WO2018130157A1

WO2018130157A1 - Enclosure for an apparatus for the separation of a gaseous mixture by distillation, and separation apparatus comprising such an enclosure

Info

Publication number: WO2018130157A1
Application number: PCT/CN2018/072121
Authority: WO
Inventors: Remy Kurtz; Patrice Cavagne; Benoit Davidian; Clement Lix; Daniel PISANO; Arnaud Favre
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2017-01-10
Filing date: 2018-01-10
Publication date: 2018-07-19
Anticipated expiration: 2019-07-10
Also published as: CN110268215B; CN110268215A

Abstract

In an enclosure for an apparatus for separation of a gaseous mixture, at cryogenic below-ambient temperature, designed to contain at least one element of the apparatus, the element having to operate at a temperature below 0℃, preferably below -50℃, or even at cryogenic temperatures, the enclosure is in the form of a caisson and consists of at least one framework comprising longitudinal posts (3) and beams and bracing connecting the posts to one another, at least one means for transporting material and/or electricity, light or information (13, 15, 17) being housed at least partially in the at least one post.

Description

Enclosure for an apparatus for the separation of a gaseous mixture by distillation, and separation apparatus comprising such an enclosure

The present invention relates to an enclosure for an apparatus for separation of a gaseous mixture by distillation at below-ambient, or even cryogenic, temperature.

An enclosure for an apparatus for separation of a gaseous mixture, in particular of air by distillation at cryogenic below-ambient temperature, contains at least one element of the apparatus having to operate at a temperature below 0℃, or even at cryogenic temperatures. The enclosure consists of at least one framework comprising longitudinal posts and beams connecting the posts to one another.

Conventionally, the framework is the framework of a closed caisson having at least four lateral walls. It can also comprise a ceiling and/or a floor. In the operational state, the closed caisson contains insulation in contact with at least one of the walls and/or with the element that has to operate at a below-ambient temperature.

By contrast, it is also known to provide a framework that contains and/or supports at least one closed caisson as described hereinabove. “Tonnage Nitrogen Generation for Oil and Gas Enhanced Recovery in the North Sea” by Goldstone et al, Proceedings of the Gas Processors Association, 1992 shows, in Figure 6, such a framework that contains and supports closed caissons containing elements of an air separation apparatus. Thus, the framework forms an open structure making it possible to introduce a closed caisson containing at least one separation column, another caisson containing another element that has to operate at a below-ambient temperature, for example a heat exchanger designed to cool the gaseous mixture that is to be separated in the column.

Apparatus for separating a gaseous mixture, for example air, using cryogenic distillation comprise a part operating at ambient temperatures and a part operating at below-ambient temperatures, that is to say temperatures below 0℃ or even cryogenic temperatures. The elements operating at below-ambient temperatures are kept in insulated enclosures that are often referred to as “cold boxes” and are filled with one (or more) insulating material (s) (perlite, rockwool, vacuum insulation panels, etc. ) . These enclosures are often in the form of a cuboid caisson having a metal framework that comprises vertical posts connected to one another by horizontal beams. The four lateral walls of the caisson are clad with metal plates. The elements operating at ambient temperature may also be placed in other frameworks to facilitate either transport or acoustic insulation thereof, or to keep them in place above the ground.

The insulated enclosures are not entirely sealed with respect to the outside air and, for thermal efficiency reasons and for safety reasons, a continuous flow of gaseous nitrogen flushes the interior of these “cold boxes” .

As shown in WO-A-2004015347, it is known to send gaseous nitrogen from the distillation into the insulation by means of a distributor placed in the middle of the mass of insulation.

In order to keep a dry atmosphere in the insulation of a cold box, use is generally made of the nitrogen from the inert gas network of the factory, having an oxygen content of less than 5%, by creating a slight overpressure with respect to atmospheric pressure in order to avoid any ingress of humid air into the insulation. This fluid must be perfectly dry and de-oiled. Indeed, any ingress of humidity into the cold box degrades the thermal performance of the insulation (perlite) . Furthermore, ingress of air –even dry –risks condensation of oxygen-enriched air once the temperature of the insulation (close to the cryogenic apparatus) is below the dew point of the air. This phenomenon can then present a risk of ignition and/or explosion with any element that is easily flammable in enriched air.

In the main envelope of the cold box, it is also necessary to ensure that the atmosphere is continuously refreshed:

· in order to evacuate the ambient air after opening and insulation.

· in order to dilute and evacuate any air that has entered.

The hourly flow rate to be taken into account for inerting must make it possible to regularly refresh the atmosphere of the coldbox.

The frameworks that are intended to contain at least one element of the air separation apparatus, at below-ambient temperatures or not, may be metal structures made up of posts, beams or joists. These posts, beams or joists may either be open-section members made of H-, I-, L-or U-section profiles, or closed-section members made of round-or rectangular-section profiles, for example square-section profiles. These profiles serve no other purpose than to hold the structures around the elements and to support the cladding, such as the metal plates, of the cold box. It is also possible to design an assembly referred to as a “truss node” comprising a closed section joined to an open section.

The framework may itself form the framework of the closed caisson that is to contain at least one element of the apparatus, or else may support and/or contain at least one such closed caisson.

A framework may for example comprise four vertical posts, each one being a rectangular-section profile, thus defining a cuboid space within each one of the four posts. The four posts are arranged parallel to one another, the vertical axis of each one defining one of the four corners of the framework. Thus, the framework has a rectangular, sometimes square, cross section.

The four posts are connected to one another by horizontal beams at several different heights.

We propose to make use of this empty space in and/or on the profiles for transporting certain particulate materials such as perlite or other powders or fluids such as instrumentation air or nitrogen for flushing the cold box, or to house cables for transferring electricity, light or information.

Preferably, the fluid or fluids, or particulate material, or electricity, light or information is required inside the enclosure or by a user of the enclosure.

The units for production of gas, for separation or for purification may comprise, among other things, at least one rotating machine (motors, compressors, turbines, pumps, valve actuators, etc. ) , at least one reservoir (storage, phase separator, etc. ) and pipes. These elements may be contained in and/or supported by solid metal frameworks or constructions made of concrete, or a combination of the two. Thus, a compressor, which may or may not be combined with other elements such as a booster compressor and coolers, may be installed in a metal framework.

FR-A-3017443 discloses the use of specific piping for the flushing nitrogen, which piping is attached to the structure.

FR-A-2769656 describes a metal framework having the general shape of a parallelepiped, comprising four longitudinal posts that are connected, on each large lateral face of the truss, by diagonal bracing and beams.

EP-A-1041353 describes the use of an I-beam to secure the column to the cold box.

WO-A-2010/067253 describes a cold box containing a column having four vertical posts, the cold box being connected to a thermally insulated enclosure containing conduits and valves but not containing a column.

FR-A-2946075 describes an enclosure according to the preamble of Claim 1 where the framework is fitted with conduits which are accessories of the column. Frameworks have been used for supporting cold boxes for very many years yet to our knowledge it has never been suggested to use the framework for transporting matter or energy into and out of the cold box. Furthermore many conduits within the cold box cannot be considered to be column accessories, such as the conduits for sending sweep gas to the insulation.

According to one subject of the invention, there is provided an enclosure for an apparatus for separation of a gaseous mixture, in particular of air by distillation at cryogenic below-ambient temperature, designed to contain at least one element of the apparatus, the element having to operate at a temperature below 0℃, preferably below -50℃, or even at cryogenic temperatures, the enclosure being in the form of a caisson and consisting of at least one framework comprising longitudinal posts and beams and bracing connecting the posts to one another, the enclosure being possibly equipped, externally, with at least one guardrail consisting of at least one bar, in which

a) the at least one post and/or the at least one beam and/or, where relevant, the at least one bar constitutes a means for transporting material and/or

b) at least one means for transporting material and/or electricity, light or information is housed at least partially in the at least one post and/or the at least one beam and/or, where relevant, the at least one bar.

According to other optional aspects:

- the framework is the framework of a closed caisson, having at least four lateral walls and possibly a ceiling and possibly a floor, and designed to contain insulation in contact with at least one of the walls and/or with the element.

- the framework contains and/or supports at least one closed caisson, having at least four lateral walls and a ceiling, and containing insulation in contact with at least one of the walls and/or with the element.

- the post and/or the beam and/or the bar is hollow and the transport means is a transport conduit housed in the post and/or the beam and/or the bar.

- the post and/or the beam and/or the bar comprises a closed space connected to a material inlet and a material outlet so as to allow the material to be transported from the inlet to the outlet, the material being in contact with the closed space.

- the enclosure is designed to be filled with insulation and the at least one transport means is a material transport conduit that emerges inside the enclosure.

- the material transport means is connected to a source of gaseous nitrogen or of air and/or to a source of particulate insulating material designed to serve as insulation, this source being located outside the enclosure.

-at least one said post is one of four main longitudinal posts positioned at the four corners of the enclosure

- the at least one transport means is an electrical cable or an optical cable or a conduit for a fluid coming from or intended for the enclosure, the cable or the conduit being preferably connected to the element.

- the at least one transport means is a conduit connected to a source of dry air, the conduit being connected to instrumentation means of the enclosure.

- the enclosure contains an element and the element is at least one column for distillation of a gas from air, a store, a heat exchange line, possibly for cooling the air intended for distillation or a set of conduits that have to operate at a temperature below 0℃.

-the element is at least one column for distillation of a gaseous or liquid product from a gaseous mixture, such as air, and the material is at least part of the gaseous mixture or the gaseous or liquid product

-the at least one post and/or the at least one beam and/or, where relevant, the at least one bar constitutes a means for transporting particulate matter to be used to fill the enclosure and/or a means for sending instrument air or nitrogen sweep gas to the interior of the enclosure.

-the at least one means for transporting material is connected to an element contained within the enclosure, such as a column, so as provide a gas thereto and/or remove a gas therefrom.

-the at least one means for transporting material is connected to an element within the enclosure other than a column.

-the enclosure contains an element and the element is at least one column for distillation of a gaseous or liquid product from a gaseous mixture and the material is at least part of the gaseous mixture or the gaseous or liquid product.

According to another subject of the invention, there is provided an air separation apparatus comprising at least one enclosure as described hereinabove, the apparatus comprising at least one distillation column and at least one heat exchanger and/or at least one rotating machine and/or an actuator and/or a sensor, and the at least one enclosure containing at least one of the distillation columns and/or at least one heat exchanger and/or at least one rotating machine and/or an actuator and/or a sensor.

The actuator may be the actuator of a valve or of a controller.

The apparatus may comprise another enclosure intended to contain at least one other element of the apparatus, the element having to operate at a temperature between O℃ and 100℃ or above 100℃, the enclosure being in the form of a caisson and consisting of at least one framework comprising longitudinal posts and beams and bracing connecting the posts to one another, the enclosure being possibly equipped, externally, with at least one guardrail consisting of at least one bar, in which

What is proposed is to use:

‐ the closed hollow posts of the cold box to blow powdery insulation material after the phase of installing this cold box and/or to remove powdery insulation material from the installed cold box

‐ the open-or closed-section posts of the frameworks, for example those of the cold box, to house electrical or optical cables, for example for instrumentation and/or control of processes or pipes for transporting fluids or powdery materials

‐ the bars of the guardrails, for example those attached to the walls of the enclosure to house at least one optical or electrical cable

‐ the bars of the guardrails, for example those attached to the walls of the enclosure to transport gaseous nitrogen or air inside a hollow bar or inside a conduit at least partially housed in the bar, wherein this fluid can be air for instrumentation, nitrogen for inerting the coldbox, or a gas for moving the actuators of pneumatic valves.

It is conceivable to send the particulate material (for example the perlite) or a gas, such as the flushing nitrogen or the instrumentation air, directly in the hollow post such that the post itself serves as a material transport conduit.

In this case, the post comprises an inlet with which it is possible to introduce the particulate material or the gas from outside the post to inside the post, and an outlet with which it is possible to introduce the particulate material or the gas from inside the post to inside the enclosure. This inlet and/or this outlet may be a simple hole in the wall of the post.

Alternatively, the particulate material or the gas may be sent through a conduit which is located in the space inside the hollow profile. This conduit emerges at the exterior of the post and of the enclosure so as to permit entry of the gas or the particulate material, and also emerges at the interior of the enclosure so that the gas or the particulate material can be sent therein.

Multiple gases which differ in composition and/or in pressure may circulate in the space inside the hollow profile, in multiple conduits.

It is possible to simultaneously use the profile itself as a conduit and a conduit inside the space inside the hollow profile. For example, a coldbox can be filled with perlite by sending the perlite in the profile without entering a conduit, and to use the same profile to convey a gas, the gas being sent in a conduit located within the space inside the hollow profile.

The profiles used can extend in a vertical, horizontal or transverse direction.

Furthermore, this invention has particular synergy with the modular construction around a matrix, as described in FR3017939, when this matrix consists of open-or closed-section beams. This modular approach to the ASU considers parts of the ASU that can be delivered on-site in packets, containers or modules. These containers are installed on a three-dimensional support matrix made of posts, beams or joists. They may be installed horizontally or vertically This matrix may contain the electrical or I&C cables, or may transport fluids such as the instrumentation air.

One aspect of the invention provides a method for providing a powdery insulating material to an enclosure as described hereinabove, in which the powdery insulating material is sent into the enclosure by sending it at least in part

a) through the at least one hollow post and/or the at least one hollow beam and/or, where relevant, the at least one hollow bar which constitutes the means for transporting material and/or

b) through a conduit for transporting material, which is housed at least partially in the at least one post and/or the at least one beam and/or, where relevant, the at least one bar.

One further aspect of the invention provides a method for removing a powdery insulating material from an enclosure as described hereinabove, in which the powdery insulating material is removed from the enclosure by sending it at least in part

a) through the at least one hollow post and/or the at least one hollow beam and/or, where relevant, the at least one hollow bar, which constitutes the means for transporting material and/or

The invention will be described in greater detail with reference to the figures. Figures 1, 2 and 3 show an enclosure for an apparatus for separation of a gaseous mixture, in particular of air by distillation at cryogenic below-ambient temperature, which is designed to contain at least one element of the apparatus, the element having to operate at a temperature below 0℃, preferably below -50℃.

Figures 1A, 1B, 1C and 1D show “truss nodes” of Figure 1 in greater detail, Figures 3A, 3B and 3C show “truss nodes” of Figure 3 in greater detail. Figure 4 shows a detail of an enclosure, such as a guardrail and the bars thereof, according to the invention and Figures 5, 6 and 7 show a section through various posts used in an enclosure according to the invention.

The figures illustrate various types of post in which a means of transporting material may be housed.

In each one of these profiles, a gas conduit, a perlite delivery conduit or a cable may be housed in the internal space of the profile.

Figure 1 shows a framework for an enclosure for a separation apparatus, prior to installation of the element that is to be insulated, for example the distillation column or the heat exchanger. The framework comprises four vertical posts 3 that are connected to one another by horizontal beams and bracings.

As shown in Figures 1A, 1B, 1C and 1D, the interior of each post forms a space of rectangular –possibly square –cross section. This space may serve for transporting various things.

In particular, perlite or another insulating material may be injected into at least one post, for example near the bottom of the post, and may exit from the post near the top so as to distribute perlite inside the framework, once this has been clad with panels to seal it. Preferably, the perlite exits from at least two of the posts, or even all four posts, so as to allow better distribution of the powder.

The perlite may also pass through the spaces inside the bracings and/or the beams.

The same technique may also be used to remove insulating material within the enclosure to empty the enclosure at least partially or even completely. The insulating material passes through the structure (post, beam or bar) and the method may be used to remove insulating material in a particular zone of the cold box by making an opening in the framework eg for removing perlite from the top of the cold box.

Dry air or dry gaseous nitrogen from outside the framework may also be sent through the framework to flush the insulation by passing through the internal space of at least one post, or even of all the posts. This dry air or gaseous nitrogen acts as a sweep gas to ensure that cold gases do not accumulate within the insulation.

Sending dry gas through the post which has already served for delivering the perlite makes it possible to evacuate any perlite lodged in the posts, and thus to avoid waste.

The same or another dry gas may serve as an instrumentation gas, for example for actuating a valve, having passed through the interior of a post.

The internal space of at least one post and/or beam and/or bracing may also contain at least one conduit for liquid or gas, for example, originating from or destined for the element inside the enclosure, for example a product of the distillation or a fluid supplied to the distillation.

The gas or liquid is not necessarily contained in a conduit but may be in direct contact with the interior of the post.

The space inside at least one post may also contain at least one electrical or optical cable. This cable may for example supply electricity for illuminating the exterior of the enclosure or for powering a rotating machine or an actuator or sensors contained in the framework.

Figure 1A shows, in greater detail, a join between a post and multiple bracings, and shows that all of these metal elements are hollow. Figure 1B is a section through Figure 1A. Figure 1C shows a join at one of the bottom corners of the framework, between the bottom of the post and bracings or beams. Figure 1D is a section through Figure 1C.

The profiles which make up a metal structure, referred to as merchant bars, are drawn, bent or re-formed in the case of non-standard iron. They are of rectangular cross section so as to form a box, which is ideal in terms of mechanical strength. However, they are limited in terms of mechanical strength, and costly.

Re-formed welded profiles are profiles made according to the specific structural requirements, using thick steel plates that are welded together. It is also possible to use different thicknesses of metal sheet for the web and for the flanges, and to create curved profiles, but the design of these requires a lot of effort to obtain just a square.

Finally, a novel type of post having particular advantages for the present invention is a re-formed welded profile. This novel form of profile brings together the advantages of the box in terms of calculations, and of the plates in terms of squeeze time. It consists of two angle irons of different sizes that are assembled in mirror image by means of two corner welds. This assembling of two distinct parts permits multiple variations: thickness of the profiles, choice of the drawn or bent profiles, universality of the systems for connecting with the sheet metal. In addition, it facilitates installation of the transport means.

Figure 2 shows a section through a framework containing two elements K1, K2, each of which may be a distillation column or a storage unit or a phase separator. The elements are surrounded by the four walls 2 of the enclosure 1, of which the four posts 3 form the corners.

Figure 3 shows a framework constructed using I-, U-, H-or T-section metal profiles. In this case, the material to be transported is transported in a conduit or a cable. One or more conduits and/or one or more cables may be housed in a hollow of a post 7 or of a bracing.

Figure 3A and 3B show a detail of the framework, and Figure 3C is a section through Figure 3B.

Figure 3 shows, at the top, a guardrail consisting of at least one bar. Similar guardrails are often installed on the exterior of the enclosure at mid-height for example to allow access to the interior and to the instrumentation. These guardrails must be illuminated. Since the bars used may comprise an internal space, this space may house an optical cable and/or an electric cable and/or a conduit for gas or liquid and/or a conduit for perlite.

The posts of Figures 1 and 3 may serve to evacuate rainwater from the roof of the enclosure or from the platforms attached to the sides of the enclosure.

Figure 4 shows, in greater detail, a guardrail protecting people on a platform at mid-height of an enclosure. Access thereto is by a flight of stairs. The guardrail consists of bars which are hollow vertical posts 103, and hollow horizontal bars 113.

The hollow bars may constitute a means for transporting material and/or electricity, light or information.

Otherwise, at least one means for transporting material and/or electricity, light or information is housed at least partially in at least one bar of the guardrail.

Figure 5 shows a hollow post belonging to one of Figures 1 to 4, in which two

conduits

13, 15 are arranged inside the post. The remaining space may be filled with a material or else may serve to transport material, for example a gas. The

conduits

13, 15 may each be a conduit for material, for electricity, for light or for information.

Figures 6 and 7 respectively show an I-section and an H-section metal profile 7. The two spaces formed on each side of the profile 7 may each house at least one

conduit

13, 15, 17.Each conduit may transport material or electricity or light or information.

In the case where the enclosure is designed to be filled with insulation, one of the

conduits

13, 15, 17 of Figures 5 to 7 may be a means for transporting the insulation that is to be transported from the exterior to the interior of the enclosure. The conduit is thus a conduit for transporting material which emerges inside the enclosure. Preferably, several or even all of the posts will contain a conduit for transporting insulation, in order to properly distribute the insulation within the enclosure. A hollow post as illustrated in Figure 5 may serve to transport the insulation from the exterior to the interior of the enclosure.

The invention relates in particular to an apparatus for separation of air comprising an enclosure, designed to contain at least one element of the apparatus, having to operate at a temperature below 0℃, preferably below -50℃, or even at cryogenic temperatures, the enclosure being in the form of a caisson and consisting of at least one framework with which it is possible to transport material and/or electricity, light or information.

The apparatus for separation of air may comprise at least one other enclosure containing at least one other element of the apparatus, having to operate at a temperature above 100℃, the enclosure being in the form of a caisson and consisting of at least one framework with which it is possible to transport material and/or electricity, light or information. The element may for example be an air purification unit for removing the carbon dioxide and/or the water contained in the air.

A post or beam or bar which is hollow may serve simultaneously for transporting material (for example a gas, a liquid or powdery material) and may possibly contain in addition at least one conduit for transporting material, electricity, light or information.

Claims

Enclosure (1) for an apparatus for separation of a gaseous mixture, in particular of air by distillation at cryogenic below-ambient temperature, designed to contain at least one element (K1, K2) of the apparatus, the element having to operate at a temperature below 0℃, preferably below -50℃, or even at cryogenic temperatures, the enclosure being in the form of a caisson and consisting of at least one framework comprising longitudinal posts (3) and beams (7) connecting the posts to one another and bracing connecting the posts to one another, the enclosure being possibly equipped, externally, with at least one guardrail consisting of at least one bar (103, 113) , in which

a) the at least one post and/or the at least one beam and/or, where relevant, the at least one bar constitutes a means for transporting material and/or

b) at least one means for transporting material and/or electricity, light or information (13, 15, 17) is housed at least partially in the at least one post and/or the at least one beam and/or, where relevant, the at least one bar.
Enclosure according to Claim 1, in which the enclosure is a closed caisson and the framework is the framework of the closed caisson, having at least four lateral walls (2) and possibly a ceiling and possibly a floor, and designed to contain insulation in contact with at least one of the walls and/or with the element.
Enclosure according to Claim 1, in which the enclosure is a closed caisson and the framework contains and/or supports the closed caisson, the caisson having at least four lateral walls and a ceiling and containing insulation in contact with at least one of the walls and/or with the element.
Enclosure according to one of the preceding claims, in which the post (3) and/or the beam (7) and/or the bar (103, 113) is hollow and the transport means is a transport conduit (13, 15, 17) housed in the post and/or the beam and/or the bar.
Enclosure according to one of the preceding claims, in which the post (3) and/or the beam (7) and/or the bar (103, 113) comprises a closed space connected to a material inlet and a material outlet so as to allow the material to be transported from the inlet to the outlet, the material being in contact with the closed space.
Enclosure according to one of the preceding claims, in which the enclosure (1) is designed to be filled with insulation and the at least one means for transporting material is a material transport conduit that emerges inside the enclosure.
Enclosure according to Claim 6, in which the means for transporting materiel is a conduit (13, 15, 17) capable of being connected to a source of gaseous nitrogen or of air, this source being located outside the enclosure.
Enclosure according to Claim 6 or 7, in which the means for transporting materiel is a conduit (13, 15, 17) capable of being connected to a source of particulate insulating material designed to serve as insulation, this source being located outside the enclosure.
Enclosure according to one of the preceding claims, in which at least one said post is one of four main longitudinal posts positioned at the four corners of the enclosure.
Enclosure according to one of the preceding claims, in which the at least one means for transporting material (13, 15, 17) is a conduit capable of being connected to a source of dry air, the conduit being capable of being connected to instrumentation means of the enclosure.
Enclosure according to one of the preceding claims in which the at least one means for transporting material (13, 15, 17) is connected to an element contained within the enclosure, such as a column, so as provide a gas thereto and/or remove a gas therefrom.
Enclosure according to one of the preceding claims in which the at least one means for transporting material (13, 15, 17) is connected to an element within the enclosure other than a column.
Enclosure according to one of the preceding claims, in which the enclosure contains an element and the element is at least one column (K1, K2) for distillation of a gaseous or liquid product from a gaseous mixture and the material is at least part of the gaseous mixture or the gaseous or liquid product.
Air separation apparatus comprising at least one enclosure according to one of the preceding claims, the apparatus comprising at least one distillation column (K1, K2) and at least one heat exchanger and optionally at least one rotating machine and/or an actuator and/or a sensor, and the at least one enclosure containing at least one of the distillation columns and/or at least one heat exchanger and/or at least one rotating machine and/or an actuator and/or a sensor.
Apparatus according to Claim 14, comprising another enclosure intended to contain at least one other element of the apparatus, the element having to operate at a temperature above 100℃, the enclosure being in the form of a caisson and consisting of at least one framework comprising longitudinal posts (3) and beams and bracing connecting the posts to one another, the enclosure being possibly equipped, externally, with at least one guardrail consisting of at least one bar (103, 113) , in which

a) the at least one post and/or the at least one beam and/or, where relevant, the at least one bar constitutes a means for transporting material and/or

b) at least one means for transporting material and/or electricity, light or information (13, 15, 17) is housed at least partially in the at least one post and/or the at least one beam and/or, where relevant, the at least one bar.