FIELD OF THE INVENTION
The invention relates to a control system of electrostatic precipitator used for air
pollution control. More particularly, the invention relates to a method and
apparatus for controlling energisation of electrostatic precipitator. The invention
further relates to an associated method to reduce cost of the control system
while maintaining optimum energisation and control of electrostatic precipitator.
BACKGROUND OF THE INVENTION
Electrostatic precipitation is one of the most effective process to control air
pollution generated by industrial emissions. This technique, which has proved to
be highly effective in controlling air pollution , is used for removal of undesirable
matter from a gas stream by electrostatic precipitation. Electrostatic precipitator
(hereafter referred to as ESP) is an air pollution control device designed to
electrically charge and collect particulates generated from industrial processes
such as those occurring in power plants, cement plants, pulp and paper mills and
utilities. The electrically charged particles are attracted towards electrode plates,
viz., discharge electrode and collection plate. ESP is divided into a plurality of
fields depending on the dust load. During continuous operation of an
electrostatic precipitator, the dust from the collector plates and the discharge
electrodes must be periodically removed for further conveying of the collected
dust.
In the ESP, the electrostatic precipitation is achieved by controlling a transformer
rectifier set by a dedicated ESP controller. ESP controller regulates the power
supplied to ESP by controlling the power input to the transformer rectifier set
through a back to back connected thyristor pair.
An ESP installation consists of a plurality of fields, each field being controlled by
a dedicated ESP controller. The ESP fields are arranged in pass-wise along the
gas flow direction.
For a typical larger ESP, there are around 8 pass's and each pass having around
8 fields depending on size of the ESP totaling 64 EC-HVRs. Typically, the
Electronic Controller (hereafter referred to as EC) and High Voltage Rectifier
(hereafter referred to as HVR) are placed at different locations in a plant due to
operating requirements.
In the prior art, mechanism exists to integrate EC & HVR through signal cables
such that signals for example, secondary voltage, secondary current, transformer
alarms and other sensor inputs are directly connected to the EC through
individual signal cables. For a typical power plant, the amount of cables required
for such signal sensing runs into kilometers thereby resulting in increased
installation cost. Also time taken to commission all these cables is very high.
In the prior arts, ESP energisation control, spark sensing & quenching, back
corona detection and control functions are through a feedback control loop using
HVR secondary voltage and/or secondary current i.e. ESP voltage and/or current
directly connected to the EC through individual signal cables. In some prior arts,
ESP spark sensing is through a feedback using HVR secondary current i.e. ESP
current directly connected to the EC through individual signal cables. But
thyristor gate firing control through a feedback control loop using HVR primary
current.
The prior arts for example, US3507096A, and US3622839, teach methods for
control of ESP energisation and automatic voltage control based on HVR primary
voltage and current feedback. However in the prior art, the parameter like HVR
secondary current and voltage feedbacks (i.e. ESP operating current and voltage)
for comparison and qualification of the HVR primary voltage and current
feedback values are not taken into account, for control purpose. Further, these
prior art systems being not wireless protocol based systems, interfacing signals
between HVRs and ECs in ESP, cannot be generated.
Prior patent publications for examples WO 2007/051239 Al, and CN101300078A,
disclose ESP energisation control through a feedback control loop using HVR
secondary voltage and/or secondary current i.e. ESP voltage and/or current
directly connected to the EC through individual signal cables. However, these
prior art are disabled to use feedback of HVR primary parameters for control.
The prior art are also not equipped with a wireless protocol based system for
interfacing signals between HVRs and ECs in ESP.
US 4390831 teaches a process of, ESP spark sensing through a feedback using
HVR secondary current i.e. ESP current directly connected to the EC through
individual signal cables. And thyristor gate firing control is through a feedback
control loop using HVR primary current. It does not have a wireless protocol
based system for interfacing signals between HVRs and ECs in ESP.
Accordingly, the prior art ESPs generally lack control mechanism based on
combined HVR primary and secondary current and voltage feedbacks. They do
not have a wireless protocol based system for interfacing signals between HVRs
and ECs in ESP.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an wire-less feedback control
system for controlling ESP energisation, which eliminate the requirements of
signal cables and associated wirings running from HVR to EC.
Another object of the invention is to propose an wire-less feedback control
system for controlling ESP energisation, which is enabled to spark/arc detection
and quenching, back corona detection and suppression by using both HVR
primary (transformer primary voltage and current) and secondary (ESP voltage
and current) parameters.
A still another object of the invention is to propose an wire-less feedback control
system for controlling ESP energisation, in which HVR primary (transformer
primary voltage and current) parameters are used for control while HVR
secondary (ESP voltage and current) parameters are compared with it for
qualification and reliability.
Yet another object of the invention is to propose an wire-less feedback control
system for controlling ESP energisation, which is enabled to interface signals
between High Voltage Rectifiers and Electronic controllers in the electrostatic
precipitators by adapting open standard Zigbee protocol based wireless mesh
network by replacing the existing signal cables running between the high voltage
rectifiers and electronic controllers.
A further object of the invention is to propose an wire-less feedback control
system for controlling ESP energisation, which substantially reduces the
commissioning and maintenance time and cost.
SUMMARY OF THE INVENTION
Accordingly, there is provided an wire-less feedback control system for
controlling ESP energisation, spark/arc detection and quenching, back corona
detection and suppression based on both HVR primary (transformer primary
voltage and current) and secondary (ESP voltage and current) parameters as
combined feedback. HVR primary (transformer primary voltage and current)
parameters are used for control while HVR secondary (ESP voltage and current)
parameters are compared with it for qualification and reliability.
The invented system has hardware (feedback sensor unit) and the associated
software for sending the operating parameters for example ESP current and
voltage feedback and HVR alarm signals from HVR to EC over a wireless mesh
network based open standard Zigbee protocol by replacing signal cables of prior
art systems running between the High Voltage Rectifiers and Electronic
Controllers. All the signal cables running from HVR to EC and all associated cable
trays and support things are completely eliminated.
The invented system further has hardware (feedback receiver in EC) and the
associated software for receiving and decoding the operating parameters for
example ESP current and voltage feedback and HVR alarm signals coming from
HVR to EC as wireless signals.
The invented system also has hardware and the associated software for receiving
and decoding the operating parameters for example, HVR transformer primary
current and voltage feedback coming from EC panel to EC as hard-wired signals.
The invented system also has hardware and the associated software for initiating
control action based on the combined feedback i.e. HVR primary (transformer
primary voltage and current) and secondary (ESP voltage and current)
parameters. It has the provision to trip the ESP field on conditions of abnormal
mismatch in HVR primary and secondary parameters of the ESP.
The hardware and the associated software of the system is enabled to transmit
and receive message/data in Zigbee protocol. Thus the system hardware for
example, feedback sensor unit at HVR and receiver unit in EC are interconnected
to each other through Zigbee protocol based wireless mesh network. Feedback
sensor unit at HVR and receiver unit in EC are the nodes in the mesh network.
Mesh network refers to a type of network where each node is not only capturing
and disseminating its own data, but also serve as a relay for other nodes, that is,
it is collaborating to propagate the data in the network so as to have a reliable
communication.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 is block diagram of the wire-less feedback control system according to the
present invention.
Fig. 2 is hardware block diagram of the Electronic Controller (EC) of the ESP.
Fig. 3 is hardware block diagram of the Field level Sensor and transmitter.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The hardware block diagram of the invented wire-less feedback control system
for controlling ESP energisation, spark/arc detection and quenching, back corona
detection and suppression based on both HVR primary (transformer primary
voltage and current) and secondary (ESP voltage and current) parameters
combined as feedback is shown in Fig.l
In Fig.l, block (1) is the EC (Electronic Controller), which executes ESP control.
The EC has means for receiving HVR secondary (ESP voltage and current)
parameter feedbacks coming from the HVR end as Zigbee wireless signals. The
EC has means for receiving HVR primary (transformer primary voltage and
current) parameter feedbacks coming as hard wired signals from EC panel. Block
(6) is the GSM antenna for transmitting and receiving Zigbee wireless
data/signals. The EC has a micro-processor for processing of the received
feedback data and transmitting corresponding control signals.
In Fig.l, block (2) is a back to back connected thyristor pair for controlling the
power supplied to the ESP. One phase of the input line power is routed through
the thyristor pair to one end of the HVR transformer primary and the other phase
of line power is connected directly to the other end of HVR transformer primary.
Firing of the back to back connected thyristor pair is controlled by the EC (1).
Firing of the thyristors is done by a firing signal transmitted from the EC based
on the feedback signals of HVR primary (transformer primary voltage and
current) parameters.
In Fig. 1, block (3) is a High Voltage Transformer and Rectifier unit (HVR). Power
input to HVR primary is through the back to back connected thyristor pairs (2)
controlled by the EC (1). Output of the HVR is connected to ESP fields.
In Fig. 1, block (5) is a field electrode of ESP. Usually a high negative potential is
applied to ESP field electrode of the ESP.
In Fig.1, (4) is the field level sensor and transmitter unit which senses the ESP
field current and voltage which interalia are the HVR secondary voltage and
current and senses all HVR alarms. It then sends the sensed data and signals to
EC (1) in control room through Zigbee wireless protocol.
In a typical operating setup, the back to back connected thyristor pair (2) and
EC(1) are situated in a panel at ESP control room and the HVR(3) is located on
ESP field roof top. Usually control room and ESP fields are 100 to 300 meters
apart.
The Electronic Controller (EC), which receives the feedback signals and decodes
and executes the software methods to control the ESP, is shown in Fig.2.
In Fig.2, block (8) is a power supply unit for the EC which provides power for the
controller and peripheral devices.
In Fig.2, block (9) is a wireless receiver unit with a GSM antenna. It is a core
module based microcontroller for Zigbee. It executes the Zigbee protocol stack.
It receives the ESP Current and voltage feedbacks and alarm status signals from
the HVR in the form of Zigbee wireless frames from the field level sensor and
transmitter unit (block (4) in Fig.l). It then gives the feedback data to a central
processor (microcontroller) (block (7) in Fig.2).
In Fig.2, block (10) is an interface connecting the wired feedback signal (HVR
primary voltage and current) from EC panel to the microcontroller.
In Fig.2, block (11) is an interface for coupling the thyristor firing control pulses
from microcontroller to the back to back connected thyristor pair. Power supplied
to ESP depends on the firing of these thyristors.
In Fig.2, block (7) is the central processor (microcontroller) which executes the
software methods for feedback control of ESP. It has provisions to take analog
and digital signals as feedback signals. It has provisions to give out control
signals based on input signals for controlling the ESP. It has inbuilt memory to
store the program (control logic). It executes the software methods to
implement the feedback control for ESP energisation, spark/arc detection and
quenching, back corona detection and suppression based on both HVR primary
(transformer primary voltage and current) and secondary(ESP voltage and
current) parameters as feedback. It has a provision to trip the ESP field on
conditions of abnormal mismatch in ESP HVR primary and secondary parameters.
The hardware block diagram of the Field level sensor and transmitter unit,
disposed at HVR end, which reads the ESP voltage and current signals and HVR
alarms status and sends it to the Electronic Controller situated at ESP control
room, is shown in Fig.3.
In Fig.3, block (13) is an interface for coupling ESP current and voltage signals
and HVR alarm signals to the microcontroller.
In Fig.3, block (14) is the power supply unit which powers the microcontroller
and other peripherals.
In Fig.3, block (12) is the wireless transmitter unit with a GSM antenna. It has a
core module based microcontroller for Zigbee which transmits the ESP current
and voltage and alarm signals as Zigbee wireless data to the Electronic Controller
situated at ESP control room.
In Fig.3, block (11) is the microcontroller which receives the ESP voltage and
current signals and HVR alarm status signals, decodes and process it according
to the logic programmed in it and give it to the transmitter unit.
WE CLAIM :
1. A wire-less feedback control system for controlling ESP energisation,
spark/arc detection and quenching, back corona detection and
suppression based on both HVR primary (transformer primary voltage and
current) and secondary (ESP voltage and current) parameters as
combined feedback. HVR primary parameters are used for control while
HVR secondary parameters are compared with it for qualification and
reliability, the electrostatic precipitator (ESP) installation comprising a
plurality of fields each controllable by a dedicated electronic controller
(EC), the electrostatic precipitation being achieved by controlling a
plurality of high voltage rectifier (HVR) through the dedicated electronic
controllers (EC), the EC-HVR disposed at various locations in an industrial
plant, the system comprising:
- an electronic controller execution module having means for
receiving signals representing HVR secondary parameters feedback
transmitted wireless from the HVR end and the HVR-primary
parameter feedback transmitted from the EC-panels; the HVR
receiving power input through a back-to back connected thyristor
pair, the output of the HVR connected to field electrodes of the ESP
maintained at a high negative potential; a field level sensor
including transmitter unit for acquiring the HVR secondary feedback
including HVR-alarm data, and transmitting to EC through wireless
protocol; at least one antenna for receiving/transmitting signal; and
a first microprocessor for processing the received feedback data
and outputting control signal;
- an EC-receiving module having a wireless receiver unit with
antenna, and a microcontroller to receive the feedback including
alarm signals from the field level sensor including transmitter;
decode the signals, process the signals, and transmit the signals to
a central processor for executing the feed back control method of
the ESP; and a power supply unit.
2. The system as claimed in claim 1, comprising an interface connecting the
HVR-primary feedback signals from the EC panel to the central processor
of EC.
3. The system as claimed in claim 1, wherein the EC-execution module based
on the HVR-primary feedback signals transmits a firing signal with specific
pulses to fire the back to back connected thyristor pair.
4. The system as claimed in claim 1, comprising an interface for coupling the
thyristor firing control pulses from the microprocessor to the back to back
connected thyristor.
5. The system as claimed in claim 1, comprising an interface for coupling
HVR-secondary feedback signals and HVR alarm signals to the
microcontroller of the field level sensor and transmitter unit.
6. The system as claimed in claim 1, having Zigbee protocol based wireless
mesh network to interface the HVR secondary parameters with the
Electronic controller.
7. The system as claimed in claim 1, which eliminates all signal cables
running from HVR to EC and all the associated cable trays and support by
using a wireless system.
8. The system as claimed in claim 1, wherein the central processor is
provided with in-built control programme.
9. An improved method and apparatus for energisation control of
electrostatic precipitator as illustrated and explained in the accompanying
diagrams.

ABSTRACT

The invention relates to an wire-less feedback control system for controlling ESP
energisation, spark/arc detection and quenching, back corona detection and suppression
based on both HVR primary (transformer primary voltage and current) and secondary
(ESP voltage and current) parameters as combined feedback. HVR primary parameters
are used for control while HVR secondary parameters are compared with it for
qualification and reliability. The electrostatic precipitator (ESP) installation comprising a
plurality of fields each controllable by a dedicated electronic controller (EC), the
electrostatic precipitation being achieved by controlling a plurality of high voltage
rectifier (HVR) through the dedicated electronic controllers (EC), the EC-HVR disposed at
various locations in an industrial plant, the system comprising: an electronic controller
execution module having means for receiving signals representing HVR secondary
parameters feedback transmitted wireless from the HVR and the HVR-primary parameter
feedback transmitted by the EC-panels; the HVR receiving power input through a back-
to back connected thyristor pair, the output of the HVR connected to field electrodes of
the ESP maintained at a high negative potential; a field level sensor including
transmitter unit for acquiring the HVR secondary feedback including HVR-alarm data,
and transmitting to EC through wireless protocol; at least one antenna for
receiving/transmitting signal; and a first microprocessor for processing the received
feedback data and outputting control signal; an EC-receiving module having a wireless
receiver unit with antenna, and a microcontroller to receive the feedback including alarm
signals from the field level sensor including transmitter; decode the signals, process the
signals, and transmit the signals to a central processor for executing the feed back
control method of the ESP; and a power supply unit.