What Is Electrostatic Precipitation?

An electrostatic precipitator is a filterless device that collects tiny particles from a flowing gas using the force of an induced electrostatic charge while obstructing the flow of gases through the unit as little as possible. Unlike wet scrubbers, which apply energy directly to the flowing fluid medium, an Electrostatic Precipitator only provides energy to the particular matter being collected, making it extremely energy efficient and a viable option in terms of utility.

Modern Day Electrostatic Precipitators:

Electrostatic Precipitators are still effective for controlling a variety of industrial particle pollutants, including smoke from coal and oil-fired power plants, salt cake collection from pulp mill black liquor boilers, and catalyst collection from fluidized bed catalytic cracker units in oil refineries, to mention a few. In the largest coal-fired boiler applications, these devices treat gas volumes ranging from a few hundred thousand ACFM to three million ACFM. For a coal-fired boiler, the collection is normally done downstream of the air preheater at around one-sixty degrees Celsius (320 °F), which ensures that the coal-ash particles have the best resistivity. Hot-end units operating above three-seventy degrees Celsius (698 °F) have been designed for some challenging applications using low-sulfur fuel.

The original parallel plate–weighted wire design has evolved as more efficient and robust discharge electrode designs have been developed, with today’s emphasis on rigid pipe-frame discharge electrodes with many sharpened spikes or barbed wire attached to maximise corona production. At relatively large current densities, transformer-rectifier systems apply voltages of fifty- hundred kV. Modern controls, such as automated voltage management, reduce electric sparking and avoid arcing which refers to sparks that are quenched within 1/2 cycle of the TR set, preventing component damage. Automatic plate-rapping systems and hopper-evacuation systems remove gathered particulate matter while the Electrostatic Precipitator is in operation, theoretically allowing it to run for years.

Plate And Bar Electrostatic Precipitators:

The simplest basic precipitator consists of a row of thin vertical wires followed by a vertical stack of big flat metal plates, with the plates commonly spaced 1 cm to 18 cm apart, depending on the purpose. The air stream goes through the stack of plates after passing horizontally via the intervals between the wires. Between the wire and the plate, a negative voltage of several thousand volts is applied. An electric corona discharge is responsible for ionising the air near the electrodes, which further ionises the particles in the air stream, provided that the applied voltage is high enough. The electrostatic force causes the ionised particles to be directed towards the grounded plates. Particles accumulate on the collection plates and are drawn out of the air stream.

The benefit of a two-stage design which refers to a separate charging portion ahead of the collecting part is that it reduces ozone formation, which would be harmful to workers working in enclosed environments. Two-stage Electrostatic Precipitators are used to clean the air in shipboard engine rooms where gearboxes emit an oil mist, enhancing the operating environment and reducing the formation of combustible oil fog. The collected oil is returned to the lubrication system for the gears.

Brief History Of Electrostatic Precipitators:

Hohlfeld was the first to employ corona discharge to remove particles from an aerosol in 1824. However, It was not popularised for nearly a century. In 1907, Frederick Gardner Cottrell, a chemistry professor at the University of California, Berkeley, filed a patent application for the first electrostatic precipitator, a device for charging particles and subsequently collecting them using electrostatic attraction. Cottrell used the apparatus to collect sulphuric acid mist and lead oxide fumes generated during various acid-making and smelting processes. Lead pollution had a negative impact on wine-producing vineyards in northern California, which could be solved with this.

The theoretical underpinning for the operation was unknown at the time of Cottrell’s discovery. Later, in Germany, with the work of Walter Deutsch and the founding of the Lurgi firm, the operational theory was established. In 1912, Cottrell established a foundation called Study Corporation, to which he assigned the patents, to use the revenue from his innovation to fund scientific research. The goal of the organisation was to commercialise discoveries produced by educators such as Cottrell himself, for the benefit of society as a whole. Royalties paid by commercial enterprises following commercialization are used to fund Research Corporation’s operations. Many scientific initiatives have benefited from Research Corporation’s support, including Goddard’s rocketry experiments, Lawrence’s cyclotron, and vitamin A and B1 production methods, are few of the important examples of this.

Western Precipitation, Lodge-Cottrell, LurgiApparatebau-Gesellschaft, and Japanese Cottrell Corporation were among the technology’s manufacturers, while Research Corporation served as a clearinghouse for any advancement in the fundamental processes. In 1946, however, antitrust lawsuits compelled Research Corporation to abandon its territorial limits.

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