Norbert Grass

Application of different types of high-voltage supplies on industrial electrostatic precipitators

Investigations of the requirements for high-voltage (HV) power supplies for zones within an electrostatic precipitator (ESP) were conducted with regard to the properties of different technologies for HV generation. The zones of an ESP show different electrical behavior and efficiency. This is a result of: 1) the different dust loads of the zones; 2) the particle size and properties; and 3) the possibility of charging the particles in the entire zone using suitable technology. An overview of common and new topologies of HV supplies and their typical properties is given. It is shown how these properties can be used to match the requirements of the different zones of an ESP regarding the actual operating conditions. Large particles and high dust loads can be addressed effectively using high-frequency dc power supplies. Fine particles, however, can be separated even more efficiently by pulsed power supplies. Additionally, the power consumption of different HV sources has been investigated in relation to the separation efficiency. Experimental results were obtained on an industrial ESP containing 3 zones in a sinter plant and on a large scale precipitator in a fossil power plant, containing 30 zones. It was shown that a high frequency IGBT inverter combined with a microsecond-pulsed power supply significantly improved the overall performance of the precipitator.

Fuzzy logic-optimising IGBT inverter for electrostatic precipitators

A voltage link transistor inverter using IGBT devices is able to control the output current at a switching frequency of typically 10 kHz. The low pass filter characteristic of an electrostatic precipitator converts this current to a smooth DC voltage. In the event of flashovers, the generation of ions (or ionized particles) in the precipitator can be minimized by switching off the current immediately. The average values of current and voltage can be increased by the method, resulting in higher efficiency of many types of precipitators. Fuzzy logic, functioning as an overlaid optimization, adapts the parameters dynamically to the charge and load conditions of the precipitators.

Application of different types of high voltage supplies on industrial electrostatic precipitators

Investigations of the requirements for high-voltage (HV) power supplies for zones within an electrostatic precipitator (ESP) were conducted with regard to the properties of different technologies for HV generation. The zones of an ESP show different electrical behavior and efficiency. This is a result of: 1) the different dust loads of the zones; 2) the particle size and properties; and 3) the possibility of charging the particles in the entire zone using suitable technology. An overview of common and new topologies of HV supplies and their typical properties is given. It is shown how these properties can be used to match the requirements of the different zones of an ESP regarding the actual operating conditions. Large particles and high dust loads can be addressed effectively using high-frequency dc power supplies. Fine particles, however, can be separated even more efficiently by pulsed power supplies. Additionally, the power consumption of different HV sources has been investigated in relation to the separation efficiency. Experimental results were obtained on an industrial ESP containing 3 zones in a sinter plant and on a large scale precipitator in a fossil power plant, containing 30 zones. It was shown that a high frequency IGBT inverter combined with a microsecond-pulsed power supply significantly improved the overall performance of the precipitator.

Fuzzy logic-based power control system for multi field electrostatic precipitators

The power consumption of large precipitators can be in the range of one MW and above. Depending on the dust load properties, the electrical power may be reduced by up to 50% by applying fuzzy logic, without significantly increasing the dust emissions. The new approach using fuzzy logic is an optimisation of the existing precipitator. Software running on a standard personal computer platform under Windows NT facilitates the reduction in power usage. The controllers of the electrostatic precipitator power supplies are linked to the computer via an industrial network (e.g. PROFIBUS). The system determines online the differentials of emission versus electrical power of each field. This measurement is difficult because of overlaid events in the other zones, and process changes. The long response time of the resultant dust emission due to electrical power changes in the precipitator is an additional complication. Rules were defined for a coarse, but fast response power adaptation of all zones. Fine tuning the running system after the coarse optimization increased the accuracy and reliability. When installed on a 4 by 5 zone precipitator in a power station meaningful results can be obtained. The power savings over 3 months of operation were 40% to 60% depending on the load and fuel characteristics. Data was recorded over the test period of 3 months. The results are presented.

Microsecond pulsed power supply for electrostatic precipitators

Fine particles emissions are much more dangerous to health than the larger ones. Collecting of fine particles below 10 /spl mu/m (PM/sub 10/) in electrostatic precipitators has not been very efficient with conventional systems. A new pulsed power supply was developed with a pulse duration below 10 /spl mu/s. To use it with existing precipitators, the current capability had to be in the kA range. It is possible to generate a high charge density in the spray wire area which leads to increased charging of the fine particles. Flashovers are mainly avoided due to the short pulse duration. Data was recorded on a real precipitator in a power station.

Electrostatic Precipitator Control Systems

Enhancing precipitation efficiency using conventional and fuzzy logic control. Modern high-voltage (HV) power supplies based on fast switching devices such as insulated-gate bipolar transistors (IGBTs) increases the performance of the corona power of electrostatic precipitators (ESPs), resulting in improved gas cleaning and higher performance of the ESP. Unfortunately, increased energy consumption of the precipitator requires a higher amount of electricity to be generated the power station, which results in higher CO2 emissions, With both centralized and decentralized control algorithms, the total energy consumption of an ESP can be significantly reduced while achieving low dust-emission values. The control system operates with a few input signals only and has been linked and extended to the plate-rapping system. Power savings depend on the operating conditions, and experiments have shown an average savings in the range of 30-60% within a longer period of operation.

150kV/ 300kW High Voltage Supply with IGBT Inverter for Large Industrial Electrostatic Precipitators

With fast switching semiconductor devices like the insulated gate bipolar transistors (IGBT) it is possible to build inverter based high voltage power supplies for electrostatic precipitators. Comparing conventional SCR (Silicon controlled rectifier) based technology the average corona power can be increased significantly to improve the precipitator efficiency. Additionally, during flashovers the fast current control of IGBT power inverters improves the precipitator performance due to fast voltage recovery resulting in further increasing of the peak and average precipitator voltage. In a new approach, the advantages of higher distances up to 400 mm between the discharge and collecting electrodes could be addressed by a voltage up to 150 kV applied to the precipitator. Due to the exact voltage control of the IGBT inverter a smooth DC voltage can be generated and therefore, the overvoltage capability of the system is much lower than it would have to be with a conventional thyristor based high voltage generation system. Thus, the IGBT inverter solution becomes more economical or less expensive to operate than the conventional supply. With the availability of the latest generation of integrated IGBT modules a very compact IGBT inverter has been developed to meet the design requirements by operating at a frequency up to 10 kHz. The new IGBT types have lower saturation voltages than the previous modules resulting in lower power losses. The HV-transformer has been designed with the required rating and stray inductance.

Electrostatic precipitator diagnostics based on flashover characteristics

Performance monitoring on large industrial precipitators is todays practice. Usually, the stack opacity is measured and recorded on a computer system. The performance is indicated through the precipitator efficiency, which is defined as the relation between input dust content N/sub 0/ and output dust content N: /spl eta/=N/sub 0/-N/N/sub 0/. The precipitator efficiency /spl eta/ is monitored not exactly due to the missing measurement of the precipitator inlet particle load of the gas. However, achieving the permitted emissions for the entire process indicates sufficient performance. Exceeding these permitted values leads to concerns about the precipitator performance. Identifying the reasons for decreasing performance can be difficult due to the high number of parameters in a precipitator system. To locate the problem either in the electrical, mechanical or the operational parts of the system, the electrical data and particularly the flashover behavior of the individual high voltage fields can be investigated. Using the data recording and display features of modern controls comprehensive precipitator diagnostics can be done and performance can be optimized based on the current system state. Possible fault conditions like dust build ups, damaged spray wires, misaligned collecting plates or faulty insulators can be distinguished by the spark voltage, frequency and required deionisation period. Additionally, performance drops caused by insufficient electrical supply and control can be detected and corrected automatically in many cases.

Enhanced Performance for Electrostatic Precipitators by Means of Conventional and Fuzzy Logic Control

Modern high voltage power supplies based on fast switching devices like IGBTs offer the performance to adjust voltage and current regarding the process conditions. Optimum performance can be achieved if the control makes use of the enhanced properties of the power supply. In critical precipitation processes the control needs to be high dynamical and accurate. Furthermore, with IGBT inverter type high voltage power supplies it is possible to increase the electrical power significantly, in many applications a factor 2 can be achieved, which leads to a significant improvement of the dedusting. Unfortunately, then the energy consumption of the precipitator increases leading to a higher amount of electricity to be generated in the power station and finally this results in higher CO2 emissions of the power station. With central and decentralized control algorithms the total energy consumption of an electrostatic precipitator can be significantly reduced by continuous adaption of the control to the process conditions. Retrieving measured data from inside an electrostatic precipitator is always difficult and unreliable due to the high temperatures, dust and high voltage. Therefore, a rule based control system has been developed which can operate with a few input signals only. Mainly the measured values of voltage and current are sufficient for the control system and additional for energy savings the stack emission signal is required.

High average power high voltage modulator using a dual pulse transformer circuit

A novel modulator concept is presented using two step-up transformers in series, with an intermediate pulse compression stage. This concept has advantages in terms of minimizing the insulation requirements and core sizes in each stage, as well as minimizing stray capacitances and inductances, respectively. Hence, although this scheme requires an additional component (the second pulse transformer), the overall setup can be optimized in terms of core sizes, insulation requirements, and energy efficiency as compared to standard circuits. Thus, it is possible to start from a comparatively low primary stage voltage of only 1 kV, using standard IGBT switches and off-the-shelf capacitors, in order to achieve pulse amplitudes of over 50 kV at pulse widths of the order of 150 ns, at pulse repetition rates of the order of kHz.