JPS621465A - Method of operating 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 [Industrial Field of Application] The present invention is a system in which an alternating current whose frequency has been converted by an electronic 111 rectifier is boosted and, in some cases, supports high voltage pulses.
The present invention relates to a method of operating an electrostatic precipitator in which the precipitator base voltage is rectified via a bridge inverter for generation.

[Prior art and its problems]

Electrostatic precipitators are often used for exhaust gas cleaning or, in general, to separate foreign substances from a fluidizing medium.

The plates and discharge wires of the electrostatic precipitator are supplied with a high voltage so that ionization of the contained foreign substances and separation of these ionized foreign substances into the plates occurs in the medium passed between them. If a high degree of separation is to be obtained, the DC voltage (supply voltage) of the plates and discharge wires is chosen as high as possible. On the other hand, when the supply voltage is high, ionization phenomena also occur in the gas itself,
This results in a sustained discharge of the precipitator leading to a corona discharge in the discharge line.

If the supply voltage exceeds a limit value, the precipitator discharges through a short arc or through a voltage collapse, leading to a steady arc, unless the direct current supplied by the power supply is interrupted. The foreign material separation described above is not possible until the high DC voltage is reestablished.

Furthermore, this process causes wear and tear on the precipitator, especially on the discharge wires, shortening the service life of the entire device.

The above-mentioned limit values of the ionization course and thus of the supply voltage depend on the distribution of the electric field strength between the plates of the electrostatic precipitator. The insulating layer of foreign material separated into plates must be collected and removed by hammering at defined time intervals, possibly with interruption of the supply voltage for as short a time as possible; Moreover, ionization creates a space charge with a strong distortion of the potential course between the plates, which can lead to a voltage gradient and a reversal of the discharge direction between the plates and the space charge.

Therefore, the above limit value is not constant during operation.

For good separation, the supply voltage of a precipitator is tried to be as close to a limit value as possible, which varies as little as possible.

Commercially available electrostatic precipitators include a power supply device that is connected to two phases of a three-phase AC power system and extracts AC current from the system via an electronic regulator. The output voltage of the regulator is firing angle controlled to provide an alternating current at the grid frequency that is phase shifted relative to the input voltage, which is then boosted and rectified and then collected as a pulsed continuous current. Supplied to dustbin. In order to approach the optimum operating conditions of the precipitator, German patent application publication no. It has therefore been proposed to build up until a limit value is reached, depending on the instantaneous state of the precipitator, leading to a voltage collapse or similar sudden discharge of the precipitator.

Generally, after the voltage collapses, the AC regulator must first be blocked to avoid arcing and wait for deionization of the nine plasma formed. The minimum idle period of no current is determined by the frequency of the regulator, ie the system frequency. As a result, the precipitator is supplied with a direct current that flows almost without interruption with pulsations depending on the system frequency and is quickly cut off after the voltage collapses. For the precipitator voltage supplied by this current, a pulsation occurs which increases in each case until the voltage collapses.

There are already some electrostatic precipitators that do not supply the precipitator with this type of continuously flowing direct current that is extracted from the power supply system and boosted and rectified by a grid frequency alternating current regulator. The precipitator is charged by a train of individual voltage pulses or current pulses. For each pulse, the average current value of these spaced DC pulses is adjusted to the respective precipitator condition in order to transfer the charge that was flowing through the medium during the pulse pause period. The frequency and/or time width of each pulse is set so as to obtain the flow target value. Otherwise, a precipitator voltage is generated which has a value as low as possible below the voltage collapse limit and pulsates in accordance with the pulse train frequency.

In this case, there are technical difficulties in meeting the energy requirements of the precipitator with short pulses.

For this purpose, US Pat. No. 3,641,740 charges capacitors connected in series with the rectified grid voltage and connects these capacitors via a thyristor, a high-voltage transformer and a half-wave rectifier to an electrostatic precipitator. It is proposed to do so. The width of the W flow pulses reaching the 'wL air precipitator is 1, for example 5% of the pulse pause period between these pulses.

Currently, the best method is to first clean the dust collector with flint.
A combination of applying an already relatively high and almost constant basic DC voltage through the device and then superimposing an AC voltage or spaced discrete voltage pulses on said basic DC voltage to generate a pulsating precipitator voltage. law has been adopted.

According to U.S. Pat. No. 3,984,215 spec.a.

The magnitude of the precipitator voltage is also far above the breakdown voltage of the precipitator, but the precipitator discharge is of very short pulse duration so as not to form an arc. The time width, waveform and pulse train frequency of these individual spaced pulses are tailored to the respective precipitator loading conditions. European Patent No. 0034075 Mei a4F
According to , spaced current pulses are supplied to a precipitator to which a constant basic DC voltage is applied, and the maximum amplitude of those current pulses is determined by the precipitator depending on the target value of the precipitator current. The battery is controlled to be charged to the maximum voltage within the Break-O voltage range. These current pulses are extracted from an intermediate circuit fed by the rectifier by a retraction circuit type frequency converter or a forced extinguishing type variable frequency converter designed to have a desired pulse width, and are boosted. Pulsations in the precipitator voltage are ensured by the diodes suppressing one polarity of the respective boosted current pulses.

In German Patent Application No. 2713675, the basic system is constructed by an AC regulator connected to two phases of a three-phase AC power supply system to control the firing angle, and a transformer and a rectifier connected downstream of the AC regulator. A simple power supply device to which voltage is supplied is proposed. The electrodes supplied with this basic DC voltage are connected via a coupling capacitor to the secondary winding of a high voltage transformer, the primary winding of which is connected via a controllable rectifier via an intermediately connected inverter. Powered. Thereby, the basic voltage has 5 Q depending on the load.
A rectified alternating current voltage with a variable frequency in the range H+a to 'l kHz is superimposed.

However, if these methods are to be used in a precipitator operation location dictated by the characteristics of the separation process,
The requirements for tat source systems, where more stringent requirements apply, should also be considered. For example, the reactive current and harmonic loads of the system as well as the limits of asymmetric loads between the three-phase AC terminals of the power system must be taken into account. Additionally, installation costs must be kept as low as possible.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method that can be adapted as optimally as possible to the ever-changing operating conditions and that provides a fast response, particularly in the event of a flashover.

Since a relatively high power must be transmitted to the precipitator, the alternating current, which is frequency-converted by an electronic regulator, is stepped up and bridge rectified to generate the basic direct voltage, in order to achieve the above objective. I5! We can go back to the traditional method of rectifying the water through a device. This means that the precipitator is supplied with almost continuous direct current and therefore has only supply voltage harmonics corresponding to the converter frequency during constant operation. This basic DC voltage can be supplemented with high-voltage pulses in a conventional manner, but with the method according to the invention these additional high-voltage pulses can be omitted in many cases.

[Means for solving problems]

According to the invention, an alternating current is generated with a converter frequency of several kHz, in particular 21 tHz.

[Action and effect]

In the prior art, frequency converters are only used when converting the device frequency V into a fundamental DC voltage for the generation of pulsations that are sought to be obtained for the separation process.
Used only if an alternating current voltage with 16 is converted without rectification, or if individual pulses separated from each other, formed by suppression of the negative voltage half-wave by diodes, are folded from the alternating voltage at the converter frequency. In contrast, according to the invention, a high-frequency alternating current is used to generate a fundamental direct voltage which is initially only weak and contains harmonics by means of an almost continuous direct current via a bridge rectifier. Ru.

This has the advantage that in the event of a flashover, the supply current of the precipitator can be erased for a fraction of a millisecond by blocking the transducer or the converter depending on the a-sock frequency.

In that case, preference is given to using an indirect frequency converter as the frequency converter. For indirect frequency converters, a regulator connected to the three-phase power supply system (e.g. a controllable three-phase rectifier or, in particular, a three-phase GL current with a downstream DC chopper for control of the intermediate circuit DC current) is used. A high-frequency inverter supplies a direct current with alternating polarity to the alternating current output terminals of the converter in the rhythm of the converter frequency to form an alternating current. In the event of a flashover, it is only necessary to block the inverter in order to interrupt the precipitator current, by means of suitable means (e.g. a bypass thyristor across the DC input terminals of the inverter or a suitable ignition pulse to the inverter valve in series connection). ) allows the DC current to be bypassed from the AC output terminal of the inverter via the idle circuit.

In this type of indirect frequency converter, the intermediate circuit current is forced through the regulator. Since the magnitude of the intermediate circuit current does not practically change within one period of the converter circuit,
Even during a flashover, no significant current rise in the transformer occurs and therefore no significant additional charging of the precipitator occurs, so that arcing is prevented and the discharge phenomenon is sustained and limited in time, which It causes only slight wear and tear on the discharge wire, extending the life of the precipitator.

On the other hand, the converter clock need only be interrupted for as many clock periods as are necessary for deionization of the gas. After that, the entire intermediate circuit current is turned off at will for power conversion and charge replenishment of the precipitator, so the separation performance of the precipitator is quickly regenerated, and the precipitator efficiency is be enhanced. As a result of the high alternating current frequency, a small transformer is required, thereby reducing equipment manufacturing costs and power losses.

Favorable transient characteristics are obtained during high-speed operating changes, and
In order to reduce the number of flashovers, such a deionization time can be provided by temporarily blocking the regulator clock after several converter clock periods from the beginning. 1,9. The nearly continuous direct current generated by kHz1 clock is divided into individual direct current packages at a low frequency. The current-free rest period that occurs in that case can be adapted to the deionization time that occurs in the respective application.

The amplitude control of the high-frequency alternating current, possible for example via control of the intermediate circuit direct current, gives an additional degree of freedom for the precipitator voltage control, e.g. the inverter amplitude after each flashover or after each converter blocking ff1K. It is preferable to start up again according to a predetermined soft start function.

In particular, through the amplitude control within the above-mentioned direct current package of one curve course, completely different curve shapes can be adapted to the precipitator supply voltage, which are considered advantageous for the respective application.

For example, a pulsating ary that can already be adjusted to the basic voltage U of the precipitator
/dt can be added depending on the amount of foreign matter remaining in the medium, for example. This is effective, for example, if the medium is already sufficiently free of foreign matter and has a very high resistance. In this case, the medium can conduct only a small current at a constant precipitator voltage.

It is possible to take in less power than K, but the energy uptake of the precipitator can be increased by higher pulsations of the supply voltage. It is also necessary to control the average level of the precipitator voltage depending on the amount of foreign matter remaining.

Separation of residual foreign matter can be carried out even with relatively high precipitator voltages and with input gas that has already been thoroughly purified.

Via the control, the respective optimal operating point for the precipitator supply is determined in an iterative manner.

For example, the precipitator voltage can be automatically increased by increasing the supplied DC current, while the frequency of 17 rushovers occurring is not significantly high.Thereby, the dependence of the precipitator voltage on the foreign matter content of the incoming gas The frequency is automatically taken into account, but it can also be done, for example, depending on the detected flashover frequency by a predetermined function for the control of the alternating current amplitude.

In particular, the periodicity of the overall voltage curve can be controlled via the converter frequency and can also be varied as a function of the load state or the foreign matter content of the incoming gas.

The regulator itself acts as a load for the power supply system, and in the case of an uncontrolled three-phase bridge with a DC chopper downstream, a symmetrical load with a very slight pulsation of only about 4.2% acts. . In that case, the power factor (Cosφ) is almost 1, and the intermediate circuit sufficiently protects the power supply system from the reaction of the inverter on the system side.

Furthermore, after a 7% rushover the duration of this short circuit is short due to the short time interval between the short circuit detection and the extinction of the high-frequency alternating current, and therefore only a small amount of energy can flow in the event of a short circuit, so that the overall As a result, a reduction in the power taken up by the electrostatic precipitator occurs.

〔Example〕

The present invention will be explained in more detail below with reference to FIGS. 1 to 3 of the drawings.

FIG. 1 is a block diagram showing the basic configuration of an apparatus for carrying out the present invention, and FIGS. 2 and 3 are circuit diagrams showing mutually different embodiments of the apparatus for carrying out the invention.

In these figures, IF designates an electrostatic precipitator, between the electrodes of which (between the electrode plate and the discharge wire) a medium (e.g. furnace gas or other exhaust gas) is passed, as indicated by the arrow M; The voltage σ detected by the measurement element Mff is to be supplied from the power supply system N. For this purpose, the input voltage of the precipitator is connected to the secondary winding 7 of the transformer via the high voltage rectifier GRH.
A frequency converter dH connected to the sun and whose primary winding wp of the transformer is controlled at a high frequency? is connected to the output terminal of

High voltage adjustment I5! The device GRH is constructed as a full-wave rectifier, in particular as an uncontrolled rectifier bridge. In particular, an indirect frequency converter is used as the high-frequency frequency converter H'EF. The block diagram of FIG. 1 shows a seven-lead wheeling path which can be opened and closed by a switch q, through which the inductive currents occurring when the converter is blocked, for example when using the current intermediate circuit of the converter, are removed. The rectified intermediate circuit current continues to flow. In most cases, the amount of high-frequency alternating current fi (
The amplitude of ia) can be controlled via a corresponding control input of the alternating current regulator HIF. It has been shown in NIPK that amplitude control can also be operated via a controllable mains frequency alternating current regulator.

In Figure 1, the control and regulation of the high-frequency alternating current is comprehensively shown in PR, which includes not only the actual value U of the precipitator supply voltage but also the appropriate actual value depending on the application. and target values are entered. Via the output signal the amplitude 2 frequency can be controlled) and the interruption of the current 1a at the output of the alternating current regulator H7 can be controlled via the bypass ignition 1 of the 7-way wheeling path q.

Considering completely different parameters for the operation of the precipitator,
Correspondingly fast control and regulation KM can be exchanged. The operation of the precipitator can therefore be optimized in many respects. This flexibility is illustrated in FIG. 2; however, depending on the application, completely different versions can be realized.

For example, the foreign material content in the raw gas (foreign material content of the inlet medium) and/or the foreign material content of the purified gas (foreign material content of the outgoing medium) can be used as input signals.The supply voltage of the precipitator and / or the supply type i can be optimized, in particular they can be controlled according to a predetermined voltage/current characteristic, which characteristic depends on the foreign material content in the raw gas, i.e. on the precipitator loading condition dK. In addition, the control can react very quickly to the start, end of each voltage collapse and non-king, and also to the voltage wave, i.e. the voltage pulsation between the upper and lower limits. It can be given in advance and optimized.

This figure 2 shows the controllable three-phase rectifier bridge DR.
A controllable rectifier is shown as .

This three-phase rectifier bridge DR is a means necessary for adjusting the amplitude of the high-frequency regulator output current with a predetermined adjustment characteristic by changing the intermediate circuit 1 (measurement element Ml) of the indirect variable wave number converter. We are equipped with this.

The mesosphere M contains two intermediate circuit reactors, which are designed for smoothing the intermediate circuit current and are optionally combined with an intermediate circuit capacitor.

The inverter R connected in the latter stage generates a high frequency alternating current. The inverter shown in FIG. 2 which is suitable for this purpose is known as a current source inverter. In principle, a multiphase bridge with three or more phases is possible, and in some cases it may be advantageous to obtain as continuous a direct current as possible after boosting and rectification, but a single-phase full-wave rectifying bridge is sufficient.

In the normal phase sequence, valves TRI and TH4 or TH2 and TH3 are fired simultaneously, and the previously fired valve is extinguished under reverse charging of 1 and 2 in the commutation capacitor. .

Bypass ignition as a means for bypass ignition
TQ is provided. During this type of bypass ignition, a certain intermediate circuit lightning continues to flow through the reactor 2, but 7 Lee Wheeling jll! The primary winding sWp is bypassed via TQ, so that the secondary winding @wp is quickly demagnetized in any phase of the inverter and, optionally after the interruption of a few converter clock pulses, is again completed in the intermediate circuit 1! It can be excited by the current. Therefore, the necessary separation voltage can be quickly re-established in the voltage breakdown junction. A bypass ignition of this type can also be effected by ignition of a series-related valve in a separate bridge circuit. They can also be provided to ensure that the conduction period of the valves fired by the regular clock train is short compared to half a period of the inverter output current. The applied intermediate circuit current itself is hardly influenced by this switching process.

In the control block PR, the target value setter 88 gives the target value of the intermediate circuit current or the amplitude of the output AC current, and the control means of the controllable rectifier is set via the current regulator 8R according to the control deviation thereof. The supply operating point is established by controlling the control unit (8DR) for the control unit (8DR).The setpoint value - is determined in particular according to the current/voltage characteristic curve stored in the setpoint setter E?8, The target value setter 88 is provided with the optimum value of the voltage U9 by the current control program P8 in order to generate the aforementioned pulsations in the precipitator supply voltage.

The voltage U* can be changed periodically depending on the amount of residual foreign matter measured by the combustion furnace gas sensor RG, for example. Optimal base level for voltage -.

The combustion furnace gas sensor KG can be determined depending on the content of foreign substances in the raw gas, or iterative search methods can be used to obtain a high separation efficiency on the one hand and to reduce the frequency of voltage breakdowns and breakdowns in the measuring element MUK on the other hand. It may be changed within the frame.

It is generally preferred to limit the voltage to a predetermined value U2, for which purpose the setpoint-actual value deviation of the supply voltage U is input to a limit regulator BR which acts on a limiter circuit BGIC which limits the current setpoint value 0, for example a gray-over IK supply. In order to be able to build up the voltage according to a predetermined curve course, a soft-start function generator HG is provided at the setpoint input of the limit regulator PR, and the final value of this function generator can be determined (e.g. by voltage measurement). Depending on the frequency of the voltage collapse measured in the element Mσ), the program section PS and P section can also be varied by the program section P and software for each possible operating state. By controlling the start function generator HG and/or the setpoint value setter SS, e.g. hammering processes (removal of separated foreign objects)
However, depending on the technique provided for the separation, other actual value-setpoint value relationships can be processed in order to enable a quantity-appropriate relationship to the control of the alternating current. Depending on the respective operating point on the precipitator characteristic curve, the voltage limit regulator BR allows stable operation of the power supply close to the voltage collapse point KL, which reduces the frequency of stain pressure collapses and increases the Dust container life is increased.

Furthermore, the pulse program part P has the purpose of generating an inverter output zero frequency, and therefore a high frequency of the inverter AR, by corresponding operation-dependent control signals for the inverter control unit. The pulse program section P also generates switching signals for the 7-lead wheeling path (valve TQ), temporary stop and restart of the inverter after a voltage collapse. Again, by periodic blocking of the high-voltage rectifier GRH, the direct current drawn off is blocked (forming the package), so that similarly i
Voltage pulsations in the generator can be forced.

This control of the basic DC voltage of the precipitator makes the use of additional insulating high voltage pulses unnecessary. However, the coupling capacitor KK shown in FIG. 2 also facilitates the additional application of such pulses, which can be applied to the corresponding input terminal HIP of the precipitator.

The high frequency used of the alternating current allows significant savings in transformers. Similar savings are controllable! This is also obtained for intermediate circuit reactors when using the circuit according to FIG. 3 as a 1Ifi device.

Therefore, a DC chopper with a control valve 8T and a 7-lead wheeling diode IFD is used for rectified DC current IO control, with a chopper frequency of kHz+a (eg 5 kHz) reactor! FD becomes smaller. The intermediate circuit is an inverter AD
The reaction from the power source to the power supply system N is suppressed.

The input voltage of the DC chopper is preferably supplied by an uncontrolled three-phase rectifier bridge, thereby providing a symmetrical, nearly reactive 'rsvft-free load for the source system H.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an apparatus for carrying out the present invention, and FIGS. 2 and 3 are circuit diagrams showing mutually different embodiments of the apparatus for carrying out the invention. ? ...Electric precipitator, VRP...Transformer - next winding, W
S...Transformer secondary winding, N...Power system, Hν...
・High frequency frequency converter (high frequency AC regulator),
N1F... Controllable grid frequency AC ammeter, Q...
・7 Lee Wheeling Road (bypass road), GRH...
High voltage adjustment +5! vessel. 'qt+11) Attorney Kiyoshi Fujita.・,2. t-zu+suhachi-

Claims (1)

[Claims] 1) An alternating current frequency-converted by an electronic regulator is stepped up and, if necessary, superimposed with high-voltage pulses to generate the precipitator basic voltage via a bridge inverter. In the operating method of an electrostatic precipitator in which the current is rectified by
A method of operating an electrostatic precipitator, characterized in that an alternating current having a converter frequency of Hz is generated. 2) The frequency-converted alternating current is generated by connecting the direct current taken out from the intermediate circuit with alternating polarity to the alternating current output terminal of the converter in accordance with the converter frequency, and the intermediate circuit is Claim 1, characterized in that it is supplied with a controllable intermediate circuit current by a controlled rectifier, which intermediate circuit current is independent of the connection to the alternating current output terminal within the period of the converter frequency. How to operate the electrostatic precipitator described. 3) characterized in that upon voltage collapse in the precipitator, the alternating current is cut off under blocking of the converter frequency and is turned on again with release of the converter frequency after a short rest period adjusted to the deionization time; A method for operating an electrostatic precipitator according to claim 1 or 2. 4) A method for operating an electrostatic precipitator according to claim 3, characterized in that the current is interrupted and reintroduced each time after several cycles of the converter clock, regardless of the occurrence of a voltage collapse. 5) The AC voltage amplitude is ramped up according to a predetermined soft start function for the AC current amplitude or the basic DC voltage after switching off the converter time wave number. How to operate an electrostatic precipitator as described in section. 6) Claims 1 to 5, characterized in that a predetermined control program is prepared for conversion control during the hammering process and/or undervoltage in the precipitator.
A method of operating an electrostatic precipitator according to any one of paragraphs. 7) Claim 1, characterized in that the basic DC voltage is given a predetermined pulsation by changing the amplitude of the AC current.
A method of operating an electrostatic precipitator according to any one of Items 6 to 6. 8) A method of operating an electrostatic precipitator according to any one of claims 1 to 7, characterized in that the converter frequency is changed depending on the operation. 9) A method of operating an electrostatic precipitator according to claim 8, characterized in that the converter frequency is changed depending on the load condition or foreign substances in the medium flowing into the precipitator. 10) By controlling the alternating current, the average level and/or pulsations of the basic direct voltage are controlled as a function of the foreign matter content of the medium flowing out of the precipitator. 9. The method of operating an electrostatic precipitator according to any one of 9 to 9. 11) The amplitude of the alternating current is controlled by a control variable, and this control variable is obtained from a target value for an optimum precipitator voltage according to a predetermined current-voltage characteristic. A method for operating an electrostatic precipitator according to any one of Items 1 to 10.