High Voltage Power Supply Design And Energy-Saving Optimal Control For High Efficiency Electrostatic Precipitator

As a main air pollution control device, electrostatic precipitator has been widely used in the industrial process of removing dust particles from flue gas. Due to large electric energy consumption and high operation cost, the demand of reducing electrostatic precipitator operation cost is more urgent for enterprises with the improvement of the flue gas emission standard of the state. In order to increase the collection efficiency of electrostatic precipitator and decrease the power consumption in the process of electrostatic precipitation, it is an effective approach to improve electrostatic precipitator design and optimize electrostatic precipitation process control.An electrostatic precipitator consists of multiple cascaded collecting zones, and electric field characteristic in each zone is the key factor to affect the collection efficiency, furthermore, the electric field characteristic is mainly determined by the geometric shape of discharge electrode and the working voltage of each collecting zone. At present, since electric field characteristics of different discharge electrodes are not clear, the unreasonable configurations of discharge electrode and high voltage source result in the poor collection efficiency easily. Moreover, the negative and high direct current voltage that is required by each collecting zone is supplied by high voltage source, and it is difficult for the existing single-phase high voltage power supply to obtain higher average voltage due to its high ripple factor and low power efficiency, which has limited the improvement of collection efficiency and resulted in serious electric energy waste. Although the existing three-phase high voltage power supply can increase the average voltage, its control is complex, and higher precision of synchronization signal is demanded, furthermore, the sequence of triggering silicon controlled rectifier is required to accord with the input phase order strictly. Besides, the spire voltage from the commutation operation of three-phase rectifier bridge may lead to the damage of silicon stack easily, which puts the three-phase high voltage power supply at high safety risk. Compared with single-phase and three-phase high voltage power supplies, high-frequency high voltage power supply can obtain higher average voltage, but high working frequency also leads to large on-off power loss, which limits the increase of its output power. Thus, it is still difficult for the existing high-frequency high voltage power supply to satisfy the application requirement of middle or large electrostatic precipitator. In addition, due to the lack of effective coordination, multiple cascaded collecting zones have to maximize their output power for ensuring the collection efficiency, which also results in unnecessary waste of a lot of electric energy. With the destination of increasing collection efficiency and decreasing power consumption, this paper focuses on high voltage power supply design and energy-saving optimal control for high efficiency electrostatic precipitator, and the main work is described as follows.1. In term of the poor collection efficiency problem that is resulted by the unreasonable configurations of discharge electrode and high voltage source due to unclear electric field characteristics and experiential selection of barbed electrodes, experimental analysis and comparison of discharge principle and electric field characteristic are completed for barbed electrodes with different geometric shapes in detail. As a result, the experiment basis of selecting barbed electrode and determining the rated current of high voltage source reasonably is suggested. Experimental results show that the current density distribution on the collecting electrode is not uniform for all barbed electrodes, and these electrodes should be applied in electrostatic precipitators that remove dusts with middle or low dust resistance for obtaining high collection efficiency. Moreover, the BS barbed electrode is the first choice for the preceding collecting zones because of its strongest corona discharge ability in order to enhance the collecting ability. As barbed electrodes are adopted, the determination that the rated secondary current of high voltage source is configured in terms of the current density of0.7mA/m2-0.8mA/m2benefits the increase of collection efficiency.2. In order to provide higher working voltage for each collecting zone and increase the collection efficiency, this paper improves three-phase high voltage power supply design and high-frequency high voltage power supply design separately. Referring to the spire voltage problem in three-phase high voltage power supply, a control method that triggers silicon controlled rectifier based on line voltage synchronization signal is presented, and the specific design of three-phase high voltage power supply is completed on the basis of the derived mathematical expressions referring to instantaneous value, average value and peak value of secondary voltage under different conduction angles. As a result, the spire voltage is avoided effectively, and the device reliability is improved, moreover, the sequence of triggering silicon controlled rectifiers can be adjusted automatically, which decreases the control complexity and increases the application convenience. Referring to the large on-off power loss problem in high-frequency high voltage power supply, a new soft switching method that the output voltage is adjusted by changing the frequency of the triggering pulse with the fixed high level width on the basis of series resonance is proposed, and zero current turning-on and zero current turning-off are realized for power devices synchronously, which decreases both turn-on and turn-off power losses effectively. According to the analysis of the working modes of resonant loop, the working circuits and the equivalent circuits in different modes are presented, and full mathematical descriptions of voltage and current are obtained in state equations. Based on these descriptions, the high-power and high-frequency high voltage power supply with the rated secondary current of1200mA and the rated secondary voltage of80kV is developed. By experimental comparison among three kinds of high voltage sources, it is verified that the developed high voltage power supplies can provide much higher average voltage than the single-phase high voltage power supply and increase the collection efficiency, and can satisfy the application requirements of electrostatic precipitators with different capacities.3. For reducing the negative impact on collection efficiency from spark discharge, a software and hardware parallel spark detection method, which is based on variation characteristics of the secondary voltage and the secondary current in spark discharge, is proposed, and the relevant theoretical detection criterion is provided. As a result, the accurate spark detection is realized, and miss spark detection and false spark detection are avoided. By distinguishing the sparks with different discharge energy and processing these sparks separately, the voltage, which is provided during the process of voltage recovery, is increased effectively. Especially, for the spark with large discharge energy, a new spark control method that tracks the spark discharge point dynamically is presented. By using this control method, the frequency of spark discharge and the recovery speed of voltage can be adjusted with the variation of field condition automatically. Compared with the traditional spark control method, the presented control method can obtain higher average voltage and enhance the ability of collecting dust particles, and can attenuate the negative effect on collection efficiency from spark discharge effectively.4. Referring to the optimal control problem in the factual electrostatic precipitation system with multiple cascaded collecting zones, a new energy-saving optimal control strategy that minimizes the total power consumption subject to satisfying the outlet concentration requirement is suggested. By employing neural network and polynomial fitting methods, the models of U2-Co, U2-I2, U2-U1and I2,I1, are established, respectively. Furthermore, the specific optimal scheme, which adopts genetic algorithm to search the optimal secondary voltage of each zone and makes use of the inner loop control of high voltage source to obtain the expected output, is also presented, and the overall coordination of output power is realized for all collecting zones. The experimental verification in factual electrostatic precipitator shows that the presented method can reduce the total power consumption effectively while satisfying the outlet dust concentration requirement.