electrostatic precipitator

electrostatic precipitator
Name	Electrostatic Precipitator
Caption	Schematic of a typical plate-wire electrostatic precipitator.
Uses	Air pollution control
Related	Baghouse, Cyclone separator, Scrubber

electrostatic precipitator. An electrostatic precipitator is a filtration device that removes fine particulate matter, such as dust and smoke, from a flowing gas using the force of an induced electrostatic charge. It is a highly efficient system widely employed in industrial settings to control air pollution emissions. The technology is fundamental to meeting environmental regulations for large-scale combustion processes.

Principle of operation

The operation relies on Coulomb's law and involves three key stages. First, particles in the gas stream are charged by passing through a corona discharge created by high-voltage electrodes, often supplied by a transformer-rectifier set. Second, the charged particles migrate toward and are collected on oppositely charged grounded plates under the influence of the electric field. Finally, the accumulated particles are removed from the collector plates, typically through mechanical rapping or washing, and collected in a hopper for disposal.

Design and components

A typical plate-wire design consists of a large steel casing containing parallel rows of vertical collecting plates, often made from carbon steel. Discharge electrodes, frequently configured as weighted wires, are suspended between these plates and are connected to a high-voltage direct current power supply. The system includes an inlet and outlet gas distributor for even flow, insulators to isolate the high-voltage system, and a rapping mechanism to dislodge collected dust. The entire structure is supported by a robust framework designed to withstand industrial conditions.

Types and configurations

The two primary configurations are the plate-wire precipitator and the tubular precipitator. Plate-wire units are common in applications like coal-fired power plant flue gas treatment. Tubular designs, where collection occurs on the inside of tubes, are often used in acid mist control, such as in sulfuric acid plant operations. Precipitators can also be categorized as dry or wet; wet ESPs handle sticky particles or mists and are used in industries like paper mill recovery boilers. Other variants include the rigid-frame electrode design and newer concepts like the pulse energization system to improve performance.

Applications

Electrostatic precipitators are critical in utilities and heavy industry for environmental compliance. Their largest application is in cleaning flue gas from fossil fuel power station boilers, particularly those burning bituminous coal. They are also extensively used in cement kilns, steel mill sinter plants, and non-ferrous metal smelters processing copper or lead. Other applications include controlling emissions from municipal solid waste incinerators, petroleum refinery fluid catalytic crackers, and in the manufacturing of gypsum.

Performance and efficiency

Collection efficiency is highly dependent on the electrical resistivity of the dust, which is influenced by flue gas conditions such as temperature and the presence of sulfur trioxide. The Deutsch-Anderson equation provides a theoretical model for predicting efficiency based on the collecting plate area and gas flow rate. High-resistivity dusts, like those from low-sulfur Powder River Basin coal, can cause back-corona, reducing performance. Modern units, especially those on ultra-low emission systems in China, often achieve efficiencies exceeding 99.9% by using advanced power controls and multiple collection fields in series.

History and development

The foundational effect was first demonstrated by Hohlfeld in 1824. The first practical device for cleaning air was invented by Frederick Gardner Cottrell in 1907, primarily to recover valuable materials like sulfuric acid mist and cement kiln dust. Cottrell's work at the University of California, Berkeley led to the formation of the Research Corporation for Science Advancement to commercialize the technology. Widespread adoption accelerated after the passage of the Clean Air Act of 1970 in the United States, which mandated stringent particulate controls. Subsequent developments have focused on improving reliability and adapting to fuels like lignite and challenging industrial processes.

Category:Air pollution control systems Category:Industrial equipment