Thinking about filtration

This article discusses the possible improvements for existing bag filter systems. Sometimes intervention become necessary after years of satisfactory operation; in some cases, however, it is necessary to repair situations that occur after just a few months after start-up, due to design problems or unexpected occurrences.

Diagnosis

The requests received for this type of intervention are mainly related to three issues:

• Early degradation of the filtering bags/high emissions.
• High pressure differential.
• Extensive degradation of metal sheets caused by corrosion.

Sometimes these problems result from the increase in capacity required for the existing equipment, others from adapting to new processes (alternative fuels, change in the composition of raw materials, higher humidity, upgrades in the grinding process, etc.), others from initially deficient projects or the incorrect selection of components, still others from improper use of the equipment, or non-compliant maintenance/operation procedures.

This phase looks like an excellent field for the application of the ‘5 Whys’ method (Sakichi Toyoda), but the problem often appears too complex to deal with.

Table 1 shows the cause-and-effect relationships concerning to the problems mentioned previously.

It is clear from the table that the correlation between the factors is very weak, in the sense that each phenomenon does not uniquely correspond to a single cause. The in-depth analysis of causes and effects is particularly important, as there are frequent overlaps of the former and concomitant consequences that make it difficult to piece together the phenomena and identify a single factor responsible for the problem.

Most often, an onsite inspection is necessary through which, in addition to ‘checking the pulse’ of the patient, it is possible, through a ‘soft’ approach, to collect from the plant staff many more elements than from the analysis of the design and operational data. Sometimes, process analysis is essential, consisting in the study of operating trends over long periods, to highlight any system anomalies or isolated events that may be at the origin of the problem.

Everything is made even more complex by the fact that the engineer is working on equipment, in most cases, previously unknown, with original design solutions that must be discovered and clearly interpreted before any kind of intervention can be conceived.

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Read the article online at: https://www.worldcement.com/special-reports/21062023/thinking-about-filtration/