Electricity: power supply or regulation systems – Output level responsive – Phase controlled switching using electronic tube or a three...
Reexamination Certificate
1999-09-28
2002-03-26
Patel, Rajnikant B. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Phase controlled switching using electronic tube or a three...
C323S903000, C363S128000
Reexamination Certificate
active
06362604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates to circuits for generating high voltage electrical pulses.
2. Background Art
With the thrust to maintain a clean environment, the need for better particulate control in industrial processes is needed. Electrostatic precipitators are one of the most widely used methods of collecting particulate matter in flue gas systems. In general, the systems are comprised of sets of collecting plates which are usually at ground potential, high voltage electrodes, and a set of power supplies which delivers the high voltage to the electrodes. The high voltage electrode is made up of either a thin wire running the length of the collecting plates or a rigid electrode.
The majority of the power supplies for the systems are made up of transformer/rectifier (T/R) sets. The T/R sets provide unfiltered, rectified high voltage (40 kV-80 kV) DC to the electrodes. It has been shown that better collection efficiency can be achieved by applying a voltage pulse (also known as pulsed energization) to the electrostatic precipitator instead of the unfiltered DC.
The idea of pulsed energization for the electrostatic precipitator (ESP) process is not new and has been studied extensively. The earliest work was performed by R. Heinrich in the 1920's. Heinrich applied radar modulator technology that was being developed for World War II. Heinrich worked with Harry White and Herb Hall at the MIT Radiation Laboratory. Later in 1952 the first full scale tests were conducted by White and Hall when they applied pulsed voltages with 50 microsecond rise-times to wire-plate ESPs using rotary spark gaps or hydrogen thyratrons, pulse transformers and blocking diodes. Improved efficiency was observed for the tests.
Masuda of Japan furthered pulsing technology in 1976 by applying a pulse to a DC bias. The bias allowed the use of halo-wave AC for corona creation. This system operated primarily as a pre-charger to a conventional ESP. In the United States numerous systems have been investigated over the years with limited success due to overall system costs and reliability.
Prior art patents that disclose related technology, however different from the present invention, include: U.S. Pat. No. 5,623,171, to Nakajima, entitled “High Voltage Pulse Generating Circuit and Electrostatic Precipitator Containing It;” U.S. Pat. No. 4,808,200, to Dallhammer et al., entitled “Electrostatic Precipitator Power Supply;” U.S. Pat. No. 4,558,404, to James, entitled “Electrostatic Precipitators;” U.S. Pat. No. 4,867,765, to Tomimatsu et al., entitled “Self-Discharge Type Pulse Charging Electrostatic Precipitator;” U.S. Pat. No. 4,600,411, to Santamaria, entitled “Pulsed Power Supply for an Electrostatic Precipitator;” U.S. Pat. No. 4,592,763, to Dietz et al., entitled “Method and Apparatus for Ramped Pulsed Burst Powering of Electrostatic Precipitators;” U.S. Pat. No. 2,509,548, to White, entitled “Energizing Electrical Precipitator;” U.S. Pat. No. 5,903,450, to Johnson et al., entitled “Electrostatic Precipitator Power Supply Circuit Having a T-Filter and Pi-Filter;” U.S. Pat. No. 5,757,169, to Terai, entitled “Electric Circuit for Pulse Energized Electrostatic Precipitator and Pulse Energized Electrostatic Precipitator Using This Circuit;” U.S. Pat. No. 5,639,294, to Ranstad, entitled “Method for Controlling the Power Supply to an Electrostatic Precipitator;” U.S. Pat. No. 4,996,471, to Gallo, entitled “Controller for an Electrostatic Precipitator;” U.S. Pat. No. 4,626,261, to Jorgensen, entitled “Method of Controlling Intermittent Voltage Supply to an Electrostatic Precipitator;” U.S. Pat. No. 4,587,475, to Finney, Jr. et al., entitled “Modulated Power Supply for an Electrostatic Precipitator;” U.S. Pat. No. 4,567,541, to Terai, entitled “Electric Power Source for use in Electrostatic Precipitator;” U.S. Pat. No. 4,541,848, to Masuda, entitled “Pulse Power Supply for Generating Extremely Short Pulse High Voltages;” U.S. Pat. No. 4,290,003, to Lanese, entitled “High Voltage Control of an Electrostatic Precipitator System;” and U.S. Pat. No. 4,061,961, to Baker, entitled “Circuit for Controlling the Duty Cycle of an Electrostatic Precipitator Power Supply.”
U.S. Pat. No. 4,558,404, to James, relates to a DC-AC inverter, whereas the present invention utilizes an inversion circuit which inverts polarity. U.S. Pat. No. 4,867,765, to Tomimatsu et al., uses an inductive isolation for the voltage pulse, while other ESP cells are used to bleed down the charge on the ESP. Only one ESP cell is pulsed at a time due to the multi-pole output switch. U.S. Pat. Nos. 4,808,200, to Dallhammer, et al. and 4,567,541, to Terai, both use a voltage pulse which is superimposed on top of a constant DC value, which is not the case in the present invention. U.S. Pat. No. 4,600,411, to Santamaria, uses a pulsed source and a transformer, as well as an LC trap circuit which is quite different from the present invention. U.S. Pat. No. 4,592,763, to Dietz, et al., discusses a pule ramping technique which is not relevant to the present invention. U.S. Pat. No. 2,509,548, to White, discloses the use of a step-up transformer or a MARX arrangement to generate high voltage output. Again, this is different from the present invention. U.S. Pat. No. 5,903,450, to Johnson et al., is an invention for an inductive PI filter on the output of a transformer/rectifier set and is not relevant to the present invention. U.S. Pat. No. 5,757,169, to Terai, discloses an energy recovery technique that is quite different from the present invention. U.S. Pat. No. 5,639,294, to Ranstad, is an invention for a short circuit protection circuit for the electrostatic precipitator. U.S. Pat. Nos. 4,996,471, 4,626,261, 4,290,003, and 4,061,961, all disclose control circuits which are unrelated to the present invention.
The present invention is of a system which improves the efficiency of ESP performance which can be used for high resistivity ash collection. The technology is based on economically converting existing capital equipment such as existing T/R sets to produce optimized power delivery to the ESP load. A power supply can alternatively be used.
Performance improvements are gained through the ability of the system to operate at higher average currents and voltages. It has been shown that if ionization potential is exceeded quickly enough, a uniform corona distribution is obtained. This leads to uniform current distribution and improved ionization of particles. The present invention is different from other pulsed energization schemes discussed earlier because it does not force fast rise-time, <1 microsecond, or square pulse shapes. In fact, the concept provides a moderate pulse rise-time in the range of 1 microsecond to 500 microseconds and then allows the voltage to decay down naturally dependent on the ESP load characteristics.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
The present invention is of a slow pulse generating circuit for generating slow rise-time, high voltage electrical pulses to a load. The circuit comprises means for producing a pulsed voltage, means for charging the means for producing pulsed voltage, an energy recovery circuit for returning unused energy from the load back to the means for producing the pulsed voltage, a load matching circuit, means for inhibiting load voltage discharge back through the circuit, and means for transferring energy from the means for producing pulsed voltage to the load matching circuit. The circuit can optionally have a transformer for stepping up voltage from the means for producing the pulsed voltage to the load matching circuit. The means for producing the pulsed voltage preferably comprises either an inversion circuit or a high voltage switching circuit. The inversion circuit comprises at least one storage capacitor that is charged by the means for charging, a primary switch that is closed when the at least one storage capacitor becomes charged, and an inductor in series with the primary switch. The high voltage switching ci
Alpha-Omega Power Technologies, L.L.C.
Mays Andrea L.
Patel Rajnikant B.
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