JPS61468A - Intermittent charge controlling system of electric precipitator - Google Patents

Abstract

PURPOSE:To conserve power, by changing the charging ratio corresponding to the amount of dust in exhaust gas. CONSTITUTION:A dust densitometer 11 is provided in the main body of an electric precipitator and the amount of dust in exhaust gas is detected while sampling dust. This detection signal is inputted to a comparator 14 through a signal converter 12. The dust concn. setting signal from a dust concn. setting device 13 is also inputted to the comparator 14 and the signal corresponding to the magnitude relation of both signals is imparted to a charging ratio change-over circuit 15. By this method, operation at a high charge ratio is eliminated and power is conserved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to an intermittent charge control method when a DC high voltage is intermittently applied between a discharge electrode and a dust collection electrode of an electrostatic precipitator.

[Prior art and its problems]

In an electrostatic precipitator, when a high DC voltage is continuously applied between the discharge electrode and the collection electrode, high-resistance dust tends to cause reverse ionization, which significantly reduces the collection efficiency. It is known that dust collection efficiency can be improved by intermittently applying a high DC voltage between both electrodes.

The high DC voltage for electrostatic precipitators is obtained by boosting the AC power supply with a step-up transformer to create an AC high voltage, which is then rectified by a rectifier. However, a semiconductor control element such as a thyristor is installed on the low voltage side of the step-up transformer. By inserting a thyristor and controlling the phase of this thyristor, the value of the above-mentioned DC high voltage is changed.

Therefore, using this thyristor, there is a charging cycle period in which a high DC voltage is charged between the two electrodes of the electrostatic precipitator in synchronization with the voltage cycle of the AC power supply, and a charging rest cycle period in which high DC voltage is not charged between the two electrodes. So-called intermittent charging is performed so that the charges are alternately applied. The charging rate of this intermittent charging is obtained by dividing the above-mentioned charging cycle period by the sum of the charging cycle period and the charging rest cycle period. For example, if the frequency of the AC power source is 50 C, the period of one cycle is 20 milliseconds, and the number of charging cycles that are charged in synchronization with this AC power source is one cycle, that is, 20 milliseconds, and the charging period is 20 milliseconds. If the number of cycles is 4 cycles, that is, 80 milliseconds, the charging rate at this time is 0.2 or 20%.

j and j6T Conventional 0 Electrical precipitator aTum) The above-mentioned charge rate is set. However, for example, in the case of an electrostatic precipitator for a boiler, it is difficult to optimize the charging rate in response to changes in the boiler's load. The charging rate is set to keep the amount of dust in the exhaust gas below the specified value. Therefore, even when the boiler is not at its maximum load, dust is removed more than necessary at a high charging rate, which has the disadvantage of unnecessarily wasting power.

[Purpose of the invention]

An object of the present invention is to provide an intermittent charging control method for an electrostatic precipitator that can save power by changing the charging rate according to the amount of dust contained in exhaust gas.

[Key points of the invention]

This invention detects the amount of dust from the soot and dust concentration of the sampled exhaust gas, and when the amount of dust is less than a set value, the number of charging rest cycles is increased by one every time sampling is performed.
When the amount of dust is above the set value, the number of charging rest cycles is decreased by one cycle, that is, the charging rate is increased, and when starting from continuous charging, the charging rate is increased by sampling. As long as the amount of dust contained in the exhaust gas is decreasing, the number of charging rest cycles is increased by one cycle for each sample period, and the charging rate is changed in accordance with the amount of dust contained in the exhaust gas, thereby reducing power consumption. It is an attempt to save money.

[Embodiments of the invention]

FIG. 1 is a control block diagram showing an embodiment of the present invention. In FIG. 1, AC power supplied from an AC power source 1 is applied to a main control thyristor 3 via a circuit breaker 2. In FIG. The output of the main control thyristor 3 becomes an AC high voltage which is boosted by a step-up transformer 4, and is converted into a DC high voltage by a rectifier 5. This DC high voltage beam is applied to the discharge electrode 7 of the electrostatic precipitator via the axle 6, and this discharge electrode 7 is charged with a loadable DC high voltage and is connected to the discharge electrode 7 and grounded. The dust contained in the exhaust gas passing between the exhaust gas and the dust collecting electrode 8 is charged by this negative DC high voltage and drawn to the dust collecting electrode, so that the dust in the exhaust gas is removed. The value of the DC high voltage applied between the discharge electrode 7 and the dust collection electrode 8 is adjusted by controlling the phase of the main control thyristor 3 in response to the glow discharge or spark discharge generated between the two electrodes. However, illustration of this part is omitted in FIG.

In the present invention, a dust concentration meter 11 is provided in the main body of the electrostatic precipitator, and the amount of dust in the exhaust gas is repeatedly detected every predetermined period. The signal is input to the comparator 14 through the. On the other hand, the soot and dust concentration setting signal from the dust concentration setting device 13 is also applied to the comparator 1.
4, and a signal corresponding to the magnitude relationship between the two signals input to the comparator 14 is given to the charge rate switching circuit 15.

The charging rate switching circuit 15 generates a signal that increases or decreases the charging rate at each sampling period of the particulate concentration meter 11 based on the input signal from the comparator 14 and various conditions, that is, a signal that decreases or increases the number of charging rest cycles one cycle at a time. According to this signal, the phase shifter 16 controls the main control zyristor 3 so that a DC high voltage synchronized with the voltage cycle of the AC power supply 1 is intermittently charged between both electrodes.

FIG. 2 is a graph explaining the intermittent charging operation by the circuit of the embodiment shown in FIG. The vertical axis shows the dust contained in the exhaust gas (-3iH), and the dashed double-dot line at DI (+m) indicates the dust amount setting. 2 is provided at J and D2 to indicate the lower limit value.
The dashed dotted line indicates the upper limit value of the dust amount. Therefore, the area between D1 and D2 mentioned above is a dead zone. Further, the double circle in the figure indicates that intermittent charge control starts from that point.

FIG. 2(A) is a graph showing the basic operation when the amount of dust at the time of starting the intermittent charging operation is below the set lower limit value D1 or within the dead zone. Broken line A', i
p', () off 8 □ ea wa 1 wa ea ah 51. care,.

The number of charging rest cycles increases by one cycle for each cycle. This increase in the number of charging rest cycles continues until the dust amount exceeds D1 or more, that is, exceeds the set lower limit. In addition, the broken line B indicates the dust amount in the dead zone, that is, Dl and D2.
Since the number of charging rest cycles increases only once when intermittent charging is started, the number of charging rest cycles does not increase or decrease even if the amount of dust changes while the dust is in this dead zone. .

FIG. 2(b) shows the operation when the amount of dust at the start of the intermittent charging operation is greater than or equal to the set upper limit value D2. In other words, since the amount of dust is large on the broken line E, the number of charging rest cycles decreases by one cycle in each sample period, and the charging rate increases, so the amount of dust also decreases, but when it enters the dead zone, the charging rest cycle occurs as described above. The number does not change. In this state, if the amount of dust becomes less than the set lower limit value D1, this indicates that the number of charging rest cycles will increase. On the other hand, in the case of broken line F, the number of charging rest cycles is zero, that is, starting from continuous charging. The number of charging rest cycles is increased by one cycle each time. Therefore, on the polygonal line F, even if the dust amount decreases to a dead zone that is smaller than the set upper limit value D2, the number of charging rest cycles continues to increase, and as a matter of course, when the dust amount becomes less than the set lower limit value D1, the number of charging rest cycles increases. continues to increase. In this state, if the amount of dust increases to the dead zone, the change in the number of charging rest cycles will stop, and if the amount of dust further increases and exceeds the set upper limit value D2, the number of charging rest cycles will start to decrease for the first time.

〔Effect of the invention〕

According to this invention, the amount of dust in the electrostatic precipitator is detected by a soot concentration meter, and if the amount of dust is less than the set value, the amount of dust in the electrostatic precipitator is The number of charging rest cycles of the DC high voltage that intermittently charges the electrode is increased one cycle at a time, in other words, the charging rate is lowered in order to save power, but when the amount of dust exceeds the set upper limit, The dust removal effect is improved by reducing the number of charging rest cycles, that is, by increasing the charging rate. However, even if the dust amount is above the set upper limit, when starting from continuous charging, as long as the amount of dust obtained in the current sampling continues to decrease compared to the amount of dust in the previous sampling, the charging will stop at every sampling period. The number of cycles is increased by one cycle to save power. In other words, the present invention determines whether the dust amount is greater or less than the set value, and compares the dust amount sampled each time to determine the tendency of the dust amount to increase or decrease.
An intermittent charging control method is used in which the number of charging rest cycles is reduced, that is, the charging rate is increased only when necessary. Therefore, even though the amount of dust is small, the device does not operate at a high charging rate, resulting in the effect of saving power.

[Brief explanation of drawings]

FIG. 1 is a control block diagram showing an embodiment of the present invention,
FIG. 2 is a graph explaining the intermittent charging operation by the circuit of the embodiment shown in FIG. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Breaker, 3... Main control thyristor, 4... Step-up transformer, 5... Rectifier, 6
... Reactor, 7... Discharge electrode, 8... Dust collection electrode,
11... Dust concentration meter, 12... Signal converter, 13.
... Dust concentration setting device, 14... Comparator, 15... Charge rate switching circuit, 16... Phase shifter. Figure 1

Claims (1)

[Claims] A DC high voltage obtained by rectifying the AC high voltage obtained by boosting the AC power supply voltage with a step-up transformer is charged between the discharge electrode and the dust collection electrode of the electrostatic precipitator in synchronization with the voltage cycle of the AC power supply. In an intermittent charging method of an electrostatic precipitator, a charging cycle period in which charging occurs and a charging rest cycle period in which the DC high voltage is not charged alternately appear;
The amount of dust in the electrostatic precipitator is repeatedly measured in a predetermined sampling period, and when the amount of dust is less than the set lower limit value, the number of charging rest cycles is increased by one cycle for each sampling period, and the amount of dust is When the amount of dust is between the set lower limit value and a higher set upper limit value, the number of charging rest cycles remains unchanged, and when the dust amount is equal to or higher than the set upper limit value, the number of charging rest cycles changes from zero. The number of charging rest cycles is decreased by one cycle for each sampling period except when the number of charging rest cycles starts, and when the number of charging rest cycles starts from zero, the current sampling dust amount is smaller than the previous sampling dust amount. An intermittent charging control method for an electrostatic precipitator, characterized in that the number of charging rest cycles is increased by one cycle for each sample period.