Note: Descriptions are shown in the official language in which they were submitted.
` . - W~ 93/16338 ~ PC-r/U593/U1808
A PROCES5 FOR EXTR~CTING V~POR FROM ~ G2!~S STRE~M
Field of the Invention Z~Z9003
The present invention relates to a process for
extracting vapor components from a multi-component gas
stream using a vortex tube.
Back~round of the Invention
Although vortex tubes are well known in the art,
such devices have not gained wide acceptance due to a
limited understanding of the thermodynamic principles
involved. As a result few practitioners have studied
the features of gas behavior in a vortex tube or adapted
use of the vortex tube into gas separation technology.
First observed in the 1930's, the vortex tube is
responsible for the so-called Ranque effect wherein a
lS gas at higher pressure which is throttled in a
centrifugal field set up in a tube will separate into
two outlet streams: one which is cooler and one which is
hotter than the temperature of the gas feed. In a
vortex tube, the gas stream is fed tangentially to the
~0 tube wall and expanded in the tube. The vortex thus
formed creates an intense centrifugal field within which
gas dynamic transport processes and to a lesser extent
Joule-Thomson (J~) cooling establish temperature,
pressure and compositional gradients in the tube both
axially and radially. The net result is that the vortex
core which becomes cooled flows in the opposite
direction to the vortex periphery which becomes heated.
The coolest gas occurs at the end of the tube in the
cool flow direction and the hottest gas occurs at the
end of the tube in the hot flow direction. Vapor
components of the feed gas, if close to their dew point,
initially condense in the core and are flung to the
periphery by centrifugal action. However, condensate
thus formed becomes heated and re-vaporized. The
3~ fraction of the peripheral stream which does not exit
the hot end migrates back to the core and gets re-
:
O93/16338 PCrl/US93/~l808Z~29003
,
condensed as it flows in the cool direction. This
condensate is then generally flung back to the
peripheral stream before it can exit the cold end. As a
result, condensate vapors entering the vortex tube with
the feed are concentrated in and mostly discharged with
the hot stream, and the cold stream exhausts as an
essentially dry, saturated stream.
Fulton U S. Patents 3,173,273 and 3,208,229, the
disclosures of which are hereby incorporated herein by
reference, describes basic designs for most efficient
vortex tube operation. The characteristic performance
curve for a typical vortex tube as described by Fulton
having the hot side insulated and operating under ideal
gas conditions, where the Joule-Thomson cooling effect
is negligible, is shown in Fig. 1, which is a graph of
the hot side and cold side outlet stream temperature
change (~Th-~Tc) with respect to the feed temperature (~f) .
versus the fraction of the feed stream (xc) which exits
~ ,. .
the tube through the cold end. Typically, the maximum
temperature drop in the cold stream is about 50 percent
of an adiabatic temperature drop occurring for the same
pressure drop a~ the cold outlet. This generally occurs
at a cold fraction of 0.4 or less. In terms of
temperature differential alone between the hot and cold
streams (~Th-aTc), however, this differential is about 83
percent of the adiabatic temperature drop. As a greater
fraction is withdrawn from the cold end up to about 7S
percent optimally, the temperature drop in the cold
stream alone becomes lower (about 30% at ~c=0.75) but the
temperature spread (~Th-~TC) increases to about 120
percent of the adiabatic temperature drop for the
corresponding pressure drop at the cold outlet. Under
real gas conditions, for example at h~gh pressures or
low temperatures, the overall cooling experienced in a
vortex tube is even larger because the Joule-Thomson
cooling effect is superimposed over the Ranque effect.
: ~:
SU8ST~TUTE SHEET
W~93/16338 ~ 3PCT/US9l/01~08
Advantageous features of a vortex tube are an
absence of moving parts and reduced utility requirements
in comparison with an expansion turbine, for example.
The cooling effect of a vortex tube has been used
in the past to recover liquids from gas streams. Fekete
U. S. Patent 3,775,988 describes the use of cold flow
vortex tube expansion principles in liquefaction and
cold-producing processes wherein the vortex `tube
substitutes for an expansion turbine. Fekete U. S.
Patent 4, 458,~94 describes the use of an improved
vortex tube in a gas-liquid separation process wherein
vaporization of the liquid in the peripheral stream of
the tube is retarded by either cooling a short section
of the periphery with a tube cooling jacket or by taking
the liquid out at a short distance from the tube inlet,
where the heating effect is minimal, and insulating the
liquid from the heating effect.
Shirokov et al. U. S. Patent 4,185,977 describes a
process of separating hydrocarbon from gaseous mixtures
to produce hydrogen. The process resides in cooling a
gas mixture comprising hydrogen, methane and olefins in
heat exchangers by stages with the resulting liquid
condensate being separated at each stage. The products
obtained are a liquid condensate of olefins, liquid
~5 methane/hydrogen, and an enriched hydrogen vapor stream.
The liquid methane condensate with an admixture of
hydrogen is evaporated and expanded with the use of a
vortex effect. The resulting cold and hot streams are
fed separately to the heat exchangers as a heating or
cooling medium. The hydrogen-rich vapor portion is also
expanded with the use of a vortex effect to yive a cold
stream consisting of pure hydrogen whereupon the cold
and hot streams are fed separately to heat exchangers
each having an appropriate temperature.
Shirokov et al. U. S. Patent 4, 257,794 describes a
process of separating a gaseous hydrocarbon mixture of
methane, olefins and hydrogen residing in cooling the
mixture by stages with the resulting liquid condensate
... _. . ~,;
~VO93/lC338 PCrt~S93/~1~08
ZlZ~OO;~ '
'!~ 4
of olefins and methane being withdrawn at each stage,
recovering a gaseous hydrogen-methane mixture with some
mixed ethylene produced by demethanization in a
demethanizer column and further cooling the same. The
resulting condensate thus withdrawn is adapted for use
as a spraying means in the demethanization. The
remaining gaseous methane-hydrogen mixture is expanded
with application of a vortex effect to produce hot and
cold streams. The hot and cold streams are mixed, with
the cold stream having first passed countercurrently
against the methane-hydrogen-ethylene mixture, and again
expanded with application of a vortex effect. The
resulting hot stream is fed countercurrently against the
hydrocarbon stream being separated and the cold stream
countercurrently against the methane-hydrogen-ethylene
mixture.
,. ~
Rosenkov et al. Russian patent publication
SU1160211-A describes a hydrocarbon cooling method
including the throttling of a liquid stream from a
~0 vortex pipe which stream is used for cooling the vortex
pipe hot end.
Heat exchanger equipment having a high thermal
effectiveness coefficient are described in W. M. Kays
and A.L. London, Compact Heat Exchanqers, 3rd ed. 1984,
~5 New York:McGraw Hill; and D. Chisolm (Ed), Develo~ments
in Heat Exchanqer _TechnoloaY-l, Applied Science
Publications, 1980, Chapter 5, Usher et al., "Compact
Heat Exchangers" which are hereby incorporated herein by
reference.
....
Other references of interest include Atkinson U. S.
Patent 2,683,972 and Fekete, The Oil and Gas Journal,
June 15, 1970, pp. 71-73.
The cooling effect of the vortex tube has generally
been utilized in combination with heat exchangers of low .
thermal efficiency ~nd has been confined to relatively
high pressure applications. It is well known that a
minimum pressure ratio for the expansion is necessary to
achieve the effect desired in a vortex tube and that
SUBSTTTUTE SHEET ~ `
` . \~'0 93/16338 ; . -- PCI/US93/01808
i ~ x~.~son3
S
increasing the expansion prèssure drop enhances the
cooling obtained. There are however, many low pressure
gas streams containing condensable vapors such as flared
waste gas streams and exhaust fumes fr~m sulfide ore
smelters where the JT cooling effect is negligible,
economic value of the gas stream is low in relation to
the cost of compressor equipment and the use of
expanders is impractical. It would be advantageous to
be able to recover valuable liquids, (e. g-,
hydrocarbons) from these streams as well.
summarv of the Invention
The liquid extraction process of the present
invention incorporates high efficiency heat exchangers
with vortex expansion to enhance the performance of a
vortex tube for condensing vapors in a feed stream. As
a result of the improvement, less e~onomic lower
pressure gas streams can be treated in the present
process to recover hydrocarbon feed components otherwise
burned.
In one embodiment, the present invention comprises
a process for ~xtracting vapor from a gas stream. As
one step, a raw high pressure gas stream rich in
condensable vapor is p~rtially condensed by an exchange
of heat with a cooling medium comprising a cold exhaust
~5 stream from a vortex tube. As another step, condensate
is separated from the raw gas stream to produce a raw
lean gas stream. The raw lean gas stream is expanded in
the vortex tube to produce the cold exhaust stream and a
hot exhaust stream. The cold exhaust stream is ejected
with the hot exhaust stream in an ejector to give a
mixed vortex tube exhaust stream and increase the
pressure differential throùgh the vortex tube. While
ejection is a particularly preferred means for mixing
the cold and hot exhaust streams, any mixing means can
be used.
`: ` :
~VO93/16338 PCT/US93/~t~i
Z~Z90103 ,'
In a preferred embodiment, a recirculating flow in
the vortex tube is cooled by an exchange of heat with
the cold exhaust stream. The hot exhaust stream is
partially condensed by an exchange of heat with the
S mixed vortex tube exhaust stream. Alternatively, the
hot exhaust stream is partially condensed by an exchange
of heat with the cold exhaust stream prior to the cold
and hot exhaust stream mixing step. The partially
condensed hot exhaust stream is optionally mixed with
the condensate separated from the raw feed stream to
form a mixed condensate-containing hot exhaust stream.
Condensate is separated from the mixed condensate hot
exhaust stream to form a mixed liquid stream and a lean
hot exhaust stream. The recirculation flow in the
1~ vortex tube is optionally further cooled by an exchange
of heat with a liquid cooling medium -comprising the
mixed liquid stream, wherein the mixed liquid stream
remains substantially liquid.
When necessary, the condensate liquid can be
stripped of any volatile components which can re~
vaporize in any cooling step employing a liquid cooling
medium. In which case, the mixed liquid stream rich in
volatiles is fed to a stripping column prior to the step
of liquid cooling the recirculation flow in the vortex
tube. Volatiles are stripped from the mixed liquid
stream to produce a volatiles-rich overhead and a
volatiles-lean liquid bottoms. The column is heated by
an exchange of heat with the raw high pressure stream
prior to the raw stream partial condensing step. The
rich gas overhead is mixed with the lean hot exhaust
stream, whereas the lean liquid bottoms comprises the
liquid cooling medium in the liquid cooling step. In an
alternative arrangement, the column is heated by an
exchange of heat with the hot exhaust stream prior to
3~ the hot exhaust stream partial condensing step.
Depending on the composition and condition of the
raw gas_stream, the hot exhaust stream can be precooled
by an exchange of heat with the mixed exhaust stream
SUBSTlTl)TE SHET
`. w~ g3/l6338 `~ ~Z~)03 ~cr/~sy3/ol8o8
prior to the hot exhaust stream partial condensing step.
The hot exhaust stream can be further precooled prior to
the hot exhaust stream partial condensing step by an
exchange of heat with the liquid cooling medium. The
cold exhaust stream comprises 50 percent or more,
preferably 60 to about 80 percent of the raw lean gas
stream.
In another embodiment, the present invention
provides an apparatus for extracting vapor from a gas
stream. The apparatus comprises a high pressure partial
condenser for condensing condensable vapor from raw high
pressure gas stream using a cold exhaust stream as a
cooling medium and a high pressure liquid-gas separator
for separating condensate from the raw gas stream. A
vortex tube expands a lean raw gas stream from the high
pressure separator to produce the cold exhaust stream
and a hot exhaust stream. An ejector is preferably used
for mixing the hot and cold exhaust streams and
increasing the pressure differential through the vortex
tube, however, any kind of mixer can be used.
In a preferred embodiment, the apparatus comprises
a first vortex tube heat exchanger integrally attached
at a hot exhaust discharge end of the vortex tube for
cooling a recirculation flow in the vortex tube using
the cold exhaust stream as cooling medium. A low
pressure partial condenser is preferably disposed
downstream of the vortex tube for partially condensing
condensable vapor in the hot exhaust stream having the
mixed exhaust stream as cooling medium. A line from the
low pressure partial condenser optionally mixes the
partially condensed hot exhaust stream with the
condensate separated from the raw high pressure stream
to form a mixed condensate hot exhaust stream. A low
pressure separator separates condensate from the
condensate-containing hot exhaust stream to form a mixed
liquid stream and a lean hot exhaust stream. An
optional second vortex tube heat exchanger integrally
attached to the hot exhaust discharge end of the vortex
~ ~",
~v093/lG338 r~CT/US93/01~08
. 2lzson3 ,
tube further cools the recirculation in the vortex tube
by employing the mixed liquid stream as cooling medium,
wherein the mixed liquid stream remains substantially
liquid.
When necessary, the apparatus can use a stripper to
remove volatile components from the liquid stream
cooling medium which can become re-vaporized in any
liquid cooled heat exchanger. Therefore, a stripping
column can be disposed upstream of the second vortex
tube exchanger and have a reflux reboiler for stripping
volatiles from the volatiles-rich mixed liquid stream to
produce a volatiles-rich gas overhead stream and a
volatiles-lean liquid bottoms stream. A line from the
low pressure liquid-gas separator directs the volatiles-
rich mixed liquid stream to the stripping column. Anoverhead line from the stripper mixes the rich overhead
stream with the lean hot exhaust stream from the low
pressure liquid-gas separator. A bottoms line from the
stripper directs the lean liquid stream as cooling
medium to the second vortex heat exchanger. A feed line
directs the raw high pressure gas prior to the raw
stream partial condenser to the reflux reboiler as
heating medium. Alternatively, the reboiler is disposed
upstream of the high pressure partial condenser and
~5 employs the hot exhaust stream as heating medium.
Depending on the composition and condition of the
raw gas stream, the apparatus can use one or more gas
and/or liquid cooled precoolers upstream of the low
pressure partial condenser and/or liquid cooled vortex
exchanger_for precooling the hot exhaust stream. The
cooling medium can be mixed exhaust stream and/or a
suitably lean liquid stream. Alternatively, the gas
cooled precooler can be disposed upstream of the mixer
or ejector and can use the cold exhaust stream as
33 cooling medium. The cold exhaust stream comprises 50
percent or more, but preferably about 60 to about 80
percent of the raw lean gas stream.
, ~,"
':
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SUBS~mJTE SHEET :~
~,', ~
W~93/16338 i~ `- PCT/US93/01808
2129003
Brief Description of the Drawinqs
Fiq. 1 is a graph of a temperature difference of
vortex tube feed and exhaust stream temperature versus
the fraction of the stream taken off as the cold exhaust
stream (QThot (Thot Tfeed~. ~Tcold=~Tcold-Tfeed) vs- xcold) showing
a representation of vortex tube expansion behavior for a
representative gas stream.
Fig. 2 is one embodiment of the present process
showing a vortex tube for expanding a feed gas to
~0 produce a cold exhaust stream, a high pressure partial
condenser for condensing condensables from the feed
stream using the cold exhaust stream as cooling medium,
a high pressure liquid-gas separator for separating the
condensate and an ejector for mixing the hot and cold
exhaust streams and increasing the pressure ratio
through the vortex tube.
Fig. 3 is another embodiment of the process of Fig.
2 showing a vortex tube heat exchanger integrally
attached to a hot discharge end of the vortex tube
cooling a recirculation flow in the vortex tube using
the cold exhaust stream as cooling medium. ,
Fig. 4 is another embodiment of the process of Fig.
3 showing another vortex tube heat exchanger integral to
the hot discharge end of the vortex tube using the
~5 condensate as the cooling medium, a low pressure partial
condenser for partially condensing condensables in the
hot exhaust gas wherein the ejector stream is used as
cooling medium and a low pressure liquid-gas separator
for separating condensa~e from the partially condensed
30 hot exhaust stream. ;~ ~ ;
Fig. 5 is a further embodiment of the process of
Fig. 4 showing a liquid cooled precooler for the hot
exhaust stream prior to the low pressure partial
condenser using the liquid stream as cooling medium.
Fig. 6 is another embodiment of the process of Fig.
4 showing-a volatiles stripping column for stripping any
::
~v093/1633s ~' 1'Cr/US93/01808
- 2129~)03
volatile components from the condensate produced 'by the
partial condensers, wherein the feed gas is heating
medium for the reboiler duty and the liquid cooled
vortex tube heat exchanger is eliminated.
Fig. 7 is another embodiment of the process of Fig.
6 showing a gas cooled precooler for the hot exhaust
stream prior to the low pressure partial condenser using
the ejector stream as cooling medium, and the precooled
hot gas stream as heating medium for the stripping
column reboiler duty.
Fig. 8 is another embodiment of the process of Fig.
5 showing a gas cooled precooler for the hot exhaust
stream disposed upstream of the liquid cooled precooler
wherein the ejector stream is used as cooling medium.
Fig. g is another embodiment of the process of Fig.
8 except that both the gas cooled precooler and the
liquid cooled precooler are removed and the cooling
medium in the low pressure partial condenser is the cold
exhaust stream instead of the ejector stream.
. .
Detailed Description of the Inve~tion
A vortex tube expansion in conjunction with high
thermal efficiency heat exchangers are used to enrich
and condense condensable vapors from a gas stream such
as natural gas. In the vortex tube, a separation effect
~5 due to gas dynamic phenomena enriches a hot exhaust
stream. A temperature differential between the hot
exhaust stream and a cold exhaust stream due to pressure
expansion can be used to partially condense the hot
exhaust stream. An ejector can be used to increase the
pressure differential through the vortex tube for
enhanced results. ,The present process efficiently takes
advantage of vortex tube behavior to eliminate the need
for equipment having moving parts such as an turbine
expander in an ordinary gas separation/vapor extraction
process.
'~
SUBSTITUTE S~IE~
WO93/16338 ~ 21~0~3 PCT/US93/01808
The basis for the present invention is: ~1) to
precool the feed gas stream prior to admission to the
vortex tube using the vortex tube cold exhaust stream as
cooling medium; (2) to cool a vortex tube hot exhaust
stream externally using the cold exhaust stream as
cooiing medium; (3) to cool the re-circulating flow
within the vortex tube directly and the hot exhaust
stream indirectly using the cold exhaust stream as
cooling medium; and (4) to preferably eject the cold or
hot exhaust stream using the other exhaust stream as
carrier. Hi~h thermal efficiency heat exchangers are
preferably used to cope with close temperature
approaches. To cool the recirculating flow, cooling is
preferably applied directly to the vortex tube walls
]S itself by integrating one or more high thermal ;~
efficiency heat exchangers into the vortex tube
construction.
By definition, "cold exhaust stream" refers to a
stream originating at a cold exhaust discharge port of
20 the vortex tube and "hot exhaust stream" refers to a i
stream originating at a hot exhaust discharge port of
the vortex tube. A "mixed exhaust stream" is a stream
comprising a mixture of a least a portion of the cold
and hot exhaust streams. However, a mixed stream
comprising, for example, a hot exhaust stream and a
portion of the raw feed gas but none of the cold exhaust
stream is still defined as a "hot exhaust stream.l' The i~
terms "thermal effectiveness" or "thermal effectiveness
coefficient" are adopted from Xays et al. to refer to
exchanger- heat transfer effectiveness. Thermal
effectiveness is defined as the ratio between the actual
heat transferred and the maximum amount of heat transfer
which is theoretically possible.
Referring to Figs. 2-9 wherein like referenced
numerals refer to like parts, a pressurized and
dehydrated raw feed gas such as natural gas from a gas
field production, for example, containing condensable
vapors such as C2~ is fed in line 12 to a high pressure
~VO93/16338 PCT/US~3/Cl"~
21ZsO03
~` 12
feed partial condenser 14 of the present vapor
extraction process 10 of the present invention. In the
partial condenser 14, condensa~le vapor components are
at least partially condensed from the raw gas by an
exchange of heat with a cooling medium in line 16
co~prising a cold exhaust stream produced by a vortex
expansion in a vortex tube 18. A partially condensed
effluent from the partial condenser 14 is fed through
line 20 to a high pressure separator 22 such as, for
example, a cyclone, filter, drum or other impingement
knockout device. In the high pressur~ separator 22,
condensate separated from an uncondensed portion of the
raw feed stream is removed through line 24 for storage
or further processing. The uncondensed portion of the
raw feed comprising uncondensed vapor and gas is fed
through line 26 to the vortex tube 18. In the vortex
tuke 18, the higher pressure raw feed is conventionally
throttled to a lower pressure in a vortex expansion.
Although not shown, the raw feed stream is fed to the
vortex tube 18 using a tangential nozzle as known in the
art. Other conventional vortex tube internal components
(not shown) include an orifice, associated ducts,
plenum, diffuser, generator, torque brake, and the like
described, for example, in Fulton and/or Fekete.
The vortex tube 18 has a warming section 28
terminating in a hot exhaust discharge port 30 and a
cooling section 32 terminating in a cold exhaust
discharge port 34. A lower pressure hot stream exhausts
from the vortex tube hot discharge port 30 through a
line 36 and a lower pressure cold stream exhausts from
the vortex tube cold discharge port 34 through line 16.
In addition to lower pressure, the hot exhaust stream in
line 36 typically has a higher temperature than the raw
feed stream in line 26 and is enriched with the
condensable vapor components of the raw feed stream.
Besides a lower pressure, which is substantially lower
than that o~ the hot exhaust stream in line 36, the cold
exhaust stream in line 16 typically has a cooler
SUBSllTUTE SHEET
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l3
temperature than the raw feed stream in line 26 and is
leaner in condensable vapor components than the raw feed
stream. The cold exhaust stream in line 16 typically
comprises at least 50 percent of the feed stream in line
26 but preferably from about 60 to about 80 percent of
the feed stream in line 26.
The cold exhaust stream, used as cooling medium in
the partial condenser 14 as described above, is fed
through line 38 to an ejector 40. In the ejector 40,
the cold exhaust stream in line 38 is ejected by the hot
exhaust stream in line 36 and mixed thereby. A mixed
stream comprising the cold and hot exhaust streams is
removed through line 42. The ejector 40 is preferably
used to lower the pressure of the ejected stream (in
this case the cold exhaust stream) to increase the
pressure ratio through the vortex tube for enhanced
efficiency. The mixed stream in line 42, if the system
is well insulated, should have an increased enthalpy
above that of the feed stream in line 26 equivalent to
the enthalpy change of the condensed vapors which are
removed as liquid in line 24.
The actual conditions and composition of the cold
and hot exhaust streams in lines 16, 36 will depend on
many factors including the condition and composition of
the raw gas feed; pressure ratio through the vortex tube
(of the expansion); cooling applied to the vortex tube
itself, the feed stream and the cold and hot exhaust
streams (subsequently described hereinbelow); design of
the vortex tube; and the like.
As seen in Fig. 3 in an alternative arrangement 100
of the present extraction process, cooling can be
applied directly to a vortex tube 102 having a heat
exchanger 104 which is integrated into the vortex tube
wall at a warming section 106 wherein a recirculation
3j flow gets progressively warmer than the feed
temperature. In the vortex tube heat exchanger 104, the
recirculation flow of the vortex tube is cooled by an
exchange of heat with the cold exhaust stream (which is
~V093/l6338 ~ PCT/US9~/0l808
9003
l4
substantially in a gas state) fed through line 108. Use
of the gas cooled vortex tube heat exchanger 10~l has
dynamic effects throughout the process 100. By cooling
the vortex tube recirculation flow, both the cold and
hot exhaust streams in lines 16, 36 are indirectly
lowered. Greater cooling enhances vapor extraction in
the partial condenser 14 which in turn effects the
stream composition of the vortex tube feed in line 26
and the dynamics in the vortex tube 102, etc. The cold
lO exhaust stream (gas) leaving the vortex tube exchanger ;~A. y'
104 is fed through line llo to a mixer 112 wherein the
cold exhaust stream in line 110 is mixed with the hot
exhaust stream in line 36 to give the mixed exhaust
stream in line 42 as previously mentioned. While any
suitable mixing device can be used, the mixer 112 is
preferably an ejector.
As seen in Fig. 4, an alternative arrangement 200
of the present process cools the hot exhaust stream in a
low pressure partial condenser 202 to at least partially
condense any condensable vapors in the hot exhaust
stream. The cold condensate which is produced from the
raw feed stream and the hot exhaust stream, is
effectively cooled to or subcooled below its saturation
temperature, and can be utilized to further promote -~ ~ b~
condensation of the vapors through heat exchange against
the raw feed stream, hot exhaust stream and/or the
vortex tube. A low pressure separator 204 separates
additional condensate from the uncondensed portion of
the hot exhaust gas. Another feature includes an
optlonal liquid cooled vortex tube heat exchanger 206
adjacent the gas cooled vortex tube heat exchanger 104
in a vortex tube 208.
The hot exhaust stream is removed from the vortex
tube 208 through line 210 and directed to the low
3~ pressure partial condenser 202. In the low pressure
partial condenser 202, an exchange of heat against a
cooling medium in line 212 at least partially condenses
condensable vapors from the hot exhaust stream in line
SUBSTITUTE SHEET
W093/16338 ~ 3~03 PC~/US9l3/0l808
210. A partially condensed stream thus formed is
removed through line 214 to the low pressure separator
204 and optionally combined with the raw feed stream
condensate from the high pressure separator 22 in line
21S. In the low pressure separator 204, condensate is
separated from the uncondensed vapor and gas portion of
the hot exhaust stream and the combined condensate from
both the raw feed stream and the hot exhaust stream is
removed in a line 216 as a liquid cooling medium in the
liquid cooled vortex tube heat exchanger 206. The
uncondensed vapor and gas portion of the hot exhaust
stream is removed from the low pressure separator though
line 218 and fed to an ejector 220. In the ejector 220,
the cold exhaust stream in line 222 is ejected using the
hot exhaust stream in line 218 to lower the pressure of
the cold exhaust stream at the vortex tube 208 and cool
the hot exhaust stream in line 218. Note that while the
ejector 220 is shown and preferred, any kind of mixing
device could be used. A mixed cold and hot exhaust
stream exiting the ejector 220 in line 212 comprises the
cooling medium for the low pressure partial condenser
202 as mentioned-above.
The recirculation flow in the vortex tube 208 is
cooled by both the gas cooled vortex tube heat exchanger
104 and the liquid cooled vortex tube heat exchanger
206. The liquid cooled exchanger 206 is also preferably
integrated into the vortex tube wall at a warming
section 224 wherein the recirculation flow gets
progressively warmer than the feed temperature. The
combined liquid stream cooling medium in line 216 should
not contain an excessive amount of volatile components
which could be re~vaporized by heat exchange in the
liquid cooled vortex tube heat exchanger 206. A
substantially liquid stream is removed from the liquid
cooled vortex exchanger 2~6 through line 226 for
storage, further processing, fuel use, etc. The mixed
stream cooling medium is removed from the low pressure
partial condenser 202 through line 228 and fed to the
WO93/1633~ ~ PCT/US93/01~08
29003
l6
gas cooled vortex tube heat exchanger 104 to provide
cooling. The mixed stream cooling medium is then fed to
the high pressure partial condenser 12 through line 230
as cooling medium and afterwards removed through line
232.
In an alternative arrangement 300 of the present
process as seen in Fig. 5, a liquid cooled precooler 302
is disposed upstream of the low pressure partial
condenser 202 to precool the hot exhaust stream from the
vortex tube 208. In the liquid cooled precooler 302,
the hot exhaust stream fed through line 304 is precooled
by an exchange of heat with the combined liquid stream
from the low pressure separator 204. The combined
liquid stream cooling medium as shown in Fig. 5 is fed
sequentially first to the liquid cooled precooler 302
through line 306 and then to the liquid cooled vortex
exchanger through line 308. However, this arrangement
could be reversed or made parallel depending on
practitioner preference and the need to minimize
pressure losses and obtain the greatest temperature
approach possible across the heat exchangers used. The
hot exhaust stream is fed from the liquid cooled
precooler 302 to the low pressure partial condenser 202
through line 310.
If the condensate cooling medium contains volatile
components much if not all such components can become
re-vaporized in the heat exchange steps described above.
In such circumstances it is preferred to recover the
volatile components by using a stripper or fractionation
column having a reboiler either external to or integral
with the column base. As seen in Fig. 6, an alternative
arrangement 400 of the present process uses a
conventional stripping column 402 to strip any volatile
components from the combined liquid stream in the low
pressure separator 204. The combined liquid stream is
withdrawn from the low pressure separator 204 through
line 404_and directed to a top section of the stripping
column 402 to strip the volatile components and
SUBSllTUTE SHEET
- W~93/16338 ~j ~~ PCT/US9.~/0~80~
9003
l7
stabilize the liquid stream as is known in the art. The
stripper 402 has an overhead line 406 for removing a
vapor stream rich in condensable components and a
bottoms line 408 for removing a liquid stream lean in
S condensable components. The stripper also has suitable
vapor-liquid contacting elements or trays 410 and a
reboiler 412 for providing reflux vapor. The raw feed
stream entering the process 400 through line 414 can be
used as a heating medium for the reboiler 412. The raw
feed stream is then fed to the high pressure partial
condenser 14 though line 416. The overhead vapor in
line 406 can be combined with the uncondensed vapor and
gas portion from the hot exhaust stream in line 418 from
the low pressure separator 204 and fed through line 419
to the ejector 220. The lean liquid stream can be
optionally fed to the liquid precooler 302 and/or the
liquid cooled vortex exchanger 206 where appropriate as
a cooling medium which is leaner in condensables thus
obviating re-vaporization of any volatile components.
In an alternative axrangement 500 of the present
process as seen in Fig. 7, a gas cooled precooler 502
can be used upstream of the low pressure partial
condenser 202 to precool the hot exhaust stream. In the
gas cooled precooler 502, the hot exhaust stream from
~S the vortex tube z08 in line 504 is precooled by an
exchange of heat with a cooling medium fed through line
506 from the high pressure partial condenser 14. The
cooling medium in line 506 comprises the mixed stream as
described above. In addition, the mixed stream is fed
as cooling medium from the low pressure condenser 202 to
the high pressure condenser 14 through line 505, from
the gas cooled precooler 502 to the gas cooled vortex
exchanger 104 through line 510 and is withdrawn from the
vortex exchanger 104 through line 509. The hot exhaust
stream is fed from the gas cooled precooler 502 to the
reboiler 412 through line 508 as heating medium and then
to the low pressure condenser 202 through line 512.
~VO93/1633S rCltUS93/Q18~8
XlZ9003
.
It can be seen that the mixed stream from the low
pressure separator 204 can be piped as cooling medium to
the above described heat exchangers in any order
desired. Furthermore, the order can be sequential as
shown in Fig. 7, parallel or a combination thereof.
However, it is desirable that the exchangers are ordered
in a fashion which maximizes the temperature approach
across each for enhanced efficiency. ` ~ -
In an alternative arrangement 600 of the present .-~
10 process as seen in Fig. 8, both the liquid cooled and ~-
gas cooled precoolers 302, 502 are used in series to
precool the hot exhaust stream from the vortex tube 208,
wherein the optional stripper column 402 for the liquid
cooling medium (as seen in Figs. 6-7) is not used.
While a serial arrangement is shown, it is understood
that a parallel arrangement or a combination series and
parallel arrangement of the precoolers could be devised.
In this case, the hot exhaust stream is fed from the gas
cooled precooler 502 to the liquid cooled precooler 302
through a line 602. Following additional precooling,
the hot exhaust stream is fed from the liquid cooled
precooler 302 to the low pressure partial condenser 202
through line 604.
In an alternative arrangement 700 of the present
~5 process as seen in Fig. 9, stream position of the low
pressure partial condenser 202 and the ejector 220 are
reversed. Also, the liquid cooled precooler 302, gas ~;
cooled precooler 502 and the stripper column 402 are not
shown. The location of the ejector 220 with respect to
the low pressure condenser 202 is immaterial to the
overall thermodynamic outcome provided that the
condenser 202 is properly sized. In this arrangement,
the hot exhaust stream is fed from the vortex tube 208
to the low pressure partial condenser 202 through line
3j 702. In the low pressure partial condenser 202, the hot
exhaust stream is cooled by an exchange of heat with the
- cold exhaust stream in line 704 as cooling medium
instead of the mixed stream cooling medium. The cold
.... _............................................ ~' .
, ~, .:' : ~,
SUBSllTtJTE SHE~
s~n.~ .
~093/16338 ~ ~ PCT/USg3~01808
19
exhaust stream cooling medium is fed to the ejector 220
through line 706 wherein the cold exhaust stream is
ejected using the uncondensed vapor and gas portion of
the hot exhaust stream from the low pressure separator
204 as mentioned previously. The mixed stream from the
ejector 220 is fed as cooling medium first to the high
pressure partial condenser 14 through line 708 and then
to the vortex exchanger 104 through line 710.
The preferred cooling path for the mixed stream
~0 medium is one which maximizes cooling potential, which
depends on whether the outlet stream temperature in
lines 232 or 509 is likely to be lower than the raw feed
steam temperature in line 12 or 414. At low to moderate
pressures, where the JT cooling effect is usually small,
the final exhaust temperature which occurs following
significant condensation is likely to be higher than the
raw feed stream temperature, in which case the cooling
paths shown where stream 509 is the final outlet stream
will very liXely be preferred, as seen in Figs. 7, 8 and
9. At very high feed stream pressures or relatively low
feed stream temperatures, where the JT cooling effect
can be very large, the final outlet temperature which
occurs following significant condensation can be lower
than the raw feed stream temperature. In this event the
preferred cooling paths for will be those where the
final outlet stream is stream 232, as seen in Figs. 4, 5
and 6.
In the manner of the present process, depending
upon the thermal effectiveness of each heat exchanger,
the residual vapor contained in the hot exhaust stream
originating from the vortex tube can ultimately be
condensed at a temperature approaching that of the cold
exhaust stream issuing from the vortex tube. Moreover,
as the hot exhaust stream issuing from the vortex tube
is at a substantially greater pressure than that of the
cold stream, the fraction of the uncondensed vapor that
finally remains at the process exit (e. g. streams 232
093/16338 ~ PC~/US~3/0~808
2129003
~; 20
or 509) can be as low as or even less than that
remaining in the cold exhaust stream.
The present vapor extraction process can be used
for most raw gas mixtures having a range of low and
higher boiling components. The present invention,
however, finds great utility for extracting higher
boiling hydrocarbons such as C2~ from methane in natural
gas produced from a gas and/or petroleum field at an
elevated pressure. The present process can also be used
for extracting acid gases such as NO2 and S2 from
combustion product gases such as CO, CO2, Oz, N2 and the
like in exhaust streams from furnaces, ore roasting
units, flare gas streams, and the like wherein the raw
gas stream has an elevated pressure. In general, the
lS present invention can be used to extract a higher
boiling component(s) and/or higher molecular weight
components from a pressurized mixed gas stream.
However, it is generally necessary for the raw gas to
initially treated for removal of potentially high
_ 20 freezing components such as water and in some
circumstances carbon dioxide, and the like.
It is understood that the above described serial
heat exchange steps could also be arranged in parallel
or a combination of series and parallel wherein the
'5 exhaust stream flows are subdivided. Countercurrent
heat exchange flows are preferred but cocurrent flows
could be used. The heat exchange steps are set forth to
obtain maximum cooling potential from the vortex tube
expansion. Therefore, it is desirable that the flows
through the exchangers be matched to maximize
temperature approach across the exchanger for maximum
heat exchange efficiency.
Useful heat exchange equipment in the present
process generally have a thermal effectiveness
3~ coefficient of at least about 0.4 but preferably from
about 0.6 to about 0.95 or more. Among well known heat
exchanger designs, shell/tube, plate/fin and other high
performance exchangers as described by Usher et al. are
SUBSTITUTE SHEET
~ .
~'093/1633~ 2~2~03 PCT/~S931~ 8
~ I .
suitable. Plate/fin and similar high performance
exchangers, however, are preferred for more difficult
extractions (i. e.. for raw feed streams having leaner
concentrations of condensable components and where
temperature approaches required are close). Plate and
fin exchanger equipment can be designed with thermal
effectiveness coefficients of 0.95 or higher. Lower
thermal efficiency heat exchangers (e. g. 0.4-0.5) could
be selectively employed in some circumstances, with
satisfactory though less efficient results obtained.
Although shown as separate units, heat exchange
equipment in the present invention can be integrated
into a compact unit as known in the art to minimize
pressure losses and maximize heat transfer efficiency
~5 while minimizing cooling losses.
A cyclone, filter or other similar agglomerative
vapor-liquid separation device is preferably used
between successive hot exhaust stream heat exchange
steps to remove any condensate formed in the prior heat
exchanger. In such manner, recovery of liquids can be
maximized by ensuring greater heat exchanger efficiency.
Liquid concentration in a hot exhaust inlet stream can
reduce heat transfer coefficients.
An ejector is a preferred means for mixing the cold
and hot exhaust streams to increase the pressure ratio
across the vortex tube. However, any suitable mixing
means known in the art could be employed instead.
Exemplary ~ortex tube design is described in Fulton
and is commercially available, for example, from Vortec
Corporation of Cincinatti, Ohio. The vortex tube
preferably comprises one or more feed nozzles, a cold
and hot exhaust stream port and is fabricated from
abrasion resistance materials having low thermal
conductivity. The vortex tube external surface, but
preferably the external surface of the-warming section
224 of the tube 208 is either extended, finned, ribbed,
dimpled, or a combination thereof, and the like
fabrications to increase a heat transfer area of the hot
.. .
O93/16338 ~'~' PCT/'US93~0t8~8
~, 2~9003
tube surface to promote efficient heat exchange o~' the
recirculation flow in the vortex tube.
The vortex tube can have radial grooves (not shown)
formed in the inside surface towards the warming end as
typified in Fekete '494 which is hereby incorporated
herein by reference. The radial grooves in the warming
section are typically placed up to about lO tube inside
diameters from the tangential feed nozzle, but
preferably from about 5 to about l0 inside diameters
from the tangential feed nozzle to draw off liquids
formed in the vortex tube. Such liquid can form a
peripheral boundary layer on the vortex tube inside wall
and inhibit heat transfer. Any liquid removed in vortex
tube groove(s) can be fed to the low pressure separator
204, for example. The vortex tube can also have an
annular slot (not shown) surrounding the orifice and
associated ducts through which liquids formed in the
core flow in close proximity to the feed nozzle inlet
plane can be drawn off. Otherwise, the core liquids
which do not get conveyed to the hot end can exit
through the cold end with the cold exhaust stream. This
circumstance can occur under conditions when the initial
vapor content in the raw feed gas is relatively high or
when,the gas pressure is so high that contribution to
'S gas cooling by the JT effect is significant.
In the practice of the present process in some
circumstances, it can be advantageous to operate a
cascaded or tandem arrangement of two or more of the
aforementioned systems. This can be the case if there
is a substantial reduction in performance for a
particular vortex tube design at very high pressure
ratios or where it is desired to separate vapors and/or
concentrate liquids having differing composition. An an
example with a two stage arrangement, the mixed exhaust
stream downstream from the ejector 220 can serve as the
feed stream to the second stage. The cold exhaust
stream from the second stage is then reinjected into the
-:
SUBSTITUTE SHEET
W~93/16338 ~ X~29~3 1'~/USg3/01808
23
first stage downstream of the ejector where the second
stage feed stream was sourced.
In other circumstances, the nature of the
condensing vapor can be such that it freezes at the
prevailing conditions of temperature and pressure in the
partial condensers 14, 202. In such instance, it can be
necessary to install twin exchangers and associated
separation apparatus in parallel and alternate the flows
between the two lines of equipment by using a valve
switching setup to establish a freeze-thaw cycle to
recover liquids ~hat have frozen.
The present process can be further illustrated by
reference to the following examples.
Examples 1-2
lS In the following examples a process scheme similar
to that shown in Fig. 8 was constructed employing a
vortex tube similar to one described by Fulton. The
efficiency of the process using both lower and higher
thermal effectiveness rated heat exchangers was compared
in terms of percent of the adiabatic temperature drop
achieved. The effectiveness rating was determined based
on tests with dry air. Both the lower and higher rated
exchangers were of the shell and tube type except that
the higher thermal coefficient exchangers has greater
tube side surface area. The cold exhaust fraction for
both examples was 0.7.
The dry raw feed gas condition and composition is
given in Table l. Temperature results following a
vortex expansion to 13 kPa(a) are given in Table 2.
_
s~
~V093/16338 PCr/US93/OlSO~
-~ 2~Z9003
~4
TABLE 1
Cas Composition .Mo\e X
Methane 87.4
Nitrogen 0.9
Carbon Dioxide 3.2
Ethane S .6
Propane 2.2
Butanes rJlus 0.7
Stream press . ~re ~kPa(a)~
Feed pressure of 300
the ra~ gas
Pressure of the 13 :~
~old exhaust at .
the vortex tube
discharge port ~ -
TABLE 2
I Example 1 Exan~le 2 .:
Estima~ed Thermal ¦ 0.47 0.78
Effe~tiveness coefficientb ¦ . .; .
Stream Temp~rature ( C) .~
: ~
Ra~l gas feed at the high 24 19
pressure partial condenser
(r~, stream 12? ,
Ra~l gas feed at vortex tube 9 -13
inlet no/~le (T;, stream 26) ~ . ...
Cold exhAust at vortex tube -18 -38
cold discharge port . :
(T,,strenm 222)
Mixed stream after the 10~- -8 -21a
pressure conderser
(Tm~ stream 505~ _
Hot exhaust at vortex tube hot 33 z5a
~Tp~iphptir 72C _
Ir.~ -Thnm~qon ..
X of Adi~batic ten~rDture 57 82 :~
drop (Tf-Tri~TadiAhA~ir)
a e5tjmated
-- b:~ased on dry air.
C-calculated
: Use of heat exchangers with a higher thermal
effectiveness coefficient improved the performance of
the vortex tube in terms of temperature of the cold . :
exhaust stream. This in turn improved the vapor
iO extraction capability of the process.
Calculations can show that a raw feed stream
condenser 14 having a thermal effectiveness coefficient .
.
SUBSTiTUTE SHEET
WO93/16338 ~ 2~9003 PCT/US93/018~8
of about O.9S would give a process temperature drop (T~-
Tc) which would approach that attainable with an
isentropic expansion.
The present vapor extracting process is illustrated
by way of the foregoing description and examples. The
foregoing description is intended as a non-limiting
illustration, since many variations will become apparent
to those skilled in the art in view thereof. It is
intended that all such variations within the scope and
spirit of the appended claims be embraced thereby.
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