Instrumentation Gary D. Nichols PPG Industries, Inc. Chemical Division-U.S. P.O. Box 1000 Lake Charles, La. 70602
Downloaded by TEXAS A&M INTL UNIV on September 9, 2015 | http://pubs.acs.org Publication Date: March 1, 1981 | doi: 10.1021/ac00226a807
Process Analyzer Sampling Systems In the past few years on-line process analyzers have become increasingly important in the chemical process and related industries (1). An excellent general discussion of process analyzers was presented in these pages recently (2). That discussion was followed by an overview of process infrared ana lyzers (3). In practice, choosing the appropriate process analyzer is only part of the problem in performing reli able process analyses. Frequently, the analyzer selection process is greatly affected by the ability to obtain a suit able sample. It is not unusual to spend as much time and money designing and building the sampling system as is spent on the analyzer. To begin this discussion, it is help ful to have working definitions of pro cess analyzers and process analyzer sampling systems. A useful definition of a process analyzer is, "an environ
incorrect analysis. A bad analysis may be economically costly in terms of ma terial waste, customer dissatisfaction, and maintenance problems. This is ex emplified by a custody transfer ana lyzer; the customer is paying only for the stream component of interest and not for whatever impurities may be in cluded. Therefore, an error of 0.01% multiplied over a year and several hundred tons per day has a significant negative economic impact on either the buyer or the seller. Additionally, a bad process analysis may permit an occupational health or environmental hazard to go unchecked. A high heavy metal content in a discharge stream may cause a fish kill and invite a fine or civil penalty to the manufacturer. An incorrect oxygen analysis in a tank or vent may cause suffocation for workers in the area or lead to a cata strophic explosion.
mentally suitable automatic device that continuously or periodically mea sures one or more chemical parame ters in a process stream and presents the results in a usable form." This def inition is exemplified in the infrared analyzer article cited above (3) and in an older article describing process gas chromatography (4). A process analyz er sampling system can be character ized as, "a device or combination of devices which will transfer a sample from a process stream to a process an alyzer in such a way as to minimize maintenance and to preserve or en hance the analytical information con tained in the sample." Close attention must be paid to the design of the sampling system as well as to the selection of the analyzer be cause of the automatic, unattended nature of the process analyzer and the importance of the potential cost of an
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Water Shutoff Valve \
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Combustible ^ G a s Sensor
Strainer Water In
Throttle Valve
Calibration Selector Valve Sample In
Filter
Flow Meters
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