U.S. patent application number 13/701326 was filed with the patent office on 2013-04-04 for cryogenic cooling method and installation using liquid co2 and employing two exchangers in series.
This patent application is currently assigned to L'Air Liquide Societe Anonyme Pour L'Etude Et L'Exploitation Des Procedes Georges Claude. The applicant listed for this patent is Thierry Dubreuil, Didier Pathier, Mohammed Youbi-Idrissi. Invention is credited to Thierry Dubreuil, Didier Pathier, Mohammed Youbi-Idrissi.
Application Number | 20130081789 13/701326 |
Document ID | / |
Family ID | 43413856 |
Filed Date | 2013-04-04 |
United States Patent
Application |
20130081789 |
Kind Code |
A1 |
Pathier; Didier ; et
al. |
April 4, 2013 |
Cryogenic Cooling Method and Installation Using Liquid CO2 and
Employing Two Exchangers in Series
Abstract
A method and installation using liquid CO.sub.2 as a cryogenic
fluid for transferring cold energy to products, wherein liquid
CO.sub.2 is sent into a heat exchanger system including first and
second heat exchangers connected in series. The liquid CO2 is
supplied to the first heat exchanger where it evaporates. Gaseous
CO2 from the first exchanger is supplied to the second heat
exchanger. The atmosphere surrounding the products is blown across
the heat exchangers to provide a cooled atmosphere with which to
cool the products. The latent heat of vaporization of the liquid
CO2 in the first heat exchanger and the sensible heat of the
gaseous CO2 in the second heat exchanger satisfies the cooling
requirement of the products. The first exchanger is kept at a
pressure higher than the triple point pressure for CO.sub.2,
whereas the second exchanger is held at atmospheric pressure or at
a pressure between the triple point of the fluid and atmospheric
pressure.
Inventors: |
Pathier; Didier; (Voisins Le
Bretonneux, FR) ; Dubreuil; Thierry; (Boissets,
FR) ; Youbi-Idrissi; Mohammed; (Massy, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pathier; Didier
Dubreuil; Thierry
Youbi-Idrissi; Mohammed |
Voisins Le Bretonneux
Boissets
Massy |
|
FR
FR
FR |
|
|
Assignee: |
L'Air Liquide Societe Anonyme Pour
L'Etude Et L'Exploitation Des Procedes Georges Claude
Paris
FR
|
Family ID: |
43413856 |
Appl. No.: |
13/701326 |
Filed: |
May 5, 2011 |
PCT Filed: |
May 5, 2011 |
PCT NO: |
PCT/FR11/51023 |
371 Date: |
November 30, 2012 |
Current U.S.
Class: |
165/104.27 |
Current CPC
Class: |
F25D 3/10 20130101; F28D
15/02 20130101 |
Class at
Publication: |
165/104.27 |
International
Class: |
F28D 15/02 20060101
F28D015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2010 |
FR |
FR 1054342 |
Claims
1-9. (canceled)
10. A process for indirectly cooling products using liquid
CO.sub.2, comprising the steps of: supplying liquid CO.sub.2 to a
heat exchanging system at which the liquid CO.sub.2 evaporates, the
heat exchanging system comprising first and second heat exchangers
connected in series, the first heat exchanger being kept at a
pressure above the triple point pressure of CO.sub.2, the second
heat exchanger being kept at atmospheric pressure or at a pressure
between the triple point pressure of CO.sub.2 and atmospheric
pressure; and removing heat from the products through heat exchange
between cold walls of the heat exchangers and an atmosphere
surrounding the products.
11. The process of claim 10, further comprising: adjusting a flow
rate of the liquid CO.sub.2 supplied to the first heat exchanger
with a liquid CO.sub.2 flow rate adjustment element disposed
upstream of the first heat exchanger, the adjustment being based
upon a cooling requirement of the products to be cooled, the liquid
CO.sub.2 flow rate adjustment element comprising either a
thermostatic regulator or a temperature probe/regulator/valve
assembly; maintaining a pressure in the first heat exchanger above
the triple point pressure of CO.sub.2; and transferring gaseous
CO.sub.2, formed from vaporization of the liquid CO.sub.2 in the
first heat exchanger, to the second heat exchanger
12. The process of claim 11, wherein the pressure in the first heat
exchanger is kept at a pressure above the triple point pressure of
CO.sub.2 by virtue of a back-pressure regulation device that is
placed at an outlet of the first heat exchanger, the back-pressure
regulation device comprising either a back-pressure regulator or a
pressure sensor/regulator/valve assembly.
13. The process of claim 12, wherein a phase separator is disposed
in fluid communication between the outlet of the first heat
exchanger and the back-pressure regulation device, the phase
separator preventing liquid CO.sub.2 from flowing into the second
heat exchanger.
14. An installation for cooling products using liquid CO.sub.2,
comprising, a first heat exchanger receiving liquid CO.sub.2, a
second heat exchanger receiving gaseous CO.sub.2 formed from
vaporization of the liquid CO.sub.2 in the first heat exchanger, a
blower operatively associated with the first and second heat
exchangers, a liquid CO.sub.2 flow rate adjustment element disposed
upstream of the first heat exchanger, and a back-pressure
regulation device, wherein: the liquid CO.sub.2 flow rate
adjustment element is adapted and configured to adjust a flow rate
of liquid CO.sub.2 into the first heat exchanger based upon a
cooling requirement of the products to be cooled and comprises
either a thermostatic regulator or a temperature
probe/regulator/valve assembly; the blower is adapted and
configured to blow an atmosphere surrounding the products to be
cooled into contact with cold walls of the heat exchange system;
the first and second heat exchangers are connected in series; the
back-pressure regulation device is disposed downstream of an outlet
of the first heat exchanger and is adapted and configured to
maintain a pressure in the first heat exchanger above the triple
point pressure of CO.sub.2.
15. The installation of claim 14, further comprising a phase
separator inserted upstream of the back-pressure regulation
device.
16. The installation of claim 14, wherein the back-pressure
regulation device comprises either a back-pressure regulator or a
pressure sensor/regulator/valve assembly.
Description
[0001] The present invention relates to the field of cooling
processes employing CO.sub.2.
[0002] The use of CO.sub.2 in such cooling processes is, as is
known, very advantageous, since this fluid has a solid phase at
-80.degree. C. at atmospheric pressure, thereby allowing dry ice to
be used in certain applications, this ice being very effective,
especially as far as localized cooling without refrigeration
equipment is concerned. Solid CO.sub.2 has many applications, such
as for example dry ice bags, which are loaded into containers for
transporting food or pharmaceutical products, or which indeed may
be used to keep meals cool in the field of aerial
transportation.
[0003] However, when this gas is used in ("indirect injection")
heat exchangers, typically tube or finned heat exchangers, this
advantage turns into a drawback because the untimely appearance of
solid CO.sub.2 (carbon snow) in an exchanger rather rapidly leads
to the latter becoming blocked.
[0004] Therefore, to prevent this drawback of transition into the
solid phase, it is sought to prevent the solid phase of CO.sub.2
from appearing, and conditions are therefore preferred that make it
possible to keep the CO.sub.2 in liquid or gaseous form in the
entire exchanger.
[0005] In order to exchange heat while ensuring the CO.sub.2
remains in its gaseous or liquid phase (vaporization of the liquid
CO.sub.2 without running the risk of forming solid CO.sub.2), the
pressure in the tube must be kept above the theoretical pressure of
5.18 bar corresponding to the triple point pressure of this fluid.
In practice, the system is restricted as it were to a pressure of 6
to 7 bar, thus ensuring a safety margin of 0.82 to 1.82 bar.
[0006] Whereas the sublimation temperature of solid CO.sub.2 at
atmospheric pressure is -80.degree. C., keeping the pressure in the
exchanger at 6 bar relative increases the vaporization temperature
to about -50.degree. C.
[0007] However, carrying out the heat exchange at 6 bar and not at
atmospheric pressure slightly decreases the cooling capacity of the
CO.sub.2. Specifically, when a kilogram of CO.sub.2 is taken out of
storage, for example under standard conditions such as 20 bar
absolute/-20.degree. C., and enters into an exchanger, it releases
277.97 kJ/kg if it is discharged at -50.degree. C. in gaseous form
at 6 bar relative, whereas the same amount of CO.sub.2 releases
292.6 kJ/kg when it is discharged at -50.degree. C. at atmospheric
pressure, i.e. an increase of 5%.
[0008] By way of example, CO.sub.2 discharged at 6 bar after
passing through an exchanger is used in applications such as
refrigerated trucks but also in freezing tunnels or chambers. In
these applications, a heat exchanger is supplied with liquid
CO.sub.2 which, by evaporating in this exchanger, extracts heat
from the medium to be cooled and thus produces the desired cooling.
Cooling of the products to be cooled is achieved via heat exchange
with the internal air of the tunnel, chamber or truck, via blowing
means associated with each exchanger.
[0009] It will therefore be understood that it would be
advantageous to be able to provide a technical solution allowing
heat exchange in a tube or finned heat exchanger (indirect
exchange), at exchanger temperatures that are nonetheless low
(typically -50.degree. C.) without of course running the risk of
forming snow and losing the cooling capacity of the CO.sub.2
following its expansion from 6 bar to atmospheric pressure.
[0010] As will be seen in more detail below, the present invention
provides a new exchange solution, the main features of which may be
summarized as follows: [0011] the solution proposed here relates to
the exchanger configuration adopted, the exchanger used, which may
for example be a tube or finned heat exchanger, consisting of two
exchangers connected in series; [0012] the first exchanger can be
supplied with liquid CO.sub.2 (for example under standard
conditions such as -20.degree. C./20 bar), the liquid encountering,
before it enters the first exchanger, a thermostatic regulator or a
temperature probe/regulator/valve assembly, or any other means
allowing the flow rate of the CO.sub.2 entering the 1st exchanger
to be matched to the cooling requirements in question, i.e.
allowing the "excess" temperature, or, in other words, the
temperature difference between the temperature corresponding to the
saturation vapor pressure (for example at 6 bar, -53.1.degree. C.)
and for example -50.degree. C., which corresponds to 3.1.degree. of
excess, to be controlled; [0013] the pressure in the first
exchanger is kept above 5.18 bar relative, i.e. the temperature of
the phase change of the CO.sub.2 (the formation of snow thus being
prevented), the pressure is, for example, kept at 6 bar absolute by
virtue of a back-pressure regulator or a pressure
sensor/regulator/valve assembly, placed at the outlet of the first
exchanger; [0014] this arrangement makes it possible to ensure that
the CO.sub.2 in the first exchanger is only present strictly in its
gas/liquid two-phase form without at any point the conditions used
allowing a solid to form; [0015] the minimum temperature obtained
in this first exchanger is then about -50.degree. C.; and [0016]
according to one embodiment, the back-pressure regulator at the
outlet of the first exchanger is preceded by a phase separator in
order to prevent any liquid from exiting the first exchanger.
[0017] The back-pressure regulator and the outlet of the first
exchanger will possibly be installed in an upper part of the
complete installation to prevent liquid from escaping, but
configurations where the two exchangers are located at the same
level may also be envisioned.
[0018] The optional presence of the aforementioned separator
increases the reliability of the system. It prevents liquid from
reaching the back-pressure regulator and therefore snow from
forming and causing a blockage at this point. [0019] In summary,
the liquid CO.sub.2 vaporizes in the first exchanger and the gas
formed in this exchanger, for example at 6 bar, is released in the
second exchanger; [0020] this second exchanger is at atmospheric
pressure (or in any case at a pressure below the triple point of
the fluid), the gas then expands, after entering this second
exchanger at 6 bar (or more generally at the pressure maintained in
the first exchanger), to atmospheric pressure (or in any case to a
pressure between the triple point of the fluid and atmospheric
pressure) which causes cooling, namely to a temperature typically
between -60.degree. C. and -70.degree. C.; [0021] and therein lies
the advantage of the present invention, since the cooling produced
by expansion to atmospheric pressure is used by the second
exchanger, and thus all the energy contained in the CO.sub.2 is
used.
[0022] The present invention thus relates to a process employing
liquid CO.sub.2 as a cryogenic fluid for cooling products, this
process being an "indirect injection" cooling process where the
liquid CO.sub.2 is transferred to a heat exchanging system where it
evaporates, the removal of heat from the products occurring by an
exchange between the atmosphere surrounding the products and the
cold walls of the heat exchanger, this process being noteworthy in
that the exchanging system consists of two exchangers connected in
series, the first exchanger being kept at a pressure above the
triple point pressure of CO.sub.2, whereas the second exchanger is
itself kept at atmospheric pressure or at a pressure between the
triple point of the fluid and atmospheric pressure.
[0023] The present invention also relates to an installation for
cooling products using liquid CO.sub.2, the installation employing
an "indirect injection" process, and comprising: [0024] a heat
exchanging system through which the liquid CO.sub.2 can pass; and
[0025] blowing means associated with the heat exchanging system,
able to bring the atmosphere surrounding the products into contact
with cold walls of the heat exchanging system,
[0026] the installation being noteworthy in that the following
measures are implemented: [0027] the exchanging system consists of
two exchangers connected in series; [0028] the installation
comprises, upstream of the inlet of the first exchanger, a means
able to adjust the CO.sub.2 flow rate and to control the excess
temperature thereof relative to the corresponding temperature at
saturated vapor pressure, such as a thermostatic regulator or a
temperature probe/regulator/valve assembly; [0029] the installation
comprises a means for keeping the pressure in the first exchanger
at a pressure above the triple point pressure of CO.sub.2,
preferably a back-pressure regulator or a pressure
sensor/regulator/valve assembly; and [0030] the second exchanger is
at atmospheric pressure or at a pressure between the triple point
of the fluid and atmospheric pressure.
[0031] The installation therefore comprises, if required, a means
for keeping the pressure in the second exchanger at atmospheric
pressure or at a pressure between the triple point of the fluid and
atmospheric pressure.
[0032] Other features and advantages of the present invention will
become more clearly apparent from the following description given
by way of completely nonlimiting illustration with regard to
appended FIGS. 1 and 2, which are partial schematic representations
of installations according to the invention, FIG. 3 showing the
temperature profile expected in the exchanger assembly on the
CO.sub.2 and heat-transfer fluid (air) sides.
[0033] The following elements, and therefore the course followed by
the CO.sub.2, in its various phases, in the installation, may be
seen in FIG. 1: [0034] the first exchanger is able to be supplied
with liquid CO.sub.2 (for example under standard conditions such as
-20.degree. C./20 bar), the liquid encountering, before it enters
the first exchanger, a thermostatic regulator (downstream of point
1) or any other means allowing the flow rate of the CO.sub.2
reaching the first exchanger to be matched to the cooling
requirements in question, i.e. to control the excess temperature,
or, in other words, the temperature difference between the
temperature corresponding to the saturated vapor pressure (for
example 6 bar, -53.1.degree. C.) and for example -50.degree. C.,
which corresponds to 3.1.degree. C. of excess temperature.
[0035] Downstream of point 2 the fluid enters into the first
exchanger. [0036] a pressure higher than 5.18 bar relative is
maintained in this first exchanger, temperature of the phase change
of CO.sub.2 (thus allowing the formation of snow to be prevented),
by virtue of the back-pressure regulator placed at the outlet of
this first exchanger in the figure (back-pressure regulator placed
between points 3 and 4); [0037] this arrangement makes it possible
to ensure that the CO.sub.2 in the first exchanger is present only
in a strictly liquid/gas two-phase form, without at any point the
conditions used allowing a solid to form; [0038] the minimum
temperature obtained in this first exchanger is then -50.degree.
C.; [0039] in the embodiment illustrated here, the back-pressure
regulator at the outlet of the first exchanger is preceded by a
phase separator (between points 3' and 3), in order to prevent any
escape of liquid from the first exchanger. In this embodiment, the
back-pressure regulator and the outlet of the first exchanger are
installed in an upper part of the complete installation, to prevent
escape of liquid. [0040] at the outlet of point 4 and therefore of
the back-pressure regulator, the gas enters into the second
exchanger, which it exits at point 5.
[0041] The table below collates the thermodynamic properties of the
fluid at various points in FIG. 1, and makes it possible to show
unambiguously the advantages of the invention in terms of cooling
efficiency. The table especially illustrates a number of
temperature conditions, at the outlets of the exchangers.
[0042] In addition, to clearly show the benefit of the present
invention, the energy efficiency of a system not employing the
invention and a system employing the present invention are
compared, in the case where the final temperature in the exchanger
is -25.degree. C. and in the case where the final temperature in
the exchanger is -5.degree. C.
[0043] Considering the first case (the final temperature in the
exchanger being -25.degree. C.) [0044] for a system employing a
single exchanger: 1 kg of CO.sub.2 releases 457-154.5=302.5 kJ;
[0045] for a system employing two exchangers according to the
invention: 1 kg of CO.sub.2 releases 464.5-154.5=310 kJ; i.e. a
2.5% increase in energy.
[0046] In the second illustrative case, where the final temperature
of the exchanger is -5.degree. C.: [0047] for a system employing a
single exchanger: 1 kg of CO.sub.2 releases 474.6-154.5=320.1 kJ;
[0048] for a system employing two exchangers according to the
invention: 1 kg of CO.sub.2 releases 480.8-154.5=326.3 kJ; i.e. a
1.9% increase in energy.
TABLE-US-00001 [0048] TABLE 1 Point on the figure T (.degree. C.) P
(bar abs) H (kJ/kg) 1 -20.0 19.7 154.5 2 -53.1 6 154.5 .sup. 3'
-53.1 6 431.6 3 -50.0 6 434.5 3 standard -25.0 6.0 457.0 3 standard
-5.0 6.0 474.6 4 -63.1 1 434.5 5 -25.0 1 464.5 5 -5.0 1 480.8
[0049] The temperature profile expected in the exchanger on the
CO.sub.2 and heat-transfer fluid (air for example in an application
such as the transportation of frozen products) sides, shown in FIG.
3, demonstrates that the present invention also has a beneficial
impact on the temperature profile in the exchangers: the fact that
the second exchanger stage is at atmospheric pressure makes it
possible to take advantage of a cryogenic effect as the curves in
FIG. 3 show.
[0050] If FIG. 1 showed a first embodiment of the invention, FIG.
2, for its part, shows another, which will not be described in
greater detail here. As will become clear on examination of the
figure, it illustrates a variant employing: [0051] upstream of the
first exchanger, an assembly consisting of a calibrated orifice and
a temperature-controlled valve, rather than a thermostatic
regulator; and [0052] at the outlet of the first exchanger of the
installation, a pressure sensor/regulator/valve assembly, rather
than a back-pressure regulator.
* * * * *