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Jul
21

Top Ten Limitations – Analyzers

Ultimately what we most need to know in each key process stream is the operating condition least measured; composition. We are largely flying blind. Neural networks and projections to latent structure technologies have proliferated because online and at-line analyzers are missing. Here is a look at the use of analyzers in the process industries. 

Advanced process control (APC) relies on knowledge of the process and thus its capability is largely limited by the ability to know compositions online. The performance of unit operations and the plant depend upon the compositions of process inputs (raw materials) and outputs from reactions and separations. Often the most mysterious and disruptive disturbance is an unknown change in raw material composition. Batch composition profiles are largely unknown. For possibilities of profile control made possible by analyzers see “Unlocking the Secret Profiles of Batch Reactors

The biopharmaceutical industry is expanding their ability to analyze batch profiles online. In mammalian cell bioreactors a dielectric spectroscopy probe is used as an online analyzer to measure viable cell concentration and glutamine besides glucose addition is scheduled. Flexible at-line analyzers using electrochemistry, digital imaging, freezing point depression, and photometry (e.g. Nova BioProfile FLEX) can measure in 2-8 minutes cell density, cell diameter, cell viability, osmolality, substrates (glucose and glutamine), and many byproducts such as carbon dioxide, lactate, and ammonia that inhibit growth and product formation. Near Infrared (NIR) spectroscopy can be used to provide online measurements of substrate, byproduct, and product concentrations. Mass spectrometers can measure the amount of oxygen and carbon dioxide in the bioreactor off-gas for oxygen uptake rate and carbon dioxide production rate calculations.

For advances in PID capability to deal with analyzer nonlinearities and delays check out “More Extraordinary PID Innovations” and “Overcoming Challenges of PID Control & Analyzer Applications

To get an idea of what is happening with analyzers in the chemical industry, I asked Jim Tatera, ISA Automation Week  analyzer track chair, a few key questions.

(1) What are some of the developments/technologies/features that make analyzers more maintainable?

Microprocessors and communications capabilities have provided cost effective analyzer diagnostics and remote monitoring that has reduced field maintenance costs. Good operational information and instrument monitoring and control can often be obtained at the shop or office, which eliminates the need for many field trips to identify the instrument status, what is wrong, what tools or parts are needed, etc.. Sometimes a trip to fix it can even be eliminated through remote software controlled adjustments.

Modular instrument designs have been touted as being more maintainable. I believe that is true as far as field maintenance and usually speed of maintenance is concerned. I am not sure it has lowered maintenance costs. Often modules are quite expensive, when compared to the portion of the module that is actually the problem/issue. Modules have also been an obsolescence issue for many, even requiring total instrument replacement when modules have become obsolete by a manufacturer. Companies like Vivicom (see www.tascorp.com ) have made a business out of supporting analyzers that manufacturers have obsoleted.

(2) Is NIR technology being increasingly used and does it eliminate the need for sample conditioning?

Increasingly being used – yes. Maybe too much. Because of promoted advantages, some are ignoring inherent disadvantages/limitations. In my experience the NIR doesn’t eliminate the need for sample conditioning and this is one of the frequently misunderstood aspects. The chemometrics models used often require even tighter control or monitoring of sample conditions. It can reduce the need for sample transport to the analyzer location, which can reduce some potential safety concerns, but often varying sample conditions in the process cannot be easily/adequately/quickly modeled and/or create very complex modeling issues. Some physical sample conditioning is often still required/desired.

(3) What is your favorite analyzer and why?

Gas Chromatography (GC) – You can do so much with it and it is easy to understand and trouble shoot. Just about anything that can be vaporized can be measured, if you select the right valves, columns, detectors, operating conditions, etc. Frequently significant process improvement changes/modifications can require changing analyzers, but usually a GC method or instrument can just be modified and keep on trucking. Even additional components (measurement or interfering) can usually be easily handled. Of course nothing is free and the GC is not usually very fast and can be too slow for some control strategies.

(4) Are analyzer staffs at corporate engineering centers and plants increasing or decreasing and why?

Decreasing or staying the same, depending on the company/industry. Many don’t see this skill set as one of their core competencies and are relying more on contractors and vendors to do it for them. Others consider the proprietary nature of their processes information too critical to share needed information with contractors and vendors. I don’t see a global dominant trend. Less proprietary/commodity industries, like refining seem to be moving more toward reducing their analyzer staffs. More proprietary industries like chemical and pharmaceutical seem to be holding their own and some are even increasing their analyzer staffs

As you can see from the bio below, Jim is a significant resource for industry and ISA.

Jim Tatera’s Process Analysis experience includes over 27 years (approximately 23 of those years involved with Process Analysis) with a major international chemical company (Dow Corning Corp.) and over 10 years of part time consulting through Tatera & Associates Inc., PAI Partners, and others. His Dow Corning experiences included both US and International assignments in analytical research, process engineering, project engineering, production management, maintenance management, and internal consulting. He has project experience with: sampling, GC, X-Ray, NIR, Raman, FTIR, Viscosity, Particle Sizing, Mass Spec., Turbidity, Color, Oxygen, Moisture, LEL, pH, Conductivity, TOC, TOD, Oil Film Monitoring, and several specialized environmental and ambient monitoring technologies. He has consulted with process analyzer users, vendors, and academia on a variety of topics ranging from specialized applications, technology adoption, instrument/equipment features and designs, to marketing.

Jim is one of the original Certified Specialists in Analytical Technology (CSAT) and an active member of the ISA and ACS. He is active in US and International Standards activities and was the ANSI USNC Technical Advisor to IEC SC 65D for 12 years and currently is an ANSI USNC Technical Advisor to IEC 65B. Additionally, he is on the Editorial Advisory Board of In Tech, an instrumentation magazine, a Fellow of the ISA and has received several honors and distinctions (both company and industry) while working in the field of Process Analysis. Jim has presented and published in several formats including conference presentations, peer reviewed papers, short courses, and nine book chapters/sections in industry standard publications like Liptak’s Instrument Engineers handbook series, Sherman’s Practical Guide for Measurement and Control – Analytical Instrumentation, Goettsche’s Maintenance of Instruments and Systems, and Trevathan’s Guide to the Automation Body of knowledge. He has prepared and/or presented short courses for the ISA, CFPA, ISA Analysis Division, and IFPAC.

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