FIELD OF THE INVENTION:
The invention relates to Air preheater rotor stoppage alarm and more
particularly to a simplified system of rotor stoppage alarm for a Regenerative
Air Preheaters, based on software logic.
BACKGROUND OF THE INVENTION & PRIOR ART :-
Rotary regenerative Air Preheaters are used in Thermal power boiler/
industrial applications to transfer the heat from the flue gas leaving the
boiler/ furnace to the entering combustion air through specially formed heat
transfer surfaces housed inside a rotor which rotates alternatively in air and
gas streams.
The Rotor of a Rotary Regenerative Air preheater shall be kept rotating
continuously to transfer heat from flue gases to air. It is not advisable to
allow the rotor to be stopped when high temperature gases are flowing
through it as this may cause unequal thermal expansion and pose problems
for restarting the rotor of the Air Preheater. To indicate the slowing down/
stopped condition of the rotor, rotor stoppage alarm is provided.
The Air Preheater rotor stoppage alarm consists of a local control panel, a
vane operated proximity switch and vanes which are mounted to the trunnion
of the rotor of Air Preheater. Two timers mounted inside the local control
panel monitors the passing of the vanes as per preset time interval. If the
vanes fail to pass under the proximity switch within the preset time interval, a

relay is closed in the local control panel to give an alarm in the Digital Data
Control and Monitoring Information system (DDCMIS) at unit control board
(UCB) to warn the operator that the rotor is slowing down / stopped.
The local control panel located near the Air Preheater does not perform
satisfactorily due to high dusty environment resulting in malfunctioning of the
rotor stoppage alarm. The timers housed inside the rotor stoppage alarm
panel also require replacement after some time.
OBJECTS OF THE INVENTION:
To overcome the drawbacks of the prior art, a few remedial measures were -
undertaken for the invention. The objects of invention are, therefore,
summarized below in concurrence with the said remedial measures.
An object invention is to propose a simplified rotor stoppage alarm for easy
operation.
Yet another object of invention is to eliminate the local control panel.
Still another object of invention is to eliminate the timers.
A further object of invention is to use software logic in DDCMIS (Digital Data
Control and Monitoring Information System) at UCB (Unit Control Board) for
generation of rotor stoppage alarm.
A still further object of invention is improve the reliability at a lower cost.
DESCRIPTION OF THE INVENTION:
According to the invention, the signal from the vane operated proximity
switch is directly connected to DDCMIS at UCB through cables. The software
logic in DDCMIS monitors the passing of the vanes as per preset time

intervals. If the vanes fail to pass within the preset time interval, then the
DDCMIS logic generates an alarm at UCB to warn the operator that the rotor
is slowing down / stopped. This improved rotor stoppage alarm eliminates the
local control panel. This also eliminates the timers. As the local control panel
is eliminated and the rotor stoppage alarm is generated by DDCMIS at UCB,
the performance of the system is greatly enhanced.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure-1 shows the prior art, arrangement of rotor stoppage alarm assembly
with local control panel.
Figure-2 shows the invented arrangement of the rotor stoppage alarm using
software logic in DDCMIS at UCB.
The invention alongwith prior art will now be described with help of the
accompanying drawings which depict exemplary embodiments of the
invention. However, there can be several other embodiments, all of which are
deemed covered by this description.
Prior art arrangement as shown in figure-1 consists of a local control panel, a
vane operated proximity switch (01) and vanes (02) which are mounted to
the trunnion of the rotor of Air Preheater. The signal from the proximity
switch is connected to a control panel (04) mounted locally near the air
preheater through cables (03). The timers (05) located inside the local control
panel monitors the passing of the vanes as per preset time intervals. If the
vanes fail to pass under the proximity switch the set time interval, a relay is
closed in the local control panel. The relay signal from the local control panel

(04) is connected to DDCMIS (07) at UCB through cables (06) to generate an
alarm to warn the operator that the rotor is slowing down / stopped.
According to the invention, rotor stoppage alarm system (200) as shown in
figure- 2, the signal from the vane operated proximity switch (10) is directly
connected to DDCMIS (40) at UCB through cables (30). The software logic is
DDCMIS monitors the passing of the vanes (20) as per preset time intervals.
The preset time interval is determined considering the rotational speed of the
rotor. If the vanes (20), which are mounted on the trunnion of the rotor of
Air preheater, fail to pass within the preset time interval, then the DDCMIS
logic generates an alarm at UCB to warn the operator that the rotor is
slowing down / stopped.
Some advantageous features of the invention are summarized
below:-
The simplified rotor stoppage alarm facilitates easy operation.
This improved device eliminates the local control panel.
This improved device eliminates the timers and uses software logic in
DDCMIS.
The performance of the device is enhanced as the signal processing is done
in DDCMIS at UCB.
The reliability of the device is increased as the local control panel located in
dusty environment is eliminated.
The initial cost of the device is reduced.

We claim
1. A system of rotor stoppage alarm (200) comprising
- a proximity switch (10);
- a plurality of vanes (20) mounted on the trunnion of the rotor;
- a DDCMIS (40) for generation of alarm and
- cable (30) connecting the proximity switch to the DDCMIS,
characterized in that the output signal from the proximity switch is fed
directly to the DDCMIS located at unit control board.

2. A system of rotor stoppage alarm (200) as claimed in claim 1 wherein the
proximity switch (10) monitors the time interval of passing of vanes.
3. A system of rotor of stoppage alarm (200) as claimed in claim 2, wherein
said time interval is pre-set considering the rotational speed of rotor.
4. A system of rotor of stoppage alarm (200) as claimed in claim 1, wherein
said alarm is operated in the case of slowing or stoppage of said rotor.

A system of rotor stoppage alarm (200) comprising
- a proximity switch (10);
- a plurality of vanes (20) mounted on the trunnion of the rotor;
- a DDCMIS (40) for generation of alarm and
cable (30) connecting the proximity switch to the DDCMIS,
characterized in that the output signal from the proximity switch is fed
directly to the DDCMIS located at unit control board.