FIELD OF THE INVENTION
The present invention generally relates to wall mounted fuel oil or fuel gas firing
burners. More particularly, the present invention relates to a mounting
arrangement for flame scanners in Heat Recovery Steam Generators (HRSGs).
BACKGROUND OF THE INVENTION
In fuel oil/fuel gas fired duct burners of HRSGs, flame scanners are installed to
sense the presence of burner flame inside the HRSG duct so that continuance of
Fuel oil/fuel gas firing can be permitted. Flame scanners are strategically
mounted on the burner panel, to sense the burner flame. Flame scanners are
exposed to hot gas emerging either from Gas turbine and/or from products of
combustion. As the Flame scanners include electronic components and are
exposed to high temperature, to safeguard the flame scanners from high
temperature, it is mandatory to cool the flame scanner assembly.
Purging/cleaning with air is done to enable the flame scanner sensors to have
clear vision on flame.

Accordingly, a mounting arrangement of flame scanners is provided to enable
cooling of the flame scanners. An arrangement as per prior art for mounting
flame scanners (5) in HRSGs (Figure 1) includes primarily a guide pipe (1) with a
Flange (2) mounted at its one end. The guide pipe (1) is mounted to the duct
wall (3) through a sleeve pipe (4). The flame scanner (5), with a first stub (6) for
providing cooling air, is mounted to the flange (2) through a connecting nipple
(7) and a swivel mount (8). To provide cooling air to the flame scanners, at least
a first Cooling air fan (20) with AC motor drive and a second air fan (21) with DC
motor drive are disposed along with required piping (23) and a first set of
instruments (24). The second air fan (21) will be in service during non-availability
of AC power. A first auto transfer damper (22) is included to connect only the
working air fan (21 or 20) to the scanner cooling air system. The first set of
instruments (24) connected through logics, enable changing-over of the cooling
air fans. The delivery piping (23) of the cooling air fans (20 and 21) is connected
to the flame scanner (5) through the first stub (6) with tubing (18) and a first
flexible hose (19). The air passing through the first stub (6) provide air for both
cooling and purging of the flame scanner. In HRSGs, a set of third AC motor
driven air fans (11) is provided to deliver cooling air to an Ignitor (10)

through a second stub (15) in a guide pipe (9). Out of the third set of air fans
(11), one fan is working and the other is stand-by. Delivery of these fans (11)
are connected through a second auto transfer damper (12) and piping (13) and a
second set of instruments (17) to provide cooling air to the ignitor (10)
through a branch off tubing (14). The second Stub (15) and the branch-off
tubing (14) are connected through a second flexible hose (16).
As per another prior art, an arrangement for mounting flame scanners (5) in
HRSGs (Figure 2) includes a primarily a guide pipe (1) with a flange (2)
mounted at its one end. The guide pipe (1) is mounted to a duct wall (3) through
a sleeve pipe (4). Flame scanner (5), with a stub (6) for providing purge air, is
mounted to the flange (2) through a connecting nipple (7), a quartz window
(25), a Tee connection (26) and a swivel mount (8). The tee connection (26) is
used to provide cooling air so that the flame scanner (5) will not be heated. To
provide cooling air and purge air, a first air fan (20) with AC motor drive and a
second air fan (21) with DC motor drive are envisaged along with required piping
(23) and a first set of instruments (24). The first air fan (20) is in service during
normal operation and the second air fan (21) is put in service during non-
availability of AC power. An auto transfer damper (22) is included to connect only
the working air fan to the flame scanner (5) cooling and purging air system.

The first set of instruments (24) connected through logics, enable the changing-
over of air fans for flame scanners. Delivery piping (23) of the air fans (20 and
21) is connected to the flame scanner (5) through a first stub (6) with tubing
(18) and a flexible hose (19). A tube (27) is tapped off from the sir piping (23)
and cooling air is made to flow through the Tee connector (26). Air through the
first stub (6) provides purge air to the flame scanner while air through the Tee
connector (26) provides cooling air. Flexible hoses (19) are used to connect the
tube (27) and the Tee connector (26) and to connect the tube (18) to the first
stub (6) . To provide sealing air and other air requirement, a third set of AC
motor driven air fans (11) is envisaged to provide cooling air to an Ignitor (10)
through a second stub (14) in a second guide pipe (9). Out of the two air fans
(11) one fan is working and the other is stand-by. Delivery of these fans are
connected through an auto transfer damper (12) and piping (13) and a second
set of instruments (17) to provide cooling air to the ignitor (10) through a
branch-off tubing (14). Stub (15) and branch-off tubing (14) are connected
through a second flexible hose (16).
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide a mounting
arrangement for flame scanners in Heat Recovery Steam Generators (HRSGs).

Another object of the present invention is to propose a mounting arrangement
for flame scanners in Heat Recovery Steam Generators (HRSGs) which eliminates
the use of dedicated air sources (air fans) for cooling the flame scanners.
Further object of the present invention is to propose a mounting arrangement for
flame scanners in Heat Recovery Steam Generators (HRSGs) which reduces
auxiliary power consumption in HRSG plants.
SUMMARY OF THE INVENTION
Accordingly, there is provided a mounting arrangement for flame scanners in
Heat Recovery Steam Generators (HRSGs). The present invention provides a
means to support the flame scanner on a cold body instead of connecting to a
hot body. High temperature from the flame source is contained by means of a
quartz window mounted on the guide pipe of the flame scanner. A hub mounted
on a cold body serves to mount the flame scanner without physical contact with
any of the hot components. Required viewing angle of the flame scanner is
achieved by a swivel mount. As the flame scanner is detached from any of the
hot objects, cooling air is not required. In the invented mounting arrangement,

air fans providing cooling air to flame scanners are not provided. Purge air,
sourced from seal air fans, at two points in the flame scanner mounting allows
the flame scanner to have clear view of the flame. Usage of flexible hoses
maintain the alignment of flame scanner with reference to the axis of the quartz
window.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows prior art Flame scanner mounting in HRSGs.
Figure 2 - Another prior art Flame scanner mounting in HRSGs.
Figure 3 - A mounting arrangement for flame scanners in HRSGs according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure 3, an arrangement for mounting flame scanners in HRSGs
includes a guide pipe (1) with a plurality of quartz windows (30) mounted on its
one end, the guide pipe (1) mounted on a duct wall (3) through a sleeve pipe

(4). The guide pipe (1) is provided with a first stub (32) to supply purge air for
quartz window (30). Without any direct contact with the quartz window (30) and
any of the hot objects, the Flame scanner (5), with a second stub (6) for
providing purge air, is mounted to a fixing hub (28) through a connecting nipple
(7) and a swivel mount (8). The fixing hub (28) is bolted to a mounting plate
(29) which is welded to an air header (14) for an ignitor (10).
In HRSGs, to provide sealing air and other air requirement, at least two air fans
(11) with AC motor drives are envisaged. Out of the two air fans (11 and 12) one
is working and the other is stand-by. Blown air from these fans (11 or 12) are
connected through an auto transfer damper (12). The auto transfer damper (12)
is included to connect only the working air fan to the sealing air piping (13). Air
to the Ignitor (10) flows through a third stub (15) in the guide pipe (9). A tube
(13) with a set of instruments (17) are envisaged to supply air to the ignitor (10)
through branch-off tubing (14). A flexible hose (16) is introduced in the air
piping (14) to the ignitor (10).
A purge air Tubing (31) is tapped off from the seal air header (14). A first
branching (27) is made from the tubing (31) to provide purge air to the quartz
window (30) and a second branching (18) is made from the tubing (31) to
provide purge air to the stub (6) in the flame scahner (5).

WE CLAIM:
1. A mounting arrangement for flame scanners in Heat Recovery Steam
Generators (HRSGs), comprising :
- a guide pipe (1) having a plurality of quartz windows (30) mounted at a
second end portion, a first end of the guide pipe (1) mounted on a duct
wall (3) through a sleeve pipe (4) and having at a proximal distance a first
stub (32) to supply purge air from the quartz window (30);
- one flame scanner (5) with a second stub (6) mounted to a fixing hub
(28) without direct contact with the quartz window (30), the fixing hub
(28) bolted to a mounting plate (29) welded to an air header (14) feeding
cold air to an ignitor (10);
- at least two air fans (11 and 12) connected to a sealing air piping (13) via
an auto transfer damper (12) for supplying air to the piping (14), one of
the at least two air fans (11 or 12) maintained in operating mode and the
other in stand-by mode; and

- a flexible hose (16) maintains an alignment of the viewing angle of the
flame scanner (5) taking care of the expansion due to heat generated
within the HRSG, wherein the fixing hub (28) is at ambient temperature
during operating which allows the flame scanner (5) being mounted
thereto at the ambient temperature, and wherein an air-gap provided
between the hub (28) and the quartz window (30) acts as a barrier for
heat transfer to the flame scanner (5).
2. The mounting arrangement as claimed in claim 1, wherein the flame
scanner (5) is mounted to the fixing hub (28) through a connecting nipple
(7) and a swivei mount (8), and wherein the first and second stub (32, 6)
providing purging air via a tap-off (31) from the seal air piping (14).
3. The mounting arrangement as claimed in claim 1, wherein air supplied to
the ignitor (10) flows through a third stub (15) provided in the guide pipe
(9)

4. The mounting arrangement as claimed in any of the preceding claims,
wherein air is supplied to the ignitor (10) through a branch-off tubing
(14).
5. The mounting arrangement as claimed in claim 1, wherein exclusive set of
cooling air fans for scanners are not required.

ABSTRACT

The invention relates to a mounting arrangement for flame scanners in heat
recovery steam generators (HRSGs), comprising a mounting arrangement for
flame scanners in Heat Recovery Steam Generators (HRSGs) a guide pipe (1)
having a plurality of quartz windows (30) mounted at a second end portion, a
first end of the guide pipe (1) mounted on the duct wall (3) through a sleeve
pipe (4) and located at a proximal distance from a first stub (32) to supply purge
air to the quartz window (30); one flame scanner (5) with a second stub (6)
mounted to a fixing hub (28) without direct contact with the quartz window (30),
the fixing hub (28) bolted to a mounting plate (29) welded to an air header (14)
feeding an ignitor (10); at least two air fans (11) connected to a sealing air
piping (14) via an auto transfer damper (12) for supplying air to the piping (14),
one of the at least two air fans (11) maintained in operating mode and the other
in a stand-by mode; and a flexible hose (16) helps to maintain an alignment of
the viewing angle of the flame scanner (5) considering the expansion of the
scanner body due to heat generated within the HRSG, wherein the fixing hub
(28) is maintained at ambient temperature during operation which allows the
flame scanner (5) being mounted thereto at the ambient temperature, and
wherein an air-gap provided between the hub (28) and the quartz window (30)
acts as a barrier for heat transfer.