Chlorine hydrate tank

In a chlorine hydrate tank wherein a chlorine gas supply pipe is inserted into a tank holding chilled water therein and chlorine gas in blown into the water through the pipe to form a chlorine hydrate, a hollow cylinder having an opening in an upper-side portion thereof is arranged around the chlorine gas supply pipe so as to form a predetermined gap therebetween so that the upper opening of the cylinder is partially or entirely submerged in the water.

BACKGROUND OF THE INVENTION 
The present invention relates to an improvement in a chlorine hydrate tank 
for efficiently forming or synthesizing chlorine hydrate and storing the 
formed chlorine hydrate, as a storage form of chlorine. 
In general, chlorine hydrate is a clathrate compound wherein a chlorine 
molecule is enclosed within 48 water molecules and has a general formula: 
Cl.sub.2 .multidot.xH.sub.2 O (where x=6 to 8). Chlorine hydrates can be 
stably stored if kept at temperatures below 9.6.degree. C. and at normal 
pressure. Thus, chlorine hydrates are good means of storing chlorine. 
Synthesis of chlorine hydrate is an exothermic reaction (80 cal/g). Thus, 
in order to form a chlorine hydrate efficiently, the heat of reaction must 
be quickly removed. In view of this, according to a conventional method, 
chlorine and chilled water at 9.6.degree. C. or lower are mixed and 
directly reacted together to form chlorine hydrate. However, it is 
extremely difficult to obtain efficient absorption of chlorine gas into 
chilled water. An improvement in the yield of chlorine hydrate is 
demanded. 
In some cased, a small amount of zinc chloride, sodium chloride or 
potassium chloride is dissolved in chilled water. In such cases, the 
formed chlorine hydrate is not deposited on a cooling heat exchanger in 
the chlorine hydrate tank, and thus the operation capacity of the heat 
exchanger is maintained. The solution temperature is generally kept at 
8.degree. C. or lower. 
An example of means for storing chlorine will be described with reference 
to a case of a zinc-chloride battery. FIG. 1 shows a conventional charging 
mechanism of a zinc-chloride battery. Referring to FIG. 1, chlorine gas 
generated by a chlorine electrode in a battery 1 is blown into a chlorine 
hydrate tank 4 by a gas pump 2 through a chlorine gas supply pipe 3. The 
chlorine gas in the tank 4 reacts with chilled water 6 held therein and 
chilled by a heat exchanger 5 so as to form chlorine hydrate 7. The 
nonreacted portion of the chlorine gas is supplied to a nonreacted gas 
circulation pipe 16 where it is recirculated for further reaction as 
indicated by the arrow. 
Zinc chloride electrolyte held in an electrolyte tank 8 is supplied to the 
battery 1 and is recirculated therebetween by a pump 9. 
FIG. 2 shows an example of a chlorine hydrate tank for mixing chlorine with 
chilled water to form chlorine hydrate. In this chlorine hydrate tank, 
chlorine is blown into chilled water 6 in a chlorine hydrate tank 4 
through a chlorine gas supply pipe 3. This tank can only provide a very 
low reaction rate between the chilled water and chlorine gas. Therefore, 
it has been proposed to use an agitator so that the chilled water is 
agitated while chlorine is blown into the chilled water. However, it is 
difficult to agitate the chilled water uniformly at all times and power is 
required for agitation. 
Furthermore, when a large amount of chlorine hydrate 7 is formed, as shown 
in FIG. 3, the chlorine hydrate has a high specific gravity and therefore 
precipitates on the bottom of the chlorine hydrate tank 4. The 
precipitated chlorine hydrate frequently clogs the distal end of the 
chlorine gas supply pipe 3 thus preventing further synthesis of chlorine 
hydrate. 
Another method which uses a gear pump has also been proposed. According to 
this method, chlorine and chilled water are drawn into the gear pump 
through inlet ports thereof and are mixed therein. The pump then delivers 
the synthesized chlorine hydrate. This method provides a high mixing 
efficiency and a high yield of chlorine hydrate. However, when the 
produced chlorine hydrate is drawn into the pump, the interior of the 
chilling tank is kept at a reduced pressure. This causes decomposition of 
the chlorine hydrate and thus reduces the overall yield thereof. In order 
to prevent this, a filter for separating out the chlorine hydrate is 
required, resulting in a complex structure. In addition, power for driving 
the pump is required. Since chlorine-containing water is strongly 
corrosive, only titanium can be used as a material of the pump, rendering 
an expensive pump necessary. 
SUMMARY OF THE INVENTION 
The present invention has been proposed based on the studies made in an 
attempt to provide a chlorine hydrate tank which gives a high yield of 
chlorine hydrate and which can operate at a reduced drive power. 
According to the present invention, there is provided a chlorine hydrate 
tank in which a chlorine gas supply pipe is inserted into a tank holding 
chilled water or a chilled aqueous chloride solution, and chlorine is 
blown into the chilled water or the chilled aqueous chloride solution 
through the chlorine gas supply pipe to form a chlorine hydrate, wherein a 
hollow cylinder with openings at upper and lower portions thereof is 
arranged around the chlorine gas supply pipe to form a predetermined gap 
therebetween so that the upper opening of the hollow cylinder is partially 
or entirely submerged in the chilled water or the chilled aqueous chloride 
solution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to a chlorine hydrate tank 4 of the present invention shown in 
FIG. 4, when chlorine gas is blow into chilled water 6 or a chilled dilute 
aqueous solution of zinc chloride 6, or the like, through a chlorine gas 
supply pipe 3 arranged inside a hollow cylinder 10 having an upper opening 
12 and a lower opening 11, the water or solution inside the hollow 
cylinder 10 absorbs chlorine. Thereafter, the portion of the water or 
solution inside the hollow cylinder 10 has a specific gravity smaller than 
that of the position of the water or solution outside the hollow cylinder. 
Then, due to this difference of specific gravities, an upward convection 
is established in the solution inside the hollow cylinder 10 without 
requiring any special drive means except one for blowing the chlorine gas. 
In the chloride hydrate tank 4 of the present invention shown in FIG. 4, 
an agitation effect is obtained by the upward convection of the water or 
solution indicated by an arrow 17. In this case, the chlorine hydrate 
yield is improved, as compared with that in the conventional chlorine 
hydrate tank wherein chlorine gas is simply blown through the chlorine gas 
supply pipe 3, as shown in FIG. 2. 
The convection also allows chilled water or solution to be constantly 
supplied to the position near the distal end of the chlorine gas supply 
pipe 3, which is the reaction site of chlorine hydrate synthesis. 
Therefore, the heat of reaction accompanying chlorine hydrate synthesis is 
immediately removed. Since this heat of reaction which inhibits the 
exothermic synthesis of chlorine hydrate is removed immediately after it 
is generated, the yield of chlorine hydrate 7 is further improved. When 
the hollow cylinder 10 is incorporated in the tank, the flow of water or 
solution below the pipe 3 becomes fast, thus preventing precipitation of 
chlorine hydrate 7 near the distal end of the pipe 3. Then, even after a 
large amount of chlorine hydrate 7 has been formed, the chlorine gas 
supply pipe 3 will not become clogged, allowing continuous and highly 
efficient synthesis of chlorine hydrate to be performed. 
Referring to FIG. 5, a heat exchanger 5 for cooling is arranged around an 
opening 12 formed at the upper portion of the hollow cylinder 10, that is, 
at the upper portion of the tank 4. The heat exchanger 5 cools the mixture 
of chlorine and chilled water or solution 6 so as to remove the heat of 
reaction, thereby further improving the yield of chlorine hydrate 7. 
Reference numeral 13 denotes a cooling device. Even after a large amount 
of chlorine hydrate is formed, the heat exchanger 5 at the upper portion 
of the tank is not emersed in the formed chlorine hydrate 7. Thus, the 
heat exchanger 5 maintains stable cooling operation and hence stable 
chlorine hydrate synthesis. The synthesized chlorine hydrate 7 can be used 
for storing chlorine or can be decomposed, when required, to give a supply 
of chlorine. In order to allow alternate formation and decomposition of 
chlorine hydrate within a single chlorine hydrate tank, a heat exchanger 
15 for heating is arranged near the bottom of the tank, as shown in FIG. 
5. Warm water or warm aqueous solution is externally supplied to the heat 
exchanger 15 so as to heat the chlorine hydrate tank 4. 
The heat exchangers for cooling and heating must both be made of a 
chlorine-resistant material such as titanium, tantalum, or a 
flourine-containing resin (e.g., tetrafluoroethylene). Referring to FIG. 
5, reference numeral 14 denotes a heater. 
The heat exchanger for heating is used for decomposing the chlorine hydrate 
and can be arranged at any position inside the chlorine hydrate tank. 
However, a better result is obtained if the heating heat exchanger is 
arranged at a lower portion of the tank. 
The heat exchanger for heating, as it is arranged at a lower portion of the 
tank, in the chlorine storage state, is emersed in the chlorine hydrate. 
When warm water or warm aqueous solution is supplied to this heat 
exchanger 15, therefore, chlorine hydrate decomposition can be immediately 
started on the surface of the heat exchanger 15, thereby producing 
chlorine. Accordingly, chlorine can be supplied without maintaining the 
overall water or solution in the chlorine hydrate tank at a temperature 
higher than 9.6.degree. C., at which chlorine hydrate decomposes. 
The present invention will now be described by way of examples. Examples 1 
and 2 
As shown in FIG. 4, chilled water 6 at 8.degree. C. (Example 1) or 3% zinc 
chloride aqueous solution 6 at 7.degree. C. (Example 2) was injected into 
a chlorine hydrate tank 4 having a height of 400 mm and a volume of 100 l 
through a heat exchanger (not shown). A chlorine gas supply pipe 3 of 13 
mm inner diameter and 350 mm height and of polyvinyl chloride was mounted 
in each tank 4. A hollow cylinder 10 of 40 mm inner diameter and 365 mm 
height was arranged around the pipe 3. The cylinder 10 had a funnel-like 
enlarged opening 11 at its lower end, and an opening 12 of about 30 mm in 
length at its upper side surface, and had its lower half submerged in the 
water or solution 6. 
When chlorine gas was blown into the water or solution at a rate of 3.5 
l/min. through the chlorine gas supply pipe 3, the chlorine gas was made 
to flow upward inside the hollow cylinder 10 while it reached with the 
water or solution. Thus, since the portion of the water or solution inside 
the hollow cylinder 10 contained a large amount of chlorine gas, it had a 
smaller specific gravity than that portion of the water or solution which 
was outside the cylinder 10. This portion of the water or solution inside, 
which had a smaller specific gravity, flowed out of the cylinder 10 
through the opening 12 at the upper side surface thereof, causing the 
natural convection as indicated by arrow 17. Thus, chlorine and the water 
or solution were efficiently mixed and the yield of chlorine hydrate was 
improved. When this experiment was continued for 8 hours, the increase in 
pressure inside the tank 4 was 0.1 kg/cm.sup.2 or less in both cases. This 
indicates that most of the chlorine gas has been converted into a chlorine 
hydrate and thus the yield of the chlorine hydrate was extremely improved. 
Although the lower end of the hollow cylinder 10 need not have a 
funnel-like shape, it preferably has such a funnel-like shape to 
facilitate the convection flow. 
For the purpose of comparison, chlorine gas was blown into chilled water or 
zinc chloride aqueous solution in the same manner to that described above, 
using the tank shown in FIG. 2. In this case, the pressure inside the tank 
4 increased to 0.3 kg/cm.sup.2 after the reaction had proceeded for 3 
hours. This indicates that the yield of chlorine hydrate was low. 
In the present invention, the opening need not be formed at the side 
surface of the hollow cylinder, but can be formed at an upper portion 
thereof and two or more openings can be formed. However, in either case, 
at least the lower portion of each opening must be submerged in the water 
or solution. 
A chlorine hydrate tank of the present invention can efficiently synthesize 
chlorine hydrate.