Electrostatic precipitators – general information

The exhaust gases produced by burning solid fuel in a furnace contain many dust particles. When the stack releases these gases into the atmosphere without filtering the dust particles, the atmosphere can become polluted. Therefore, special filters are used in fuel combustion applications to remove the dust particles of the combustion gases as much as possible before they are discharged into the atmosphere. In this way, we can control air pollution.

The electrostatic precipitator does this work for the furnace systems. We install this device on the flue gas path from the furnace to the chimney so that it can filter the flue gas before it enters the chimney.

Principle of electrostatic precipitator operation

The way an electrostatic precipitator works is fairly simple. The filter has two sets of electrodes - one positive and one negative. The negative electrodes come in the form of rods or wire mesh. The positive electrodes are plates. The positive plates and negative electrodes are placed vertically in the precipitator, alternating one behind the other. The negative electrodes are connected to the negative terminal of the high-voltage DC source, and the positive plates are connected to the positive terminal of the DC source. The positive terminal of the DC source may be grounded to provide a stronger negative voltage to the negative electrodes.

The distance between each negative electrode and the positive plate and the DC voltage applied to them are selected so that the voltage gradient between each negative electrode and the adjacent positive plate becomes large enough to ionize the medium between them. The medium between the electrodes is air, and because of the high negativity of the electrodes, corona discharge may occur around the electrode rods or wire mesh. Air molecules in the field between the electrodes become ionized, so there will be a large number of free electrons and ions in the space.

The entire system is enclosed in a metal container with the exhaust gas inlet on one side and the filtered gases outlet on the other. As soon as the exhaust gases enter the electrostatic precipitator, the dust particles in the gases collide with the free electrons available in the medium between the electrodes and the free electrons are attached to the dust particles. As a result, the dust particles become negatively charged. Then these negatively charged particles will be attracted due to the electrostatic force of the positive plates.

Consequently, the charged dust particles will move towards the positive plates and settle on the positive plates. Here the extra electron from the dust particles will be removed on the positive plates and the particles will fall down due to the gravitational force. The positive plates are called collecting plates. After passing through the electrostatic precipitator, the exhaust gases become almost free of ash particles and are finally discharged into the atmosphere through the chimney. The electrostatic precipitator does not directly contribute to the production of electricity in the thermal power plant, but it helps to keep the atmosphere clean, which is very important for living beings. Funnels are installed under the electrostatic precipitator chamber to collect dust particles. To accelerate the removal of dust from the collection plates, water modules can be used on top.

Features and applications of electrostatic precipitators

Advantages of electrostatic filters

• Continuous extraction of significant volumes of flue gases;
• High filtering efficiency resulting from, among other things, low flow resistance of gas mixtures;
• Possibility of obtaining high efficiencies - up to 99%;
• Filtering of high temperature gases.

Disadvantages of electrostatic filters

• The need for additional protection or more expensive solutions due to the risk of ignition of flammable gases;
• High manufacturing cost;
• Large dimensions of the filters;
• Sensitivity to environmental changes and flue gas characteristics - temperature, humidity, resistivity.

Application of electrostatic filters

• Extraction of coal dusts from boilers;
• Extraction of gases from metallurgical processes e.g. sintering of raw materials
• Extraction and desalting of raw gas in coking plants;
• Extraction of gases from kilns in cement plants;
• Extraction of combustion gases in coal-fired power plants.

What is a high voltage power supply?

A high voltage power supply is a complex power conversion circuit that converts a lower voltage potential to a higher voltage potential. The term "high voltage" is relative, not quantitative. Typical output voltages for high voltage power supplies range from a few tens of volts to about 500 kV.

High-voltage power supplies can operate with either DC or AC input voltages. DC input voltages are economical for use in low power applications (1 W to 125 W). Typical DC input voltages are +12 Vdc and +24 Vdc. High voltage AC input power supplies can operate with a variety of input voltages from 100 Vac to 480 Vac, single phase or three phase depending on the design. High voltage power supplies with power factor correction/universal input can operate from 90 to 264 Vac without user intervention.

Note the polarity of the DC high voltage power supply. Units with fixed positive polarity, fixed negative polarity, or reversible polarity are available. Some application-specific power supplies can electronically reverse the output polarity with a switch or remote control signal.

The output from a high-voltage power supply is delivered to the customer via a high-voltage cable of the appropriate capacity. Smaller, economical units use a permanently attached high voltage cable, while larger units use a detachable shielded high voltage coaxial cable.

Service of high voltage power supplies for electrostatic filters

Dacpol Service offers professional servicing of high voltage power supplies for electrostatic precipitators in the field of start-up, maintenance and repair. Thanks to many years of experience with the manufacturer of NWL high voltage power supplies, we provide comprehensive servicing of NWL PowerPlus and other power supplies available on the market. More information can be found on our website in the SERVICE, REPAIRS tab. If you have any questions, please contact us directly!