FIELD OF INVENTION
The present invention generally relates to a microprocessor based rapping control system for
controlling energisation of rapping motors in electrostatic precipitators (ESP) used for air
pollution control.
BACKROUND OF THE INVENTION
Electrostatic precipitators (ESP) electrically charge and collect particulates generated in
industrial processes such as those occurring in power plants, cement plants, and paper mills.
During operation of an electrostatic precipitator, collecting and emitting electrodes are
periodically cleaned to remove any dust build-up that has accumulated on their surfaces. A
mechanical rapper is used to dislodge dust from the ESP electrodes by periodic rapping
process. An electronic control system determines the sequence and duration of energisation of
the rapping motors. Particulates dislodged from the plates fall into collection hoppers at the
bottom of the precipitator.
Energisation of the rapping motors is done by a micro processor based controller through an
output card and the motor running feedback is obtained through an input card.
The sequence and frequency of rapping are critical to the performance of the ESP as a low
frequency of rapping will permit accumulation of large amount of ash on the electrodes and a
high frequency will cause frequent re-entrenchment of dislodged ash into the gas stream.
Hence the availability of automatic rapping control system is very important to sustain the
rapping process at optimum intervals and sequence for various fields of the ESP.
A rapping control system consists of a microprocessor based electronic controller interfaced to
an input card and output card for the input and output signal coupling from and to the rapper
motor respectively . The supply and feedback lines to the motor are hardwired to the controller
and thus for each rapper, two pair of lines are run from motor switchgear panel to the
electronic control panel room which houses rapping control panel. This approach necessitates
laying of large amount of cable thus increasing the total cost and time taken towards
commissioning the system, maintenance and troubleshooting efforts.
There is a need for a rapping control system for transferring the motor energisation and
feedback data from the microprocessor based control unit to the rapping motors and vice
versa, so that the cable length required can be reduced.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide a rapping control system with reduced
cable length for transferring the motor energisation and feedback data from the
microcontroller based controller to the rapping motors and vice versa. To achieve this a new
method is adopted for interfacing the controller, the output card and the input card in the
rapping control system
In the present invention the rapping controller, the input card and the output card are
interfaced through two wire serial communication link. The input and output of the rapping
controller are transferred to and from the output and input cards over two wire serial
communication link, like an RS485 link using standard MODBUS protocol.
Another object of the invention is to ensure the sustained rapping operation in spite of failure
of the interface between the controller, the output card or the input card and also on failure of
any one component and in some cases two components of the electronic rapping control
system.
The microcontroller based output and input cards of the present invention are developed with
in-built intelligence to handle the communication with rapping controller.
Advanced redundancy logic can be introduced by using a pair of output cards for a single
rapping controller so that on failure of the active output card, the redundant output card can
become active and on failure of the controller itself, the active output card will sustain the
rapping process based on its pre-programmed timing sequences.
Thus, in a preferred embodiment of the present invention it provides a microcontroller based
rapping control system for controlling energisation of rapping motors in electrostatic
precipitators, said system comprises: a microcontroller based rapping controller for
coordinating the rapping process based on its rapping sequence programme; at least one
output card for receiving the rapping motor ON/OFF information transmitted from said rapping
controller; and an input card for receiving rapping motor ON/OFF information and transmitting
it to said controller; characterised in that said rapping controller, said at least one output card
and said input card is interfaced through a two wire serial communication link for transferring
over said communication link the input and output data of said rapping controller to and from
said at least one output card and said input card, thereby controlling the energisation of the
rapping motors.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be explained with the reference to the accompanying drawings where
Figure 1 shows the microcontroller based rapping control
system of the present invention.
DETAILED DESCRIPTION
As shown in Figure 1 the rapping control system of the present invention consists of a rapping
controller 1, an output card 3 and an input card 5. The controller is interfaced to the output
card 3 and the input card 5 through a two wire serial communication link 2, like an RS 485
link. In a preferred embodiment, besides the first active output card 3 there is also provided a
second redundant output card 4. The pair of output cards 3, 4 has a second communication
link 6, like RS 485 between them. The controller 1 is located in the rapping control panel 7 in
the electronic control panel room while the output cards 3, 4 and input card 5 are located in
the motor switchgear control panel.
The rapping controller 1 is provided with programmable logic control for coordinating the
rapping process based on the rapping sequences programmed. The rapping motors associated
with various fields of the electrostatic precipitator (ESP) are switched ON/OFF at optimum
periodic intervals based on the inputs provided by the operator or a centralized monitoring
system for the ESP.
The rapping motors are actuated by relays of the output card 3.
In this system, the motor ON/OFF information is transmitted to the output card 3 over the
serial communication link 2 using standard MODBUS protocol. The output card 3 decodes this
packet and subsequently switches ON/OFF the relays based on the information from the
controller.
Rapping motor ON/OFF feedback is received at the input card 5 which transmits this
information to the controller 1 over the serial communication link 2 using standard MODBUS
protocol.
The feedback of the rapping motor actuation is obtained through opto-couplers provided on
the input card 5.
The active output card 3 always monitors the soundness of the redundant output card 4 over
the second communication link 6 and communicates the same to the controller 1. The
redundant output card 4 also keeps track of the soundness of the active output card 3 and on
its failure, takes over as the active output card without hindering the rapping operation. Any
one output card, active output card 3 or redundant output card 4 can be removed from the
system online, without affecting the rapping operation. A redundant output card 4 can also be
added to the system, online, without affecting the rapping operation.
If there is a failure of the communication link 6 between the active 3 and redundant 4, output
cards, the output card addressing logic in controller 1 communication ensures that only-one
card is active at any point of time. This prevents the condition of both output cards driving the
motors in an overlapping manner in case of a communication link 6 failure.
The active output card 3 also monitors the soundness of the controller 1. If it detects a failure
of controller 1, the rapping operation is still sustained by the active output card 3 by using its
pre-programmed rapping tables to switch on-off the rapping motors.
The redundant output card 4 is configured to differentiate between the failure of the active
output card 3 and communication failure between the redundant output card 4 and the active
output card 3 to designate said redundant card 4 as the active output card only on failure of
the active output card 3 and not on failure of communication link 6 between the redundant
output card 4 and the active output card 3.
The advanced redundancy logic introduced in the rapping control system makes the rapping
operation immune to the conditions like failure of the active output card 3, failure of the
rapping controller 1 and failure of the communication link 2 between the rapping controller 1
and the output and input cards 3,4 and 5.
WE CLAIM
1. A microcontroller based rapping control system for controlling energisation of rapping
motors in electrostatic precipitators, said system comprises:
- a microcontroller based rapping controller for coordinating the rapping process based
on its rapping sequence programme;
- at least one output card for receiving the rapping motor ON/OFF information
transmitted from said rapping controller; and
- an input card for receiving rapping motor ON/OFF information and transmitting it to
said controller;
characterised in that said rapping controller, said at least one output card and said input
card is interfaced through a two wire serial communication link for transferring over said
communication link the input and output data of said rapping controller to and from said at
least one output card and said input card, thereby controlling the energisation of the
rapping motors.
2. The system as claimed in claim 1, wherein said rapping controller is provided with the
(pre-programmed) logic to switch on and off the rapping motors at optimum periodic
intervals.
3. The system as claimed in claim 2, wherein said rapping controller is configured to
switch ON/OFF the rapping motors at optimum intervals based on inputs provided by
the operator or a centralised monitoring system for the ESP.
4. The system as claimed in claim 1, wherein relays are provided on said output card for
performing actuation of the rapping motors.
5. The system as claimed in claim 1, wherein said serial communication link is an RS 485
link using standard MODBUS protocol.
6. The system as claimed in claim 1, wherein a pair of output cards is provided having a
second communication link RS 485 there between so that on failure of the first active
output card, the second redundant output card can become active and on failure of the
rapping controller itself, the active output card can sustain the rapping process based
on the pre programmed rapping process of said active output card.
7. The system as claimed in the preceding claims, wherein said input card is provided with
opto-couplers for obtaining feedback information of the rapping motor actuation.
8. The system as claimed in preceding*claims, wherein actuation and feedback information
are transferred within the constituency of the rapping control system with the help of
said two wire serial communication link.
9. The system as claimed in claim 1, wherein a second redundant output card can be
introduced in said system for sustaining the rapping operation in the event of failure of
the first active output card.
10. The system as claimed in claim 6, wherein said redundant output card is adapted to
differentiate between the failure of active output card and communication failure
between said redundant output card and the active output card to designate said
redundant output card as the active output card only on failure of the active output
card and not on failure of communication link between the redundant output card and
the active output card.
11. A microcontroller based rapping control system for controlling energisation of rapping
motors in electrostatic precipitators, substantially as herein described and illustrated in
the accompanying drawing.

1. A microcontroller based rapping control system for controlling energisation of rapping
motors in electrostatic precipitators, said system comprises:
- a microcontroller based rapping controller for coordinating the rapping process based
on its rapping sequence programme;
- at least one output card for receiving the rapping motor ON/OFF information
transmitted from said rapping controller; and
- an input card for receiving rapping motor ON/OFF information and transmitting it to
said controller;
characterised in that said rapping controller, said at least one output card and said input
card is interfaced through a two wire serial communication link for transferring over said
communication link the input and output data of said rapping controller to and from said at
least one output card and said input card, thereby controlling the energisation of the
rapping motors.