FIELD OF THE INVENTION
The present invention relates to a reliable inverted strap type support device for
supporting one horizontal tube and two fluid cooled hanger tubes.
BACKGROUND OF THE INVENTION
In conventional pulverized coal fired boilers and CFBC boilers, horizontal heat
transfer surface like Superheaters, Reheaters and Economisers are normally
located in the second pass. The flue gas from the furnace flows vertically
through the heat transfer surfaces. In tower type boilers or oil and gas fired
boilers, these horizontal heat transfer surfaces are located over the furnace in
the first pass itself. These horizontal heat transfer surfaces consists of serpentine
type coils. The tube elements are arranged in rows and columns with defined
spacing between them.
If the span of the tube element is large, vertical fluid cooled hanger tubes of two
or more rows are used to avoid sagging of horizontal tubes There will differential
thermal expansion between the adjacent tube elements due to the difference in
in temperature of fluid passing through the tubes and the gas temperature

the upper and lower portion of the tube bundle. The support shall allow the free
movement of the tube elements due to the differential thermal expansion. In
some cases, there are more vertical tubes than the horizontal tube elements
where evaporator bundle tubes are converted as vertical hanger tubes. In such
cases, two vertical hanger tubes carry one horizontal tube assembly.
US 4307777 teaches a support arrangement for horizontal tube in a vertical gas
pass. Vertical hanger tubes have fins on opposite sides and a U strap is arranged
to surround the horizontal tube to be supported to the U strap to be welded only
to the longitudinal fin.
US 2221070 described steam-cooled hanger tubes for supporting horizontal
Superheaters and preheaters. A plurality of L shaped vertical fins are welded to
the hanger tubes. The horizontal tubes are attached to the hanger tube through
the bands which surrounds the tubes. The bands are welded only to the fins and
not with the tubes. This arrangement permits relative movement between the
tubes and bands to reduce the stresses.
US 3265044 discloses a slidable supporting arrangement for supporting a
horizontal heat transfer serpentine tube o a vehicle tube, which 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.

US 3267913 teaches 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 tubes are cooled to a high degree
with reduced stress levels.
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 cylinder 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 bar and welded to the vertical tubes along
the lateral edges.
OBJECTS OF THE INVENTION
It is therefore, an object of the invention to propose a reliable inverted strap
type support device for supporting one horizontal tube with two fluid cooled
hanger tubes.
Another object of the invention is to propose a reliable inverted strap type
support device for supporting one horizontal tube with two fluid cooled hanger
tubes which is capable to accommodate the differential thermal expansion
between the tub elements due to difference in temperature of fluid passing
through the tubes and the difference in gas temperature at different zones.

SUMMARY OF THE INVENTION
In conventional pulverised coal fired boilers and CFBC boilers horizontal heat
transfer surfaces like Superheaters, Reheaters and Economisers are normally
located in the second pass. A 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 and temperature. If the span of the tube
element is large, vertical fluid cooled hanger tubes of two or more rows are used
to support the horizontal tubes to avoid the sagging of the horizontals tubes.
The present inventors recognized if the bottom most Evaporator bundle tubes
are converted as vertical hanger tubes for supporting other bundles, there will be
available more hanger tubes than the horizontal tubes. In such cases, two cooled
hanger tubes can be used to support one horizontal tube with an inverted strap
type support to allow free thermal growth of tube elements.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows an overview of horizontal and vertical tube bundles in the
boilers.
Figure 2 - shows the tube bundles in assembled condition.
Figure 3 - shows an exploded view of the support device of the invention.

Figure 4 - shows a sectional view of the support device in assembled condition
providing support through the hanger tubes
DETAILED DESCRIPTION OF THE INVENTION
In support system for horizontal tube bundles, there are certain cases where
there are two vertical fluid cooled hanger tubes (1) available for supporting each
horizontal tube element (2). The vertical fluid cooled hanger tubes (1) are placed
on both sides of the horizontal tube element (2). The horizontal tube is fixed in
position with two vertical hanger tubes by means of two vertical strap plates (3)
and two 'C' shaped spacer plates (4). The vertical strap plates (3) are having
semicircular holes on both sides with size slightly larger than the diameter of the
tube element so that the tube can move freely inside the hole due to thermal
expansion. The strap plates are pushed against each other tightly and welded
together with one another. There should not be any welding between the strap
plates either with hanger tube or with horizontal coil.
The space between the two vertical hanger tubes (1) is maintained by providing
two 'C' shaped spacer plates (4) in between the vertical hanger tubes and
horizontal coil. The 'C' shaped spacer plates (4) are profiled suitably so that they
can be accommodated in between hanger tube and horizontal coil and at the
same time guide the movement of the horizontal tube properly. The spacer
plates can be tack welded inside the strap plates to retain in its position after the

assembly is completed. To arrest the downward movement of the entire strap
assembly along the vertical tube, two stopper plates (5) are welded on the
hanger tube only, just touching the strap plates. The load of the horizontal tube
is transferred to the vertical hanger tubes though these stopper plates (5). The
differential thermal expansion between the adjacent tube elements are better
accommodated by this support system. The same assembly procedure can be
adopted for the remaining horizontal tubes also. In this system the number of
hanger tubes per row of support is double the number of horizontal coils. Above
the roof of the boiler, the hanger tubes are connected to a collection header and
the loads on the hanger tubes are transferred to the ceiling structure through
lugs welded on hanger tubes.

WE CLAIM:
1. A reliable inverted strap type support device for supporting one horizontal
tube with two fluid cooled hanger tubes comprising:
- at least two vertical fluid cooled hanger tubes (1) placed on both sides of
a horizontal tube element (2);
- two vertical strap plates (3) and two 'C' shaped spacer plates (4) allows
fixing of the horizontal tube in between the two vertical hanger tubes;
- the vertical strap plates (3) configured with a plurality of semicircular
holes on both sides of the plates (3), the holes having size larger than
the diameter of the tube element allowing the horizontal tube elements
to freely move within the holes adjusting the thermal expansion; and
- the strap plates are welded after inserting one strap plate with the other
avoiding any welding between the strap plates with the hanger tube.
2. The device as claimed in claim 1, comprising at least two stopper plates
which are welded on the hanger tubes (1) so that the load of the
horizontal tube (2) is transferred to the hanger tube (1).

3. The device as claimed in claim 1, wherein the pacer plates (4) are profiled
to be accommodated between the hanger tube (1) and the horizontal coil

ABSTRACT

The invention relates to a reliable inverted strap type support device for
supporting one horizontal tube with two fluid cooled hanger tubes comprising at
least two vertical fluid cooled hanger tubes (1) placed on both sides of a
horizontal tube element (2); two vertical strap plates (3) and two 'C' shaped
spacer plates (4) allows fixing of the horizontal tube in between the two vertical
hanger tubes; the vertical strap plates (3) configured with a plurality of
semicircular holes on both sides of the plates (3), the holes having size larger
than the diameter of the tube element allowing the horizontal tube elements to
freely move within the holes adjusting the thermal expansion; and the strap
plates are welded after inserting one strap plate with the other avoiding any
welding between the strap plates with the hanger tube.