Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates generally to a pollution control
process for removing solid contaminates from an air stream moved
by a fan. In particuIar, the invention is directed to a glass
wool product forming process to be employed in the field of
pollution control.
In the manufacture of glass fiber wool-type products,
molten glass from a melting and refining tank flows into and
through a centrifuge forming step downwardly onto a foraminous
belt. As the glass fibers are falling onto the belt, a curable
organic resin binder is sprayed into the stream of fibers. The
foraminous belt conveys the fiber and resin mixture through a
curing oven, wherein the resin is cured to bind the fibers into a
wool-like product.
Located beneath the foraminous conveyor is an air
intake chute into which air is induced from the falling fiber-
resin mixture, along with induced factory air. This air flow is
induced by a fan pulling air through the chute and discharging
air into an upper fallout chamber or "penthouse" from which the
air passes into a vertical exhaust stack for flow into the
ambient atmosphere.
The fans are quite large and huge volumes of air, on
the order of 150,000 standard cubic feet per minute (scfm) flow
through the chute directly beneath the glass fiber supporting
belt. This induced air contained miscellaneous solid particles,
e.g. glass fibers, unreacted phenol and aldehyde components of
the resin, uncured liquid resin, factory air entrained solids and
calcium sulfate, phosphate, or carbonate which is utilized as
the catalyst for the phenol formaldehyde resin. The particulate
content of this air is on the order of 0.400 grams per scfm.
According to present Environmental Protection Agency standards,
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the maximum effluent from the stack is 0.020 grams per scfm, so
removal of 95% of the particulate content is necessary to comply
with the EPA regulations.
Prior to the present invention, the particulates in
the forming air exhaust have been treated primarily by the use of
ndropout boxesn. Such boxes are interposed between the forming
conveyor and the fan, and water is sprayed into the box. Due to
the large cross-sectional area of the box and the water spray
thereintot large particulate particles drop out in the box
through a combination of water impingement with the particulate
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,' and settling of the particulate from the slow moving air
', travelling through the box. As a result, the total particulate
~,, count at the outlet of the box drops to about 0.040 grams per
. i ,
;, scfm. Although 90% of the particulates have been removed by use
,~, of the drop box, the remaining particulatçs,are all fine particles,
,,' in the nature of aersols, which follow the air flow through the
~, forming fan and the final settling penthouse. It is these
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particles in the stack gas which make up the chemical plume or
,,~ haze issuing from the stacks in typical glass wool forming
20 operations. ' ,
It i8 necessary that these fine particulates be removed
from the forming air in order to conform with EPA regulations. ,
The present invention now proposes a method of removing '~ '
extremely fine particulate (lOO microns or less in size) from the
forming air exhaust gases of glass fiber wool manufacturing
processes.
The concept of the present invention resides in the
:
~, utilization of massive quantities of water sprayed into the
~, forming fan so that the aersol particles are agglomerated and
, 30 coalesced by impact between the particles and the water droplets
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as well as between the particles and the wet surfaces of the
fan and the fan shroud or hood. The fan is provided with a ~;
venturi throat inlet and massive amounts of water, on the order -
of 40 gallons per minute per fan, is introduced into the venturi
inlet as a spray of water droplets. -
Of course, upon the initial spraying, some of the
particles will be intercepted by impingement with the water.
More importantly, the water droplets impinge on the fan backplate,
on the fan rotor blades, and on thè fan shroud. Further, the air
with its aersol particles must change direction from axial flow
into the rotor to a radial flow through the rotor and a rotary
; flow to exit from the rotor. As a result of the significant
mass difference between the air, the water and the particulates,
and also because of the large wetted surfaces of the fan and
the fan shroud, the probability of water and partiale intercep-
tion and coalescing is greatly increased, and the partlcles are
;~ converted into sizes large enough to be susceptible to simple
inertial-type collection. Such inertia-type collection can take
place at the wetted surfaces of the shroud surrounding the fan
or in the penthouse interposed between the fan and the exhaust
stack.
The effectiveness of the method of the present invention
in removing heretofore non-removable aersol particles has been
confirmed by actual plant trials where 40 gallons per minute of
water sprayed at each fan reduced the particulates by 42%.
One surprising aspect of the present invention is that
the normal wash water which re-circulates through the wool-type
process can be utilized. This means that fresh water is not
required, and that a closed water loop can be provided to
conserve water and to avoid major water handling system changes
in the overall process.
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It is, therefore, an object of the present invention
to provide an improved pollution control system for fiber glass
wool-type processes wherein extremely fine, aerosol particulate
material is removed from the forming air by the injection of water .
into the intake of the forming fan.
ccording to the invention there is provided, in a
glass wool product forming process wherein a stream of process air
containing gaseous contaminants and solid contaminants of the
size on the order of 100 microns or less flows through a centri-
fugal fan provided with a shroud and interposed between a drop out
box and a penthouse communicating with an exhaust stack, the im- .
provement comprising the steps of (1) injecting water into the
intake of said fan to thoroughly wet the fan rotor and shroud,
(2) agglomerating said contaminants into composite masses of
substantially greater size due to particle-water contact during
passage of said process air stream through said fan, and (3)
separating the agglomerated particles from said air stream prior
to the passage of said air stream up the exhaust stack due to the
increased inertia of the agglomerated composite masses in said
air stream.
An embodiment of the invention will now be described
with reference to the accompanying drawings in which:
. Figure 1 is a schematic representation of a glass fiber
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wool-type forming process equipped with apparatus for carrying
out the method of the present invention; :~
Figure 2 is an enlarged sectional view, with parts
shown in elevation, of a fan shown in Figure 1. :~
According to the present invention a glass wool product
forming process wherein a stream of process air containing
gaseous contaminants and solid contaminants of the size on the
order of 100 microns or less flows through a centrifugal fan
interposed between a drop out box and a penthouse communicating
with an exhaust stack comprises the steps of (1) injecting at
least 40 gallons per minute of water into the intake of said fan
to thoroughly wet the fan rotor and shroud, (2) agglomerating
said particles into composite masses of substantially greater
size due to particle-water contact during passage of said
processed air stream through said fan, and (3) separating the
. agglomerated particles from said air stream prior to the passage
of said air stream up the exhaust stack due to the increased :
inertia of the agglomerated composite masses in said air stream.
In Figure 1, reference numeral 10 refers generally
to an apparatus for carrying out a glass fiber wool-type
manufacturing process, which apparatus is provided to carry out
the method of the present invention.
More specifically, the apparatus 10 includes a batch
hopper 11 discharging into a glass melting and refining tank
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provided with a forehearth 13 receiving molten and refined glass
from the tank 12. Molten glass issuing from the forehearth 13
passes through a centrifugal forming means 14, the glass issuing
from the forming means 14 as a stream of glass fibers 15 falling
gravitationally onto a foraminous forming conveyor 16 trained
about a pair of guide drums 17 for passage through a curing oven
18. During their free fall from the forming means 14 onto the .
conveyor 16, the fibers 15 are sprayed with a binder issuing from
a pair of spray nozzles 20. From the nozzles 20, the organic
resinous binder, such as a phenol formaldehyde resin, is
introduced from a hopper 21 into the spray nozzle conduit 22,
this conduit receiving wash water 23 from a hopper 24, the wash
water 23 passing through the conduit 22 under pressure from a
pump (not shown).
Located directly beneath the foraminous conveyor 16
and directly in the path of the glass fiber flow into the
conveyor 16 is a collection hopper 25 communicating with a drop
box 27 ~hereinafter more fully described in detail) and finally
through a second conduit 28 with the axial intake of a fan 30.
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. 20 The discharge of the fan 30 is upwardly through a discharge
: conduit 31 to an upper collection space or n penthouse" 32
provided with internal, vertical, staggered baffles 33 interposed
between the conduit 31 and an exhaust stack 34. A drain conduit
3S is provided from the penthouse to the drain receptacle 24.
Thus the air flow of the forming air occurs from the
receptacle 25 and the conduit 26 through the drop box 27 and the
conduit 28 to the inlet of the fan 30. From the fan 30, the
forming air passes through the conduit 31 into the penthouse
i
~:. 32 and through the penthouse 32 out through the exhaust stack 34.
Primary particulate separation occurs at the drop box 27. More
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specifically, it will be noted that the drop box 27 communicates
with a wash water conduit 40 interconnecting the drain receptacle
24 with an inlet manifold 41 from which spray conduits depend
into the drop box 27, as at 42. rl'he wash water under pressure
from a pump (not shown) sprayed into the drop box 27 through the
manifold 41 affects a first separation of particulate materials
from the forming air as hereafter more fully described. The drop
box 27 is provided with a drain 43 leading back to the receptacle
24.
As illustrated in Figures 1 and 2, the fan 30 is
surrounded by a scroll-type shroud or housing 50, and the cen-
trifugal fan has radial blades 51 opening fully onto the hollow
cylindrical support for the fan blades 51, this central hollow
support terminating in a radial fan plate 52 defining an abutment
surface for purposes hereinafter more fully described. The con-
duit 28 from the drop box 27 to the fan 30 is contoured to
define a venturi-type inlet 53 terminating interiorally of the
fan 30 and in spaced relation to the abutment surface 52.
Located at the entrance to the venturi 53 is a spray nozzle 55
connected by conduit 56 to the receptacle 24 to receive wash
- water therefrom. A pump or other pressurizing device (not shown)
supplies wash water under pressure through the conduit 56 to the
spray nozzle 55.
The hopper 25 receives process air from the forming
means 14, as well as factory air induced into the hopper by
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! virtue of operation of the fan 30. The air induced into the
hopper 25 typically has the following characteristics:
1. lS0,000 scfm (standard cubic feet per minute).
2. Relative humidity less than 100%.
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3. TeDper~eur~ 1~09F. ~
4O Impurities amounting to approximately 0.400
grams per scfm particulate plus gaseous impurities
(aldehyde plus phenol).
5. The solid particulates consist of less than ~-
5% glass fiber, unreacted resin components (phenol and
formaldehyde), uncured but reacted liquid resin,
factory air entrained solids, and catalytic solids
(calcium sulfate, phosphate or carbonate as the phenol
formaldehyde catalyst).
Since the Environmental Protective Agency maximum
standards at the stack 34 call for not more than 0.020 grams
per scfm, it is obvious that substantial amounts of particulate
; must be removed from the process air at the hopper 25 before it
is released through the stack 34.
It will be noted that the cross-sectional area of the
drop box 27 is substantially greater than the cross-sectional
area of the conduit 26. Further, from 1500 gallons per minute
~, to 2500 gallons per minute of wash water are introduced into the
drop box 27 through the conduit 40 and the manifold 41. After
passage through the drop box, the air in the conduit 28 has the
following properties:
1. Volume 150,000 scfm.
2. Relative humidity of 100%.
3. Temperature 100F. (approx.).
The total particulate count in the air exiting from the
drop box through the conduit 28 is about 0.040 grams per scfm
or about 10% of the particulate count at the hopper 25. This
90% particulate reduction drop occurs because (1) the large
particulate drops out, (2) the velocity impingement of particulate
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512
with the large volume of water sprayed through the manifold 41
- into the drop box 27, and (3) the particulate agglomerates and
settles out of the lower velocity air flow through the drop box. -
Further, some of the volatiles (primarily aldehyde and phenol
gases) are dissolved in the wash water in equilibrium with the
air which is at 100% relative humidity.
Although the total particulate count is reduced to
about 10% of that in the initial process air, all of the
remaining particulate is so fine as to be airborne in the air
stream in the conduit 28. These fines actually constitute aersol
particles which are so small (on the order of 100 microns or less)
as to follow the air flow aerodynamically and, as such, have
little susceptibility to filtration or settling.
In view of the nature of the particulate and further in
view of the fact that the particulate still exceeds the
Environmental Protective Agency maximum standard allowable
particulate count, it is necessary to take other removal steps.
This additional removal is accomplished at the fan
indicated generally at 30. More particularly, massive amounts
of water, i.e. in excess of 40 gallons per minute and preferably
in excess of 60 gallons per minute,are introduced into the
Venturi inlet 53 of the fan through the spray nozzle 55.
The basic mechanism of the concept of introducing such
massive amounts of water is that agglomeration of the particles
is effected by impact between the particles and the water
droplets as well as between the particles and the wet surfaces of
the fan. The first action which occurs is the typical Venturi
effect of acceleration and dispersion of the water droplets from
the nozzle 55 as the water droplets enter the Venturi area 53.
At this time, some minor particle agglomeration will occur because
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of direct impingement of the particles with the water droplets.
However, the major effect is obtained within the core
of the fan rotor 30. First, the water droplets and some of the
aersol particles will impinge on the surface 52 of the fan
backplate. Secondly, the air and the aersol particles are
subject to extremely high acceleration as the particles and the
air change direction. More specifically, the air stream
direction changes from the axial flow into the rotor to a radial
flow outwardly along the fan vanes 51 and to a rotary flow as
the radially flowing air is deflected by the fan shroud. There
is a substantial mass difference between the air, the water and
the aersol particles, thus the water and the particulates lag
behind the air in the rotary direction. The statistical
.~ .,
probability of impingement between the particulates and the water
is a function of the relative speeds of the air, the water and
the particulates and the available surface of the water. me
fan rotor blades are wetted and provide positive relative motion
between these wetted surfaces and the air. Further, the
extremely large fan blade surfaces (relative to the particulates
size) combines with the relative motion to significantly increase
the effective interception and coalescence of the aersol
particles. Also, the particulate is being conveyed in process
air which is already at 100~ relative humidity. All of the added
water is available for particulate removal.
The coalescence of the aersol particles creates larger
solid particles which then are more readily susceptible to
inertia-type separation from the air. The first such inertia-
type separation occurs in the zone defined by the inner surface
of the fan shroud 50 immediately surrounding the outer periphery
of the rotor 30. Here, the air component is moving in a rotary
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direction, while the entrained particles and the water will tend
to move in a radial direction. As a result, the water and
the particles are deposited on the inner surface of the fan
shroud.
Although unagglomerated aersol particles follow the
air stream in general, they still have sufficient mass to tend
to follow the radial direction toward the fully wetted fan
housing inner surface. This provides an additional stage of
agglomeration and collection.
Thus, it will be seen that the massive amounts of
water fed into the fan provides favorable conditions to increase
the probability of water-particle interception and coalescence,
thereby converting the particles into sizes large enough to be
susceptible to simple inertia type collection. The extremely
high accelerating forces in the fan provide the mechanism and
location for such conversion. Since it is axiomatic in air
cleaning that the effectiveness of an air cleaning device is
generally proportional to the amount of energy dissipated during
the collection, it is obvious that the forming exhaust fans are
extremely high energy dissipating machines and that this high
energy dissipation can be utilized as a cleaning mechanism to
agglomerate and later separate those particles which heretofore
had gone up the stack.
Any wetted or agglomerated particles carried in the
fan outlet stream are removed at the penthouse 32 by slowing the
air stream and/or by the deflection vanes 33.
So far as the gaseous pollutants are concerned, these
gases (typically aldehydes and phenols) are soluble in water and
exist in a vapor phase equilibrium between the forming air and
the wash water system. Since the wash water is utilized for
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injection into the fan, this equilibrium should be upset because
the process of the present invention significantly increases the
air/water interface.
The cleaning of particulates from the air by the
process of the present invention is affected to a very small
extent by the cleanliness or dirtiness of the water, within
reasonable limits. Further, the presence or absence of gaseous
pollutants in the wash water does not affect the particulate
removal efficiency.
This is one of the surprising aspects of the present
invention. The utilization of the wash water means that the
closed water loop can be used and reused for all phases of the
production process, including pollutant removal by the present
invention. The elimination of the requirement of fresh water
for pollutant removal means that existing recirculatory wash
water systems need not be changed to utilize the present
invention.
It will be appreciated that the numerical values here-
inbefore set forth are representative of actual plant values.
Generally, the method of the present invention is applicable to
large volume process air flows in e~cess of about 75,000 scfm.
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