produce cooled feed gas and vapor for the
column;
a first pressure reduction device for reducing the pressure of a second
nitrogen-enriched
bottoms liquid to produce reduced pressure bottoms liquid;
a second heat exchange system for cooling said cooled feed gas by indirect
heat exchange
against said reduced pressure bottoms liquid to produce at least partially
condensed feed
gas and at least partially vaporized bottoms liquid; and
a second pressure reduction device for reducing the pressure of said at least
partially
condensed feed gas to produce at least partially condensed feed gas at reduced
pressure
for use as said feed to the distillation column.
[0008] According to an alternative arrangement of the second aspect, there is
provided
apparatus for recovering helium from a nitrogen-rich feed gas comprising
helium, said apparatus
comprising:
a distillation column system for operation at an elevated operating pressure
to separate at
least partially condensed feed gas into helium-enriched overhead vapor and
nitrogen-
enriched bottoms liquid;
an overhead condenser for partially condensing helium-enriched overhead vapor
by indirect
heat exchange to produce helium-enriched vapor as product and liquid for
reflux in the
column system;
a first pump for pumping a second nitrogen-enriched bottoms liquid to produce
pumped
bottoms liquid;
a first heat exchange system for cooling feed gas by indirect heat exchange
with said
pumped bottoms liquid to produce cooled feed gas and nitrogen-enriched vapor;
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a second heat exchange system for cooling said cooled feed gas by indirect
heat exchange
against a first nitrogen-enriched bottoms liquid to produce at least partially
condensed feed
gas and vapor for the column system; and
a pressure reduction device for reducing the pressure of said at least
partially condensed
feed gas to produce at least partially condensed feed gas at reduced pressure
for use as
said feed to the distillation column system.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0009] FIG. 1 is a flowsheet depicting a comparative process for recovering
helium from nitrogen-
rich natural gas in which the feed to the column system is predominantly
gaseous (see
Comparative Example 1);
[0010] FIG. 2 is a flowsheet depicting a helium recovery process in which the
feed to the column
is predominantly liquid (see Example 1);
[0011] FIG. 3 is a flowsheet depicting a modified process of FIG. 2 in which a
further portion of
the bottoms liquid is expanded to an intermediate pressure and used to provide
refrigeration duty in
the separation (see Example 2);
[0012] FIG. 4 is a flowsheet depicting a modified process of FIG. 3 where the
feed is at higher
pressure and part of the helium-free product is pumped and used to cool the
feed upstream of the
column reboiler (see Example 3);
[0013] FIG. 5 is a flowsheet depicting a preferred process in which most of
the nitrogen product is
expanded to provide refrigeration to provide some helium-free liquid nitrogen
as product (see
Example 4);
[0014] FIG. 6 is a flowsheet depicting a modified process of FIG. 5 in which
liquid product is
subcooled in the column overhead condenser before being reduced in pressure to
the storage tank
(see Example 5);
[0015] FIG. 7 is a flowsheet depicting a process in which the helium recovery
process is
integrated with an upstream an NGL recovery column (see Example 6);
[0016] FIG. 8 is a flowsheet depicting the helium recovery process integrated
with a downstream
nitrogen purification column system (see Example 7); and
[0017] FIG. 9 is a flowsheet depicting a fully integrated scheme for
processing nitrogen-rich
natural gas from an underground source involving NGL recovery, HP and LP
columns for nitrogen
production, liquid nitrogen production and helium purification by PSA (see
Example 8).
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DETAILED DESCRIPTION
[0018] All references herein to pressure are references to absolute pressure
and not gauge
pressure unless expressly stated otherwise. In addition, references to the
singular should be
interpreted as including the plural and vice versa, unless it is clear from
the context that only the
singular or plural is meant. Further, unless expressly stated otherwise, fluid
compositions are
calculated in mol. % on a "dry" basis, i.e. excluding any water content from
the calculations. In
reality, to avoid operating problems, water content must be low enough,
typically no more than 10
ppm, to avoid freeze-out and/or hydrate formation at the cold end of the
process.
[0019] The terms "elevated pressure" and "pressurized" are intended to mean a
pressure that
.. significantly more than atmospheric pressure. The terms are intended to
exclude insignificant
increases in pressure, e.g. produced by a fan, simply to overcome pressure
drop in apparatus that
is operating at about atmospheric pressure. By use of the terms "elevated
pressure" and
"pressurized", the Inventors are typically referring to absolute pressures of
at least 1.5 bar, e.g. at
least 2 bar.
[0020] The term "indirect heat exchange" means that sensible and/or latent
heat as appropriate is
transferred between fluids without the fluids in question coming into direct
contact with each other.
In other words, heat is transferred through a wall of a heat exchanger. The
term is intended to
include the use of an intermediate heat transfer fluid where appropriate.
[0021] The term "distillation" is intended to include rectification and
fractionation.
Overview of the process
[0022] The process involves cooling a pressurized nitrogen-rich feed gas
comprising helium to
produce cooled feed; and separating the feed in a first distillation column
system operating at an
elevated operating pressure to produce helium-enriched overhead vapor and
nitrogen-enriched
bottoms liquid. The feed to the first distillation column system is at least
partially condensed. The
cooling of the feed gas is achieved by indirect heat exchange against at least
a first nitrogen-
enriched bottoms liquid at a first elevated pressure and a second nitrogen-
enriched bottoms liquid
at a second elevated pressure that is different from the first elevated
pressure.
[0023] The first and second nitrogen-enriched bottoms liquids are typically
taken from the sump
of the first distillation column system and may be different portions of the
same bottoms liquid.
However, one of the bottoms liquids could be taken from a different point at
the bottom of the
distillation column system.
[0024] The compositions of the first and second nitrogen-enriched bottoms
liquids are usually at
least substantially identical although slight variations may be observed
depending on the precise
location in the sump of the distillation column system at which the bottoms
liquid is used to cool the
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feed, or from which the bottoms liquid is extracted for use in cooling the
feed. However, any
variations in composition that may be present would be too small to have any
significant effect on
the operation of the process.
Cooling and condensing the feed
[0025] The first elevated pressure is typically equal to the elevated
operating pressure of the first
distillation column system. In this regard, the first elevated pressure is
usually from about 2 bar to
about 35 bar, and preferably from about 10 bar to about 30 bar.
[0026] The second elevated pressure may be more than or less than the elevated
operating
pressure of the first distillation column system. The difference between the
first and second
elevated pressures is typically at least 1 bar, e.g. at least 2 bar, for
example at least 5 bar or, in
some embodiments, at least 10 bar.
[0027] Typically, the vaporization pressure of the second nitrogen-enriched
bottoms liquid is
relatively close to the feed pressure (either pumped or expanded) whether it
is taken as pressurized
product or it gets expanded.
[0028] In embodiments in which the second elevated pressure is less than the
elevated operating
pressure of the first distillation column system, the second elevated pressure
is typically
significantly more than 1 bar, e.g at least 1.5 bar or from 2 bar to about 30
bar, and preferably from
5 bar to 25 bar. In such embodiments, bottoms liquid is expanded to produce
the second bottoms
liquid.
[0029] In embodiments in which the second elevated pressure is greater than
the elevated
operating pressure of the first distillation column system, the second
elevated pressure may be
from about 3 bar to about 150 bar, and preferably from about 10 bar to 100
bar. In such
embodiments, bottoms liquid is pumped to produce the second the bottoms
liquid.
[0030] The feed gas may be at subcritical pressure or supercritical pressure.
[0031] In embodiments in which the feed gas is at subcritical pressure, the
feed gas may cooled
(and possibly partially condensed) by indirect heat exchange against the first
bottoms liquid and
then at least partially condensed (or a further portion condensed) by indirect
heat exchange against
the second bottoms liquid.
[0032] In embodiments in which the feed gas is at supercritical pressure, the
feed gas may be
cooled by indirect heat exchange against the first bottoms liquid and then
further cooled by indirect
heat exchange against the second bottoms liquid. The pressure of the cooled
feed is let down prior
to being fed to the first distillation column system.
[0033] The feed to the first distillation column system typically has a vapor
fraction of no more
than 0.5, e.g. no more than 0.3 or no more than 0.2 or even no more than 0.05.
In some preferred
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embodiments, the feed to the first distillation column system is at least
substantially fully
condensed.
[0034] The pressurized nitrogen-rich feed gas is usually at a pressure greater
than the elevated
operating pressure of said first distillation column system. In this regard,
the pressurized feed is
typically taken from a natural underground source. Where the pressurized feed
is at a pressure
greater than the elevated operating pressure of the first distillation column
system, the process
comprises expanding the at least partially condensed feed prior to separation.
[0035] The pressure of the pressurized nitrogen-rich feed gas may be from
about 2 bar to about
200 bar, and is typically from about 10 bar to about 100 bar.
[0036] The elevated operating pressure of the distillation column system is
usually from about 2
bar to about 35 bar, and preferably from about 10 bar to 30 bar.
Additional refrigeration requirement
[0037] Throughout this specification, the term "expanding" is intended to
include expanding to
produce work ("work expansion") and expanding isenthalpically, typically
across a Joule-Thomson
(or "J-T") valve. Gases are typically work expanded in an expander whereas
liquids are usually
expanded isenthalpically across a valve.
[0038] The process may comprise expanding vaporized bottoms liquid, or a fluid
derived
therefrom, to produce expanded nitrogen-enriched gas and using the expanded
gas to provide a
part of the refrigeration duty of the process. The vaporized bottoms liquid is
usually work expanded
in an expander.
[0039] The second nitrogen-enriched bottoms liquid is usually at least
partially vaporized as a
result of the indirect heat exchange against the feed gas. In such
embodiments, the process may
comprise warming the vaporized bottoms liquid by indirect heat exchange to
produce warmed
nitrogen-enriched gas; expanding the warmed nitrogen-enriched gas to produce
expanded
nitrogen-enriched gas; and cooling the feed gas by indirect heat exchange with
the expanded
nitrogen-enriched gas to produce cooled feed gas. The warmed nitrogen-enriched
gas is usually
work expanded in an expander.
[0040] In some embodiments, the process comprises expanding a third nitrogen-
enriched
bottoms liquid to produce expanded nitrogen-enriched fluid; vaporizing the
expanded nitrogen-
enriched fluid by indirect heat exchange against condensing nitrogen in the
first distillation column
system to produce nitrogen-enriched gas; expanding the nitrogen-enriched gas
to produce
expanded nitrogen-enriched gas; and condensing nitrogen gas in the first
distillation column system
by indirect heat exchange against the expanded nitrogen-enriched gas to
produce liquid reflux for
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the first distillation column system. The nitrogen-enriched gas is typically
work expanded in an
expander.
[0041] The pressure at which the expanded third bottoms liquid is vaporized is
typically less than
the pressure at which the expanded second bottoms liquid is vaporized.
[0042] The process may comprise expanding a fourth nitrogen-enriched bottoms
liquid to produce
further expanded nitrogen-enriched fluid; and vaporizing the further expanded
nitrogen-enriched
fluid by indirect heat exchange against condensing nitrogen in the first
distillation column system to
produce further nitrogen-enriched gas.
[0043] The pressure at which the expanded fourth bottoms liquid is vaporized
is typically less
than the pressure at which the expanded third bottoms liquid is vaporized.
[0044] Where the second bottoms liquid is vaporized as a result of the
indirect heat exchange
against the feed gas, the process may comprise expanding the vaporized bottoms
liquid to produce
expanded nitrogen-enriched gas; and condensing nitrogen gas in the first
distillation column system
by indirect heat exchange with the expanded nitrogen-enriched gas to produce
liquid reflux for the
first distillation column system and warmed nitrogen-enriched gas.
[0045] In such embodiments, the process may comprise expanding a third bottoms
liquid to
produce further expanded nitrogen-enriched fluid; and vaporizing the further
expanded nitrogen-
enriched fluid by indirect heat exchange against condensing nitrogen in the
first distillation column
system to produce further nitrogen-enriched gas. The vaporization pressure of
the further expanded
nitrogen-enriched fluid will typically be less than the vaporization pressure
of the second bottoms
liquid.
[0046] A fourth bottoms liquid may be expanded to form an expanded fluid which
is then
separated into a vapor phase and a liquid phase. The vapor phase may be warmed
by indirect
heat exchange to produce a gaseous nitrogen product.
[0047] Flash vapor may be formed on expanding bottoms liquid to form expanded
bottoms liquid.
Alternatively, the bottoms liquid could be subcooled prior to expansion and
thereby avoid the
formation of flash vapor. Such subcooling could be effected by indirect heat
exchange against
expanded nitrogen-enriched gas.
[0048] The bottoms liquid evaporated in the overhead condenser and not
expanded in an
expander is typically at the lowest pressure (e.g. from about 1 bar to about
10 bar) as it needs to
boil at low temperature to condense as much nitrogen as possible from the
helium.
[0049] The bottoms liquid evaporated in the overhead condenser and expanded in
an expander is
at an intermediate pressure (e.g. from about 2 bar to about 25 bar), and is
typically only there if the
vapour from the second bottoms liquid is taken as product and not expanded
(e.g see Fig. 3), so
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there is no other source of expander refrigeration. This stream can be
evaporated at an
intermediate pressure and higher temperature to optimise the cooling in the
condenser over the
whole temperature range ¨ most of the condensing duty is needed at the higher
temperature where
the nitrogen concentration in the helium is highest.
[0050] The third and fourth nitrogen-enriched bottoms liquids are typically
taken from the sump of
the first distillation column system and may be different portions of the same
bottoms liquid.
However, one or more of the bottoms liquids could be taken from a different
point at the bottom of
the distillation column system. In some embodiments, the first, second, third
and fourth bottoms
liquids are different portions of the same bottoms liquid.
[0051] The process is preferably autorefrigerated. The term "autorefrigerated"
is intended to
mean that all of the refrigeration duty required by the process is provided
internally, i.e. by indirect
heat exchange against fluid streams within the process. In other words, no
additional refrigeration
is provided from an outside source.
Origin of the feed
[0052] The feed gas may be taken from a natural gas liquid (NGL) recovery
column. Thus, the
process may comprise cooling and at least partially condensing pressurized
dry, carbon dioxide-
free natural gas to produce at least partially condensed natural gas; and
separating the at least
partially condensed natural gas in a second distillation column system
operating at an elevated
operating pressure to produce C2+-depleted overhead vapor and C2+-enriched
bottoms liquid. In
such embodiments, the C2.-depleted overhead vapor is the nitrogen-rich feed
gas.
[0053] The process may be integrated with a process for recovering helium and
NGL from
pressurized natural gas comprising predominantly nitrogen with smaller amounts
of methane, C2,
hydrocarbons and helium.
[0054] The pressurized natural gas is usually extracted from an underground
source, such as a
geological deposit or a natural gas field. The natural gas is typically
extracted at a pressure in the
range from about 2 bar to about 200 bar, preferably from about 10 bar to about
100 bar.
[0055] The composition of natural gas depends on the source. However, some
embodiments
concern recovering valuable components of nitrogen-rich natural gas, i.e.
natural gas having a low
calorific value, e.g. a calorific value of no more than 300 BTU/scf ("British
thermal units/standard
cubic foot"), i.e. about 11.2 MJ/sm3 ("mega Joules/standard metre cubed" at 15
C). The natural
gas comprises at least about 70%, e.g. at least about 80% and preferably at
least about 90%,
nitrogen. The nitrogen content of the pressurized natural gas is usually no
more than 99% and
typically no more than 95%.
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[0056] Other components of the natural gas suitable to be processed include
methane, helium
and C2+ hydrocarbons, typically together with one or more impurities such as
carbon dioxide, water
and hydrogen sulfide.
[0057] Methane is typically present in the natural gas in an amount in the
range from about 0.1%
to about 30%, for example from about 0.1% to about 20% or from about 0.1% to
about 10%.
[0058] Helium is typically present in an amount in the range from about 0.01%
to about 10%, for
example from about 0.01% to about 5%.
[0059] C2+ hydrocarbons typically comprise C2 to C4 hydrocarbons, often
together with C5 and C5
hydrocarbons. Typical C2+ hydrocarbons include one or more hydrocarbons
selected from the
group consisting of ethane (C2), propane (C3), butanes (C4), pentanes (C6) and
hexanes (C6). The
natural gas typically comprises at least ethane, propane and butane. The total
amount of C2+
hydrocarbons in the natural gas is typically in the range of about 0.01% to
about 5%.
[0060] The process may comprise extracting the pressurized natural gas from an
underground
source and pre-treating the pressurized nitrogen-rich natural gas to remove
one or more impurities
.. incompatible with the process and thereby produce pre-treated natural gas.
[0061] Purities that are incompatible with the process include carbon dioxide,
water and hydrogen
sulfide. These impurities are incompatible because at least a portion of the
pressurized natural gas
is cooled to a low temperature, typically below -100 C. At such cryogenic
temperatures, these
impurities freeze out of the gas causing blockages in pipework and channels
within heat
.. exchangers, etc. Therefore, such "freezable" components are removed before
the natural gas is
cooled.
[0062] The impurities may be removed using conventional techniques. In this
regard, water may
be removed in a selective adsorption process, e.g. using a zeolite adsorbent;
and carbon dioxide
and/or hydrogen sulfide may be removed in an absorption process, e.g. using an
amine such as
monoethanolamine.
[0063] The natural gas being pre-treated for impurity removal is typically at
a pressure in the
range from about 2 bar to about 100 bar, for example from about 40 bar to
about 60 bar, e.g. about
50 bar. If the pressure of the natural gas after extraction is within this
range, then the natural gas
could be pre-treated without pressure adjustment. If the pressure of the
natural gas is significantly
more than 100 bar, then the pressure of the natural gas would be reduced prior
to undergoing the
pre-treatment.
[0064] The pre-treated natural gas is cooled to produce cooled pre-treated
natural gas which is
separated by distillation in the second distillation column system (i.e. an
NGL recovery column
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system) to produce NGL and C2+ hydrocarbon-depleted natural gas comprising
helium and
methane.
[0065] The skilled person would appreciate that the temperature to which the
pre-treated gas is
cooled depends on the pressure and composition of the gas. With this data, it
is possible to
determine the temperature to which the gas is cooled prior to being fed to the
NGL recovery
column.
[0066] The second distillation column system may comprise more than one
distillation column
although, in preferred embodiments, the system comprises a single distillation
column. The column
may be trayed and/or packed as required or as desired.
[0067] The second distillation column system usually operates at a pressure
from about 2 bar to
about 35 bar, for example from about 25 bar to 35 bar, e.g. about 30 bar. In
embodiments in which
the pressure of the cooled pre-treated gas is within these ranges, the pre-
treated gas could be fed
to the second distillation column system without pressure adjustment. However,
the pressure of
the cooled pre-treated gas is typically substantially more than 35 bar.
Therefore, the pressure of
the cooled pre-treated gas is usually reduced prior to being fed to the second
distillation column
system.
Purification of helium product
[0068] The helium-enriched overhead vapor typically comprises at least 50%,
for example at least
65%, preferably at least 80%, e.g. about 90%, helium. The remainder of the
helium-enriched
overhead vapor is usually predominantly nitrogen.
[0069] The helium-enriched overhead vapor may be purified. In such
embodiments, the process
may comprise warming the helium-enriched overhead vapor by indirect heat
exchange to produce
helium-enriched gas; and purifying the helium-enriched gas to produce pure
helium gas. The
purified helium gas typically comprises at least 99% helium.
[0070] The helium-enriched gas is typically purified by a pressure swing
adsorption (PSA)
process. Tail gas from the PSA process may be recycled to the first
distillation column system after
suitable pressure and temperature adjustment.
[0071] If the feed gas contains hydrogen, the purification process may also
include a catalytic
oxidation step (e.g. a NIXOX unit). The catalytic oxidation step may be
carried out upstream of the
PSA, and the tail gas from the PSA recycled upstream of the feed pretreatment
unit to remove
resultant CO2 and water, or to an intermediate point in the pretreatment unit,
such as between the
CO2 and water removal steps if only water was produced in the NIXOX unit, or
water and only small
amounts of CO2 that can be removed in the water removal step, or it may be
treated separately in a
TSA system.
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[0072] In embodiments in which liquid nitrogen is produced as product, at
least a portion of the
liquid nitrogen may be used as a refrigerant in a process to liquefy the
purified helium.
Recovery of methane from nitrogen-enriched bottoms liquid
[0073] Where the feed gas comprises methane, methane is typically recovered
from nitrogen-
enriched bottoms liquid as fuel gas and/or liquefied natural gas (LNG). In
such embodiments, the
methane is typically separated by distillation in a third distillation column
system (i.e. a methane
recovery column system) operating at elevated operating pressure(s) to produce
nitrogen overhead
vapor and methane-enriched bottoms liquid.
[0074] Methane-enriched bottoms liquid typically comprises at least 90%, for
example about 95%,
methane. The bottoms liquid may be removed from the process without
vaporization to form an
LNG product. Additionally or alternatively, a portion of the methane-enriched
bottoms liquid may be
vaporized to produce fuel gas.
[0075] Nitrogen-enriched overhead vapor typically comprises at least 99%
nitrogen. The nitrogen
overhead vapor may be warmed by indirect heat exchange to produce warmed
nitrogen gas.
Additionally or alternatively, at least a portion of the nitrogen in the
nitrogen-enriched overhead
vapor is condensed and removed as liquid nitrogen. The liquid nitrogen
typically comprises at least
99% nitrogen.
[0076] A portion of the nitrogen gas may recycled to the third distillation
column system after
suitable pressure and temperature adjustment. The nitrogen gas may be recycled
from any point
downstream of the third distillation column system, e.g. after warming,
compression, cooling and/or
expansion. Such a recycle can increase the refrigeration available to the
process, and therefore
increase the quantity of liquid products that can be made.
[0077] Additionally or alternatively, a portion of the nitrogen gas may be
expanded to produce
expanded nitrogen gas, which is then warmed by indirect heat exchange to
produce warmed
expanded nitrogen gas. In such embodiments, the nitrogen gas is usually work
expanded in an
expander to provide refrigeration for the production of liquid from the
process.
[0078] The third distillation column system may comprise a single distillation
column, or more
than one distillation column in which each column operates at the same or
different elevated
pressures. In some preferred embodiments, the third distillation column system
comprises a higher
pressure distillation column (HP column) and a lower pressure distillation
column (LP column).
The column(s) may be trayed and/or packed as required or as desired.
[0079] The third distillation column system may comprise a condenser for
condensing overhead
vapor. A portion of the condensed phase is typically returned to the top of
the column system as
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reflux. The condenser may be a stand alone unit, or in preferred embodiments,
is a section in the
main heat exchanger.
[0080] The or each elevated operating pressure of the third distillation
column system is typically
less than the pressure of the bottoms liquid in the first distillation column
system. Therefore, the
process typically comprises expanding the bottoms liquid to the or one of the
elevated pressures of
the third distillation column system prior to separation.
[0081] The third distillation column system typically operates at one or more
pressures in the
range from more than 1 bar to about 35 bar. Where the third distillation
column system comprises
an HP column and an LP column, the HP column typically operates at a pressure
from about 20 bar
to about 35 bar, for example at about 25 bar, and the LP column typically
operates at a pressure
from more than 1 bar to about 10 bar, for example about 1.5 bar. The pressure
of the nitrogen-
enriched bottoms liquid is adjusted as required prior to being fed to the
methane recovery column
system.
[0082] In a first arrangement of the apparatus, there is comprised a
distillation column system for
operation at an elevated operating pressure to separate at least partially
condensed feed gas into
helium-enriched overhead vapor and nitrogen-enriched bottoms liquid; an
overhead condenser for
partially condensing helium-enriched overhead vapor by indirect heat exchange
to produce helium-
enriched vapor as product and liquid for reflux in the column system; a first
heat exchange system
for cooling feed gas by indirect heat exchange with a first nitrogen-enriched
bottoms liquid to
produce cooled feed gas and vapor for the column system; a first pressure
reduction device for
reducing the pressure of a second nitrogen-enriched bottoms liquid to produce
reduced pressure
bottoms liquid; a second heat exchange system for cooling said cooled feed gas
by indirect heat
exchange against said reduced pressure bottoms liquid to produce at least
partially condensed
feed gas and at least partially vaporized bottoms liquid; and a second
pressure reduction device for
reducing the pressure of said at least partially condensed feed gas to produce
at least partially
condensed feed gas at reduced pressure for use as said feed to the
distillation column system.
[0083] The apparatus may comprise a separator to separate partially condensed
overhead vapor
into helium-enriched vapor and liquid reflux.
[0084] Preferably, this arrangement comprises a third pressure reduction
device for reducing the
pressure of a third nitrogen-enriched bottoms liquid to produce reduced
pressure bottoms liquid for
vaporization by indirect heat exchange in said overhead condenser to produce
nitrogen-enriched
vapor.
12
CA 02957141 2017-02-06
[0085] These preferred arrangements usually comprise an expander for expanding
said nitrogen-
enriched vapor to produce expanded nitrogen-enriched vapor for warming by
indirect heat
exchange in said overhead condenser to produce warmed nitrogen-enriched vapor.
[0086] Preferably, this arrangement of the apparatus also comprises a fourth
pressure reduction
device for reducing the pressure of a fourth portion of said bottoms liquid to
produce reduced
pressure bottoms liquid for vaporization, optionally by said indirect heat
exchange in said overhead
condenser to produce nitrogen-enriched vapor.
[0087] An alternative embodiment of the first arrangement of the apparatus may
comprise an
expander for expanding said vaporized bottoms liquid to produce expanded
nitrogen-enriched
vapor for warming by indirect heat exchange in said overhead condenser to
produce warmed
nitrogen-enriched vapor.
[0088] In these embodiments, the apparatus preferably comprises a fourth
pressure reduction
device for reducing the pressure of a fourth portion of said nitrogen-enriched
bottoms liquid to
produce reduced pressure bottoms liquid; and a storage vessel for storing said
reduced pressure
bottoms liquid.
[0089] In a second arrangement of the apparatus, there is comprised a
distillation column system
for operation at an elevated operating pressure to separate at least partially
condensed feed gas
into helium-enriched overhead vapor and nitrogen-enriched bottoms liquid; an
overhead condenser
for partially condensing helium-enriched overhead vapor by indirect heat
exchange to produce
helium-enriched vapor as product and liquid for reflux in the column system; a
first pump for
pumping a second nitrogen-enriched bottoms liquid to produce pumped bottoms
liquid; a first heat
exchange system for cooling feed gas by indirect heat exchange with said
pumped bottoms liquid
to produce cooled feed gas and nitrogen-enriched vapor; a second heat exchange
system for
cooling said cooled feed gas by indirect heat exchange against a first
nitrogen-enriched bottoms
liquid to produce at least partially condensed feed gas and vapor for the
column system; and a
pressure reduction device for reducing the pressure of said at least partially
condensed feed gas to
produce at least partially condensed feed gas at reduced pressure for use as
said feed to the
distillation column system.
[0090] Preferably, this arrangement comprises a third pressure reduction
device for reducing the
pressure of a third portion of said bottoms liquid to produce reduced pressure
bottoms liquid for
vaporization by indirect heat exchange in said overhead condenser to produce
nitrogen-enriched
vapor.
13
CA 02957141 2017-02-06
[0091] These preferred arrangements usually comprise an expander for expanding
said nitrogen-
enriched vapor to produce expanded nitrogen-enriched vapor for warming by
indirect heat
exchange in said overhead condenser to produce warmed nitrogen-enriched vapor.
[0092] Preferably, this arrangement of the apparatus also comprises a fourth
pressure reduction
device for reducing the pressure of a fourth portion of said bottoms liquid to
produce reduced
pressure bottoms liquid for vaporization by indirect heat exchange in said
overhead condenser to
produce nitrogen-enriched vapor.
[0093] The or each heat exchange system may be an independent unit. In other
embodiments,
the two or more heat exchange systems may be different sections of a single
heat exchange unit.
In preferred embodiments, all of the heat exchange systems identified above
are different sections
of a primary (or main) heat exchanger.
[0094] The disclosure will now be further described with reference to the
comparative process
depicted in FIG. 1 and the embodiments depicted in FIGs. 2 to 9.
[0095] The comparative process depicted in FIG. 1 is based on the process
disclosed in
US5167125 integrated with a main heat exchanger 92 and with a gaseous feed
comprising 93%
nitrogen, 5% methane and 2% helium. The feed is at a temperature of about 49 C
and a pressure
of 30 bar.
[0096] A stream 90 of feed gas is cooled by indirect heat exchange in the main
heat exchanger
92 to form a stream 100 of cooled gas. The cooled gas is fed to reboiler 108
of distillation column
102 where it is further cooled by indirect heat exchange against bottoms
liquid in the column to
form a stream 110 of further cooled feed. A small amount (-11%) of the feed is
condensed.
Stream 110 is then expanded across valve 112 to about 25 bar and the expanded
stream 113 fed
to the distillation column where it is separated into nitrogen-enriched
bottoms liquid and helium-
enriched overhead vapor.
[0097] A stream 104 of bottoms liquid is removed from the column 102, expanded
across valve
122 to about 1.5 bar and then used to partially condense overhead vapor from
the column 102 by
indirect heat exchange. In this regard, a stream 114 of overhead vapor is fed
to condenser 116
where it is partially condensed by indirect heat exchange against vaporizing
bottoms liquid to
produce liquid reflux 120 for the column and a stream 118 of crude helium gas
which is warmed by
indirect heat exchange in the main heat exchanger 92, thereby producing a
stream 119 of warmed
helium gas (-90%) containing nitrogen (-10%).
[0098] A stream 126 of nitrogen-enriched bottoms liquid vaporized by the
condensing overhead
vapor is then used to cool the feed by indirect heat exchange in the main heat
exchanger 92 to
produce stream 128 of warmed nitrogen gas (-95%) containing methane (-5%).
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[0099] All of the refrigeration for the comparative process depicted in FIG. 1
is provided by Joule-
Thomson expansion.
[0100] In this example, there is no liquid product 124 from the boiling side
of the condenser 116.
Heat balance means that, because all of the feed is in the gaseous phase and
no significant
refrigeration is provided, all of the products must also be in the gaseous
phase.
[0101] FIG. 2 depicts in an embodiment an improved process over FIG. 1. Common
features have
been given the same reference numerals. The following is a discussion of the
new features.
[0102] FIG. 2 depicts a process where stream 100 is gaseous or two phase. The
feed is fully, or
almost fully, condensed in heat exchanger 136 which is cooled by boiling a
stream 168 of helium-
free bottoms liquid at elevated pressure. In this regard, a portion 164 of the
bottoms liquid is
expanded across valve 166 and fed as stream 168 to the heat exchanger 136 to
form stream 170
of vaporized bottoms liquid. Additional refrigeration is provided by expanding
stream 170 in
expander 174 and using the expanded stream to help cool the feed 90 in the
main heat exchanger
92. A stream 172 of warmed nitrogen gas is then removed from the heat
exchanger and may be
purified.
[0103] An advantage in some embodiments of the process of FIG. 2 over the
comparative
process depicted in FIG. 1 is that because of the additional condensation of
the feed in heat
exchanger 136, the vapor part of the feed and therefore the vapor flow in the
column 102 above the
feed location is reduced significantly leading to a reduction in the diameter
of that section of the
column.
[0104] FIG. 3 depicts in an embodiment an improved process over FIG. 2. Common
features
have been given the same reference numerals. The following is a discussion of
the new features.
[0105] In FIG. 3, a further portion 132 of helium-free bottoms liquid is
expanded across valve 133
and the expanded stream 134 is fed to the overhead condenser 116 where it is
boiled and
superheated at an intermediate pressure. Stream 138 of vaporized bottoms
liquid is expanded in
expander 140 and the expanded stream 142 and reheated in condenser 116 to
produce a stream
144 of reheated nitrogen gas which is used to help cool the feed 90 in the
main heat exchanger 92.
Stream 146 of the resultant nitrogen gas is taken from the heat exchanger 92
and is available as a
product or for further purification.
[0106] Stream 170 is used without expansion to cool the feed 90 in the main
heat exchanger 92.
[0107] An advantage in some embodiments of the process of FIG. 3 over the
process depicted in
FIG. 2 is that refrigeration is integrated with the separation process, and
the amount of product
available at pressure is increased.
CA 02957141 2017-02-06
[0108] FIG. 4 depicts a modified process of FIG. 3 in which the feed pressure
is greater.
Common features have been given the same reference numerals. The following is
a discussion of
the new features.
[0109] Stream 164 of helium-free bottoms liquid is pumped in pump 16510
produce a stream 168
of pumped bottoms liquid which is used to cool the feed in heat exchanger 169
upstream of the
column reboiler 108. The refrigeration provided by the expander 140 offsets
the energy input to the
process of the pump 168.
[0110] FIG. 5 depicts a preferred process in which most of the nitrogen
product is boiled and
expanded to provide refrigeration for production of some of the nitrogen
product as liquid.
[0111] Feed 90 is cooled initially by indirect heat exchange in the main heat
exchanger 92 to
produce stream 100 and then subsequently further cooled and condensed by
indirect heat
exchange in the column reboiler 108 and heat exchanger 136. Stream 111 of
condensed feed is
expanded across valve 112 and fed to column 102 for distillation. The column
102 is reboiled by
the feed in reboiler 108, and nitrogen in the overhead vapor is condensed in
condenser 116 to
provide reflux 120 for the column 102. A stream 118 of impure helium gas is
removed from the
condenser 116 and warmed against the feed 90 in the main heat exchanger 92 to
produce a helium
gas stream 119 suitable for purification by PSA or by some other means.
[0112] A first portion of the helium-free bottoms liquid 104 is boiled in the
bottom of column 102 to
provide vapor for the column.
[0113] A second portion 132 of helium-free bottoms liquid 104 is expanded
across valve 133 and
the expanded stream 134 is used to cool and condense the feed by indirect heat
exchange in heat
exchanger 136. A stream 138 of vaporized bottoms liquid is work expanded in
expander 140 to
produce expanded stream 142 which is then fed to the overhead condenser 116 to
condense
nitrogen in the overhead vapor for reflux 120. Stream 144 of nitrogen gas is
then fed to the main
heat exchanger 92 to help cool the feed 90, thereby producing a stream 146 of
impure nitrogen gas
suitable for further purification.
[0114] A third portion of helium-free bottoms liquid 104 is expanded across
valve 122 to produce
expanded stream 105 which is fed to the overhead condenser 116 to help
condense nitrogen in the
overhead vapor. Stream 126 of nitrogen gas is then fed to the main heat
exchanger 92 to help cool
the feed 90, thereby produce another stream 128 of impure nitrogen gas
suitable for further
purification.
[0115] A fourth portion 180 of helium-free bottoms liquid 104 is expanded
across valve 182 to
form a two phase stream 184 which is fed to a storage tank 185 where it is
separated into a liquid
stream 186 and a vapor stream 188. Liquid stream 186 could be vaporized to
provide refrigeration,
16
CA 02957141 2017-02-06
for example in a downstream helium liquefier, or exported as a product, for
example for fracking.
The vapor stream 188 is used to help cool the feed 90 in the main heat
exchanger 92 to produce a
further stream 190 of impure nitrogen gas suitable for further purification.
[0116] FIG. 6 depicts a modified process of FIG. 5 in which liquid product is
subcooled in
condenser 116. Common features have been given the same reference numerals.
The following is
a discussion of the new features.
[0117] The fourth portion 180 of helium-free bottoms liquid is fed without
expansion to the
condenser 116 where it is subcooled to form stream 181 of subcooled bottoms
liquid. Stream 182
is expanded across valve 182 to produce expanded stream 184 which is two
phase. Stream 184 is
fed to the storage tank 185 where it is separated into the liquid stream 186
and the vapor stream
188.
[0118] If the feed contains C2+ hydrocarbons, a hydrocarbon (NGL) recovery
column may be
added upstream of the helium separation column 102, as illustrated in FIG. 7.
[0119] Feed 90 is cooled in the main heat exchanger 92 and divided into a
first portion 191 and a
second portion. The first portion 191 is work expanded in expander 192 and the
expanded stream
193 is fed back to the main heat exchanger 92 where it is further cooled to
produce stream 194
which is fed to an intermediate location in an NGL recovery column 96. The
second portion is
further cooled and condensed by indirect heat exchange in the main heat
exchanger to form stream
196 of liquid feed which is expanded across valve 94 to produce expanded feed
stream 198 which
is fed to the top of the NGL recovery column 96.
[0120] The feeds to the column 96 are separated into C2+ hydrocarbon bottoms
liquid, removed
as stream 199, and C2+ hydrocarbon-depleted overhead vapor. Column 96 is
reboiled in reboiler
98 using an external heat source such as steam, hot oil or cooling water.
[0121] A stream 100 of overhead vapor is removed from column 96 and used to
reboil the helium
recovery column 102 to produce a stream 110 of cooled and partially condensed
overhead vapor.
Stream 110 is further cooled and condensed in heat exchanger 136 by indirect
heat exchange
against helium-free bottoms liquid 134 from column 102. The further condensed
stream 111 is then
expanded across valve 112 and fed as stream 113 to column 102 where it is
separated into
nitrogen-enriched bottoms liquid and helium-enriched overhead vapor.
[0122] A stream 114 of helium-enriched overhead vapor is taken from column 102
and nitrogen in
the vapor is condensed by indirect heat exchange in heat exchanger 116 to form
a two phase
stream 115 that is separated in phase separator 103. A stream 120 of nitrogen-
enriched liquid is
used to provide reflux to column 102. A stream 118 of impure helium gas is
warmed by indirect
heat exchange in heat exchanger 116 to form stream 121 of warmed helium gas
which is then used
17
CA 02957141 2017-02-06
to help cool the feed 90 by indirect heat exchange in the main heat exchanger
92. The stream 119
of impure helium gas from the main heat exchanger 92 is suitable for
purification by PSA or by
some other means.
[0123] A first portion of the helium-free bottoms liquid 104 is boiled in the
bottom of column 102 to
provide vapor for the column.
[0124] A second portion of nitrogen-enriched bottoms liquid 104 is expanded
across valve 122
and the expanded stream 105 is used to provide refrigeration duty in heat
exchanger 116. The
resultant stream 126 of vaporized liquid is then used to help cool the feed 90
by indirect heat
exchange in the main heat exchanger 92 to produce a stream 128 of warmed
impure nitrogen gas
suitable for further purification.
[0125] A third portion 132 of the helium¨free bottoms liquid 104 is expanded
across valve 133
and then used to provide refrigeration duty in heat exchanger 136. The stream
137 of impure
nitrogen gas is then removed from heat exchanger 136 and fed to the main heat
exchanger 92
where is helps cool the feed 90. A stream 138 of warmed impure nitrogen gas is
then work
expanded in expander 140 and the expanded stream 142 is used to provide
refrigeration duty in
heat exchanger 116. The resultant stream 144 of impure nitrogen gas is then
used to help cool the
feed in the main heat exchanger 92.
[0126] A fourth portion 180 of the helium-free bottoms liquid is subcooled in
heat exchanger 116
and the resultant stream 181 is expanded across valve 182 to form a two phase
stream 184 which
is fed to a storage tank 185 from which a stream 186 of liquid nitrogen may be
removed. A stream
188 of impure nitrogen gas is taken from the storage tank 185 and used to help
cool the feed 90 by
indirect heat exchange in the main heat exchanger 92. Stream 190 of warmed
impure nitrogen gas
is suitable for further purification.
[0127] If pure nitrogen and/or a fuel stream are required, the helium-depleted
bottoms liquid from
the helium recovery column may be separated before and/or after work
expansion, as illustrated in
FIG. 8.
[0128] The feed 90 is cooled initially by indirect heat exchange in the main
heat exchanger 92
and then further cooled and condensed by indirect heat exchange in the
reboiler 108 of the helium
recovery column 102 and heat exchanger 136. The condensed stream 111 is
expanded across
valve 112 and then fed as stream 113 to the column 102 where it is separated
into helium-enriched
overhead vapor and nitrogen-enriched bottoms liquid.
[0129] Overhead vapor is removed as stream 114 and nitrogen in the stream is
condensed by
indirect heat exchange in heat exchanger 116 to form a two-phase stream 115
which is phase
separated in phase separator 103. The liquid portion 120 is fed back to the
top of the column 102
18
CA 02957141 2017-02-06
as reflux. The vapor portion 118 is used to help cool the overhead vapor in
heat exchanger 116
and is then further warmed in the main exchanger 92 against the cooling feed
90. The resultant
stream 119 of helium gas is suitable for further purification.
[0130] A portion 132 of the bottoms liquid 104 is expanded across valve 133
and the expanded
stream 134 is warmed by indirect heat exchange in heat exchanger 136 before
being fed as stream
200 to a first nitrogen purification column 208. The feed 200 is separated
into methane-enriched
bottoms liquid and nitrogen-enriched overhead vapor.
[0131] Overhead vapor 230 is condensed by indirect heat exchanger against
expanded bottoms
liquid 214 in overhead condenser 232 to produce reflux 234 for the column 208,
and a stream 130
.. of liquid nitrogen. Stream 130 is cooled by indirect heat exchange in heat
exchanger 136 and the
cooled stream 180 is subcooled in heat exchanger 116. Subcooled stream 181 is
expanded across
valve 182 and the expanded stream 184 is fed to storage tank 185. A stream 186
of pure nitrogen
liquid can be removed from tank 185. Vapor 188 from the tank is used to help
cool the feed 90 in
the main heat exchanger 92 to produce stream 190 of nitrogen gas.
[0132] A stream 210 of bottoms liquid is expanded across valve 212 and the
expanded stream
214 is fed to the overhead condenser for refrigeration duty. Vaporized bottoms
liquid is removed
from the overhead condenser 232 as stream 216. Unvaporized bottoms liquid is
removed as
stream 218, vaporized by indirect heat exchange in heat exchanger 136 and the
vaporized stream
220 is combined with stream 216 to form combined stream 222 which is used to
help cool the feed
90 in the main heat exchanger 92 and then work expanded in expander 140. The
expanded
stream 142 is then fed to a second nitrogen purification column 258 operating
at a lower pressure
than the first nitrogen purification column 208.
[0133] A second portion 250 of bottoms liquid 104 from the helium recovery
column 102 is
subcooled by indirect heat exchange in heat exchanger 116 and the subcooled
liquid 252 is
expanded across valve 254 and the expanded stream 256 is fed to the top of the
second nitrogen
purification column.
[0134] The feeds to the second nitrogen purification column 258 are separated
into methane-
enriched bottoms liquid and nitrogen-enriched overhead vapor. A first portion
262 of the methane-
enriched bottoms liquid is reboiled in heat exchanger 116 and fed back to the
column 258 to
provide vapor for the distillation. A second portion 270 of the bottoms liquid
is pumped in pump 272
and the pumped stream 274 is used to help cool the feed 90 in the main heat
exchanger 92 to
produce a stream 276 of fuel gas.
[0135] A stream 226 of nitrogen vapor is warmed in heat exchangers 116 and 92
to provide a
vent gas stream 146.
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CA 02957141 2017-02-06
[0136] FIG. 9 depicts a fully integrated scheme with NGL recovery, HP and LP
columns and liquid
nitrogen production from an underground gas source, and helium purification by
PSA to produce a
stream 302 pure helium that can be fed directly to a helium liquefier.
[0137] Feed gas 70 from an underground source is pre-treated 72 to removed
water and carbon
dioxide to produce stream 90 of dry, CO2-free feed gas which is cooled by
indirect heat exchange in
the main heat exchanger 92. A first portion 191 of the cooled feed is expanded
in expander 192 to
produce a two phase stream 193 which is phase separated in separator 95. The
liquid phase 197
is fed directly to an NGL recovery column 96. The vapor phase 195 is cooled in
the main heat
exchanger 92 and the cooled stream 194 is also fed to the NGL recovery column
96. A second
portion of the cooled feed is further cooled in the main heat exchanger 92,
expanded in valve 94
and fed to the column 96 as reflux stream 198.
[0138] The feeds to the NGL column 96 are separated into a C2+-enriched
bottoms liquid and C2,-
depleted overhead vapor. The bottoms liquid is reboiled with external heat in
reboiler 98 to provide
vapor for the separation, and an NGL stream 199 is removed. Further vapor
(stream 402) for the
column 96 is provided by reboiling a stream 400 of liquid taken from an
intermediate location of the
column 96 in the main heat exchanger 92.
[0139] A stream 100 of overhead vapor is cooled and condensed in the main heat
exchanger 92
by indirect heat exchange against reboiling helium-free bottoms liquid 410 and
expanded bottoms
liquid 204 from the helium recovery column 102. The condensed feed 111 is then
expanded across
valve 112 and the expanded stream 113 fed to the helium recovery column 102
where it is
separated into the helium-free bottoms liquid and helium-enriched overhead
vapor.
[0140] A stream 114 of overhead vapor is fed to the main heat exchanger 92
where nitrogen in
the stream in condensed to form a two phase stream 115 which is phase
separated in separator
103. The liquid phase 120 is fed as reflux to the helium recovery column 102.
The vapor phase
118 is used to help cool the feed 90 in the main heat exchanger 92 and the
resultant warmed
stream 119 is fed to a helium PSA unit 300 which produces a stream 302 of pure
helium. A stream
304 of tail gas from the PSA unit 300 is compressed in compressor 306 and the
compressed
stream 308 is cooled by indirect heat exchange in aftercooler 310 and the main
heat exchanger 92
before being recycled as stream 314 to the helium recovery column 102.
[0141] After cooling the feed to the helium recovery column 102, a portion of
the expanded
helium-free bottoms liquid is fed as stream 200 from the main heat exchanger
to a first nitrogen
purification column 208 where it is separated into methane-enriched bottoms
liquid and nitrogen-
enriched overhead vapor.
CA 02957141 2017-02-06
[0142] A stream 230 of nitrogen-enriched overhead vapor is condensed by
indirect heat
exchange in the main heat exchanger. A portion 234 of the condensed stream is
fed to the first
nitrogen purification column as reflux. The remaining portion is cooled by
indirect heat exchange in
the main heat exchanger 92 and the cooled stream 181 expanded across valve 182
to form two
phase stream 184. Stream 184 is fed to a storage tank 185 from which a stream
186 of liquid
nitrogen may be taken. Vapor stream 188 is warmed in the main heat exchanger
92 to produce
nitrogen gas stream 190.
[0143] A stream 210 of methane-enriched bottoms liquid is expanded across
valve 212 and
expanded stream 214 is warmed and vaporized by indirect heat exchange in the
main heat
exchanger 92. Gaseous stream 138 is expanded in expander 140 and the expanded
stream is fed
to a second nitrogen purification column 258. Reflux to the second nitrogen
purification column 258
is provided by a portion 252 of the expanded bottoms liquid 204 from the
helium recovery column
102. Stream 252 is expanded across valve 254 and fed as reflux stream 256 to
the column 258.
[0144] The feeds to the second nitrogen purification column are separated into
methane-enriched
bottoms liquid and nitrogen-enriched overhead vapor. The column is reboiled by
vaporizing a
stream 260 of bottoms liquid in the main heat exchanger 92. A stream 270 of
bottoms liquid is
pumped in pump 272 and pumped stream 274 is used to help cool the feed 90 in
the main heat
exchanger 92 to produce fuel gas stream 276.
[0145] A stream 226 of overhead vapor is warmed by indirect heat exchange in
the main heat
exchanger 92 and divided into two portions, streams 147 and 280. Stream 147
may be a product
stream but it is usually vented. Stream 280 is compressed in compressor 282
and the compressed
stream 284 is cooled in aftercooler 286. The cooled stream 288 is cooled in
the main heat
exchanger 92 before being combined with stream 214 after it has been vaporized
to form combined
stream 138 from the first nitrogen purification column 208 to the second
nitrogen purification
column 258.
[0146] Aspects include:
#1. A process for recovering helium from a nitrogen-rich feed gas
comprising helium, said
process comprising:
cooling a pressurized nitrogen-rich feed gas comprising helium to produce
cooled feed; and
separating said feed in a first distillation column system operating at an
elevated operating
pressure to produce helium-enriched overhead vapor and nitrogen-enriched
bottoms
liquid(s);
wherein said feed to the first distillation column system is at least
partially condensed; and
21
CA 02957141 2017-02-06
wherein said cooling of said feed gas is achieved by indirect heat exchange
against at least a first
nitrogen-enriched bottoms liquid at a first elevated pressure and a second
nitrogen-enriched
bottoms liquid at a second elevated pressure that is different from said first
elevated pressure.
#2. A process according to aspect #1, wherein said first elevated pressure
is equal to the
elevated operating pressure of said first distillation column system.
#3. A process according to aspect #1 or aspect #2, wherein said first
elevated pressure is from
about 2 bar to about 35 bar.
#4. A process according to any of aspects #1 to #3, wherein the second
elevated pressure is
less than the elevated operating pressure of said first distillation column
system.
#5. A process according to aspect #4, wherein the second elevated pressure
is from about 1
bar to about 30 bar.
#6. A process according to aspect #4 or aspect #5 comprising expanding
bottoms liquid to
produce said second bottoms liquid.
#7. A process according to any of aspects #1 to #6, wherein said feed gas
is at subcritical
pressure.
#8. A process according to aspect #7, wherein said feed gas is cooled by
indirect heat
exchange against said first bottoms liquid and then at least partially
condensed by indirect heat
exchange against said second bottoms liquid.
#9. A process according to any of aspects #1 to #3, wherein the second
elevated pressure is
.. greater than the elevated operating pressure of said first distillation
column system.
#10. A process according to aspect #9, wherein the second elevated pressure is
from about 3
bar to about 150 bar.
#11. A process according to #9 or #10 comprising pumping bottoms liquid to
produce said
second bottoms liquid.
.. #12. A process according to any of aspects #1 to #3 and #9 to #11, wherein
said feed gas is at
supercritical pressure.
#13. A process according to aspect #12, wherein said feed gas is cooled by
indirect heat
exchange against said first bottoms liquid and then further cooled by indirect
heat exchange against
said second bottoms liquid.
#14. A process according to aspect #12, comprising expanding said cooled feed
prior to feeding
said cooled feed to said first distillation column system.
#15. A process according to any of aspects #1 to #14, wherein the feed to the
first distillation
column system has a vapor fraction of no more than 0.5.
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CA 02957141 2017-02-06
#16. A process according to any of aspects #1 to #15, wherein the feed to the
first distillation
column system is at least substantially fully condensed.
#17. A process according to any of aspects #1 to #16, wherein said pressurized
nitrogen-rich
feed gas is at a pressure greater than said elevated operating pressure of
said first distillation
column, said process comprising expanding said at least partially condensed
feed prior to
separation.
#18. A process according to any of aspects #1 to #17, wherein the pressure of
said pressurized
nitrogen-rich feed gas is from about 2 bar to about 200 bar.
#19. A process according to any of aspects #1 to #18, wherein said elevated
operating pressure
of the distillation column system is from about 2 bar to about 35 bar.
#20. A process according to any of aspects #1 to #19 comprising expanding
vaporized bottoms
liquid, or a fluid derived therefrom, to produce expanded nitrogen-enriched
gas and using said
expanded gas to provide a part of the refrigeration duty of the process.
#21. A process according to any of aspects #1 to #20, wherein said second
bottoms liquid is at
least partially vaporized as a result of said indirect heat exchange against
said feed gas, said
process comprising:
warming said vaporized bottoms liquid by indirect heat exchange to produce
warmed
nitrogen-enriched gas; and
expanding said warmed nitrogen-enriched gas to produce expanded nitrogen-
enriched gas;
and
cooling said feed gas by indirect heat exchange with said expanded nitrogen-
enriched gas
to produce cooled feed gas.
#22. A process according to any of aspects #1 to #21 comprising:
expanding a third bottoms liquid to produce expanded nitrogen-enriched fluid;
vaporizing said expanded nitrogen-enriched fluid by indirect heat exchange
against
condensing nitrogen in said first distillation column system to produce
nitrogen-enriched
gas;
expanding said nitrogen-enriched gas to produce expanded nitrogen-enriched
gas; and
condensing nitrogen gas in said first distillation column system by indirect
heat exchange
against said expanded nitrogen-enriched gas to produce liquid reflux for said
first distillation
column system.
#23. A process according to aspect #22 comprising:
expanding a fourth bottoms liquid to produce further expanded nitrogen-
enriched fluid; and
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vaporizing said further expanded nitrogen-enriched fluid by indirect heat
exchange against
condensing nitrogen in said first distillation column system to produce
further nitrogen-
enriched gas.
#24. A process according to any of aspects #1 to #20, wherein said second
bottoms liquid is
vaporized as a result of said indirect heat exchange against said feed gas,
said process
comprising:
expanding said vaporized bottoms liquid to produce expanded nitrogen-enriched
gas; and
condensing nitrogen gas in said first distillation column system by indirect
heat exchange
with said expanded nitrogen-enriched gas to produce liquid reflux for said
first distillation
column system and warmed nitrogen-enriched gas.
#25. A process according to #24 comprising:
expanding a third bottoms liquid to produce further expanded nitrogen-enriched
fluid; and
vaporizing said further expanded nitrogen-enriched fluid by indirect heat
exchange against
condensing nitrogen in said first distillation column system to produce
further nitrogen-
enriched gas.
#26. A process according to aspect #24 or aspect #25 comprising expanding a
fourth bottoms
liquid to form an expanded fluid; and separating said expanded fluid into a
vapor phase and a liquid
phase.
#27. A process according to aspect #26, wherein said vapor phase is warmed by
indirect heat
exchange to produce a gaseous nitrogen product.
#28. A process according to aspect #26 of #27, comprising sub-cooling said
fourth bottoms liquid
prior to expansion to form said expanded two phase fluid.
#29. A process according to aspect #28, wherein said fourth bottoms liquid is
sub-cooled by
indirect heat exchange against expanded nitrogen-enriched gas
#30. A process according to any of aspects #1 to #29, wherein the process is
autorefrigerated.
#31. A process according to any of aspects #1 to #30, wherein said feed gas is
taken from a
natural gas liquids (NGL) recovery column.
#32. A process according to any of aspects #1 to #31 comprising:
cooling and at least partially condensing pressurized dry, carbon dioxide-free
natural gas to
produce at least partially condensed natural gas; and
separating said at least partially condensed natural gas in a second
distillation column
system operating at an elevated operating pressure to produce C2+-depleted
overhead
vapor and C2+-enriched bottoms liquid,
wherein said C2.-depleted overhead vapor is said nitrogen-rich feed gas.
24
CA 02957141 2017-02-06
#33. A process according to aspect #32, wherein said natural gas comprises at
least 70%
nitrogen (N2).
#34. A process according to aspect #32 or aspect #33, wherein said pressurized
dry, carbon
dioxide-free natural gas is at a pressure of from about 2 bar to about 200
bar.
#35. A process according to any of aspects #32 to #34, wherein said elevated
pressure of said
second distillation column system is less than the pressure of said
pressurized dry, carbon dioxide-
free natural gas, said process comprising expanding said at least partially
condensed natural gas to
said elevated pressure of said second distillation column system prior to
separation.
#36. A process according to any of aspects #32 to #34, wherein said elevated
operating pressure
of said second distillation column system is from about 2 bar to about 35 bar.
#37. A process according to any of aspects #1 to #36 comprising:
warming said helium-enriched overhead vapor by indirect heat exchange to
produce helium-
enriched gas; and
purifying said helium-enriched gas to produce pure helium gas.
#38. A process according to aspect #37, wherein said helium-enriched gas is
purified by a
pressure swing adsorption (PSA) process.
#39. A process according to aspect #38, wherein tail gas from said PSA process
is recycled to
said first distillation column system after suitable pressure and temperature
adjustment.
#40. A process according to any of aspects #1 to #39, wherein said feed gas
comprises
methane, said process comprising recovering methane from said bottoms liquid
to produce fuel gas
or LNG.
#41. A process according to any of aspects #1 to #40 comprising separating
bottoms liquid in a
third distillation column system operating at elevated operating pressure(s)
to produce nitrogen
overhead vapor and methane-enriched bottoms liquid.
#42. A process according to aspect #41 comprising warming said nitrogen
overhead vapor by
indirect heat exchange to produce warmed nitrogen gas.
#43. A process according to aspect #41 or aspect #42 comprising recycling a
portion of said
nitrogen gas to said third distillation column system after suitable pressure
and temperature
adjustment.
#44. A process according to aspect #42 comprising expanding a portion of said
nitrogen gas to
produce expanded nitrogen gas, and warming said expanded nitrogen gas by
indirect heat
exchange to produce warmed expanded nitrogen gas.
#45. A process according to any of aspects #41 to #44 comprising warming and
evaporating said
methane-enriched bottoms liquid by indirect heat exchange to produce fuel gas.
CA 02957141 2017-02-06
#46. A process according to any of aspects #41 to #45, wherein said third
distillation column
system additionally produces a nitrogen-enriched overhead vapor, said process
comprising
condensing said nitrogen-enriched overhead vapor to produce condensed vapor
and removing a
portion of said condensed vapor as a liquid nitrogen product.
#47. A process according to any of aspects #41 to #46, wherein the or each
elevated pressure of
said third distillation column system is less than the pressure of the bottoms
liquid, said process
comprising expanding said bottoms liquid to the or one of the elevated
pressures of said third
distillation column system prior to separation.
#48. A process according to any of aspects #41 to #47, wherein said elevated
pressure of said
third distillation column system is from more than 1 bar to about 35 bar.
#49. A process substantially as described herein with reference to the
examples and/or
drawings.
#50. Apparatus for recovering helium from a nitrogen-rich feed gas comprising
helium, said
apparatus comprising:
a distillation column system for operation at an elevated operating pressure
to separate at
least partially condensed feed gas into helium-enriched overhead vapor and
nitrogen-
enriched bottoms liquid(s);
an overhead condenser for partially condensing helium-enriched overhead vapor
by indirect
heat exchange to produce helium-enriched vapor as product and liquid for
reflux in the
column system;
a first heat exchange system for cooling feed gas by indirect heat exchange
with a first
nitrogen-enriched bottoms liquid to produce cooled feed gas and vapor for the
column
system;
a first pressure reduction device for reducing the pressure of a second
nitrogen-enriched
bottoms liquid to produce reduced pressure bottoms liquid;
a second heat exchange system for cooling said cooled feed gas by indirect
heat exchange
against said reduced pressure bottoms liquid to produce at least partially
condensed feed
gas and vaporized bottoms liquid; and
a second pressure reduction device for reducing the pressure of said at least
partially
condensed feed gas to produce at least partially condensed feed gas at reduced
pressure
for use as said feed to the distillation column system.
#51. Apparatus according to aspect #50 comprising a third pressure reduction
device for
reducing the pressure of a third nitrogen-enriched bottoms liquid to produce
reduced pressure
26
CA 02957141 2017-02-06
bottoms liquid for vaporization by indirect heat exchange in said overhead
condenser to produce
nitrogen-enriched vapor.
#52. Apparatus according to aspect #51 comprising an expander for expanding
said nitrogen-
enriched vapor to produce expanded nitrogen-enriched vapor for warming by
indirect heat
exchange in said overhead condenser to produce warmed nitrogen-enriched vapor.
#53. Apparatus according to aspect #51 or aspect #52 comprising a fourth
pressure reduction
device for reducing the pressure of a fourth nitrogen-enriched bottoms liquid
to produce reduced
pressure bottoms liquid for vaporization by indirect heat exchange in said
overhead condenser to
produce nitrogen-enriched vapor.
#54. Apparatus according to #50 comprising an expander for expanding said
vaporized bottoms
liquid to produce expanded nitrogen-enriched vapor for warming by indirect
heat exchange in said
overhead condenser to produce warmed nitrogen-enriched vapor.
#55. Apparatus according to #54 comprising:
a fourth pressure reduction device for reducing the pressure of a fourth
nitrogen-enriched
bottoms liquid to produce reduced pressure bottoms liquid; and
a storage vessel for storing said reduced pressure bottoms liquid.
#56. Apparatus for recovering helium from a nitrogen-rich feed gas comprising
helium, said
apparatus comprising:
a distillation column system for operation at an elevated operating pressure
to separate at
least partially condensed feed gas into helium-enriched overhead vapor and
nitrogen-
enriched bottoms liquid(s);
an overhead condenser for partially condensing helium-enriched overhead vapor
by indirect
heat exchange to produce helium-enriched vapor as product and liquid for
reflux in the
column system;
a first pump for pumping a second nitrogen-enriched bottoms liquid to produce
pumped
bottoms liquid;
a first heat exchange system for cooling feed gas by indirect heat exchange
with said
pumped bottoms liquid to produce cooled feed gas and nitrogen-enriched vapor;
a second heat exchange system for cooling said cooled feed gas by indirect
heat exchange
against a first nitrogen-enriched bottoms liquid to produce at least partially
condensed feed
gas and vapor for the column system; and
a pressure reduction device for reducing the pressure of said at least
partially condensed
feed gas to produce at least partially condensed feed gas at reduced pressure
for use as
said feed to the distillation column system.
27
CA 02957141 2017-02-06
#57. Apparatus according to aspect #56 comprising a second pressure reduction
device for
reducing the pressure of a third nitrogen-enriched bottoms liquid to produce
reduced pressure
bottoms liquid for vaporization by indirect heat exchange in said overhead
condenser to produce
nitrogen-enriched vapor.
#58. Apparatus according to aspect #57 comprising an expander for expanding
said nitrogen-
enriched vapor to produce expanded nitrogen-enriched vapor for warming by
indirect heat
exchange in said overhead condenser to produce warmed nitrogen-enriched vapor.
#59. Apparatus according to aspect #57 or aspect #58 comprising a third
pressure reduction
device for reducing the pressure of a fourth nitrogen-enriched bottoms liquid
to produce reduced
pressure bottoms liquid for vaporization by indirect heat exchange in said
overhead condenser to
produce nitrogen-enriched vapor.
#60. Apparatus substantially as described herein with reference to the
accompanying examples
and/or drawings.
COMPARATIVE EXAMPLE 1
[0147] A computer simulation of the process depicted in FIG. 1 has been
carried out using Aspen
Plus (version 7.2, Aspen Technology Inc.). The resultant heat and mass
balance data for the key
streams is presented in Table 1.
90 100 104 105 106 110 111 114 118 119 124
Temperature C 48.9 -144.5 -151.8 -191.4 -147.3 -
154.5 -189.3 45.2
Pressure bar 30.0 30.0 25.0 1.5 30.0 25.0
25.0 25.0
Molar Flow kmol/s 0.278 0.278 0.272 0.272 0.000 0.278
0.000 0.169 0.006 0.006
Vapor Fraction 1.00 1.00 0.00 0.49 0.89 1.00
1.00 1.00
Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9489 0.9300
0.9590 0.1000 0.1000
Mole fraction Methane 0.0500 0.0500 0.0511 0.0511 0.0500
0.0020 0.0000 0.0000
Mole fraction Helium 0.0200 0.0200 0.0000 0.0000 0.0200
0.0390 0.9000 0.9000
126 128
Temperature C -184.1 45.2
Pressure bar 1.5 1.5
Molar Flow kmol/s 0.272 0.272
Vapor Fraction 1.00 1.00
Mole fraction Nitrogen 0.9489 0.9489
Mole fraction Methane 0.0511 0.0511
Mole fraction Helium 0.0000 0.0000
Product recompression 2899 kW
Total 2899 kW
TABLE 1
28
CA 02957141 2017-02-06
[0148] The power to recompress the product 128 to the feed pressure of 30 bar
is 2899 kW.
EXAMPLE 1
[0149] A computer simulation of the process depicted in FIG. 2 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 2.
90 100 104 105 106 110 111 114 118 119 124
Temperature C 48.9 -142.8 -151.8 -191.4 -147.3 -
155.5 -158.8 -189.3 46.9
Pressure bar 30.0 30.0 25.0 1.5 30.0 30.0
25.0 25.0 25.0
Molar Flow kmol/s 0.278 0.278 0.272 0.036 0.278
0,278 0.031 0.006 0.006 0.000
Vapour Fraction 1.00 1.00 0.00 0.49 0.90 0.04
1.00 1.00 1.00
Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9489 0.9300
0.9300 0.8150 0.1000 0.1000
Mole fraction Methane 0.0500 0.0500 0.0511 0.0511 0.0500
0.0500 0.0009 0.0000 0.0000
Mole fraction Helium 0.0200 0.0200 0.0000 0.0000 0.0200
0.0200 0.1841 0.9000 0.9000
126 128 134 138 142 144 164 168 170 172
Temperature C -160.8 46.9 -151.8 -157.5
-154.4 46.9
Pressure bar 1.5 1.5 25.0 18.6
18.6 18.2
Molar Flow kmol/s 0.036 0.036 0.236 0.236
0.236 0.236
Vapour Fraction 1.00 1.00 0.00 0.14
1.00 1.00
Mole fraction Nitrogen 0.9489 0.9489 0.9489 0.9489
0.9489 -- 0.9489
Mole fraction Methane 0.0511 0.0511 0.0511 0.0511
0.0511 0.0511
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000
Product recompression 806 kW
Expander power -10 kW
Total 796 kW
TABLE 2
[0150] In this example, only 13% of the helium-free product stream is boiled
at low pressure in
the column condenser. Product stream 170 is boiled at 18.6 bar and expanded to
18.2 bar in
expander 174. The total power (mostly product recompression power for streams
128 and 172) is
reduced by 73% from 2899 kW to 796 kW. In addition, because the vapour
fraction of the feed is
reduced, the vapor flow in the column above the feed location is reduced
significantly leading to a
reduction in the column diameter.
EXAMPLE 2
[0151] A computer simulation of the process depicted in FIG. 3 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 3.
29
CA 02957141 2017-02-06
90 100 104 105 106 110 111. 114 118 119 124
Temperature C 48.9 -140.7 -151.8 -191.4 -147.2 -
158.9 -161.9 -189.3 46.8
Pressure bar 30.0 30.0 25.0 1.5 30.0 30.0
25.0 25.0 25.0
Molar Flow kmolis 0.278 0.278 0.272 0.007 0.278 0.278
0.019 0.006 0.006
Vapour Fraction 1.00 1.00 0.00 0.49 0.92 0.02
1.00 1.00 1.00
Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9489 0.9300
0.9300 0.7038 0.1000 0.1000
Mole fraction Methane 0.0500 0.0500 0.0511 0.0511 0.0500
0.0500 0.0005 0.0000 0.0000
Mole fraction Helium 0.0200 0.0200 0.0000 0.0000 0.0200
0.0200 0.2957 0.9000 0.9000
126 128 134 138 142 144 146 164 168 170 172
Temperature C -163.3 46.8 -174.8 -163.3 -187.1 -
163.3 46.8 -151.8 -160.9 -155.5 46.8
Pressure bar 1.5 1.5 6.4 6.4 1.5 1.5 1.5
25.0 15.4 15.4 15.4
Molar Flow kmol/s 0.007 0.007 0.010 0.010 0.010 0.010
0.010 0.254 0.254 0.254 0.254
Vapour Fraction 1.00 1.00 0.36 1.00 0.96 1.00
1.00 0.00 0.20 1.00 1.00
Mole fraction Nitrogen 0.9489 0.9489 0.9489 0.9489 0.9489
0.9489 0.9489 0.9489 0.9489 0.9489 0.9489
Mole fraction Methane 0.0511 0.0511 0.0511 0.0511 0.0511
0.0511 0.0511 0.0511 0.0511 0.0511 0.0511
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
Product recompression 788 kW
Expander power -8 kW
Total 779 kW
TABLE 3
[0152] The advantage in this example is that the refrigeration is integrated
with the separation
process, and the amount of product available at pressure is increased - only
6.3% of the product is
at low pressure. The total power consumption is also slightly reduced (by
2.1%) to 779 kW.
EXAMPLE 3
[0153] A computer simulation of the process depicted in FIG. 4 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 4.
CA 02957141 2017-02-06
90 100 104 105 106 110 111 114 118 119 124
Temperature C 48.9 434.1 451.8 491.4 -144.0 -
149.9 -157.2 -189.3 46.9
Pressure bar 50.0 50.0 25.0 1.5 50.0 50.0
25.0 25.0 25.0
Molar Flow kmol/s 0.278 0.278 0.272 0.008 0.278 0.278
0.045 0.006 0.006
Vapour Fraction 1.00 1.00 0.00 0.49 1.00 0.00
1.00 1.00 1.00
Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9489 0.9300
0.9300 0.8711 0.1000 0.1000
Mole fraction Methane 0.0500 0.0500 0.0511 0.0511 0.0500
0.0500 0.0013 0.0000 0.0000
Mole fraction Helium 0.0200 0.0200 0.0000 0.0000 0.0200
0.0200 0.1276 0.9000 0.9000
126 128 134 138 142 144 146 164 168 170 172
Temperature C -159.3 46.9 -172.2 -159.3 -187.3 -
159.3 46.9 -151.8 -149.2 -140.0 46.9
Pressure bar 1.5 1.5 7.7 7.7 1.5 1.5 1.5
25.0 39.5 39.5 39.5
Molar Flow kmolis 0.008 0.008 0.038 0.038 0.038 0.038
0.038 0.226 0.226 0.226 0.226
Vapour Fraction 1.00 1.00 0.34 1.00 0.95 1.00
1.00 0.00 0.00 1.00 1.00
Mole fraction Nitrogen 0.9489 0.9489 0.9489 0.9489 0.9489
0.9489 0.9489 0.9489 0.9489 0.9489 0.9489
Mole fraction Methane 0.0511 0.0511 0.0511 0.0511 0.0511
0.0511 0.0511 0.0511 0.0511 0.0511 0.0511
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
Product recompression 765 kW
Expander power -35 kW
Pump power 28 kW
Total 757 kW
TABLE 4
[0154] In this case, part of the helium-free product 164 is increased in
pressure in a pump 165
and used to cool the feed in heat exchanger 169 upstream of the column
reboiler 108. The
refrigeration provided by the expander offsets the energy input to the process
in the pump. In the
example, the total power including recompression of the products back to the
feed pressure (50 bar
in this case) is 757 kW.
EXAMPLE 4
[0155] A computer simulation of the process depicted in FIG. 5 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 5.
31
CA 02957141 2017-02-06
90 100 104 105 106 110 111 114 118 119 124
Temperature C 48.9 -122.4 -151.8 -191.4 -134.2
-150.9 -156.1 -189.3 46.9
Pressure bar 30.0 30.0 25.0 1.5 30.0 30.0
25.0 25.0 25.0
Molar Flow kmoVs 0.278 0.278 0.272 0.005 0.278
0.278 0.066 0.006 0.006
Vapour Fraction 1.00 1.00 0.00 049 1.00 0.18
1.00 1.00 1.00
Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9489
0.9300 0.9300 0.9084 0.1000 0.1000
Mole fraction Methane 0.0500 0.0500 0.0511 0.0511
0.0500 0.0500 0.0017 0.0000 0.0000
Mole fraction Helium 0.0200 0.0200 0.0000 0.0000
0.0200 0.0200 0.0899 0.9000 0.9000
126 128 134 138 142 144 146 164 168 170 172
Temperature C -158.1 46.9 -156.3 -136.2 -188.3
-158.1 46.9
Pressure bar 1.5 1.5 19.8 19.8 1.5 1.5 1.5
Molar Flow kmoVs 0.005 0.005 0.215 0.215 0.215
0.215 0.215
Vapour Fraction 1.00 1.00 0.12 1.00 0.93 1.00
1.00
Mole fraction Nitrogen 0.9489 0.9489 0.9489 0.9489 0.9489
0.9489 0.9489
Mole fraction Methane 0.0511 0.0511 0.0511 0.0511 0.0511
0.0511 0.0511
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000
180 181 186 188 190
Temperature C -151.8 -194.2 -194.2 46.9
Pressure bar 25.0 1.1 1.1 1.1
Molar Flow kmoVs 0.052 0.025 0027 0.027
Vapour Fraction 0.00 0.00 1.00 1.00
Mole fraction Nitrogen 0.9489 0.8994 0.9957 0.9957
Mole fraction Methane 0.0511 0.1006 0.0043 0.0043
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000
Product recompression 2957 kW
Expander power -316 kW
Total 2640 kW
Liquid production (1.1 bow) 59 TPD
Power with no Squid (Example 3) 779 kW
Additional power for Liquid 1861 kW
Liquid specific power 762 kWh/t
TABLE 5
[0156] In the example, 9.2% of the product is produced as saturated liquid at
1.1 bar. The total
power including product recompression to 30 bar and net of the power
generation from the
expander of 316 kW is 2342 kW. 59 tonnes (t) per day of liquid is produced.
Compared to
Example 2, the total power is 1861 kW higher for the production of 59 tonnes
per day liquid,
meaning that the specific power for the liquid production is 762 kWh/t.
EXAMPLE 5
[0157] A computer simulation of the process depicted in FIG. 6 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 6.
32
c CA 02957141 2017-02-06
90 100 104 105 106 110 111 114 118 119 124
Temperature 48.9 -117.1 -151.8 -191.4 -130.0
-151.5 -156.4 -189.3 46.9
Pressure bar 30.0 30.0 25.0 1.5 30.0 30.0
25.0 25.0 25.0
Molar Flow kmol/s 0,278 0.278 0.272 0.005 0.278
0.278 0.059 0.006 0.006
Vapour Fraction 1.00 1.00 0.00 0.49 1.00 0.14
100 1.00 1.00
Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9489
0.9300 0.9300 0.8983 0.1000 0,1000
Mole fraction Methane 0.0500 0.0500 0.0511 0.0511
0.0500 0.0500 0.0016 0.0000 0,0000
Mole fraction Helium 0.0200 0.0200 0.0000 0.0000
0.0200 0.0200 0.1001 0.9000 0.9000
126 128 134 138 142 144 146 164 168 170 172
Temperature C -156.5 46.9 -154.0 -132.0 -1883 -
156.5 46.9
Pressure bar 1.5 1.5 22.4 22.4 1,5 1.5 1.5
Molar Flow krnol/s 0.005 0,005 0.235 0.235 0.235
0.235 0.235
Vapour Fraction 1.00 1.00 0.07 1.00 0.93 1.00
1,00
Mole fraction Nitrogen 0.9489 0.9489 0.9489 0.9489 0.9489
0.9489 0.9489
Mole fraction Methane 0.0511 0.0511 0.0511 0.0511 0.0511
00511 0.0511
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000
180 181 186 188 190
Temperature C -151.8 -186.8 -194.6 -194.6 46.9
Pressure bar 25.0 25.0 1.1 1.1 1.1
Molar Flow krnol/s 0.032 0.032 0.029 0.003 0.003
Vapour Fraction 0.00 0.00 0.00 1.00 1.00
Mole fraction Nitrogen 0.9489 0.9489 0.9442 0.9976 0.9976
Mole fraction Methane 0.0511 0.0511 0.0558 0.0024 0.0024
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
Product recompression 2935 kW
Expander power -364 kW
Pump power kW
Total 2570 kW
Liquid production (1.1 bare) 69 TPD
Power with no liquid (Example 31 779 kW
Additional power for Liquid 1791 kW
Liquid specific power 619 kWhit
TABLE 6
[0158] In this case, 107% of the product is produced as saturated liquid at
1.1 bar. The total
power including product recompression to 30 bar and net of the power
generation from the
expander of 364 kW is 2570 kW. 69 tonnes per day of liquid is produced.
Compared to Example
2, the total power is 1791 kW higher for the production of 69 tonnes per day
liquid, meaning that the
specific power for the liquid production is 619 kWh/t.
EXAMPLE 6
[0159] A computer simulation of the process depicted in FIG. 7 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 7.
33
CA 02957141 2017-02-06
90 100 104 105 106 110 111 114 118 119 124
Temperature C 48.9 -144.7 -151.7 -191.4 -147.3
-154.9 -158.5 -189.3 47.0
Pressure bar 50.0 30.0 25.0 1.5 30.0 30.0
25.0 25.0 25.0
Molar Flow kmolis 0,278 0.275 0.269 0.025 0.275
0.275 0.033 0.006 0.006
Vapour Fraction 1.00 1.00 0.00 0.49 0.85 0.05
1.00 1.00 1.00
Mole fraction Nitrogen 0.9200 0.9283 0.9473 0.9473
0.9283 0.9283 0.8271 0.1000 0.1000
Mole fraction Methane 0.0500 0.0504 0.0515 0.0515
0.0504 0.0504 0.0010 0.0600 0.0000
Mole fraction Helium 0.0200 0.0202 00000 0.0000
0.0202 0.0202 0.1719 0.9000 0.9000
Mole fraction Ethane 0.0080 0.0011 clam 0.0012
0.0011 0.0011 0.0000 0.0000 0.0000
Mole fraction Propane 0.0020 0.0000 a0000 0,0000
0.0000 0.0000 0.0000 0.0000 0.0000
126 128 134 138 142 144 146 164 168 170 172
Temperature C -157.0 47.0 -156.9 -109.5 -181.0
-157.0 47.0
Pressure bar 1.5 1.5 19.2 19.2 1.5 1.5 1.5
Molar Flow kmolis 0.025 0.025 0.200 0.200 0.200
0.200 0.200
Vapour Fraction 1.00 1.00 0.13 1.00 1.00 1.00
1.00
Mole fraction Nitrogen 0.9473 0.9473 0.9473 0.9473 0.9473
0.9473 0.9473
Mole fraction Methane 00515 0.0515 0.0515 00515 0.0515
0.0515 0.0515
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000
Mole fraction Ethane 0.0012 0.0012 00012 0.0012 0.0012
0.0012 0.0012
Mole fraction Propane 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000
180 181 186 188 190 191 193 194 196 199
Temperature C -151.7 -187.3 -194.6 -194.6 47.0
-37.7 -65.7 -142.9 -150.7 18.5
Pressure bar 25.0 25.0 1.1 1.1 1.1 50.0
30.0 30.0 50.0 30.0
Molar Flow kmoVs 0.044 0.044 0.040 0.004 0.004
0.262 0.262 0.262 0.015 0.002
Vapour Fraction 0.00 0.00 0.00 1.00 1.00 1.00
1.00 0.99 0.00 0.00
Mole fraction Nitrogen 0.9473 0.9473 0.9428 0.9976 0.9976
0.9200 0.9200 0.9200 0.9200 0.0000
Mole fraction Methane 0.0515 0.0515 00559 0.0024 0.0024
0.0500 0.0500 0.0500 0.0500 0.0100
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
00200 0.0200 0.0200 0.0200 0.0000
Mole fraction Ethane 0.0012 0.0012 0.0013 0.0000 0.0000
0.0080 0.0080 0.0080 0.0080 0.7685
Mole fraction Propane 0.0000 0.0000 0.0000 0.0000 0.0000
0.0020 0.0020 0.0020 0.0020 0.2215
Product recompression . 3411 kW
Expander power -363 kW
Warm expander power -183 kW
Total 2864 kW
Liquid production (1.1 bare) 94 TPD
Power with no liquid (Example 4) 757 kW
Additional power for Liquid 2107 kW
Liquid specific power 537 kWh/T
TABLE 7
[0160] In this case, the feed is at 50 bar as in Example 3, but is expanded in
warm expander 192
prior to separation in NGL recovery column 96. A small part of the high
pressure feed is
condensed and fed to the top of the NGL recovery column as reflux. This column
is reboiled with
an external heat source such as steam, hot oil or cooling water. The liquid
production is higher
than in Example 5 because of the higher feed pressure and additional
refrigeration provided by the
warm expander. The specific power for liquid production is also lower as the
warm and cold
expander system provides refrigeration more efficiently than a single
expander. The total power
including product recompression to 50 bar and net of the power generation from
the expanders of
546 kW is 2864 kW. 94 tonnes per day of liquid is produced. Compared to
Example 3 (which also
has a feed pressure of 50 bar), the total power is 2107 kW higher for the
production of 94 tonnes
per day liquid, meaning that the specific power for the liquid production is
537 kWh/t.
34
CA 02957141 2017-02-06
EXAMPLE 7
[0161] A computer simulation of the process depicted in FIG. 8 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 8.
90 100 104 105 106 110 111 114 118 119 124
leer C perature 48.9 -144.6 -151.8 -147.5 -
155.7 -159.0 -189.3 46.9
Pressure bar 30.0 30.0 25.0 30.0 30.0
25.0 25,0 25.0
Molar Flow kmol/s 0.278 0.278 0.272 0.278
0.278 0.030 0.006 0.006
Vapour Fraction 1.00 1.00 0.00 0.85 0.04
1.00 1.00 1.00
Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9300
0.9300 0.8090 0.1000 0.1000
Mole fraction Methane 0.0500 0.0500 0.0511 0.0500
0.0500 0.0009 0.0000 0.0000
Mole fraction Helium 0.0200 0.0200 0.0000 0.0200
0.0200 0.1902 0.9000 0.9000
126 128 134 138 142 144 146 164 168 170 172
Tem C perature -151.8 -116.3 -183.7 -155.6
46.9
Pressure bar 25.0 18.2 1.5 1.5
1.5 .
Molar Flow kmol/s 0.239 0.208 0.208 0.227
0.227
Vapour Fraction 0.00 1.00 0.99 1.00 1.00
Mole fraction Nitrogen 0.9489 0.9413 0.9413 0.9947
0.9947
Mole fraction Methane 0.0511 0.0587 0.0587 0.0053
0.0053
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000
0.0000
180 181 186 188 190 191 193 194 196 199 200
Temperature C -153.2 -188.2 -195.1
-195,1 46.9 -151.6
Pressure bar 25.0 25.0 1.1 1.1
1.1 25.0
Molar Flow kmol/s 0.031 0.031 0.029
0.002 0.002 0.239
Vapour Fraction 0.00 0.00 0.00 1.00
1.00 0.22
Mole fraction Nitrogen 0.9990 0.9990 0.9989
0.9999 0.9999 0.9489
Mole fraction Methane 0.0010 0.0010 0.0011
0.0000 0.0000 0.0511
Mole fraction Helium 0.0000 0.0000 0.0000
0.0001 0.0001 0.0000
210 222 226 250 252 270 274 276
Temperature C -151.6 -150.3 -191.3 -151.8 -188.5
-167.1 -166.3 46.9
Pressure bar 25.0 18.2 1.5 25.0 25.0 1.5
6.0 6.0
Molar Flow kmol/s 0.208 0,208 0.227 0.033 0.033
0.013 0.013 0.013
Vapour Fraction 0.00 1.00 1.00 0.00 0.00 0.00
0.00 1.00
Mole fraction Nitrogen 0,9413 0.9413 0.9947 0.9489 0.9489
0.0500 0.0500 0.0500
Mole fraction Methane 0,0587 0.0587 0.0053 0.0511 0.0511
0.9500 0.9500 0.9500
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000
Product recompression 2868 kW
Expander power -354 kW
Pump power 1 kW
Total 2515 kW
Liquid production (1.1 bare) 70 TPD
Power with no liquid (Example 3) 779 kW
Additional power for Liquid 1736 kW
Liquid specific power 596 kWhir
TABLE 8
[0162] In this case, the total power including product recompression to 30 bar
and net of the
power generation from the expander of 354 kW is 2515 kW. 70 tonnes per day of
liquid is
produced. Compared to Example 2, the total power is 1736 kW higher for the
production of 70
tonnes per day liquid, meaning that the specific power for the liquid
production is 596 kWh/t.
EXAMPLE 8
[0163] A computer simulation of the process depicted in FIG. 9 has been
carried out using Aspen
Plus. The resultant heat and mass balance data for the key streams is
presented in Table 9.
CA 02957141 2017-02-06
90 100 104 105 106 110 111 114 118 119 124
Temperature C 48.9 -145.4 -151.8 -155.6 -
159.9 -189.3 46.9
Pressure bar 50.0 30.0 25.0 30.0 25.0
25.0 25.0
Molar Flow krnol/s 0.278 0.275 0.270 0.275
0.032 0.008 0.008
Vapour Fraction 1.00 1.00 000 0.04 1.00
1.00 1.00
Mole fraction Nitrogen 0.9200 0.9286 0.9477 0.9286
0.7784 0.1000 0.1000
Mole fraction Methane 0.0500 0.0504 0.0514 0.0504
0.0008 0.0000 0.0000
Mole fraction Helium 0.0200 0.0202 0.0000 0.0202
0.2208 0.9000 0.9000
Mole fraction Ethane 0.0080 0.0008 0.0008 0.0008
0.0000 0.0000 0.0000
Mole fraction Propane 0.0020 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000
126 128 134 138 142 144 146 164 168 170 172
Temperature C -123.0 -184.9 46.9
Pressure bar 18.2 1.5 1.5
Molar Flow kmol/s 0.227 0.227 0.243
Vapour Fraction 1.00 0.98 1.00
Mole fraction Nitrogen 0.9442 0.9442 0.9947
Mole fraction Methane 0.0549 0.0549 0.0053
Mole fraction Helium 0.0000 0.0000 0.0000
Mole fraction Ethane 0.0009 0.0009 0.0000
Mole fraction Propane 0.0000 0.0000 0.0000
180 181 186 188 190 191 193 194 196 199 200
Temperature C -189.2 -195.1 -195.1 46.9 -33.6 -
66.6 -143.6 -160.0 18.2 -151.4
Pressure bar 250 1.1 1.1 1.1 50.0 30.0
30.0 50.0 30.0 25.0
Molar Flow kmol/s 0.044 0.041 0.003 0.003 0.264
0.264 0.264 0.014 0.003 0.241
Vapour Fraction 0.00 0.00 1.00 1.00 1.00 1.00
0.98 0.00 0.00 0.30
Mole fraction Nitrogen 0.9990 0.9989 0.9999 0.9999 0.9200
0.9200 09200 0.9200 0.0000 0.9477
Mole fraction Methane 0.0010 0.0011 0.0000 0.0000 0.0500
0.0500 0.0500 0.0500 0.0100 0.0514
Mole fraction Helium 0.0000 0.0000 0.0001 0.0001 0.0200
0.0200 0.0200 0.0200 0.0000 0.0000
Mole fraction Ethane 0.0000 0.0000 0.0000 0.0000 0.0080
0.0080 0.0080 0.0080 0.7759 0.0008
Mole fraction Propane 0.0000 0.0000 0.0000 0.0000 0.0020
0.0020 0.0020 0.0020 0.2141 0.0000
210 222 226 250 252 270 274 276 280 288 302
Temperature C -151.4 -191.3 -189.0 -164.1 -163.2
46.9 46.9 40.0 46.9
Pressure bar 25.0 1.5 25.0 1.5 6.0 6.0 1.5
18.2 25.0
Molar Flow kmolis 0.196 0.243 0.029 0.013 0.013 0.013
0.031 0.031 0.006
Vapour Fraction 0.00 1.00 0.00 000 0.00 1.00
1.00 1.00 1.00
Mole fraction Nitrogen 0.9362 0.9947 0.9477 0.0330 0.0330
0.0330 0.9947 0.9947 0.0000
Mole fraction Methane 0.0628 0.0053 0.0514 0.9500 0.9500
0.9500 0.0053 0.0053 0.0000
Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 1.0000
Mole fraction Ethane 0.0010 0.0000 0.0008 0.0167 0.0167
0.0167 0.0000 0.0000 0.0000
Mole fraction Propane 0.0000 0.0000 0.0000 0.0003 0.0003
0.0003 0.0000 0.0000 0.0000
304 312 314
Temperature C 46.9 40.0 -150.0
Pressure bar 1.3 25.0 25.0
Molar Flow kmolfs 0.002 0.002 0.002
Vapour Fraction 1.00 1.00 1.00
Mole fraction Nitrogen 0.3571 0.3571 0.3571
Mole fraction Methane 0.0000 0.0000 0.0000
Mole fraction Helium 0.6429 0.6429 0.6429
Mole fraction Ethane 0.0000 0.0000 0.0000
Mole fraction Propane 0.0000 0.0000 0.0000
Product recompression 3741 kW
Expander power -369 kW
Warm expander power -183 kW
Tail gas compression 29 kW
Recycle compression 332 kW
Pump power 1 kW
Total 3550 kW
Liquid production (1.1 bare) 100 TPD
Power with no liquid (Example 4) 757 kW
Additional power for Liquid 2793 kW
Liquid specific power 670 kWhil-
TABLE 9
36
CA 02957141 2017-02-06
[0164] The total power including recycle and tail gas compression as well as
product
recompression to 50 bar and net of the power generation from the expanders of
552 kW is 3550
kW. 100 tonnes per day of liquid is produced. Compared to Example 3 (which
also has a feed
pressure of 50 bar), the total power is 2793 kW higher for the production of
100 tonnes per day
liquid, meaning that the specific power for the liquid production is 670
kWh/t.
[0165] While the above has been described with reference to the preferred
embodiments
depicted in the figures, it will be appreciated that various modifications are
possible within the spirit
or scope of the disclosure.
[0166] In this specification, unless expressly otherwise indicated, the word
'or' is used in the
sense of an operator that returns a true value when either or both of the
stated conditions are met,
as opposed to the operator 'exclusive or' which requires only that one of the
conditions is met. The
word 'comprising' is used in the sense of 'including' rather than to mean
'consisting of'. No
acknowledgement of any prior published document herein should be taken to be
an admission or
representation that the teaching thereof was common general knowledge in
Australia or elsewhere
at the date thereof.
37
