Analyze this!

Measurement and control of physical properties such as level and flow are the heart of process control. But measurement and control of the molecular composition of a process stream are also of vital importance.

By Dan Hebert

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The Scott’s Specialty Gases application for low-level analysis of moisture in corrosive gases for the electronics industry shows the difficulty of delivering samples for measurement. “Delivery of a representative sample of corrosive gas to the analyzer unit remains a challenge. We also need to provide independent verification of the moisture concentration reported by the analyzer in corrosive gas matrices,” reports Miller. “Our vendor, Tiger Optics, has worked closely with metrology institutes around the world so that the moisture concentration determined by their analyzers in an inert gas matrix seems to have been properly validated. But no such independent confirmation is available for pure corrosive gases, so validation must be done experimentally. The basic scientific principles of cavity ring-down spectroscopy are helpful in this regard in that moisture/matrix gas spectroscopic interactions appear to be less complicated,” he adds.

 

Online Analysis Challenges

  • Degradation of the sensing element
  • Achievement of the required high precision, often in the parts per million range
  • Conversion of the output signal to a format recognizable by control system
  • Extensive maintenance often required by analyzers
  • Highly trained personnel needed for maintenance, calibration and operation
  • High cost of the analyzers
  • High cost and complexity of the sample delivery systems
  • Selection the right analyzer for the application
  • Verification of online analyzer measurements in the lab
  • Process stream must sometimes be oxidized or otherwise broken down prior to analysis

 

How to Go Online
The first “must-do” when going online is to make sure that the analyzer can survive in the process stream. There are two areas of concern—the instrument itself and the probe. Make sure that the instrument is field-ready. The analyzer probe itself must be able to stand up long-term in your process stream.
This can be done in one of two ways. Either install a single analyzer and monitor its operation or speak with others who have successfully installed analyzers in similar applications.

Your instrument technicians will probably need to be trained by the supplier. The cost of this training should be factored into purchase decisions.

Analyzers typically need more maintenance than standard plant instruments. The analyzer should be equipped with an easy method of adding calibration gasses or liquids. Even the best probes will fail, so replacing probes should be straightforward and should not require an undue amount of time.
Buy analyzers that can be integrated into your existing control system without a lot of custom programming.

The interfaces most used in the lab are not the same as the ones used by process control systems, and problems can result. Converting an RS-232 serial output to a format recognizable by your control system can be an expensive proposition requiring custom software development, a situation best avoided if possible.

Finally, make sure that the online and real-time data delivered by the analyzer is used to improve control of your process. Moving a measurement online from the lab should yield more than just savings in lab costs. It should also deliver measurable improvements in process efficiency, up-time, and cycle time.

 

Best Practices for Going Online

  • Make sure the selected analyzer can survive long-term in your process stream
  • Make sure that your plant personnel are trained to operate the analyzer
  • Consider maintenance as a key part of your purchase decision
  • Select an analyzer that can interface to your control system without custom programming
  • Make sure that the online results are used to improve your process

 

Online Analysis Reaps Benefits

lanbia ingredients, Ballyragget, Ireland, manufactures a wide range of dairy products including whey, casein, cream and cheese. Waste from the individual plants feeds to an in-house wastewater treatment plant. Organics, nitrates and phosphates are removed, and clean water is discharged to the local river. The entire plant previously relied on grab samples and laboratory measurements to determine the level of waste from each of the process plants, the total loading to the bio-tower treatment plant and the success or failure of the treatment facility.

According to Eamon Ryan, the assistant manager services/environmental at Glanbia, the company installed seven online BioTector total organic carbon analyzers. They monitor the amount of waste product discharged from each of the process plants in order to facilitate the implementation of a waste minimization program. The analyzers also measure total organic loading to the treatment plant to ensure the plant operates within its designed specification and regulatory requirements for discharged water to the river.

 

    

CLICK HERE 
to open a spreadsheet
that illustrates the
Glanbia Process Flow Representation.

Using online analysis has reaped multiple benefits for Glanbia. “We saw a dramatic reduction in the amount of waste product discharged from each of the process plants, with some plants showing a reduction of up to 40% and a payback of less than three months,” reports Ryan. “We also saw a reduction in the loading to the treatment plant, thus ensuring the plant operated at its optimum level. This yielded reduced running costs and the total elimination of an odor problem which had been an issue for more than 17 years. By controlling the waste load to the treatment plant and operating within specifications, the final discharge regulatory requirements were easily achieved. There was also a reduction in CO2 emissions from the treatment plant in excess of 40%. Installation of the analyzers contributed to our ISO 14001 Award for environmental excellence.”

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