Abstrict Disclosed is a new form of brine flow meter necessary in metering
brine to an electrolytic cell for the production of chlorine and
caustic (sodium hydroxide). The flow meter is made advantageously
of a plastic material resistant to the various pH ranges necessary
for brine being fed to such an electrolytic cell with the additional
advantage of clarity for visual observation of the flow rate and
resistance qualities.
Claims What is claimed is:
1. An electrolytic brine cell including a flow meter for metering
the flow of brine into the electrolytic cell for the production
of chlorine and caustic, said flow meter comprising: a float tube
made of UDEL polysulfone injection molded; said float tube being
of a fluted design so as to provide uniform float tube guides over
an ever increasing cross-sectional area; the smaller diameter conjugate
plane of said float tube being the float tube ingress and connected
to the supply of brine for use in a chlor-alkali electrolytic cell;
the larger diameter conjugate plane of said float tube being at
the top of the float tube and being the float tube egress as connected
to the piping for transfer into a chlor-alkali electrolytic cell
for the production of chlorine and caustic; a float riding in the
interior of said float tube along said float tube guides in close
tolerance thereto so as to restrain horizontal movement thereof
during the passage of flow by said float in said float tube; said
float tube having a float tube protector completely surrounding
said float tube and being of a visually transparent material resistant
to the transmittance of UV radiation; and said float tube, along
with said float tube protector being connected to associated piping
for transmitting the supply of brine having a high pH therethrough
by means of an O-ring seal at each end of said float tube.
2. An electrolytic cell brine flow meter according to claim 1 wherein
the brine has a high pH.
3. An electrolytic cell brine flow meter according to claim 2 wherein
said float is a cylinder having equal larger diameter conjugate
plane cylinders at either end thereof.
4. An electrolytic cell brine flow meter according to claim 3 wherein
said O-ring seals are made of Neoprene having a 70 durometer hardness.
5. An electrolytic cell brine flow meter according to claim 4 wherein
said O-ring seals are lubricated with a high velocity silicone oil
prior to assembly.
Description BACKGROUND OF THE INVENTION
The present invention relates generally to the use of a brine flow
meter for metering brine (sodium chloride solution) to an electrolytic
cell for the production of chlorine and caustic. More particularly,
the present disclosure relates to an improved brine flow meter made
of a plastic material advantageously resistant chemically to a wide
range of pH necessary for brines of various pH levels being utilized
in today's commercial chlorine and caustic cells. This employs the
use of a polysulfone material, which retains the clarity necessary
for visual perception of the flow of brine into the electrolytic
cell, while providing substantially increased resistance to chipping
and breaking due to chemical attack from brines having a high pH.
Furthermore, this flow meter utilizes an additional tube around
the outside of the polysulfone material to prevent ultraviolet attack
of the polysulfone used for the brine meter itself.
Chlorine and caustic are essential in large volume basic commodity
chemicals required by all industrialized societies. They are produced
almost entirely electrolytically from aqueous solutions of alkali
metal chlorides, with the major portion of such production coming
from diaphragm-type electrolytic cells. In the diaphragm cell process,
brine is fed continuously to the anode compartment and flows through
the diaphragm usually made of asbestos, backed by a cathode. To
minimize back migration of hydroxide ions, the flow rate is always
maintained in excess of the conversion rate so that the resulting
catholyte solution has unused alkali metal chloride present. However,
to maintain the amount of unused alkali metal chloride present to
an absolute minimum, it is essential to very carefully meter in
the brine to the electrolytic cell by utilizing a brine flow meter
or some device for such careful control. It is very important that
the operator be permitted to visually perceive the amount of brine
flowing into the electrolytic cell and to control such flow so as
to run a constant check on the amount of unused alkali metal chloride
present in the catholyte. The hydrogen ions are discharged from
the solution at the cathode in the form of hydrogen gas. The catholyte
solution containing caustic soda, unreacted sodium chloride and
other impurities then must be concentrated and purified to obtain
marketable alkali metal hydroxide commodity and alkali metal chloride,
which can be reused in the chlorine and caustic electrolytic cell
for further production of chlorine and caustic. Recent advances
in hydraulically impermeable cation-exchange membranes have allowed
the electrolytic cell to produce a much higher quality caustic product
by significantly reducing the impurities present in the product
and also increasing the concentration of that product. These cells
also require the careful control of brine flow so as to provide
the best operating conditions for the electrolytic cells.
Much research and development attention has been directed to various
components of the electrolytic cell, such as the anodes, anode coatings
therefor and the cation-exchange hydraulically impermeable membranes.
One problem that has received very little attention, though, is
the brine flow meter, which is so necessary to the successful operation
of an electrolytic cell. It has been found that glass flow meters
for brine metering have a fatal characteristic in that they are
not resistant to solutions of high pH. Thus, the use of a glass
flow meter for brine metering has caused problems in those instances
where the brine is maintained at a high pH to obtain economy of
use of HCl used to lower the brine pH. In fact, in most instances,
the glass is very often chipped by the float utilized in such flow
meters, partly because of the lack of uniformity caused by use of
the glass tubes, and also because of the lack of chemical resistivity
to high pH levels. This very often causes chipping and, ultimately,
causes a breaking of the tube because the glass is brittle and prone
to mechanical damage. Such breakage has been very detrimental in
interrupting the operation of an electrolytic cell and, perhaps,
even a bank of electrolytic cells, in addition to causing major
spill problems when the flow of brine is interrupted to the electrolytic
cell.
Thus, it would be very beneficial and advantageous to the operation
of an electrolytic cell to provide a brine flow meter capable of
resisting brine solutions of a high pH and additionally maintaining
a higher degree of uniformity in the internal wall structure of
said brine meters so as to advance this ideal characteristic of
brine flow meters.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide
a brine flow meter capable of withstanding chemical attack by any
brine flow therethrough.
Another object of the present invention is to provide an improved
brine flow meter having superior quality of uniformity of interior
wall construction so as to avoid the chipping and breaking attendant
to glass brine flow meters.
It is a still further object of the present invention to provide
a brine flow meter capable of withstanding chemical attack over
a wide range of pH.
These and other objects of the present invention, together with
the advantages thereof over existing and prior art forms which will
become apparent to those skilled in the art from the detailed disclosure
of the present invention set forth hereinbelow, are accomplished
by the improvements herein shown, described and claimed.
It has been found that a brine flow meter for an electrolytic cell
for the production of chlorine and caustic can be made of an injection
molded polysulfone material having a high degree of uniformity of
internal wall structure; and a surrounding cylinder of transparent
ultraviolet light resistant and mechanically rigid material for
protection of the float guide tube.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation view of a brine flow meter according
to the concepts of the present invention which can be used for the
metering of a brine to an electrolytic cell for the production of
chlorine and caustic.
FIG. 2 is a side section view taken substantially along line 2--2
of FIG. 1.
FIG. 3 is a top section view taken substantially along line 3--3
of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An electrolytic cell brine flow meter according to the concepts
of the present invention is generally referred to by numeral 10
in the figures of the drawings. Such a brine flow meter is contemplated
to be a variable area type flow meter, which simply is a device
for measuring the flow through the instrument into the electrolytic
cell of a brine stream. It consists of a float tube 12 which is
generally a tapered tube mounted vertically in the fluid stream
with its smaller diameter conjugate plane being at the bottom or
at the float tube ingress 16 and the larger diameter conjugate
plane being at the top of the float tube 12 or at the float tube
egress 18. Such a tube can have various cross-sectional areas; but,
as seen in FIG. 3 the fluted design is preferred, which presents
float tube guides 14 for the float 20 to ride against, up and down,
the tube for measuring the flow through the tube. Within the float
tube 12 the float 20 is free to move up and down the float tube
12 in accordance with the fluid that is flowing through the tube
from the bottom float tube ingress 16 to the top float tube egress
18. As the fluid flows through the tube, the float rises within
the area between it and the tube wall until the diameter is just
large enough to pass the amount of fluid flowing through the float
tube 12. The height of such a float tube 12 therefore, is a measure
of the flow rate through the float tube 12. In use, such an electrolytic
cell brine flow meter 10 would be connected at the bottom or float
tube ingress 16 to the brine supply for the electrolytic cell bank,
and the top or float tube egress 18 is connected to the electrolytic
cells being fed with brine.
The basis for operation of the float tube 12 in this given instance
is that the float tube 12 has integral flutes or float tube guides
14 as shown in the drawings formed on the inside of the tube at
the time of manufacture. Thus, although the flute walls themselves
are tapered, the diameter of the enclosed flutes or float tube guides
14 is nearly constant over the length of the tube so as to provide
a smooth guide path for the float 20 up and down the entire length
of the float tube 12. Of course, as the flow rate changes, the float
20 moves freely in the vertical direction, up and down the float
tube 12 but is restrained by the float tube guides 14 from all
but very minor amounts of horizontal motion. Consequently, the readings
of the float 20 on a vertical scale placed upon the float tube 12
provides an extremely accurate and repeatable measurement of the
flow through the float tube 12. The float tube 12 will be connected
into either end to appropriate fittings by the use of an O-ring
seal 26 at each end thereof to assure proper sealing engagement
of the float tube to each end fitting block 24 therewith for connecting
the electrolytic cell brine flow meter 10 to the brine supply for
the electrolytic cell. Such O-ring seals 26 should preferably be
made of a rubber or elastomeric composition such as Neoprene having
a 70 durometer hardness. In assembly of the flow meter 10 the O-ring
seals 26 should be lubricated using a substance such as a high velocity
silicone oil.
At the float tube ingress 16 and float tube egress 18 are float
stops 28 to retain the float 20 within the float tube guides 14
and to maintain the alignment of the float 20. As seen in FIGS.
1 and 2 the float stops 28 protrude slightly into the float tube
12 from each end fitting block 24.
It is very important that the float tube 12 be manufactured of
a polysulfone material and injection molded to assure a high degree
of quality and close tolerances of the float tube guides 14. The
reason for this is that brine flow meters of the prior art utilizing
glass have lacked the uniformity of the float tube guides 14 necessary
to withstand the caustic brine flow therethrough. Furthermore, glass
is not resistant to caustic (sodium hydroxide) and, therefore, chipping
and eventual breakage occurs with glass. It has been found that
the float tube 12 can be advantageously made of polysulfone material,
which is quite resistant to potassium hydroxide or sodium hydroxide
up to strengths of 50 percent and up to temperatures of 185.degree..
Thus, polysulfone appears to be the only transparent material adequate
for handling a hot caustic brine solution for feeding to an electrolytic
cell. Furthermore, such polysulfone material can be purchased from
Union Carbide Corporation under the trademark UDEL. UDEL polysulfone
is a high performance thermoplastic known for its high temperature
resistant up to 300.degree. F. UL listing for continuous use, hydrolytic
stability and excellent close tolerance moldability. The close tolerance
moldability for injection molding is very important in the present
instance in that only with close tolerances of the float tube guides
14 can the float tube 12 be successfully utilized in this particular
application. Therefore, the particular qualities of UDEL polysulfone
are particularly suited for this particular application of high
temperature, high pH brine flow for feeding electrolytic cells.
Furthermore, UDEL polysulfone is particularly useful from the standpoint
that production costs for such a flow meter can be reduced significantly
over those for glass flow meters for the same general purpose.
Polysulfone, though, does have a weakness which must be compensated
for in its use. This weakness is ultraviolet radiation. It has a
tendency to cause polysulfone to crack and otherwise deteriorate.
Thus, it has been found that an electrolytic cell brine flow meter
10 having a float tube 12 made of polysulfone must utilize a float
tube protector 22 made of acrylic or other material which will not
transmit UV radiation. Thus, as seen in the drawings, the float
tube protector 22 is a cylinder surrounding the outside edge of
the float tube 12 made of polysulfone to protect it from ultraviolet
radiation, which is harmful to polysulfone material. Furthermore,
the float tube protector 22 still allows ample visability of the
float 20 as it rides vertically in the float tube guides 14 of float
tube 12 for a measurement of the brine flow therethrough.
While many forms of float 20 could be utilized in such a flow meter
10 it has been found that the cylinder having equal larger diameter
conjugate plane cylinders at either end thereof works well for the
metering of brine into electrolytic cells.
Thus, it should be apparent from the foregoing description of the
preferred embodiment that the device for the metering of a brine
to an electrolytic cell herein shown and described accomplishes
the objects of the invention and solves the problems attendant to
metering brines to electrolytic cells, especially those brines having
high temperature and high pH. |