Focus on Filters

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A new focus on the environment and the role of filters 

By Antonio Zocche, senior global consultant for air pollution control 


In dealing with the impact of industrial revolutions around the globe—which has led to an ever-increasing drive towards productivity—humankind has put mechanisms in place to improve production processes, lower dust pollution levels, and utilize ever more sophisticated technologies, such as bag filters. Putting that in today’s terms: a bag filter is like a filter mask, crucial for protecting the environment from industrial production processes.

A fabric that filters gasses, more or less noble, retains the dust before it can be released into the atmosphere. It works the same way as the filter masks being used during the pandemic in order to avoid contagion.

Surgical filter masks were employed for the first time to avoid mutual contamination in 1897 when French surgeon Paul Berger recorded the use of this technique during an operation he performed.

There are many technologies available to combat environmental pollution. Among them is the technology that involves the use of what are known in the industry as “bag filters”, to reduce industrial dust emissions.

To explain what a bag filter is, we can say that it is very much like a filter mask positioned between industrial production processes—in which dust emissions are generated—and the environment. The goal is the same: to avoid contamination.

Bag filters are mainly used in industries and processes such as cement plants, steel mills, waste-to-energy plants, glassworks, energy production, petrochemical and pharmaceutical plants, among others. 

There are reports of the first rudimentary bag filters being installed in the last century, around the 1950s, to replace old technologies such as cyclones and electrostatic filters, with the aim of lowering dust emissions, which the old technologies could no longer guarantee.

A physical barrier, the bag filter—which is a fabric like that which surgical masks may be made of—retains the dust inside the filtering chamber and then emits the purified air into the atmosphere through a fan and a chimney.  The bag filter must be frequently cleaned with the injection of a high-pressure blast of compressed air so that it will not become clogged and can therefore be used longer.

The filter bag can be made from a variety of fabrics, which material is chosen depends on the temperature of the gases to be filtered. Polyester, polypropylene, Nomex, P84, meta aramid, acrylic, fabric and fiberglass felts are the most commonly used materials. 

Lunar missions, and manned space exploration in general, has given a major boost to research focused on new fabrics in the filtration industry. These missions have driven the use of increasingly high-tech fabrics, used by astronauts, which are able to withstand temperatures and atmospheric conditions different from those on earth.

The maximum temperature at which a filter bag can be used is 250 °C—with peaks up to 280 °C—so this filtering technology is able to cover a wide range of production processes. The filtering action of a high-tech bag filter is very important for the environment, especially for the reduction of what’s known as PM10.

Currently, perhaps the best and most advanced technology being used to improve the performance of bag filters (through more complete cleaning) is sonic wave technology. When combined with the best choice of filter fabric, atmospheric emissions of lower than 1 mg/Nmc can be achieved!

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