JPH0461695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a charge rate control method for an electrostatic precipitator (hereinafter abbreviated as EP) having an intermittent charging function.

[Conventional technology]

In conventional EPs with intermittent charging function, the charging rate is mainly set by manually changing the charging rate while monitoring the EP outlet concentration to find the optimum condition. An automated method as shown in FIG. 6 is also known.

In the case shown in FIG. 6, the optimum value of the intermittent charging rate changes depending on the dust conditions, so the charging rate is changed so that the amount of dust monitored at the outlet of the EP is minimized. As shown in Figure 3, intermittent charging is a charging method in which the current is turned on and off periodically in accordance with the commercial frequency, and the charging rate γ is defined as charging time T ₁ and pause time T ₂ . Time, γ=T ₁ /T ₁ +T ₂
It is expressed in

However, in this case, there were disadvantages in that a dust monitor was required at the outlet of the EP, and that individual power supply units could not be optimally adjusted.

On the other hand, as a method of setting the optimal charging rate for each power supply device based on the voltage waveform of each power supply category, there is also a control method that maximizes the product Vp × Vm of the voltage peak value Vp and the voltage average value Vm. A correlation with dust collection performance has also been confirmed. However, in this case, for dust that causes back ionization, lowering the charge rate can suppress back ionization, and even though the dust collection is high,
Since the average voltage becomes higher when the charge rate is higher, a phenomenon in which Vp×Vm becomes larger depending on the dust conditions has been observed, and reverse ionization may not be suppressed completely and optimal adjustment may not be obtained. It was hot.

In FIG. 6, 10 is an EP, 11 is a power supply unit, 12 is a control device, and 14 is a dust collection monitor.

[Problem that the invention seeks to solve]

Generally, in EP for coal-fired boilers, the electrical resistance of the collected dust fluctuates depending on the operating conditions such as the coal used and the operating temperature, and with conventional charging methods, the dust collection performance fluctuates significantly. As a countermeasure to this problem, intermittent charging can suppress the decline in dust collection performance due to reverse ionization when the dust to be collected has high resistance, and has been put into practical use, but the optimal setting value varies depending on the dust conditions. It has been confirmed that this occurs (see Figure 4).

However, in order to automatically set the optimal conditions for intermittent charging in response to these condition variations, conventionally this was done by feeding back the dust concentration signal at the EP outlet, which required a signal from the dust monitor. Furthermore, since multiple power supply units were controlled to a uniform setting value, it was not possible to optimally adjust each power supply.

As a result of investigating the relationship between performance and voltage waveform under various dust conditions, the present invention focused on the fact that there is a certain relationship between the charge rate of intermittent charging of EP and the smallest value of each cycle of the EP voltage waveform. This is an EP charging rate that allows the optimal charging rate setting for intermittent charging to be automatically, reliably and quickly set for each power supply unit without the need for a dust monitor or external control unit. The purpose is to provide a control method.

[Means for solving problems]

The charging rate control method for EP according to the present invention includes:
During normal charging, the charging rate is controlled so that the minimum value per cycle of voltage becomes the maximum value, and when reverse ionization occurs, the charging rate is controlled so that the minimum value per cycle of voltage becomes the maximum value. It is characterized by That is, in the present invention, as a means for setting the charge rate of intermittent charging, in the case of dust conditions where the smallest value V _b of each cycle of the voltage waveform causes reverse ionization, the normal charge rate is set as the charge rate changes. Focusing on the fact that the charge is a monotonically decreasing function and that during reverse ionization it takes a maximum value below a certain charge rate, V _b always takes the maximum value during normal charging and the maximum value during reverse ionization. The charging rate can be set in various ways. For example, Figure 5 shows the relationship between the charge rate and the value of V _b under various dust conditions, but it is important to set the charge rate so that V _b takes the maximum or local maximum value under each dust condition. This allows optimal dust collection performance to be obtained.

[Effect]

For example, as shown in Figure 3, when reverse ionization occurs,
Since the apparent corona resistance of EP is small, the rate of decrease of the voltage waveform per unit time is large, and therefore the minimum voltage value per cycle of continuous charging V _b
is a smaller value than when charged normally.

However, by lowering the charging rate through intermittent charging, the average current decreases, making it possible to suppress reverse ionization, which increases the apparent corona resistance, which reduces the drop in voltage per unit time.
As a result, V _b increases.

As a result of organizing the relationship between the charge rate of intermittent charging and dust collection, and the minimum value V _b during one cycle of the voltage waveform, and the charge rate of intermittent charging under various dust conditions based on the above principles,
For example, as shown in FIG. 5, it was found that the best performance as shown in FIG. 4 can be obtained at a charge rate where V _b takes a maximum value or a local maximum value.

In other words, since reverse ionization does not occur in medium-low resistance dust, V _b takes a monotonically decreasing curve as the charge rate decreases, and performance also becomes a monotonically decreasing function. However, in dust that causes reverse ionization, V _b is necessary. However, the maximum value is obtained in the region where the charging rate is γ = 1/3, and the setting of the charging rate at that time coincides with the optimal performance adjustment point of EP.

Therefore, by changing the charging rate during operation and setting it at the point where it takes the maximum value or local maximum value,
No external equipment such as a dust monitor is required, and the best performance can be obtained for each power supply unit.

In addition, during normal charging, the minimum voltage V _b per cycle becomes a monotonically decreasing function by lowering the charging rate γ, but under operating conditions that generate a reverse current, V _b becomes the charging rate γ = ≦ 1/ By utilizing the characteristic that the maximum value occurs in the region 3, it is possible to distinguish between normal charging and reverse ionization, and when normal charging is performed, the maximum value within the charging rate setting range is set, and when reverse ionization occurs, V _b is set to the maximum value. By performing floating control,
The optimum charge rate can be quickly set without scanning the entire charge rate setting range.

Here, the maximum value within the charging rate setting range is usually γ=
1, but it goes without saying that if there is room for performance, γ may be set to 1/2, 2/3, etc. in consideration of energy saving.

Also, EP may cause spark discharge,
At that time, V _b becomes OKV, but it goes without saying that the detection accuracy of V _b can be improved by excluding such abnormal voltages and by detecting V _b by sampling multiple V _b values. stomach.

〔Example〕

FIG. 1 is a diagram showing an example of a power supply configuration used to carry out the method of the present invention, and FIG. 2 is a diagram showing an example of a flowchart of operation control according to an embodiment of the present invention.

In FIG. 1, an alternating current power supply AC is supplied to a thyristor circuit 1, and is inputted from the same circuit to a high voltage transformer 2. A DC high voltage is supplied from the secondary side of the transformer 2 to the EP 4 via the rectifier 3.

The signals from the current detector 5 and voltage detector 6 are input to the control device 8 in the control unit 7, and the microcomputer unit 9 determines the operating state of the EP 4, so that the control device 8 sets the optimum charging rate. A predetermined charging rate can be set by controlling the thyristor circuit 1 according to the following.

Figure 2 shows a flowchart of the control method according to the present invention. Basically, under conditions where reverse ionization occurs, the operation is performed at a charge rate γ = 1/3 or less, so V _b is set to the maximum value. Therefore, as long as there is no significant change in operating conditions, floating control is always used to maintain the maximum value, so there is no need to scan the entire charge rate setting range.

On the other hand, during normal charging, V _b becomes a monotonically decreasing function, so if the range from the initial value γ = 1/1 (continuous charging) to the point exceeding γ = 1/3 is covered, normal charging can be considered as a reverse ionization condition. Since it is possible to determine the condition, there is no need to apply conditions to a state lower than that. Therefore, the charging state can be determined without significantly reducing the high dust collection efficiency during normal charging.

In other words, V _b is a monotonically decreasing function during normal charging, and V _b takes a maximum value when γ < 1/3 when reverse ionization occurs. control is possible.

Note that the change to the state of normal charging←→reverse ionization occurs when the operating conditions change significantly, but in that case, the flow is such that it is possible to escape from each state.

Next, the operation of one embodiment of the method of the present invention will be explained based on the flowchart shown in FIG.

In the method of the present invention, the current charging rate γ and the minimum voltage value V _b per cycle are periodically monitored. is the operating mode during normal charging. Here, set the charging rate γ to γ=1,
2/3, 1/2, 1/3, 1/5, 1/7, 1/
11, 1/21, 1/31, 1/61.

At this time, if EP is in a normal charged state, as γ decreases (for example, γ = 1 → 2/3 →
1/2 → 1/3), the minimum value of one cycle of each waveform
V _b decreases with a monotonically decreasing function. and γ<
If the charge continues to decrease monotonically even when it reaches 1/3 (for example, γ = 1/5), it is determined that the current charge is in a normal charge state, and the optimal setting value for normal charge γ = 1.
, and one cycle of control is completed.

On the other hand, if V _b tends to increase during this process, then
It is determined that it is under the charge condition of reverse ionization, and γ is set to 1
Set with lower rank. Generally, when reverse ionization occurs, V _b tends to increase near γ = 1/2 or γ = 1/3, so the setting at this time is γ = 1/3 or less, and the control Ends the cycle.

Next, after a certain period of time, control for optimal adjustment is performed again, but in this case, if the charge is the same normal charge as at the beginning, from γ = 1 to γ < After changing 1 way until 1/3, γ=1 again
The settings are as follows.

On the other hand, if EP is initially normally charged but changes to reverse ionization conditions due to changes in operating conditions, etc.
Since V _b improves in the process of decreasing γ,
After setting γ=1/3 or less, one cycle of control ends.

Further, in a state where the reverse ionization state continues, by determining γ≦1/3 at the first stage of one cycle of control, the control immediately shifts to control to make V _b the maximum value. In other words, compare the previous V _b and the current V _b ,
It constantly increases or decreases the charge rate in the direction of becoming larger than the previous V _b , for example, γ =
If 1/11 is the maximum value, the current setting value is γ = 1/
3, if the previous value was 1/2, control is performed so that it approaches the maximum value by further lowering γ, as shown in FIG. On the other hand, if the current set value is γ = 1/11 and the previous setting was γ = 1/7, an attempt is made to further lower γ and the setting is γ = 1/21, but in this case, the next control Since it is determined that V _b has decreased compared to the previous time, the next setting will try to increase γ, so γ
= Floating control around 1/11.

In other words, control is performed to constantly aim for γ=1/11.

Also, when normal charge is restored from reverse ionization,
Since V _b improves each time γ is increased, γ is increased until γ is set to <1/3, and in the next loop, a transition is made to the normal charging loop.

〔Effect of the invention〕

According to the present invention, the following effects can be achieved.

(1) For EPs that have an intermittent charging function, by optimizing the charging rate setting by determining the minimum value per cycle of the voltage waveform, it is possible to use an individual power supply unit without the need for a dust monitor. Optimum adjustment can be made for each case.

(2) In the above, the minimum value per cycle of the voltage waveform is a monotonically decreasing function during normal charging, and the maximum value is in the region where the charging rate is 1/3 or less when reverse ionization occurs. Speeding up of control is possible by controlling according to the conditions.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a configuration example of a power supply used to carry out the method of the present invention, Fig. 2 is a diagram showing a flow of a control method for controlling the power supply, and Fig. 3 is an EP
Figure 4 shows a comparative example between continuous charging and intermittent charging regarding the relationship between the charging state and current/voltage waveform. Figure 4 shows the relationship between the charge rate and dust collection for intermittent charging for each dust condition. 5 is a diagram showing the relationship between the minimum voltage value V _b per cycle at that time and the charging rate, and FIG. 6 is a diagram for explaining an example of a conventional method for setting intermittent charging. 1... Thyristor circuit, 4... EP, 5... Current detector, 6... Voltage detector, 7... Control unit.

Claims (1)

[Claims] 1. In the charging rate control method for an electrostatic precipitator with an intermittent charging function, when charging is normal, the voltage is 1
An electric concentrator characterized in that the charge rate is controlled so that the minimum value per cycle becomes the maximum value, and when reverse ionization occurs, the charge rate is controlled so that the minimum value per cycle of voltage becomes the maximum value. Charge rate control method for dust equipment.