JPH0199659A - Charge controlling method for pulse charge-type electrostatic precipitator - Google Patents

Abstract

PURPOSE:To realize the uppermost dust collection efficiency by feeding pulses of maximum pulse voltage capable of being impressed without generating a spark at a pulse frequency above which the above-mentioned maximum pulse voltage lowers according to the increase of the pulse frequency. CONSTITUTION:Both DC basic voltage and pulse voltage are overlapped and impressed. The pulse of maximum pulse voltage capable of being impressed without generating a spark is fed at a pulse frequency in the case incapable of maintaining the above-mentioned maximum pulse voltage according to increase of pulse frequency and allowing it to be lowered. Further the basic voltage is maintained at the voltage for starting corona in case of performing DC charge without overlapping the pulse voltage or at the voltage slightly higher than it. As a result, the upper-limit dust collection efficiency can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrostatic precipitator, and more specifically, a pulse charging type in which a DC base voltage and a pulse voltage are applied in a superimposed manner. The present invention relates to a charge control method for an electrostatic precipitator.

BACKGROUND OF THE INVENTION Conventional electrostatic precipitators have been controlled to apply a high voltage within a range that does not cause excessive sparks. Among these, the pulse charging method, which can dramatically improve the performance of dust collectors by instantaneously applying high voltage, has been attracting attention in recent years.

As shown in FIG. 1, this pulse charging method is a method in which a DC voltage (referred to as base voltage) and a pulse voltage are applied in a superimposed manner to an electrostatic precipitator. This pulse charging method consists of a base voltage, a pulse voltage, a pulse frequency f (however, 1/f=T
(Pulse repetition period)) can be controlled independently, making it possible to collect various types of dust such as dust with high electrical resistance.

However, even with the pulse charging method, it is necessary to control the base voltage, pulse voltage, and pulse frequency so as not to generate excessive sparks.

The purpose of controlling spark generation to prevent it from becoming excessive is to maintain dust collection performance as high as possible. When a spark occurs, among the base voltage, pulse voltage, and pulse frequency,
If you make a mistake in which one should be controlled, the dust collection performance will deteriorate.

The inventor of the present invention conducted various studies in order to find optimal values for base voltage, pulse voltage, and pulse frequency to achieve the best dust collection performance.

Research results show that the most important factor determining dust collection performance in pulsed charging is the peak voltage of the pulse. The higher the peak voltage, the better the dust collection performance. On the other hand, if the peak voltage is kept constant, the higher the base voltage and pulse frequency, the better the dust collection performance will be.

However, when both the base voltage and the pulse frequency exceed a certain value, sparks tend to occur suddenly (and it becomes impossible to maintain a high peak voltage. This is because reverse ionization occurs in the dust layer on the surface of the precipitator. When the peak voltage is low, as in the case of DC charging without superimposed pulses, reverse ionization takes the form of a corona called back corona, but when the peak voltage is high, as in pulse charging,
Be sure to move to Spark.

Therefore, it is impossible to obtain a high peak voltage with a base voltage or pulse frequency that causes reverse ionization. In summary, in order to obtain high dust collection performance, a high peak voltage is required, and in order to obtain this high peak voltage, a base voltage and pulse frequency that are as low as possible without causing reverse ionization are required.

Therefore, when considering the generation of sparks in the pulse charging method by focusing on the relationship between the peak voltage and the base voltage, we find that:
The peak voltage at which a spark occurs sharply decreases when the base voltage exceeds the value.

This phenomenon is particularly noticeable when the electrical resistance of the collected dust is 10 Ω·cm or more.

In collecting dust with such high electrical resistance, such a marginal base voltage is the corona onset voltage in DC charging or only slightly higher. At base voltages lower than the corona initiation voltage, the corona current is almost zero or completely zero, and there is little possibility that reverse ionization will occur due to the base voltage. Also,
When the voltage exceeds the corona starting voltage to a certain extent, reverse ionization occurs at least locally in the precipitator.

This is because the corona current locally has a fairly large current density. In addition, in the pulse charging method, if the base voltage is below the corona starting voltage limit, back ionization and sparks will not occur. Even if the pulse frequency is too high, back ionization will occur, but at least the base voltage It is possible to prevent excessive voltage from causing reverse ionization.

In conclusion, the optimal value for the base voltage is just slightly above the corona initiation voltage for DC charging. but,
Even if sparks occur, as long as the frequency is small, there is no need to suppress the base voltage unnecessarily.

On the other hand, since pulse charging itself has not yet been widely and generally adopted, there are few published documents regarding the control method for sparks caused by pulse charging. For example, JP-A-57
In Japanese Patent No. 127462, the timing of spark generation is divided into several types and controlled differently depending on whether it is "during application of pulsed vehicle pressure" or "during application of base voltage between pulses".

However, the method disclosed in JP-A-57-127462 could not achieve sufficient dust collection efficiency.

Problems to be Solved by the Invention Therefore, the present invention aims to provide a pulse voltage control method for a pulse charging type electrostatic precipitator that can realize maximum dust collection efficiency.

Means for Solving the Problems According to the first feature of the present invention, in an electrostatic precipitator in which a DC base voltage and a pulse voltage are applied in a superimposed manner, the maximum pulse voltage that can be applied without sparking is a pulse voltage. Provided is a charging control method for a pulse charging type electrostatic precipitator, characterized in that pulses of the maximum applicable pulse voltage are supplied at a pulse frequency when the voltage cannot be maintained and must be lowered as the frequency increases. .

In the above method, the base voltage is preferably maintained at the corona initiation voltage or only slightly higher than the corona initiation voltage when direct current charging is performed without superimposed pulses.

According to the second feature of the present invention, in an electrostatic precipitator to which a DC base voltage and a pulse voltage are applied in a superimposed manner, when no spark is generated in the precipitator, either the pulse voltage or the pulse frequency is changed at regular intervals. When a spark occurs, the pulse voltage is lowered if the spark occurs within a certain period of time after the pulse frequency has increased, and if the spark occurs within a certain period of time after the pulse frequency has increased. lowers the pulse voltage and decreases the pulse frequency by a width greater than the pulse frequency increase width, and then, if no spark occurs, the pulse voltage is first increased stepwise at regular intervals to a voltage just before the pulse voltage at which a spark occurred last time. A charge control method for a pulse charging type electrostatic precipitator, characterized in that the pulse frequency is increased stepwise to supply pulses at the maximum pulse voltage that can be applied and at the maximum pulse frequency at the maximum pulse voltage that can be applied. is provided.

In addition, in the above method, if there is no spark even if either the pulse voltage or the pulse frequency reaches the upper limit, it is preferable to increase the pulse voltage or pulse frequency that has not reached the upper limit in stages after a certain period of time has elapsed. .

In a preferred embodiment of the invention, the period of time is about 5 seconds. Further, when lowering the pulse voltage, the pulse voltage is lowered by 5 to 10%, and when increasing the pulse voltage, the pulse voltage is increased by 2 to 3%. Further, when decreasing the pulse frequency, the pulse frequency is decreased by 30 to 50%, and when increasing the pulse frequency, the pulse voltage is increased by 10 to 20%.

In the active pulse charging system, if the base voltage is properly controlled near the corona initiation voltage, there are only two things that are controlled to suppress spark generation: pulse voltage and pulse frequency. In the pulse charging method, if the base voltage is considered constant, the peak voltage is determined by the pulse voltage.

As mentioned above, the higher the pulse voltage, the better the dust collection performance.If the pulse frequency exceeds this value, it becomes impossible to maintain a high pulse voltage due to sparks, but up to that value, the pulse frequency is higher. Good.

FIG. 2 shows the spark generation area based on the pulse frequency and pulse voltage on the X-Y plane.

When a spark occurs, the electric charge stored between the discharge electrode and the dust collection electrode of the electrostatic precipitator is lost, the potential difference between the electrodes decreases, and the dust collection efficiency decreases significantly, so the non-spark area in Figure 2 , is the drivable area.

As can be seen from Figure 2, when the base voltage is properly controlled, the maximum pulse voltage that can be applied without sparking is constant regardless of the pulse frequency when the pulse frequency is low; Once the pulse frequency is exceeded, it decreases as the pulse frequency increases. Therefore, when operating at a pulse frequency just before the maximum pulse voltage that can be applied and the maximum pulse voltage at that time, the dust collection performance is maximized without generating sparks, as indicated by the circle in Figure 2. This is also confirmed by the specific data that will be presented later.

Therefore, in the method according to the first feature of the present invention, since the pulse charging type electrostatic precipitator is operated in the region indicated by the circle in FIG. 2, maximum dust collection efficiency can be achieved.

According to the method according to the second aspect of the invention, a pulsed voltage;
The pulse frequency is changed little by little for a certain period of time, that is, for each stage, and the control method is changed depending on which stage the spark is generated. Note that within the same stage period, it does not matter whether the spark is "applying a pulse" or "applying a base voltage between pulses."

If a spark occurs, the pulse voltage, pulse frequency, or both are reduced to prevent the spark from occurring again. And if a period without spark continues for a certain amount of time,
The pulse voltage and pulse frequency are recovered or increased, and finally the pulse voltage and pulse frequency reach the area marked O in FIG. 2.

According to the method according to the second feature of the present invention, even if the area marked with a circle in FIG. 2, which differs depending on the dust collector and the nature of the dust collected, is unknown, the area marked with a circle in FIG. The pulse voltage and pulse frequency can be changed. Therefore, the operating state can be converged to the optimal pulse frequency and pulse voltage, and the maximum dust collection efficiency can be achieved.

Embodiment FIG. 3 is a block diagram showing an example of a power supply device for a pulse charging type electrostatic precipitator that implements the charge control method according to the present invention.

The illustrated power supply device for the electric precipitator includes a pulse power source 6 and a base power source 8 that are connected to the discharge electrode of the electric passenger seat machine main body 9. The base power supply 8 may have any configuration as long as it controls the base voltage to an appropriate value (near the corona starting voltage).

The pulse power source 6 includes a step-up transformer 2 whose primary side is connected to a commercial AC power source via a thyrisk gate circuit 1 consisting of a pair of thyrisks connected in opposite directions, and a secondary side of the step-up transformer. The rectifier bridge 3 is connected to the rectifier bridge 3.

The output terminal of the rectifying bridge 3 is connected to a pulse generating circuit 4. Furthermore, a pulse power supply measuring device 5 such as a voltage dividing resistor is connected to the output terminal of the rectifying bridge 3 in order to detect the pulse power supply voltage, and its inverse output terminal is manually inputted to the control device 10 .

On the other hand, the opposite output terminal of the rectifier bridge 3 is grounded.

In the control device 10, a bird issues a signal to the pulse generation circuit 4, and the pulse generation circuit 4 outputs a pulse for each trigger signal. The output of the pulse generation circuit 4 is the electrostatic precipitator main body 9
The collecting electrode of the electrostatic precipitator main body 1 is grounded.

Further, a spark detection device 7 such as a voltage dividing resistor is connected to the discharge electrode of the electrostatic precipitator main body 9 in order to monitor the electrostatic precipitator voltage and detect sparks, and its output terminal is input to the control device 10. has been done.

The control device 10 is programmed, for example, by a computer, to perform the operations described in detail below. Basically, the voltage from the pulse power measuring device 5 is compared with the target value set by the control device 10, and the firing angle of the thyrisk of the thyrisk gate circuit 1 is controlled, thereby controlling the firing angle of the thyrisk to the transformer 3. The supplied power is controlled and the pulse voltage is feedback-controlled to the target value. On the other hand, the control device 10 monitors the voltage detected by the spark detection device 7, and determines that a spark has occurred when a sudden drop in voltage is detected.

In that case, as will be described later, if the pulse voltage is increased during a certain period before spark generation, the power supplied to the transformer 2 is reduced by controlling the firing angle of the thyristor gate circuit l, and the pulse voltage is increased. Reduce voltage. However, if the pulse frequency is increased during a certain period before spark generation, the pulse voltage is similarly lowered and the pulse generation circuit 4 is controlled to lower the pulse frequency.

Next, how to determine the pulse voltage and pulse frequency will be described with reference to FIG.

If there is no spark for a certain period of time (for example, 5 seconds), the control device 10 increases the pulse voltage or pulse frequency a little. Furthermore, if there is no spark for a certain period of time, the pulse voltage or pulse frequency is increased slightly.

If a spark occurs at point 3 in Figure 4, the pulse voltage will be reduced by a certain amount, for example 5 to 10%.If this spark occurred during a certain period of time immediately after increasing the pulse frequency, the The frequency is also to a certain extent, for example 3
Lower it by 0-50%.

After a spark, as described above, if there is no spark, the pulse voltage is increased little by little, for example, by 2 to 3%, at regular intervals, until it is slightly lower, for example, by 1 to 2%, than the pulse voltage at which the previous spark occurred. (point ■ in Figure 4).

After the next fixed period has elapsed, the pulse frequency is increased at point (3) in FIG. The amount of increase is 10 to 20%, which is smaller than the amount of decrease for each spark.

Even in this state, if no spark is generated yet, the pulse voltage is increased a predetermined number of times (for example, 2 to 4 times) at regular intervals while maintaining the increased pulse frequency. If no spark still occurs after that, the pulse frequency is increased once after a period of time. If no spark is generated yet, the pulse voltage is increased at regular intervals while maintaining the increased pulse frequency.

In this way, the pulse voltage or pulse frequency is increased until a spark occurs (Fig. 4 - ■).

By controlling the pulse voltage and pulse frequency in this way, the fifth
When a spark occurs when the pulse frequency is lower than the optimum point as at point A in the figure, the operating point returns to ■, then the pulse voltage is restored to ■, and the pulse frequency is increased to ■. After that, when it moves to ■ and a spark is generated, ■° → ■ as shown by the arrow in the figure.

Repeat →■”→■′→■”. In this way, the operating point approaches the optimal point marked O. That is, if a spark occurs only when the pulse voltage is increased, the pulse voltage and pulse frequency reach the optimum point while the pulse frequency gradually increases.

On the other hand, when a spark occurs when the pulse frequency is higher than the optimum point as at point A in FIG. 6, the pulse voltage is lowered to ■ and then recovered to ■.

Furthermore, if a spark occurs when the pulse frequency is increased to (■), the process moves to (2) where both the pulse voltage and the pulse frequency are decreased.

In addition, the increase in pulse frequency when moving from ■ to ■ is greater than the increase in pulse frequency when moving from ■ to ■.
Decrease the pulse frequency when moving from to ■°.

After ■° in FIG. 6, as the pulse voltage and pulse frequency are increased from ■°→■'→■°, sparks occur again at ■°. Since the transition from ■' to ■' is an increase in the pulse voltage, only the pulse voltage is lowered and the pulse voltage transitions to ■''.Then, it is restored to ■''. When the pulse frequency is further increased to ■'' and a spark is generated, both the pulse voltage and the pulse frequency are further decreased to ■°.

In this way, the operating point approaches the optimal point marked with a circle. In other words, if a spark occurs not only when the pulse voltage is increased but also when the pulse frequency is increased, the pulse frequency decreases more than the increase, so the pulse frequency gradually decreases and the pulse The voltage and pulse frequency reach an optimum point.

Note that both the pulse voltage and the pulse frequency have upper limits depending on the rated capacity of the device. Alternatively, conditions may be intentionally set below the rated capacity for reasons such as not wanting to cause too much sparring. If either the pulse voltage or the pulse frequency is increased for a certain period of time, and even if either reaches its upper limit, no spark is generated for a certain period of time, increase the pulse voltage or pulse frequency that has not reached the upper limit. There's room. In such a case, as shown in Figure 7, wait for a certain period (this may be longer than the previous fixed period), and if there is no spark, change the variable (pulse) that has not reached the upper limit a little. voltage or pulse frequency).

Here, referring again to Fig. 2, on the pulse voltage-pulse frequency coordinate plane, the boundary line between the non-spark region and the spark region is such that even if the pulse frequency increases, it can be applied without causing sparks. It has a horizontal line where the maximum pulse voltage is constant, and a downward-sloping line where the maximum pulse voltage that can be applied decreases as the pulse frequency increases. The bent part (the part marked O) between the horizontal line and the line downward to the right will be referred to as the "shoulder" hereinafter.

The inventor of the present invention measured the dust collection performance for various dust-containing gases by changing the pulse frequency and applying a pulse voltage on the verge of sparking. The results are shown in FIGS. 8 to 11.

In FIGS. 8 to 11, the apexes of Δ are measurement points of the pulse voltage on the verge of sparking and the maximum pulse frequency at that time, and are connected by solid lines. Moreover, the center of the circle is the normalized dust collection performance at the measurement point of pulse voltage and pulse frequency, and is connected by a dotted line.

The standardized dust collection performance is expressed by how many times the dust collection movement speed according to the Toichie formula below is compared to the conventional DC charged dust collection movement speed.

However, ω: Dust collector movement speed CI = Dust collector black dust concentration: Dust collector outlet dust concentration A: Dust collector electrode area Q: Dust collector gas amount As is clear from the examination of Figures 8 to 11, there are four types of dust. No matter where the dust is collected, a "shoulder" can be seen, and the maximum dust collection performance is obtained at that "shoulder". Therefore, it can be seen that the charging control method of the pulse charging type electrostatic precipitator according to the present invention can maximize the dust collection efficiency.

Effects of the Invention As described above, in the charging control method of the pulse charging type electrostatic precipitator according to the present invention, maximum dust collection efficiency is achieved by performing pulse charging with the above-mentioned "shoulder" pulse voltage and pulse frequency. can.

Then, at the time of sparking, the pulse voltage and, if necessary, the pulse frequency are lowered, and if there is no spark for a certain period of time, either the pulse voltage or the pulse frequency is gradually increased. Even if the value of the frequency is not specifically known, it is possible to reliably converge to the pulse voltage and pulse frequency at the "shoulder". Therefore,
No matter what type of dust is collected by any type of dust collector, dust collection performance can be automatically maintained at the highest value.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram of the voltage of a pulse charging type dust collector. FIG. 2 is a graph showing the relationship between pulse voltage, pulse frequency, and spark in the pulse charging method. FIG. 3 is a configuration diagram of a pulse charging type electrostatic precipitator that implements the charging control method according to the present invention. FIG. 4 is a graph showing changes in pulse voltage and pulse frequency to illustrate the charge control method according to the present invention. 5, 6 and 7 are diagrams illustrating the operation of the method of the invention under different conditions. FIGS. 8, 9, 10, and 11 are graphs illustrating the relationship between pulse voltage, pulse frequency, and dust collection performance when various types of dust are collected. [Main reference numbers] 1. Thyristor 2. Transformer 3. Rectifier bridge 4. Pulse generation circuit 5. Pulse power measuring device 6. Pulse power source 7. Spark detection device 8.
Base power supply 9... Electrostatic precipitator 10... Control device Patent applicant Sumitomo Heavy Industries, Ltd. Sub-agent Patent attorney Takashi Koshiba Figure 5 Figure 6 Figure 7 Figure 10 Pulse frequency (Pulse/#)

Claims (7)

[Claims] (1) In an electrostatic precipitator where a DC base voltage and a pulse voltage are applied in a superimposed manner, the maximum pulse voltage that can be applied without sparking cannot be maintained as the pulse frequency increases and must be lowered. A charging control method for a pulse charging type electrostatic precipitator, characterized by supplying pulses of the maximum pulse voltage that can be applied at a pulse frequency of . (2) The pulse according to claim (1), characterized in that the base voltage is maintained at the corona start voltage or a voltage slightly higher than the corona start voltage when direct current charging is performed without superimposing pulses. Charge control method for charged electrostatic precipitator. (3) In an electrostatic precipitator where a DC base voltage and a pulse voltage are applied in a superimposed manner, if no spark is generated within the precipitator, increase either the pulse voltage or the pulse frequency little by little at regular intervals to generate a spark. When a spark occurs, if the spark occurs within a certain period of time after the pulse voltage increases, the pulse voltage is lowered, and if the spark occurs within a certain period of time after the pulse frequency increases, the pulse voltage is lowered and the pulse frequency increases. Then, if no spark occurs, the pulse voltage is increased step by step at regular intervals to a voltage just before the pulse voltage at which a spark occurred last time, and then the pulse frequency is reduced step by step. 1. A charge control method for a pulse charging type electrostatic precipitator, comprising: supplying pulses at a maximum pulse voltage that can be applied, and at a maximum pulse frequency at the maximum pulse voltage that can be applied. (4) A patent characterized in that when there is no spark even if either the pulse voltage or the pulse frequency reaches the upper limit, the pulse voltage or pulse frequency that has not reached the upper limit is increased in stages after a certain period of time has elapsed. A charging control method for a pulse charging type electrostatic precipitator according to claim (3). (5) A charging control method for a pulse charging type electrostatic precipitator according to claim (3) or (4), wherein the certain period is about 5 seconds. (6) When lowering the pulse voltage, 5 to 5 of the pulse voltage
10%, and when increasing the pulse voltage, the pulse voltage is increased by 2 to 3%.
The charging control method for a pulse charging type electrostatic precipitator according to any one of items 3) to 5). (7) When lowering the pulse frequency, 30% of the pulse frequency
-50%, and when increasing the pulse frequency, the pulse voltage is increased by 10 to 20%, according to any one of claims (3) to (6). Charge control method for electrostatic precipitator.