Self-cleaning collecting device

A self-cleaning collecting device for cleaning a dirty gas stream including a flow-through housing having a dirty gas inlet at the base of the housing and a clean gas outlet at the top of the housing interconnected by a gas treating passage adapted to direct a gas stream vertically through the housing. As the dirty gas stream enters the housing, it is circulated through a liquid bath where noxious vapors and larger particulates are entrained in a mist of liquid droplets which are in turn captured and removed from the gas stream as it moves through a separating panel positioned above the liquid bath. As the gas flows upwardly out of the panel, the captured liquid is circulated to the liquid bath to maintain a flow of liquid within the panel which acts to continuously wash the particulates from the panel. At the same time, the gas stream continues upwardly in the treating passage where it flows through an electrostatic precipitator which removes the smaller particulates from the gases prior to their being discharged from the housing through the gas outlet at the top of the housing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a selfcleaning collecting device for 
removing vapors and solid particulates from a gas stream. 
2. Description of the Prior Art 
The prior art includes a variety of collecting arrangements for removing 
noxious vapors and solid particulates from a dirty gas stream generated by 
the various metal working and chemical processes used in automotive 
plants, foundries, and the like. 
U.S. Pat. No. 2,966,958 discloses a typical collecting device wherein 
noxious vapors and larger particulates are removed from a dirty gas stream 
by passing the gas stream through a porous media flooded with a liquid 
which coalesces with the vapors and entrains the particulates so they can 
be removed by separating the liquid from the gas stream. While this type 
of arrangement has been satisfactory in many applications, experience has 
indicated it usually is most effective where the clean air is discharged 
into the atmosphere away from the work area as it is primarily intended to 
remove larger particulates having a diameter in excess of 1 micron. Thus, 
this type of arrangement would generally be inappropriate where it is 
desired to recycle the air within a plant to save heating or cooling of 
the air where a substantial portion of the particulates smaller than 1 
micron would still be entrained in the air. 
The electrostatic precipitator shown in U.S. Pat. No. 3,016,980 represents 
one method of cleaning the air in a factory prior to recycling it within 
the plant. In that arrangement, the dirty gases are circulated through one 
or more collecting cells having a plurality of spaced parallel collecting 
plates which are charged to attract oppositely charged particles in the 
dirty gases as they flow through the cell between the collecting plates. 
In the typical plant application, a plurality of cells are secured to a 
grid-like frame to form a bank of side-by-side cells sized according to 
the air cleaning requirements of the installation. While this approach has 
proven to be extremely effective in many applications, when it is used to 
remove the particulates and oil vapors generated during flame cutting and 
various die casting operations, the rapid agglomeration of the 
particulates resulting from those processes on the collecting plates tends 
to clog up the cells, and localized accumulations of liquid on the plates 
often lead to excessive arcing within the individual cells. Consequently, 
where this type of arrangement has been used to clean the gases resulting 
from those processes, it has generally been necessary to construct a very 
large installation to maintain the air flow through each of the cells at a 
level low enough to prevent these problems. 
SUMMARY OF THE INVENTION 
The present invention relates to a self-cleaning collecting device for 
cleaning a dirty gas stream. 
The collecting device includes a flow-through housing having a dirty gas 
inlet at the base of the housing and a clean gas outlet at the top of the 
housing interconnected by a gas treating passage adapted to direct the gas 
stream vertically through the housing. The lower portion of the treating 
passage encloses a liquid bath treating section wherein an apertured plate 
is secured across the passage above a liquid reservoir connected with a 
pneumatic lift adapted to disperse a predetermined flow of liquid onto the 
upper surface of the plate which is entrained in the gas stream as the 
liquid flows into the apertures in the plate. This results in the noxious 
vapors and the larger particulates in the gas stream being entrained in a 
mist of liquid droplets formed in the gas stream as it passes through the 
plate. Then, as the gas stream moves upwardly in the treating passage from 
the apertured plate, it flows through a filter panel formed of a fiberous 
material secured across the passage above the plate. The filter panel 
separates the liquid droplets from the gas stream whereafter the liquid 
accumulating in the panel from the droplets is circulated back to the 
reservoir to maintain a flow of liquid within the panel which acts to 
continuously wash the particulates from the panel. The self-cleaning 
action provides a better operating condition and a smaller collecting 
device and less downtime for servicing. Thereafter, as the gas stream 
continues upwardly in the treating passage, it flows through an 
electrostatic precipitator which removes the smaller particulates from the 
gas stream which is ultimately discharged from the housing through the 
clean gas outlet. The clean gas emerging from the clean gas outlet is 
adequately cleaned for recirculation through the circulating gas system. 
From the foregoing, it can be seen that the self-cleaning collection device 
embodying the invention is of a relatively straightforward, durable design 
which is easy to monitor and maintain in the field. However, it is to be 
understood that various changes can be made in the arrangement, form and 
construction of the apparatus disclosed herein without departing from the 
spirit and scope of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIGS. 1-3, the self-cleaning collecting device 1 embodying the 
invention includes a vertical housing 2 having a dirty gas inlet duct 3 at 
its lower end and a clean gas outlet duct 4 at its upper end 
interconnected by a gas treating duct 5 extending vertically through the 
housing 2. As will be described, the treating duct 5 is divided into a 
liquid bath treating section 6, a separating section 7, and an 
electrostatic precipitating section 8 which are arranged in series within 
the treating duct 5 to clean the dirty gas stream as it is drawn into the 
housing 2 through the inlet duct 3 and circulated upwardly through the 
treating duct 5 by a blower or fan 9 mounted in the top of the housing 
which in turn directs the gas stream out of the housing through the outlet 
duct 4 to a ventilating duct 70 and the ventilated room 71 of a plant and 
to return conduit 72. 
As shown in the drawings, an apertured plate 10 is secured across the gas 
treating duct 5 in the liquid bath treating section 6. The apertured plate 
10 is positioned above a liquid reservoir 11 formed in the bottom of the 
housing 2 from which liquid is aspirated onto the upper surface of the 
apertured plate 10 where it is entrained in the gas stream as the liquid 
flows into the apertures in the plate 10 during gas cleaning operations. 
The liquid, which may be a paraffin base mineral oil having a mean 
viscosity of about 1500 SSU (Seconds Saybolt Universal), is aspirated onto 
the apertured plate 10 by a pneumatic lift assembly 12 operating as a pump 
means including a cup 13 secured in the reservoir 11 to provide a liquid 
sump having a conventional fluid metering valve 14 secured to the cup 13 
adapted to meter a predetermined flow of liquid from the reservoir 11 into 
the cup 13, and a tube 15 extending from the cup 13 through the apertured 
plate 10. The aspirating action of the lift assembly 12 is effected by the 
pressure differential created in the gas stream as it flows through the 
apertures in the plate 10 since the lower pressure above the plate 10 
serves to draw the liquid into the cup 13 through the valve 14 and then 
aspirate it upwardly through the tube 15 whereafter it falls onto the 
upper surface of the plate. In the embodiment shown, a plurality of 
apertures in the range of 3/4-2 inches in diameter are provided in the 
plate 10 so that about 6-10 percent of the plate is open area, although 
this arrangement will still function effectively where as much as 25 
percent of the plate is open area. This results in a pressure differential 
of about 3/4-11/2 inches water gauge when the gas stream is flowing 
through the housing at a velocity in the range of 200-500 feet per minute. 
Experience has indicated this pressure differential is sufficient to 
aspirate the liquid upwardly through the tube 15 so it is distributed 
relatively uniformly on the upper surface of the plate 10 where it 
migrates to the apertures where it is entrained in the gas stream flowing 
through the apertures to effect coalescence of the noxious vapors and 
entrainment of the larger particulates in a mist of liquid droplets formed 
in the gas stream as it flows through the plate 10 and into the separating 
section 7. 
The separating flat or planar section 7 includes a separating panel 16 
secured in flow-through relation across the treating duct 5 at an acute 
angle of 30-45 degrees to the horizontal. As shown in FIG. 4, panel 16 is 
formed by sandwiching a plurality of parallel, contiguous layers or 
strands of crimped wire material 17 forming a maze of tortuous passages 
within the panel between comparatively rigid expanded screening 18. Thus, 
as the gas stream flows upwardly through the panel 16, it must pass 
through a maze of tortuous passages which effect impingement and inertial 
separation of the liquid droplets carrying the noxious vapors and the 
larger particulates from the gas stream as it flows upwardly out of the 
panel 16. Then, due to the angular alignment of the separating panel 16 in 
the treating duct 5, the liquid flows or migrates to the lower edge 19 of 
the panel where it flows into a trough 20 secured across the treating duct 
5 beneath the lower edge 19 which in turn channels the liquid into a 
vertical conduit 21 which circulates it back into the reservoir 11. This 
arrangement effectively removes the liquid mist from the gas stream while 
at the same time utilizing the liquid flow within the panel to clean it 
during operation of the device. In this regard, it should be noted as the 
liquid is circulated back to the reservoir, the particulates in the liquid 
tend to settle to the bottom of the reservoir enabling them to be 
periodically removed as a sludge through an access or cleaning door 22 
provided in the bottom of the housing. The panel 16 may be replaced 
through access door 31. 
Referring to FIG. 1, a pair of electrostatic collecting units 23 and 24 are 
secured in serially aligned flow-through relation in the precipitating 
section 8. The electrostatic precipitator precipitates particulate of 
submicron size and fumes to further condition the gas for recirculation 
through the gas system. The lower or upstream collecting unit 23 is 
similar to that shown in U.S. Pat. No. 3,016,980 which is incorporated by 
reference in this specification. As discussed in that patent, the 
precipitator 23 includes an electrostatically charged ionizing or 
discharge zone 26 and a collecting zone 27 extending between a pair of 
spaced end plates of panels 25 which are supported by a frame 30 secured 
to the inner periphery of the housing in the precipitating section 8 in a 
fashion which accommodates installation and renewal of the precipitator 
through an access door 31 provided in the wall of the housing. Although 
the construction of the precipitator 23 is well known in the art and 
therefore is not described in detail in this specification, it should be 
noted the collecting zone 27 is comprised of interleaved sets of grounded 
plates 33 and electrically charged plates 32 secured in spaced parallel 
relation between the end panels 25 connected with electrical contacts 34 
mounted on the end panel 25. Additionally, as shown in the drawings, a 
selected number of the grounded plates 33 extend into the ionizing zone 
26. The portions of the grounded plates 33 which extend into the ionizing 
zone 26 serve as collector plates for that zone, cooperating with spaced 
discharge electrodes or ionizing wires 37 connected with an electrical 
contact 36 which is similarly mounted on the end panel 25. 
The upper or downstream collecting unit 24 is in effect an extension of the 
collecting zone 27 of the lower or upstream unit 23. The collecting unit 
24 is comprised of interleaved sets of grounded plates 44 and electrically 
charged plates 43 secured in spaced parallel relation between its end 
panels 42 which are adapted to be slid into the housing and secured in the 
precipitating section 8 on a supporting frame 56 mounted on the inner 
periphery of the housing. As shown in FIG. 5, the charged plates 43 are 
connected with electrical contacts 41. 
During normal precipitating operations, a potential of about 14,000 volts 
is maintained between the ionizing wires or discharge electrodes 37 and 
the grounded collecting plates 33. This is maintained by a first DC power 
source 49 connected to the discharge electrodes through an electrical 
contact 50 which engages the contact 36 when the unit 23 is mounted in the 
housing. At the same time, a potential of about 6,800 volts is maintained 
between the charged and grounded plates in the collecting zones of both 
the units 23 and 24 by a second DC power source 52 connected to the 
electrical contacts 53 and 54 which similarly mate with the contacts 34 
and 41 when the units are mounted within the housing.