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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