FR2629903A1 - Process and plant for the production of ground solid carbon dioxide from liquid carbon dioxide - Google Patents

Abstract

Production of cold. The plant comprises: an exchanger 1 including: - an inlet pipe 7 equipped with a valve 8 and intended to be connected to a reservoir 10 of liquid carbon dioxide, - an ejection pipe 3 equipped with a valve 4, - a rotor 22 for scraping its inner wall, a jacket 13, 14 at least locally surrounding the exchanger and defining an expansion chamber 15 for a refrigerant fluid, and a storage and/or cooling enclosure 5 connected to the ejection pipe. Application to the production of ground or chipped ice.

Description

PROCESS AND PLANT FOR THE PRODUCTION OF CRUSHED CARBONIC ICE
STARTING FROM LIQUID CARBON DIOXIDE
The present invention relates to the technical field of the production of frigories useful in numerous applications and uses and it relates, more particularly, to the production of frigories from carbon dioxide.

 When carbon dioxide is intended to be used as a lost fluid refrigerant, it is stored under pressure in a tank with enhanced thermal insulation. The storage conditions involve a pressure between 17 and 25 bar absolute and a temperature at equilibrium between 249 and 2610 K.

 From such storage, the refrigeration is carried out by direct expansion of the liquid carbon dioxide to a pressure close to atmospheric pressure. As this expansion pressure is lower than the pressure corresponding to the triple point of carbon dioxide, ie 5.18 bar absolute, the expansion produces the formation of a solid phase and a gas phase. It can be considered that a kilogram of liquid carbon dioxide, taken under 20.9 bar absolute and at a temperature of 2550 K, absorbs 73.8 kilocalories to find itself gaseous at a pressure of 1 bar absolute and at a temperature of 2530 K.

 The refrigeration restitution takes place in a gaseous carbon dioxide atmosphere, which makes it possible to preserve the qualities of the cooled products and, more particularly, in the food sector. For a pressure of 1 bar absolute, it is possible to envisage a refrigeration return up to a temperature level of 1940 K.

 However, it is known that, during expansion, the frigories are mainly transported by the solid phase. It would therefore be advantageous to favor your formation of the solid phase to the detriment of the production of the gas phase and, consequently, to lower the enthalpy level of the liquid phase until solidification.

 The present invention relates, precisely, to such an objective and relates to a method and an installation for introducing frigories into the liquid phase of carbon dioxide up to the border of the production of the solid phase.

 The present invention relates to a method and an installation making it possible to produce, at a particularly attractive cost price, ground dry ice directly usable, from liquid carbon dioxide.

 The invention relates to a particularly simple and reliable method and installation, capable of providing, continuously, a production of ground or fragmented dry ice, easily usable in most fields of application where it is necessary to be able to have, more or less temporarily, from a certain and relatively durable source of frigories.

To achieve the above objectives, the method according to the invention is characterized in that it consists of
- introduce, under pressure, into a heat exchanger
liquid carbon dioxide now, by
sky of this exchanger, a gas phase whose
pressure is between the pressure
supply and the pressure of the triple point,
- cool the exchanger by expansion, in a
double jacket of this exchanger, of a fluid
refrigerant to crystallize, on the wall
internal heat exchanger, carbon dioxide
liquid,
- scrape the internal wall of the exchanger to
take off the crystallized carbon dioxide and
produce an ice slurry,
- periodically expel this porridge in
management of a storage enclosure and / or
cooling by means of the gas phase.

The invention also relates to an installation for the production of dry ice ground from liquid carbon dioxide, characterized in that it comprises
- an exchanger comprising
an inlet pipe fitted with a valve
and intended to be connected to a
tiquid carbon dioxide tank,
an expulsion manifold fitted with a
valve,
- a scraping mobile on its internal wall,
- a double envelope surrounding, at least
locally, the interchange and delimiting a
expansion chamber for a refrigerant,
- and a storage enclosure and / or
cooling connected to the tubing
deportation.

 Various other characteristics will emerge from the description given below with reference to the appended drawings which show, by way of nonlimiting examples, embodiments of the object of the invention.

 Fig. 1 is a schematic sectional elevation of an installation for implementing the method of the invention.

 Fig. 2 is a cross section taken substantially along line II-II of FIG. 1.

 Fig. 3 is a sectional elevation illustrating an alternative embodiment of the installation according to the invention.

 The process for producing ground dry ice from liquid carbon dioxide is advantageously carried out from an installation, an exemplary embodiment of which is illustrated in FIGS. 1 and 2. Such an installation comprises an exchanger 1, preferably of revolution, the axis x-x 'of which is oriented vertically. The exchanger 1 is made of a very good thermally conductive material, such as steel, aluminum or copper. The heat exchanger 1 internally delimits a useful volume 2, of generally cylindrical shape, the lower part of which is extended by an outlet pipe 3 controlled by a valve 4 with control, preferably automatic. The pipe 3 opens downstream of the valve 4 in a cooling enclosure 5 and / or cooling having, internally, preferably, a fragmentation screen 6 extending at a distance and facing the orifice of the outlet pipe 3.

 The exchanger 1 comprises, slightly set back from its upper part, a tube 7, called the inlet, controlled by a valve 8, preferably also with automatic control. The inlet pipe 7 is connected to a circulation pipe 9 coming from a tank 10 for storing liquid carbon dioxide. The typical storage conditions for liquid carbon dioxide involve a pressure between 17 and 25 bar absolute and an equilibrium temperature between 249 and 2610 K.

 The inlet tubing 7 is located at a level lower than a tubing It capable of injecting a gaseous phase of carbon dioxide coming from or taken from the tank 10 and expanded by means of a regulator 12.

The exchanger 1 is produced so as to comprise an envelope 13, called internal, and a double envelope 14, called external. The envelopes 13 and 14 together define an annular chamber 15 capable of ensuring the expansion of an auxiliary refrigerant, for example constituted by monobromotrifluoromethane (C Br F3) known in commerce under the reference R 13 B1. Preferably, the refrigerant is maintained to be evaporated at a temperature below 2160 K at
The interior of the chamber 15 and, for example, 2130 K. Preferably also, the refrigerant is maintained in circulation in the annular chamber 15 by means of a circuit 16 forming part of a refrigerating machine 17, such a circuit being connected to an inlet pipe 18, as well as to an outlet pipe 19 opening into the chamber 15. The inlet pipe 18 is preferably preceded by a pressure reducer 20 whose adjustment is controlled by l 'via a thermosensitive sensor 21 assessing the temperature of the gas phase coming from the outlet pipe 19.

 The exchanger 1 comprises, internally, a mobile 22 for scraping the inner peripheral surface of the wall 13. The mobile scraping 22 can be produced in various suitable ways and, in particular, comprise a shaft 23 extending over L ' axis xx 'and carried by bearings 23a. The shaft 23 is moved in rotation by means of a motor member 24 of the external electric type. The exchanger 1. The shaft 23 carries, by means of radial arms 25, scraper blades 26, for example rectilinear and parallel to the axis xx 'and intended to rub on the inner face of the wall 13.

 The installation described above is intended to allow the implementation of the method of the invention consisting in maintaining, in the annular cooling chamber 15, the expansion of the auxiliary refrigerant at a temperature below 2160 K via of the refrigerating machine 17. When the suitable cooling temperature is reached, the valve 4 is closed, while the valve 8 is open, so as to admit, in the volume 2, liquid carbon dioxide taken from the tank 10 at a pressure, for example of the order of 20.9 bar absolute, and at a temperature in the region of 2550 K.

 The admission of liquid carbon dioxide is carried out so as to maintain, always, in the sky above volume 2, a gaseous phase maintained at a pressure between the supply pressure by the inlet pipe 7 and the pressure corresponding to the point triple carbon dioxide.

 The admission of dioxide into volume 2 produces, due to the cooling of the wall 13, a crystallization of the dioxide on the internal face of the latter. The rotation drive, in the direction of your arrow f1 of the shaft 23 by the motor 24, allows the scraper blades 26 to take off the carbon dioxide crystallized on the wall 13. As the mobile rotates 22, the blades 26 provide a production of crushed ice accumulating at the bottom of the exchanger 1. When a sufficient mass of crushed ice has been produced, the valve 8 is closed, while, simultaneously, the valve 4 The gaseous phase under pressure, occupying the sky in volume 2, then assumes, in addition to the admission of an additional gaseous phase through the tube 11, the expulsion of the mass or the ice slurry. crushed, by means of the outlet tube 3 in the direction of the enclosure 5. The pressure prevailing in the sky of volume 2 makes it possible to produce an energetic expulsion of the mass of crushed ice which is projected against the screen 6 intended for ensuring fragmentation on the one hand and a sensiblem distribution on the other homogeneous inside the enclosure 5. It should be considered that the enclosure 5 can constitute either a storage tank or a cooling volume in which or on which the products to be cooled are placed.

 As an indication, it is possible to produce an exchanger 1, so as to make it have a scraped surface of 8 dm2 for an internal volume of 1.5 dm3. In such a case, the scraping mobile can comprise two scraper bars supported by a shaft 23 rotated at 15 rpm by a motor 23 of 1 kw of power.

 With liquid carbon dioxide admission conditions, as recalled above, and an expulsion phase frequency every four minutes, it is possible to produce 11 kg / h of crushed dry ice. In such a case, the power consumed by the refrigerating machine 17 to maintain the evaporation of the auxiliary refrigerant is close to 0.1 kWh / kg of ground carbon dioxide produced.

 These conditions make it possible to consider that ground dry ice produced by the process and an installation for its implementation according to the invention can be obtained at a particularly advantageous cost price.

 The examination of the technical means used also made it possible to consider that the installation for the production of ground dry ice involves simple technical factors which are relatively inexpensive, reliable and which require little or no adjustment of commissioning or maintenance.

 It should be considered that the tube 11 makes it possible to ensure in the sky of volume 2 the introduction of a gaseous phase of carbon dioxide assuming an addition for the expulsion, but also the introduction of a gaseous phase of sweeping during the same phase to avoid, inside volume 2, any entry of moisture detrimental to the course of the subsequent crystallization phase.

 Fig. 3 shows an alternative embodiment according to which the exchanger 1 contains, internally, a stirring mobile 22 produced in the form of an Archimedes screw 30 supported by bearings 30a and the axis of rotation of which coincides with the geometric axis xx 'of volume 2. In such an example, the exchanger 1 is always of the double-walled type to delimit the annular chamber 15 whose inlet 18 and outlet 19 pipes are connected to a refrigerating machine 17.

 In this exemplary embodiment, the exchanger 1 has an intake manifold 7 in relation to the circuit 9 and which is located at the lower part of the volume 2. The upper part of this volume is extended by an outlet manifold 31 provided with a control valve 32. Beyond the valve 32, the tubing 31 is connected to an intermediate capacity 33 of temporary storage extending parallel to the axis x-x '. The lower part of the capacity 33 is provided with the outlet pipe 3 controlled by the valve 4 and opening into the storage and / or cooling enclosure 5, which is internally provided with the fragmentation screen 6.

 Valves 32 and 4 are controlled simultaneously to occupy opposite states, that is to say, for one to go from an open state to the closed state, while the other goes simultaneously from the closed state in the open state.

 Archimedes' screw 30 is that in rotation via a motor member 34 responsible for driving it in a direction such that, depending on the helical winding which characterizes it, the carbon dioxide crystallized on the wall peripheral. internal 13 is scraped and urged in an upward vertical movement, so as to naturally borrow the tubing 31 to pass through the open valve and be discharged into the tank 33, the valve 4 of which is closed.

 As in the previous example, the upper part of volume 2 maintains a gaseous phase sky under pressure, as well as in the upper part of capacity 33. Thus, periodically, it becomes possible to close the intake valve 81 equipping the inlet pipe 71 to close the valve 32 and to open the valve 4, so that the gaseous phase under pressure, occupying the upper part of the capacity 33, expels, in the direction of the enclosure 5, the mass of crushed dry ice temporarily stored in the cavity 33.

 After expulsion, the valve 4 is closed, while simultaneously the valves 32 and 81 are open.

 For example, an exchanger 1, of the above type, produced to have a scraped surface of 4 dm2 and the screw of which is driven by a 0.75 kw motor rotates at a speed between 10 and 50 rpm and, for example, at 20 rpm, produces 5 kg / h of dry ice. The conditions for storing and admitting the auxiliary refrigerant are the same as those described above, as are those for admitting the liquid carbon dioxide.

 The invention is not limited to the examples described and shown, since various modifications can be made thereto without departing from its scope.

Claims (14)

 1 - Process for producing crushed dry ice from liquid carbon dioxide,  characterized in that it consists of:  - introduce, under pressure, into a heat exchanger  liquid carbon dioxide now, by  sky of this exchanger, a gas phase whose  pressure is between the pressure  supply and the pressure of the triple point,  - cool the exchanger, by expansion, in a  double jacket of this exchanger, of a fluid  refrigerant to crystallize on the wall  internal exchanger, carbon dioxide  liquid,  - scrape the inner wall of the exchanger to  take off the crystallized carbon dioxide and  produce an ice slurry,  - periodically expel this boil in  management of a storage enclosure and / or  cooling by means of the gas phase.  2 - Process according to claim 1, characterized in that liquid carbon dioxide is introduced into the exchanger at a pressure close to 20.9 bar absolute and at a temperature close to 2550 K and in that cools the exchanger with a refrigerant maintained in evaporation at a temperature below 2160 K.  3 - Method according to claim 1 or 2, characterized in that the refrigerant is monobromotrífluorométhane maintained in circulation by a refrigerating machine.  4 - Process according to claim 1, characterized in that the expulsion of the ice slurry is produced with the injection of a gaseous phase to make up carbon dioxide.  5 - Process according to claim 1 or 4, characterized in that the expulsion of the ice slurry is produced directly from the production exchanger in the direction of the enclosure.  6 - Process according to claim 1 or 4, characterized in that the expulsion of the ice slurry is produced from an intermediate transfer capacity interposed between the exchanger and the enclosure.  7 - Installation for the production of dry ice ground from liquid carbon dioxide, characterized in that it comprises  - an exchanger (1) comprising  an inlet pipe (7) equipped with a  valve (8) and intended to be connected to  a carbon dioxide tank (10)  liquid,  an expulsion pipe (3) fitted with a  valve (4),  a mobile (22) for scraping its wall  internal,  - a double envelope (13, 14) surrounding, at  less locally, the interchange and delimiting a  expansion chamber (15) for a fluid  refrigerant,  - and an enclosure (5) for storage and / or  cooling connected to the tubing  deportation.  8 - Installation according to claim 7, characterized in that the exchanger is constituted by a body of revolution and contains a mobile scraper (22) rotating.  9 - Installation according to claim 8, characterized in that the rotating mobile (22) is constituted by a rotating shaft (23) extending on the axis of revolution of the body and carrying scraper blades (26).  10 - Installation according to claim 8, characterized in that the rotating mobile is constituted by an Archimedes screw (30).  11 - Installation according to one of claims 7 to 10, characterized in that the expulsion manifold (3) is located in the lower part, the inlet manifold (7) is located near the upper part and below the opening of a pipe (11) for injecting a gaseous phase under make-up pressure of carbon dioxide.  12 - Installation according to one of claims 7 to 10, characterized in that the inlet pipe (71) is located in the lower part of the exchanger whose upper part is provided with an outlet pipe (31) equipped a valve (32) and connected to the upper part of an intermediate transfer capacity (33) provided, in the lower part, with the expulsion pipe (3) in the direction of the enclosure (5).  13 - Installation according to claim 7, characterized in that the double jacket (13, 14) is connected to a circuit (16) for circulation of a refrigerant, maintained by a thermal machine (17).  14 - Installation according to claim 7, characterized in that the enclosure (5) comprises, internally, a fragmentation screen (6) facing the expulsion pipe.