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Thursday, January 23, 2014

#168 - Nova Analyzers from the Field – Episode 4

We received this beauty into our service department recently. This is a continuous H2 / CO2 analyzer that has been connected to a heat treat furnace for about 14yrs now.




As can be seen, the unit is covered inside and out with black grime. The tubing has turned yellowish-brown. The jet black bowl filters at the bottom of the picture were actually transparent when they were new. It is a small miracle that the detectors were able to function for so many years in such harsh conditions.

Some of the black grime may be soot resulting from combustion of fuel in a low O2 environment. Some furnaces are operated this way intentionally to produce a certain atmosphere around the metal products that are being heat treated. However, most of the surfaces on / in this analyzer are also quite tacky / sticky.

Some types of metal heat treating, such as sintering, employ waxes and binders as part of the manufacturing process that later burn off in the heat treat furnace. These oil vapor products can later condense onto cooler surfaces and gradually accumulate there. That may be what is coating the various surfaces of this analyzer. This coating is probably also present on the optical surfaces in the detector assembly.

Infra-red detectors need to ‘see’ through a set of glass barriers and then through a volume of the sample gas. Some vapors deposit a colored film which will eventually become opaque like the black bowl filters mentioned above. If the detector can’t see through its window, it cannot make measurements.

Even non-optical detectors are sensitive to oil vapor contamination. We see this issue in the power industry on large generators. Electric generators are sealed with oil which can be vaporized over time and be pulled into a hydrogen purity analyzer. Oil-contaminated hydrogen detectors will not function properly. So we always provide an oil vapor filter assembly with the generator atmosphere analyzers. Maybe that would have been a good investment on this analyzer from the field.

I notice that this particular analyzer has a water-cooled condenser mounted on the left side of the cabinet (not visible in this picture). The purpose of this component is to help remove water from the sample gas. The condenser is basically a tube within a tube. Cold water is filtered and flowed into one end of the outer tube, and out at the other end. 

The cold water surrounds the inner tube and keeps it cool. On the inside of the inner tube, the cool tubing wall causes moisture in the sample gas to condense out. The condensed water runs down and is collected and drained in the condensate traps which mount on the bottom of the analyzer. The dried sample gas continues on into the analyzer. Of course, this whole concept only works if there is a continuous supply of cold water. In some regions, this cannot be guaranteed.

Another quirk of this analyzer is the fact that there is only a display for the H2 reading even though there is also a CO2 detector. In this application, the H2 reading was critical, but the CO2 reading was not. However, the presence of CO2 will interfere with accurate an accurate H2 reading. So we measure the CO2 and actively compensate the H2 reading. This keeps the H2 reading accurate even if the CO2 levels vary continuously.

It is hard to say what the future of this particular analyzer will be. I assumed that it was un-repairable. However, the owner wanted to try replacing the tubing and some of the other internal components. They probably also had to clean the optical surfaces in the detector as much as possible. How much longer the analyzer will stay functional, is anyone’s guess. But we are pleased to see that a Nova instrument has remained operational in adverse conditions for this long.

A new version of this equipment is still readily available. Check here in the heat treat section of our website.

Episode 1 - old portable flue gas with dual CO channel
Episode 2 - portable ppm H2 analyzer for university metallurgical lab
Episode 3 - ex-proof H2 analyzer in South Africa

If a system like this is of interest to you, contact Nova for details.

1-800-295-3771
sales at nova-gas dot com
websales at nova-gas dot com
http://www.nova-gas.com/
https://twitter.com/NOVAGAS
http://www.linkedin.com/company/nova-analytical-systems-inc-
http://www.tenovagroup.com/

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