Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
9~58
POPPET VALVE FOR BAGHOUSE OUTLET PLENUM
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention pertains generally to
baghouses for separating dust from gas streams.
More particularly, the present invention pertains
to means for controlling the re-inflation of bag filters
in a baghouse following reverse gas flow cleaning.
State of the Prior Art
-
Many kinds of dust produced in industrial processes
can be separated from gas streams by fabric filters
made of natural or synthetic fibers. A prevalent dust
filtration technique utilizes a plurality of tubular
bag-like fabric filtersS referred to as bag filters,
mounted in an enclosed structure called a baghouse.
The bag filters are usually mounted vertically ~^Jithin
the baghouse, and are open at their bottom ends. In a
typical baghouse arrangement, streams of a dust-laden
gas to be filtered are passed into the interiors of the
bag filters through the open bottom ends. Dust from
~ the gas streams is retained on the inside surfaces and
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in the irlterstices of the fabric of the bag filters,
and dust-free gas is drawn through the fabric into the
interior of the baghouse external to the ~ag filters.
A pressure di~ference (maintained by conventional
means) between the interior of the baghouse and a clean
gas plenum causes dust-free gas to be drawn into the
clean gas plenum for passage either to a region where
the gas is to be used or further processed, or to a
stack for release to the atmosphere.
The dust that collects on the inner surfaces of a
bag filter forms a cake, referred to as the dust cake,
which acts as a filter medium for removing other dust
from the gas stream. However, the dust cake increases
the impedence of the bag filter to the passage of gas
therethrough. Consequently, the bag filters in a baghouse
must be cleaned periodically to remove a major portion
of the dust cake therefrom so that gas flow therethrough
can be maintained at an acceptable rate.
A method for removing the dust cake from the inner
surfaces of the bag filters in a baghouse involves
periodically stopping the flow of dust-laden gas into
the baghouse and closing an opening to the clean gas
plenum, and then directing a flow of dust-free gas from
the clean gas plenum back into the baghouse for passage
through the bag filters in the opposite direction.
This method is called reverse gas flow cleaning.
Dust-laden gas flow in the normal direction through
the filter fabric ti-e-, in the direction of dust cake
formation) tends to press the dust cake against the
fabric. Stopping the flow of dust-laden gas in the
normal direc~ion serves to release the dust cake from
the fabric; and directing the burst of dust-free gas in
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the reverse direction through the fabric serves to push
the dust cake away from the fabric. The dust cake thus
removed from the bag ilters falls into a hopper for
collection and e~entual removal from the ~aghouse. A
discussion of particular baghouse designs, applications
and filter cleaning techniques known to the prior art
can be found in an article by Milton N. Kraus entitled
"Baghouses: Separating and Collecting Industrial Dusts"
published in Chemical Engineering, April 9, 1979, pages
94-106.
During bag filter cleaning by the reverse gas flow
method, the bag filters in a baghouse tend to collapse
inward or deflate due to the greater pressure on the
outside surfaces than on the inside surfaces of the bag
filters. Upon re-establishment of dust-laden gas flow
in the normal direction following completion of the
reverse gas flow cleaning of the fabric, the bag filters
are re-inflated to their normal configurations. Rapid
and uncontrolled re-inflation of the ~ag filters,
however, can have a deleterious effect on the filter
fabric. Sudden resumption of the gas flow in the
normal direction can tear the fabric, a phenomenon
lcnown as "bag popping".
Various valving techniques have been developed in
the prior art for controlling gas flow in baghouse
operations. Examples of such techniques are described
in U.S. patents 3,057,137 to D. B. Perlis et al.;
3,396,516 to W. E. Ballard; 3,521,430 to H. D. Vanderlip
et al.; 3,540,193 to J. Pauscl~; 3,898,062 to P. B. Slakey;
3,926,595 to O. K. Bockman; 3,945,400 to P. B. Slakey;
and 3,963,467 to D. W. Rolschau. Until the present
invention, however, a reliable and relatively inexpensive
valving technique for precisely controlling the re-
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inflation rate of bag filters in a baghouse had not
been known, which could readily take into account such
variables as the dimensions and material of the bag
filters, the nature and flow rate of the gas stream,
the nature and concentration of ~he dust in the gas
stream, and the rapidity of change of any of these
variables.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide
a means for precisely controlling the re-inflation rate
of bag filters in a baghouse following reverse gas flow
cleaning.
In accordance with the present invention, a poppet
valve is provided to enable precisely controllable
dust-free gas flow from the interior of a baghouse into
a clean gas plenum during re-establishment of dust-
laden gas flow in the normal direction through bag
filters in the baghouse following reverse gas flow
cleaning of the bag filters. A poppet valve according
to the present invention is disposed at an opening into
the clean gas plenum from the interior of the baghouse.
The poppet valve comprises a plate mounted on a stem
for translational movement perpendic~llar to the opening,
so that the opening can be sealingly closed when the
valve plate covers the opening and opened when the
valve plate is moved away from the opening.
Generally, severa; openings from the baghouse into
the clean gas plenum are provided, with a valve according
to the present invention being mounted at each opening,
to enable precisely controllable dust-free gas flow
- from the baghouse into the clean gas plenum as dust-
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laden ga~ f~ow into the bag filters is re-established
following reverse gas flow cleaning of the bag filters.
A feature of a poppet valve according to the
present invention is a cylindrical skirt mounted on the
valve stem to restrict the entry of dust-free gas
through the opening into the clean gas plenum when the
valve plate is initially raised away from the opening.
The end of the cylindrical skirt adjacent the valve
plate of each valve is covered, so that gas can pass
from the interior of the baghouse into the clean gas
plenum only via the clearance between the edge of each
opening and the outer wall of the cylindrical skirt
positioned in that opening. Each valve skirt is
sufficiently long so that the valve skirt remains in
its corresponding opening to restrict the flow of gas
through the opening as the valve stem to which the
skirt is attached rises, until the bag filters in the
baghouse are re-inflated sufficiently to prevent "bag
popping" or other damage to the fllter fabric.
In a particular embodiment of the present invention,
one or more longitudinally extending orifices are
provided in the cylindrical wall of each valve skirt.
Without such longitudinal orifices, the rate of gas
flow from the baghouse through each opening into the
clean gas plenum would depend only on the area of the
annular clearance between the circumference of the
opening and the outer wall of the valve skirt as long
as the valve skirt is present in the opening. With
such longitudinal orifices, however, the rate of gas
flow through each opening into the clean gas plenum can
be gradually increased as the valve skirt is raised.
In this way, precise control of the rate of gas flow
from the baghouse into the clean gas plenu~ can be
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~ poppet valve according to the present invention
serves as a flow-restricting damper during re-inflatiOn of the
bag filter~, ye-t does not restrict dust-Eree gas flow into the
clean gas plenum after the bag filters have been re-infla-ted.
Thus, with the present invention, a separate flow-restricting
damper is not necessary to prevent abrupt pressure change in
the baghouse during re-establishment of dust-laden gas flow in
the normal direction a~ter completion of reverse gas flow
cleaning of the bag filters. With the need for a separate flow-
restricting damper eliminated, the concomitant need for
associated air cylinders, solenoids and limit switches is
likewise eliminated, thereby providing a significant reduction
in the overall cost of the baghouse installation.
DESCRIPTION OF THE DRAWING
FIG. 1 is a side view of a poppet valve according to
the present invention, shown in flow-restricting open condition.
FIG. 2 is a cross-sectional side view of the
poppet valve of FIG. 1, but shown in closed condition.
FIG. 3 is a cross-sectional side view of a dust
removing apparatus utilizing the poppet valve o~ FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
~ poppet valve according to the present invention
is indicated by the reference number 10 in FIGS. 1 and 2.
The valve 10 is mounted in an opening 15 in a wall 16 of a
baghouse 17. The opening 15 provides gas flow communication
between the baghouse 17 and a clean gas plenum 20. When the
valve 10 is open, dust-free gas from the baghouse 17 can
be drawn through -the opening
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15 into the plenum 20 by a pressure diference maintained
by conventional means ~e.g., an exhaust fan) not shown
in the drawing.
The opening 15 is preferably but not necessarily
of circular configuration; and the edge of the opening
15 outside the baghouse 17 and within the plenum 20 is
rimmed by a circular seating ridge 21. The valve 10
comprises a plate 30 mounted on a stem 31. The valve
plate 30 is preferably circular, conforming to the
configuration of but having a larger diameter than the
opening 15 and the seating ridge 21.
The valve stem 31 is mounted by conventional means
within the baghouse 17 to extend through the opening
15, so as to support the valve plate 30 in the interior
of the plenum 20 over the opening 15. The valve stem
31 is generally perpendicular to the plane of the
opening 15, and supports the valve plate 30 so as to
overlap the seating ridge. As shown in FIGS. 1 and 2,
the valve plate 30 has a central aperture through which
the upper end of the valve stem 31 passes; and the
valve plate 30 may be secured to the valve stem 31 by
nuts 34 and 35, one on either side of the valve plate
30.
Affixed to the valve stem 31 as an integral part
of the valve 10 is a cylindrically configured skirt 32.
A cover member 33 closes the upper end of the skirt 32
adjacent the valve plate 30, while the lower end of the
skirt 32 remote from the valve plate 30 is open. As
shown in FIG. 2, the cover member 33 has a central
aperture through which the valve stem 31 passes. The
skirt 32 is positioned so that the cover member 33 is
~ separated from the underside of the valve plate 30 by
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the nut 34. A cylindrical sleeve 36 fits over the
valve stem 31 and is positioned to press against the
underside of the cover me~ber 33 so as to hold the
cover member 33 against the nut 34. The sleeve 36 is
held in position on the valve stem 31 by a washer 37
and one or more lock nuts 38. A plurality of symmetri-
cally arranged elongate strut members 39 affixed to the
sleeve 36 as by welding extend radially outward to the
cylindrical wall of the skirt 32 to reinforce the skirt
32. The strut members 39 are preferably welded to the
interior of the skirt 32, and p~event wobbling of the
skirt 32.
The valve stem 31, and hence also the attached
valve plate 30 and the cylindrical skirt 32, are
translatable in the vertical direction (i.e., up and
down) by means of a conventional poppet valve actuating
mechanism 40, so that the opening 15 can be opened or
closed depending upon whether the valve plate 30 is
positioned away from or in contact with the seating
ridge 21. As shown in FIG. 1, the valve actuating
mechanism 40 may advantageously be located outside the
baghouse 17, in which case the valve stem 31 extends
outside the baghouse 17 to the valve actuating mechanism
40 through an aperture in bottom wall 41 of the bag-
house 17.
In a baghouse instal]ation where poppet valvesaccording to 4the present invention are utiliæed, bag
filters (not~ ow~ are mounted by conventional means
in the interior of the baghouse 17. Typically, a
stream of dust-laden gas is directed into the interior
of each bag filter, whereupon dust is removed from the
gas stream and deposited as a cake on the inner surface
of the bag filter. Dust-free gas then passes through
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the fabric of each bag filter into the interior of the
baghouse 17. The dust-free gas is thereupon drawn
through opening 15 (or more typically through a plurality
of such openings) into the clean gas plenum 20. ThP
present invention, however, is not dependent upon the
direction of gas flow through the bag filters during
the filtering mode, and could be utilized in a baghouse
ins~allation wherein dust-laden gas flow during the
filtering mode proceeds in a direction from the exterior
into the interior of the bag filters so that the dust
cake forms on the exterior surfaces of the bag filters.
Regardless of w~lether the dust cake forms on the interior
or on the exterior surfaces of the bag filters in any
particular baghouse installation, a poppet valve according
to the present invention provides a reliable and relative-
ly inexpensive means for facilitating the cleaning of
the bag filters in the baghouse by the reverse gas flow
method.
Dust-laden gas flow in the normal direction must
be stopped and the valve 10 must be closed before/~
reverse flow of dust-free gas through bag filters~in
the baghouse 17 can be initiated. As indicated in FIG.
2, the force applied by the valve actuating mechanism
40 in moving the valve plate 30 into contact with the
seating ridge 21 may advantageously be large enough to
cause deflection of the valve plate 30 in order to
insure a gas-tight seal between the valve plate 30 and
the seating ridge 21.
Reverse gas flow serves to loosen the dust cake
from the surfaces of the bag filters~,Ywhereupon the
dust cake material can fall into appropriately disposed
hoppers of conventional design (not shown) for collection
and eventual removal from the baghouse 17. Reverse
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flow of dust-free gas through the bag filters tends to
collapse the bag filters inward (i.e., to deflate the
bag filter~). Upon re-establishment of dust-laden gas
flow in the normal direction, however, the bag filters
re-inflate to their normal configurations. If re-
inflation of the bag filters were to occur too abruptly,
the filte~ fabric might become weakened, unevenly
stretched, or torn. It is therefore important to
provide for gradual re-establishment of the normal
pressure difference between the baghouse 17 and the
clean gas plenum 20, following completion of reverse
-~ gas flow cleaning of the filter bags~ in the baghouse
17.
After the reverse gas flow cleaning operation has
been completed, dust-free gas flow in the reverse
direction through the bag filters is stopped and dust-
laden gas flow in the normal direction is re-established.
To re-establish gas flow in the normal direction, the
poppet valve 10 is opened (i.e., the valve stem 31 is
raised) by the valve actuating mechanism 40 at a con-
trolled rate that is determined on the basis of such
variables as the dimensions and material of the bag
filters, the nature and flow rate of the dust-laden gas
stream into the bag filters~, the nature and concentration
of the dust carried by the gas stream, and the rate at
which any of these variables changes or is likely to
change.
As the valve stem 31 is raised, the cylindrical
skirt 32 remains in the opening 15 until the bottom end
of skirt 32 is lifted fully into the clean gas plenum
20. The cylindrical skirt 32 is long enough in the
axial dimension to enable restricted gas flow through
- the opening 15 to be maintained until the bag filters ~4
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in the baghouse 17 have gradually re-inflated to a
sufficient e~tent so that "bag popping" or other adverse
consequences to filter fabric can be prevented. The
axial length of the cylindrical skirt 32 is selected as
appropriate for the variables that significantly affect
bag filter~ longevity at the particular baghouse installa-
tion.
Longitudinally extending slots 50 are provided on
the wall of the cylindrical skirt 32 to ena~le fine
control of the rate of gas flow through the opening 15
into the clean gas plenum 20. Alternatively, a longitu-
dinally extending array of holes could be used in
place of each longitudinally extending slot 50. Without
at least one such longitudinally extending orifice
portion on the skirt 32, the rate of gas flow through
the opening 15 would depend only upon the area of the
annular clearance between the circumference of the
opening 15 and the cylindrical wall of the skirt 32,
and would nct be affected by the rate at which the
valve stem 31 is raised as long as the skirt 32 is
still within the opening 15. With the slots 50, however,
the rate of gas flow through the opening 15 can be
gradually increased in a continuous manner by raising
the valve stem 31. The portion of each slot 50 extending
above the baghouse wall 16 increases as the valve stem
31 is raised, thereby enabling the rate of gas flow
through the opening 15 into the clean gas plenum 20 to
be precisely controlled by adjusting the rate at which
the valve stem 31 is raised.
1~
After the bag filters~ in the baghouse 17 have re-
inflated to their normal configurations, the valve stem
31 is further raised to where the cylindrical skirt 32
is positioned above the opening 15 to enable unrestricted
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gas flow from the baghouse 17 into the clean gas plenum
20. Filtration of dust from the dust-laden gas stream
passing through the fabric of the bag filters~Ythen
continues until the next time that reverse gas flow
cleaning of the bag filters~/~is scheduled to occur,
whereupon the poppet valve 10 is again closed and
reverse gas flow cleaning is repeated.
The present invention has been described above in
terms of a particular em~odiment, which is not to be
cônstrued in limitation of the invention but rather as
a disclosure of the best mode presently contemplated by
the inventor of carrying out his invention. The scope
of the invention is defined by the following claims and
their equivalents.
