The present invention relates to a device for controlling
the flow of air into a direct fired air heater. More
specifically, the invention relates to a device for controlling
the flow of non-combustion air into a direct fired air heater.
The products of combustion in the direct fired air heater
mix freely with the non-combustion air and exit as a single
stream of gas. The combustion normally takes place inside a
combustion chamber. The burner that burns the fuel is mounted
to the end wall of the combustion chamber.
A large passage is normally provided for the entry of the
non-combustion air which is allowed to mix with the products
of combustion. This passage may take the form of a circular
opening on the shell itself.
In other improved designs, for example, in the air heater
of the co-pending application this may take the form of an
annular opening at the upstream end of the direct fired heater
between the outer diameter of the combustion chamber and the
inner diameter of the outer casing of the heater.
However, to create a desirable stream velocity in the
outgoing gas, it may be required to control the flow of the
non-combustion air into the direct fired air heater.
Usually a number of vanes are provided in the cirular or
the annular passage. These vanes are operated manually for
controlling the opening through the vanes, thus controlling
the flow of non-combustion air.
Controlling the vane openings individually can be a difficult
process to carry out and the air flow achieved will not be
uniform.
The object of this invention is to provide a control device
for achieving the desired uniform flow of non-combustion air
through the vanes of a direct fired air heater.
This objective is achieved by connecting the operating
stems of all the identical vanes of the air heater by means
of a wire rope passing through a block. Movement of the wire
rope in either of the two directions causes the vane to rotate
along its axis between full open and full shut position.
Thus the present invention provides a device for controlling
the flow of non-combustion air into a direct fired air heater
comprising a plurality of identical vanes formed in the annular
space between inner and outer walls of air heater, each vane
capable of rotation about respective vane axis by means of a
stem brought out on the outer casing of the heater, a block
attached to a screw, a lever fitting slidably through the head
of said screw and connected to a hub attached to said stem,
a hollow screw located between two cleats provided on the outer
casing of air heater, said screw held in position by a nut so
that said screw can move along its axis by turning said nut
a wire rope connected to all of said blocks, passing through
said hollow screw and looped, so that longitudinal motion of
said screw results in corresponding movement of wire rope turning
all the vanes.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig.l shows the annular space between the outer casing
and the combustion chamber provided with a number of identical
vanes.
Fig. 2 shows the arrangement for simultaneously rotating
the vanes along their respective axis.
Fig.3 shows the device for effecting the required movement
of the wire rope for operation of the vanes.
The device will now be described in detail with the help
of the accompanying drawings.
In Fig.l an annular area is formed by the wall 4 of the
outer casing of the air heater and the wall 5 of the combustion
chamber of the air heater.
This annular area is covered by a number of identical vanes
1. These vanes are formed by attaching two sheets of metal covers
around a stem 2. This stem is supported by two bushes 3 welded
to the walls 4,5.
Details of the arrangement for turning the vanes
simultaneously about their respective axis through the same
angle is shown in Fig.2.
A hub 9 is attached to the stem 2 on its outer side. This
may be locked by a grub screw not shown. A lever 8 made from
a round bar is screwed on to the hub 9. This may also be locked
by a hexagonal nut. This lever 8 passes through the head of
a screw 10 where a cross hole is drilled to result in a sliding
fit.
The screw 10 is fitted to a block 6 where a cross hole
is also drilled. A small diameter wire rope 7 passes through
the block 6. This is also locked by a grub screw.
Movement of the wire rope 7 in the direction of the arrow
shown results in the rotation of the vane. It is adequate to
impart a rotation of nearly 90° to the vanes which covers all
positions between full open to full shut. Therefore, the bar
8 need only swing between _+ 45°.
In order to effect the required movement of the wire rope
7 a mechanism shown in Fig.3 is used.
Two small cleats 11 are welded to the outer shell of the
direct fired heater with a central hole and bottom clearance.
A long screw 12 with a hexagonal head and a central hole
is passed through the cleats 11 and is retained by a hexagonal
nut 13 located between the two cleats. If the hexagonal nut
13 is turned while the screw 12 is held, it moves along its
axis through a specific distance, depending on the number of
turns.
The screw 12 is made hollow by drilling through its axis.
The hole is also counter-sunk at both ends.
The wire rope 7 is passed through the hole in the screw
12 and looped,so that the longitudinal motion of the screw 12
results in the corresponding movement in the wire rope 7. To
ensure better locking and eliminate slippage, a grub screw 17
may be used in the head of the screw 12, to bear on to the wire
rope 7.
The wire rope 7 is made to pass around the wall 4 of the
outer casing of the heater, passing through all the blocks 6,
turning all the vanes 1 .
The ends of the wire rope 7 are connected by a suitable
tensioning device,not shown, like a turn buckle, so that no
slack is created in the wire rope and there is no lost motion
in the vanes 1.
A graduation 18 on the outer surface of the outer casing
near the screw 12 exhibits the angular position of the vanes
1.
The wire rope 7 may be guided by short tubes 14 attached
to the outer wall 4 of the outer casing.
The system described allows a large number of vanes to be
formed through the a sarae angle within an annular area.
WE CLAIM:
1. A device for controlling the flow of non-combustion air
into a direct fired air heater, comprising
a plurality of identical vanes formed in the annular
space between inner and outer walls of air heater;
each vane capable of rotation about respective vane axis
by means of a stem brought out on the outer casing of the
heater;
a block (6) attached to a screw (10);
a lever (8) fitting slidingly through the head of said
screw (10) and connected to a hub (9) attached to said stem
(2);
a hollow screw (12) located between two cleats (11)
provided on the outer casing of air heater, said screw (12)
held in position by a nut (13) so that said screw (12) can move
along its axis by turning said nut (13);
a wire rope (7) connected to all of said blocks (6),
passing through said hollow screw (12) and looped;
so that longitudinal motion of said screw (12) results
in corresponding movement of wire rope (7) turning all the vanes.
2. The device as claimed in claim 1, wherein said stem (2)
of the vane is supported by two bushes (3) welded on to the
inner and outer walls.
3. The device as claimed in claims 1 and 2, wherein said
hub (9) is attached to the outer side of stem (2).
4. The device as claimed in preceding claims wherein said
lever (9) screwed on to said hub 9.
5. The device as claimed in preceding claims, wherein said
lever (8) screwed to said hub (9) is locked by a hexagonal nut
(19).
6. The device as claimed in preceding claims wherein said
cleats (11) are welded on to the outer casing of the heater
with a hole and bottom clearance.
7. The device as claimed in preceding claims wherein said
hollow screw (12) is with a hexagonal nut and the central hole
is counter-sunk at both ends.
8. The device as claimed in preceding claims wherein said
wire rope (7) is locked on to the hollow screw (12) by means
of a grub screw (17) to eliminate slippage.
9. The device as claimed in preceding claims wherein the
ends of said wire rope (7) are connected by a tensioning device
to avoid a slack in the wire rope.
10. The device as claimed in claim 9 wherein said tensioning
device is a turn buckle.
11. The device as claimed in preceding claims wherein a
graduation is provided on the outer surface of the outer casing
near said screw (12) showing the angular position of vane
opening.
12. The device as claimed in preceding claims wherein said
wire rope (7) is guided by short tubes (14) attached to the
wall of the outer casing.
13. The device substantially as herein described and
illustrated in the accompanying drawings.

A device for controlling the flow of non-combustion air
into a direct fired air heater, comprising
a plurality of identical vanes formed in the annular
space between inner and outer walls of air heater;
each vane capable of rotation about respective vane axis
by means of a stem brought out on the outer casing of the
heater;
a block (6) attached to a screw (10);
a lever (8) fitting slidingly through the head of said
screw (10) and connected to a hub (9) attached to said stem
(2);
a hollow screw (12) located between two cleats (11)
provided on the outer casing of air heater, said screw (12)
held in position by a nut (13) so that said screw (12) can move
along its axis by turning said nut (13);
a wire rope (7) connected to all of said blocks (6),
passing through said hollow screw (12) and looped;
so that longitudinal motion of said screw (12) results
in corresponding movement of wire rope (7) turning all the vanes.