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ANALYTICAL PROCESSING - REF. #AP001 | View PDF
THE CHALLENGE
Process analyzers are designed to accurately and continuously measure a target analyte in a process stream. Gas chromatographs, moisture analyzers, and process photometers are a few examples of analyzer technologies commonly found in process industries. Quite frequently, the process stream is combustible, toxic, corrosive, or otherwise hazardous.
Sampling is the single most critical issue for process analysis, and sampling system plugging is one of the worst problems that a customer can encounter. Unless the sample flow instrument can detect a ‘low flow’ or ‘stopped flow’ condition, the analyzer will continue to give an output even though it’s actually starved of sample. For this reason, most customers use a flow switch in conjunction with the flow control instrument, such as a rotameter. In the event of incipient plugging, flow drops below the switch set-point and an alarm is triggered; however, this is not a good solution. In these days of skeleton maintenance staffs, about the worst thing that can happen is for a process analyzer to suddenly go from ‘in the green’ to ‘in the red’.
 THE BROOKS SOLUTION
Using a Brooks Model 3750C with 4-20 mA output, users can continuously monitor flow to the analyzer at their DCS. Unlike the flow switch, the 3750C continuously outputs a flow signal. When flow to the analyzer starts to drop, the user knows plugging is starting and can schedule maintenance. Key benefit #1: No more sudden ‘in the red’ conditions because service can be scheduled before sample flow drops below the minimum. Key benefit #2: The preventive maintenance schedule can be reduced or eliminated because the operator knows when plugging is starting.
 Some users are taking this a step further and putting a 3750C on the inlet to the sample system, too. This allows them to determine whether the incipient plugging is taking place between the sample tap and sample system, or inside the system itself. This makes maintenance even more efficient. In addition, the Brooks 3750C is a single, compact device approved for hazardous area service.
Note: If the sample system includes ‘fast loop’ bypass flow, it may need a 3750C to control flow through the bypass. |
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