FIELD OF INVENTION
The present invention generally relates to cleaning of the fireside deposits of
fossil fuel fired heat recovery equipment. More particularly the invention relates
to a protection device against a reverse running of a soot blower in case the
input power supply gets altered to a wrong-phase sequence.
BACKGROUND OF THE INVENTION
In fossil fuel-fired boilers, the residue of combustion sticks to the heat transfer
surfaces of the boiler and acts as a bad conductor of heat, affecting the heat
transfer. Such deposit has direct implication on efficiency of the boiler. The soot
blowers are used to remove such deposits and improve the efficiency of the
boiler. The soot blowing is undertaken by steam or air as the blowing medium.
A soot blower mainly consists of a motor, a plurality of push buttons, a gearbox
with housing, a valve head assy., a traveling carriage, and a feed pipe. The
traveling carriage is fixed to the gearbox. A lance assy of the boiler is fixed to the
traveling carriage and moves over the feed pipe. Packings for leak proof
operation of the blower is provided between the traveling carriage and the feed
pipe. The lance has at least two nozzles at the end. The steam passes through
the Soot Blower Valve (SBV) Head assy at a recommended pressure for blowing.
Among the electrical components required for operation of the soot blower, the
motor, the limit-switches and the pushbuttons are generally construed as integral
parts of the soot blower. The electrical control gears (i.e. motor starters) for
forward and reverse running of the soot blower are arranged outside the soot
blower. Sometimes these motor starters are also mounted on the soot blower.
The motor starters are provided with forward and reverse contacts, overload
relays, circuits for interfacing the limit switches. However, the motor starters do
not have provision to check the correct direction of movement of the soot
blower, i.e. in case of a reversal of the 3ph power supply sequence, the soot
blower might move in a direction opposite to what it is intended, and may cause
severe damage to the soot blower including personal injury to the operator.
Such possibility of reverse movement may take place during initial commissioning
and maintenance of the soot blower or during maintenance of the incoming
switch gears of the blower.
The phase sequence reversal is encountered frequently during erection of new
plant and is one of the major causes of the damages during installation. Further,
during maintenance of the soot blower such phase interchange might arise.
According, to the existing system, the only way to check the correct direction of
rotation of the motor, is to decouple the motor from the lance in case of wrong
phase sequence and run them.
OBJECTS OF INVENTION
It is therefore an object of the invention to propose a protection device against a
reverse running of the soot blower in case input power supply gets altered to a
wrong phase sequence, which eliminates the disadvantages of prior art.
Another object of the invention is to propose a protection device against a
reverse running of the soot blower in case input power supply gets altered to a
wrong phase sequence, which is enabled to provide an indication of the reverse
sequence so that a corrective measure can be implemented.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a protection device against a reverse
running of a soot blower in case input power supply gets altered to a wrong-
phase sequence. The protective device is enabled to reduce the chances of
failures of the soot blower and facilitates a safe erection and maintenance.
Accordingly, there is provided a protection device against a reverse running of a
soot blower in a fuel-fired boiler in case of a wrong-phase sequence input of the
power supply, comprising a three-phase power supply source capable of
inputting direct power to at least one motor of the blower including a controlled
input to a plurality of starter control means; a control circuit enabled to monitor
and control a forward including reverse movement of a lance assembly
attachable to a traveling carriage, the control circuit comprising a home-position
limit switch, a forward position limit switch, and at least one indication lamp; and
a phase-sensing relay interfaced to the power-supply source, the relay is enabled
to allow supply of the controlled power when the input is in correct phase-
sequence, and disallowing the input of a wrong-phase sequence based on a
corresponding indication by an indication lamp, the soot blower being disabled to
operate due to absence of power supply on wrong-phase input.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig -1 a schematic illustrating a protective device for a single motor soot blower
according to the invention.
DETAILED DESCRIPTION OF INVENTION
As shown in Fig - 1 the device comprises a 3 phase power supply source (1)
supplying direct and controlled power respectively to the motor (2) and the
control components (4). The starter control (4) for forward and reverse
movement of the lance is controlled by a control circuit (5). The circuit (5)
comprises a home position limit switch (6), a forward end position limit switch
(7), and indication lamps (4). There is a phase sequence relay and terminals for
the external connections (not shown). The blower motor (2) is controlled
through a motor starter (3).
A phase sensing relay (PSCR) operably connected (not shown) to the power
supply source (1) is set to switch on the controlled supply only when the phase
sequence of the incoming 3 Phase supply is correct. Otherwise the indication
lamp (PSELT) "Power supply fault" (4) is switched ON. When the incoming phase
sequence is wrong, the operation of the soot blower is prevented as there is no
control supply, which effectively prevents the soot blower motor (2) from
running in the reverse direction and getting damaged.
WE CLAIM
1. A protection device against a reverse running of a soot blower in a fuel-
fired boiler in case of a wrong-phase sequence input of the power supply,
comprising:
- a three-phase power supply source (1) capable of inputting direct power
to at least one motor (2) of the blower including a controlled input to a
plurality of starter control means (4);
- a control circuit (5) enabled to monitor and control a forward including
reverse movement of a lance assembly attachable to a traveling carriage,
the control circuit (5) comprising a home-position limit switch (6), a
forward position limit switch (7), and at least one indication lamp (4); and
- a phase-sensing relay interfaced to the power-supply source (1), the relay
is enabled to allow supply of the controlled power when the input is in
correct phase-sequence, and disallowing the input of a wrong-phase
sequence based on a corresponding indication by the indication lamp (4),
the soot blower being disabled to operate due to absence of power supply
on wrong-phase input.
2. A protection device against a reverse running of a soot blower in a fuel-
fired boiler in case of a wrong-phase sequence input of the power supply,
as substantially herein described with reference to the accompanying
drawings.

A protection device against a reverse running of a soot blower in a fuel-fired
boiler in case of a wrong-phase sequence input of the power supply, comprising
a three-phase power supply source (1) capable of inputting direct power to at
least one motor (2) of the blower including a controlled input to a plurality of
starter control means (4); a control circuit (5) enabled to monitor and control a
forward including reverse movement of a lance assembly attachable to a
traveling carriage, the control circuit (5) comprising a home-position limit switch
(6), a forward position limit switch (7), and at least one indication lamp (4); and
a phase-sensing relay interfaced to the power-supply source (1), the relay is
enabled to allow supply of the controlled power when the input is in correct
phase-sequence, and disallowing the input of a wrong-phase sequence based on
a corresponding indication by the indication lamp (4), the soot blower being
disabled to operate due to absence of power supply on wrong-phase input.