Wet flue gas desulfurizer

Details Wet flue gas desulfurizer Wet flue gas desulfurizer

1998-11-04

2001-02-20

Tran, Hien (Department: 1764)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Waste gas purifier

C422S169000, C422S170000, C422S224000, C422S225000, C422S231000, C422S234000

Reexamination Certificate

active

06190620

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART STATEMENT
This invention relates to wet flue gas desulfurizers. More particularly, it relates to a wet flue gas desulfurizer for removing SO
2
from the exhaust gas of a boiler or the like by wet desulfurization, and an oxygen-containing gas blowing device for use therein.
When a sulfur-containing fuel is burned, the sulfur is discharged into the atmosphere in the form of sulfur dioxide (SO
2
), except for that fixed in ash. This sulfur dioxide exerts a significant harmful influence not only on human beings and animals, but also on the environment by causing acid rain to fall on the earth.
For this reason, large-scale combustion facilities and plants have conventionally been equipped with flue gas desulfurizers, most of which are wet flue gas desulfurizers.
In such a wet desulfurization process, exhaust gas is brought into gas-liquid contact with an absorbing fluid containing an alkali such as lime, so that SO
2
is absorbed and removed from the exhaust gas. As a result, the SO
2
absorbed from the exhaust gas forms sulfites in the absorbing fluid. In order to oxidize these sulfites and thereby form stable sulfates, it has been common practice to oxidize them by blowing air into the absorbing fluid.
Commonly employed wet flue gas desulfurizers are of the so-called tank oxidation type. In this type of wet flue gas desulfurizer, an oxygen-containing gas (typically air) is blown into an tank of an absorption tower, where it is brought into contact with a slurry (containing a calcium compound such as limestone) having sulfur dioxide absorbed therein so as to oxidize the sulfur dioxide. Thus, the necessity of an oxidation tower is eliminated.
In this case, it is necessary to bring air into efficient contact with the slurry in the aforesaid tank. For this purpose, various methods and devices have been known in the prior art.
FIG. 7
illustrates an oxygen feeding device described in Japanese Patent Provisional Publication No. 61-74630. In this device, air is blown into a slurry oxidation tank
201
by means of an oxygen feeding means
202
. The blown-in air is dispersed with an agitator
203
to improve the efficiency of air utilization.
However, the conventional device of
FIG. 7
has difficulties in that unduly great power is required to agitate the slurry within oxidation tank
201
, and the efficiency of utilization of the injected oxygen is low.
Moreover,
FIG. 8
illustrates a device constructed according to Japanese Patent Publication No. 6-91939. Also in this device, air is blown into a region in the vicinity of an agitator
302
by means of an oxygen feeding means
303
. However, the device of
FIG. 8
also has difficulties in that unduly great power is required to agitate the slurry within oxidation tank
301
, and the efficiency of utilization of the injected oxygen is low.
The present inventor has also employed a stationary oxidation device in prior art oxidation equipment (Japanese Patent Provisional Publication No. 9-10546). However, owing to its low efficiency of oxygen utilization (usually about 20%), the flow rate of oxidizing air or the number of sparger nozzles must be increased to cause problems from the viewpoint of equipment cost and maintainability.
Moreover, in the device which has conventionally been employed by the present inventor as described in Japanese Patent Provisional Publication No. 9-10546 or the like, the sparger itself is rotated to produce finely divided air bubbles and agitate the liquid at the same time. However, since this device masticates air, a loss in agitation capability is caused and unduly great power is required.
On the other hand,
FIG. 9
illustrates a wet flue gas desulfurizer having such an oxygen-containing gas blowing means (hereinafter referred to as a first example of the prior art). As shown in
FIG. 9
, this wet flue gas desulfurizer is constructed so that it has an absorption tower
2
for effecting wet desulfurization, a fluid reservoir
31
for storing an absorbing fluid b containing an alkaline absorbent d (e.g., lime) is disposed below absorption tower
2
, and the absorbing fluid b within fluid reservoir
31
is raised by means of a circulating pump
6
and sprayed through spray pipes
30
disposed in the lower part of absorption tower
2
.
In the above-described equipment construction, combustion exhaust gas a is introduced into absorption tower
2
at the top thereof, and brought into gas-liquid contact with the alkali-containing absorbing fluid sprayed through spray pipes
30
so as to absorb and remove SO
2
from the exhaust gas. Thereafter, the cleaned exhaust gas c is discharged to the outside through an exhaust duct
38
. The absorbing fluid in which sulfites have been formed from SO
2
absorbed from the exhaust gas is returned to fluid reservoir
31
, where the aforesaid sulfites are oxidized to sulfates with the aid of an oxygen-containing gas e fed by an oxygen-containing gas blowing means. Thereafter, an amount of the sulfates which is stoichiometrically equivalent to that of SO
2
absorbed are discharged as waste fluid f by way of circulating pump
6
and a pipeline
40
. On the other hand, the alkaline absorbent d (e.g., lime) is supplied to the aforesaid fluid reservoir
31
by way of a pipeline
39
.
The aforesaid oxygen-containing gas blowing means comprises a plurality of nozzle headers
102
which extend from the sidewall of fluid reservoir
31
in a downwardly inclined direction and are each equipped with a plurality of feed nozzles
101
. These nozzle headers
102
are disposed so as to cover substantially the entire bottom surface of fluid reservoir
31
. Thus, using a blower
36
, oxygen-containing gas e is fed through a pipeline
37
and nozzle headers
102
, and injected from the injection orifices
35
of feed nozzles
101
into the absorbing fluid b for the purpose of oxidizing the sulfites.
FIG. 10
illustrates the construction of a wet flue gas desulfurizer having another oxygen-containing gas blowing means. This represents a practically employed oxidation method in which an injection orifice
35
at the tip of a pipeline
37
is disposed in front of an agitator
203
attached to the sidewall of fluid reservoir
31
, and an oxygen-containing gas e fed through pipeline
37
by means of a blower
36
is injected from injection orifice
35
into the absorbing fluid b so as to promote the dispersion of oxygen-containing gas e by the jet of the absorbing fluid b that is driven by the aforesaid agitator
203
. (This oxygen-containing gas blowing means will hereinafter be referred to as a second example of the prior art.)
Moreover, as illustrated in
FIG. 11
, Japanese Utility Model Provisional Publication No. 4-137731 discloses an oxygen-containing gas blowing means comprising a plurality of jet nozzles
151
for injecting a jet of an absorbing fluid in a direction forming a predetermined angle with the corresponding diameter of a fluid reservoir
150
. These jet nozzles
151
are attached to the sidewall of fluid reservoir
150
at a predetermined vertical position so as to inject the absorbing fluid in the circumferential direction of the sidewall. The basal end of each jet nozzle
151
is provided with an absorbing fluid pipeline
153
communicating with fluid reservoir
150
and having a jet pump
152
installed in an intermediate part thereof, and a gas pipe
154
is connected to absorbing fluid pipeline
153
between jet pump
152
and jet nozzle
151
. (This oxygen-containing gas blowing means will hereinafter be referred to as a third example of the prior art.)
Furthermore, a further oxygen-containing gas blowing means has been known. Specifically, as illustrated in
FIG. 12
, a delivery pipe
161
is attached so as to penetrate into a fluid reservoir
160
through the sidewall thereof, and connected with a circulating fluid pipe
163
for sucking out an absorbing fluid from fluid reservoir
160
and circulating it by means of a fluid pump
162
. Moreover, a gas blowing pipe
164
is attached so as to penetrate into an intermediate part of the aforesa

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