FIELD OF THE INVENTION
The present invention relates to a device known as soot blower used for cleaning
of the fireside deposits of the fossil fuel fired heat recovery equipment. More
particularly, the present invention relates to an improved control apparatus to
prevent damages of soot blowers according to the invention.
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 vis-vis the efficiency of the boiler. The soot blowers are used to remove
such deposits and improve the boiler efficiency. Steam or air is used as the
medium for soot blowing.
A soot blower mainly consist 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 on the traveling carriage
which moves over the feed pipe having packings for leak proof operation of the
blower. The lance has at least two nozzles at the end. The steam passes
through the valve head assy at a recommended pressure for blowing.

Among the electrical components required for operation of the soot blowers, the
motor, limit-switches and pushbutton box constitute an integral assembly. The
electrical control gears (i.e. motor starters) for forward and reverse running of
soot blowers are arranged outside the soot blowers. Sometimes these starters
are also mounted on the soot blower. Presently, there is no provision for
checking the correct direction of movement of the soot blower upon initial
commissioning.
In case of reversal of 3ph power supply sequence, the soot blower will try to
move in opposite direction to what is intended and severe damage can occur to
the soot blower and can also lead to personnel injury. There is also a possibility
of such phenomenon during maintenance of the soot blower.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose an improved control
apparatus to prevent damages of soot blowers.
Another object of the invention is to propose an improved control apparatus to
prevent damages of soot blowers which eliminates reverse running of soot
blower.

A further object of the invention is to propose an improved control apparatus to
prevent damages of soot blowers, which allows automatic correction of the
phase sequence of incoming power to the motor through prior sensing of the
power supply.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved control apparatus to prevent
damages of soot blowers, the soot blower for boilers comprising a traveling
carriage movable over a feed pipe and having a lance with at least two nozzles,
the traveling carriage being controlled by a gear box; a valve head assembly
allowing passage of steam at predetermined pressure for blowing the
combustion-residues from the heat transfer surfaces of the boiler; an electrical
motor with motor starters for moving the soot blower within the boiler; one each
home-position, and end-position limit switch; a control circuit; and indication
lamps, the improved apparatus comprising a phase sequence relay (PSCR)
disposed being operably connected to the control circuit for sensing the phase
sequences (R-Y-B, B-Y-R) of the power supply; and a direction relay (DR)
connected to the phase-sequence relay (PSCR) to receive the input on sensing
result and correspondingly channelize the power supply to the electrical wires
transmitting power to the motor such that the motor is enabled to always
operate in same phase sequence irrespective of the existence or otherwise of
reverse phase sequence.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows an improved control apparatus to prevent damages of soot
blowers according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows an electrical line diagram for 3 phase power supply to a motor
and control components of a soot blower. A starter relay (DR) is provided for
forward and reverse movement of the lance controlled by the control circuit.
Other components in the circuit are home position limit switch, forward end
position limit switch, indication lamps. There is a phase sequence relay and
terminals for external connections.
A phase sequence Rely (PSCR) along with other components in the circuit senses
the phase sequence of the power supply. Based on this phase sequence rotation
(R-Y-B or B-Y-R), a direction relay (DR) switches the wires going to the motor
such that the motor always operates in the same phase sequence even under
reverse phase sequence at the incoming power supply. This effectively prevents
the soot blower motor from running in a reverse direction and getting damaged.
Earlier the only way to check the correct direction of rotation was to decouple
the motor from the lance and conduct a trial run. Now this work is eliminated.
The above improvement allows damage prevention of soot blower during
erection, commissioning and maintenance.

WE CLAIM:
1. An improved control apparatus to prevent damages of soot blowers, the
soot blower for boilers comprising a traveling carriage movable over a
feed pipe and having a lance with at least two nozzles, the traveling
carriage being controlled by a gear box; a valve head assembly allowing
passage of steam at predetermined pressure for blowing the combustion-
residues from the heat transfer surfaces of the boiler; an electrical motor
with motor starters for moving the soot blower within the boiler; one each
home-position and end position limit switch; a control circuit; and
indication lamps, the improved apparatus comprising:
- a phase-sequence relay (PSCR) disposed being operably connected to the
control circuit for sensing the phase sequences (R-Y-B, B-Y-R- of the
power supply; and
- a direction relay (DR) connected to the phase-sequence relay (PSCR) to
receive the input on sensing result and correspondingly channelize the
power supply to the electrical wires transmitting power to the motor such
that the motor is enabled to always operate in same phase sequence
irrespective of the existence or otherwise of reverse phase sequence.