Process GC involves the deployment of rugged, reliable gas chromatographs in demanding process environments. Where traditional sampling and analysis occurs off-site in analytical laboratories, process GC brings the “lab” to the production site, providing realtime product analysis.
Although most common in oil and gas industries, process GC is slowly entering other process markets. Al Kania, GC product manager for North America at Siemens (Houston, TX), estimates that such esoteric measurements as acetic acid in ketchup, alcohol in whiskey, aerospace materials analysis, monitoring the destruction of nerve gases, and others may compose two percent of sales.
Although laboratory and process GCs are based on the same principles, significant differences exist. Where lab analysis can take half an hour or more, process analytics are quite rapid—most being over in a few minutes. “For decades, process GC has been using multidimensional analysis to speed things up,” Kania observes. Multidimensional GC, only now catching on for lab applications, involves autoinjection of samples onto one column, separating and backflushing matrix or background components, and rerouting the analytes to as many as seven different columns.
Like QA/QC chromatographs, process GCs operate nearly continuously and tend to be dedicated to picking out specific analytes. Pure research GCs are much more flexible with respect to operation and detection mode.
Perhaps the most striking difference is the ruggedness of process instruments. GCs mounted in metal sheds in the middle of a refinery experience temperature extremes and explosive gases, which seriously restrict their electronics and detector choices. “Lab instruments exist in more of an office environment,” Kania says.
Process GCs cannot use high-voltage pulsed-discharge detectors because of the potential for explosions. And since they operate unattended, detectors must be extremely stable. Only a handful of detectors fit the bill: thermal conductivity, flame ionization, and flame photometric detectors are most common; photoionization or electron capture detectors less so. Even these must be mounted in explosion-proof steel blocks.
Ruggedness extends to reliability as well. Even today labs usually have one or two individuals who perform routine maintenance and diagnostics. Refinery engineers have little experience in instrument operation and care. Process GCs must therefore be self-correcting and self-diagnosing, and components must be plug-and-play.
Despite obvious differences, there is significant crossover between lab and process instrumentation. Wasson ECE Instrumentation (Fort Collins, CO) is one company that repackages and ruggedizes laboratory instrumentation for process environments, particularly those with unusual detector requirements. These instruments will not be as rugged or reliable as much more costly process instruments, but they serve niche markets.
Conversely, some process industries with widely dispersed points of production will use automated sample collection in the field and bring the samples to a continuously operating process GC located in a lab.
By no means have process GCs made lab instruments obsolete in their industries. “Workers still take physical samples, and at the end of the day, laboratory GC is still employed for spot tests, for troubleshooting, and to validate answers from process GCs,” Kania tells Lab Manager. “Lab instruments remain the gold standard, the stamp of approval, for product release.”
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