JPS6115752A - Lamp pulsated burst voltage driveing of electric precipitator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrostatic precipitators, and more particularly to circuits and methods for operating electrostatic precipitators.

An electrostatic precipitator is an electrical device used to remove particulate matter from a stream of gas passed between oppositely charged collecting electrodes. Electrostatic precipitators are used in many industrial fields, for example in chemical plants, as well as in power plants and other places where particulate pollution can occur. recently,
Electrostatic precipitators are being used more often than in the past because of the increasing need to remove particles and gases from gases that are exhausted to the atmosphere. The primary concern with electrostatic precipitators is that they are high-energy devices, typically in the tens of kilowatts.
It should be understood that this is a device that consumes a lot of electrical energy. Therefore, it is important to appropriately energize the electrostatic precipitator not only from the viewpoint of particle collection efficiency but also from the economical and reliability points of operation of the precipitator.

Many precipitator configurations have been used in the past. However, each of them fundamentally operates on fairly well-established principles. Precipitators typically have a pair of conductive electrodes. One of the electrodes typically has two parallel planar metal sheets spaced about 9 inches apart. These sheets are typically operated at ground potential. Additionally, a planar array of wires arranged parallel to and intermediate the conductive sheet and electrically connected to each other is provided to constitute a second electrode. This planar liner array electrode is maintained at a high potential. It is also possible to install a wire electrode and apply a high voltage to the sheet electrode, but this mode of operation is usually not adopted for safety reasons. A number of parallel planar electrodes are assembled within a housing that defines a plurality of parallel gas flow paths through the spaces between the precipitator electrodes. These channels are also defined, at least in part, by the structure and arrangement of the plate electrodes. Generally, commercially available precipitators use a plurality of plate electrode and wire grid electrode pairs. The typical area of a precipitator has a practical area of up to approximately 30,000 square feet of electrode area. Naturally, in such a configuration there will be some amount of electrical capacitance between the wire electrode and the plate electrode. Typical precipitator section capacitance is on the order of 0.05 to 0.15 μF.

Although the operation of such a precipitator appears to be relatively @Qi, several phenomena may occur that limit the particle collection efficiency of the precipitator. When the same type of particles is removed in the same amount from the gas stream in the same precipitator,
The amount of electrical energy and power consumed by using a precipitator with different biasing methods or different voltage application methods is significantly affected. It should be noted that precipitators typically operate at approximately 40,000 volts and 80,000 volts.
Operating at peak voltages between 0 volts and each section approximately 1.
A current of 5 amperes may be passed through it.

Therefore, it is easily understood that a power level of 80 kilowatts is typical for the precipitator. Therefore, electrical efficiency is an important economic factor in plants that use electrostatic precipitators to remove particulate matter. Furthermore, for continuous plant operation, the reliability of the precipitator and the components that power the precipitator is extremely important.

In normal operation, particulate matter within the gas to be treated acquires a negative charge primarily as a result of induced ionization effects occurring in the vicinity of the precipitator cathode wire. The dust particles thus charged are then attracted to the precipitator anode plate, where an anode dust layer accumulates. As this dust layer accumulates, a thicker dust layer is formed on the plate (sheet) electrode. If a significant portion of the particle object is formed from a high resistivity material, the voltage drop between the cathode and the dust layer is reduced by the voltage drop across the high resistivity dust layer in the vicinity of the anode plate 1. , thereby reducing particle charging and collection.

Furthermore, a high electric field is formed within this dust layer, and back corona discharges tend to occur within the dust layer, which degrades the efficiency. Such a high resistivity dust layer generates a back-corona phenomenon, in which ions are actually ejected from the dust layer towards the cathode wire. This back-corona phenomenon thus functions to reduce particle charging and collection.

Although it is possible to periodically remove the dust layer by vibrating, lapping or bending the anode plate, the formation of such a high resistivity layer has a corresponding effect on efficiency. There is a decrease. In the case of high resistivity dust, it is desirable to limit the current through the dust layer to eliminate such back-corona phenomena. One proposed solution to this problem is to operate the electrostatic precipitator near the corona onset voltage.

However, this method results in non-uniform current flow, loss of efficiency, and control difficulties. Therefore, an efficient, effective, and economical method for energizing electrostatic precipitators is desired, especially for high resistivities, i.e., resistivities greater than about 10-"Ω.0m. This is the case with the recovery of resistive dust particles. For example, such dust is generated when burning low sulfur coal used by the power generation industry.

=8- In order to devise a method of operating an electrostatic precipitator that is efficient, reliable, controllable, and relatively inexpensive to implement, the construction of an electrical circuit for energizing the precipitator A lot of research has been done on this and its operation. Additionally, there is no general consensus among those skilled in the art regarding the optimal precipitator energization method. That different engineers were moving in different directions will be appreciated by reviewing the specific literature and patents described below. However, the various pulse energization methods considered by others in the art are generally divided into two types.
It is understood that there are two types: wide pulse drive and narrow pulse drive. It should also be understood that electrical circuits for energizing precipitators are typically limited to producing two basic pulse waveforms: a sine wave pulse and a square pulse. It is.

Traditional precipitator configurations that use primarily sinusoidal waveform pulses do not suffer from high-speed switching problems;
It will be appreciated that the cost of circuitry capable of performing such operations is generally relatively low. However, the characteristics of sinusoidal pulses are inherently limited. For example, in a wide pulse drive method using sinusoidal pulses, a sinusoidal waveform with a relatively long period (typically a rectified sinusoidal waveform) must be used due to the wide pulse width. There is a need not to. However, such sinusoidal waveforms with large periods have slow rise and fall times and relatively small times of peak precipitator activation. Therefore, the amount of power that can be effectively applied to dust collection within this time is significantly reduced.

As an alternative to the sinusoidal pulse energization method, rectangular pulses with relatively rapid rise and fall times and relatively flat peak levels can be effectively used to energize the precipitator. be. However, it must be noted that in this case "activating the precipitator" means rapid switching of very high voltage and current levels. Although it is possible to generate and use such rectangular pulses, it is difficult to do so without incurring the high cost of the switching elements required to perform the rapid switching function. is impossible. Furthermore, even with the expense of such high-voltage switching equipment, such high-voltage, high-speed,
Long-term reliability is often a major issue in field operation due to the large electrical stresses that are unavoidably applied to high-energy switching components. Therefore, the rectangular pulses used to energize electrostatic precipitators impose significant limitations.

Various experiments in electrostatic precipitator technology have proposed various means of electrically increasing the collection efficiency of electrostatic precipitators beyond that achieved with conventional rectified AC drives. These methods use electrical pulses superimposed on a constant reference voltage and are classified into the two general types mentioned above: wide pulse drive and narrow pulse drive. The narrow pulse driving method is described, for example, in the 1979 Technical Bulletin of Research Cottrell Incorporated, "Technological Development of Pulse Activation", 1.
opment of ['ulse-Energjza
In the narrow pulse drive method disclosed therein, the extremely short (
Pulses of approximately 1 microsecond or less) are produced using conventional rectified 6
Applied with a reference voltage of 0 Hz. However, there are several important issues associated with narrow pulse drive schemes. First is the cost of the circuit components required to perform the high speed switching function. Furthermore,
Energy recovery in narrow pulse drive schemes is extremely difficult and rarely, if ever, possible. The reason why it is not possible to recover the energy supplied during part of the cycle in narrow pulse driving is that a significant portion of the energy supplied to the wire or plate is actually radiated as electromagnetic waves. That's true. This not only results in the loss of some of the available energy, but also causes radio frequency interference and associated EM1
This will cause problems. Another important issue associated with narrow pulse drive schemes is the reliability of circuit components as described above. Therefore, it is understood that the narrow pulse energization method is quite limited as an energization method for an electrostatic precipitator.

Another circuit for pulse driving an electrostatic precipitator using pulses having a pulse width of about 70 microseconds is
“New Trends in Electrostatic Precipitators: Wide Duct Spacing, Pre-Charging” by Elge H. Petersen.

Pulse energization (New Trends jn Elect
Rostatjc Precjpi, tatjon:
Wjde Duct Spacing, Prech
arging.

Pu1se Energjzatjon)”, IEE
E-Transactions on Industry Applications, No. 5. IA-Volume 17, 1
It is described in the literature published in September 981/Re0, pp. 496-501.

In the operation of the circuit disclosed in the Petersen reference, the DC component of the energizing waveform is kept just below the corona onset level, so that the pulses provide the major portion of the energy for particle retrieval. is provided. The precipitator current is controlled by changing the pulse frequency. In order to provide the desired pulse power level, Petersen discloses that a pulse voltage is applied to the precipitator over a relatively long period of time in order to do any significant amount of work on the particles. It is usually necessary to apply

Furthermore, the voltage pulses generated by the circuit shown in the Petersen reference exhibit voltage undershoot characteristics, which, while not a major problem in themselves, become more pronounced when the pulse frequency is increased. The magnitude increases so that the voltage applied to the precipitator is essentially a continuous sinusoidal waveform symmetrically superimposed on the DC reference voltage. As a result, the pulsed voltage subtracts each half period from the reference voltage and becomes less effective than the unidirectional pulse in improving the particle charging and collection process, especially when the reference voltage is reduced to the current onset voltage. This can be said if they are close. Therefore, there is a need to develop an electrostatic precipitator pulse drive system that can overcome these difficulties.

Precipitator drive schemes that use pulse durations of about 0.2 to 2 milliseconds usually belong to the wide pulse drive scheme. Optimal or sub-optimal waveforms for pulsing the precipitator ensure that high current and high voltage are applied simultaneously for maximum duration without causing back corona discharge. Continuous operation at high voltages maximizes particle charging, directs particle movement, and provides uniform current density.

A wide pulse drive system with many of these characteristics is co-authored with ``High Voltage Thyristor for Use in Precipitators'' (lljgh Voltage Thyristor).
s Used In Precipitators)
”, Control Engineering, ] 981. In the scheme described in the above-mentioned literature, two high-voltage valves are required, each of which has a They have multiple thyristors connected in series with a voltage balancing component. However, these valves have reliability problems due to the voltage stress generated on them. Additionally, these valves are relatively It's expensive.

Gay published October 28, 1975], ord.
In U.S. Pat. No. 3,915,672 to L. Penney, an electrostatic precipitator activation circuit is disclosed.
The circuits disclosed therein require high voltage switching operations, which can therefore have a significant impact on the cost and reliability of the circuit. In addition, Penn
The precipitator disclosed in the ey patent specifically relates to a precipitator using a three-pole construction.

Generally, in the wide pulse drive method, the pulse waveform represents a flat waveform whose peak level is maintained for a sufficient time to provide the desired amount of power to enable the precipitator to accomplish its dust collection function. was needed. In the case of high resistivity dust, it is possible to substantially increase particle collection efficiency for waveforms with short rise and fall times compared to the pulse duration. It has been learned by the inventors that an additional improvement can be obtained by using a rapidly pulsed electric field, in which the rapid fluctuations cause the formation of blobs in the dust layer. This is based on the fact that the back corona is suppressed, and the effect of suppressing back corona is even lower in an electric field that changes relatively slowly. The inventors believe that this phenomenon is due to the effective presence of a relatively large RC time constant. This time constant is derived from a model of the dust layer as a parallel combination of a resistor and a capacitor. Of course, this dust layer exhibits both of these effects.

Lejf Kjde published October 4, 1977
No. 4,052,177 discloses a circuit that partially returns capacitive energy stored in an electrostatic precipitator to a DC storage capacitor, reducing the overall electrical efficiency of the circuit. is increasing.

However, the pulse drive method disclosed in the Kide patent is essentially the same as that described in the Petersen reference cited above. The rise and fall times of the pulse waveform shape are determined by the half-sine waveform of the pulses generated by the circuitry of such a system.

Another background technology related to driving an electrostatic precipitator is 11°J,
``Pulsing Method for Supplying High Voltage Power to Electrostatic Precipitators'' (A Pu1.se Met
hod for 5upp1. ying H,igh
Volt;age Power for E], ect
rostaticPrecipitation)”,
IEEE Transactions, November 1952,
It is described in the literature on page 326.

In summary, it can be seen that the need to control the collection current to prevent back corona while maintaining high efficiency is one of the more important issues driving electrostatic precipitators. Increasing dust collection efficiency and preventing back-corona IF have generally been considered to be contradictory control and design objectives. However, there is a need for an economical and easily controllable actuation method that provides simultaneous application of voltage, particle charging, and current. Additionally, it is believed that the peak voltage of the pulse should be maintained for a controllable period to provide the required collection energy. However, Kide and Pete
A system connected to an rSen transformer produces a sine wave rather than a flat-topped pulse, so its peak voltage is L u g for a given level of pulse energy.
This exceeds that used by the wide pulses generated by the a r and 5houp or Penney systems. As a result, back-corona conditions are more likely to occur. However, because of the cost, difficulty, and reliability issues associated with high voltage electrical switching components in wide pulse drive systems, it is possible to reap the benefits of wide pulse drive schemes at lower cost with improved reliability. Other methods and devices are desired. Additionally, control of the power and current level of the precipitator.”
It is desirable that these improvements be made without incurring losses of - or producing undesirable and blinding levels of radio frequency radiation. As described below, the present invention is capable of achieving these objectives.

Additionally, in another patent application filed concurrently today by the applicant, the applicant obtains the benefits of a wide pulse drive scheme without the attendant problems associated with high current and high voltage electrical signals for rapidly switching operations. A method and apparatus for driving a pulse beam is disclosed.

The present invention relates to an improvement of the pulse burst drive method disclosed in the co-filed patent application referred to in J-A. The pulse width of a wide drive system is typically chosen to be on the order of the ion transit time in the precipitator or somewhat shorter, so that substantially all of the injected into the precipitator during the pulse period is Charge exists in the gas between the electrodes at the end of the pulse. This large space charge can function to shield the corona electrode and reduce the electric field in the vicinity of the H-shaped electrode. Therefore, the injected current is maximum at the beginning of the pulse and decreases with time. This phenomenon generally applies to wide pulse drive systems. However, the precipitator activation (driving) of the present invention using a ramp-type pulse burst
The method significantly alleviates the problems mentioned above.

As is clear from the description of energizing or driving a dual electrostatic precipitator, there is considerable disagreement among engineers in the field as to what constitutes an optimal energizing method. There is disagreement. Furthermore, on the theoretical side, there are even more differences of opinion when it comes to explaining the effectiveness of Fufu's method compared to other methods. This means that although precipitators operate on basic principles that are fairly well understood, there are a number of critical secondary effects and controls that can be employed in the design of precipitator drive circuits. It is a result that is directly derived from the fact that the variable exists. However, the pulse burst energization method disclosed herein is proposed as a solution to a number of conflicting problems associated with precipitator energization, particularly when collecting high resistivity dust. I've never done it before. The method of the present invention overcomes a number of problems associated with energizing precipitators, such as those mentioned above, and in particular, the method of the present invention:
It can exhibit effects such as high reliability, low cost, low level electromagnetic radiation, and energy recovery ability.

In a preferred embodiment of the invention, a wide pulse driving method is used to drive or energize the precipitator, in which the voltage of the wide pulse increases over time. This driving method generally
It is not only applicable to the wide pulse driving method, but also to the pulse burst instant action method disclosed in the above-mentioned simultaneously filed patent application. When applied to a pulse burst driving method, the pulse burst according to the invention exhibits successively increasing voltage levels of the pulses within each pulse burst. The effect of this ramp voltage is to increase the average electric field and ion density during the pulse period. As a result, particle charging is significantly higher, thereby improving particle collection efficiency. Therefore,
Each successively applied pulse within a burst is more effective than a constant peak pulse voltage scheme.

This is because the preceding pulses within the burst do not create as large a space charge shield around the corona electrode (usually a wire electrode). According to the invention, the current injected into the precipitator is therefore distributed more evenly during a single pulse burst.

According to a preferred embodiment of the invention, a method of operating an electrostatic precipitator comprises applying a series of high voltage unidirectional pulses superimposed on a DC reference voltage between the electrodes of the precipitator. be. Additionally, each successive pulse within a pulse burst has a higher peak voltage than the previous pulse. Typically, during a single pulse burst,
The peak pulse voltage increases linearly. As used herein and in the claims, the term "pulse burst" has its ordinary meaning as used in the electrical engineering field, namely, a sequence of pulse waveforms that are closely spaced from each other. It means that. According to a preferred embodiment of the invention, the pulse burst is about 0.1 and 5
It has a period between milliseconds. According to another preferred embodiment of the invention, each waveform within the pulse burst may have a duration between about 0.02 milliseconds and about 0.7 milliseconds.

Typically, the applied DC voltage level is approximately 15 kpol 1
~ and about 50 kilovolts, typically chosen below the corona onset voltage level. Furthermore, a description will be given of an apparatus for carrying out a series of the methods of the present invention. Furthermore, although the invention is described herein with particular reference to a pulse burst drive method and apparatus, the invention is applicable to conventional wide pulse drive schemes in which the pulse voltage is increased during the pulse period. One thing should be noted.

It is an object of the present invention to provide a method and device for operating an electrostatic precipitator, which has the advantages of a wide pulse drive system.

Another object of the present invention is to provide an electrostatic precipitator operating technique that does not require the provision of multiple high voltage series connected semiconductor valves.

Yet another object of the present invention is to provide a technique for recovering reaction energy that is periodically transferred to an electrostatic precipitator. .

Still another object of the present invention is to provide a technique for more precisely controlling the electric power supplied to the electrostatic precipitator.

Yet another object of the present invention is to provide a technique for applying an energizing voltage level to a precipitator that has rapid rise and fall times.

Yet another object of the present invention is to provide a technique that alleviates the problems associated with space charge shielding of corona electrodes.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The pulse burst driving method disclosed in the above-mentioned present application and the patent application filed at the same time is well represented by the waveform shown in Figure 1, which plots the precipitator voltage v8 as a function of time. It is something. V in Figure 1
From the reference directions given in FIG. 3 for , and vS, it is easily understood that wire electrodes are preferably negatively charged in electrostatic precipitator applications. . Furthermore, it is understood from FIG. 1 that a DC component VB exists in v8. This DC component is usually selected at a level below the corona onset voltage. In this method of operation, the DC power source does not provide power to the precipitator, but instead precharges the capacitance of the precipitator at qt, reducing the power required from the pulsed source. , and allows complete control of the power delivered to the precipitator, which is done by controlling the height and width of each pulse burst. Of particular note are the
The height and width of the pulse burst can be easily controlled on the low voltage side of the device shown in FIG. 3 by appropriate selection of the turn-on times for thyristor Q1 and transistor Q2. The low voltage side of the device shown in FIG. 3 is comprised of the elements on the primary side of the setup pulse transformer Tp.

In the pulse burst driving method shown in FIG.
A pulse burst with a duration of □ seconds is applied to the precipitator. The multiple pulses that make up this pulse burst are T
It has a period of 2 seconds.

Of course, T2 is less than T1. After applying the pulse burst for T1 seconds, the pulse burst is 9G at time T3.
- Interrupted for a period of time. However, during this interruption period there is a voltage across the precipitator, in particular due to the collapsing induced electric field in the secondary winding S of the transformer Tp. However, this induced voltage disappears after a time determined primarily by the capacitance Cc, the resistance and inductance of the secondary winding, and the effective resistance component RS of the precipitator Pr.

Factors such as the electrode spacing of the precipitator, the desired collection rate, and the pulse size (vS-VB) are determined depending on the nature of the dust to be collected, and the pulse burst period T1 is usually about 0.1 milliseconds and 5 Selected between milliseconds. Primarily to control the formation of back-corona discharges, the period T2 of the individual pulses is typically about 0.02 milliseconds and about 0.2 milliseconds.
7 milliseconds. Additionally, the duty cycle T□/(Tl
+T3). T□+T3 is
Usually at least 1 burst per second, but usually about 4. It is selected to produce a pulse burst repetition rate that is less than or equal to the OO burst. Therefore, T2 and T3
can be selected in combination to control the formation of the back corona and the power supplied to the precipitator.

These pulse bursts create a high-intensity corona discharge on the precipitator electrode wire and increase the average field strength over a selected time, causing the wire electrode and collector plate 1
increase the charging of particles by negative ions in the region between the dust layer covering the During each pulse burst, the precipitator voltage rises and falls rapidly several times. This variation controls the precipitator current and acts to limit the voltage drop across the dust layer. The precipitator current is determined by the number of pulses per burst, their magnitude, the width of each pulse,
It can be easily controlled by changing the pulse burst repetition rate, and it is possible to perform a desired operation. This is done by using relatively low power, low cost electronic components.

Furthermore, the rise and fall times at the beginning and end of each pulse burst are rapid and typically equal to the rise and fall times of the individual pulses. A circuit for achieving these objectives is shown in FIG. 3 and will be described below.

However, the main features of the invention can be best understood by understanding the voltage waveforms shown in FIG. FIG. 2 is similar to FIG. 1, but in accordance with a preferred embodiment of the present invention, the pulses during a single pulse burst continue to increase in voltage from one pulse to the next. In a typical precipitator configuration, when VS is established in the reference direction described below in FIG. 3, the actual increase in peak pulse voltage occurs in the negative direction. Therefore, the pulse burst in the present invention tends to exhibit a substantially trapezoidal envelope as shown by the dotted line in FIG.

However, since the invention is not limited to use with pulse burst drive methods, the trapezoidal pulses shown in dotted lines in FIG. It may be configured. In short, one form of wide drive is to use a series of trapezoidal pulses, with the pulse voltage increasing during the pulse period. Consideration regarding the timing of the waveform shown in Figure 2 is as follows:
This is substantially the same as described above with respect to the waveform shown in FIG.

The width of the pulse in a wide-pulse precipitator drive scheme is typically on the order of the same or somewhat shorter than the ion transit time, so that all charge injected during the pulse period fills the space between the electrodes when the pulse ends. exists within. This large space charge shields the corona electrode and reduces the electric field in the vicinity of the electrode. Therefore, the injected current is maximum at the beginning of the pulse and decreases with time during the pulse. Although this aspect of wide pulse driving is a disadvantage to the method, it is alleviated by using pulse burst driving, which provides the same effect as conventional wide pulse driving.

A circuit implementing the method of the invention is shown in FIG. This circuit is the same as the circuit described in the aforementioned same application, but the control signals provided for its operation are different. Control signals used in the present invention are shown in FIG.

In the circuit of FIG. 3, the high voltage side will be explained first. The circuit has a capacitor Cc, which supplies the voltage from the secondary side S of the transformer TP to the precipitator Pr, whose internal effective capacity is Cc, and whose internal effective load resistance is is represented by R5. The positive swing of the secondary voltage charges the capacitor CC via the diode D2.

The voltage across capacitor C6 is loaded with the negative swing of the secondary voltage. Diode D2 is reverse biased and the precipitator voltage is raised above the reference voltage VB (in the negative direction). It should be noted that a precipitator constructed and operated in accordance with the present invention does not necessarily require the presence of a reference voltage VB, but it is possible that such a voltage may be present. desirable.

The presence of diode D2 provides significant advantages to the operation of the invention. The advantage of this is that during time T□, each pulse in the pulse burst is clipped along the lower part of the positive swing, as shown in FIG.
It is best understood by noting that voltage 18 is prevented from decreasing below the DC reference level VB, which is normally maintained below 40 kilovolts. Additionally, bypass capacitor CB provides a low impedance path for charging current to flow through capacitor C6 and diode D2 during pulse operation.

Next, the low voltage side, ie, the primary side, of the circuit shown in FIG. 3 will be explained. Capacitor C2 is charged from DC power supply VA via pulse width modulation transistor Q2. The width of the pulses in the voltage waveform V, applied to the base of transistor Q2 controls the level of voltage charged to capacitor C2.

Such a waveform is shown in FIG. It is the voltage on capacitor C2 that provides the energy to form the pulse burst applied to the precipitator. Therefore, in this way voltage v2 controls the pulse burst amplitude.

Flyback diode D3 cooperates with choke L2,
At the end of each two pulses, transistor Q2 is turned off, transferring the energy stored in choke L2 to capacitor C2. Further, as can be seen from FIG. 3, the circuit is powered by a negative voltage source VA to avoid the need to reverse the phase of the secondary voltage with respect to the primary voltage of the transformer TP. configured to be supplied. Furthermore, in the primary circuit, a single sirisk inverter Q1 with a feedback diode D1 for reverse conduction is used to drive the primary winding of the transformer Tp. The number of thyristor switching elements is
It depends on the applied voltage, the rating of the thyristor and the required primary inductance. The capacitance of the precipitator together with the capacitor C6 is reflected in the primary circuit of the transformer Tp as C□, and together with the inductance L□ (external to the transformer Tp) functions as a series resonant rectifier circuit for the thyristor Q□. In particular, the value of the inductance L□ is selected to contribute to controlling the width of the individual pulses within the pulse burst. Furthermore, inductance L2 and capacitor C2 are selected to resonate at a frequency significantly lower than the resonant frequency of inductance L1 and effective capacitance C3 reflected in the primary circuit. Due to the presence of diode D□, recovery of the pulse burst energy takes place during the quiescent portion of the pulse burst. This recovered energy is stored in capacitor C2. This configuration is particularly effective in lowering energy costs and increasing the electrical efficiency of the pulse circuit. In other precipitator pulse drive circuits, this energy is dissipated by resistive means, which must therefore be provided with separate cooling capacity. In this respect, the device of the present invention is similar to the circuit shown in FIG. 7 of the Petersen reference cited above. However, there are significant differences in the way the pulses are applied and the way they are connected to the precipitator. Therefore, a significantly different waveform is applied to the precipitator of the present invention than that produced by the circuit shown in the Petersen reference cited above.

A significant advantage of the present invention is that rapidly controllable means for varying the amplitude of the individual pulses in the burst sequence and for varying the amplitude of the pulse bursts in each burst are provided on the primary side of the apparatus of FIG. That is, it is provided on the low voltage circuit side. especially,
4 and 5 illustrate a consistent set of waveforms that can be applied to thyristor Q1 and transistor Q2 to produce the desired waveforms at precipitator Pr.

The duration of the pulse burst is preferably controlled by applying and removing a gate voltage pulse applied to the gate of thyristor Q□. In particular, this period is shown as T1 in FIG. The trigger pulse waveform ■□ applied to the thyristor Q□ also controls the length of time during which no pulse burst is present, and that time T
It is indicated by 3.

In a typical application, inductance L1 (part or all of which can be formed by the primary leakage reactance of transformer Tp) has an inductance of approximately 400 μH, and inductance L2 has an inductance of approximately 2000 μH or more. It has inductance. Capacity C2 is typically 300
7z F, and capacitor Cc typically has a value of about 5 μF. The effective capacity of the dust collector Pr is approximately 0 at most.
．． It is 15μF. It is desirable that the power supply supplying the DC bias voltage vB has a larger internal capacitance (4) than CC. Under such conditions, T1 is preferably
T3 is selected to be approximately 2000 microseconds, and T2 is selected to be approximately 140 microseconds.

As is clear from the above description, the present invention is capable of producing several significant effects not found in conventional methods and devices for driving electrostatic precipitators. In particular, the present invention provides a wide pulse drive method that is capable of delivering a relatively uniform current level to an electrostatic precipitator during a pulse or pulse burst. In addition to achieving this objective, the present invention makes it possible to supply a precipitator with rapidly increasing and decreasing voltage levels.

Additionally, several variables are given in controlling the power drive of the precipitator, such as pulse burst duration, pulse burst amplitude, pulse burst frequency, and peak voltage level for each pulse within the burst. Control of voltage across the precipitator is accomplished by using low voltage circuitry. Such low voltage circuit components are
They are generally less expensive and more reliable than high voltage circuit components. Furthermore, the circuit and method of the present invention particularly reduces the phenomenon of back corona and the problems associated therewith.
- is effective. The method of the invention is not only efficient but also extremely reliable. The invention also allows the use of inexpensive step-up transformers. Furthermore, it is possible to control that the voltage present across the precipitator does not drop below the DC reference voltage level, and furthermore, the circuit of the invention recovers the energy stored in the precipitator itself. This makes it possible.

It should also be noted that the present invention applies to cases where the peak-to-3 false voltage level within a pulse burst increases linearly with time during the pulse burst, and whose envelope is substantially trapezoidal. There are no restrictions. Therefore, the present invention encompasses other cases where the peak pulse voltage level increases monotonically over the duration of the wide pulse.

Although specific embodiments of the present invention have been described in detail above, the present invention should not be limited only to these specific examples, and various modifications can be made without departing from the technical scope of the present invention. Of course there is.

[Brief explanation of the drawing]

FIG. 1 is a graph illustrating the precipitator voltage as a function of time for repeated pulse bursts and DC reference voltage, and FIG. 2 shows the dust collection when the present invention is applied to a pulse burst precipitator drive system. FIG. 3 is a schematic diagram illustrating a preferred embodiment of the present invention; FIG. 4 is a diagram illustrating the trigger pulse waveform used to control the initiation and interruption of pulse bursts; Graph diagram shown, 5th
The figure is a graph showing a pulse width control waveform used to control the peak pulse burst voltage. (Explanation of symbols) vs: Precipitator voltage B: DC reference voltage Ql: Thyristor Q2: Transistor TP step-up pulse transformer Pr: Electrostatic precipitator Patent applicant General Electric Environmental Services, Inc. 159 = Tomi Masashi 琥” 'j''J＞”17
In front of Fort

Claims (1)

[Scope of Claims] In a method of operating an electrostatic precipitator having one or two electrodes, the period T_1 is provided between the electrodes of the precipitator for a period T_1.
applying a high voltage pulse of substantially monotonically increasing voltage for a period of time T_1, and interrupting the application of the pulse for a time T_1;
A method characterized in that the applying step and the discontinuing step are periodically repeated. 2. The method according to claim 1, characterized in that a DC voltage is simultaneously applied between the electrodes, and the polarity of the DC voltage matches the polarity of the pulse. 3. The method according to claim 2, characterized in that the DC voltage is selected to be lower than the starting voltage of corona discharge between the electrodes. 4. In claim 1, T_1 is about 0.1
A method characterized in that the duration is between milliseconds and about 5 milliseconds. 5. The method of claim 2, wherein the DC voltage is selected between approximately 15 and 50 kilovolts. 6. In claim 1, T_3 is approximately 1 per second.
The method is selected to provide between 1 and about 400 pulses. 7. In the method of operating an electrostatic precipitator having two electrodes, the period T_1 is provided between the electrodes of the precipitator for a period T_1.
applying a burst of high voltage pulses of substantially monotonically increasing voltage for a time period of 1, wherein the period between successive ones of said pulses is T_2, T_1 being greater than T_2, and a period of time T_3; A method characterized in that burst application is interrupted, and the application step and the interruption step are periodically repeated. 8. The method according to claim 7, characterized in that a DC voltage is simultaneously applied between the electrodes, and the polarity of the DC voltage matches the polarity of the pulse. 9. The method according to claim 8, characterized in that the DC voltage is selected to be lower than the starting voltage of corona discharge between the electrodes. 10. The method of claim 7, wherein the DC voltage is selected between about 15 and 50 kilovolts. 11. In claim 7, T_1 is about 0.
A method characterized in that the time period is between 1 millisecond and about 5 milliseconds. 12. In claim 7, T_2 is about 0.
0.02 msec and about 0.7 msec. 13. The method of claim 7, wherein T_3 is selected to provide between about 1 and about 400 pulse bursts per second.