U.S. patent application number 10/576330 was filed with the patent office on 2007-03-29 for cooling device for end-box of mercury cathode chlor-alkali cells.
Invention is credited to David Francis, Dario Oldani, Salvatore Peragine.
Application Number | 20070068825 10/576330 |
Document ID | / |
Family ID | 34509452 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070068825 |
Kind Code |
A1 |
Oldani; Dario ; et
al. |
March 29, 2007 |
Cooling device for end-box of mercury cathode chlor-alkali
cells
Abstract
The invention describes heat exchange devices for dry-type inlet
end-boxes of mercury cathode chlor-alkali electrolysis cells. The
devices increase the heat exchange between recycled mercury and
feed brine with the purpose of reducing the temperature of mercury
to a substantial extent The devices consist of a first element
directed to subdivide the mercury flow into a fine and a stable
dispersion of rivulets and droplets and of a second element capable
of increasing the brine level to allow the prolonged contact
thereof with mercury. The decrease of mercury temperature below the
critical value of 90-95 .degree. C. determines an advantageous
duration improvement of the end-box internal lining.
Inventors: |
Oldani; Dario; (Milan,
IT) ; Francis; David; (Belle Mead, NJ) ;
Peragine; Salvatore; (Giovanni, IT) |
Correspondence
Address: |
HEDMAN & COSTIGAN P.C.
1185 AVENUE OF THE AMERICAS
NEW YORK
NY
10036
US
|
Family ID: |
34509452 |
Appl. No.: |
10/576330 |
Filed: |
October 21, 2004 |
PCT Filed: |
October 21, 2004 |
PCT NO: |
PCT/EP04/11917 |
371 Date: |
April 19, 2006 |
Current U.S.
Class: |
205/359 ;
204/205; 205/556 |
Current CPC
Class: |
C25B 11/033 20210101;
C25B 9/70 20210101; C25B 9/303 20210101 |
Class at
Publication: |
205/359 ;
205/556; 204/205 |
International
Class: |
C25B 1/26 20060101
C25B001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2003 |
IT |
MI2003A002040 |
Claims
1. A dry operated inlet end-box for a mercury cathode chlor-alkali
cell comprising a brine feed conduit, a slit for the admission of
recycled mercury and at least one internal device for W heat
exchange between said brine feed and said recycled mercury.
2. The end-box of claim 1 further comprising a bafle for the
formation of a mobile film of mercury of predetermined
thickness.
3. The end-box of claim 1 or wherein said at least one internal
device comprises a first element for the dispersion of said
recycled mercury.
4. The end-box of claim 3 wherein said at least one internal device
comprises a second element for raising the level of said brine
feed.
5. The end-box of claim 1 wherein said thermal exchange internal
device is formed by elements made of or lined with a material
chemically resistant in the operating conditions of a chlor-alkali
cell, optionally selected from the group comprising titanium and
alloys thereof, perfluorinated plastic materials,
polycyclopentadiene, polyvinylidenfluoride, and
polychlorotrifluoroethylene.
6. The end-box of claim 3 wherein said first element for the
dispersion of mercury consists of a horizontal cylindrical
distributor provided with perforations along the lower
generatrix.
7. The end-box of claim 4 wherein said first element for the
dispersion of mercury consists of a horizontal tray provided with
lifted edge.
8. The end-box of claim 7 wherein said lifted edge provided with at
least one multiplicity of upper openings.
9. The end-box of claim 8 wherein said upper openings have a
passage section of triangular shape.
10. The end-box of claim 8 wherein said edge is provided with a
double multiplicity of respectively upper and lower openings,
optionally having a triangular passage section.
11. The end-box of method of claim 3 wherein said first element for
the dispersion of mercury is connected to a wall of said end-box
and said slit is sealed.
12. The end-box of method of claim 3 wherein said first element for
the dispersion of mercury is connected to a coaxial pipe internal
to the brine feed conduit and said slit is sealed.
13. The end-box of method of claim 3 wherein said first element for
the dispersion of mercury is connected to a pipe coupled to said
slit.
14. The end-box of method of claim 4 wherein said second element
for raising the brine level is a case provided with an
overflow.
15. The end-box of claim 14 wherein said case is provided with a
damper of the falling brine which pours out above said
overflow.
16. The end-box of method of claim 4 wherein said second element
for raising the level is connected to the brine feed conduit.
17. The end-box of method of claim 4 wherein said first element for
the dispersion of mercury is inserted inside said second element
for raising the level.
18. The end-box of claim 17 wherein said first element for the
dispersion of mercury is placed below the brine level in said
second element.
19. The end-box of method of claim 14 wherein the said case for
raising the level is provided with one or more ducts for the
discharge of mercury containing a level of mercury in the
interior.
20. The end-box of claim 19 wherein said one or more ducts are made
of or lined with electrically non conductive and chemically inert
material.
21. The end-box of claim 1 made of metallic material provided with
an eboite or rubber coating, or of non metallic material.
22. The end-box of claim 1 wherein said internal device for the
heat exchange is electrically insulated from the chlor-alkali
cell.
23. Mercury cathode chlor-alkali electrolysis cell comprising the
inlet end-box of claim 1.
24. Process of electrolysis of brine for the production of chlorine
and caustic soda or potash, comprising using a cell of claim
23.
25. The process of claim 24 wherein the thermal longitudinal
distribution in the cell is uniform.
26. (canceled)
Description
DESCRIPTION OF THE PRIOR ART
[0001] The production of chlorine by electrolysis of alkali
chloride solutions, in particular of sodium chloride and potassium
chloride (hereafter brine), is currently carried out by means of
three different processes, respectively the ion-exchange membrane,
the porous diaphragm and the mercury cathode ones. The latter type
is based on a long-time known technology which has experienced a
continuous improvement in the cell structure (Ullmann's
Encyclopaedia of Industrial Chemistry, VCH, Vol. A6, page 416)
essentially directed to the reduction of electrical energy
consumption and to the lessening of mercury release in the
environment.
[0002] The problem of the reduction of energy consumption has been
successfully tackled by replacing the original graphite anodes with
titanium anodes activated with a catalytic coating based on
platinum group metal oxides which are also advantageously
characterised by a long operative lifetime. This latter aspect
allowed to substantially decrease the frequency of cell shut-downs
imposed by the replacement procedures of graphite anodes, which
were subject to a quite intense corrosion. Since the maintenance
shut-down is critical in terms of mercury release in the
environment, the benefit imparted by the activated titanium anodes
is apparent also under this point of view. A reduction in the loss
of mercury was further granted by the current employment of
re-crystallised salt which allows minimising the amount of
mercury-polluted sludges purged from the brine purification
section, although involving a higher cost. Finally, a further
decrease in the mercury release, particularly in the waters, was
achieved by eliminating the demineralised water rinsing
conventionally effected on the recycled mercury and on the amalgam
respectively before entering the inlet end-box and after extraction
from the outlet end-box. In this case the two end-boxes are known
as dry end-boxes.
[0003] As a consequence of all these measures, it can be
demonstrated at present that the release of mercury from a well
designed and correctly managed plant does not exceed 1 gram/tonne
of product chlorine versus the value of 10 grams of about ten years
ago (Ullmann's Encyclopaedia of Industrial Chemistry, VCH, Vol. A6,
page 424).
[0004] Nevertheless, the adoption of dry end-boxes involves a
quicker deterioration of the ebonite or of the vulcanised synthetic
or natural rubbers commonly used as lining of the inlet end-boxes
manufactured out of carbon steel. The observed problem originates
by the relatively quick chemical attack of the lining as a
consequence of the combination of the aggressiveness of fluids, in
particular of chlorine, with the significantly higher temperature
of the mercury which enters the cell at about 120.degree. C.; this
temperature level directly derives from the lack of cooling
consequent to the elimination of the rinsing with demineralised
water and from the absence of external thermal exchange devices as
preferred for the sake of installation simplicity. Furthermore an
evident loss of adhesion to the underlying carbon steel occurs,
with the consequence of making the start-up and shut-down thermal
transients critical. To worsen the situation finally concurs the
difficulty, not to say the impossibility, of repairing the damaged
zones.
[0005] All of this forces the operators to perform shut-downs to
proceed with replacing the deteriorated end-boxes with new ones
every 3-4 years on the average. The replacement in its turn
introduces an additional problem which makes the already expensive
operation even more onerous: the lining of the disassembled end-box
in fact contains non negligible amounts of highly toxic products
such as dioxins and furanic compounds, generated by the reaction
with chlorine at the cell operating temperatures. It follows a
remarkable complication in the operations of detachment of the worn
rubber and a considerable cost of disposal.
[0006] To overcome the problem, many different types of lining
provided with higher chemical inertia and applied with different
procedures have been proposed: one example is given in U.S. Pat.
No. 6,200,437, wherein the use of fluorinated polymers such as
polyvinylidenfluoride (PVDF), polychlorotrifluoroethylene (PCTFE)
and tetrafluoroethylene--hexafluoropropylene copolymer (FEP) is
disclosed. However, the employment of the application procedures
disclosed in U.S. Pat. No. 6,200,437 is feasible, for instance, for
lining the cell sidewalls, while it is practically not possible for
the end-boxes because of the very complicated structure with the
presence of several corners.
[0007] Entirely similar problems are presented by the end-boxes
wholly made of plastic material, for instance polycyclopentadiene,
commercialised under the trade-mark Telene.RTM. by BFGoodrich
Co./USA, or other types of polymers optionally reinforced with
glass fibres, aramidic fibres such as polyparaphenylen
terephthalamide (commercialised as Kevlar.RTM. by DuPont/USA) or
carbon fibres. Although marginally extended operative life-times
can be obtained, in all cases not longer than 6-7 years, this
solution is hardly appreciated by the plant operators as it
involves substantially higher manufacturing costs and a certain
design rigidity, due to the necessity of using moulds, which makes
the introduction of subsequent improvements problematic.
[0008] The object of the invention is to overcome the constructive
limitations of the cell inlet end-boxes of the prior art.
[0009] Under a first aspect the present invention is directed to a
device capable of ensuring a much greater lifetime to the
conventional end-box linings.
[0010] Under a second aspect the device of the invention ensures an
extended operative lifetime by reducing the mercury temperature at
the cell inlet.
[0011] Under a third aspect of the invention the device achieves
the reduction of the recycled mercury temperature before entering
the cell by a thermal exchange between the mercury and the feed
brine effected inside the dry operating inlet end-box.
[0012] Under a fourth aspect of the invention the thermal exchange
between mercury and feed brine is intensified by the dispersion of
mercury into rivulets and/or droplets falling through the
brine.
[0013] Under a fifth aspect of the invention the device constitutes
a preassembled object which is installed inside new or used
end-boxes independently from the design type or size.
[0014] Under a sixth aspect of the invention the device is easily
repairable in case of accidental damages, in particular mechanical
damages originated during the transport phase from the manufacturer
to the user plant and during the phases of assembly in the cells
and of plant general maintenance.
[0015] Finally, under a further aspect of the invention the inlet
end-box equipped with the device allows minimising the temperature
profile inside the cells with an improved current density
distribution.
THE INVENTION
[0016] Under a first aspect, the invention consists of a
dry-operating inlet end-box for mercury cathode chlor-alkali cell,
provided with a conduit for feeding brine, a slit for the inlet of
recycled mercury and a baffle for the generation of a mercury
mobile film of predetermined thickness, further provided with an
internal device for the thermal exchange between the brine feed and
the recycled mercury. In a preferred embodiment, said internal
thermal exchange device comprises an element deputed to the
dispersion of the recycled mercury, for instance consisting of a
distribution tank provided with holes or of a horizontal tray with
lifted edge, and a second element deputed to the raising of the
brine feed level, for instance a box provided with an overflow.
[0017] Under a second aspect, the invention consists of a mercury
cathode chlor-alkali cell comprising a dry inlet end-box provided
with an internal device for the thermal exchange between the brine
feed and the recycled mercury.
[0018] Under a third aspect, the invention consists of a mercury
cathode chlor-alkali electrolysis process carried out in the cell
of the invention and characterised by a uniform longitudinal
thermal distribution.
[0019] The invention will be described hereafter by resorting to
the appended figures, which have a merely exemplifying function and
do not wish to limit the scope thereof in any way.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1: longitudinal section of a mercury cathode
chlor-alkali electrolysis cell provided with a rinsing device with
demineralised water effected before the inlet end-box and after the
outlet end-box.
[0021] FIG. 2: front-view (A) and relevant cross-section along the
line O-O (B) of a dry-operating inlet end-box.
[0022] FIG. 3: cross section of a dry-operating inlet end-box
according to a first embodiment of the invention
[0023] FIG. 4: cross section of a dry-operating inlet end-box
according to a second embodiment of the invention
[0024] FIG. 5: cross section of a dry-operating inlet end-box
according to a third embodiment of the invention
[0025] FIG. 6: cross section of a dry-operating inlet end-box
according to a fourth embodiment of the invention
DETAILED DESCRIPTION OF THE DRAWINGS
[0026] In FIG. 1 it is sketched a conventional mercury cathode
chlor-alkali cell section wherein (1) indicates the activated
titanium anodes provided with catalytic film for chlorine
evolution, (2) the cathode consisting of a layer of mercury flowing
on the carbon steel bottom (dashed zone), (3) the brine feed, (4)
the brine level inside the cell, (5) the decomposer where the
amalgam forms, upon reacting with demineralised water, caustic soda
or potash (6), hydrogen (7) and mercury (8) to be recycled to the
cell through the pump (9), (10) the chlorine outlet, (11) and (12)
the sections of rinsing of the recycled mercury before the inlet
end-box (13) and of the amalgam downstream the outlet end-box (14).
The terms inlet end-box and outlet end-box are intended as
indicating the sections respectively connected to the initial part
of cell, with the purpose of ensuring the uniform non-turbulent
feeding of the sodium or potassium chloride solution and of the
recycled mercury, and to the terminal part of the cell for the
separation of the sodium amalgam from the chlorine-containing
diluted brine.
[0027] For a better understanding of the invention it is convenient
to describe the functioning of the conventional dry inlet end-box
sketched in FIG. 2 as front-view (A) and as cross-section along the
line O-O (B), wherein (15) indicates the conduit for feeding brine
at about 60.degree. C. (8-18 m.sup.3/hour depending on the current
density and on the cell size), (16) a cylindrical horizontal
distributor provided with perforations along the lower generatrix
through which the brine percolates, (17) the brine level (uniform
dashed line), (18) the gaseous atmosphere essentially consisting of
chlorine and water vapour, (19) the slit for the recycled mercury
inlet at about 120.degree. C. coming from the circuit of the
decomposer (4-8 m.sup.3/hour depending on the current density and
on the cell size), (20) the level of mercury (dashed and dotted
line), (21) a baffle allowing to introduce a mobile layer of
mercury of predetermined thickness into the cell (22) through the
passage (23), (24) the end-box body of carbon steel lined with a
continuous sheet of vulcanised rubber.
[0028] The mercury and brine flows indicated by the arrows of FIG.
2 are substantially of the laminar type and are characterised by
very reduced contact times which do not allow to achieve any
significant thermal exchange: in fact, temperatures of brine (34)
and mercury (35) were determined in correspondence of the inlet of
cell (22) different by only 4-5.degree. C. with respect to the feed
values.
[0029] With the above indicated operating conditions the rubber,
inspected after one year of functioning, results in general already
characterised by a powdery appearance extended to the whole surface
and by a corrosion in form of an about 1 mm deep groove
approximately in correspondence of the level of mercury. The
powdering is attributable to the reaction with the chlorine in the
gaseous atmosphere, the groove formation to the presence of
substantial amounts of hypochlorite and chlorate in the liquid film
present in the interstice formed by the mercury meniscus against
the rubber wall.
[0030] The industrial experience indicates that the chemical
reactions at the basis of the described types of deterioration are
very sensible to temperature, in particular when the latter exceeds
the critical level of 90-95.degree. C.
[0031] Starting from this basis of knowledge the inventors have
studied the efficiency of modifications in the design of inlet
end-boxes with the main purpose of decreasing the temperature of
mercury at the cell inlet point. In particular, the internal
thermal exchange devices illustrated in the following have been
considered, suitable for being installed on the existing or newly
manufactured inlet end-boxes independently from the model type and
size and consisting of a first element for the dispersion of the
recycled mercury and preferably by a second element for raising the
brine level: [0032] inlet end-box A, illustrated in FIG. 3,
provided only with the first element consisting of a horizontal
cylindrical distributor connected to one of the sidewalls and
perforated along the lower generatrix for the distribution of
mercury, identified with (25). In the figure an end-box section is
sketched in which the slit (19) is sealed with a bolted sheet
provided with a perimetrical sealing gasket. The other constituent
parts of the end-box were entirely equivalent to those already
identified in FIG. 2. [0033] inlet end-box B, illustrated in FIG.
4, equivalent to end-box A and further equipped with the second
element consisting of a case (26) directed to establish, through
the overflow (27), a new brine level (28) with the purpose of
increasing the thermal exchange with mercury. The case (26) was
further provided with a damper (29) of the kinetic energy of the
brine falling from the overflow (27), with the purpose of
preventing undesired turbulences of the mercury layer. [0034] inlet
end-box C, illustrated in FIG. 5, equivalent to end-box B but
equipped with the first element comprising a horizontal tray (30)
provided with a lifted edge, installed inside the case (26) and in
particular below the brine level (28). The lifted edge was provided
with a multiplicity of upper openings (31), having a triangular
passage section (in less preferred embodiments of the invention the
lifted edge may also be free of openings or the opening passage
section may also have a different geometric shape, for instance
rectangular). The multiplicity of openings was directed to achieve
a mercury flow dispersion into a multiplicity of rivulets and
droplets. The mercury feed to the tray was again realised with a
perforated horizontal cylindrical distributor (25) secured to the
sidewall of the end-box with the slit (19) sealed. Alternatively it
is possible to resort, for the feeding of mercury, to a vertical
pipe connected through an appropriate connection to the feed slit
(19) which in this case is obviously not sealed, or to a coaxial
pipe internal to the brine feed conduit (15), with the slit (19)
also in this case sealed. The latter solution is particularly
interesting for its constructive simplicity, however with the
disadvantage of introducing a higher hydraulic head on the
circulation of mercury, with for certain types of pumps (element
(9) in FIG. 1) may lead to lower flow-rates. [0035] inlet end-box
D, illustrated in FIG. 6, equivalent to type C, but with the tray
edge provided with a double multiplicity of upper and lower
openings (31) with triangle-shaped sections.
[0036] The cases (26) of end-boxes B, C and D directed to raise the
brine level were provided of one or more ducts (32) on the
back-wall, for discharging the mercury which established a level
(33) in their interior, so as to oblige the brine to pour out above
the overflows (27).
[0037] The perforated distributors (25), the trays (30) with the
relevant edges, the boxes (26) and the connecting tubes were made
of titanium and preferably maintained electrically insulated from
the carbon steel of the end-boxes. It is evident that, given the
simplicity of the design, these elements may as well be constructed
with other materials, provided they resist to the harsh operating
conditions typical of chlor-alkali cells: for example, one may
suppose resorting to polymeric materials such as the aforementioned
Telene.RTM. or even better to easily mouldable and weldable
polymeric perfluorinated materials, such as PVDF, FEP, PCTFE. The
ducts (32) were manufactured with polytetrafluoroethylene (PTFE)
tube. Metal ducts are also acceptable provided they are lined with
electrically insulating material.
[0038] End-boxes A, B, C and D, internally provided with rubber
commercialised under the trade-mark Akorros.RTM. CS 1710 by A.
Tamburini & C. S.r.l./ltaly, were installed each on a cell of a
mercury cathode chlor-alkali electrolysis industrial circuit
characterised by the following features: [0039] Brine fed at about
60.degree. C. with average flow-rate of 8 m.sup.3/hour/cell [0040]
Mercury fed at about 120.degree. C. with average flow-rate of 4
m.sup.3/hour/cell [0041] Operative current: 180 kA/cell,
corresponding to a density of 12 kANm.sup.2 [0042] Anodes of
activated titanium, provided with ruthenium-iridium-titanium mixed
oxide-based catalytic coating [0043] Thermocouples inserted in each
of the four test cells and in particular in the brine at the cell
inlet (indicated as (34) in FIG. 3), in the mercury immediately
downstream passage (23) (indicated as (35) in FIG. 3), and in the
mercury admission and brine feed conduits.
[0044] Before staring the operation, the hydraulic behaviour was
checked by supplying mercury and brine at the above indicated
flow-rates to each of the four still opened cells. In particular,
it was observed that the fall of mercury from the perforations of
the distributing pipe (25) of end-boxes A and B occurred in form of
almost continuous and relatively coarse rivulets, while in the case
of end-box C the same fall appeared as a rather fine dispersion of
rivulets and droplets, even though with a certain tendency to
coalesce in coarser rivulets; finally, in the case of end-box D the
mercury fall appeared as a stable dispersion of fine rivulets and
droplets.
[0045] The four cells were then started up and after a period of a
few days of stabilisation, temperatures were detected through the
various thermocouples installed, with the following results: [0046]
Cell equipped with end-box A--Temperature of mercury in the
admission conduit: 120.degree. C. and in (35): 116.degree. C.,
temperature of brine in the feed conduit: 60.degree. C. and in
(34): 62.degree. C., temperature of brine at the cell outlet:
90.degree. C. [0047] Cell equipped with end-box B--Temperature of
mercury in the admission conduit: 119.degree. C. and in (35):
99.degree. C., temperature of brine in the feed conduit: 60.degree.
C. and in (34): 70.degree. C., temperature of brine at the cell
outlet: 89.degree. C. [0048] Cell equipped with end-box
C--Temperature of mercury in the admission conduit: 118.degree. C.
and in (35): 90.degree. C., temperature of brine in the feed
conduit: 60.degree. C. and in (34): 74.degree. C., temperature of
brine at the cell outlet 88.degree. C. [0049] Cell equipped with
end-box D--Temperature of mercury in the admission conduit:
122.degree. C. and in (35): 90.degree. C., temperature of brine in
the feed conduit: 60.degree. C. and in (34): 76.degree. C.,
temperature of brine at the cell outlet 91.degree. C.
[0050] After 13 months of operation the functioning of the four
cells was stopped and the conditions of the inlet end-box lining
were checked.
[0051] End-box A showed the superficial powdery aspect commonly
observed with the conventional dry inlet end-boxes operating with
mercury at temperatures substantially higher than 90.degree. C. and
the characteristic groove, in this case about 1.5 millimetre deep,
along the end-box periphery in the meniscus zone between mercury
and sidewall. This state of conservation allowed foreseeing a
residual life slightly higher than 2 years.
[0052] End-box B resulted to be affected by a totally marginal
powdering, while the perimetrical groove was reduced to a simple
band of different colour from the surrounding surface. In principle
for this end-box an operating lifetime certainly superior to the
average duration of 3 years, typical of the conventional dry inlet
end-boxes, can be foreseen.
[0053] End-box C looked very well preserved, with no significant
traces of powdering and with only a slight discontinuous band with
a different colouring from that of the surrounding material, while
end-box D appeared practically unvaried to a visual survey with
respect to the situation of the first start-up. For both of the
end-boxes C and D a much higher lifetime could thus be foretold
than the average duration of 3 years of the conventional dry inlet
end-boxes.
[0054] The positive result observed with the testing of end-boxes B
and especially C and D is attributable beyond any doubt to the
strong reduction in the temperature of the mercury coming in
contact with the lining. The temperature reduction is in its turn
due to the much more efficient thermal exchange between mercury and
brine feed within the device of the invention. In particular, the
higher efficiency is the result of the concurrence between the
splitting of mercury in a particularly stable fine dispersion in
the case of end-box D and the higher level of brine through which
the mercury dispersion falls, with the overall consequence of an
increase both of the contact time and of the heat exchange surface.
The thermal exchange is especially effective with the adoption of
the tray with edge provided with a multiplicity of openings of
end-box C and even more with the kind of tray of end-box D
characterised by a double multiplicity of openings which, as seen,
stabilises the dispersion of falling mercury.
[0055] The disappointing result of end-box A is evidently caused by
the lack of one of the two factors of success of end-boxes B, C and
D: in end-box A, in fact, where the device of the invention is
reduced to the distributing perforated pipe alone, the brine level
is rather low as happens in the conventional inlet end-boxes and
therefore the contact time of mercury with brine is much limited.
It follows a modest heat exchange which diminishes only marginally
the mercury temperature. A side advantage of the invention,
particularly when practised by employing end-boxes of type B, C and
D, is given by the temperature levels at which mercury and brine
enter the cell: these levels allow achieving a temperature
longitudinal distribution along the cell much more uniform than
what occurs in the cells equipped with the conventional inlet
end-boxes. The moderate temperature profile reflects in its turn on
a physiologically better current density distribution, and hence on
an easier automated regulation of the functioning with a
prolongation of the anode average duration.
* * * * *