Contaminated air purifying apparatus

A contaminated air purifying apparatus capable of decreasing particles such as dust floating in air, soot produced by a combustion engine and the like and air pollutants such as nitrogen oxides (NOx) contained in exhaust gas. Particulates such as dust, soot and the like are electrostatically negatively charged and collected in a purifying filter section by coulombic force. NOx is converted into N.sub.2 and CO.sub.2 by an action of carbon fiber or carbon particles, resulting in decreased in concentration. The carbon fiber and carbon particles are preferably modified into an increased surface area of 200 to 2000 m.sup.2 /g.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus for purifying contaminated air, and 
more particularly to a contaminated air purifying apparatus which is 
adapted to decrease particulates such as dust or the like floating or 
suspended in air, particulates such as soot or the like produced by a 
combustion engine, and air pollutants such as nitrogen oxides (NOx) 
contained in exhaust gas of a combustion engine or the like. 
Conventionally, filtration using various kinds of filters has been used for 
removing particulates such as dust or the like which is one of air 
pollutants. However, the filtration often fails to catch particulates of a 
microscopic size depending on a filter used and tends to cause a filter 
used to be clogged with particulates of a rather large size. 
In view of such a disadvantages, it is proposed that an electric dust 
collecting equipment is used in combination with or in place of a filter. 
A typical example of such an electric dust collecting equipment is 
generally constructed so as to utilize corona discharge due to application 
of a high voltage to particulates. More particularly, this is accomplished 
by electrostatically charging particulates by corona discharge due to 
application of a voltage as high as about 6 to 10 kV thereto and then 
catching the particulates by means of the electric dust collecting 
equipment having a voltage of about 3.3 to 6 kV. 
Unfortunately, the dust collecting equipment thus constructed causes 
various problems due to application of a high voltage to particulates, 
such as generation of large unpleasant sound, production of ozone harmful 
to the human body and the like. Also, the dust collecting equipment 
exhibits another disadvantage of being large-sized because it is required 
to use an insulating material in a largo amount. 
Further, materials which have been recently noticed as air pollutants 
include particulates such as soot contained in exhaust gas or the like and 
NOx. Removal of soot is carried out by collecting it by means of a ceramic 
filter or the like. Alternatively, it may be made by the above-described 
electric dust collecting techniques using corona discharge under a high 
voltage of 6 to 10 kV. However, both techniques fail to be put into 
practice because they cause a disadvantage of requiring additional 
equipment when they are applied to a small type combustion engine such as 
an automobile or the like. Also, they have another disadvantage of causing 
the equipment to be large-sized. 
A decrease in concentration of NOx in exhaust gas is significantly 
accomplished by an ammonia catalytic reduction method or the like when 
production of NOx is carried out by a fixed producing source as seen in 
factory flue gas or the like. However, there has not been yet developed a 
denitration equipment effective to remove NOx produced by a moving 
producing source such as an automobile or the like, particularly, a diesel 
engine. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the foregoing disadvantage 
of the prior art. 
Accordingly, it is an object of the present invention to provide a 
contaminated air purifying apparatus which is capable of significantly 
decreasing particulates such as dust or the like contained in air, 
particulates such as soot or the like contained in gas exhausted by a 
combustion engine and air pollutants such as NOx or the like. 
In accordance with the present invention, a contaminated air purifying 
apparatus is provided. The contaminated air purifying apparatus includes a 
contaminated air influx path, an electrifying mesh section containing a 
porous conductive material and connected to a negative electrode of a DC 
power supply, and a purifying filter section including a layer containing 
a conductive material and connected to a positive electrode of the DC 
power supply. The electrifying mesh section and purifying filter section 
are arranged in turn in a direction of flow of contaminated air in the 
contaminated air influx path. 
In a preferred embodiment of the present invention, the DC power supply may 
comprise a cell, wherein the contaminated air purifying apparatus may be 
used as a mask. 
In a preferred embodiment of the present invention, the contaminated air 
purifying apparatus may further include a high efficiency particulate 
absolute filter section arranged on a downstream side based on the 
purifying filter section in the contaminated air influx path. 
Also, in a preferred embodiment of the present invention, the contaminated 
air purifying apparatus may further include a denitration filter section 
arranged in the contaminated air influx path. The denitration filter 
section includes a layer containing one of carbon fiber and carbon 
particles. 
The contaminated air purifying apparatus of the present invention 
constructed as described above permits particulates such as dust in air, 
soot in exhaust gas and the like to be effectively removed, as well as a 
concentration of NOx in exhaust gas to be significantly reduced. 
In the contaminated air purifying apparatus of the present invention, 
particulates such as dust in air, soot in exhaust gas and the like are 
electrostatically negatively charged in the electrifying mesh section and 
then electrically adsorbed on the purifying filter section by coulombic 
force. A voltage applied to the particulates for this purpose is as low as 
12 to 500 V, resulting in production of unpleasant noise and ozone harmful 
to the human body being effectively prevented. 
Down-sizing of components of the contaminated air purifying apparatus and 
use of a cell or battery of a low voltage as the power supply permits the 
apparatus to be used as a mask for covering the nose, the mouth and the 
like. 
Also, incorporation of the high efficiency particulate absolute filter 
(hereinafter referred to as "HEPA filter") in the contaminated air 
purifying apparatus permits adsorption and removal of particulates of a 
rather larger size to be carried out in the purifying filter section and 
adsorption and removal of particulates of a small size to be carried out 
in the HEPA filter section. Such arrangement leads to an improvement in 
durability of the HEPA filter. 
Further, incorporation of the denitration filter section in the 
contaminated air purifying apparatus results in NOx, which mainly consists 
of NO, being converted into N.sub.2 and CO.sub.2, as well as a slight 
amount of CO according to the following expressions: 
##STR1## 
wherein C is derived from carbon fiber or carbon particles and (C--O) is 
an intermediate product and designates an active group. 
The contaminated air purifying apparatus of the present invention can be 
directed to a variety of applications. For example, it may be applied to 
ventilation in a dwelling house and an office building and ventilation in 
vehicles such as an automobile, a train, a ship, an airplane and the like; 
ventilation and sterilization in a hospital, a clean room, a bacteria 
culture room, various research facilities, food producing facilities, 
cosmetic producing facilities, medicine producing facilities, facilities 
for producing electronic equipments and the like; and ventilation of 
facilities in which electronic equipments such as computers, word 
processors and the like are installed and protection of the electronic 
equipments. Also, it may be applied to masks for prevention of pollinosis, 
house dust, a cold and the like; and working and medical masks for 
prevention of suction of dust such as soot, fly ash, asbestos, bacteria 
and the like. Further, it may be used as an exhaust gas purifying 
apparatus for a fixed combustion engine such as a boiler, a heating 
furnace or the like, as well as for a moving combustion engine such as an 
automobile, a ship, a train, an airplane or the like. In particular, it is 
conveniently used as an exhaust gas purifying apparatus for a diesel 
engine. 
BRIEF DESCRIPTION OF THE DRAWINGS

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, a contaminated air purifying apparatus according to the present 
invention will be described hereinafter with reference to the accompanying 
drawings. 
Referring first to FIGS. 1 to 5, an embodiment of a contaminated air 
purifying apparatus according to the present invention is illustrated, 
which is adapted to treat or purify contaminated air containing 
particulates such as dust or the like. 
A contaminated air purifying apparatus of the illustrated embodiment which 
is generally designated at reference numeral 1 includes an air flow pipe 3 
constituting a contaminated air influx path (hereinafter referred to as 
"air flow path" or "exhaust gas flow path"). The air flow pipe 3 is 
provided therein with an electrifying mesh section 10 and a purifying 
filter section 20, which are arranged in order from an air inlet or 
suction port 5 or in a direction in which contaminated air flows in the 
air flow pipe 3 as indicated at arrows in FIG. 1. In the illustrated 
embodiment, the air flow pipe 3 is an example of the air flow path. 
Therefore, in the present invention, the air flow path may be formed by an 
air flow pipe member provided with an air inlet port and an air outlet 
port and a closed vessel or container of desired configuration and volume 
such as a cylindrical container of an increased diameter. 
The electrifying mesh section 10 is arranged in the air flow pipe 3 through 
a support 14 in a manner to be fitted in an inner surface 12 of the air 
flow pipe 3 and perpendicular to a longitudinal direction of the air flow 
pipe 3 or a direction indicated at the arrows in FIG. 1. Also, the 
electrifying mesh section 10 is electrically connected through a conductor 
27 to a negative electrode of a DC power supply 16. The support 14 is 
preferably formed of an electrically insulating material so as to prevent 
a current from flowing from a positive electrode of the power supply to 
the negative electrode thereof through the air flow pipe 3 which 
constitutes a body of the contaminated air purifying apparatus 1. The DC 
power supply preferably generates a voltage of about 12 to 500 volts. 
A conductive material of which the electrifying mesh section 10 is made is 
not limited to any specific material so long as it is air-permeable. The 
electrifying mesh section 10 may be formed of any suitable material such 
as a net material of 40 to 500 meshes, a punched metal material of 40 to 
500 meshes, a woven fabric material of 40 to 500 meshes, a nonwoven fabric 
material. The materials therefor include, for example, carbon fiber felt, 
carbon fiber cloth, stainless steel wire net, stainless steel wire felt, 
synthetic fiber woven fabric to which powders of metal such as copper, 
titanium, nickel, iron or the like are applied by electroless plating or 
electroplating or by means of an adhesive material, and synthetic fiber 
nonwoven fabric having such metal powders as described above applied 
thereto by techniques as described above. Alternatively, formation of the 
metal powders on the woven or nonwoven fabric may be carried out by 
coating. Two or more such materials may be used in combination with each 
other. 
The carbon fiber felt or cloth may be made of carbon fiber conventionally 
known in the art without subjecting it to any treatment. Alternatively, 
the felt or cloth may be made of carbon fiber which has been subjected to 
a modification treatment or formed into a multi-cellular structure, 
resulting in a surface area thereof being increased to a level as high as 
about 200 to 2000 m.sup.2 /g. Such modified carbon fiber may be obtained 
by subjecting conventional carbon fiber to any suitable treatment. For 
example, it may be obtained by contacting conventional carbon fiber with 
water vapor of a temperature as high as about 1000.degree. C. for about 1 
to 2 hours. Alternatively, it may be prepared by contacting the carbon 
fiber with nitrogen monoxide gas at a temperature of about 100.degree. to 
500.degree. C. for about 7 to 12 hours. Also, it may be prepared by 
contacting the carbon fiber with a nitric acid solution of up to 63.1% in 
concentration at a temperature between a room temperature and 75.degree. 
C. for about 5 minutes to 2 hours. 
The purifying filter section 20 is arranged in the air flow pipe 3 through 
a support 22 in a manner to be fitted in the inner surface 12 of the air 
flow pipe 3 and perpendicular or parallel to the longitudinal direction of 
the air flow pipe 3 (FIGS. 4 and 5). The purifying filter section 20 is 
electrically connected to a positive electrode of the DC power supply 16 
through the conductor 27. A conductive material for the purifying filter 
section 20 and a material for the support 22 may be the same as those for 
the electrifying mesh section 10 and support 14 described above. 
The purifying filter section 20 may include a layer containing carbon fiber 
or carbon particles or a layer containing felt or cloth made of carbon 
fiber or carbon particles. Alternatively, it may include a layer 
containing an electrically conductive material other than carbon fiber and 
carbon particles described above. The carbon fiber or the felt or cloth 
made of carbon fiber used for this purpose may be the modified carbon or 
the felt or cloth made of the modified carbon fiber described above with 
respect to the electrifying mesh section 10. The carbon particles may be 
modified in substantially the manner as the above-described modification 
of the carbon fiber. 
The purifying filter section 20 may be constructed into any desired 
structure depending on the electrically conductive material used therefor. 
For example, as shown in FIG. 2, it may be constructed into a structure 
wherein felt 32 made of carbon fiber is interposedly arranged between 
woven or nonwoven fabrics 30 made of synthetic fiber having copper powders 
applied thereto by electroless plating or electroplating. The woven or 
nonwoven fabric 30 may be replaced with stainless steel wire net and the 
felt 30 may be replaced with stainless steel wire net or stainless steel 
wire felt. Also, as shown in FIG. 3, it may be formed by arranging a 
plurality of such electrically conductive materials as described above in 
a manner to be spaced from each other at intervals of 2 to 5 mm. Further, 
as shown in FIG. 4, it may be formed by arranging a plurality of the 
electrically conductive materials so as to be spaced from each other at 
intervals of 2 to 5 mm and in parallel with each other. Alternatively, as 
shown in FIG. 5, it may be constructed by forming the carbon fiber felt 
materials or stainless steel wire felt materials with a plurality of 
through-holes of any desired configuration. Formation of such 
through-holes is carried out for the purpose of reducing a pressure loss. 
The through-holes each are preferably formed into a shape extending in a 
corrugated manner in a longitudinal direction of the purifying filter 
section 20, because such a shape permits the electrically conductive 
material to be significantly increased in area contacted with air to be 
treated. 
The contaminated air purifying apparatus 1 may include a filter made of, 
for example, wire net and functioning to filter dust of a rather large 
size such as lint or the like, which may be arranged on an upstream side 
in the air flow path based on the electrifying mesh section 10. Also, an 
air blower for forcibly feed air to the contaminated air purifying 
apparatus 1 or the like may be provided at any desired position. 
Further, the contaminated air purifying apparatus of the illustrated 
embodiment may include a plurality of sets of electrifying mesh section 
and purifying filter section combination combinations each comprising the 
electrifying mesh section and purifying filter section. 
Now, the manner of operation of the contaminated air purifying apparatus of 
the illustrated embodiment constructed as described above will be 
described hereinafter with reference to FIGS. 1, 6 and 7. 
Contaminated air introduced through the air inlet or suction port 5 into 
the air flow pipe 3 of the contaminated air purifying apparatus 1 is 
guided to the electrifying mesh section 10, wherein dust 70 which is kept 
electrically neutral is electrostatically negatively charged. Then, the 
air is guided to the purifying filter section 20, resulting in the 
negatively charged dust being electrostatically adsorbed on the purifying 
filter section 20 by coulomb force and kept adsorbed thereon. Now, the 
adsorption will be described in connection with the purifying filter 
section 20 made of a composite material prepared by interposedly arranging 
carbon fiber felt between woven or nonwoven fabric layers made of 
synthetic fiber having copper powders applied thereto by electroless 
plating or electroplating, as shown in FIG. 2. First, dust 71 of a 
relatively large size is adsorbed as shown in FIG. 6 and dust 72 of a 
relatively small size is adsorbed on copper powders 74. Dust 72 which 
passed therethrough is adsorbed on a surface of carbon fiber felt 76 as 
shown in FIG. 7. The air passing through the carbon fiber felt 76 is 
subject to such an adsorption treatment as shown in FIG. 6 again. The air 
thus purified is outwardly discharged through an air outlet or discharge 
port 7 to an exterior of the contaminated air purifying apparatus 1. 
The purifying filter section 20 is turned off and then external vibration 
is applied thereto, so that dust adsorbed on the purifying filter section 
20 may be removed therefrom. Thus, the purifying filter section 20 and 
therefore the contaminated air purifying apparatus 1 may be operated over 
a long period of time. Alternatively, the purifying filter section 20 may 
be detached from the contaminated air purifying apparatus 1 for cleaning. 
Use of carbon fiber or the like subjected to a modifying treatment permits 
the contaminated air purifying apparatus to effectively exhibit a 
deodorizing function in addition to a dust collecting function. 
TEST EXAMPLE 1 
A dust collecting test was carried out using a contaminated air purifying 
apparatus constructed in such a manner as shown in FIG. 1. The results 
were as shown in FIG. 8. 
Test Procedure 
Cigarette smoke was continuously blown upon an air inlet port from the 
human mouth, and the number of particulates (particle diameter: 0.3 to 10 
.mu.m) at the air inlet port of the contaminated air purifying apparatus 
and that at an air outlet port thereof were measured. The measurement was 
carried out by means of a particle counter having a read function by 
laser. A degree of dust collection was obtained according to the following 
expression: 
EQU Degree of Dust Collection (%)=(A-B)/A.times.100 
wherein A is the number of particulates at the air inlet port and B is the 
number of particulates at the air outlet port. 
Test Conditions 
Electrifying mesh section: Six pieces of stainless steel wire net (200 
meshes, 380 mm.times.125 mm) were used for an electrifying mesh section. 
Purifying filter section: A purifying filter section was constructed by 
interposing carbon fiber felt (length of fiber: 14 .mu.m, thickness of 
felt: 20, 90 and 140 mm) between two pieces of non-woven fabric having 
copper powders applied thereto by electroless plating in a manner as shown 
in FIG. 2. Thus, three kinds of purifying filter sections different in 
thickness of carbon fiber felt were prepared. 
Voltage applied: 50 V 
Flow rate of air introduced: 3 m.sup.3 /min 
TEST EXAMPLE 2 
FIG. 9 shows the results of FIG. 8 which are represented by a degree of 
dust collection obtained depending on a voltage and a diameter of 
particulates. The results shown in FIG. 9 relate to only the carbon fiber 
felt of 140 mm in thickness. 
TEST EXAMPLE 3 
A dust collecting test was carried out using a contaminated air purifying 
apparatus constructed in such a manner as shown in FIG. 1. Results of the 
test were as shown in FIG. 10. 
Test Procedure 
The number of particulates produced by burning five incense sticks in a 
closed space of 1.94 m.sup.3 in volume were measured by means of the 
above-described particle counter. Then, the contaminated air purifying 
apparatus of the present invention was operated in the same closed space, 
resulting in the number of particulates remaining in the space being 
measured at every predetermined time interval to obtain a degree of dust 
collection in connection with particulates of 0.3 and 0.5 .mu.m in 
particle diameter according to the following expression: 
EQU Degree of Dust Collection (%)=(C-D)/C.times.100 
wherein C is the number of particulates prior to the operation and D is 
that after the operation. For comparison, the test was repeated on the 
prior art. The results were as shown in FIG. 10. 
Test Conditions 
(Present Invention) 
Electrifying mesh section: Seven pieces of nonwoven fabric each having 
copper powders applied thereto by electroless plating were used for an 
electrifying mesh section. 
Purifying filter section: A purifying filter section was used which is 
constructed by interposing carbon fiber felt (thickness: 10 mm) between 
two pieces of nonwoven fabric each having copper powders applied thereto 
by electroless plating (see FIG. 2). 
Voltage applied: 200 V 
(Prior Art) 
Electrifying section: Electrodes for corona discharge under 6.6 kV were 
used for an electrifying section. 
Dust collecting section: Two sets of 3.5 kV electrodes each comprising 37 
electrode plates were used for a dust collecting section. 
Referring now to FIGS. 11 and 12, a second embodiment of a contaminated air 
purifying apparatus according to the present invention is illustrated, 
wherein contaminated air to be treated contains particulates such as dust 
and the like. A contaminated air purifying apparatus of the second 
embodiment is adapted to be used as a mask and includes an electrifying 
mesh section and a purifying filter section which are constructed in 
substantially the same manner as those in the first embodiment. 
A mask 101 in which the present invention is embodied includes an outer 
mesh section 102, an electrifying mesh section 104, a purifying filter 
section 106 and an inner mesh section 103 which are arranged in turn in a 
direction of flow of contaminated air indicated at arrows in FIG. 11. The 
mask 101 also includes an insulation section 105 arranged between the 
electrifying mesh section 104 and the purifying filter section 106. 
The outer mesh section 102 functions to catch dust of a large diameter. The 
outer mesh section 102 may be made of any suitable material such as open 
weave fabric such as gauze, woven fabric of synthetic fiber, wire net or 
the like. The inner mesh section 103 may be formed of any suitable 
material so long as it exhibits air-permeability. However, in the 
illustrated embodiment, the inner mesh section 103 is contacted with the 
skin, therefore, it is preferably made of a material harmless to the human 
body such as gauze, woven fabric of synthetic fiber or the like. 
The electrifying mesh section 104 is arranged so as to be perpendicular to 
the direction of flow of the contaminated air described above and 
electrically connected through a conductor 108 to a negative electrode of 
a power supply 109. The power supply 109 may comprise a plurality of 
small-sized and light-weight cells of a low voltage connected together as 
required. A voltage of the power supply 109 is preferably within a range 
between about 1.5 V and about 15 V. 
The purifying filter section 106 is arranged in a manner to be 
perpendicular to the direction of flow of the air and electrically 
connected through the conductor 108 to a positive electrode of the power 
supply 109. The purifying filter section 106 may be formed by filling 
powdered activated charcoal prepared from wood waste, coal, coconut shell 
or the like in a bag of synthetic resin. Carbon fiber may be substituted 
for the powdered activated charcoal. The powdered activated charcoal used 
preferably has a particle diameter of 1 mm or less because it effectively 
prevents a thickness of the mask 101 from being excessively or 
significantly increased. 
Also, the mask 101 may include a plurality of sets of electrifying mesh 
section and purifying filter section combinations, wherein each 
combination comprises the electrifying mesh section 104 and purifying 
filter section 106. 
Now, the manner of operation of the mask constructed as described above 
will be described hereinafter with reference to FIG. 11. 
Dust of a rather large size contained in contaminated air is caught by the 
outer mesh section 102. Dust 110 in the air which passes through the outer 
mesh section 102 without being caught by the section 102 is 
electrostatically negatively charged in the electrifying mesh section 104. 
Then, the dust 110 is adsorbed on the purifying filter section 106. This 
results in the air being purified, which then passes through the inner 
mesh section 103, to thereby be used for breathing. 
TEST EXAMPLE 4 
Two cylindrical vessels 130 of which a bottom is closed were prepared as 
shown in FIGS. 12A and 12B and charged with yellow chalk powders (particle 
diameter: 2 to 10 .mu.m) 131 of the same quantity. Then, an open end or 
opening of one of the vessels was covered with a mask 101 of the present 
invention as shown in FIG. 12A and the other vessel was covered with a 
commercially available mask 120 as shown in FIG. 12B. Then, the masks each 
were subject to suction by a vacuum cleaner and then subject to visual and 
microscopic observation. In the mask 101 of the present invention, an 
electrifying mesh section and a purifying filter section each were made of 
a single piece of nylon nonwoven fabric (thickness: 0.3 mm) having copper 
powders applied thereto by electroless plating, an outer mesh section 102 
and an inner mesh section 103 each were made of a single piece of gauze, 
and a power supply (3 V) comprised two cells connected together. The 
commercially available mask 120 comprised two gauze layers 120a and 120b 
laminated on each other. 
In the commercially available mask 120, the upper gauze layer 120b was 
rendered yellow one minute after start of the test. On the contrary, in 
the mask 101 of the present invention, any change was not observed in the 
inner mesh section 103. Also, enlarged observation of the purifying filter 
section 106 of the mask 101 through a microscope of 30 magnifications 
indicated that chalk powders adhered to the nylon fiber and copper 
powders. 
Referring now to FIG. 13, a third embodiment of a contaminated air 
purifying apparatus according to the present invention is illustrated, 
which is adapted to treat or purify contaminated air containing 
particulates such as dust or the like. In the third embodiment, an 
electrifying mesh section and a purifying filter section may be 
constructed in substantially the same manner as those in the first 
embodiment described above. 
A contaminated air purifying apparatus of the third embodiment which is 
generally designated at reference numeral 201 in FIG. 13 includes an air 
flow pipe 203 constituting an air flow path, in which an electrifying mesh 
section 210, a dust collecting filter 220 and an HEPA filter 230 are 
arranged in order from an air inlet or suction port 205 or in a direction 
of flow of contaminated air indicated at arrows in FIG. 13. Reference 
numeral 235 designates a filter made of wire net or the like, which may be 
provided as required. 236 is a fan such as an axial blower, a cirrocco fan 
or the like. In the illustrated embodiment, the air flow pipe 203 is an 
example of a means for forming the air flow path. Therefore, in the 
illustrated embodiment, the air flow path may be formed of an air flow 
pipe of a reduced diameter provided with an air inlet port and an air 
outlet port and a closed container or vessel of desired configuration and 
volume such as a cylindrical vessel of an increased diameter or the like 
connected to the air flow pipe. 
The electrifying mesh section 210 is arranged in the air flow pipe 203 in a 
manner to be fitted in an inner surface 212 of the air flow pipe 210 
through an insulating support 214 and perpendicular to a longitudinal 
direction of the air flow pipe 203 or in the direction of flow of the air 
in the air flow pipe 203. Also, the electrifying mesh section 210 is 
electrically connected through a conductor 227 to a negative electrode of 
a DC power supply 216. The DC power supply 216 preferably generates a 
voltage of about 12 to 500 volts. 
The dust collecting filter section 220 is positioned on a downstream side 
in the direction of flow of the air based on the electrifying mesh section 
210 and arranged on the inner surface 212 of the air flow pipe 203 through 
an insulating support 222 in a manner to be perpendicular to the 
longitudinal direction of the air flow pipe 203. Also, the dust collecting 
filter 220 is electrically connected to a positive electrode of the DC 
power supply 216 through the conductor 227. 
The HEPA filter section 230 is positioned on a downstream side in the 
direction of flow of contaminated air based on the dust collecting filter 
section 220 and arranged on an inner surface 212 of the air flow pipe 203 
through a seal member (not shown) in a manner to be perpendicular to the 
longitudinal direction of the air flow pipe 203. 
The contaminated air purifying apparatus of the illustrated embodiment may 
include a plurality of sets of electrifying mesh section and dust 
collecting filter section combinations each comprising the electrifying 
mesh section 210 and dust collecting filter section 220. In this instance, 
one or more such HEPA filter sections 230 may be suitably arranged. 
Now, the manner of operation of the contaminated air purifying apparatus 
230 of the illustrated embodiment will be described hereinafter with 
reference to FIG. 13. 
Contaminated air introduced through the air suction port 205 into the air 
flow pipe 203 by an action of the fan 236 is guided to the filter 235, 
wherein dust of a large size such as lint or the like is removed from the 
air. Then, the air is guided to the electrifying mesh section 210, wherein 
dust 270 which is kept electrically neutral is electrostatically 
negatively charged. Subsequently, the air is fed to the dust collecting 
filter section 220, so that the dust 270 is adsorbed on the filter section 
220 by coulombic force and held thereon. Thus, the air passing through the 
dust collecting filter section 220 is further guided to the HEPA filter 
section 230, resulting in being filtered and outwardly discharged through 
the fan 236. 
TEST EXAMPLE 5 
A dust collecting test was carried out using a contaminated air purifying 
apparatus 210 constructed according to the third embodiment described 
above. The test took place according to the following procedure and under 
the following conditions. For comparison, a test was carried out using a 
dust collecting unit comprising only an HEPA filter. Results were as shown 
in Table 1. 
Test Procedure 
The number of particulates produced by fully burning three incense sticks 
which are were placed in an air flow pipe in proximity to an air suction 
port was measured by means of a particle counter having a read function by 
laser, to thereby obtain a degree of dust collection for every particle 
diameter. The degree of dust collection was calculated according to the 
following expression: 
EQU Degree of Dust Collection (%)=(A-B)/A.times.100 
wherein A is the number of particulates at the air suction port and B is 
the number of particulates at the air suction port. 
Test Conditions 
Electrifying mesh section: A piece of nonwoven fabric (300 mm.times.300 mm) 
was used for an electrifying mesh section. 
Dust collecting filter section: A dust collecting filter section was 
constructed by interposing a carbon fiber felt layer of 10 mm in thickness 
between two pieces of non-woven fabric (300 mm.times.300 mm) having copper 
applied thereto by plating. 
Voltage applied: 200 V 
TABLE 1 
______________________________________ 
Degree of 
Pressure Loss 
Dust Collection (%) 
(mmAg) 0.3 .mu.m 
0.5 .mu.m 
1.0 .mu.m 
______________________________________ 
Third Embodiment 
18.35 88 93 100 
Comparison Example 
18.3 78 82 96 
______________________________________ 
Referring now to FIGS. 14 to 16, a fourth embodiment of a contaminated air 
purifying apparatus according to the present invention is illustrated, 
which is adapted to treat or purify exhaust gas of a combustion engine. 
Thus, a contaminated air purifying apparatus of the fourth embodiment is 
in the form of an exhaust gas purifying apparatus. In the fourth 
embodiment, an electrifying mesh section and a purifying filter section 
may be constructed in substantially the same manner as those in the first 
embodiment described above. 
The contaminated air purifying apparatus of the illustrated embodiment 
which is generally designated at reference numeral 301 includes an air 
flow pipe 303 forming an exhaust gas flow path and acting as an exhaust 
gas flow pipe. The exhaust gas flow pipe 303 is provided therein with an 
electrifying mesh section 310, a purifying filter section 320 and a 
denitration filter section 330, which are arranged in turn on a downstream 
side in the exhaust gas flow pipe 303 based on a combustion engine or in a 
direction of flow of exhaust gas. In the illustrated embodiment, the 
exhaust gas flow pipe 303 is an example of a means for forming the exhaust 
gas flow path. Therefore, in the illustrated embodiment, the exhaust gas 
flow path may be formed of an exhaust gas flow pipe of a reduced diameter 
provided with an exhaust gas inlet or suction port and an exhaust gas 
outlet or discharge port and a closed vessel of desired configuration and 
volume such as a cylindrical vessel of an increased diameter or the like 
connected to the exhaust gas flow pipe. 
The electrifying mesh section 310 is fittedly arranged in an inner surface 
of the exhaust gas flow pipe 303 through an insulating support 314 in a 
manner to be perpendicular to a longitudinal direction of the exhaust gas 
flow pipe 303 or in the direction of flow of exhaust gas as in the 
above-described embodiments. Also, the electrifying mesh section 310 is 
electrically connected through a conductor 327 to a negative electrode of 
a DC power supply 316. A voltage produced by the DC power supply 316 is 
preferably about 12 to 500 volts. 
The dust collecting filter section 320 is positioned on a downstream side 
in the direction of flow of exhaust gas based on the electrifying mesh 
section 310 and fittedly arranged in the inner surface of the exhaust gas 
flow pipe 303 through an insulating support 322 so as to be perpendicular 
to the longitudinal direction of the exhaust gas flow pipe 303 in which 
the exhaust gas flow path is defined. Also, the dust collecting filter 
section 320 is electrically connected through a conductor 327 to a 
positive electrode of the DC power supply 316. 
The denitration filter section 330 includes a pair of covering elements 332 
made of a porous conductive material and a carbon layer 334 made of carbon 
fiber or carbon particles and interposedly arranged between the covering 
elements 332. The denitration filter section 330 may be arranged in 
proximity to a combustion engine as compared with the electrifying mesh 
section 310 or on an upstream side in the direction of flow of the exhaust 
gas based on the combustion engine. 
The porous conductive material of which the covering elements 332 are made 
includes a wire net material, a punched metal material and the like, It is 
preferable that such wire net and punched metal each may be formed into 
about 40 to 500 meshes because of permitting carbon fiber and carbon 
particles to be satisfactorily supported thereon. 
Any suitable carbon fiber or carbon particles widely known in the art may 
be used for the carbon layer 334. However, such modified carbon fiber or 
carbon particles of an increased surface area as described above are 
preferably used for this purpose. Also, the carbon fiber preferably has a 
fiber length of 0.5 to 15 .mu.m. The carbon fiber may be used in the form 
of its original shape. Alternatively, it may be used in the form of woven 
felt, mat or cloth. The carbon particles preferably have a substantially 
spherical shape of which a diameter is between 0.01 mm and 2 mm. 
Now, the manner of operation of the exhaust gas purifying apparatus 301 
will be described hereinafter with reference to FIG. 14. 
Particulates such as soot and the like contained in exhaust gas fed from 
the combustion engine are electrostatically negatively charged in the 
electrifying mesh section 310 and then absorbed on the purifying filter 
section 320. The exhaust gas from which the particulates are thus removed 
is then contacted with the carbon layer 334 in the denitration filter 
section 330 while still containing nitrogen oxides (NOx) mainly consisting 
of NO. In the denitration filter section 330, NO is reacted with carbon 
atoms to form an intermediate product (C-O), which is adsorbed on the 
carbon layer 334 made of carbon fiber or carbon particles. This causes N 
to be converted into N.sub.2 and the above-described intermediate product 
adsorbed to be converted into CO.sub.2 and a slight amount of CO due to a 
high temperature atmosphere. Thus, the exhaust gas passing through the 
denitration filter section 330 is free of particulates and mainly contains 
N.sub.2, CO.sub.2 and CO in place of the nitrogen oxides as can be seen 
form the above-described reactions. 
Referring now to FIG. 15, a modification of the exhaust gas purifying 
apparatus of the fourth embodiment is illustrated. An exhaust gas 
purifying apparatus of the modification which is generally designated at 
reference numeral 401 includes an exhaust gas inlet pipe 402, an exhaust 
gas outlet pipe 403, and an expansion chamber 405 arranged between the 
exhaust gas inlet pipe 402 and the exhaust gas outlet pipe 403 so as to 
communicate with both. An electrifying mesh section 406 is arranged in the 
exhaust gas inlet pipe 402 through an insulating support (not shown). 
Also, the electrifying mesh section 406 is electrically connected to a 
negative electrode of a DC power supply (not shown). The exhaust gas 
purifying apparatus of the modification also includes a purifying filter 
section 407 carrying thereon or containing carbon fiber or carbon 
particles and acting also as a denitration filter section. The purifying 
filter section 407 is arranged in the expansion chamber 405 through an 
insulating support 410. The purifying filter section 407 is electrically 
connected to a positive electrode of the DC power supply. The exhaust gas 
purifying apparatus 401 further includes a soot reservoir 408 arranged 
below the expansion chamber 405, which soot reservoir is provided on a 
bottom surface thereof with a heater 409 connected to an external power 
supply. 
Now, the manner of operation of the exhaust gas purifying apparatus 401 of 
the modification will be described hereinafter with reference to FIG. 15. 
Particulates in exhaust gas fed into the exhaust gas inlet pipe 402 are 
electrostatically negatively charged by the electrifying mesh section 406 
and then adsorbed on the purifying filter section 407. The purifying 
filter section 407 contains carbon fiber or carbon particles, resulting in 
also serving as the denitration filter section as described above. 
Therefore, the purifying filter section 407 carries out adsorption of the 
particulates thereon, as well as denitration. The exhaust gas thus 
purified is discharged through the exhaust gas outlet pipe 403. The 
particulates adsorbed on the purifying filter section 407 by repeating the 
above-described operation, when the power supply is turned off and 
external vibration is applied to the purifying filter section 407, is 
caused to drop into the soot reservoir 408, resulting in being collected 
therein. The particulates thus collected are heated by the heater 409, 
resulting in being burned to form CO.sub.2, which is then discharged 
through the exhaust gas outlet pipe 403. 
Referring now to FIG. 16, another modification of the exhaust gas purifying 
apparatus shown in FIG. 14 is illustrated. An exhaust gas purifying 
apparatus of the modification generally designated at reference numeral 
501 likewise includes an expansion chamber 505 arranged between an exhaust 
gas inlet pipe 502 and an exhaust gas outlet pipe 503. An electrifying 
mesh section 506 is made of stainless steel wire net and arranged in the 
exhaust gas inlet pipe 502 through an insulating support. Also, the 
electrifying mesh section 506 is electrically connected to a negative 
electrode of a DC power supply. 
A purifying filter section 508 is made of stainless steel wire net and is 
arranged in the expansion chamber 505 through an insulating support 509. A 
denitration filter section 511 which acts also as a purifying filter 
section is arranged in an inner space of the expansion chamber 505 in a 
manner to be fitted in an inner surface of the expansion chamber 505. The 
denitration filter section 511 is electrically connected to a positive 
electrode of the DC power supply, resulting in serving also as the 
purifying filter section as described above. Open ends of the exhaust gas 
inlet pipe 502 and exhaust gas outlet pipe 503 through which both pipes 
502 and 503 are permitted to communicate with the expansion chamber 505 
are positioned in spaces separated from each other through one of filters 
of the purifying filter section 508. 
Now, the manner of operation of the exhaust gas purifying apparatus 501 
will be described hereinafter with reference to FIG. 16. 
Particulates such as soot and the like contained in exhaust gas fed from a 
combustion engine to the exhaust gas inlet pipe 502 are electrostatically 
negatively charged by the electrifying mesh section 506 as in the 
contaminated air purifying apparatus 1 of the first embodiment. Then, the 
particulates are adsorbed on the purifying filter section 508, The 
above-described open ends of the exhaust gas inlet pipe 502 and exhaust 
gas outlet pipe 503 are positioned in the inner spaces of the expansion 
chamber 505 in a manner to be separated from each other as described 
above, respectively, so that the exhaust gas introduced through the 
exhaust gas inlet pipe 502 into the expansion chamber 505 may be contacted 
with the purifying filter section 508. Also, the denitration filter 
section 511 is electrically connected to the power supply, so that 
particulates contained in the exhaust gas are likewise adsorbed thereon. 
The exhaust gas from which the particulates are thus removed is then 
contacted with carbon fiber or carbon particles contained in the 
denitration filter section 511 while still containing nitrogen oxides 
mainly consisting of NO, resulting in the nitrogen oxides being converted 
into N.sub.2, CO.sub.2 and CO through a series of reactions as described 
above. Thus, the exhaust gas is purified and then outwardly discharged 
through the exhaust gas outlet pipe 503. 
Now, examples of combinations of components of the exhaust gas purifying 
apparatus described above will be described with reference to FIGS. 17 to 
20. 
In each of FIGS. 17 to 20, reference character "D.E." designates a diesel 
engine, "Comb. 1" is a combination of the electrifying mesh section and 
purifying filter section (containing a non-denitration material), and 
"Comb. 2" is a combination of the electrifying mesh section and purifying 
filter section (containing the denitration material or the carbon fiber or 
carbon particles). Thus, it will be noted that the purification filter 
section in Comb. 2 acts also as the denitration filter section. "D.N.F." 
designates denitration filter section which is not connected to the power 
supply. Each solid line between the components indicates the exhaust gas 
flow path and a degree of length of the solid line indicates a positional 
relationship between the components. Also, the components may be arranged 
together in the same closed space (closed vessel or container). 
Alternatively, they may be arranged separate from each other in two or 
more closed spaces (closed vessels or containers). 
The exhaust gas flow path for exhaust gas of the combustion engine is 
varied in temperature depending on a position thereof. More particularly, 
a portion of the exhaust gas flow path in proximity to the combustion 
engine is increased in temperature and gradually decreased in temperature 
with an increase in distance from the combustion engine. Also, materials 
to be used each have a temperature suitable therefor. For example, carbon 
fiber and carbon particles generally exhibit a satisfactory function at a 
temperature of about 550.degree. C. or below. Therefore, the components 
Comb. 2 and D.N.F. containing the carbon fiber or carbon particles each 
are preferably arranged so as to interpose the component Comb. 1 between 
the component and the diesel engine D.E. as shown in FIGS. 17, 18 and 20. 
Alternatively, they may be preferably arranged so as to be spaced at a 
predetermined interval or more from the diesel engine D.E. as shown in 
FIG. 19. Also, it is often required to arrange the components Comb. 2 and 
D.N.F. in proximity to a combustion site from a structural viewpoint of 
the combustion engine or treat exhaust gas of an excessively increased 
temperature. In this instance, a cooling fin for cooling the exhaust gas 
may be provided at any desired position in the exhaust gas flow path. Such 
arrangement of the cooling fin permits the components Comb. 2 and D.N.F. 
to be located in close proximity to the combustion engine. Also, this 
permits the exhaust gas purifying apparatus to be applied to a combustion 
engine which discharges exhaust gas of a higher temperature. 
Referring now to FIG. 21, the exhaust gas purifying apparatus of the 
present invention which is incorporated in an exhaust gas circulating path 
of a diesel engine D.E. is illustrated. In the example shown in FIG. 21, 
an exhaust gas purifying apparatus a is arranged in an exhaust gas 
discharge path between the diesel engine D.E. and an exhaust gas discharge 
port. An exhaust gas recirculating path is connected at one end thereof 
between the exhaust gas purifying apparatus a and the exhaust gas 
discharge port and at the other end thereof to an air inlet or suction 
path. The exhaust gas recirculating path is provided with an exhaust gas 
purifying apparatus b, a cooler and a fan. 
Exhaust gas discharged from the diesel engine D.E. is purified by the 
exhaust gas purifying apparatus a in such a manner as described above. 
Then, the exhaust gas purified is discharged at a part thereof through the 
exhaust gas discharge port and the remaining of the exhaust gas is fed to 
the exhaust gas recirculating path. The exhaust gas fed to the exhaust gas 
recirculating path is first fed to the exhaust gas purifying apparatus b 
by the fan. The exhaust gas purifying apparatus b functions to purify the 
exhaust gas and decrease a temperature of the exhaust gas due to 
contacting of the exhaust gas with the apparatus b. Then, the exhaust gas 
purified is further cooled by the cooler. Thus, the exhaust gas is 
purified twice, to thereby substantially reduce pollution of the cooler, 
so that the cooler may fully exhibit cooling performance. The air cooled 
is delivered to the air inlet path and then fed to the diesel engine D.E. 
together with air introduced into the air inlet path. 
The exhaust gas recirculating path constructed as described above permits 
exhaust gas recirculated to be decreased in temperature, resulting in a 
temperature difference between the introduced air and the exhaust gas of 
the diesel engine D.E. being substantially reduced to a level as small as 
about 28.degree. C. as compared with a temperature difference of about 
175.degree. C. in the prior art. Thus, recirculation of the exhaust gas 
permits fuel consumption to be improved or production of CO to be reduced, 
so that an output of the diesel engine D.E. may be increased. Further, 
incorporation of the exhaust gas purifying apparatus in the diesel engine 
significantly reduces an NOx concentration at an entrance to the engine as 
compared with that free of the apparatus, to thereby lower a combustion 
temperature, leading to a decrease in production of NOx. 
TEST EXAMPLE 6 
An exhaust gas purifying test was carried out using an exhaust gas 
purifying apparatus constructed in a such manner as shown in FIG. 14. Test 
conditions described hereinafter were employed. Measurement of a 
concentration of particulates took place by means of Bosch smoke 
densitometer according to JIS D8004. A degree of collection of 
particulates or a degree of dust collection was calculated according to 
the following expression: 
EQU Degree of Dust Collection (%)=(E-F)/E.times.100 
wherein E is an initial concentration of particulates and F is a 
concentration of particulates after treatment. 
The results were as shown in FIG. 22. 
Test Conditions 
Electrifying filter: Two pieces of stainless steel wire net (60 meshes) 
were used for an electrifying filter. 
Purifying Filter: Twelve pieces of nylon nonwoven fabric (300 mm.times.300 
mm) each having copper powders applied thereto by electroplating and 
twelve pieces of stainless steel wire net (200 meshes, 300 mm.times.300 
mm) were used for a purifying filter. The purifying filter was detached 
every twelve hours to remove material adhered thereto, followed by being 
reused. 
Voltage applied: DC 24 V 
Engine used: 500 ml diesel engine 
Displacement: 1.2 m.sup.3 /min 
TEST EXAMPLE 7 
An exhaust gas purifying test was carried out using an exhaust gas 
purifying apparatus constructed in such a manner as shown in FIG. 16. Test 
conditions described hereinafter were employed. Measurement of 
particulates and calculation of a degree of dust collection were carried 
out as described above. A degree of denitration was obtained according to 
the following expression: 
EQU Degree of Denitration (%)=(G-H)/G.times.100 
wherein G is an initial concentration of NOx and H is a concentration of 
NOx after treatment. 
Test Conditions 
Electrifying filter: Two pieces of stainless steel wire net (60 meshes) 
were used for an electrifying filter. 
Purifying filter: Three pieces of stainless steel wire net (60 meshes, 300 
mm.times.300 mm) were used for a purifying filter. The purifying filter 
was detached every six hours to remove materials adhered thereto, followed 
by being reused. 
Denitration filter: A denitration filter containing a mixture (101 g, 
thickness: 10 mm) of carbon fiber and carbon particles was arranged at 
three places. The carbon fiber and carbon particles were treated with a 
nitric acid solution (63.1%) for two hours. The surface area was 500 
m.sup.2 /g. 
Voltage applied: DC 100 V, 24 V, 12 V, 0 V (comparison) 
Engine used: 199 ml diesel engine 
Displacement: 0.47 m.sup.3 /min 
While preferred embodiments of the invention have been described with a 
certain degree of particularity with reference to the drawings, obvious 
modifications and variations are possible in light of the above teachings. 
It is therefore to be understood that within the scope of the appended 
claims, the invention may be practiced otherwise than as specifically 
described.