FIELD OF THE INVENTION
The present invention relates to a supporting and guiding assembly for FBHE
(Fluidized Bed Heat Exchanger) coils. In particular, the invention relates to a
supporting and guiding assembly which permits relative free thermal movement
longitudinally and vertically and allow to maintain predetermined spacing
between the coils of vertically disposed bundles of tubes in thermal environment.
More particularly, the invention relates to an improved supporting and guiding
device for coils of the Fluidized bed heat exchanger (FBHE) which allows free
relative motion in axial and transverse direction.
BACKGROUND OF THE INVENTION
It is known that Primary function of a Heat Exchanger is to cool solids and
absorb heat to maintain a desired furnace operating temperature. Which is
normally done by cooling the solid collected from a cyclone separator and
circulating back the solid to a circulating Fluidized Bed (CFB) combustor through
a FBHE, where it gets cooled before being returned to the combustor. This
process enhances the performance and operational flexibility of a CFB Boiler.
A secondary function of the FBHE is to absorb heat from the solids to generate
steam, Superheat or reheat the steam to the level required for operation. A high
heat transfer rate is achieved resulting from such convective heat transfer from
particularto the submerged tube coils.
In order to increase quality of the steam, several approaches have been
proposed in the art. Among the known systems, circulating Fluidized Bed (CFB)
combustors have gained reputation as one of the most feasible means of solid
fuel combustion units.

In a FBHE Coils the bundles are vertically disposed in a refractory chamber and
are supported only at ends. Each coils assembly consists of a row of tubes and
only the extreme tubes are supported and rest of the tubes is supported on
extreme coils. The coils are placed in a bubbling bed of solid ash of maximum
temperature up to 600°C-700°C. Top portion of the coils are placed at maximum
temperature while bottom portion of the coils are placed at relatively lower
temperature.
US 4619315 A (Fluidized bed boiler in-bed tube support bracket), US 4637455 A
(Support rack for tubes immersed in a fluidised bed) discuss about supporting of
FBHE coils with a bottom support bracket and a support rack having plurality of
plates forming the support structure which is immersed in the fluidized.
However, the prior art do not teach supporting FBHE coils under thermal loads
(with differential expansion) without inducing high thermal stresses.
FBHE Coils are currently support on a sleeve and rod arrangement. The major
drawback of this prior art is that the coils are bunched together by sleeves at a
few discrete locations. However, the tube and the sleeve are subjected to
different temperatures. The tubes being susceptible to flowing steam, are always
maintained at a lower temperature compared to that of the sleeves which
directly get the bed temperature. Apart from the difference in temperature the
materials of the two components are also different for obvious reason. Hence,
differential thermal expansion of the two components poses a problem. In
normal course, the top sleeve and its pipe are welded at one end. All other tubes
are free in their sleeves. But due to hazardous operating atmosphere, the free
relative movement of the tubes is hindered. These two situations are studied by
a three dimensional analysis under differential temperatures, which show a high
stresses development in the tube sleeve junction which might initiate the failure.

Failures have been observed at these sleeve junctions which eventually lead to
bursting of the tubes.
The sleeve junctions which are welded together with connecting rods and tubes
forms three parts in the prior art with dissimilar materials, following are the
major issues related to this arraignment which have been emerged out during an
operating are-
Main failure observed in the prior art devices as noted, is for example shearing of
connecting rods due to weld failures between the rod and the sleeve junction,
which causes consistent friction between the sleeves and the tubes leading to
partial erosion of the tubes.
The fixed-sliding supporting systems of prior art is exposed to non-uniform
temperature along the different, longitudinal tube resulting in variation in the
thermal expansion of each tube, thereby inducing large bending stresses near
the connecting rod and sleeve junction. The thermal stresses so induced in the
rods and sleeve junctions are found to be on higher side than the allowable
stress limits leading to failure of weld or the rod whichever is weaker.
It has also been observed that high stresses are also induced in the prior art
system especially around fixed sleeve locations due to the fact that the welding
on both sides of the sleeve with tube leads to restraining of thermal strains, as
both are of dissimilar materials and with differential thermal expansions.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved supporting and
guiding device for Fluidized bed heat exchanger (FBHE) of the coils which allows
free relative motion in axial and transverse direction.

Another object of the invention is to propose an improved supporting and
guiding device for Fluidized bed heat exchanger (FBHE) of the coils which allows
free relative motion in axial and transverse direction, which is capable to
maintain predetermined closed spacing between the coils.
A still another object of the invention is to propose an improved supporting and
guiding device for Fluidized bed heat exchanger (FBHE) of the coils which allows
free relative motion in axial and transverse direction, which can delimits the total
deflection and thermal stresses to an acceptable limits.
A further object of the present invention is to propose an improved supporting
and guiding device for Fluidized bed heat exchanger (FBHE) of the coils which
allows free relative motion in axial and transverse direction, which is simple in
construction, and effective in operation.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved supporting and guiding device for
Fluidized bed heat exchanger (FBHE) of the coils which allows free relative
motion in axial and transverse direction. Thus, all the round sleeves are replaced
by end plates and intermediated circular stubs. This avoids welding of the tubes.
The lateral movement is arrested by means of stoppers welded to the tubes
which are of same material as coils.
The device comprises a plurality of held together by two vertical slide plates. This
sub-assembly of vertical sleeve holds all the tubes in their position with a
required gap. The sub-assembly is fitted on to the tube assembly by simply
sliding into tube bundle and at least two stopper plates (of same material as
tubes) are provided on both side of the tube bundle at top and bottom locations.
The tubes are supported in similar arrangement through the rod and slide plates

to allow sliding between the two stoppers. By this arrangement the rod is free to
slide over the tube bundle in longitudinal and transverse direction. Each of the
contact between the tube and rod is only a point contact. Thus, the tubes are
free to take up the deflected shape due to thermal or gravity load without
generating any extra stress in the device. This device also prevents any ash
locking inside the sleeve when cooling there by eliminating the ash fusion inside
the sleeve.
According to the invention the device consists of following constituent
components which are tabulated below in Table-I


BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows an elevation of the FBHE (Fluidized Bed Heat Exchangers)
Coils along with the supporting and guiding device of the invention.
Figure 2 - Shows an enlarged plan view of the supporting and guiding device
of the invention along with tubes of the FBHE.
Figure 3 - Shows the slide plates of the inventive device, oriented in (Y-
Direction) with the welded rods oriented in Z-direction.
Figure 4 - Shows the slide plats oriented in (Z-Direction) with welded rods
oriented in Y-direction.
Figure 5 - Shows a close up view of the stoppers location for the slide plates
in the inventive device.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Figure 1 - Shows the elevation of the coils of the FBHE (Fluidized Bed Heat
Exchangers) along with the supporting and guiding device. The coils are fixed at
the extreme end of the tubes. Figures 2,3 show the supporting arrangement
where, multiple front slide plates (1) are welded to plurality of first supporting
rods (5). This sub-assembly of front slide plates (1) and the first support rods (5)
are inserted into a tube bundle assembly form the side and a back slide plate (2)
is welded to the first support rods (5). All the slide plates (1 and 2), the first rods
(5) and the welds are same material which eliminates the problem of differential
thermal expansion, figures 2 and 5 show a top slide plate (3) a second plurality

of support rods (6), and a bottom slide plate (4) which are assembled and
welded as shown to maintain relative space between the tube bundles sets in Z
direction. Figure 5 shows a stopper plate (70 which is of same material as of the
tube bundle and welded on to the tubes to stop free sliding of all the slide plates
(1,2,3,4) and the rod (5,6) across the length (X direction) of the tube.

WE CLAIM
1. An improved supporting and guiding device for Fluidized bed heat
exchanger (FBHE) of the coils which allows free relative motion in axial
and transverse direction, the FBHE having coils in bundles vertically
disposed, the bundles consisting of a row of tubes in which only the
extreme tubes are supported and the remaining tubes of the bundle
supported on the extreme coils, the device comprising:-
- a plurality of front slide plates (1) welded to a first plurality of
supporting rods (5), each of the sub-assembly (1,5) sideably
inserted into a tube bundle and at least one back side plate (2)
welded to said first plurality of rods (5);
- at least one top slide plate (3), a second plurality of support rods
(6), and at least one bottom slide plate (4) welded together by
maintaining optimum gaps between the tube bundles; and
- at least one stopper plate (7) welded onto the tubes to prevent free
sliding of the slide plates (1,2,3,4) and the support rods (5,6)
across the length in X-direction of the tubes, wherein:-

- the front and back slide plates (1,2), the first plurality of support
rods, and the welds are of same material to eliminate differential
thermal expansion,
- said optimum gaps are maintained between the tube bundles in
Z-direction,

- the stopper plate is made of material identical to that of the tube
bundle.
2. The device as claimed in claim 1, wherein the front slide plates (1), and
the back slide plates (2) are disposed along vertical direction, and wherein
the top slide plates (3) and the bottom slide plates (4) are located along
out of plane direction.
3. The device as claimed in claim 1, wherein the first plurality of support
rods (5) are placed along Y-direction with rod-axis along Z-direction, and
wherein the second plurality of rods (6) are positioned along Z-direction
with rod-axis along Y-direction.

ABSTRACT

The invention relates to an improved supporting and guiding device for Fluidized
bed heat exchanger (FBHE) of the coils which allows free relative motion in axial
and transverse direction, the FBHE having coils in bundles vertically disposed,
the bundles consisting of a row of tubes in which only the extreme tubes are
supported and the remaining tubes of the bundle supported on the extreme
coils, the device comprising a plurality of front slide plates (1) welded to a first
plurality of supporting rods (5), each of the sub-assembly (1,5) sideably inserted
into a tube bundle and at least one back side plate (2) welded to said first
plurality of rods (5); at least one top slide plate (3), a second plurality of support
rods (6), and at least one bottom slide plate (4) welded together by maintaining
optimum gaps between the tube bundles; and at least one stopper plate (7)
welded onto the tubes to prevent free sliding of the slide plates (1,2,3,4) and the
support rods (5,6) across the length in X-direction of the tubes, wherein the front
and back slide plates (1,2), the first plurality of support rods, and the welds are
of same material to eliminate differential thermal expansion, said optimum gaps
are maintained between the tube bundles in Z-direction, the stopper plate is
made of material identical to that of the tube bundle.