Note: Descriptions are shown in the official language in which they were submitted.
CA 02583651 2007-04-12
Device for generating highly compressed gas
The invention refers to a device for generating highly compressed gas with a
single-stage or a multistage compressor. Besides various other applications,
the present device is useful in a gas fueling system for fueling vehicles
running
on natural gas, methane or similar gases or on hydrogen.
A problem with gases as an energy storage in vehicles is the greater storage
'-Milume'req-uired as compared to liquid energy sources, which, for'ng*ural
gas,
is greater by three orders of magnitude under ambient conditions. For this
reason, it has been regulated that natural gas is available at gas stations at
a
pressure of 250 bar so that, as defined by technical rules, a pressure of 200
bar is reached and not exceeded in the pressure gas container of a vehicle at
a
reference temperature of 15 C. Thus, compared to a fuel-operated vehicle, at
least only three times the storage volume has to be made available in a car.
In gas fueling installations, the pressurizing work to be performed causes a
heating of the gas in the pressure gas container. The Joule-Thomson effect (a
change in the gas temperature by throttling) of the real gas generally counter-
acts this heating. However, it is only under very favorable conditions, i.e.
at
sufficiently low temperatures, that the Joule-Thomson effect and the heat dis-
sipation to the environment suffice to compensate for the heating caused by
the pressurizing work of the gas. In gas fueling installations without a
cooling
device, if these favorable conditions do not exist, the pressure gas container
will be filled short upon decanting. This is due to the fact that the
pressurizing
work creates a high temperature and thus a corresponding high pressure in
the pressure gas container, whereby the available pressure difference for_
fill-
ing is reduced to such an extent that the fueling operation takes a long time
and is therefore terminated before the pressure gas container holds the vol-
ume of gas possible according to technical specifications.
CA 02583651 2007-04-12
2
DE 197 05 601 Al describes a natural gas fueling method without cooling of
the gas, wherein the fueling of the pressure gas container is continued until
the pressure in the conduit to the pressure gas container exceeds a maximum
pressure. Another possibility provides that the fueling operation is
terminated
as soon as the mass flow falls below a limit value.
WO 97/06385 Al describes a gas charging system for high-pressure gas bot-
tles. Here, the gas is cooled by flushing the high-pressure gas bottle to be
filled, whereby two connections for the feed and the return flow are needed.
In
the flushing circuit, t.".- ~as is coo!ed via a heat exchanger or by mixing it
with
gas in a reservoir.
EP 0 653 585 Al describes a system for fueling a pressure gas container.
Here, a test pulse is performed, which is evaluated with reference to the ther-
mal equation of state for the real gas. Further, a switching to reservoirs at
higher pressures (multiple unit method) during the fueling is described. The
fueling operation is performed intermittently. No cooling device is provided
for
the gas.
DE 102 18 678 Al describes a method and a device, wherein the gas for filling
the pressure gas container is fed from a high-pressure reservoir through a
vortex tube acting as a cooling device. The vortex tube takes advantage of the
differential pressure prevailing in the fueling system to separate the gas
flow
into a hot gas flow and a cold gas flow. The latter is then supplied to the
pres-
sure gas container. The functionality of this method is based on the fact that
the gas is fed to a swirl generator at a supercritical pressure ratio, the
genera-
tor being arranged axially between two pipes having different inlet diameters.
A decrease in temperature through the use of a vortex tube can be achieved
if, and only if, supercritical pressure ratios exist. At a critical pressure
ratio for
natural gas of n * = 0.5427 and a pressure in the reservoir of p,=250 bar,
which is generally not reached, when a plurality of vehicles are refueled in
shirt succession, a subcritical condition is obtained when the pressure in the
pressure gas container has risen to po = 135 bar. This means that, when
filling
CA 02583651 2007-04-12
3
a pressure gas container with natural gas in a pressure range from po=135 bar
to po=200 bar, the use of a vortex tube will result in no further decrease in
the
gas temperature under the preconditions defined by the technical specifica-
tions.
A direct fueling is feasible where setting up publicly accessible natural gas
fu-
eling stations is not economic. Vehicles - and not only those of individual
transport - could be refueled where they are during their standstill times.
This
may be in industrial parks, garages or car boards. Many households or build-
ings have natural gas available for heatir:g.,A compressor (natural gas com-
pressor) could compress this natural gas at night from the regular natural gas
network level of 50 mbar to 200 bar at a reference temperature of 15 C. A
vehicle could be fueled therewith.
Another possible field of application for such a fueling system is seen in
agri-
culture, where large volumes of biological gas are produced. Instead of feed-
ing this biological gas into a public gas network, it could be compressed in
situ
and be used to operate agricultural vehicles and machines. In the future, this
would allow to replace biodiesel in agriculture.
One requirement to be fulfilled by this compressor is that the compressor has
to be configured such that a complete filling with fuel has to be possible
within
one night (about 8 hours) at 200 bar and a reference temperature of 15 C.
The major problems of a multistage high-pressure compressor are the inter-
mediate cooling and the cooling of the gas at the compressor outlet, which,
when entering the pressure gas container, must not exceed 60 C at any time
during fueling.
It is an object of the invention to provide a device for generating highly com-
pressed gas, wherein the compressed gas, which heats up during compres-
sion, is cooled in a cooling device which is of simple structure, provides a
high
cooling performance and is adapted to be realized with small dimensions.
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The device of the present invention is defined in claim 1. According to the in-
vention, the cooling device arranged downstream of the compressor stage is
designed as a vortex tube.
Vortex tubes are particularly well suited for ultra-short time decreases in
tem-
perature. In contrast to conventional gas coolers, these decreases in tempera-
ture can be achieved over very short path lengths. Moreover, the invention is
based on the insight that the pressure ratio in the compressor stages of the
high-pressure compressor is larger than 3. Thereby, it is guaranteed that the
vortex tu,hes in all compressor stages will be in the supercritical range,.
which
is essential for a trouble-free operation of the vortex tubes.
A particular embodiment of the invention provides to maintain, in direct fuel-
ing, the reference temperature of 15 C at a pressure of 200 bar in the pres-
sure gas container to be filled even if the decrease of the gas temperature in
the vortex tubes is longer sufficient for this purpose under unfavorable
periph-
eral and environmental conditions. Suitably, after the last compressor stage
with an adjoining throttle point, the gas is not introduced into the pressure
gas
container to be filled, but is returned to the compressor inlet after an
adiabatic
throttling (Joule-Thomson effect). In the closed gas circuit, the gas tempera-
ture decreases continuously under isotropic compression and adiabatic throt-
tling (production of cold by adiabatic throttling, caused by the Joule-Thomson
effect in real gases). According to the invention, the gas circuit will remain
closed until the decrease in temperature required by the technical specifica-
tions for the filling of the pressure gas container is reached.
A particularly suitable embodiment of the invention provides for using the
heat
produced in the vortex tubes to heat water for domestic use or to use it for
heating a b.railding. _r,
Suitably, the output pressure of a multistage compressor is set so high that
this pressure is above the critical pressure of the pressure gas container to
be
filled. In contrast to the filling of a pressure gas container by an overflow
from
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a reservoir in which the gas pressure is limited to 250 bar according to the
technical specifications for natural gas, these regulations do not apply to
direct
fueling using a high-pressure compressor, provided that the legal provisions
for the pressure gas container are observed.
In a preferred embodiment of the invention, throttling via an expansion unit
takes the gas flow leaving the final stage of the high-pressure compressor to
the pressure allowed in the pressure container. The mechanical work arising at
the expansion unit is used to drive a compressor for pre-compressing the gas
taken from the gas network. Using the pre-compression, the output pressure at
the compressor can be var-
ied via the input pressure at the high-pressure compressor. By throttling a de-
fined output pressure, the ambient conditions during the fueling can be taken
into account and the gas temperature in the pressure gas container can be
influenced indirectly.
The invention further refers to a device for decreasing the temperature of a
gas from a reservoir containing pressurized gas, comprising a feed pipe lead-
ing to a swirl generator, a filling pipe leading to the pressure gas
container,
and a vortex tube branching from the swirl generator for conducting a rotating
vortex flow.
At higher temperatures, the volume of a gas is larger. Thus, for reasons of
space, it is often necessary to cool the gas since then a larger gas mass can
be stored in a determined volume. A typical application for gas cooling are
gas
fueling operations.
For a fast fueling of a gas-fueled vehicle, a fueling installation is required
that
is adapted to perform a fast decantation of high-pressure gas from a reservoir
to a pressure gas container. Such gases to be decanted may comprise natural
gas or methane or similar gases, as well as gases such as nitrogen, oxygen,
argon, air or hydrogen.
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In gas fueling operations it is intended to fill such a mass of gas into the
pres-
sure gas container, independent of the ambient temperature, that a limit value
of pressure defined by the technical specifications is possibly reached in the
pressure gas container at a predetermined reference temperature. For exam-
ple, technical specifications provide that a pressure of 200 bar at a
reference
temperature of 15 C must not be exceeded in a pressure gas container. For a
fast fueling operation by overflow, the reservoir must be under high pressure
for the required mass of gas to be transferred into the pressure gas
container.
In gas fueling installations, the pressurizing work to be performed causes a
heating o the gas in the pressure gas container. The Joule-Thomson effect
(change in temperature of the gas by throttling) of the real gas generally
counteracts this heating. However, it is only under very favorable conditions,
i.e. at sufficiently low temperatures, that the Joule-Thomson effect and the
heat dissipation to the environment will suffice to compensate the heat caused
by the pressurizing work of the gas. If these favorable conditions do not
exist,
a fast decanting in gas fueling installations without cooling device will
result in
a short-filling of the pressure gas container. This is due to the fact that a
high
temperature and a corresponding high pressure are caused in the pressure gas
container by the pressurizing work, whereby the pressure difference available
for fueling is lowered to such a degree that the fueling operation takes a
long
time and is therefore terminated before the pressure gas container holds the
mass of gas possible according to the technical specifications.
It is another object of the invention to provide a device for lowering the tem-
perature of a gas, which can be manufactured with small dimensions, is of a
simple structure and has a short response time with a great cooling effect.
The present device for lowering temperature has the features of claim 17. The
device is characterized in that the outside of the vortex tube is exposed to a
cooling device, that a swirl brake for slowing the vortex flow is arranged in
the
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vortex tube, and that a flow path leads from the swirl brake to the discharge
pipe.
In the present device for lowering temperature, the entire gas flow is made
substantially free of swirls after the temperature of the vortex flow has been
lowered, and the gas flow is fed to the pressure gas container. No throttling
means for controlling a hot gas flow is required. Compared to the known
methods for filling pressure gas containers by overflow, it is an essential ad-
vantage that the pressure of the gas flow is lowered only to the instantaneous
pressure in the pressure gas container, which is energetically udvantageous:
In the present device, the gas is supplied tangentially to a swirl generator
at a
supercritical pressure ratio, i.e. at a speed just below the speed of sound.
The
swirl generator introduces a rotating vortex flow into the vortex tube. The
vor-
tex flow expands in the vortex tube at a high axial speed, whereby the tube
wall is heated up strongly. The heavily turbulent mixing causes an adiabatic
layering, and, due to the high centrifugal pressure, the outer portion of the
vortex flow has a higher static temperature than the inner portion. The vortex
flow is cooled by the cooling device acting on the vortex tube from outside,
and is then slowed down by a swirl brake. The flow is then fed over a flow
path to the filling tube leading to the pressure gas container. In this
manner,
the entire gas taken from the reservoir reaches the pressure gas container.
According to a preferred embodiment of the invention, it is provided that the
flow path extends centrally through the vortex within the vortex flow. While
the vortex flow rotates, a centric return flow forms along its axis. While the
outer vortex flow continues to heat up, the linear inner return flow is much
colder.
In an advantageous embodiment of the invention provides that the filling pipe
also branches from the swirl generator and that the diameter of the filling
pipe
is smaller than the diameter of the vortex tube. In the process, the swirl-
free
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linear return flow again reaches the swirl generator from where it gets into
the
filling pipe.
Preferably, the swi-rl brake is a closure arranged in the vortex tube. The
same
slows down the vortex flow near the wall because of the absence of centrifugal
forces so that a radial inward flow is obtained. For reasons of continuity, a
centric return flow in the form of a core flow is thus produced in the axial
di-
rection, flowing in a direction opposite to the rotating vortex flow. The
lower
speed of the return flow, as compared to the vortex flow, has effect in a fur-
ther reduction of the static.temperature of the inner flow with respect to the
surrounding vortex flow, whereby the temperature difference between these
two flows is still increased.
The invention starts from the insight that it is advantageous to dissipate the
heat transferred from the rotating flow to the tube wall, which, as experience
has shown, is at a high temperature level there.
According to a preferred embodiment of the invention, a water cooler designed
as a coaxial pipe is used to cool the tube wall of the vortex tube in a
counter
current process. Thus, it is achieved, overall, that by cooling the tube wall,
which is the more effective, the greater the temperature difference between
the object to be cooled and the cooling medium is, an additional reduction in
temperature of the inner flow in the tube is effected through a reduction in
temperature of the outer flow of the tube.
A particularly advantageous embodiment of the invention provides that the
closure forming the swirl brake is a piston adapted to adjusted axially in the
vortex tube. Thereby, the effective length of the vortex flow is variable so
as
to optimize the filling operation in dependence on the pressure and the tem-
perature of the gas in the reservoir. The effective length of the vortex tube,
i.e. the length of the effective vortex tube section, can be changed by adjust-
ing the piston, e.g. by means of a threaded bar.
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The following is a detailed exemplary description of the invention with refer-
ence to a four-stage high-pressure compressor and to the accompanying
drawings.
In the figures:
Fig. 1 is a schematic general view of the gas fueling system comprising
a high-pressure compressor using a vortex tube according to Ranque-Hilsch
for lowering the temperature of the gas after compression, wherein a separa-
tion into cold gas and hot gas is effected in the vortex tube,
Fig. 2 shows the same gas fueling system as Fig. 1, however, using the pres-
sure energy with its work capacity in an adiabatic throttling process after
the
last compressor stage in an expansion unit,
Fig. 3 illustrates the same gas fueling systems as Fig. 2, however, using the
heat in the hot gas for heating domestic and/or heating water via a heat ex-
changer,
Fig. 4 shows the same gas fueling system as Fig. 3, however, using a vortex
tube without gas separation, wherein the vortex tube is cooled from outside
and the heat in the cooling water is available for heating domestic and/or
heating water,
Fig. 5 is a longitudinal section through a device for lowering the temperature
of gases, and
Fig. 6 is a perspective view of the device of Fig. 5 to illustrate the feeding
and
the distribution of the gas flow and the water cooling.
The gas fueling system illustrated in Fig. 1 has a take-off pipe 1 leading to
the
series-connected compressor stages 10a, 10b, 10c and 10d. A check valve
iia, 11b, lic, 11d is arranged in the pipeline 1 upstream of each compressor
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stage. An inlet pipe 12a, 12b, 12c, 12d leads from the check valve to the fol-
lowing compressor stage. The outlet of the compressor stage is connected to
the inlet of a vortex tube 20a, 20b, 20c, 20d via a take-off pipe 13a, 13b,
13c,
13d. The vortex tubes are generally structured as described in DE 102 18 678
Al so that a detailed explanation of the structure of the vortex tubes can be
omitted. The vortex tubes 20a, 20b, 20c, 20d serve to decrease the gas tem-
perature after a previous compression.
The vortex tubes 20a, 20b, 20c, 20d operating according to the counter-
current method are connected to the compressor stages 1.0a, 10b..10c; _ lOd
via the take-off pipes 13a, 13b, 13c, 13d. Through the take-off pipes 13a,
13b, 13c, 13d, the gas flow reaches the inflow nozzles forming the narrowest
flown-through cross section 21a, 21b, 21c, 21d between two compressor
stages. As a vortex flow at the speed of sound, the gas flows from the inflow
nozzles into the central tube of the vortex tube where a separation into a
cold
gas flow and a hot gas flow is effected. At one end of the central tube, the
cold
core of the forming swirl is collected and fed to the subsequent compressor
stage via the inlet pipes 12b, 12c, 12d. At the opposite end of the central
tube, the hot gas flow 23a, 23b, 23c, 23d is collected and discharged via the
pipelines 24a, 24b, 24c, 24d. The throttle points 25a, 25b, 25c, 25d provided
in the pipelines 24a, 24b, 24c, 24d serve to preset the mass ratio between the
cold gas and the hot gas portions. Downstream of the throttle points 25a, 25b,
25c, 25d, the hot gas flow flows through the return flow pipes 26a, 26b, 26c,
26d into the same compressor stage from which the gas was taken. The check
valves 27a, 27b, 27c, 27d in the return flow pipes 26a, 26b, 26c, 26d and the
check valves 11a, 11b, 11c, 11d in the inlet pipes 12a, 12b, 12c, 12d allow
the
gas to flow from the return flow pipes 26a, 26b, 26c, 26d into the inlet pipes
12a, 12b, 12c, 12d.
From the gas supplied, each vortex tube produces a hot gas flow 23a, 23b,
23c, 23d and a cold gas flow 22a, 22b, 22c, 22d. The hot gas flow 23a, 23b,
23c, 23d is returned to the respective compressor stage 10a, 10b, lOc, 10d.
On the other hand, the cold gas flow 22a, 22b, 22c, 22d is fed to the subse-
CA 02583651 2007-04-12
11
quent compressor stage. The check valves 11a, llb, iic, 11d prevent re-
turned gas from entering the cold gas outlet of the previous vortex tube. The
check valves 27a, 27b, 27c, 27d help to avoid that the cold gas of the previ-
ous vortex tube gets into the return pipe of the hot gas of the subsequent vor-
tex tube.
From the vortex tube 20d of the last compressor stage 10d, the cold gas flow
22d reaches the pressure pipe 4. If the gas temperature there, measured by a
temperature measuring means 100, is above a predetermined reference value,
the three-way. .;*opcockG 1,01, 102 are operated as triggered by a measure-
ment signal. Normally, these are set such that the gas flow leads from the
take-off pipe 1 to the series-connected compressor stages 10a, 10b, 10c, 10d
and the cold gas flow 22d is fed into the pressure gas container 7 through the
pressure line 6. If the cold gas temperature exceeds a predefined limit value
at the measuring point 100, the cold gas flow 22d is redirected via the return
manifold 104 using the three-way stopcock 101. Before the cold gas flow is
again fed to the first compressor stage 10a through the return manifold 104
via the three-way stopcock 102 and the inlet pipe 12a, the cold gas flow is
subjected to a further reduction in temperature at the throttle point 103. The
three-way valve 102 is operated simultaneously with the three-way valve 101
so that no gas is supplied through the take-off line 1 and a closed circuit is
established after the three-way stopcocks 101, 102 have been operated. In
this closed system, an adiabatic throttling (Joule-Thomson effect) reduces the
temperature in the hot gas flow 23a, 23b, 23c, 23d at the throttle points 25a,
25b, 25c, 25d and in the cold gas flow 22d at the throttle point 103. Due to
the Joule-Thomson effect, the decrease in temperature obtained by throttling
is larger with a real gas like natural gas than the increase in temperature in
the gas caused by the compression in the previous compressor stages 10a,
10b, lOc, lOd. Thus, in a closed gas circuit, the gas temperature can be low-
ered by compression and adiabatic throttling. As soon as the temperature
measuring means detects that the temperature in the cold gas flow 22d corre-
sponds to a predefined reference temperature, a measurement signal is trig-
gered operating the three-way stopcocks 101, 102 so that the take-off pipe 1
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12
is again in communication with the compressor stages 10a, lOb, 10c, 10d and
the cold gas flow 22d is introduced into the pressure gas container 7 via the
pressure pipe 6.
Other than the system in Fig. 1, the gas fueling system illustrated in Fig. 2
has
a pre-compressor 2 connected to the take-off pipe 1. A pipeline 3 leads from
the pre-compressor 2 to the series-connected compressor stages 10a, 10b,
10c, 10d. A check valve 11a, 11b, 11c is provided in the pipeline 3, upstream
of each compressor stage. The last compressor stage 10d is not provided with
a check valve. An inlet pipe 12a, 12c leads from the check valve to the
subsequent compressor stage. The outlet of the compressor stage is con-
nected to the inlet of a vortex tube 20a, 20b, 20c via a take-off pipe 13a,
13b,
13c.
From the last compressor stage lOd, a pressure pipe 4 leads to an expansion
unit 5. In the expansion unit, the gas flow is subjected to a reduction in tem-
perature after the last compressor stage 10d, before the gas is introduced
into
the pressure gas container 7. Normally, the three-way stopcock 101 is set
such that the pressure pipe 6a, 6b is connected through. At the same time,
mechanical work is taken from the gas flow in the expansion unit 5 that is
used to drive the pre-compressor 2. The expansion unit 5 drives the pre-
compressor 2.
The gas compressed in the pre-compressor 2 is fed to the first compressor
stage 10a through the pipeline 3 via the inlet pipe 12a provided with the
check
valve 11a. The vortex tubes 20a, 20b, 20c operating according to the counter-
current process are connected to the compressor stages 10a, 10b, 10c via the
take-off pipes 13a, 13b, 13c. Through the take-off pipes 13a, 13b, 13c, the
gas flow reaches the inflow nozzles that form the narrowest cross section 21a,
21b, 21c between the compressor stages 20, 20b, 20c. The cold gas flow 22a,
22b, 22c of the vortex tubes 20a, 20b, 20c is fed to the following compressor
stage via the inlet pipes 12b, 12c, 12d, and the hot gas flow 23a, 23b, 23c is
discharged via the pipelines 24a, 24b, 24c. The throttle points 25a, 25b, 25c
CA 02583651 2007-04-12
13
provided in the pipelines 24a, 24b, 24c serve to preset the mass ratio between
the cold gas and the hot gas portions. Downstream of the throttle points 25a,
25b, 25c, the hot gas flow 23a, 23b, 23c returns, via the return pipes 26a,
26b, 26c, into the same compressor stage from which the gas was taken. The
check valves 27a, 27b, 27c in the return pipes 26a, 26b, 26c and the return
valves 11a, iib, 11c in the inlet pipes 12a, 12b, 12c allow the gas to flow
from the return pipes 26a, 26b, 26c to the inlet pipes 12a, 12b, 12c.
From the gas supplied, each vortex tube produces a hot gas flow 23a, 23b,
23c and a cold gas flow 22a, 22b, 22c. The hot gas flow 23a, 23b, 23c is re-
turned to the respective compressor stage 10a, 10b, 10c. On the other hand,
the cold gas flow 22a, 22b, 22c is fed to the subsequent compressor stage.
The check valves iia, lib, iic prevent returned gas from entering the cold
gas outlet of the previous vortex tube. The check valves 27a, 27b, 27c help to
avoid that the cold gas of the previous vortex tube gets into the return pipe
of
the hot gas of the subsequent vortex tube.
As is further obvious from Fig. 2, the closed gas circuit can be designed as
de-
scribed with respect to Fig. 1, so as to start a decrease in the gas
temperature
when the gas temperature exceeds a predetermined reference temperature at
the temperature measurement point 100.
The embodiment of Fig. 3 differs from that of Fig. 2 in that the hot gas flow
23a, 23b, 23c of the vortex tubes is fed via a respective return pipe 26b,
26c,
26d that leads back to the inlet pipe 12a, 12b, 12c of the compressor stage
10a, 10b, 10c. The return pipes 26a, 26b, 26c each include a gas cooler 30a,
30b, 30c to draw heat from the gas. Downstream of each gas cooler, a throttle
point 25a, 25b, 25c is mounted in the return pipe.
~ ...
The gas coolers 30a, 30b, 30c are water-cooled heat exchangers. By forced
circulation, a circulation pump 8 driven by the expansion unit 5 feeds the wa-
ter through a pipe 31 to the gas coolers 30a, 30b, 30c that are connected in
parallel to corresponding feed pipes 31a, 31b, 31c. From the gas coolers, the
CA 02583651 2007-04-12
14
cooling medium flows in return pipes 32a, 32b, 32c that combine to a return
manifold 32. The return manifold 32 leads to a heat exchanger 33. Here, the
cooling medium that acts as a heat carrier transfers the heat received in the
gas coolers to a second heat transfer medium that is supplied from a feed 34-
1 of the secondary circuit and exits from the heat exchanger through a drain
34-2. The heat transfer medium conveyed in the secondary circuit may be
domestic water and/or heating water for a building heating. Having left the
heat exchanger 33, the heat transfer medium conveyed in the primary circuit
returns to the intake side of the circulation pump 8 via a pipe 35.
In the gas fueling system of Fig. 4, a vortex tube is employed that operates
without gas separation. The gas taken from the take-off pipe 1 is brought to a
higher pressure level in a pre-compressor 2 driven by the expansion unit 5.
Via the pipe 3, the pre-compressed gas is fed to the inlet pipe 12a of the
first
compressor stage 10a of the high-pressure compressor. After compression in
the first compressor stage 10a, the gas reaches the vortex tube 40a via the
take-off line 13a for a reduction in the temperature of the gas. The same is
valid for the following compressor stages 10b, 10c with the take-off pipes
13b,
13c and the vortex tubes 40b, 40c.
The vortex tubes 40a, 40b, 40c are connected to the compressor stages 10a,
10b, 10c through the take-off pipes 13a, 13b, 13c. Through the take-off pipes
13a, 13b, 13c, the gas flow reaches the inflow nozzles that form the narrowest
flown-through cross section 41a, 41b, 41c between two compressor stages. As
a vortex flow at the speed of sound, the gas flows from the inflow nozzles
into
the central tube of the vortex tubes 40a, 40b, 40c which are closed at one end
43a, 43b, 43c. At the solid bottom of the closed-end tube, the flow is slowed
down near the wall because of the absence of centrifugal forces so that at the
end, near the bottom, a radial inward flow is obtained. For reasons of continu-
ity, a rising flow is produced in the axial direction, which flows as a core
flow
in the direction opposite to the rotating flow and flows out at the opposite
ends 42a, 42b, 42c of the closed tubes into the inlet pipes 12a, 12b, 12c.
CA 02583651 2007-04-12
The increase in static temperature on the outside and its decrease on the in-
side necessarily cause different temperatures between the inner flow in the
tube and the outer flow in the tube. All in all, a decrease in temperature of
the
outer flow in the tube by cooling the tube wall allows for an additional de-
crease in the temperature of the inner flow in the tube. Thus, the vortex
tubes
40a, 40b, 40c are equipped with water coolers 44a, 44b, 44c that surround
the central tube of the vortex tubes 40a, 40b, 40c and are used for cooling
the
outer wall of the tube according to the counter-current technique. As is
further
obvious from Fig. 4, the primary and the secondary circuit can be designed
according to the cooling circuit descr.ibed in connection with Fig. 3.
The gas is supplied to the last compressor stage 10d via the inlet pipe 12d.
In
the expansion unit 5, the gas flow is subjected to further temperature reduc-
tion downstream of the compressor stage 10d, before the gas is introduced
into the pressure gas container 7. At the same time, mechanical work is taken
from the gas flow in the expansion unit 5, which is used to drive the pre-
compressor 2 and the circulation pump 8.
The device for reducing the temperature illustrated in Figures 5 and 6 com-
prises a feed pipe 101 coming from a reservoir and leading to a swirl genera-
tor 102. The functionally essential parts thereof are an annular plenum cham-
ber 103, from which tangential inflow nozzles 104 are directed inward and
lead into the end of a vortex tube 105. Adjoining the end of the vortex tube
105 is an oppositely directed pipe section 106 that is connected with a
filling
pipe 107 leading to the pressure gas container (not illustrated). The inner di-
ameter of the pipe section 106 is clearly smaller than that of the vortex tube
105. As a consequence, the rotating vortex flow 121 produced in the swirl
generator 102 flows into the vortex tube where it moves away from the swirl
generator 102 (to the left in Fig. 1). The throttle point with the narrowest
flown-through cross section between the reservoir and the pressure gas con-
tainer to be filled is formed by the inflow nozzles 104 of the swirl generator
102. From the inflow nozzles 104, the gas flows into the vortex tube 105 as a
rotating vortex flow 121 at almost the speed of sound. For dissipating the
heat
CA 02583651 2007-04-12
16
caused by the vortex flow 121 from the tube wall of the vortex tube 105, a
cooling device 130 is provided around the vortex tube 105. The same com-
prises a cooling jacket 131 coaxially surrounding the vortex tube, which is
provided with a feed pipe 132 and a drain pipe 133 and forms a water cooler
according to the counter-current technique.
At the end averted from the swirl generator 102, the vortex tube 105 is pro-
vided with a swirl brake 109. The same comprises an axially adjustable piston
110 that is arranged in the vortex tube, closing it off sealingly. To adjust
the
piston 110, a spindle 111 is used that can be turned ma,uaIly. The y_or.tex
flow
121 is slowed down at the closure 110 so that, for reasons of continuity, an
axially directed return core flow flowing back along a flow path 122 is
formed,
flowing in a direction opposite to the vortex flow 121. The flow path 122 ex-
tends coaxially within the vortex flow 121. The pressure difference between
the inner and the outer flow in the vortex tube 105 has the effect that the
core
flow flowing along the inner flow path 122 flows through the pipe section 106
into the filling pipe 107 that is connected with the pressure gas container to
be
filled.
The perspective view in Fig. 6 represents the flow course of a gas in the de-
vice, the gas supply being effected through the feed pipe 101 in the direction
of the arrows 120. From here, the gas, e.g. natural gas, reaches the vortex
tube 105 at a supercritical pressure ratio and at the speed of sound via the
plenum chamber 103 and the inflow nozzles 104 of the swirl generator 102.
Caused by the swirl generated in the swirl generator 102, the rotating flow
121 is formed in the vortex tube. Near the wall, due to the absence of cen-
trifugal forces, this rotating flow is slowed down so far at the solid bottom
of
the vortex tube closed by the closure 110 that an oppositely directed core
flow
122 is,formed. The latter is then fed to the pressure gas container via the
pipe
section 106.
