RU2455075C2 - Method of automatic control over electric filter by discharges - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to cleaning gases by electrical means from dust and mist and may be used in ACSs of electric filter supply converters. Proposed method consists in varying adjustment angle of thyristor or symistor gate of filer power supply. Note here that mean current at filter before puncture of electrode gap is measured to set suppression pause depending upon filer mean current immediately before puncture. Larger pause corresponds to higher current while smaller pause corresponds to lower current. During time interval T, from puncture origination to termination of filter current, filter current and voltage are measured. In case current exceeds zero and voltage equals it, suppression pause is set by switching off power thyristors for suppression time T_supr. In case current and voltage exceed zero at T, then T_supr is set to zero. At punctures in pause between currents with current and voltage equal to zero, T_supr is set to zero.

EFFECT: higher efficiency of cleaning.

2 dwg

Description

The invention relates to the field of electric cleaning of gases from dusts and mists in various industries and agriculture and can be used in automatic control systems for high-voltage converting power units of electrostatic precipitators. Known methods for automatically controlling the maximum average value of the operating voltage on the electrostatic precipitator, at which the angle of regulation of the thyristor switch increases to achieve a natural maximum average value of the operating voltage, limited either by the nominal parameters of the converter unit or by the current-voltage characteristic of the electrostatic precipitator (the presence of a “reverse corona”, spark and arc breakdown of precipitation space, etc.). There are also known methods that are technically close to the present invention — methods for automatically controlling the voltage of an electrostatic precipitator by changing the angle of regulation of the thyristor switch depending on the magnitude of the operating voltage on the electrostatic precipitator, in which, in order to prevent prolonged breakdowns, they suppress electric breakdowns — relieve tension from the electrostatic precipitator after each breakdown by locking the thyristor key (see ed. certificate of the USSR No. 355606, publ. 30.09.72 and No. 1798004, publ. 28.04.93).

The closest in technical essence of the present invention is a method for automatically controlling the voltage of the electrostatic precipitator by changing the angle of regulation of the thyristor (triac) key in the power supply circuit of the electrostatic precipitator, at which the average value of the current through the electrostatic precipitator is measured before the breakdown of the interelectrode space and the damping time in the electrostatic precipitator is set in depending on this value. If its value exceeds a certain critical value, it is assumed that a spark breakdown in an electrostatic precipitator can turn into an arc one. In this case, the duration of the blanking pause is set depending on the absolute value of the average current value - a longer blanking pause duration corresponds to a larger current value. A smaller current value means a shorter blanking time. If this current is less than the critical value, the blanking pause duration is set equal to zero (see RF patent No. 2147469, published on 04/20/2000).

A significant drawback of these methods is that when electrostatic precipitators are supplied with pulsed current, which is carried out in the vast majority of cases when powered from single-phase converter units with one- and two-half-wave rectification schemes, as well as when powered from special pulse sources, the time for suppressing electrical breakdowns (voltage relief with an electrostatic precipitator) is installed according to formal signs, regardless of whether there is an arc or spark breakdown. In the first case, each breakdown is extinguished. In the second - if the current value exceeds a certain critical value. However, the absolute value of the critical current is not constant and depends on a number of factors: both on the dimensions of the electrostatic precipitator and the power of the converter unit, and on the operating mode and technological parameters of the gases being cleaned. In fact, in the process of working, it is very difficult to reliably predict its value.

This leads to an unjustified decrease in the average value of the voltage on the electrostatic precipitator and, as a result, to a deterioration in the degree of gas purification.

The aim of the present invention is to increase the degree of purification of gases by increasing the average voltage on the electrostatic precipitator in the mode of spark and arc breakdowns.

This goal is achieved by the fact that in the known method of automatic voltage regulation, which consists in changing the angle of regulation of the thyristor switch of the high-voltage converter power supply unit of the electrostatic precipitator to maintain the average voltage value of the electrostatic precipitator at the highest possible level, the system automatically determines the nature of the breakdown. Arc or spark discharge.

The difference of the proposed method of regulation is that during the time interval "T", from the moment of breakdown to the end of the current of the electrostatic precipitator of the current half-period, the current value and voltage of the electrostatic precipitator are measured, and if the current value is greater than zero and the voltage is zero, an arc takes place discharge. Set the duration of the blanking pause by closing in the next half-cycle the power thyristors of the unit for a while - Tgash, the value of which depends on the absolute value of the average current of the electrostatic precipitator immediately before breakdown. A larger current value corresponds to a longer blanking pause. A lower value means a shorter pause duration.

Another difference of the proposed method is that, if during the interval "T", the current and voltage values are greater than zero, - spark breakdown. Set the duration of the blanking pause - Tgash equal to zero.

The third difference of the proposed method is that during breakdowns in the inter-pause, when the current of the electrostatic precipitator and the voltage on the electrostatic precipitator are equal to zero, there is a spark breakdown. Set the length of the blanking pause - Tgash equal to zero.

This allows you to increase the average voltage of the electrostatic precipitator when operating in the mode of alternating spark and arc breakdowns by 5-10% and to reduce dust emission into the atmosphere by 10-20%.

These differences in the proposed method of regulation in comparison with the prototype are significant. This allows us to conclude that it meets the criterion of "inventive step".

Figure 1 presents a possible variant of a block diagram of a device for implementing the inventive method.

The block diagram contains a thyristor switch 1, a current-limiting inductor 2, a high-voltage conversion unit 3, an electrostatic precipitator 4, an electrostatic precipitator voltage sensor 5, an electrostatic precipitator current sensor 6, a damping-off pulse length generator 7 Tgash proportional to the average value of the electrostatic precipitator current, a breaker of 8 breakdowns in the electrostatic precipitator, charging current integrator 9, phase shifter 10, key 11, thyristor key 1 control pulse shaper 12, “T” time shaper 13, from the moment of breakdown to the eye chania AC current half-cycle, the nature of analyzer 14 Breakdown "arc-spark", the timer 15.

The scheme works as follows:

When applying voltage to the converter unit and the voltage regulator of the mains and performing the “Start” operation, control pulses from shaper 12 appear on thyristor key 1, the phase position of which is set by phase shifting device 10. The initial control angle has a minimum value. Thyristor key opens. A voltage appears on the electrostatic precipitator 4.

As the voltage on the integrator 9 increases, the control angle increases, therefore, the magnitude of the voltage on the electrostatic precipitator increases.

The process of accelerating the system of the unit-electrostatic precipitator occurs at a speed determined by the time constant of the integrator 9, and continues until one of the following situations occurs:

1. The angle of regulation - will reach its maximum value. The voltage on the electrostatic precipitator in this case will be the greatest.

The acceleration process will stop.

2. The current value of the electrostatic precipitator will reach the rated current value of the converter unit.

3. In the electrostatic precipitator, at a certain voltage level, breakdowns of the precipitation space will occur.

When breakdowns occur in the sedimentation space of the filter, voltage pulses appear at the output of the selector 8. They are fed to the inputs of the shaper 7, the integrator 9 and the input 16 of the shaper 13 of the time interval "T". The input 17 of the shaper 13 is fed with the current value of the signal from the current sensor 6, the output signal of which is fed to the input 18 of the analyzer 14 of the nature of the breakdown "arc-spark". At the same time, the current values of the signals from the outputs of the voltage sensors 5, current 6 and timer 15 are supplied to the inputs 19, 20, 21 of the analyzer 14 of the nature of the breakdown.

During the time interval - "T", from the moment of breakdown to the end of the current of the electrostatic precipitator of the current half-period, measure the current value and voltage of the electrostatic precipitator. The measurement time is set by timer 15. If the current value is greater than zero, and the voltage is zero, there is an arc breakdown. At the output of the analyzer 14, an arcing discharge quenching signal appears. Acting on the inputs 22 and 23 of the key 11, the supply of control pulses to the input of the shaper 12 and, therefore, to the thyristor key 1 in the power circuit of the converter unit 3 and the electrostatic precipitator 4 for the time Tgash, determined by the signal value at the input 23 of the key 11 from the output of the shaper 7 is interrupted .

Thus, a damping pause is established by turning off the power thyristors of the unit in the next half-cycle for a while - Tgash.

If during the interval “T” the current and voltage values are greater than zero, this is a spark breakdown. At the output of the analyzer 14, there is no signal. The blanking pause - Tgash, is zero.

In case of breakdowns in the inter-current pause, the current of the electrostatic precipitator and the voltage on the electrostatic precipitator are equal to zero - spark breakdown. At the output of the analyzer 14, the signal is also absent. The blanking pause duration is also zero.

As an illustration, Figure 2 shows the oscillograms obtained during the implementation of the method on the model - "control system - converting unit - electrostatic precipitator."

Oscillograms No. 16, 17, 18, 19, 20, 21, 22, 23 correspond to the signals at the inputs of the same name in the blocks of the circuit shown in Figure 2.

Claims (1)

A method of automatically adjusting the voltage of an electrostatic precipitator by changing the angle of regulation of a thyristor or triac switch in a power supply circuit of an electrostatic precipitator, measuring the average value of the current through the electrostatic precipitator before the breakdown of the interelectrode space and setting the duration of the blanking pause on the electrostatic precipitator, the value of which depends on the absolute value of the average current of the electrostatic precipitator before the breakdown, a longer blank pause time corresponds to a larger current value a smaller value - a shorter pause time, characterized in that during the time interval “T” from the moment of breakdown to the end of the current of the electrostatic precipitator of the current half-period, the current value and voltage of the electrostatic precipitator are measured, and if the current value is greater than zero and the voltage is zero, set the duration of the blanking pause by turning off the power thyristors of the unit in the next half-cycle for the time Tgash, if during the interval "T" the current and voltage values are greater than zero, set the duration of the gash pause Nia Tgash zero when breakdowns in mezhdutokovuyu pause when electrostatic current and voltage of an electrostatic precipitator are zero pause duration is set equal to zero blanking Tgash.

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