FIELD OF INVENTION
The present invention generally relates to soot blowers used for cleaning of the
fireside deposits of the fossil fuel fired heat recovery system. More particularly,
the invention relates to an improved device to prevent failures of a soot blower
in a heat recovery system.
BACKGROUND OF INVENTION
In fossil fuel, the residue of combustion gets deposited on the heat transfer
surfaces of a boiler and acts as a bad conductor of heat, affecting the heat
transfer, which in turn reduces the efficiency of the boiler. Normally, soot
blowers are used to remove such deposits and improve the boiler efficiency. The
soot blower adapts steam or air as the blowing medium.
A Soot blower mainly consists of a motor, a plurality of push buttons, a gearbox
housing, a valve head assy., a traveling carriage and a feed pipe. The traveling
carriage is fixed to the gearbox. A lance assy is fixed with the traveling carriage
and moves over the feed pipe, with suitable packings interposed between the
carriage and the assy to ensure a leak proof operation of the blower. The lance
has two nozzles at the end. The steam passes through the Valve (SBV) Head
assy with a designed pressure for blowing.

Among the electrical components required for operation of the soot blower, the
motor, limit-switches and the pushbuttons are integrated to the blower, wherein
the electrical control gears (i.e. motor starters) for forward and reverse running
of the soot blowers are arranged outside the soot blower. In some cases, the
motor starters are also mounted on the soot blower to form an integral
component.
The motor starters are provided with forward and reverse contactors, overload
relays, circuits for interfacing the limit switches. However, the prior art motor
starters are not provided with any protection means. In case, the forward end
limit switch becomes mal-functional, the drive chain gets cut and the lance rams
on to the mechanical stopper, causing a damage to the soot blower. Further
damage to the lance may occur if the lance is not retracted manually within a
specified time. These are some of the possibilities, which might happen either
during initial commissioning or maintenance of the soot blower or during a
maintenance of the incoming switch gears. Similarly, the limit switches for the
initial position might fail which may cause damage to the soot blower due to
overrunning of the lance.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved device to
prevent failure of a soot blower in a heat recovery system which eliminates the
disadvantages of the prior art.

Another object of the invention is to propose an improved device to prevent
failure of a soot blower in a heat recovery system which is enabled to
automatically stop the forward movement including simultaneous retraction of
the lance over the carriage in case of failure of the electrical limit switches of the
motor starter.
A still another object of the invention is to propose an improved device to
prevent failure of a soot blower in a heat recovery system which is enabled to
automatically stop the forward movement including simultaneous retraction of
the lance in case of failure of the mechanical limit switches.
Accordingly, there is provided an improved device to prevent failure of a soot
blower in a heat recovery system, the soot blower comprising at least one
electrical motor; a plurality of motor starters with electrically operated limit
switches; a traveling carriage fixed to a gearbox; a lance assembly attached to
the traveling Carriage and enabled to move over a feed pipe, the lance assembly
having at least two nozzles for pressure blowing of steam; a valve head
assembly enabling supplying steam at a designed pressure to the nozzles; and a
plurality of mechanically operated limit switches; the limit switches preventing
overrunning of the lance assembly including retraction of the lance assembly
during operation of the soot blower, the device comprising a three-phase
electrical power source supplying power to the electrical motor of the soot
blower and enabled to further supply a controlled power to the plurality of motor
starters; a control circuit to control the motor Starter dedicatedly assigned for
forward and reverse movement of the lance; a home position limit switch
controllable by the motor starter; and a timer means incorportable into the
control Circuit, the timer means being enabled to automatically activate a
forward end position limit switch when none or either of the electrical or

mechanical limit switches remains operable, the timer means being set with a
time representing an expected time for the lances to reach the forward end, and
allow retraction of the lance before any damage is caused to the soot blower due
to overreach of the lance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a schematic illustration of the device for a single motor soot
blower according to the invention.
DETAILED DESCRIPTION OF INVENTION
As shown in figure 1, the device comprises a 3 phase input power source (1)
Supplying power to a motor starter (2) and to a starter control means (3). The
supply to the starter control means (3) is a controlled one. The starter control
means (3) comprises a control circuit (4) which causes a forward and reverse
movement of a lance (not shown). The device further comprises a home position
limit switch (7) and a forward end position limit switch (8).
The other major cause of damage to the soot blower during operation being the
mal-operation of the mechanical limit switches, a timing device (5) is introduced
in the circuit (4). This timer (5) is set to a time by which the lance is expected to
reach the forward end. In case, the limit switch is not operating, the timer (5)
automatically gets activated to retract the lance before any damage can be
caused to the soot blower (6) due to overreach of the lance. The timer device
(5) can be set to operate before the limit switch starts operating or after the limit
switch commences operation based on the technical preference by the user.

The above improvement is to prevent the damage to the soot blower during the
erection, commissioning and maintenance.
The timing means (5) has contacts enabled to reverse the direction of motion of
the lance. The timing means (5) can have a dial type setting which can be set
easily including a locking arrangement to prevent the change due to vibration.

WE CLAIM :
1. An improved device to prevent failure of a soot blower in a heat recovery
system, the soot blower comprising at least one electrical motor; a
plurality of motor starters with electrically operated limit switches; a
traveling carriage fixed to a gearbox; a lance assembly attached to the
traveling Carriage and enabled to move over a feed pipe, the lance
assembly having at least two nozzles for pressure blowing of steam; a
valve head assembly enabling supplying steam at a designed pressure to
the nozzles; and a plurality of mechanically operated limit switches; the
limit switches preventing overrunning of the lance assembly including
retraction of the lance assembly during operation of the soot blower, the
device comprising :-
a three-phase electrical power source supplying power to the electrical
motor of the soot blower and enabled to further supply a controlled
power to the plurality of motor starters;
a control circuit to control the motor Starter dedicatedly assigned for
forward and reverse movement of the lance;
a home position limit switch controllable by the motor starter; and
a timer means incorportable into the control Circuit, the timer means
being enabled to automatically activate a forward end position limit
switch when none or either of the electrical or mechanical limit
switches remains operable, the timer means being set with a time
representing an expected time for the lances to reach the forward end,

and allow retraction of the lance before any damage is caused to the
soot blower due to overreach of the lance.
2. The device as claimed in claim 1, wherein the timer means is enabled
to operate before or after the limit switches commence operation
3. The device as claimed in claim 1, wherein the timer means (5)
comprises contacts which reverse the direction of the lance movement.
4. The device as claimed in any of the preceding claims, wherein the
timer means (5) comprises locking means to prevent any change in
the motion direction due to vibration.
5. An improved device to prevent failure of a soot blower in a heat
recovery system, as substantially described and illustrated herein with
reference to the accompanying drawings.

The invention relates to an improved device to prevent failure of a soot
blower in a heat recovery system, the soot blower comprising at least one
electrical motor; a plurality of motor starters with electrically operated
limit switches; a traveling carriage fixed to a gearbox; a lance assembly
attached to the traveling Carriage and enabled to move over a feed pipe,
the lance assembly having at least two nozzles for pressure blowing of
steam; a valve head assembly enabling supplying steam at a designed
pressure to the nozzles; and a plurality of mechanically operated limit
switches; the limit switches preventing overrunning of the lance assembly
including retraction of the lance assembly during operation of the soot
blower, the device comprising a three-phase electrical power source
supplying power to the electrical motor of the soot blower and enabled to
further supply a controlled power to the plurality of motor starters; a
control circuit to control the motor Starter dedicatedly assigned for
forward and reverse movement of the lance; a home position limit switch
controllable by the motor starter; and a timer means incorportable into
the control Circuit, the timer means being enabled to automatically
activate a forward end position limit switch when none or either of the
electrical or mechanical limit switches remains operable, the timer means
being set with a time representing an expected time for the lances to
reach the forward end, and allow retraction of the lance before any
damage is caused to the soot blower due to overreach of the lance.