Fused bath cell lid having corrosion protection means and method of using same

A method for exhausting a substance through a port in a lid of a chamber, comprising conducting the substance through a tube within the port, which tube is more resistant to corrosion by the substance than is the port, and supporting the tube on a support means extending into the interior of the port, while cooling the support means to a temperature such that it too is more resistant to corrosion by the substance than is the port. A cell lid having a metallic port, metallic protrusion means extending into the port, cooling means for extracting heat from the protrusion means, and a carbon or ceramic tube supported on the protrusion means.

BACKGROUND OF THE INVENTION 
The present invention relates to structure and method for exhausting a 
corrosive substance from a chamber. More particularly, this invention 
relates to a method of exhausting chlorine from a molten salt electrolysis 
cell. 
An example of such a cell is disclosed in U.S. Pat. No. 3,822,195 of Dell 
et al., issued July 2, 1974, for "Metal Production". This cell has a port 
12 through which chlorine produced in the electrolysis can be exhausted 
from the cell. This chlorine is very hot, for example, 600.degree. C, and 
can carry with it constituents spewed and/or evaporated from the molten 
salt bath in the cell. This mixture of hot chlorine and salt is highly 
corrosive, and during experimentation with the cell, the practice has 
developed to provide the interior of port 12 with a corrosion resistant 
tube lining, for example, a tube made of quartz. In practice, it has been 
found to be very difficult to retain the lining in place. Often, the 
experience has been that the tube will fall down into the molten salt 
bath. When the quartz falls out of place, the port itself quickly corrodes 
away, following which chlorine gas can escape out into the room containing 
the cell. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide structure whereby the 
above outlined problems can be overcome. It is another object of the 
invention to provide corresponding process techniques by which the above 
outlined problems can be avoided in processes requiring the exhausting of 
a corrosive substance from a chamber. 
These, as well as other objects which will become apparent in the 
discussion which follows, are achieved according to the present invention 
by (1) providing a method for exhausting a substance through a port in a 
lid of a chamber, including the steps of conducting the substance through 
a tube within the port, which tube is more resistant to corrosion by the 
substance than is the port, and supporting the tube on a support means 
extending into the interior of the port, while cooling the support means 
to a temperature such that it too is more resistant to corrosion by the 
substance than is the port; and (2) providing a cell lid having a metallic 
port, metallic protrusion means extending into the port, cooling means for 
extracting heat from the protrusion means and a carbon or ceramic tube 
supported on the protrusion means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the FIGS. 1 and 2, the invention is illustrated in terms 
of use with a cell like that in the above-mentioned U.S. Pat. No. 
3,822,195. With reference to FIG. 1 of that patent, lid 9 there 
corresponds to lid 10 here, while port 12 there corresponds to port 12 
here. The cell partially illustrated here, however, has been modified with 
respect to that shown in U.S. Pat No. 3,822,195 to the extent that water 
cooling is provided on the top of lid 10 here, and the refractory roof 8 
of that patent has been eliminated here. Thus, a cooling jacket 14 here 
covers the lid of the cell. And, lid 10 is exposed directly to chlorine 
and molten salt vapors and is made of a suitably chlorine-resistant metal, 
such as nickel or the alloy nominally containing 80% Ni, 15% Cr and 5% Fe, 
and sold under the trademark INCONEL. 
While reference is made to the above-mentioned U.S. Pat. No. 3,822,195 for 
further exemplary details of the electrolysis in the cell, it is noted 
that the molten salt bath 16 may, for example, be at 715.degree. C and 
have the following composition in weight-percent: 
______________________________________ 
NaCl 51.0 
LiCl 40.0 
AlCl.sub.3 6.5 
MgCl.sub.2 2.5 
______________________________________ 
Water is circulated through jacket 14 to keep the undersurface of lid 10 at 
120.degree. F (about 50.degree. C). Partitions 18 are for the purpose of 
assuring a uniform flow of water over all parts of the lid. 
In practice, it is found that essentially no incrustation of bath on the 
undersurface of the lid is noted nor is the lid corroded by the chlorine. 
(The INCONEL metal of lid 10 does corrode in this environment when the 
undersurface temperature goes above 530.degree. C.) It is noted that the 
sublimation temperature of AlCl.sub.3 is certainly above the 120.degree. F 
temperature of the lid undersurface, but the bath constituents reaching 
the lid exert a fluxing action to prevent AlCl.sub.3 from depositing in 
solid form on the lid. 
Referring now to the details of FIG. 1 specifically relating to the present 
invention, there is shown in port 12 nickel fingers 20a, 20b, 20c, etc. 
(collectively referred to with the numeral 20) welded to the interior of 
the metal port 12, which is likewise made of nickel, or INCONEL metal. 
These fingers support the graphite ring 22. Resting on the graphite ring 
is quartz tube 24. In practice, it is found that the nickel fingers 20 
will corrode back to a point where their temperature is below the 
temperature at which they will corrode, the temperature gradient being, of 
course, due to the fingers being in contact with the water in jacket 14 
through the metal wall of port 12 on one end and subjected to hot chlorine 
gas on the other end. There remains, however, enough of the fingers to 
support the graphite ring which will not corrode. While making the fingers 
20 of metal is disadvantageous in that they corrode more easily, it is 
advantageous because of the ability to connect them strongly on the inner 
wall of port 12 by welding and because they then bear-up better to the 
tensile and shear portions of the bending stress on them than would be the 
case if they were ceramic or carbon. The quartz tube 24, graphite ring 22 
and fingers 20 are not bonded to one another, but the interfaces between 
them and between port 12 and graphite ring 22 become wetted by spewed or 
condensing constituents from the bath and the resulting films of liquid 
and even solidified material prevent chlorine from getting up into the 
upper regions of port 12 where the port temperature can rise in the 
presence of hot chlorine to a corrosion dangerous level due to the longer 
distance away from the water in jacket 14. The outer surface of the quartz 
tube 24 is packed with ceramic fiber rope 26 maintained by packing gland 
28. 
A pipeline 30 leading to a chlorine and evaporated bath recovery operation 
(as described, for example, in U.S. Pat. No. 3,904,494, issued in the name 
of S. C. Jacobs et al. on Sept. 9, 1975, for "Effluent Gas Recycling and 
Recovery in Electrolytic Cells for Production of Aluminum from Aluminum 
Chloride") is connected via bolts 32, there being interposed a metal 
hold-down ring 34 and ceramic-fiber-based gaskets 36 and 38, the last 
being set on rubber or plastic electrical insulation ring 40 for added 
protection against electrical current leakage. The pipe 30 is provided 
with a flange 42, insulation 44, and a quartz lining tube 46. Ring 34 and 
flange 48 of port 12 provide the seats for bolts 32. 
Explanatory of the broad concept of the present invention, the quartz tube 
24 is more resistant to corrosion by the corrosive substance, e.g. 
chlorine, than is the port, considering the whole of the port, it being 
recognized that the lower end of the port is maintained at a low 
temperature by the water in jacket 14 to render that particular region 
non-corrosive. The portions of the fingers 20 that remain after their ends 
are corroded back to the critical temperature location are likewise more 
resistant to corrosion than is the port considered as a whole. The present 
invention is effective to maintain quartz tube 24 in place so that 
chlorine is prevented from getting into contact with the portions of port 
12 remote from cooling jacket 14, so that there is no danger of chlorine 
corroding through the port wall and getting out into the environment. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.