U.S. patent application number 09/974868 was filed with the patent office on 2002-02-14 for method of detecting the presence of impurities, unit and method for vaporizing liquid, and double air distillation column.
This patent application is currently assigned to L'air Liquide, Societe Anonyme Pour L'Etude et L'Exploitation Des Procedes Georges Claude. Invention is credited to Lehman, Jean-Yves.
Application Number | 20020017112 09/974868 |
Document ID | / |
Family ID | 9522729 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020017112 |
Kind Code |
A1 |
Lehman, Jean-Yves |
February 14, 2002 |
Method of detecting the presence of impurities, unit and method for
vaporizing liquid, and double air distillation column
Abstract
A film-type vaporizer (2) in a vaporization enclosure (1), for
example the upper column of a double air-distillation column, is
associated with a measurement and analysis box (3) where a polished
surface (4) and a spillway (6) reconstruct the flow of liquid in
the vaporizer in order to check for the absence of the deposition
of impurities in the liquid that is to be evaporated or, if such a
deposition occurs, to quantify and analyse the impurities involved
and take appropriate action on the settings of the machine.
Application in particular to the distillation of air for the
production of oxygen
Inventors: |
Lehman, Jean-Yves; (Maisons
Alfort, FR) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
L'air Liquide, Societe Anonyme Pour
L'Etude et L'Exploitation Des Procedes Georges Claude
Paris
FR
|
Family ID: |
9522729 |
Appl. No.: |
09/974868 |
Filed: |
October 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09974868 |
Oct 12, 2001 |
|
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09247101 |
Feb 9, 1999 |
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Current U.S.
Class: |
62/643 ;
62/902 |
Current CPC
Class: |
F25J 2245/50 20130101;
Y10T 436/12 20150115; F25J 2235/50 20130101; F25J 3/04969 20130101;
F25J 2280/02 20130101; Y10T 436/115831 20150115; F25J 2250/04
20130101; Y10T 436/177692 20150115; B01D 1/0082 20130101; Y10T
436/255 20150115; Y10T 436/17 20150115; F25J 3/04793 20130101; F25J
3/04412 20130101; F25J 3/0486 20130101; Y10S 62/913 20130101 |
Class at
Publication: |
62/643 ;
62/902 |
International
Class: |
F25J 003/00; F25J
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 1998 |
FR |
98 01477 |
Claims
What is claimed is:
1. A vaporizing unit comprising, within an enclosure: at least one
vaporizer; means of supplying the vaporizer with a stream of liquid
to be vaporized; a circuit for diverting part of the stream to be
vaporized, the circuit being connected to the supply means and
comprising a means of spraying part of the diverted stream onto a
receiving surface; and means of detecting the formation of solid
deposits on the receiving surface.
2. The unit according to claim 1, wherein the enclosure comprises a
distillation column.
3. The unit according to claim 2, wherein the supply means consists
of a spillway in the column.
4. The unit according to claim 1, wherein the receiving surface is
polished.
5. The unit according to claim 2, wherein the supply means
comprises a pump for recirculating the liquid at the bottom of the
column.
6. The unit according to claim 5, further comprising a filter
module between the pump and the diversion circuit.
7. A double air-distillation column comprising a vaporizing unit
according to claim 2.
8. A double air-distillation column comprising, at the base of an
upper column, a vaporizer without a recirculating pump.
Description
[0001] The present invention relates to methods and units for
vaporizing liquids, particularly for distilling air.
[0002] All gaseous mixtures that are to be separated, and in
particular atmospheric air, contain numerous and varied impurities
of varying volatility and in highly varying contents. Not being
readily soluble, these impurities, alone or in combination, present
risks of malfunctioning, particularly of explosion.
[0003] In the case of air-distillation apparatus, atmospheric air
to be separated is purified prior to liquefaction in an
adsorption-type purification unit which holds back almost all of
the water, carbon dioxide and unsaturated hydrocarbon impurities
present in the air.
[0004] This prepurification is not, however, sufficient, and it is
therefore envisaged that it be supplemented by a system for
reducing the impurities concentration by continuous cleaning and/or
adsorption in the liquid phase, as described, for example, in
document DE-A-1,936,049.
[0005] What is more, when a perfectly identified and detectable
difficult-to-remove impurity may pose a problem, then the measuring
of the presence of this impurity in a critical region of the
apparatus is advantageously envisaged, as described, for example,
in the case of the impurity N.sub.2O in document U.S. Pat. No.
5,629,208 (Darredeau et al.).
[0006] It is nonetheless still the case that many impurities, for
example temporary, local or unpredictable impurities, are not taken
into account, existing purification devices allowing some of these
to be held back but being relatively transparent in the case of
others which, depending on their limits of solubility and of
concentration, may be deposited on the heat-exchange surfaces of
the apparatus, particularly the vaporizers.
[0007] To avoid this risk, use is made of bath-type vaporizers in
which a thermosiphon allows a high flow rate of liquid to be
circulated through the exchanger so as to thoroughly wash these
surfaces. Use is also made of vaporizers known as falling film or
liquid-film wetting vaporizers, in which the liquid to be vaporized
is finely distributed at the upper part of the surface and trickles
over this surface in thin films allowing a smaller temperature
difference. To avoid the deposition of solid particles on the
surface, care is taken to ensure that this surface is kept very
wet, right down to the bottom of the vaporizer, by supplying it
with a flow rate of liquid that is markedly higher than the flow
rate vaporized, usually by resorting to the use of a recirculating
pump. The latter does, however, have the drawback of concentrating
the residual impurities in the liquid bath, that the filtration
device in the aforementioned recirculation circuit may not be
adequate to hold back.
[0008] The object of the present invention is to propose methods
and devices that will make it possible, not to detect the presence
of impurities in the liquid that is to be evaporated, but to detect
any formation of depositions of impurities on the critical
heat-exchange surfaces and therefore take rapid action to change
the operating conditions of the plant and/or provide greater
purification, at least temporarily, and/or shut down the plant.
[0009] In order to achieve this, according to one aspect of the
invention, this invention proposes a method of detecting the
presence of residual impurities in at least one stream of liquid
intended to be at least partially vaporized in at least one
vaporizing unit, in which part of the stream entering the
vaporizing unit is diverted so that at least part of it is directed
onto a receiving surface that is held at a temperature slightly
above the temperature of the liquid being monitored, and in which
any formation of solid deposits on the surface is detected.
[0010] Typically, according to the invention, the amount of solid
material deposited and the amount of diverted liquid vaporized on
the surface are also measured, so as to establish, from
correlations, the presence, nature and content of impurities during
the period preceding these measurements.
[0011] Thus, whatever the quality of the purification operations
performed upstream or locally, the absence of the formation of
solid deposits on the receiving surface, which reconstructs on a
small scale and in a directly accessible manner, the situation of
the heat-exchange surface within the apparatus, demonstrates that
under the prevailing operating conditions, the risks of the
deposition or build up of undesired solid particles on the
heat-exchange surface are zero. By contrast, whatever the impurity
involved, whether or not it has been previously identified, the
appearance of a deposition on the receiving surface indicates a
risk condition that allows corrective measures to be taken
swiftly.
[0012] Another subject of the present invention is a vaporizing
unit that is appropriate for the implementation of the method,
comprising, within an enclosure, at least one vaporizer, means of
supplying the vaporizer with a stream of liquid to be vaporized, a
circuit for diverting part of the stream to be vaporized, this
circuit being connected to the supply means and comprising a means
of spraying part of the diverted stream onto a receiving surface
and means of detecting the formation of solid deposits on this
surface.
[0013] Such a vaporizing unit can be readily implemented in
numerous applications, possibly by making quick modifications to
existing vaporizing units. It finds a particularly advantageous
application in vaporizer-condensers at the base of the upper
columns of double-column distillation devices, with simple gravity
feed and/or fed at least partly by a recirculating pump.
[0014] Real-time checks for the absence of formation of deposits
(or, in the other case, the appearance of such deposits) makes it
possible to operate under perfectly reliable conditions, without
having to resort to preventive measures that are not necessarily
needed such as, for example, overwetting the vaporizer or running
it at a high pressure. Thus, according to one aspect of the
invention, it is possible to vaporize oxygen at a pressure not
exceeding 3.5.times.10.sup.5 Pa and to produce a double
air-distillation column comprising, at the base of the upper
column, a liquid-film wetting vaporizer that is entirely devoid of
a recirculating pump.
[0015] Other features and advantages of the present invention will
emerge from the following description of embodiments, given by way
of illustrative but non-limiting example, and made with reference
to the appended drawings, in which:
[0016] FIG. 1 is a diagrammatic view of a vaporizing unit according
to the invention;
[0017] FIG. 2 is a diagrammatic view of one embodiment of a double
air-distillation column according to the invention; and
[0018] FIG. 3 is a diagrammatic view of a box for measuring and
analysing deposits, according to the invention.
[0019] In the description which will follow and in the drawings,
elements which are identical or analogous bear the same reference
numerals, possibly with indices.
[0020] FIG. 1 depicts diagrammatically, within an enclosure 1, a
film vaporizer of the open type 2 receiving, under gravity, a
spillway 24, a stream F of liquid to be vaporized. According to the
invention, located in a box 3 mounted outside the enclosure 1, is
an optically polished receiving surface 4 heated by a heating
device 5 and over which there extends, like a spillway, the end of
a small-section pipe 6 drawing off liquid from the stream F,
typically in the distribution manifold above the vaporizer 2. The
receiving surface 4 is monitored by an optical device 7, for
example of the type viewed directly by an observer and/or
advantageously of the type having a photoelectric detector
analysing a signal of reflected light from a source 8 in the box 3.
The mini-stream of gas flowing through the pipe 6 trickles, like
the main stream F in the vaporizer 2, over the hot surface 4 where
it vaporizes, the gas vaporized in the chamber 3 returning to the
enclosure 1 along a gas-return pipe 9.
[0021] As explained above, it will be readily understood that the
inspected surface of the receiving surface 4 very exactly
reproduces the most severe conditions that exist in the vaporizer 2
which means that, as long as no deposition is seen on the surface
4, the vaporizer 2 can operate in a so-called partially dry
operating mode, with a very limited flow rate of liquid at the
lower part of the exchanger, down to 0% in the case of the
production of gaseous oxygen, and that this can be so irrespective
of the pressure in the enclosure 1, which pressure can even be
below the values usually considered as being "threshold" pressures,
for example below 3.5.times.10.sup.5 Pa in the case of the
vaporizing of oxygen.
[0022] FIG. 2 illustrates one application of the invention to the
production of a double air-distillation column for the production
of oxygen.
[0023] This FIG. 2 shows a double column with an upper enclosure 1,
known as the low-pressure column, and a lower enclosure known as
the medium-pressure column 10, the latter being supplied by a
compressor 11 with pressurized air that has been purified in a
purification unit 12 of the adsorption type.
[0024] Placed in the bottom of the upper enclosure 1 is a double
vaporizer-condenser consisting, in the example depicted, of an open
vaporizer 2 receiving directly under gravity a stream of liquid
that is to be vaporized F, like in the previous example, here
associated with a closed vaporizer box 13 itself supplied with
liquid to be vaporized F' recycled from the bath 14 at the bottom
of the base by a recirculating pump 15. As mentioned above, a
purification device of the type with solid adsorbent 16 is
advantageously provided in the delivery circuit of the pump 15, in
order to avoid the bath 14 becoming overenriched with impurities
and to limit the risk that these impurities will be deposited in
the vaporizer 13.
[0025] According to the invention, the tapping-off pipe 6 dripping
onto the receiving surface 4 is in this case tapped off downstream
of the purification device 16, the box 3 advantageously being
mounted directly on the exterior wall, depicted as 17, of the cold
box enclosing the double distillation column. Advantageously, a
second box 3 may be provided, to represent the situation in the
open vaporizer 2 by taking away some of the stream F, like in the
example described above.
[0026] FIG. 3 depicts in greater detail a box 3 for analysing and
measuring deposits. The box 3 comprises a removable lid 18 allowing
access to the receiving surface 4 for taking and analysing the
non-vaporizable deposits. The box comprises a pipe 19 for
selectively conveying a clean gas for de-icing and the gas-return
pipe 9 is equipped with a shut-off valve 20 and with an analyzer 21
for analysing the deposited impurities vaporized during the
de-icing of the box. The capillary tube 6 along which the liquid
arrives by gravity is also equipped with a flow detector 22 for
measuring the amount of diverted liquid vaporized in the box and
correlating it with the contents of impurities deposited in the,
variable, period preceding the measurements. In FIG. 3, the light
source 8 is a collimated source and the detection device comprises
a photoelectric cell 7 and a window 23 for visual inspection. For
enhancing the sensitivity and/or the collimation of the optical
detection device, the polished receiving surface 4 may be curved,
at least orthogonally to the light beam, for instance cylindrical
and/or in the shape of a U or of a J.
[0027] Although the present invention has been described in
relation to particular embodiments, it is not restricted thereto
but, on the contrary, can be modified and varied in ways that will
be obvious to the person skilled in the art, within the scope of
the claims which follow.
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