Predictive, Indicative & Alert Indicators - Baghouse Monitoring Metrics

Posted by Earl Parker on Aug 15, 2017 10:00:00 AM

Direct and Indirect Dust Collector Performance Metrics

On smaller dust collection systems, differential pressure often is the only metric used by operators to monitor the performance and condition of the system. For smaller systems this often proves sufficient. However, as systems get larger and more complex, plants usually start including additional monitoring metrics into the mix with the goal of early warning and predictive monitoring to reduce down-time, prevent reportable incidents and manage the maintenance burden and costs. 

Predictive, Indicative & Alert Dust Collector Monitoring Metrics

Indicative

After differential pressure, most commonly monitored metrics include air temperature, airflow (CFM), fan RPMs and stack emissions. Stack emissions, particularly when monitored with continuous opacity monitoring, is a classic alert metric. By the time an alarm is triggered, there's typically a reportable event. In contrast temperature, CFM and fan RPMs all have more to do with mechanical performance of the system. They can indicate a developing mechanical problem, or that mechanical systems are compensating for another issue. In that sense they are indicative metrics.

In other words, this sort of parametric monitoring doesn't track a direct exceedance, but hints that something may be developing. In some cases they are tracked with gradual alert levels (depending on the control system and monitoring software) for early warnings, and in others, simple relay type systems trigger alarms when conditions exceed set parameters. 

Predictive

Predictive monitoring is less commonly seen because the advances in instrument sensitivity and reliability, and the ability of control systems to consolidate signals and provide progressive warnings, post dates many grandfathered air permits and dust control systems.

Triboelectric bag leak detection systems installed at the compartment, and even row level, are an example of predictive systems which observe ongoing particle levels, both during and between cleaning cycles, to detect gradually increasing emissions. These observations don't mean there's a failure, but there's a trend which merits investigation. Causes could include deteriorating filter media nearing failure, for instance, and early warning allows for planned maintenance rather than unplanned downtime and expensive remediation.

Regulatory Confirmation

Emissions monitoring includes a range of different technologies and strategies for different purposes. In addition to differential pressure readings, air quality regulators require many larger plants submit to regular testing to determine their total emissions over a certain period of time (mass flow rate). This means measuring the amount of dust emitted during a given span of time (usually pounds/kilos per hour). An isokinetic stack test is the most common measurement for mass flow.  A sample of the exhaust gas is passed through a rig holding a paper filter, thereby collecting the dust particles on the filter paper. This is then weighed to determine the exact amount of particles being emitted. 

Dust Collector Isokinetic Stack TestingThe isokinetic testing requires special testing equipment and procedures and cannot be run continuously during normal operation.

They're intended as periodic confirmations and not a substitute for indicative and predictive dust monitoring technologies.

Traditional and Improved Predictive Tools

Traditional bag leak detection systems straddle these lines. Opacity meters, limited by their sensitivity, cannot directly measure the total amount of particles emitted. In contrast, triboelectric dust detectors from Auburn have what we term predictive monitoring capabilities.

Since Auburn’s propreitary DC/AC dual band triboelectric technology can detect such minute dust concentrations (down to 0.000002 g/dscf), its data can allow maintenance planners to accurately predict when filters will begin to fail. By analyzing trending data showing a steady rise in emissions from the TRIBO.dsp unit and combining it with dust collector differential pressure readings they can easily plot the near term efficiency of the filters to collect the target dust. This allows them sufficient warning to start planning for filter replacement and avoid last minute change outs that entail higher materials and labor costs in addition to costs related to unscheduled downtime. 

Conclusion

Dust collector monitoring almost always starts with differential pressure. This however is just the start. Especially as the system(s) grow in size and complexity adding additional monitoring metrics provides operators with additional resources to effectively maintain and operate these vital systems. 

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Topics: Dust Collection, Baghouse Maintenance