Note: Descriptions are shown in the official language in which they were submitted.
BAC~GROUND OF THE INVE21TION
The present invention relates to a damper assembly
for closure of a gas duct ancl in particular is d~rected to a
valve assembly for closure of a duct used for conveying hot t
corrosive gas which carries a substantial quantity of dust.
In the oxidation of metal sulphides, e.g., by
roasting, sulphur dioxide is evolved which may be used in the
manufacture of sulphuric acid. Most of the dust in gas from
a roaster is separated in a precipitator be~ore the gas enters
a manifold from which gas streams from more than one roaster
are passed through scrubbing towers for further cleaning before
entering the sulphuric acid making process. Periodically it is
desirable to close off one duct to the manifold without inter-
rupting the flow from other ducts and without causing the
sulphur dioxide gas to escape to atmosphere or back up into the
closed duct However, since the gas is hot and corrosive and
since it carries a substantial quantity of dust which is not
removed by the precipitator, usual means of providing duct
; closure have proven to be ineffective.
In an operation in which a large rectangular cross
section duct has been closed by inserting a metal damper plate
transversely across the duct, corrosion and dust deposits
around the plate have made it difficult to move the plate between
open and shut positions. Presence of dust and corrosion products
has made it difficult to obtain adequate seals, either between
the upstream and downstream parts of the duct or between the
interior of the dust and the outer atmosphere. Use of manually
operated tools to force the damper plate into either open or
closed positions has obviated effective sealin~, and use of
mechanical driving means has been encumbered by unbalanced
forces resulting from uneven deposits of dust and corrosion
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products. Such unbalanced forces tend to buckle the damper
plate.
U.S. Patent 1,953,828 provides a horizontally acting
valve which prevents gushing of oil from a well. The valve
plate is guided by flanges on upper and lower casing plates as
rotation of a threaded shaft moves the plate into open and
closed positions.
U.S. Patent 1,97~,885 provides a vertically operating
gate in a hot gas line. Spring diaphragms spaced about the
conduit on one side of a gate plate act against mechanical
means applied to the other side of said plate to provide a
~ tight seal on closure and to release the plate for opening.
; Actuating mechanisms are isolated from the gas to protect them
from heat and dust.
The body of the blind assembly of U.S. Patent
2,354,967 for completely blanking off pipe lines has a
transverse slot with machined faces. Either a flow controlling
member or a blind having peripheral grooves to hold rubber
sealing members is inserted into the slot. Flexible lips of
the sealing members engage the machined faces of the body so
that, with any difference in pressure between the inslde and
the outside, outer or inner lips will move to make a seal.
l'he apparatus of U.S. Patent 2,702,178 has a valve
plate which is held in position between kwo disc sealing
members which encircle a gas conduit. Difficult operation of
the control mechanism due to settling of dust is prevented by
having one of the sealing members suspended about its section
of condult with sliding movement along the conduit being
controlled by a guiding ring which is between the sealing
member and the conduit. This ring and an outwardly bulging
elastic member together prevent gas escape.
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The slide valve assembly of U.S. Patent 3,047,024
moves vertically between flanged sections of gas lines. The
valve gate has a circular orifice to permit gas flow and a
solid disc blind which are supported by three coplanar plate
sections held together by edye strips. The circular orifice
and the solid disc have peripheral grooves which are filled
with gasket rings of rubber or with mixed rubber and asbestos
to provide gastight seals when the valve is open or closed.
Means are provided for exerting pressure on the seals in the
direction of the gas line axis. ~he slide gate may be guided
by side rollers mounted in the housing. The operating
mechanism is isolated from dust in the gas stream.
I'he line blind of U.S. Patent 3,099,292 discloses
the use of a pivotal flat spectacle plate in combination with
a pair of triangular body plates. Sealing is provided by
O-rings set into peripheral grooves formed in the end surfaces
:".
~ of aligned pipe sections and wedging means are provided to
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~ exert pressure on the rings.
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', In U.S. Patent 4,043,534, a sliding gate valve for
~ 20 a rectangular cross section gas duct is provided with side
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sealing means in the form of a resilient metal strip a,ttached
to the frame. The side edges of the gate make sealing contact
with the spring strip, and slide along the strip when the gate
is being closed. A flange mounted on the bottom of the frame
and extending inwar~ly to contact the downstream surface of
the gate when the gate is closed provides a bottom seal when
upstream fluid pressure presses the gate against the flange.
Top edge sealing may be provided by a similar flange or by
flat sealing strips mounted on opposing sides of the aperture.
U.S. Patent 4,093,245 provides tadpole tape sealiny
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means at the bottom of a rectangular cross section gas duc~.
Resilience of the tadpole tape~ backed by Z bar mounting,
causes shaped shim stock strips to bear against a closed
guillotine blade and to bear against each other when the
blade is withdrawn.
The foregoing patents are aenerally directed to the
application of mechanical or hydraulic forces along the axis
of the conduit to provide tight sealing against stationary
b~ffles and generally do not provide the maintenance of a gas
10 tight seal as the valve plate is being moved between open
and closed positions. When the damper plates of Patents
4,043,534 and 4,093~245 are open, there is no protection of
sealing means within the ducts against encrustation with
solids deposited from the gas stream. Good sealing engagements
on closure of the plates are not assured.
~ The damper asser~ly of the present invention
;~ provides sealing against gas leakage during movement between
~ ~.
~` open and closed positions, provides protection of sealing
surfaces against dust encrustation and does not require
20 movement of structural parts towards the plate faces for the
application of axial pressure necessary to maintain the seal
in the open and closed positions. Other advantages will
become apparent as the methbd and apparatus are described.
SUMMARY OF THE INVENTION
A damper assembly of our invention for use with a
rectangular cross section gas duct having a pair of aligned
duct sections with opposed open ends of equal height and
width spaced apart to define a transverse slot therebetween
broadly comprises a rectangular frame having vertical side
r,lembers substantially coextensive with and secured to sides
of the duct and extending both above and below the duct a
distance at least equal to the heiyht of the duct, frame
cross members substantially coextensive with and secured to
the upper and lower edges of the duct, a top frame cross
member spaced from the upper edge of the duct a distance
substantially equal to the height of the duct, a clamper plate
:~ having a length at least twice the height of the duct and a
width substantially equal to the width of the frame, said plate
having an opening formed therein at one end thereof substan-
. . tially equal to the duct opening, said damper plate slidably
; 10 supported within said frame for vertical reciprocal travel
whereby the opening in the damper plate can be moved into and
'::. out of alignment with the duct, a pair of upper and lower
~ cross-bars pivotally secured to upper and lower ends of said
:~ plate respectively mounted in said frame for reciprocal
:~/ vertical travel therein, piston-cylinder means connected to
each end of the upper and lower cross-bars for raising and
lowering the cross-bars and damper plate whereby the opening :
. formed in said damper plate can be alisned with the duct, and
means for sealing the damper plate against the frame to
:
prevent egress of gas from said duct when said damper plate
:~ is in an opened, closed or transitional position.
BRIEF DFSCRIPTION OF THE DRAWINGS
The damper assembly of the present invention will
: now be described with reference to the accompanying drawings
in which:
Figure 1 is a perspective view of the damper
assembly of the present invention,
mounted between opposing flanges of
a gas duct depicted by ghost lines,
shown in an open position;
Figure 2 is a front elevation of the dampex assembly
shown in Figure 1 in an open position;
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:. , ... ; : : ~
Figure 3 is a side elevation of the damper
assembly shown in Figure 1, in an open
position, illustrating the gas duct with
flexible connectoxs and duct supports;
Figure 4 is a verticaI section of the damper
assembly, .in an open position, taken
along line 4-4 of Figure 1;
Figure 5 is a vertical section of the damper
assembly corresponding to the view
1~ shown in Figure 4, in a closed position;
Figure 6 is a sectional view illustrating a
guide roller assembly and side sealing
;~: . means taken along line 6-6 of Figure 2;
Figure 7 is a perspective view oE the damper
; plate of the invention;
: Figure 8 is a cross section of the knife edge
: along the upper edge of the damper plate
opening taken along line 8-8 of Figure 7;
and
Figure 9 is an enlarged portion of Figure 4
illustrating upper sealing means.
Like reference characters refer to like parts
throughout thç description of the drawings~
: DESCRIPTION OF THE PREFERRED EMBODIMENTS
With ref~rence first to Figure 1, rectangular
frame 10 of the damper assembly of the invention is shown
- mounted between sections of a gas duct depicted by ghost
lines. Figure 3 illustrates more clearly the relationship
between Frame 10 and duct 12 wherein spaced apart and
aligned opposing duct flanges 14 define a transverse slot
therebetween for receiving frame 10. Flexible expansion
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joints 16 are rigidly secured to duct flanges 14 on one side
and to flange adapters 18 on the other and the flange adapters
in turn secured to frame 10 by a plurality of cap screws, not
shown. Duct 12 is supported by posts 200 Damper frame 10 is
separately supported by footings 22 and is therefore not
affected by stresses that would otherwise be caused by thermal
expansion of the duct.
;~ As shown most clearly in Figures 1, 2, 4 and 5,
frame 10 preferably consists of two spaced-apart pairs 24 of
rectangular tubular members 26 defining slot 27 and inter-
connected by upper, central and lower cross-bars~ Central
cross-bars 28 at the upper edge of duct 12, and upper and
lower cross-bars 30~32 respectively, are rigidly a~tached
to tubular members 26. Central cross-bars 28 and lower cross-
bar 32 are aligned with the front and rear faces of members 26
to proyide a planar surface for sealing engagement with flange
~; adapters 18. Upper cross-bar 30 is shown by ghost lines in
; Figure 1 for clarity of illustration of the underlying
components. Each pair 24 of tubular members 26 and central
cross-bars 28 are spaced apart as shown by slot 27 in
Figures 4, 5 and 6 to accommodate the thickness of damper plate
34 and sealing means 36,38 therebetween, to be descrihed.
External arcuate reinforcing structures 40l Figures 1 and 2,
and equi-spaced transverse spacers 42, Figure 6, are provided
to rigidly secure the side members 26 of frame 10 a fixed
distance apart.
Damper plate 34, shown most clearly in Figures 7 and
8, is formed of a corrosion resistant rigid material, prefer~
ably a one-piece stainless steel sheet, having a solid
imperforate upper baffle portion 44 which provides closure of
the duct and a rectangular opening 46 in the lower portion 48
which can be aligned with rectangular cross section duct 12 to
permit gas to flow through the duct. Top edge 50 of damper
openlng 46 is tapered to provide downwardly pointing knife edge
52 which, on lowering of the damper plate, contributes to
improved closure, as hereinafter explained. Reinforcing bars
54 are attached to both faces of damper plate 34 near side
edges 56.
As shown in detail in Figure 6, damper plate 34
extends laterally between opposed pairs of tubular members 26
with attached reinforcing side bars 54 being adapted to move
~;~ freely between members 26. Central location of damper plate
34 between members 26 is provided by guide rollers 58 which
~: are journalled equi-spaced along the central portions 60 of
the sides of frame lO by pairs of pillow block bearings 62.
- Preferably, side edges 56 of damper plate 34 project beyond
guide bars 54 to be engaged by peripheral grooves 64 formed
in rollers 58. Grooves 64 are sufficiently wide to accommodate
thermal expansion of plate 34.
Referring now to Figures l and 2, brackets 66,68
centrally mounted on the upper and lower edges respectively
: of damper plate 34 are pivotally attached to upper and lower
horizontal support cross-bars 70,72. Roller assemblies 74,
each comprising four cam yoke rollers 76, are mounted near the
ends of upper and lower cross-bars 70,72 exterior of frame-lO
and are spaced to engage parallel, vertical tracks 78 attached
to the sides of frame lO and extending respectively above and
below gas duct 12. These rollers provide primaxy guidance for
vertical reciprocal travel of damper plate 34 within frame lO.
Two double-acting hydraulic cylinders 80 are
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pivotally attached to brackets ~2 whicll in turn are fastened
to central port~ons 60 of ~he sides of frame 10, as shown most
clearly in Figures 1 and 2. Piston rods 84 extend through
cylinders 80 and engage notches 86 at the ends of upper and
lower cross-bars 70,72 by a c]evis 87 at each end of rods 84
; (shown partly cut away in Figure 1). Hydraulic activating
means, well known in the art and not shown, apply fluid
pressure through tubes 88, Figure 2, to effect selective upward
and downward reciprocal movement of damper plate 34. Piston
rods 80 exert only pushing forces on the cross-bars. There is
no pulling that may impose compressive, buckling force on the
damper plate.
Sealing means comprising upper, side and lower means
36,38 and 90 respectively are provided to prevent passage of
gas to atmosphere while the damper is open, closed or is being
` moved between open and closed positions, and to prevent passage
of gas between upstream and downstream portions of the duct
when the damper is closed. Sealing means 38 on each side of
the damper plate is provided by two elongated strips of
tadpole tape 9~ which are vertically disposed adjacent side
edges 93 of plate openings 46 and which are supported by a
plurality of rigid holding means 94 mounted along the inner
faces of tubular frame members 26. The ends of strips 92
abut the ends of upper sealing means 36 and lower sealing
; means 90 in a sealing contact. As shown in Figure 6, tadpole
tape 92 comprises cylindrical body portion 96 wherein core 98
lS enclosed by cover 100 and a tail portion 102 in which the
ends of cover 100 are sealed together. Correspondingly
;~ cylindrically curved recesses 104 in holding means 94 partially
envelope the ~ody portion to restrain it against lateral
displacement. Top sealing means 38 is shown more clearly in
Figure 9, an enlargement of part of Figure 4. Horizontal
g
strips of the tadpole tape 106 are supported by holding means
108 mounted on underfaces of cross-bars 28 of frame 10l and
span the width of baffle portion 44 at a level adjacent th0
top wall of the gas duct. The tadpole tape strips are adjus-ted
to bear securely against opposite faces of damper plate 34.
; On opening or closing of the clamper, side strips 92
continuously engage clean face portions of damper plate 34 in
paths which are parallel to and adjacent the sides of damper
plate opening 46~ These paths are covered by the strips at
all times. On closing of the damper, the top mountecl strips
of tadpole tape sweep surfaces of the damper plate which were
outside the duct zone. On opening of the damper, dust which
may be on the damper plate surface falls into the duct as the
plate advances past the horizontal strips. The dust does not
accumulate against the strips if a smooth face, corrosion
resistant damper piate, e.g., stainless steel, is used. Only
a small amount of dust accumulates on a smooth plate while it
is in its closed position, and use of stainless steel provides
resistance to corrosion that would cause pitting of the
surface and increased dust retention.
Tadpole tape for providing seals is commercially
available in materials of construction which meet speciic
tempexature and the like operating requirements. It is
generally reco~nended for applications in which sealing
surfaces are brought together without relative movement in
directions other than that in which contact pressure is
applied, e.g. the metal strip enclosed tape of United States
Patent 4,093,245. For the present application, i.e. the
handling of hot, dust-bearing sulphur dioxide, corrosion
resistance at high temperatures, low gas permeability,
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resilience when compressed and an erosion resistant cover
are required~ Tadpole tape having a stainless steel or
INCONEL (Trade Mark for a corrosion resistant nickel-chromium
alloy) wire mesh core and covered by woven, wire-reinforced
asbestos strands has ability to withstand gas temperatures of
; 400C. Sealing of the surface, e.g. with aluminum paint,
reduces gas porosity.
As previously stated, the body of the tadpole tape
is supported by partial enclosure within complementary
recesses 104,110 of tha holding means. Because of lateral
thrust which tends to dislodge the horizontally disposed top
strips as the damper plate is moved,`enclosure of about one-
half of the diameter of the body of the tape by recesses 110,
Figure 9, is preferred. Since the vertically disposed side
tapes are not subjected to this lateral thrust, enclosure of
one-third of diameter of the tape by recesses 104, Figure 6,
is sufficient for the side tapes. This is advantageous in
that the tape may be compressed to a greater extent in its
engagement with the damper plate, thus providing a wider,
flattened sealing surface. Tadpole tape having a diameter of
0.75 inch provided effective sealing. A larger diameter,
e.g. 1.25 inch, provides more sealing surface and is preferred.
When the damper is open, as shown in Figure 4,
bottom sealing to prevent passage of gas to atmosphere is
provided by a horizontal corrosion resistant plate 90 mounted
on lower cross-bars 32 to span, at the level of the inside of
the floor of the duct, the gap within which damper plate 34
moves. A slot 112 at each end of plate 90, Figure 1, permits
vertical travel of the sides 114 of damper plate 34 adjacent
the gas flow opening 46 which are in engagement with tadpole
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,
tape strips 92. The bottom ends of side strips 92 butt
against portions of the cross-bar which enclose the slot, in a
gas tight sealing contact. The edges of the slots and the
damper plate are in a close fitting arrangement which, with
accumulated dust on the duct floor, completes the seal. When
the damper is in its elevated open position, the bottom border
116 o gas flow opening 46 is below but adjacent horlzontal
plate 90.
Top border 50 of damper plate opening 46 is provided
with a knife edge 52 so that, when the plate is lowered, as
shown in Figure 5, the knife edge penetrates into dust which
tends to accumulate and cake on the duct floor to form a zone
of packed dust between knife edge 52 and horizontal plate 90
to provide an effective bottom seal. Knife edge 52 is
machined to engage the full length of a clean plate 90 closely
to ensure closure in the absence of dust, and its faces
preferably are symmetrical, meeting at a 90 angle.
Damper plate 34 is moved vertically between open
and closed positions by action of hydraulic cylinders 80 which
push on upper and lower cross-bars 70,72~ The hydraulic
mechanism, with engagement of the piston rods by slots at the
ends of the cross-bars, assures tension on the damper plate
during both opening and closing. No compressive ~orces are
exerted on the plate as piston rods retract towards the
cylinder. This action, with pivotal mounting and side roller
guidance previously described, avoids torques which could
buckle the plate, while independent support means for the
assembly provides freedom from stresses that might be caused
by thermal expansion of the duct.
All guiding means are mounted outside the duct,
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away from corrosive gases, while corrosion resistant material
is used for all parts having contact with the gases. The
sealing means prevents passage of gas to atmosphere while the
damper is open, closed or is being moved between open and
closed positions.
.~ .
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