MXPA00004828A - Cold box for cryogenic distilling plant - Google Patents

Abstract

The invention concerns a distilling plant (4 to 8), comprising at least a cryogenic distilling column (4) and at least a heat exchanger (5), arranged in a chamber (2) with a double casing in which the intermediate partition contains a solid insulator (17, 18). The invention is applicable to air distilling plants on board offshore floating terminals and drilling platforms.

Description

CRYOGENIC DISTILLATION UNIT The present invention relates to a cryogenic distillation unit, in particular air distillation, of the type comprising on the one hand a distillation apparatus consisting of at least one cryogenic distillation column and at least one heat exchanger, and on the other hand thermal insulation means of said apparatus. This applies, for example, to oxygen production units shipped on oil platforms at sea or on vessels.

US-A-4038060 discloses a cryogenic distillation unit of a radioactive gas which prevents dangerous gases from escaping around the double-wall apparatus filled with pearlite and which uses an absorbent inside the inner lining to absorb the gases. radioactive gases in case of accident - In the classical technique, the cryogenic distillation columns and all the associated equipment (heat exchangers, cryogenic pumps, cryogenic valves, connection ducts, etc.) operating at low temperature are arranged in a "cold box", usually parallelepiped, filled with REF .: 120412 a bulk insulator such as expanded perlite. This insulator thermally protects each constituent at the same time from the external temperature and that of the other constituents with a different temperature. This type of material owes its insulating qualities both to the low thermal conductivity (<0.05 /m.°C) and to a high load loss, favorable against the phenomenon of convection.

However, this technique presents a drawback from the point of view of safety. In fact, in case of significant loss of gas or cryogenic liquid, coming for example from an accidental rupture of the pipe, the strong loss of charge of the pearlite opposes the evacuation of this fluid into the atmosphere. This results in a brutal cold exposure of the cold box liner and the structure that supports it, which can lead to ruptures due to embrittlement and the emission of cryogenic fluid in the environment, which is dangerous for personnel.

Oil platforms in the sea produce waste gases. For economic and environmental reasons, it is becoming increasingly necessary to recover those gases. One method consists of its conversion into heavier hydrocarbons, in liquid form and therefore more easily transportable, by the Fischer-Tropsch process, which consumes large amounts of oxygen.

Consequently, it would be interesting to be able to ship an air distillation column on a platform or a boat, but the safety problem described above must be solved, since the distillation unit is fixed on a metal structure, and also the personnel can not quickly evacuate the surroundings of this unit.

The invention therefore aims to provide a cryogenic distillation unit, which comprises an effective protection against the losses of cryogenic fluid.

For this purpose, the invention relates to a cryogenic distillation unit according to claim 1.

The distillation unit according to the invention may comprise one or more of the following characteristics: the inner lining of the chamber is constituted, at least in its lower part, by a resilient metal, in particular stainless steel or aluminum; - the solid insulation located around and above the distillation apparatus is a bulk insulator, in particular expanded perlite; - a solid insulator that supports the inner lining of the chamber is interposed between the bottoms of the two linings; the distillation column and the heat exchanger are supported by supports which pass through the bottom of the inner lining to a seal and rest on the outer lining; - at least one chimney for access to auxiliary equipment of the distillation apparatus such as pumps or valves is provided, this chimney passing through the double coating and being blocked by a fixed plug; - the heat exchanger, and possibly other equipment inside the chamber and whose operating temperature is different from that of the distillation column, are provided with additional insulation, in particular by coating with a sheet or band insulator; - the inner lining is equipped with a valve for limiting its internal pressure; the chamber is provided with means for introducing a dry, particularly inert gas into the inner lining and / or the separating wall; - the separating wall is equipped with a valve for limiting its internal pressure; - the camera is attached to a structure in the sea such as an oil rig or a boat; - the camera is fixed to a base which in turn is fixed to a base of said structure by means of piles.

An exemplary embodiment of the invention will be described below with reference to the appended drawing, in which: - Figure 1 schematically represents, in vertical section, a distillation unit according to the invention; and - Figure 2 is a sectional view taken along line II-II of Figure 1.

The air distillation unit 1 shown in FIGS. 1 and 2 essentially comprises a double-walled chamber 2 in whose interior space 3 there are arranged a double air distillation column 4, heat exchangers 5, connecting ducts 6 and cryogenic accessories such as cryogenic pumps 7, cryogenic valves 8, etc.

Column 4 is constituted by two distillation columns, respectively medium pressure and low pressure, as is well known in the art. These two columns 4A and 4B are arranged side by side, as seen in Figure 2, but have been brought to the middle plane in Figure 1 for clarity of the drawing. In addition, the distillation unit certainly includes the set of usual accessories and equipment.

Chamber 2 is double coated. The inner lining 9 comprises a flat bottom 10, a cylindrical side wall 11 and a dome roof 12, being made of stainless steel. The outer skin 13 comprises a flat bottom 14, a cylindrical side wall 15 and a dome roof 16, made of carbon steel. In any case, the bottom 14 can also be made of stainless steel.

A first solid insulator 17, constituted by blocks of insulating material, such as "Foam Glass", is disposed over the entire surface of the bottom 10, between it and the bottom 14. A second solid insulator 18, consisting of expanded perlite in bulk , it fills the rest of the separating wall of the chamber, around and above the components of unit 1 arranged in space 3, which is devoid of any kind of solid insulation.

The components disposed in the space 3 are carried by supports 19 which pass through the seal 10 in a sealed joint and rest on the bottom 14. In this way, the insulator 17 supports the inner lining 9, but it is the bottom 14 and consequently the base 20, constituted for example by a steel structure on which said bottom is placed, those that support the weight of the components of the unit located inside the chamber 2. In turn, this base 20 is fixed to the structure of support 21, for example a metallic oil platform or boat bridge, by means of piles 22 that have an air gap 23 between them.

An access chimney 24, blocked by a fixed plug 25, passes through the double roof 12, 16 of the chamber 2 and leads to the components that need some maintenance, such as pumps 7 and valves 8.

Each component operating at a temperature different from that of column 4, is provided with a supplementary insulation 26 in the form of a coating with glass wool or analogous material. These are in particular heat exchangers 5, ducts 6 connected at the hot end of the latter, as well as the chimney 24. In this way, the convection phenomena become minimal.

A supply conduit 27 in dry nitrogen at ambient temperature, provided with regulating valves 28, makes it possible to keep the space 3 and the separating wall of the chamber under slight overpressure. This allows on the one hand to inert those volumes, and on the other hand to avoid appearing in the same condensation phenomena that threaten to put them in depression.

To avoid any kind of risk of excessive overpressure, each of the ceilings 12 and 16 are equipped with a pressure limiting valve 29. It will be observed that the cylindrical and domed shape of the chamber favors its resistance to overpressure.

In case of significant loss of cryogenic fluid, this fluid is efficiently retained by the inner liner 9 of stainless steel, which is a resilient metal, the gas resulting from the eventual evaporation of liquid being evacuated by means of the valve 29 of the roof 12.

Furthermore, the cold is practically not transmitted to the external cladding and with greater reason to the base 20 or to the underlying metal structure 21. In this way, the risks of breakage of elements due to embrittlement are ruled out.

It will be noted that, thanks to the presence of the chimney 24, organs such as the organs 7 and 8 can be accessed without having to remove the pearlite 18 in each intervention.

It is noted that in relation to this date, the best method known to the applicant, to carry out the aforementioned invention is that which is clear from the manufacture of the objects to which it refers.

Having described the invention as above, property is claimed as contained in the following:

Claims (12)

1. Cryogenic distillation unit, in particular air distillation, of the type comprising on the one hand a distillation apparatus, containing at least one cryogenic distillation column, and at least one heat exchanger, and on the other hand of thermal insulation of this apparatus, characterized in that the distillation apparatus is arranged in a double-walled chamber whose separating wall contains a solid insulator, and because it is neither bulk nor absorbent insulator inside the inner shell.

2. Unit according to claim 1, characterized in that the inner lining of the chamber is constituted, at least in its lower part, by a resilient metal, in particular stainless steel or aluminum.

3. Unit according to claim 1 or 2, characterized in that the solid insulator located around and above the distillation apparatus is a bulk insulator, in particular expanded perlite.

4. Unit according to any one of claims 1 to 3, characterized in that a solid insulator that supports the inner lining of the chamber is interposed between the bottoms of the two liners.

5. Unit according to claim 4, characterized in that the distillation column and the heat exchanger are supported by supports that pass through the seal of the inner cladding to a sealed joint and rest on the outer cladding.

6. Unit according to any one of claims 1 to 5, characterized in that at least one access chimney is provided for auxiliary equipment of the distillation apparatus such as pumps or valves, through this chimney the double coating and being plugged by a fixed plug .

7. Unit according to any one of claims 1 to 6, characterized in that the heat exchanger, and possibly other equipment inside the chamber and whose operating temperature is different from that of the distillation column, are provided with additional insulation, in particular by coating with a sheet or band insulator.

Unit according to any one of claims 1 to 7, characterized in that the inner lining is equipped with a valve for limiting its internal pressure.

Unit according to any one of claims 1 to 8, characterized in that the chamber is provided by means of introducing a dry, particularly inert gas into the inner lining and / or the separating wall.

10. Unit according to claim 9, characterized in that the separating wall is equipped with a valve for limiting its internal pressure.

11. Unit according to any one of claims 1 to 10, characterized in that the camera is fixed to a structure in the sea such as an oil platform or a boat.

12. Unit according to claim 11, characterized in that the chamber is fixed to a base which in turn is fixed to a base of said structure by means of piles.