FIELD OF THE INVENTION
The present invention relates to a rigid and reliable support device for heat transfer
surfaces in a fluidized bed combustion boiler.
BACKGROUND OF THE INVENTION
Heat transfer surfaces such as Superheater, Reheater and Evaporator bundles are
provided and kept immersed inside an inert bed material to recover the heat of solid
particles available in the bed of fluidized bed combustion boilers. The bundles are
kept inside a chamber with inlet and outlet headers of the bundles kept outside of
the chamber being connected through tubes penetrating the walls of said bundle
chamber. The bundles are either suspended from top or supported from bottom
based on a coil penetration location with respect to walls of the bundle chamber.
There are number of tube rows or parallel flow paths with defined spacing in
between the tube elements. Just below the tube bundle, a plurality of air nozzles are
provided in grate for proper fluidisation of the bed material.
In fluidized bed combustion boilers, heat transfer surfaces for example, tube bundles
are immersed in the fluidized bed material which consists of inert particles and
crushed coal particles. The plurality of tubes are arranged as rows and columns with
definite spacing in between the tubes. The tube elements are subjected to internal
steam pressure, temperature and other dynamic forces of fluidization.
Normally the supports provided for said horizontal heat transfer surfaces are located
in second pass of the conventional boilers, and the surfaces are exposed only flue
gas flow as to the external medium. But, in case of a fluidized bed, the tube
bundles are in physical contact with agitating solid particles since they are
immersed in the fluidized bed. Hence, conventional supports are not adequate for
fluidized bed environment due to the dynamics of fluidisation. In order to overcome
the problems , the tube bundles need to be supported inside the bundle chamber to
cater for the self weight of the bundle, tube thermal expansion and the dynamic

forces due to fluidisation. Further, the supports need be rigid enough to take care of
the above forces. Considering the operating regime inside the fluidized bundle
chamber, new kind of support for the tube bundles inside the fluidized bed need to
be developed.
US 4270599 teaches a support structure for supporting the tube bundles in a
fluidized bed heat exchanger. A grid plate is supported in the housing for receiving
bed particulate material. A perforated support pier projects out from the grid plate
and supports the tube bundles and passes the air over the tubes. A ladder type
support structure is provided between adjacent tube sections to support the tube
sections relative to each other.
US4619315, describes a hot support bracket for supporting an in bed heat
exchanger tubes inside a fluidized bed furnace. It comprises a plurality of plates
having openings or cut outs at one edge for housing the tubes. Adjacent plates are
connected for stability. The vertical support plate rests on a wear channel on which
the load of the tubes are transferred and having provision for sliding.
US 4637455, discloses a hot support rack for supporting an in bed heat exchanger
tubes inside a fluidized bed furnace. It consists of number of support plates disposed
diagonally between spaced vertical support posts.The support platesforms criss-
cross array of quadrangular openings through which the tube elements passes and
supported.

US 5943985 teaches Welded bracket for supporting SH & RH coils inside a fluidized
bed, and engages one tube firmly with other vertical tube. The bracket is welded on
both the tubes to prevent a relative movement between the tubes. The tubes can
not move with respect to each other. The tubes have angular surface contact with
bracket for an intimate thermal contact with the tubes.
US 4961402 discloses a device for suspending a horizontal tube on a vertical support
tube. An element for securing the horizontal tube in the general form of a cradle
consists of two symmetrical cylindrical cross bars and two connecting members in
the cross bars forming an arc of the circle. Two elements for securing the vertical
tubes and interlocking by engagement of their recess with the wedge shaped parts
of the cross bars and welded to the vertical tubes along the lateral edges.
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose a rigid and reliable support
device for heat transfer surfaces in a fluidized bed combustion boiler.
Another object of the invention is to propose a rigid and reliable support device for
heat transfer surfaces in a fluidized bed combustion boiler, which is capable to
withstand the harsh operating temperature inside the bed including thermal
expansion forces and the dynamic forces of fluidisation.

SUMMARY OF THE INVENTION
Accordingly, there is provided a rigid and reliable support device for heat transfer
surfaces in a fluidized bed combustion boiler, comprising at least one vertical steam
cooled hanger tube placed in between a pair of horizontal coil assemblies ; and a
solid forged strap connecting the horizontal coils to the vertical tube the vertical
tube having a central hole configured with close tolerances to allow insertion of the
forged strap into the vertical tube by shrink fit and welded.
According to the invention the cooled and rigid support device is formed of solid forged
strap along with steam cooled hanger tubes to support the tube bundle.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Fig 1.- shows overall view of a tube bundle acting as heat transfer surfaces in a fluidized bed
combustion boiler.
Fig. 2- shows elevational and plan views of the tube bundles.
Fig. 3- shows assembled view of the tube bundles
Fig. 4 - shows single starp exploded view
Fig. 5- shows split starp exploded view
DETAILED DESCRIPTION OF THE INVENTION
As shown in fig. 3, a vertical steam cooled hanger tube (1) is placed in between two
horizontal coil (2) assemblies. The two horizontal coils (2) are connected to the
hanger tube (1) through a solid forged strap (3) having corresponding configuration
to accommodate the hanger tube (1) and the coil assemblies (2). The forged straps
(3) are inserted by shrink fit into the vertical hanger tubes (1) and held in position

by welding with the hanger tube (1). A central hole as shown in fig. 4 for inserting
the strap (3) into the hanger tube (1) is made with close tolerances to allow the
shrink fit. Alternatively, the forged strap (3) may also be split into two pieces (3) and
as shown in fig. 5, welded together with the hanger tube (1) to form an integral
assembly. The assembled straps (3) along with the vertical hanger tube (1) is
inserted in between the two horizontal coil (2) assemblies. The horizontal coil
elements are pushed into a semicircular profile available on both sides of the strap
(3). Two semicircular end caps (4) are assembled from both ends of the strap (3) to
keep the horizontal coil element (2) in position. The end caps (4) are welded with
the strap (3) after inserting the coil (2) into position. It is ensured that welding
over the horizontal tube element (2) is completely avoided. The welding process
adapted according to the invention , allows the tube (1) to move along its length
inside the strap freely due to thermal expansion. Similarly, each pair of the
remaining horizontal coils (2) are assembled to the vertical hanger tubes (1). The
number of hanger tubes (1) per row of support is half the number of horizontal coil
assemblies (2) since there is one hanger tube (1) for each pair of coil assemblies
(2). The vertical hanger tubes (1) are suspended from a roof casing of the bundle
chamber. There are two rows of hanger tube support for the tube bundle to make it
a simply supported configuration.

WE CLAIM
1. A rigid and reliable support device for heat transfer surfaces in a fluidized bed
combustion boiler, comprising:
- at least one vertical steam cooled hanger tube (1) placed in between a pair of
horizontal coil assemblies (2); and
- a solid forged strap (3) connecting the horizontal coils (2) to the vertical tube
(1), the vertical tube (1) having a central hole configured with close tolerances
to allow insertion of the forged strap (3) into the vertical tube (1) by shrink fit
and welded.

2. A rigid and reliable support device for heat transfer surfaces in a fluidized bed
combustion boiler, wherein the forged strap (3) comprises semicircular profile
at both ends, and wherein end caps (4) are provided to maintain the
horizontal coils (2) in position.
3. A rigid and reliable support device for heat transfer surfaces in a fluidized bed
combustion boiler, wherein the vertical tube (1) is axially movable within the
forged strap (2) even when the tube undergoes thermal expansion, and
wherein welding over the horizontal tubes (2) is avoided during the assembly
of the forged strap (3), the vertical tube (1) and the horizontal tubes.
4. A rigid and reliable support device for heat transfer surfaces in a fluidized bed
combustion boiler, wherein the number of vertical tubes (1) per row of support
is half the number of horizontal coil assemblies (2).
5. A rigid and reliable support device for heat transfer surfaces in a fluidized bed
combustion boiler, wherein the vertical tubes are suspended from a roof
casing of a bundle chamber.
6. A rigid and reliable support device for heat transfer surfaces in a fluidized bed
combustion boiler, wherein the forged strap comprises multiple pieces welded
together with the vertical tube to form an integral assembly.

ABSTRACT

The invention relates to a rigid and reliable support device for heat transfer surfaces
in a fluidized bed combustion boiler, comprising at least one vertical steam cooled
hanger tube (1) placed in between a pair of horizontal coil assemblies (2); and a
solid forged strap (3) connecting the horizontal coils (2) to the vertical tube (1), the
vertical tube (1) having a central hole configured with close tolerances to allow
insertion of the forged strap (3) into the vertical tube (1) by shrink fit and welded.