CA1220510A - Detecting, measuring and applying back corona parameters on an electrostatic precipitator - Google Patents
Detecting, measuring and applying back corona parameters on an electrostatic precipitatorInfo
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- CA1220510A CA1220510A CA000434463A CA434463A CA1220510A CA 1220510 A CA1220510 A CA 1220510A CA 000434463 A CA000434463 A CA 000434463A CA 434463 A CA434463 A CA 434463A CA 1220510 A CA1220510 A CA 1220510A
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- emitter
- back corona
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Abstract
TITLE: "DETECTING, MEASURING AND APPLYING BACK CORONA
PARAMETERS ON AN ELECTROSTATIC PRECIPITATOR"
ABSTRACT
The detection of the presence of back corona in an electrostatic precipitator, the measurement of para-meters associated with back corona and the control of the electrostatic precipitator system and associated plant.
The parameters detected provide indication of the sensit-ivity of the precipitator and dust to back corona formation, the severity of back corona occuring within the precipitator, the efficiency of the dust collection process and the level of dust build-up on the electrodes within the precipitator.
These parameters may be displayed to the operator and used in controlling precipitator systems and associated plant.
PARAMETERS ON AN ELECTROSTATIC PRECIPITATOR"
ABSTRACT
The detection of the presence of back corona in an electrostatic precipitator, the measurement of para-meters associated with back corona and the control of the electrostatic precipitator system and associated plant.
The parameters detected provide indication of the sensit-ivity of the precipitator and dust to back corona formation, the severity of back corona occuring within the precipitator, the efficiency of the dust collection process and the level of dust build-up on the electrodes within the precipitator.
These parameters may be displayed to the operator and used in controlling precipitator systems and associated plant.
Description
--- lZZQSlV
1. Field of the Invention This invention relates to a method of detecting back corona in electrostatic precipitators, measuring parameters, which indicate back corona susceptibility, precipitation performance and electrode contamination, and determine the back corona current and conductivity in order to control the precipitator and associated plant to limit back corona.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an electrostatic precipitator energi-sation circuit using silicon controlled rectifiers, a voltage transformed and half-wave rectification to supply a high voltage to an electrostatic precipitator emitter electrode.
Figure 2 illustrates the voltage and current wave forms at the emitter electrode of an electrostatic precipitator for low, medium and high energisation levels from a circuit similar to that shown in Figure 1.
1. Field of the Invention This invention relates to a method of detecting back corona in electrostatic precipitators, measuring parameters, which indicate back corona susceptibility, precipitation performance and electrode contamination, and determine the back corona current and conductivity in order to control the precipitator and associated plant to limit back corona.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an electrostatic precipitator energi-sation circuit using silicon controlled rectifiers, a voltage transformed and half-wave rectification to supply a high voltage to an electrostatic precipitator emitter electrode.
Figure 2 illustrates the voltage and current wave forms at the emitter electrode of an electrostatic precipitator for low, medium and high energisation levels from a circuit similar to that shown in Figure 1.
2. Brief Description of the Prior Art An electrostatic precipitator is a device which uses electricity to collect dust particles suspended in a gas. The device consists of two sets of electrodes, one of which is energised from a high voltage electricity supply while the second is earthed. The gas-particle mixture is passed between the two electrodes. The particles are charged by ions created by a corona about the energised, emitter electrode. The particles are then attracted to the collector electrode by the electric field.
Each precipitator may have one or more electrical zones, each energized from a single high voltage supply.
Each electrical zone norma~ly has many emitter electrodes connected in parallel and many connector electrodes connected to earth by the precipitator frame. This may result in an extremely large and expensive device.
The emitter electrodes are energised using a ; power control unit and a transformer to provide the high voltage necessary.. Figure 1 depicts a block diagram of a.
- 2a -.A
~-- lZZ~S10 typical electrostatic precipitator energisation system.
The power control unit regulates the primary A.C. input to the transformer using a silicon controlled rectifier phase angle controller or a magnetic amplifier. The high voltage transformer input is adjusted by varying the control unit output using a reference or setpoint signal.
Adjustment of the control unit reference signal will cause both the emitter voltage and emitter current to change.
The emitter voltage level signal and emitter current level signal are available, or can be obtained using voltage divider resistor networks, for each electrical section of ; the precipitator.
As the control unit reference signal is increased from zero, the emitter voltage increases but the emitter current remains at zero. At a certain emitter voltage, termed the "Emitter Corona Onset Voltage", the emitter current commences. Further increases in the control unit reference signal will cause the emitter current to increase.
The emitter voltage may increase or decrease depending on the precipitator conditions and energisation level.
Figure 2 depicts the emitter voltage waveform and emitter current waveform for low, medium and high energisation, or control unit reference signal, levels on a typical precipitator with 50 Hz.A.C. energisation. The emitter current is a pulsed waveform, coincident with increasing emitter voltage, while the emitter voltage has an A.C.
component superimposed on a D.C. level.
Back corona is the term used to describe the gaseous breakdown which occurs in the collected dust layer.
The breakdown is a result of intense electric fields -lZ20S10 created in the collected dust by the conduction of charge through the high resistive dust. The collection efficiency of the electrostatic precipitator is reduced by the presence of back corona. The detection and limit-ation of back corona is important when highly resistivedusts, such as Queensland coal fly ash, are being collected in an electrostatic precipitator.
As the energisation level of the electrostatic precipitator is increased, the precipitation of particles improves due to the higher inter-electrode electric fields and particle charge. Once sufficient charge flow exists for back corona to form, the detrimental effects caused by back corona will restrict the improvement attained from increasing energisation. The back corona effects, increas-ing rapidly with energisation, will cause a reduction in theelectrostatic precipitator's collection efficiency. A
maximum efficiency will occur at or just above the back corona formation energisation level.
In order to prevent back corona, gases are intro-duced into the precipitator intake gas before it reachesthe precipitator. The use of substances, such as Sulphur-triocide, Ammonia or Steam, to improve precipitator perform-ance by reducing or eliminating back corona has been pract-iced for some time. Since the cost of some of the substances used is high, the operating cost of the precipitator can increase dramatically if the addition of the conditioning agent is not regulated properly.
SUMMARY OF THE INVENTION
-It is an object of the present invention to detect the presence of back corona in an electrostatic ~ -' 1220510 . precipitator by monitoring the "Minimum Secondary Voltage".
; According to the present invention, this problem iY
solved by monitoring the minimum voltage level of the A.C.
component of the emitter voltage, termed the "Minimum Secondary Voltage". Back corona is detected if, for an increase in energisation, the "Minimum Secondary Voltage"
decreases or remains constant or if, for a constant energis-ation, the "Minimum Secondary Voltage" decreases.
In this manner the presence of back corona may be detected at normal operating energisation or during an increase or decrease in energisation. The detection of back corona would indicate a cause for reduced precipitator efficiency and is therefore of great significance.
A preferred object of the present invention is to measure important parameters at the minimum energisation level at which back corona can be detected. Parameters to be measured include "Effective Back Corona Onset Voltage", "Effective Back Corona Onset Current" and "Effective Back Corona Onset Minimum Voltage".
This problem is solved by lowering or raising the energisation, depending on the presence of back corona at the current operating energlsation, until, using the process previously described for the detection of back corona, the lowest energisation level at which back corona can be detected is found.
In this manner parameters which give an indication of the following may be measured:-(a) Precipitator or dust sensitivity to back corona -"Effective Back Corona Onset Current"
(b) Precipitator performance --~ ~Z2(~510 "Effective Back Corona Onset Voltage"
(c) Emitter electrode contamination -"Effective Back Corona Onset Minimum Voltage".
These parameters provide important date which can be used by operators or plant control systems to ensureoptimum precipitator operation.
An additional preferred object of the present invention is to determine important parameters associated with back corona at the normal energisation. Parameters to be obtained include "Effective Back Corona Current", "Effective Back Corona Conductivity" and "Effective Precipitator Conductivity".
This problem is solved by using calculations involv-ing the "Effective Back Corona Onset Current", the "Effective Back Corona Onset Voltage", the "Emitter Corona On~et Voltage",~the present average emitter voltage and the present average emitter current.
In this manner the parameters which give an indicat-ion of the following present operating conditions may be measured:-(a) Severity of back corona -"Effective Back Corona Current"
; (b) Collector electrode contamination -~ "Effective Precipitator COnductivity".
; 25These parameters provide continuous information on the operation of the precipitator. This information may be used by operators or plant control systems.
An additional preferred object of the present invention is to control the precipitator energisation level, electrode cleaning systems, conditioning system~ and assoc-~Z2(~S~O
iated plant using the information obtained from the previous measurements.
In this manner the control of the precipitator and associated plant can be maintained at an optimum. The use of these parameters would allow precipitator systems in which back corona occurs, to be operated at a lower cost while attaining better performance.
An additional preferred objective of the present invention is to display one or more of the precipitator conditions derived by the previously described methods.
In this manner indication of important precipitator conditions may be provided to the operating and maintenance personnel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The object of the invention is to detect the form-ation of back corona by measuring the emitter electrode electric current and voltage. The voltage at the emitter electrode is a D.C. level with a superimposed waveform. To detect the onset of back corona, the D.C. voltage of the lowest point of the wave must be measured. This value is called the "Minimum Secondary Voltage". Three possible measurement techniques are:-(a) Using an analogue peak detection and measurement circuit.
(b) Using a computer system to monitor the voltage level and determine the minimum level.
(c) Measurement of the voltage level immediately prior to energising the emitter electrode using a silicon controlled rectifier.
Back corona is detected if the "Minimum Secondary lZZC~S10 Voltage" decreases when the precipitator energisation is increased or held constant. The point at which a small change in electrostatic precipitator energisation results in one change in "Minimum Secondary Voltage" is termed the "Effective Back Corona Onset Point". This point may be determined by using an electronic system to control the electrostatic precipitator energisation and monitor the "Minimum Secondary Voltage". The control system could use two techniques to determine the "Effective Back Corona Onset Point":~
(a) Slowly increase or decrease the energisation and test for zero rate of change of the "Minimum Secondary Voltage".
(b) Slowly increase or decrease the energisation until a maximum level of "Minimum Secondary Voltage" is found.
Since the "Minimum Secondary Voltage" increases with energisation below the "Back Corona Onset Point" and decreases as the energisation is increased beyond this point, either of the methods described may be used to determine the "Back Corona Onset Point". The "Back Corona Onset Point" is an indieation of the energisation level at which back corona forms.
A preferred object of the invention is to measure ~ 25 relevant parameters assoeiated with the baek eorona deteetion.
; These parameters may be used in eontrol systems which adjust the energisation, electrode eleaning or gas eondition, as well as providing information on the suseeptibility of the dust to baek eorona, the precipitator performanee and the eleetrode eontamination.
-- 12Z~510 The average emitter current measured at the "Effective Back Corona Onset Point" is termed the "Effective Back Corona Onset Current". This parameter is an indication of the dust and the electrostatic precipit-ator susceptibility to back corona. A lower "EffectiveBack Corona Onset Current" indicates a higher susceptibility to back corona.
The average emitter voltage measured at the "Effective Back Corona Onset Point" is termed the "Effective Back Corona Onset Voltage". This parameter is an indication of the electrostatic precipitator performance. A higher "Effective Back Corona Onset Voltage" indicates higher electrostatic precipitator performance. By monitoring the "Effective Back Corona Onset Current" and the "Effective Back Corona Onset Voltage" an indication of the plant per-formance and back corona susceptibility is available.
The "Minimum Secondary Voltage" measured at the "Effective Back Corona Onset Point" is termed the "Effect-ive Back Corona Onset Minimum Voltage". By monitoring this voltage an indication of the emitter contamination or dust build-up is provided. Increasing "Effective Back Corona Onset Minimum Voltage" indicates an increase emitter contam-ination.
An additional preferred object of this invention is to determine a signal which is an indication of back corona current and a signal which is an indication of back corona conductivity. The signals which are determined are termed "Effective Back Corona Current" and "Effective Back Corona Conductivity" respectively. In order to determine these parameters it is necessary to determine the "Emitter Corona ~;~Z~S10 Onset Voltage", the "Effective Back Corona Onset Voltage"
and the "Effective Back Corona Onset Current" by reducing the energisation level, or increasing the energisation level from zero, until these points are detected, as described previously.
The average level of the emitter voltage and the average level of the emitter current must be measured at the operating energisation level. Two possible measurement techniques are:-(a) Using an analogue averaging circuit.
(b) Using a computer system to sample the signals a sufficient number of times, more than five samples per A.C. energisation cycle would be required, and average the sampled values over a time period equal to an integer number of A.C. energisation cycles.
The "Effective Back Corona Current" is determined byimplementing the following equation:-IB = IE ~ K (VE - VO) VE
where:- IB = "Effective Back Corona Current"
IE = measured average emitter current VO = "Emitter Corona Onset Voltage"
VE = Measured average emitter voltage.
The value of the constant K is determined by implementing the following equation:-K = IEBO
(VEBo-vo) VEBO
where:- IEBo = "Effective Back Corona Onset Current"
VEBO = "Effective Back Corona Onset Voltage"
The "Effective Back Corona Current" is an indication of the severity of the back corona present in the precipitator.
~Z2QS10 .. .
The higher the "Effective Back Corona Current", the more severe the back corona condition. As back corona is a prime cause for deteriorating precipitator efficiency, the "Effective Back Corona Current" signal would be used to ensure the energisation control was below the back corona severity at which precipitator efficiency deteriorates.
The "Effective Back Corona Conductivity" is determined by implementing the following equation:-B = B
VE
where: CB = "Effective Back Corona Conductivity".
The "Effective Precipitator Conductivity" is deter-mined by implementing the following equation:-CEp = (IE - IB) / VE
where: CEp = "Effective Precipitator Conductivity".
The "Effective Precipitator Conductivity" provides an indication of collector electrode contamination or dust build-up. An increase in the rate of change of "Effective ; Precipitator Conductivity" with changing emitter voltage indicates an increase in collector plate build-up.
An additional preferred object of this invention is to provide indication of precipitator conditions to the operator and to provide signals to precipitator and assoc-iated plant control systems. The control systems, which could use the signals derive by the method described above, include the precipitator energisation controller, the pre-cipitator electrode cleaning system and gas conditioning unit control systems. The implementation of the method described, or part thereof, may be included in one or more
Each precipitator may have one or more electrical zones, each energized from a single high voltage supply.
Each electrical zone norma~ly has many emitter electrodes connected in parallel and many connector electrodes connected to earth by the precipitator frame. This may result in an extremely large and expensive device.
The emitter electrodes are energised using a ; power control unit and a transformer to provide the high voltage necessary.. Figure 1 depicts a block diagram of a.
- 2a -.A
~-- lZZ~S10 typical electrostatic precipitator energisation system.
The power control unit regulates the primary A.C. input to the transformer using a silicon controlled rectifier phase angle controller or a magnetic amplifier. The high voltage transformer input is adjusted by varying the control unit output using a reference or setpoint signal.
Adjustment of the control unit reference signal will cause both the emitter voltage and emitter current to change.
The emitter voltage level signal and emitter current level signal are available, or can be obtained using voltage divider resistor networks, for each electrical section of ; the precipitator.
As the control unit reference signal is increased from zero, the emitter voltage increases but the emitter current remains at zero. At a certain emitter voltage, termed the "Emitter Corona Onset Voltage", the emitter current commences. Further increases in the control unit reference signal will cause the emitter current to increase.
The emitter voltage may increase or decrease depending on the precipitator conditions and energisation level.
Figure 2 depicts the emitter voltage waveform and emitter current waveform for low, medium and high energisation, or control unit reference signal, levels on a typical precipitator with 50 Hz.A.C. energisation. The emitter current is a pulsed waveform, coincident with increasing emitter voltage, while the emitter voltage has an A.C.
component superimposed on a D.C. level.
Back corona is the term used to describe the gaseous breakdown which occurs in the collected dust layer.
The breakdown is a result of intense electric fields -lZ20S10 created in the collected dust by the conduction of charge through the high resistive dust. The collection efficiency of the electrostatic precipitator is reduced by the presence of back corona. The detection and limit-ation of back corona is important when highly resistivedusts, such as Queensland coal fly ash, are being collected in an electrostatic precipitator.
As the energisation level of the electrostatic precipitator is increased, the precipitation of particles improves due to the higher inter-electrode electric fields and particle charge. Once sufficient charge flow exists for back corona to form, the detrimental effects caused by back corona will restrict the improvement attained from increasing energisation. The back corona effects, increas-ing rapidly with energisation, will cause a reduction in theelectrostatic precipitator's collection efficiency. A
maximum efficiency will occur at or just above the back corona formation energisation level.
In order to prevent back corona, gases are intro-duced into the precipitator intake gas before it reachesthe precipitator. The use of substances, such as Sulphur-triocide, Ammonia or Steam, to improve precipitator perform-ance by reducing or eliminating back corona has been pract-iced for some time. Since the cost of some of the substances used is high, the operating cost of the precipitator can increase dramatically if the addition of the conditioning agent is not regulated properly.
SUMMARY OF THE INVENTION
-It is an object of the present invention to detect the presence of back corona in an electrostatic ~ -' 1220510 . precipitator by monitoring the "Minimum Secondary Voltage".
; According to the present invention, this problem iY
solved by monitoring the minimum voltage level of the A.C.
component of the emitter voltage, termed the "Minimum Secondary Voltage". Back corona is detected if, for an increase in energisation, the "Minimum Secondary Voltage"
decreases or remains constant or if, for a constant energis-ation, the "Minimum Secondary Voltage" decreases.
In this manner the presence of back corona may be detected at normal operating energisation or during an increase or decrease in energisation. The detection of back corona would indicate a cause for reduced precipitator efficiency and is therefore of great significance.
A preferred object of the present invention is to measure important parameters at the minimum energisation level at which back corona can be detected. Parameters to be measured include "Effective Back Corona Onset Voltage", "Effective Back Corona Onset Current" and "Effective Back Corona Onset Minimum Voltage".
This problem is solved by lowering or raising the energisation, depending on the presence of back corona at the current operating energlsation, until, using the process previously described for the detection of back corona, the lowest energisation level at which back corona can be detected is found.
In this manner parameters which give an indication of the following may be measured:-(a) Precipitator or dust sensitivity to back corona -"Effective Back Corona Onset Current"
(b) Precipitator performance --~ ~Z2(~510 "Effective Back Corona Onset Voltage"
(c) Emitter electrode contamination -"Effective Back Corona Onset Minimum Voltage".
These parameters provide important date which can be used by operators or plant control systems to ensureoptimum precipitator operation.
An additional preferred object of the present invention is to determine important parameters associated with back corona at the normal energisation. Parameters to be obtained include "Effective Back Corona Current", "Effective Back Corona Conductivity" and "Effective Precipitator Conductivity".
This problem is solved by using calculations involv-ing the "Effective Back Corona Onset Current", the "Effective Back Corona Onset Voltage", the "Emitter Corona On~et Voltage",~the present average emitter voltage and the present average emitter current.
In this manner the parameters which give an indicat-ion of the following present operating conditions may be measured:-(a) Severity of back corona -"Effective Back Corona Current"
; (b) Collector electrode contamination -~ "Effective Precipitator COnductivity".
; 25These parameters provide continuous information on the operation of the precipitator. This information may be used by operators or plant control systems.
An additional preferred object of the present invention is to control the precipitator energisation level, electrode cleaning systems, conditioning system~ and assoc-~Z2(~S~O
iated plant using the information obtained from the previous measurements.
In this manner the control of the precipitator and associated plant can be maintained at an optimum. The use of these parameters would allow precipitator systems in which back corona occurs, to be operated at a lower cost while attaining better performance.
An additional preferred objective of the present invention is to display one or more of the precipitator conditions derived by the previously described methods.
In this manner indication of important precipitator conditions may be provided to the operating and maintenance personnel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The object of the invention is to detect the form-ation of back corona by measuring the emitter electrode electric current and voltage. The voltage at the emitter electrode is a D.C. level with a superimposed waveform. To detect the onset of back corona, the D.C. voltage of the lowest point of the wave must be measured. This value is called the "Minimum Secondary Voltage". Three possible measurement techniques are:-(a) Using an analogue peak detection and measurement circuit.
(b) Using a computer system to monitor the voltage level and determine the minimum level.
(c) Measurement of the voltage level immediately prior to energising the emitter electrode using a silicon controlled rectifier.
Back corona is detected if the "Minimum Secondary lZZC~S10 Voltage" decreases when the precipitator energisation is increased or held constant. The point at which a small change in electrostatic precipitator energisation results in one change in "Minimum Secondary Voltage" is termed the "Effective Back Corona Onset Point". This point may be determined by using an electronic system to control the electrostatic precipitator energisation and monitor the "Minimum Secondary Voltage". The control system could use two techniques to determine the "Effective Back Corona Onset Point":~
(a) Slowly increase or decrease the energisation and test for zero rate of change of the "Minimum Secondary Voltage".
(b) Slowly increase or decrease the energisation until a maximum level of "Minimum Secondary Voltage" is found.
Since the "Minimum Secondary Voltage" increases with energisation below the "Back Corona Onset Point" and decreases as the energisation is increased beyond this point, either of the methods described may be used to determine the "Back Corona Onset Point". The "Back Corona Onset Point" is an indieation of the energisation level at which back corona forms.
A preferred object of the invention is to measure ~ 25 relevant parameters assoeiated with the baek eorona deteetion.
; These parameters may be used in eontrol systems which adjust the energisation, electrode eleaning or gas eondition, as well as providing information on the suseeptibility of the dust to baek eorona, the precipitator performanee and the eleetrode eontamination.
-- 12Z~510 The average emitter current measured at the "Effective Back Corona Onset Point" is termed the "Effective Back Corona Onset Current". This parameter is an indication of the dust and the electrostatic precipit-ator susceptibility to back corona. A lower "EffectiveBack Corona Onset Current" indicates a higher susceptibility to back corona.
The average emitter voltage measured at the "Effective Back Corona Onset Point" is termed the "Effective Back Corona Onset Voltage". This parameter is an indication of the electrostatic precipitator performance. A higher "Effective Back Corona Onset Voltage" indicates higher electrostatic precipitator performance. By monitoring the "Effective Back Corona Onset Current" and the "Effective Back Corona Onset Voltage" an indication of the plant per-formance and back corona susceptibility is available.
The "Minimum Secondary Voltage" measured at the "Effective Back Corona Onset Point" is termed the "Effect-ive Back Corona Onset Minimum Voltage". By monitoring this voltage an indication of the emitter contamination or dust build-up is provided. Increasing "Effective Back Corona Onset Minimum Voltage" indicates an increase emitter contam-ination.
An additional preferred object of this invention is to determine a signal which is an indication of back corona current and a signal which is an indication of back corona conductivity. The signals which are determined are termed "Effective Back Corona Current" and "Effective Back Corona Conductivity" respectively. In order to determine these parameters it is necessary to determine the "Emitter Corona ~;~Z~S10 Onset Voltage", the "Effective Back Corona Onset Voltage"
and the "Effective Back Corona Onset Current" by reducing the energisation level, or increasing the energisation level from zero, until these points are detected, as described previously.
The average level of the emitter voltage and the average level of the emitter current must be measured at the operating energisation level. Two possible measurement techniques are:-(a) Using an analogue averaging circuit.
(b) Using a computer system to sample the signals a sufficient number of times, more than five samples per A.C. energisation cycle would be required, and average the sampled values over a time period equal to an integer number of A.C. energisation cycles.
The "Effective Back Corona Current" is determined byimplementing the following equation:-IB = IE ~ K (VE - VO) VE
where:- IB = "Effective Back Corona Current"
IE = measured average emitter current VO = "Emitter Corona Onset Voltage"
VE = Measured average emitter voltage.
The value of the constant K is determined by implementing the following equation:-K = IEBO
(VEBo-vo) VEBO
where:- IEBo = "Effective Back Corona Onset Current"
VEBO = "Effective Back Corona Onset Voltage"
The "Effective Back Corona Current" is an indication of the severity of the back corona present in the precipitator.
~Z2QS10 .. .
The higher the "Effective Back Corona Current", the more severe the back corona condition. As back corona is a prime cause for deteriorating precipitator efficiency, the "Effective Back Corona Current" signal would be used to ensure the energisation control was below the back corona severity at which precipitator efficiency deteriorates.
The "Effective Back Corona Conductivity" is determined by implementing the following equation:-B = B
VE
where: CB = "Effective Back Corona Conductivity".
The "Effective Precipitator Conductivity" is deter-mined by implementing the following equation:-CEp = (IE - IB) / VE
where: CEp = "Effective Precipitator Conductivity".
The "Effective Precipitator Conductivity" provides an indication of collector electrode contamination or dust build-up. An increase in the rate of change of "Effective ; Precipitator Conductivity" with changing emitter voltage indicates an increase in collector plate build-up.
An additional preferred object of this invention is to provide indication of precipitator conditions to the operator and to provide signals to precipitator and assoc-iated plant control systems. The control systems, which could use the signals derive by the method described above, include the precipitator energisation controller, the pre-cipitator electrode cleaning system and gas conditioning unit control systems. The implementation of the method described, or part thereof, may be included in one or more
3 of the above control systems or be an independent measure-ment system.
12Z~510 The energisation control unit could use the "Effective Back Corona Current" signal. The energisat-ion level would be adjusted until the desired level of "Effective Back Corona Current" was attained. Alternat-ively the energisation control unit could use the"Effective Back Corona Onset Current" as a reference point and adjust the energisation level until the ; emitter current was the desired amount above or below this reference point.
The electrode cleaning systems are operated at set intervals of time with, in some cases, a variable intensity.
By monitoring the change in electrode contamination, using the methods previously described, the cleaning period and intensity can be adjusted to ensure excessive contamination does not occur and cleaning is not excessive.
Gas conditioning apparatus is used to improve the dust resistivity by injecting chemicals into the gas-particle mixture. The prime objective of this is to eliminate back corona. By monitoring the "Effective Back Corona Current" for a constant energisation level or by monitoring the "Effective Back Corona Onset Current", the amount of chemical injected may be restricted to that necessary to achieve the back corona reduction desired. The volume of conditioning agent would be adjusted automatically until the desired "Effective Back Corona Current" or "Effective Back Corona Onset Current" was achieved. The conditioning agent could be injected when back corona is detected at the operating energisation level or when the "Effective Back Corona Current" rises above a desired level.
- ~ZZQ510 The detection methods, described previously, could be implemented by an analogue electronic system but, in practice, a microcomputer would be used to carry out the required measurements. Inputs to the microcomputer would include emitter voltage signal, emitter current signal, maximum emitter voltage, "Minimum Secondary Voltage", and maximum emitter current. The last three signals would be obtained, from the emitter voltage and emitter current signals, using analogue peak detectors or microcomputer sampling techniques, as described previously. The micro-computer would have an output signal which would allow the energisation level to be varied.
The parameters measured would be available to the operator via an indicator, display or printer. The micro-computer could be used to carry out other functions, suchas energisation control, electrode cleaning control or conditioning control, in addition to the measurements deseribed in this invention. The back eorona deteetion system eould be incorporated as a part of the appropriate eontrol system, possibly an existing mierocomputer, and may not require any additional equipment.
3o
12Z~510 The energisation control unit could use the "Effective Back Corona Current" signal. The energisat-ion level would be adjusted until the desired level of "Effective Back Corona Current" was attained. Alternat-ively the energisation control unit could use the"Effective Back Corona Onset Current" as a reference point and adjust the energisation level until the ; emitter current was the desired amount above or below this reference point.
The electrode cleaning systems are operated at set intervals of time with, in some cases, a variable intensity.
By monitoring the change in electrode contamination, using the methods previously described, the cleaning period and intensity can be adjusted to ensure excessive contamination does not occur and cleaning is not excessive.
Gas conditioning apparatus is used to improve the dust resistivity by injecting chemicals into the gas-particle mixture. The prime objective of this is to eliminate back corona. By monitoring the "Effective Back Corona Current" for a constant energisation level or by monitoring the "Effective Back Corona Onset Current", the amount of chemical injected may be restricted to that necessary to achieve the back corona reduction desired. The volume of conditioning agent would be adjusted automatically until the desired "Effective Back Corona Current" or "Effective Back Corona Onset Current" was achieved. The conditioning agent could be injected when back corona is detected at the operating energisation level or when the "Effective Back Corona Current" rises above a desired level.
- ~ZZQ510 The detection methods, described previously, could be implemented by an analogue electronic system but, in practice, a microcomputer would be used to carry out the required measurements. Inputs to the microcomputer would include emitter voltage signal, emitter current signal, maximum emitter voltage, "Minimum Secondary Voltage", and maximum emitter current. The last three signals would be obtained, from the emitter voltage and emitter current signals, using analogue peak detectors or microcomputer sampling techniques, as described previously. The micro-computer would have an output signal which would allow the energisation level to be varied.
The parameters measured would be available to the operator via an indicator, display or printer. The micro-computer could be used to carry out other functions, suchas energisation control, electrode cleaning control or conditioning control, in addition to the measurements deseribed in this invention. The back eorona deteetion system eould be incorporated as a part of the appropriate eontrol system, possibly an existing mierocomputer, and may not require any additional equipment.
3o
Claims (20)
1. A method for operating an electrostatic precipitator including an emitter electrode having a voltage and a current and being energized by a control unit which supplies to the emitter electrode a voltage and a current and which allows an energization level to be varied, the energization level being determined by both the voltage and the current supplied by the control unit, the method comprising monitoring the emitter electrode voltage for operating the precipitator in dependence on detected relation of energization level and emitter electrode voltage, operating the emitter electrode with the emitter electrode voltage having an AC component superimposed on a DC level, characterized in monitoring the minimum level of the AC component of the emitter electrode voltage and the emitter electrode current when operating the precipitator with an emitter electrode current dependent on the detection of the onset of a back corona phenomenon, wherein the back corona phenomonon is assumed to be detected whenever the minimum emitter electrode voltage level is constant or decreases during an increase in energization level, the minimum emitter electrode voltage level decreases during a constant energization level or the minimum emitter electrode voltage level is constant or increases during a decrease of energization level.
2. A method for operating an electrostatic precipitator according to claim 1, characterized by determining the back corona onset point by raising or lowering the energization level to determine the lowest energization level at which back corona is detected, this energization level being the back corona onset point.
3. A method for operating an electrostatic precipitator according to claim 1, characterized by determining the change in precipitator efficiency when raising or lowering the energization level while detecting the presence of back corona, where an in-crease, or decrease, in the change in the minimum voltage level of the AC component of the emitter (or high tension) voltage in-dicates an increase, or decrease respectively, in the precipitator performance.
4. A method for operating an electrostatic precipitator according to claim 2, characterized by determining the precipitator or dust susceptibility to back corona including the steps of:
a) measuring the average emitter current at the back corona onset point; and b) monitoring the average emitter current where an in-crease, or decrease, in the average emitter current indicates a decrease, or increase, respectively, in the susceptibility.
a) measuring the average emitter current at the back corona onset point; and b) monitoring the average emitter current where an in-crease, or decrease, in the average emitter current indicates a decrease, or increase, respectively, in the susceptibility.
5. A method for operating an electrostatic precipitator according to claim 2, characterized by determining the change in precipitator performance including the steps of:
a) measuring the average emitter (or high tension) volt-age at the back corona onset point; and b) monitoring the change in the average emitter (or high tension) voltage where an increase, or decrease, in the aver-age emitter (or high tension) voltage indicates an increase, or decrease, respectively, in precipitator performance.
6. A method for operating an electrostatic precipitator according to claim 2, characterized by determining a change in emitter electrode contamination including the steps of:
a) measuring the average emitter (or high tension) volt-age at the back corona onset point; and b) monitoring the change in the average emitter (or high tension) voltage where an increase, or decrease, in the aver-age emitter (or high tension) voltage indicates an increase, or decrease, respectively, in precipitator performance.
6. A method for operating an electrostatic precipitator according to claim 2, characterized by determining a change in emitter electrode contamination including the steps of:
Claim 6 cont.
a) measuring the minimum AC component of the emitter (or high tension) voltage at the back corona onset point; and b) monitoring the change in the minimum AC component of the emitter (or high tension) voltage where an increase, or decrease, in the minimum AC component at the emitter (or high tension) voltage indicates an increase, or decrease, respectively, in emitter electrode contamination.
7. A method for operating an electrostatic precipitator according to claim 2, characterized by determining the back corona current including the steps of;
a) periodically measuring the maximum average emitter (or high tension) voltage at which the average emitter current is zero, this voltage being the average emitter (or high tension) voltage at which emitter corona commences;
b) periodically or continuously determining the back corona onset point;
c) operating the precipitator at or above the back corona onset point;
d) measuring the average emitter (or high tension) volt-age at the operating point;
e) measuring the average emitter current at the oper-ating point;
f) calculating the back corona current at the operating point by the formula:
IB = IE - K (VE - VO) VE
wherein:
IB = back corona current at the operating point IE = average emitter current at the operating point
a) measuring the minimum AC component of the emitter (or high tension) voltage at the back corona onset point; and b) monitoring the change in the minimum AC component of the emitter (or high tension) voltage where an increase, or decrease, in the minimum AC component at the emitter (or high tension) voltage indicates an increase, or decrease, respectively, in emitter electrode contamination.
7. A method for operating an electrostatic precipitator according to claim 2, characterized by determining the back corona current including the steps of;
a) periodically measuring the maximum average emitter (or high tension) voltage at which the average emitter current is zero, this voltage being the average emitter (or high tension) voltage at which emitter corona commences;
b) periodically or continuously determining the back corona onset point;
c) operating the precipitator at or above the back corona onset point;
d) measuring the average emitter (or high tension) volt-age at the operating point;
e) measuring the average emitter current at the oper-ating point;
f) calculating the back corona current at the operating point by the formula:
IB = IE - K (VE - VO) VE
wherein:
IB = back corona current at the operating point IE = average emitter current at the operating point
Claim 7 cont.
VE = average emitter voltage at the operating point VO = average emitter voltage at which emitter corona commences K = a constant.
VE = average emitter voltage at the operating point VO = average emitter voltage at which emitter corona commences K = a constant.
8. A method for operating an electrostatic precipitator according to claim 7, characterized by determining the severity of back corona by monitoring the back corona current where an increase, or decrease, in the back corona current indicates an increase, or decrease, respectively, in back corona severity.
9. A method for operating an electrostatic precipitator according to claim 7, characterized by determining the precip-itator conductivity including the steps of:
a) measuring the average emitter current at the oper-ating point;
b) measuring the average emitter (or high tension) volt-age at the operating point; and c) calculating the precipitator conductivity at the operating point by the formula:
CEP = (IE - IB) / VE
when: CEP = precipitator conductivity at the operating point IE = average emitter current at the operating point IB = back corona current at the operating point VE = average emitter voltage at the operating point.
a) measuring the average emitter current at the oper-ating point;
b) measuring the average emitter (or high tension) volt-age at the operating point; and c) calculating the precipitator conductivity at the operating point by the formula:
CEP = (IE - IB) / VE
when: CEP = precipitator conductivity at the operating point IE = average emitter current at the operating point IB = back corona current at the operating point VE = average emitter voltage at the operating point.
10. A method for operating an electrostatic precipitator according to claim 9, characterized by determining a change in the collector electrode contamination by monitoring the changes in precipitator conductivity where an increase or decrease , in the precipitator conductivity indicates a decrease, or increase, respectively, in the collector electrode contamination.
11. A method for operating an electrostatic precipitator according to claim 9, characterized by determining the collector electrode contamination including the steps of:
a) measuring the average emitter (or high tension) voltage at the operating point;
b) increasing or decreasing the energization level to change the operating point;
c) measuring the increase or decrease in conductivity d) measuring the increase or decrease in average emitter (or high tension) voltage at the same point relative to that measured in step (a);
e) determining the ratio of the change in conductivity to the change in average emitter (or high tension) voltage, where this valve indicates the level of collector contamination.
a) measuring the average emitter (or high tension) voltage at the operating point;
b) increasing or decreasing the energization level to change the operating point;
c) measuring the increase or decrease in conductivity d) measuring the increase or decrease in average emitter (or high tension) voltage at the same point relative to that measured in step (a);
e) determining the ratio of the change in conductivity to the change in average emitter (or high tension) voltage, where this valve indicates the level of collector contamination.
12. A method for operating an electrostatic precipitator according to claim 7, characterized by measuring the back corona conductivity including the steps of:
a) measuring the average emitter (or high tension) volt-age at the same point; and b) calculating the back corona conductivity by the formula:
CB = IB/VE
when: IB = back corona current VE = average emitter voltage CB = back corona conductivity.
a) measuring the average emitter (or high tension) volt-age at the same point; and b) calculating the back corona conductivity by the formula:
CB = IB/VE
when: IB = back corona current VE = average emitter voltage CB = back corona conductivity.
13. A method for operating an electrostatic precipitator according to claim 2, characterized by controlling the precip-itator energization level including the steps of:
a) at given intervals of time, determining the back corona onset point;
b) measuring the emitter current at the back corona onset point;
c) between the given intervals of time, adjusting the energization level to maintain the emitter current at a set level relative to the emitter current measured at the back corona on-set point.
a) at given intervals of time, determining the back corona onset point;
b) measuring the emitter current at the back corona onset point;
c) between the given intervals of time, adjusting the energization level to maintain the emitter current at a set level relative to the emitter current measured at the back corona on-set point.
14. A method for operating an electrostatic precipitator according to claim 7, characterized by controlling the precip-itator energization level by adjusting the energization level to maintain a set level of back corona current.
15. A method for operating an electrostatic precipitator according to claim 6, characterized by controlling the emitter electrode cleaning including the steps of:
a) mechanically vibrating the emitter electrode;
b) at given intervals of time, measuring the change in emitter electrode contamination;
c) increasing, or decreasing the period and/or intensity depending on an increase, or decrease, respectively, in the emitter electrode contamination.
16. A method for operating an electrostatic precipitator according to claim 10, characterized by controlling the collector electrode cleaning including the steps of:
a) mechanically vibrating the collector electrode;
b) at given intervals of time, measuring the change in collector electrode contamination;
a) mechanically vibrating the emitter electrode;
b) at given intervals of time, measuring the change in emitter electrode contamination;
c) increasing, or decreasing the period and/or intensity depending on an increase, or decrease, respectively, in the emitter electrode contamination.
16. A method for operating an electrostatic precipitator according to claim 10, characterized by controlling the collector electrode cleaning including the steps of:
a) mechanically vibrating the collector electrode;
b) at given intervals of time, measuring the change in collector electrode contamination;
Claim 16 cont.
c) increasing, or decreasing, the period and/or inten-sity of the mechanical vibrations depending on an increase, or decrease, respectively, on the collector electrode contamination.
c) increasing, or decreasing, the period and/or inten-sity of the mechanical vibrations depending on an increase, or decrease, respectively, on the collector electrode contamination.
17. A method for operating an electrostatic precipitator according to claim 11, characterized by controlling the collector electrode cleaning including the steps of:
a) mechanically vibrating the collector electrode;
b) at given intervals of time, measuring the collector contamination;
c) adjusting the period and/or intensity of the mechan-ical vibrations to maintain a set level of collector contamination.
a) mechanically vibrating the collector electrode;
b) at given intervals of time, measuring the collector contamination;
c) adjusting the period and/or intensity of the mechan-ical vibrations to maintain a set level of collector contamination.
18. A method for operating an electrostatic precipitator according to claim 1, characterized by controlling the period and/or level of gas conditioning including the steps of:
a) at a set precipitator energization level, or set emitter current, detecting if back corona is present;
b) if back corona is present, increasing the level and/or period of gas conditioning until back corona is not detected; and c) if back corona is not present, decreasing the level and/or period of gas conditioning until back corona is detected.
a) at a set precipitator energization level, or set emitter current, detecting if back corona is present;
b) if back corona is present, increasing the level and/or period of gas conditioning until back corona is not detected; and c) if back corona is not present, decreasing the level and/or period of gas conditioning until back corona is detected.
19. A method for operating an electrostatic precipitator according to claim 4, characterized by controlling the period and/or level of gas conditioning by adjusting the period and/or level of conditioning to maintain a set level of back corona susceptibility.
20. A method for operating an electrostatic precipitator according to claim 7, characterized by controlling the period and/or level of gas conditioning by adjusting the period and/or level of conditioning to maintain a set level of back corona current.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000434463A CA1220510A (en) | 1983-08-12 | 1983-08-12 | Detecting, measuring and applying back corona parameters on an electrostatic precipitator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000434463A CA1220510A (en) | 1983-08-12 | 1983-08-12 | Detecting, measuring and applying back corona parameters on an electrostatic precipitator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1220510A true CA1220510A (en) | 1987-04-14 |
Family
ID=4125852
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000434463A Expired CA1220510A (en) | 1983-08-12 | 1983-08-12 | Detecting, measuring and applying back corona parameters on an electrostatic precipitator |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1220510A (en) |
-
1983
- 1983-08-12 CA CA000434463A patent/CA1220510A/en not_active Expired
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