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Determining Alarm Levels in Millwatch

Determining Alarm Levels In MillwatchAMETEK Land’s Millwatchanalyzer is designed to detect the carbon monoxide (CO) given off when the fuel within a coal mill oxidizes rapidly, an indication that spontaneous combustion is beginning. This early detection gives the operator time to take preventative action such as inerting the mill or stopping the fuel supply.

One of the biggest challenges in configuring a Millwatch system is the determination of suitable alarm levels. A carbon monoxide concentration greater than 200 ppm can be seen during mill startup, but in normal operation the CO concentration is usually below 10 ppm. That makes it difficult to select an alarm point which will provide adequate warning of spontaneous combustion without generating an excessive number of nuisance alarms.

Determining Alarm Levels In MillwatchMillwatch analyzers offer two independent alarm points, so it is possible to set an alarm level of 300 ppm during startup and 100 ppm in normal operation. These are good starting points, but they should be refined as experience shows the range of CO concentrations which occur in normal operation. One user set an alarm level as low as 50 ppm, but found occasional spikes to 75 ppm which did not indicate a hazardous condition. At that site, the alarm level was increased several times to a final figure of 125 ppm. This avoided nuisance alarms, while providing good sensitivity and response to abnormal operating condition.

To find out more about strengthening plant safety in coal grinding mills and storage silos with carbon monoxide monitoring, read our application note here

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