Process for the construction of a cryogenic unit for the separation of gas, cryogenic unit, subassembly and transportable assembly for the construction of such a unit

A cryogenic unit for the separation of gases includes at least one distillation column (1) is preassembled in the factory. The column (1) with added tubing elements (2) constitutes a pre-equipped subassembly which is transported and installed at the worksite. The tubing elements are disposed so as to be inscribed in at least one elongated volume (3; 3.sub.1, 3.sub.2) lateral to the column and of reduced section. The subassembly (1,2) is disposed on at least one transport cradle (4, 4') and transported to the worksite on the cradle and mounted at the worksite in a cold box (10) Preferably, all the tubing elements are disposed in the cradle. The subassembly, with or without the cradle, is mounted adjacent one side wall of the cold box (10) and is spaced by insulation (13) from at least one liquid gas reservoir (11; 12) also in the cold box (10).

The present invention relates to processes for the construction of 
cryogenic units for the separation of gases, typically air gases, 
comprising at least one distillation column and including the steps of 
preassembling in the factory the column with its added tubing elements 
including instrumentation tubing to constitute a pre-equipped subassembly, 
transporting and installing this subassembly at the worksite. 
Conventionally, cryogenic units for the separation of gases comprise at 
least one distillation column which is disposed in an insulating structure 
called a cold box having usually a substantially parallelepipedal shape so 
as to provide about the column a predetermined thickness of insulation. 
With a view toward limiting the costs of mounting and above all with a 
view to quality, the column is preassembled with tubing elements in a 
factory of the builder with a framework corresponding to that of the 
future cold box, and of a cross section integrating the future insulation 
thicknesses all about the column, before transporting and installing the 
assembly at the worksite, a so-called "cold box package". Apart from their 
weight, sharply driving up the cost of transportation, such completely 
preassembled assemblies are confronted, largely because of their great 
volume, with serious transportation problems (bridge clearance, cornering 
. . . ), as mentioned on page 25 of the 1989 Annual Report of the Linde 
company, when the dimensions of the column are great, as is the case 
nowadays for massive production of gas. 
The present invention has for its object to provide a process permitting 
maintaining the quality criteria of preassembly in the factory of the 
elements requiring high quality control (typically all the cryogenic 
part), greatly limiting the problems and the costs of transport toward the 
utilization site and facilitating its installation on site in various 
types of cold boxes. 
To do this, according to a characteristic of the invention, the 
construction process comprises the steps of forming the subassembly 
pre-equipped with the tubing elements so arranged as to be inscribed 
within at least one, and preferably only one, elongated volume lateral to 
the column and of reduced section, not taking account of the insulating 
thickness required for the operation of the column on the site, having 
typically a maximum width not or only a little exceeding the diameter of 
the column, disposing this subassembly on at least one transport cradle, 
preferably a single transport cradle defining an internal volume of a 
cross section adapted to receive at least one of the lateral volumes 
corresponding to the tubing elements, transporting the subassembly and its 
cradle and mounting at the worksite the subassembly in a cold box, then 
applying the thickness of insulation required all about the subassembly. 
According to other characteristics of the invention: 
the process comprises the step of protecting the tubing elements by a cap; 
the pre-equipped subassembly is disposed partially in a transport cradle 
defining an interior volume of a cross section adapted to receive at least 
one of the lateral volumes of the tubing elements; 
the tubing elements are regrouped into a lateral volume, this subassembly 
being disposed in the cradle with the column resting on the upper portion 
of the cradle; 
the process comprises the steps of mounting at the worksite the subassembly 
in a casing in which is also disposed at least one reservoir of cryogenic 
liquid and filling the casing with a first insulation; 
the subassembly is disposed in the casing with the lateral volume adjoining 
one lateral wall of the casing at a distance of this latter sufficient to 
restore the necessary insulation distance. 
Such a process, no longer taking account, for its preassembly and 
transport, of the volume of insulation necessary to the column, permits 
increasing the possibilities of transport of a subassembly of a cryogenic 
unit in quasi operating condition, including as the case may be the 
functions of supervision, control and security, while diminishing the 
overall dimensions, as well as the number of structural elements of the 
cradle, particularly for units of high capacity with column diameters 
between 2 and 5.5 meters. 
The present invention also has for its object a subassembly for carrying 
out the process, characterized in that the column is preassembled with 
tubing elements disposed so as to be inscribed within at least one 
elongated volume lateral to the column, of reduced section, typically a 
single lateral volume adapted to be received in a cradle for transport 
and/or mounting. 
The present invention has for another object a transportable assembly 
comprising such a subassembly mounted on a transport cradle, preferably 
disposed partially in a cradle sheltering the lateral volume of the tubing 
elements and supporting the column along the generatrices of this latter. 
The present invention has further for its object a new architecture of 
cryogenic unit for the production of gases, particularly from air, 
comprising a subassembly such as that defined above disposed adjacent a 
lateral wall of a casing, typically cylindrical or if desired prismatic, 
in which is also disposed at least one reservoir of liquified gas, the 
casing being filled with at least one insulation, especially a particulate 
or fibrous material.

In FIG. 1 is shown a column 1 for the distillation of air gases whose 
diameter can be as much as 5.5 meters and the height 50 meters. As is 
better seen in FIG. 2, the column 1 is arranged and preassembled such that 
the different tubing elements 2 which fit into it will be disposed on one 
lateral side of the column so as to be inscribed within a lateral 
elongated volume 3 whose maximum width is limited to or only a little 
exceeds the maximum diameter of the column and whose height h is 
independent of the thickness of insulation ultimately required for the 
operation on the worksite of the column 1 in its cold box. According to 
the invention, once tested, the column 1 and its tubing elements 2 are 
mounted in a cradle 4 of generally prismatic configuration and with a 
typically trapezoidal cross section to offer an increased base surface, 
comprising two lateral flanges 5A, 5B, defining an internal volume adapted 
to receive the lateral volume 3 of the tubing elements 2, the column 
bearing, along generatrices, substantially below or at the level of its 
horizontal diameter, on the parallel edges 6A, 6B of the flanges 5A, 5B 
and being maintained in position on the cradle for example by encircling 
straps 7. The cradle 4 has a frame constituting a trellis of angle irons 
or of tubes. In a preferred embodiment, the cradle 4 comprises flat 
lateral flanges 5A, 5B formed by metallic plates, at least one portion of 
the base 8 of the cradle 4 being constituted by metallic plates 9. 
It will thus be seen from FIG. 2 that with respect to the existing 
transportable assemblies, the size of the transportable assembly according 
to the invention is limited to that of the cradle 4 and the upper 
cylindrical portion of the column 1. 
As will be seen in FIG. 3, according to another aspect of the invention, 
instead of being disposed in a parallel-epipedal cold box at a distance 
from insulated independent reservoirs of liquified gas, the column 1 is 
disposed vertically in an internal space available in a cylindrical or 
polygonal casing 10, of metal or concrete, in which are disposed several 
uninsulated or individually insulated vertical reservoirs 11, 12, for 
storage of cryogenic liquid, typically liquid nitrogen and liquid oxygen 
produced by the column 1. This latter is disposed, with its cradle 4, in 
the casing 10 in a position facing the lateral wall of casing 10 and the 
reservoirs 11, 12 permitting retaining the insulation distance necessary 
for its good functioning. It is thus positioned on the base of the 
envelope 10 and the tubing elements 2 are connected to fluid circuits 
internal and external to the casing 10, particularly for the connection of 
heat exchangers. The cradle 4 can be dismounted and reused and, before 
closure (by a cover) of the casing 10, the internal volume of this latter 
is filled with solid insulation 13, typically perlite. 
According to a modification of the invention, the cradle 4 is maintained in 
the casing and, in the embodiment in which its lateral flanges 5A, 5B are 
flat, the internal volume of the cradle is filled with a second solid 
insulation 14, for example glass fibers. 
As a variation, and particularly for high columns but of a diameter not 
exceeding 4.5 meters, the added tubing elements 2 can be disposed in two 
groups inscribed in two lateral volumes of sections reduced as much as 
possible, particularly in thickness. There is thus shown in FIG. 4, a 
subassembly in which the tubing elements, including the instrumentation 
tubing, are assembled in two groups 2.sub.1, 2.sub.2 bisymmetric with each 
other in a vertical plane (in FIG. 4). The lateral volumes in which are 
inscribed the tubing elements are embodied here in protective caps 31 and 
32, for example of sheet metal, mounted on the column and ensuring their 
protection during transport and the emplacement at the worksite of the 
subassembly, after which the caps are removed. One of these caps can be 
reinforced to constitute a transport cradle, as previously seen in 
connection with FIGS. 1 and 2. However, one of the critical parameters for 
the transport being the overall height (and particular for the passage 
below bridges or electric lines), there will preferably be disposed, as 
shown in FIG. 4, the pre-equipped and protected subassembly 1, 2.sub.1, 
2.sub. 2, 31, 32 on a cradle 4' of a height reduced to the strict minimum 
and of suitable shape. 
Although the present invention has been described in connection with 
particular embodiments, it is not thereby limited but is on the contrary 
susceptible to modifications and variations which will be apparent to one 
skilled in the art.