Ozone generator

Details Ozone generator Ozone generator

2000-01-27

2001-07-24

Mayekar, Kishor (Department: 1741)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

With means applying electromagnetic wave energy or...

Reexamination Certificate

active

06264897

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an ozone generator for industrial use, such as water supply and sewage treatment, pulp-bleaching, and the like, which require a large amount of ozone.
A well-known ozone generator for industrial use changes an oxygen-containing feed gas to an ozonized gas or ozone gas by using silent discharge and is disclosed in Japanese Laid-Open Patent Publication No. 2-184506 (U.S. Pat. No. 5,034,198) or Japanese Laid-Open Patent Publication No. 9-315803, filed by the applicant of the present invention.
FIGS.
8
(
a
) and
8
(
b
) illustrate the structure of a conventional ozone generator disclosed in Japanese Laid-Open Patent Publication No. 9-315803. In FIG.
8
(
a
), reference number
1
designates a gas chamber formed of stainless steel or similar material having high corrosion resistance to ozone, and reference number
2
designates ozone-generating pipes arranged in a central portion of the gas chamber
1
to be parallel to each other.
The gas chamber
1
is formed of a cylindrical or rectangular hollow body portion
1
a
, end plates
1
b
occluding opposite ends of the body portion
1
a
, and a pair of support plates
1
c
laterally spaced at an interval in order to support all parallel ozone-generating pipes
2
in the central portion of the body to maintain their horizontal position. The body has a feed gas chamber
1
d
formed between a left-end portion or plate
1
b
and the support plate
1
c
, and an ozonized gas chamber
1
e
between the right-end portion and the support plate
1
c
. A water jacket if is formed between the pair of the support plates
1
c
to cool the ozone-generating pipes
2
. Furthermore, the body portion la has on its peripheral surface a feed gas inlet
1
g
, an ozonized gas outlet
1
h
, and an inlet
1
i
and an outlet
1
j
for ozone-cooling water, which are lead to the water jacket
1
f
. The body portion
1
a
and the end plate
1
b
are coupled via gaskets or air-tight seals, such as O-rings, using screws.
As shown in FIG.
8
(
b
), an ozone-generating pipe
2
is formed of a tube shaped ground electrode
2
a
made of ozone-resistant stainless steel, a glass dielectric layer
2
b
lying on an inner surface of the ground electrode
2
a
, and a high-voltage electrode
2
d
of a hollow structure placed concentrically inside the ground electrode
2
a
to oppose to the dielectric layer
2
b
with a discharge gap
2
c
located between the high-voltage electrode
2
d
and the dielectric layer
2
b
. The ozone-generating pipes
2
are held between the support plates
1
c
of the gas chamber
1
and penetrate the support plates
1
c
laterally. Both ends of the ozone-generating pipe
2
respectively open to corresponding openings for the starting gas chamber
1
d
and the ozonized gas chamber
1
e
, which are formed in the gas chamber
1
.
In addition, feeding leads
3
, drawn out from each end surface of the high-voltage electrodes
2
d
of the ozone-generating pipes
2
inside the body of the gas chamber
1
, i.e. feed gas chamber
1
d
, are connected to an external high-frequency power supply
5
via a bushing
4
, which is provided on a peripheral surface of body portion
1
a.
As a water-coolant system for the ozone-generating pipe
2
, cooling water is supplied through an external cooling water circulating line
6
to the water jacket if of the gas chamber
1
and to each hollow-structured high-voltage electrode
2
d
of the ozone-generating pipes
2
.
6
a
is a heat exchanger interposed between the water-cooling system and a secondary water-cooling system,
6
b
is a circulating pump,
6
c
is an ion exchanger, and
6
d
are manifolds. Cooling water conduit (insulating tube)
6
e
connected to the high-voltage electrodes
2
d
are drawn out to the ozonized gas chamber
1
e
in the body, and are branched and connected to the manifolds
6
d.
As shown in
FIG. 9
, the ozone generator is combined with an oxygen production apparatus (feed gas source)
7
and an ozone-processing apparatus
8
(water supply and sewage treatment facility, or pulp-bleaching treatment facility) to introduce and supply a feed gas through a gas line
10
located between the feed gas inlet
1
g
of the gas chamber
1
and the oxygen production apparatus
7
, and to supply the ozonized gas through a gas line
11
located between the ozonized gas outlet
1
h
and the ozone-processing apparatus
8
. Reference number
12
designates a compression apparatus (pump) for compressing and transferring the ozonized gas.
With this structure, the oxygen-containing feed gas is introduced from the oxygen production apparatus (feed gas source)
7
into the body of the gas chamber
1
through the gas line
10
, and is then discharged into the feed gas chamber
1
d shown in FIG.
8
(
a
). The gas is then distributed to the ozone-generating pipes
2
, where the gas flows into the discharge gaps
2
c
. As the gas flows, a high-frequency voltage is applied to an area between the high-voltage electrode
2
d
and the ground electrode
2
a
, causing a silent discharge between the two electrodes and ozonizing a part of the feed gas, which then flows into the ozonized gas chamber
1
e
. In addition, the ozonized gas flown into the ozonized gas chamber
1
e
is supplied to the ozone-processing apparatus
8
through the gas line
11
, which is connected to the ozonized gas outlet
1
h.
An exhaust valve (not shown) is connected to the gas line connected to the gas outlet
1
h
, and the exhaust valve is adjusted to control the operating pressure of the ozone generator—that is, to adjust the pressure of the feed gas to a certain level, e.g. 0.17 MPa, for example. For example, when the ozonized gas generated by the ozone generator is to be used for a water supply treatment, the operating pressure of the apparatus is maintained at 0.17 Mpa. For pulp-bleaching treatment, the compression apparatus
12
(often a water-sealing pump) is installed in the middle of the gas line
11
, as shown in
FIG. 9
, to increase the pressure of the ozonized gas to approximately 1 MPa before supplying it to the end use. Recently, the capacity and concentration of the ozone generators have increased as the scale of ozone-processing facilities has grown, due to the application of ozone for water supply sterilization and deodorization. However, it appears that as the ozone concentration generated in the ozone generator becomes higher, there raises the problems, which are described below.
Namely, when a voltage applied to the ozone-generating pipe is increased to produce thick or highly concentrated ozone efficiently, variation in the power supply voltage or the nature of the feed gas causes electric discharge in the discharge gap to shift from silent discharge to spark discharge, which ignites and decomposes ozone to thereby increase the gas pressures in the discharge space, thereby propagating flame outward. This phenomenon may be induced by ignition resulting from the system-generated static electricity, or by the ignition of an externally heated surface.
A graph in
FIG. 10
shows the results of experiments on ozonolysis or ozone decomposition performed by the inventors. During the course of these experiments, ozonized oxygen of high ozone concentration was sealed in a closed container at an absolute pressure between 0.1 and 1.5 Mpa. An electric current was conducted through a nichrome wire placed inside the container to heat. With the heat of the nichrome wire acting as an ignition energy, ozone was subjected to decompose by itself, i.e. autolysis, producing rapid increase of a gas pressure in the closed container. If a gas pressure ratio is defined as the ratio of a maximum pressure to an initial pressure, the gas pressure ratio begins to increase rapidly when an ozone concentration approaches 220 g/Nm
3
(in terms of 0° C. and 1 atom.), and reaches a value between 3.0 and 3.5 at approximately 250 g/Nm
3
or more. This trend is applicable to cases in which the sealing pressure of ozonized oxygen is changed from 0.1 to 1.5 MPa.
The ozone deco

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