FIELD OF INVENTION
The present invention relates to heat transfer surfaces such as superheater,reheater
and evaporator bundles disposed in fluidized bed combustion boilers.
More particularly, the present invention relates to a heat conducting support device
for horizontal coils located in the bundle chamber of fluidized bed combustion
boilers.
BACKGROUND OF 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 3267913 describes a support arrangement for bundle of heat transfer tubes
located in the vertical pass. The vertical support tubes are having fins on both sides
having recess or cutouts to suit the profile of the horizontal tubes. The horizontal
tubes are welded with the fins with the are of the notched out surface. The fins
serving as support element for bundle tubesare cooled to a high degree with
reduced stress levels.
US 4270599 discloses 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.
US 5943985 teaches Welded bracket for supporting SH & RH coils inside the
fluidised bed engages one tube firmly with other vertical tube. The bracket is welded
on both tubes that will prevent the relative movement between the tubes. The tubes
can not move with respect to each other. The tubes have angular surface contact
with bracket for intimate thermal contact with the tubes.

US4619315, describes a hot support bracket for supporting the in bed heat
exchanger tubes inside the fluidized bed furnace, it comprised 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 3265044 describes a device for supporting a horizontal heat transfer serpentine
tube on a vertical tube with slidable arrangement. It is free to expand without
overstressing the support tube. One part of the support is welded to the vertical
tube where as another part with groove is welded to the horizontal tube. The sliding
joints are free from jamming due to ash accumulation.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a heat conducting support device
for horizontal coils located in the bundle chamber of fluidized bed combustion
boilers.
Another object of the invention is to propose a heat conducting support device for
horizontal coils located in the bundle chamber of fluidized bed combustion boilers.
Another object of the invention is to propose a heat conducting support device for
horizontal coils located in the bundle chamber of fluidized bed combustion boilers,
which can withstand the operating temperature inside the bed including thermal
expansion forces and the dynamic forces of fluidisation.

A further object of the invention is to propose a heat conducting support device for
horizontal coils located in the bundle chamber of fluidized bed combustion boilers,
which is capable of being cooled properly during operation of the boiler.
SUMMARY OF INVENTION
Accordingly, there is provided a heat conducting support device for horizontal coils
located in the bundle chamber of fluidized bed combustion boilers comprising at
least one vertical steam cooled hanger tube allowing a plurality pairs of horizontal
coils to be shrink fitted through at least one solid forged strap with the vertical
tube; and a spacer sleeve provided in between each pair of forged straps , wherein
each strap is provided with a central hole including a countersunk groove, and
wherein the central hole is constructed with close tolerance to allow the shrink-fil of
the forged strap and the tube assembly .
Thus the invention provides a cooled and rigid support arrangement with solid forged
tight fitting heat conducting straps along with steam cooled hanger tubes are
envisaged as tube bundle support.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1- shows an overview of tube bundle following a heat transfer surface of a
fluidized bed combustion boiler.
Fig. 2- shows a plan view and an elevational view of the tube bundle .
Fig. 3- shows an assembled view of the heat transfer surface supported by a heat
conducting supporting device of the invention.
Fig. 4- shows an exploded view of the heat conducting support device of the
invention.

DETAILED DESCRIPTION OF THE INVENTION
A vertical steam cooled hanger tube (1) is disposed in between two horizontal coil
(2) assemblies. The two horizontal coils are connected to the hanger tube through a
solid forged shrink fit strap (3) with a configuration to accommodate the hanger
tube (1) and coil assemblies (2). The forged straps (3) are inserted into the vertical
hanger tubes (1) by shrink fit between the strap and tube. A spacer sleeve (5) is
provided in between the forged straps (3) which fits into a countersunk groove
provided in the strap (3). Only the top most and bottom straps (3) are welded with
the hanger tube. The central hole (b) for inserting the strap into the hanger tube is
made with close tolerances so that a shrink fit is ensured between the forged strap
and the hanger tube for effective cooling of the strap. The assembled straps along
with the vertical hanger tube (1) is inserted in between the two horizontal coil (2)
assemblies. The horizontal coil elements (2) are pushed into a semicircular profile
available on both sides of the strap. There is a groove available in the forged strip
(3) to accommodate the end caps (4). The two semicircular end caps (4) are
inserted into the groove (6) in the forged strap and assembled from both ends to
keep the horizontal coil element in position. The end caps (4) are welded with the
forged strap (3) after inserting the coil (2) into the position. Because of this groove
fitting, a tight fit is ensured between the forged strap and the horizontal coils so that
there is better cooling of the strap during operation. Care should be taken that there
should not be any welding over the horizontal tube element (2) so that the tube can
move along its length inside the strap freely due to thermal expansion. Similarly
each pair of the remaining horizontal coils (2) are assembled to vertical hanger tubes
(1). The number of hanger tubes (1) per row of support (1) 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 of the boiler. There are two rows of hanger tube support for the
tube bundle to make it a simply supported configuration.

WE CLAIM
1. A heat conducting support device for horizontal coils located in the bundle
chamber of fluidized bed combustion boilers comprising:
- at least one vertical steam cooled hanger tube (1) allowing a plurality pairs of
horizontal coils (2) to be shrink fitted through at least one solid forged strap
(3) with the vertical tube (1); and
- a spacer sleeve (5) provided in between each pair of forged straps (3),
wherein each strap (3) is provided with a central hole (6) including a
countersunk groove, and wherein the central hole (6) is constructed with
close tolerance to allow the shrink-fil of the forged strap (3) and the tube
assembly (1,2).

2. A heat conducting support device for horizontal coils located in the bundle
chamber of fluidized bed combustion boilers, wherein the horizontal coils (2)
are provided with semicircular profile at both ends which are cover with end
caps (4).
3. A heat conducting support device for horizontal coils located in the bundle
chamber of fluidized bed combustion boilers, wherein the horizontal coils (2)
in the welded assembly (1,3) is free from any welding such that the coil (2)
can axially move within the strap (3) due to thermal expansion during
operation of the boiler.
4. A heat conducting support device for horizontal coils located in the bundle
chamber of fluidized bed combustion boilers, wherein the number of vertical
tube (1) per row of the device is half the number of horizontal coil assemblies
(2).

5. A heat conducting support device for horizontal coils located in the bundle
chamber of fluidized bed combustion boilers, wherein the vertical tubes (1)
are suspended from a roof casing of the bundle chamber of the boiler.

ABSTRACT

The invention relates to a heat conducting support device for horizontal coils located
in the bundle chamber of fluidized bed combustion boilers comprising at least one
vertical steam cooled hanger tube (1) allowing a plurality pairs of horizontal coils (2)
to be shrink fitted through at least one solid forged strap (3) with the vertical tube
(1); and a spacer sleeve (5) provided in between each pair of forged straps (3),
wherein each strap (3) is provided with a central hole (6) including a countersunk
groove, and wherein the central hole (6) is constructed with close tolerance to allow
the shrink-fil of the forged strap (3) and the tube assembly (1,2).