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A baghouse born again – part one

World Cement,


Ash Grove Cement in Louisville, Nebraska, USA, made significant investments to install new kiln baghouses to meet the recent, and very strict, National Emission Standard for Hazardous Air Pollutants (NESHAP) environmental regulations. The existing Humboldt Wedag line clinker cooler baghouse, however, had been left unchanged, and needed to be upgraded. High differential pressure and short bag life required frequent servicing to keep outlet dust emissions under the limits of the recently imposed US environmental regulations.

IAC worked with Ash Grove to evaluate the installed equipment, review operation and present the option to rebuild it, considering possible upgrades before the project scope was finalised. This allowed Ash Grove to technically and economically evaluate the possible upgrades and choose the ones that offered the right balance between the required investment and improved performance.

Trouble ahead

Typical symptoms of an underperforming baghouse include high differential pressure and short filter bag life, ultimately resulting in increased particle emissions. When facing this situation, the common and obvious conclusion is that the unit needs increased capacity.

While having spare capacity can make up shortcomings in other components, this is not always possible without a major investment. More importantly, some modifications made to increase capacity can have negative effects, or they may simply be the wrong approach when comparing the investment required with the benefit obtained.

Detailed knowledge of all available technologies, their costs and their effect on the project can be helpful in determining the right solution. This upgrade project is an example where a non-obvious modification, one that can be considered counter-intuitive, can be the option that provides the needed results most competitively.

Baghouse technology

Baghouse technology began with shaker filter cleaning systems, where flow is interrupted and the filtration media is violently shaken to remove filtered dust. The cleaning action caused accelerated wear on the filter bags and exposed moving mechanisms that required excessive maintenance.

Reverse air technology followed, promising much longer filter bag life through a gentle cleaning action that pushed process gas or ambient air backwards through the filter media to remove filtered particles. This was a major success in extension of bag life, but it required a very large filtration area for the amount of gas flow filtered, resulting in a very large footprint and equally large initial investment.

Other ideas were tested through the years, but none had a significant impact on baghouse design until pulse jet cleaning technology was introduced. This filter cleaning method uses a blast, or pulse, of compressed air directly into each filter bag to remove filtered dust. This proved to be very effective, so the overall size of the equipment was significantly reduced, utilising less space in the plant and lowering the required investment. The use of modern pneumatic components largely eliminated mechanical moving parts, increasing long term reliability of the filtering system. This technology was so successful that practically all modern baghouses are made using some variation of this concept.

Although the clinker cooler baghouse at Louisville was installed in the early 1980s, it was already a pulse jet baghouse, so a major improvement through a typical conversion project was not possible. Upgrade options were then limited to newer developments in pulse jet baghouse technology.

This is part one of a three-part article written for World Cement’s May issue and abridged for the website. Subscribers can read the full May issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Non-subscribers can access a preview of the April 2016 issue here.

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