It is common to see reverse pulse filters applied to any process that creates dust in an industrial plant. Collecting the dust is sometimes part of the industrial process, or it could be applied for pollution control, preventing the dust from contaminating the neighborhood.
Within these dust collectors are an array of filter elements, sometimes filter cartridges — and sometimes long socks called bags stretched over a wire frame. As dust-laden air is blown up through the filter by a fan, the dust particles collect on the surface of the filter elements, forming a cake. Every so often, the cake needs to be removed so the filter does not become clogged. Reverse pulse dust collectors use a blast of compressed air in the reverse direction to shock the filter elements and remove the collected material.
In Figure 1, we can see the large blast valves used for cleaning, within this filter is an array of nine bags cleaned by three large valves that pulse one at a time in a cycle every 10 seconds. When everything is working correctly, the valves provide a short quick blast that consumes a reasonable amount of compressed air. But if the cleaning control system fails, there can be trouble due to the size of the valves.
Such was the experience of one food products plant. Control system operators noticed their air compressor, normally loaded between 40% and 60% capacity was, for some reason, suddenly running at 100% capacity, and with plant pressures falling to very low levels. This problem continued for a number of days until maintenance personnel thought they heard a large compressed air demand in one of their production processes. Sure enough, when the source of the sound was tracked down it seemed to be coming from within a dust collector. One valve had failed open, consuming 250 cfm due to the problem.
The faulty valve was quickly isolated and compressed air demands went back to normal. The plant is now considering the installation of flow restriction orifices on all 10 of their dust collectors to prevent this problem from taking down production again.