CA1063512A

CA1063512A - Pollution control system for removing particles in stack gases

Info

Publication number: CA1063512A
Application number: CA238,737A
Authority: CA
Inventors: Roland E. Langlois
Original assignee: Owens Corning Fiberglas Corp
Current assignee: Owens Corning
Priority date: 1974-12-12
Filing date: 1975-10-31
Publication date: 1979-10-02
Also published as: BE836395A; FR2294138A1; FI753517A; IT1050100B; AU8626275A; AU503502B2; NL7513494A; JPS5175268A; DE2553124A1; GB1500308A; NZ179511A; LU73979A1; ZA756778B; SE7513923L

Abstract

ABSTRACT OF THE DISCLOSURE
A pollution control system to reduce the presence of fine aerosol particles in stack gases from the manufacture of glass fiber wool-type products. After larger particles are removed from the forming fan gas, massive quantities of water are injected into the fan intake. The aerosol particles are agglo-merated by impact with the air-borne water droplets and the wet surfaces of the fan. The larger, coalesced or agglomerated particles are more readily susceptible to inertia-type separation from the air by either the action of the fan or in a later separation operation. It has been found that more than 40% of the fine, aerosol particles introduced to the fan can be removed in this way. Further, the re-circulating process water can be utilized, reducing or eliminating the consumption of fresh water and maintaining the normal process water system of the manufac-turing operation.

Description

- ~06;~512 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 ... .
,' 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 ,, ,! .
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.

;j , . 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 .: ,. .
! 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 '~ ~ ' ' ' 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 _ g - ..

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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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- 1~63512 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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. 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 centrifugal fan provided with a shroud and interposed between a drop out box and a penthouse communicating with an exhaust stack, the improvement 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.

2. In a process as defined in claim 1, the further im-provement wherein the water injected in Step 1 is recirculating process water containing some particulate solids and dissolved gaseous resin components in equilibrium therein.

3. In a process as defined in Claim 1 or 2, the further improvement wherein the separating Step 3 is carried out at least partially at the location of said fan.

4. In a glass wool product forming process wherein a stream of process air containing dissolved gaseous resin compo-nents and particulate contaminants of a size on the order of 100 microns or less, said stream of process air having a relative humidity of 100%, flows through a centrifugal fan interposed between a drop out box and a penthouse communicating with an exhaust stack, the stack gas flow rate being in excess of 75,000 scfm, the improvement comprising the steps of (1) circulating process water containing some particulate solids and dissolved gaseous resin components in equilibrium therein through a closed loop including said centrifugal fan, (2) injecting at least 40 gallons per minute of the recirculating process water into the intake of the fan, (3) radially and rotationally conveying the water in the form of discrete droplets suspended in the process air through the fan rotor, (4) agglomerating at least a portion of the particulate contaminants in said stream of process air by contact with the water wetting the fan components and (5) separating at least a portion of the injected process water and said agglomerated particles from the gaseous stream as it flows through the fan.

5. In a glass wool product forming process wherein a stream of process air containing dissolved gaseous resin compo-nents and particulate contaminants of a size on the order of 100 microns or less, said stream of processed air having a relative humidity of 100%, flows through a centrifugal fan having rotor and shroud components, said fan being interposed between a drop out box and a penthouse communicating with an exhaust stack, the stack gas flow rate being in excess of 75,000 scfm, the improve-ment comprising the steps of (1) circulating process water containing some particulate solids and dissolved gaseous resin components in equilibrium therein from a process water collection location through a closed loop including said centrifugal fan, (2) injecting at least 40 gallons per minute of the recirculating process water into the intake of the fan, (3) radially and rotationally wetting the fan components with a film of said process water, (4) agglomerating at least a portion of the par-ticulate contaminants in said stream of process air by contact with the water wetting the fan components, (5) separating additional process water and agglomerated particles from the stream of process air as said stream passes through the penthouse, (6) draining said additional separated water and particles from the penthouse, and (7) collecting the drained water at said collection location for re-use.

6. In a glass wool product forming process wherein a stream of process air containing gaseous contaminants and solid contaminants of a size on the order of 100 microns or less flows through a centrifugal fan having rotor and shroud components and a Venturi inlet interposed between a drop out box and a penthouse communicating with an exhaust stack, the improvement comprising the steps of (1) injecting a stream of water into the Venturi inlet of said fan to break-up the water stream into droplets thoroughly wetting 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 in contact with the fan rotor and shroud, and (3) separating the agglomerated particles from said air stream through the fan and through the penthouse.