Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method and apparatus
for removing impurity particles on the order of one micron from
a gas stream, wherein a liquid mist pattern is established in
the gas normal to the direction of flow thereof, whereby the
particles are moisturized for removal from the gas.
In various production processes -- such as in the steel,
cement and other industries -- gases, smoke or fumes are produced
which contain impurity particles of relatively small size (speci-
- fically, particles less than one micron). Consequently, before
10 using the gases or fumes (in heaters or motors) or before expel-
ling the smoke to atmosphere, it is necessary to purify the gases
by removing the impurity particles therefrom.
Various gas purifying techniques have been proposed in
the prior art, as for example, by moisturizing the gas, mechanic-
al collision of the particles, condensation, diffusion in atom-
, ized liquid electrostatic separation, and ultrasonic treatment ~
< of the gases. ~ -
~,
' The impact processes employ mechanical collision be-
tween the liquid and impurity particles. It has been established
20 that the efficiency of particle removal increases with the dif-
ference in the relative speeds of the liquid drops and the parti-
cles. But when the particles are very fine (for example, less -`~
than 1 ,u), the efficiency drops down to zero because the parti- -
cles behave like an aerosol.
Condensation methods operate by lowering the temper-
ature of the gas below its dew point. This mechanism is good for
subsequent impact purification but it must be possible to bring
about a strong temperature drop which can be obtained only with 1-
low-temperature gas and by a strong pneumatic expansion of that
gas.
In electrostatic field separation processes, the ion-
ized particles are attracted by an electrode with an opposite
, polarity. In order to get good purification, it is necessary to
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obtain relatively constant dust contents at the input of the
electrofilters. Moreover, the cost of maintaining electrofil-
ters is very high when it comes to purifying corrosive gases
(for example, carbon dioxide or sulfur dioxide).
Ultrasonic procedures operate by applying resonance to
the dust and the liquid droplets. ~owever, this method also re-
quires a relatively heavy energy consumption.
Diffusion methods consist in mixing the impurity-
contaminated gas with a liquid which is in the aerosol state.
The inconvenience of this procedure resides in the difficulty
` of pulverizing the liquid very finely. In effect, if mechanical
pulverization is employed, the nozzles must be very fine and
there is a risk that they might become clogged with industrial
- liquids. Mechanical pulverization moreover requires very high
; liquid pressures.
In pneumatic pulverization processes, very high gas `
pulverization speeds are required, thereby resulting in a very
great energy expenditure. Finally, centrifuge pulverization
utilizing a centrifuge bowl revolving at great speed is a deli-
cate operation because of the operating and maintenance difficul-
ties.
In industrial practice, a first rough-cleaning stage
employs impact purification and permits the elimination of al-
most all of the coarse dust (~ 10 ~u). On the other hand, there
is no way of economically achieving moist particle removal in a
gas containing fine dust (< 1 ,u). The method used in the latter ~-
case is the venturi washer which operates correctly at a con- ;
stant gas flow rate and with a major head loss (on theQrder of
0.3 bar) so as to give the gas the necessary speed in order to
trap the fine dust.
The present invention was developed to provide a method
and apparatus for removing from a gas stream impurity particles
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iO~ 78
of less than one micron with a very low head loss.
According to a primary object of the instant invention,
a mist pattern of liquid droplets is formed in the gas stream by
means of a pair of generally opposed liquid jets, said liquid
jets being so arranged relative to the gas stream that a liquid
mist pattern is formed which extends normal to the gas stream.
It is another object of the present invention to pro-
vide a method of purifying a stream of gas containing impurity
particles, the size of which is less than about 1 ~. The method
comprises directing a pair of spaced jets of pressure liquid in
- generally opposed relation to establish a liquid mist pattern
extending generally normal to the direction of flow of the gas.
In this manner the impurity particles are moisturized for removal
- from the gas.
According to another object of the method and apparatus
of the present invention, the generally opposed liquid jets are
arranged at an obtuse angle less than 180. In the preferred
embodiment, the gas stream to be purified is conducted via a
conduit that contains longitudinally spaced wall openings through
which the linear nozzles are introduced. In accordance with a
specific feature of the invention, the liquid jet velocity rela-
tive to the gas stream velocity is regulated to produce a ratio
greater than 0.6.
According to another object of the invention, ~e appa-
ratus which is used to carry out the method according to the in-
vention comprises a conduit into which the gas stream is intro-
duced for longitudinal flow in the conduit. The apparatus also
comprises nozzle means connected with the conduit for introducing
a pair of liquid jets in generally opposed relation into the con-
duit to establish a liquid mist pattern which extends generallynormal to the flow of the gas stream. This enables the moisture
particles to be moisturized for removal from the gas.
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,~ In accordance with a more specific object of the inven-
.
tion, the linear nozzle means for producing theliquid jets are
each arranged for axial displacement (preferably by the provi-
', sion of a telescopic mounting), whereby the depth of penetration
of the angularly arranged nozzles into the gas conduit may be
adjusted as desired.
According to another object, one or both of the linear
nozzles is connected for angular adjustment relative to the gas
conduit, thereby to permit variations in the liquid mist pattern
produced by the liquid jets.
According to a further object, valve means and pressure
gages are provided for varying the pressure of the liquid jets,
'- or for varying the pressures of the jets relative to each other.
- According to anbther object, the nozzles are connected
to a metal plate that is removably connected with the gas conduit,
thereby to permit ready disassembly of the apparatus.
Other objects and advantages of the invention will be-
come apparent from a study of the following specification when
viewed in the light of the accompanying drawing, in which:-
Fig. 1 is a diagrammatic view illustrating the liquid
mist pattern produced by the method and apparatus of the instant
invention when the liquid jets are identical and have the same
pressure,
Fig. 2 is a view of the spray mist pattern produced by
the apparatus of Fig. 1:
Fig. 3 is a schematic illustration of the conical li-
quid mist pattern produced by nozzles having orifices of differ-
ent diameters:
Fig. 4 is a longitudinal sectional view of a preferred
embodiment of the present invention:
~; Fig. 5 illustrates a second embodiment wherein the
liquid jets have the same pressure: and
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Fig. 6 is a modification of the apparatus of Fig. 5
wherein one of the liquid jets has a higher pressure than the
other.
.j `:
Referring first more particularly to Fig. l, a pair of
identical tubular injector members l and 2 terminating in nozzles
la and 2a are connected with conduit means 3 that supply press-
ure liquid, such as water. The injector members 1 and 2 are
^ supplied with liquid at the same pressure, whereby a planar mist
pattern N is produced which is symmetrical to the liquid jets.
The nozzles are arranged at the angle ~ to the horizontal and are
thus arranged at an obtuse angle which is less than 180, the
liquid mist pattern N being normal to the horizontal plane P.
Since the axes of the two injectors form an angle, the mist sheet
with the elliptical form shown in Fig. 2 is not homogeneous, be-
cause the center G of the mist sheet is displaced to the opposite
side of the obtuse angle formed by the two jets.
' If, in the case shown in Fig. 3, a pair of nozzles 4
and 5 are used one of which has an outlet orifice which is of
greater diameter than the other, the mist sheet 6 produced-has
the configuration of a cone whose apex is the meeting point 7 of
the two jets, while the base is on the side of the jet supplied
by the injector with the smaller diameter. This results from the
. - . .
difference in the moments involved in these two jets. The same
conical shape is obviously obtained if the two jets have the
, same diameter but are supplied with liquid at different pressures.
The invention essentially consists in using the mist ~ -
sheets thus produced by forming them in a conduit containing the
- gas to be purified. - -
- In Fig. 4 a conduit 8 is provided in which a gas to be
; 30 purified is supplied. A pair of injector members 9 and 10,
equipped with nozzles 9a, lOa are provided, the axes of the in- -
; jectors being inclined with respect to the axis of the conduit 8.
.
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The injectors are attached to a plate 11 connected in a removable
` manner to the conduit 8. Telescopic devices 12 and 13 make it
possible to advance and retract the injectors relative to the
conduit as desired. Finally, joint connections 14 and 15 connect
the injectors to an industrial liquid pipeline.
In accordance with a modification of the invention,
one or both of the nozzles may be mounted for angular adjustment
relative to the longitudinal axis of the conduit, thereby to vary
the liquid mist pattern as desired. As shown in Fig. 4, the in-
jector 10 is connected with plate 11 for pivotal movement aboutthe pivot axis 30, the injector extending in a longitudinal slot
31 that is contained in the wall of conduit 8 and that is sealed
by the sliding seal 32 carried by the injector 10.
Referring now to Fig. 5, the ends of the injectors 9'
and 10' which extend normal to the axis of the conduit are bent
inwardly toward each other with the nozzles 9a' and lOa' being
spaced longitudinally of the conduit. The nozzles have the same --
orifice diameter and are supplied with liquid at the same press-
ure, thereby producing the illustrated parabolic liquid mist
; 20 pattern 19. The nozzles are mounted on the plate 11 which is
removably connected with the conduit by means of bolt means 16.
` Gage 17 indicates the pressure of the branch conduits leading to
the nozzles, valve means 18 arranged in the main supply conduit
~connected with the source of pressure liquid, not shown) being
provided for regulating the pressure of the liquid supplied to
the branch conduits.
In the modification of Fig. 6,the branch conduit lead-
ing to nozzle 9a" contains a valve 20 and a supplemental gage 21,
said valve 20 being adjusted to cause the pressure of the liquid
jet produced by nozzle 9a" to be greater than that of the jet
produced by nozzle lOa". Consequently, a resulting liquid mist
pattern 22 is produced having the reversely bent back configura-
` lO~U7'78
tion illustrated in the figure.
;
The devices illustrated in Figs. 4, 5 and 6 each havetheir advantages and disadvantages. In the case of the devices
of Figs. 5 and 6, the advantage is produced of symmetry and homo-
geneousness of the mist patterns, but on the other hand, the
cleaning of the conduit is not practical because, although there
is a stopper in the conduit, one cannot run through a metal rod
along the axis in order to break the stopper up or clean it out,
owing to the hindrance produced by the bent injector tubes. In
the case of the embodiment of Fig. 4, the advantage of symmetry
of the mist pattern is omitted, but the cleaning of the conduit
is facilitated. Moreover, one or both of the injectors may be
axially slidably or pivotally mounted so as to modify the mist
pattern in order to get the best result. `
To make sure that purification of blast furnace gases
will be as efficient as possible, it is important that the ratio:
R = speed of water iets
."
gas speed
will be as large as possible. To make the purification accep-
table, we must have R >0.6 and if we have R = 0.8, then the effi-
ciency of impurity removal will be 80%. But the larger we make R,
the greater will be the head loss in the gas pipeline.
The following table on the other hand presents the re-
sults obtained for the purification of blast furnace gas by means
of the device in Fig. 4.
_ _ _
last Gas In- head Purifica- Water Ratio
urnace flow jector loss, tion n q/m3 flow pres- R
~peration rate ~ mm m bar input output rate sure,
i m3/hr l m3/hr bar _
30 ~lmost about about about
ormal 80/
90,000 20 160 200 7 95 13 1.4 _
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¦~educed about
- 40,000/ up to
- 16,000 20 < 80 200 15/30 95 13 3/13
On the other hand, tests have been conducted on a steel conver- -
ter with oxygen being blown in at the bottom, on a pilot scale,
and the following results were obtained. These results evidently
differ from the results for the blast furnace since the purifica-
tion purpose is different.
The impurity particle concentration deriving from the
purification device according to the invention was 100 mg per
standard cubic meter for a head loss of less than or equal to
400mm water column, whereas on the same converter and with the
same known purification processes, the same result was obtained
for a head loss of 1500 mm water column. This resulted in an
energy consumption gain in the smoke and fume aspiration fan or
- ventilator of the impurity particle removal plant which would be
very large on an industrial scale.
The advantages of the method and the device according
to the invention are quite considerable. After moist purifica-
tion, it is unnecessary to provide electrostatic safety filters.
~; ~he head loss due to the method is small, which reduces the
- pneumatic energy losses. Finally the device is rather sturdy,
requires little maintenance, and its operation is satisfactory
in a wide range of gas flows to be purified.
While in accordance with the Patent Statutes, the pre-
ferred forms and embodiments of the invention have been illus-
trated and described, it will be apparent that changes and modi-
fications may be made without deviating from the inventive con-
cepts set forth above.
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