Exhaust gas processing system

In order to economically remove harmful components in exhaust gases by using a simple and extremely durable system, an exhaust gas to be treated is introduced into a neutralizing tower provided with a first duct and a second duct. Harmful components in the exhaust gas chemically react with a neutralizing agent randomly stacked within the neutralizing tower, and such components become deposited on the surface of the neutralizing agent. Water is supplied from a water supply pipe to the surface of the neutralizing agent by driving a pump after passage of a predetermined period of time, and the surface of the neutralizing agent is washed thereby. Additional exhaust gases are further fed and reacted with the neutralizing agent, which has a renewed surface exposed again. The neutralizing agent can thus be repeatedly used for removal of harmful components in the exhaust gases.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an exhaust gas processing system, and in 
particular relates to an exhaust gas processing system in which harmful 
components in exhaust gases generated upon incineration of vinyl chloride 
and the like are neutralized and released to atmosphere, and wherein 
processing of such exhaust gases is enabled by washing and repeatedly 
using a neutralizing agent. 
2. Description of the Related Art 
At present, general and industrial waste is processed either by burying the 
waste or through incineration. A relatively large amount of macromolecular 
compounds including vinyl chloride are contained in the waste. It is often 
pointed out correctly that harmful gases are released into the atmosphere 
due to burning of such waste materials. 
Trials have hitherto been made to decrease such harmful gases as low as 
possible. For example, in a wet neutralizing tower, neutralization is 
achieved by spraying an aqueous alkali dissolved in water onto the harmful 
components, such as hydrogen chloride, contained in exhaust gases. 
However, in the case of such a wet neutralizing tower, the processing 
system itself is relatively expensive, handling of the system is 
troublesome, and the amount of exhaust gas supplied from an incinerator 
side of the system in not specified. As a result, it is impossible to 
recognize the degree at which harmful components are contained in the 
exhaust gas. Thus, it is also impossible to specify a proper amount of an 
aqueous alkali to be supplied to the inside of the wet neutralizing tower, 
inevitably resulting in complicated processing operations. Further, the 
equipment constituting the neutralizing tower is subjected to extremely 
accelerated corrosion, and the like, due to alkaline components, and 
consequently a drawback arises in durability of the equipment. 
SUMMARY OF THE INVENTION 
The present invention has been made in order to overcome the disadvantages 
described above. It is an object of the present invention to provide an 
exhaust gas processing system having both a simple construction and 
excellent durability, in which a neutralizer capable of repeated use is 
used, and whereby the running cost of the system can be kept inexpensive. 
In order to achieve the objects described above, the present invention 
comprises an exhaust gas processing system comprising a first duct which 
communicates with an exhaust port of an incinerator generating an exhaust 
gas, a neutralizing tower to which the first duct is connected, and a 
second duct which is connected to a discharge port of the neutralizing 
tower, and wherein; 
a water supply means is arranged on the inside of the neutralizing tower, a 
large number of pellet-shaped pieces of a neutralizing agent are charged 
into the neutralizing tower, and components in the exhaust gas introduced 
from the first duct are reacted with the neutralizing agent in the 
neutralizing tower and discharged to the outside from the second duct, and 
further wherein; 
the water supply means is energized after passage of a predetermined period 
of time to supply water to the inside of the neutralizing tower, whereby 
reacted components deposited on a surface of the neutralizing agent are 
removed. 
The exhaust gas introduced from the first duct contacts with the 
neutralizing agent made up of a large number of pellet-shaped pieces in 
the neutralizing tower. At this time, the exhaust gas forms a turbulent 
flow and rises in the neutralizing tower because the neutralizing agent is 
randomly and sufficiently charged in the neutralizing tower. Further, 
harmful gases contained in the exhaust gas, for example gases containing 
HCl generated after the incineration of vinyl chloride and the like, react 
with the neutralizing agent and become neutralized, and the reacted 
components are deposited on the surface of the neutralizing agent. The 
exhaust gas itself, having been neutralized and made harmless in such a 
manner, is discharged to the outside through the second duct. 
On the other hand, the reacted components deposited on the neutralizing 
agent are removed from the surface layer of the neutralizing agent by 
water, which is vigorously jetted from the water supply means, after the 
passage of a predetermined period of time, and such reacted components 
naturally fall toward a lower portion of the neutralizing tower. The 
reacted components are then removed from the lower portion of the 
neutralizing tower. The neutralizing agent acquires a renewed reactive 
surface which is exposed to the space within the neutralizing tower, and 
the system waits in preparation for the next exhaust gas processing.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference numeral 10 in FIG. 1 shows an exhaust gas processing system 
according to the present invention. The exhaust gas processing system 10 
includes a cylindrical neutralizing tower 12. A seamless first duct 14, 
which communicates with an exhaust gas outlet of an incinerator (not 
shown), is connected to a lower portion of the neutralizing tower 12. The 
first duct 14 faces a bottom portion of the neutralizing tower 12, and a 
connecting port therebetween is provided with a net member 16 having a 
relatively fine mesh size. A lid member 15 which can be freely opened or 
closed is provided at a bottom portion of the first duct 14, and is used 
to take out and remove relatively large dust trapped by the net member 16. 
A second duct 18, for discharging harmless exhaust gas to the outside 
after reaction and processing in the neutralizing tower 12, is provided at 
an upper side wall of the neutralizing tower 12. The bottom of the 
neutralizing tower 12 has an inclined bottom plate 20, as illustrated, 
wherein the bottom plate 20 is selected to have an inclination angle of 
about 5 degrees with respect to the horizontal plane. Two layers of 
perforated metals 22a, 22b are arranged over the bottom plate 20. A water 
supply pipe 24 extends upward from an approximately central portion of the 
bottom plate 20 along the axis of the neutralizing tower 12. A large 
number of holes are pierced through a cylindrical circumferential wall of 
the water supply pipes 24, and nozzles 24a are installed on the holes. A 
pump 26 is inserted into a lower end portion of the water supply pipe 24. 
Washing water is forcibly supplied by the pump 26 from the water supply 
pipe 24 to the inside of the neutralizing tower 12. 
A cleaning port 30 and a drain withdrawal hole 32 are provided at bottom 
portions of the neutralizing tower 12. Holes 34 for discharging 
overflowing washing water to the outside, and a lid member 37 including an 
explosion-proof valve 36 which closes an upper opening of the neutralizing 
tower 12 and which can be optionally and freely opened and closed, are 
provided at upper portions of the neutralizing tower 12. 
Upon use of the construction as described above, a neutralizing agent 39 is 
charged to the inside of the neutralizing tower 12 up to a level L. The 
neutralizing agent 39 preferably comprises almond-shaped pellets (see FIG. 
2), composed from raw materials of slaked lime (Ca(OH).sub.2), cement and 
water. Preferably, slaked lime is 70-90% by weight, cement is 5-25% by 
weight, and water is 5-25% by weight. These raw materials are mixed and 
kneaded in a mill, the mixed and kneaded neutralizing components are 
pressurized and molded at a pressure of 100-200 kg/cm.sup.2, and are 
naturally dried. Because cement is added to the neutralizing agent 39, 
advantageous effects are obtained in that the strength of the pellets by 
far increases as compared with a single molding of slaked lime, and the 
pellets are prevented from collapsing during the neutralization reaction. 
When pieces of the neutralizing agent 39 thus formed are charged to the 
inside of the neutralizing tower 12 up to the level L, gaps between the 
pellets make up 15-20% of the total volume occupied by the pallets. In 
this case, the almond-shaped pellet 39, as shown in FIG. 2 may also be 
divided in two along a longitudinal direction thereof to form divided 
halves of pellet pieces 39a, 39b. By doing so, the contact area between 
the pallets 39 and the exhaust gas increases, when the exhaust gas enters 
the neutralizing tower 12, as described in more detail below. 
The exhaust gas processing system according to the present invention is 
basically constituted as described above. Next, its operation will be 
explained. 
An exhaust gas discharged from an incinerator (not shown) is introduced 
into the neutralizing tower 12 through the first duct 14. During this 
time, the net member 16 removes dust larger in size than the mesh size of 
the net member. The exhaust gas introduced into the neutralizing tower 12 
passes through the perforated metals 22a, 22b, which are aligned with 
their holes formed alternately to one another, and the gas forms a 
turbulent flow and diffuses into the neutralizing tower 12 thoroughly. 
The exhaust gas comes into contact with the surface of the neutralizing 
agent 39 because of the gaps formed between adjacent pieces of the 
neutralizing agent 39, which make up 15-20% of the total volume occupied 
by the pellets 39. With respect to the reaction between the neutralizing 
agent 39 and the exhaust gas, for example, CaCl.sub.2 is generated after 
processing when HCl is contained in the exhaust gas, and CaSO.sub.3 is 
generated when SO.sub.2 is contained in the exhaust gas, after the exhaust 
gas has passed through the neutralizing agent 39. Therefore, only a 
substantially harmless exhaust gas is discharged to the outside through 
the second duct 18. The reacted components, as described above, are 
gradually deposited on the surface of the neutralizing agent 39. The pump 
is energized after the passage of a predetermined period of time. As a 
result, water passes through the water supply pipe 24, and is vigorously 
jetted through nozzles to the inside of the neutralizing tower 12. The 
reacted components on the surface of the neutralizing agent 39 are washed 
by the forcibly fed water, and gradually accumulate on the bottom plate 20 
having an inclination angle of about 5 degrees. The reacted components, 
having been washed and accumulated on the bottom plate 20, are of course 
also harmless, and are removed by opening the cleaning port 30. Additional 
exhaust gases are then fed through the first duct 14 to the neutralizing 
agent 39, which has a new reaction surface exposed thereon due to the 
spraying of washing water. 
When a gradual decrease in the neutralizing agent 39 is confirmed, for 
example, the lid member 37 including the explosion-proof valve 36 is 
opened, and new pieces of the neutralizing agent 39 may be introduced into 
the neutralizing tower 12. Overflow holes 34 are provided for discharging 
excess water when the water for washing the neutralizing agent supplied 
from the water supply pipe 24 exceeds the height of the overflow holes. 
Another embodiment of the present invention is shown in FIG. 4. As easily 
comprehended from FIG. 4, this embodiment comprises a second exhaust gas 
processing system 10a having the same construction as that of the exhaust 
gas processing system 10, connected in series with the exhaust gas 
processing system 10. Thus the same constituent elements as those of the 
exhaust gas processing system 10 are represented by adding "a" to the 
reference numerals in the exhaust gas processing system 10a, and detailed 
explanation thereof is omitted. 
When two exhaust gas processing systems 10 and 10a are connected in series, 
the second duct 18 of the exhaust gas processing system 10 constituting a 
first stage is connected to the first duct 14a of the exhaust gas 
processing system 10a constituting a second stage. In this arrangement, 
the net member 16a of the exhaust gas processing system 10a of the second 
stage may be of a finer mesh than the net member 16 of the exhaust gas 
processing system 10 of the first stage, and hence finer dust can be 
trapped by the net member 16a. On the other hand, if dust is sufficiently 
trapped by the net member 16 of the exhaust gas processing system 10 of 
the first stage, it is unnecessary to install any net member in the 
exhaust gas processing system 10a of the second stage. 
In the embodiment described above, the exhaust gas processing system 10a of 
the second stage neutralizes and processes exhaust gas discharged from the 
second duct 18 of the exhaust gas processing system 10 of the first stage, 
in the same manner as the exhaust gas processing system 10 of the first 
stage. 
Results of experiments run using the above-described systems are shown in 
Table 1. In these experiments, hydrogen chloride gas was supplied in first 
through fourth trials, and its recovery ratios were measured. In each 
experiment, gas could be recovered at an efficiency of 90% or more. 
TABLE 1 
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First Second Third Fourth 
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Inlet (HCl, mg/Nm.sup.3) 
4208 631 2879 6732 
Outlet (HCl, mg/Nm.sup.3) 
259 43 283 342 
Efficiency (%) 
93.8 93.2 90.2 94.9 
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According to the present invention, harmful components in exhaust gases can 
be sufficiently removed using a neutralizing agent in a dry state as 
described above. Further, the neutralizing agent can be thoroughly brought 
into contact with the exhaust gas because it is stacked sufficiently and 
randomly within the neutralizing tower. Thus, harmful components in 
exhaust gases can be effectively removed owing to chemical reactions with 
the neutralizing agent. 
Further, reacted components are removed from the surface of the 
neutralizing agent by washing water supplied from the water supply means, 
and a renewed reactive surface can be exposed. Consequently, the 
neutralizing agent can be used repeatedly. The present invention has an 
extremely simple construction, and is excellent in durability when 
compared with the prior art. Thus an effect is obtained in that it is 
extremely economic to implement and use.