Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND AND SIlMMARY OF THE I2~VENTION
The term ~foam", as used herein, designates a mixture
. . .
of liquid, gas, and a surfactant ~hat gives the liquid a film
strength which permits the forma~ion of long lasting bubbles
when the mixture is agitated to con~er~ it into a mass of
bubbles. The liquid used is normally water, and the gas is
usually air, because these ingredients are of low cost, but
2~ bther gas and/or liquid can be used when compatible with the
fiur actant. ~ ~
Various compounds are used as surfactants, and these
can be purchased on the open market. Some of these compounds
are proprietary. The strength of the film depends upon the
characteristics of the surfactant, and the amount of the sur-
factant in the liquid-gas mixture, as will be more fully
explained.
In order to have small particulate matter efficiently
trapped, it is necessary for the particle to contact with a
bubble of the foam and burst the bubble. As the bubble bursts,
the gas in the bubble escapes; the bubble implodes; and the
liquid film of which the bubble was made coats the particle.
Small particles do not burst large bubbles and are not wetted or
trapped by the foam. The smaller the bubble, the smaller the
particles that can be trapped. This invention traps all
detectable particles as a result of smaller buhbles made with
higher strength foam.
The foam described in this specification has the
bubbles burst by contact with small particles of material (dust)
and the bursting bubble wets the particle. Particles as small
as one micron are readily wetted. As this effect proceeds, the
foam is destroyed by contact with the particles. The wetted
particles must then be either
1) brought together,
2) made to contact larger particles, or
3) brought into contact with a surface, which may
be additional foam.
If the foam is injected into a free-falling aggregate
(at a transfer point between belts, for example, or injected into
a crusher along with the aggregate), the mechanical motion of
the aggregate will provide the required particle-to-particle
contact. When the foam is injected into an aggregate which is
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all fines (one to two hundred micron), some means must be
provided to cause the wetted particles to coalesce. This is
readily accomplished by use of a cyclone.
Another advantage of small bubble foam is that it can
be ejected from nozzles at considerable pressure and resulting
high velocity. This will be explained more fully in the des-
cription of the preferred embodiment.
According to a broad aspect the invention relates
to a method of preventing respirable dust and other particulate
matter from becoming airborne, which method comprises causing
contact of the particular and the outside surfaces of foam,
which is made of water, surfactant and air and which has
bubbles of an average size less than .015 inch in diameter
when in contact with the particles, wetting the particles
by implosion of the foam bubbles which are burst by contact
with the particles, trapping the wetted particles on the
surfaces of adjacent material and carrying the wetted particles
away from the zone on said adjacent material.
Other objects, features and advantages of the inven-
tion will appear or be pointed out as the description proceeds.
BRIEF DESCRIPTION OF DRAWINGS
In the drawing, forming a part hereof, in which like
reference characters indicate corresponding parts in all the
views-
Fig. 1 is a diagrammatic sectional view showing a foamgenerator for making small bubble foam which is used with
this invention;
Figure 2 is a diagrammatic view showing a cyclone
separator e~uipped with a foam supply and with means for
withdrawing particulate matter from the cyclone chamber in
a foam slurry;
Fig. 3 is a sectional view taken on the line 3-3 of
Fig. 2; and
Fig. 4 is a diagrammatic view of a transfer point for
dust-laden material with foam projected into the transferring
material. _ 4 _
DESCRIPTION OF PREFERRED EMBODIMENT
. . . _ . ~
The mixture used for this invention is preferably a
mixture of air, water and a surfactan~ that is made for "high
expansion foam." Such a foam has a high expansion ratio when
the foam is developed by conventional fire equipment; that is,
an ultimate volume of foam which is from 100 to 1000 times, or
more, of the volume of the water and surfactant from the foam is
formed~
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While the present inVention uses a surfactant of this
type in order to obtain great film strength, the expansion ratio
is reduced by the fact that the foam is made with small bubbles.
Bubble formation in making foam with my equipment is the result
of vortex effect in a passage. The boundary layer of the un-
foamed mixture drags on the sides of the passage, and the
smallex the passage, the more the turbulence and vortex action. -
Fig. 1 is a diagrammatic sectional view of apparatus
for making the small bubble oam of this invention. The mixture
of water, air and surfactant ("foaming agent") is forced by the
pump 10 into a foamer 12 which contains a cartridge pad 14.
This pad 14 has a myriad of small interconnecting
interstices. It may be a sponge made of polyurethane or other
plastic; but the preferred structure is a stainless steel
scouring pad sold under the trademark "CHORE BOY" and manufac
tured by Metal Textile Co., P.O. Box 315, South Bound Brook,
New Jersey, 08B80.
One or more of these pads 14 are stuffed into the
hollow interior of the container 12 until the full cross-section
of the container is evenly filled across one end of the interior
of the container, as shown in Fig. 1. A perforated partition 16
in the container is positioned to divide the container into
a pad chamber 18 and a foam chamber 20. The small bubble size
is obtained by pushing the unfoamed mixture through a myriad of
tortuous passages under sufficient pressure to obtain a high
velocity that will result in the small foam bubbles.
With the CHORE BOY scouring pad 14 stuffed into the
chamber 18 of the container 12, with a diameter "D" of three
inches, and with the scouring pad of an axial length of approxi-
mately three inches, the foam should be discharged rom an outlet22 at the rate of from five to ten cubic feet per minute in order
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to have the necessary velocity through the foaming pad 14 to
produce the small bubbles required by this invention. This
example is given merely by way of illustration. The mixture
supplied to the foamer 12 has water equal to from 1 to 4% of
the volume of the air and the surfactant is from 1 to 6~ of the
volume of the water and preferably 2%. The expansion ratio of
the foam may be from 25 to 100.
Expansion Ratio -
Vol. gas
Vol. liquid
Suitable surfactants can be purchased from suppliersof fire-fighting foam as listed in the yellow pages of the
telephone directory of any city of moderate size. It can also
be obtained from the DeTer Company, Inc., of Mountain Lakes,
New Jersey.
Conventional foams can flow by gravity and can be
pushed through passages if the pressure is low. High velocity
foam has to have considerable pressure behind it, and this is
possible with foam having very small bubbles but cannot be used
for large bubble foam because the bubbles collapse. Thus small
bubble foam can be penetrated into a dusty mass of material
such as at material transfer points already described. The
equipment shown in Fig. 1 will produce foam having bubbles
between .0005 and .015 inch. This will trap particulate matter
as small as 1 micron in diameter and ~arry large pieces up to
1 inch in size. The foam can effectively trap such small par-
ticles if the average size of the foam bubbles in less than
.015 inch; but the same amount of foam will trap more particles
if all of the bubbles are smaller than .015 inch and preferably
between .0005 and .015 inch, as already described.
r,~43
The outlet 22 of the fo~mex 12 has a flexible pipe or
hose 24 leading to a nozzle 26 from which foam 27 is discharged
under substantial velocity for permeation through a mass of dusty
. material at a transfer point or other location where the material
is in motion, and dust would be discharged into the ambient
atmosphere if the foam 27 were not used to suppress the dust.
Fig. 2 of the drawing shows a cyclone separator 30
which has a frusto-conical separation chamber 32 with a wall 34
that extends downward to an opening 36.
-. 10 Gas, laden with particulate matter, flows into the
chamber 32 from a passage 40 at the upper end of the chamber 32.
This passage 40 is positioned to discharge its gas stream
tangentially around the circumference of the upper part of the
chamber 32 and in contact with the wall 34.
The passage 40 discharges gc3s into the separation
chamberr which has a cover 35 and the gas flows downwardly with
a swirling movement and increasing velocity as the cross-
section of the separation chamber decreases. Particulate
matter in the gas is thrown outward by centrifugal force, and the
gas, separated from its particulate matter, reverses its Xlow
at the center region of the separation chamher and flows upward
to an outlet discharge 44 which extends upward through the top
of the chamber and in substantial alignment with the axis of
~he chamber 32~ The construction and operation of the cyclone
separator, thus far described, is in accordance with conventional
practice.
This invention introduces foam into the particulate
laden gas stream~ In the illustrated embodiment, the foam is
injected into the gas stream by a nozzle 46 which extends into
the gas inlet passage 40 upstream fro~ the outlet of this passage
40 where the gas flows into the separation chamber 32. The
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foam traps the particulate matter and forms, with the particu-
late matter, a slurry.
The coating of slurxy, indicated by the reference
: character 48, on the wall of the separation chamber is indicated
in elevation by stippling in the drawing and i5 shown in section
where the wall 34 is shown in section. The slurry 48 runs
down the wall and accumulates in the lower part of the separa-
tion chamber 32 at the opening 36 which is normally closed by a
` bottom 50.
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5~L3~ .;
In the c~nstruction illustrated, the bot~om 50 ;.s
supported from the wall 34 b~ a bracket 52 to which the b~ttom
is connected by a hinge comprisins a pin 54 ~7hich extends
: through one 5i~e of the bottom 50 and through aligned openings
S in the brac~et 52. A spring 56 is connected at one en~ to
the bracket 52,.and the other end of the spring 56 contacts
ith the bottom 50 to hold the bottom in a position to close
the op~ning 36, as indicated in full lines in Fig.2. When
sufficient ~7eight ~f slurry accumulates in ~he lower end ~f
ln the separation cham~er 32, the weight of the slur~y overcomes
the force of the spring 56 and causes the bottom ~0 to swiny
into an open position, as indicated in dotted lines in ~ig~ ~.
The accumulated slurry drops out of the chamber, and the
spxiny 56 pushès the bottom 50 back into closed position.
1~ A foam generator 60 supplies the nozzle ~6. ~oam
generators are well-known, and the :block diagram of Fig. 2
is sufficient for a complete understanding of this invention.
Water, air and foaming.ag~nt are supplied to the foamer 60
~rom a mixer 62; and the water, air and-~oaming agent are
supplied to the mixer 6~ through pipes 6~, 65 and 66, re-
spectively.
Each of the pipes 64, 65 and 66 is shown ~Jith a
~àlve 68 for regulating the supply of water, air or foaming
agent, and the proportions in which these ingredients are
supplied to the mixer 62~ These valves 68 are merely repre-
sentatiYe of means for controlling the supply o~ the ingre-
dients to the mixe- 62 and for proportioning the ingredients.
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.
.
~lore elaborate controls for t~e ingredients
supplied to the mixers 62 can be used, such as fluid flow
regulators that rec~ive flui~ at variable pressure and
- deliver it at a uniform pressure and/or flow. Tnese controls
are adjustable to regulate the pro~ortions supplied to a
mixer. Such controls are also well-known,~nd ~he particulax
apparatus used for controlling the ~low and proportions of
the ingredients is a matter of choice
~xperie*ce has shown that it is not essential to .:
supply foam continuously to the separator. It is sufficient
that the wall of the separation chamber be at least.partially
coated with foam at all times. In order to conserve foa~,
a control valve 70 is located bet~een the mixer and the
foamer ~or shutting off the mixture at times when no foam is
required.
. In order to program the sup21y of foam with the
opera.ion of the cyclone separator of a cycle timer 72 control~
a po-~er supply to a solenoid or other actuator 7a for the
valve 70. The cycle timer 72 opens.and closes the ~alve 70
periodically and for such length of time as necessary to
maintain th~ required amount of foam in the separation chamber
. In accordance with conven~ional practice, the gas
and par~iculate matter is supplied to the separa~or by a
centrifugal blower 76 or other apparatus for moving the air
and solids.
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., .
Fig. 4 shows a belt conveyor ~0 ~hich transfers
coal 82i or other dusty material, to truc~ 86. As the coal
falls into the truck 86, dust would float off into the
ambient atmosphere; and the s,maller particles are the most
objectionable because they are lighter and remain airborne
for larger periods of time.
Fo~m nozzles discharye small bubble foam 90 into
the moving mass of coal, and the foam contacts with the dust
present in the fàlling coal. The dust particles burst the
bubbles wlth ~hich they contact, and the implosion of the
bursting bubble traps and coats the dust particles with ~he
liquid of which the bubble was formed.
This traps the wetted particles on the sur~ace of
adjacent mzterial. ~7ith broken dusty material, the dust
is suppressed by projecting the small bubble foam into the
broken material whi~e ~aid ma~erial is in motion.
~ere the transfer of dusty material from one
support to another is by free fall to the other support,
the small bubble foam is projec~ed into the material to
trap ~he dust thereo~ while larger particles of the material
are separated from one another as a result of the free fall.
The preferxed embodiment of this invention has been
illus rated and described, but changes and modifications
can be made, and some features can be used in different
combinations without departing from the invention as de-
fined in the claims.
