Nitrogen generators for anoxic pest treatment

Jessie Firth <jessie.firth<-at->awm<.>gov<.>au> writes

>...  Firstly we want to know what purity or grade of nitrogen
>is required for 100% kill?  And secondly, there are two types of
>nitrogen generators available, membrane and chemical.  Does anyone
>have experience with either system?  We are asking for advice and
>peoples experience in terms of purity/grade of produced Nitrogen,
>portability, initial cost and ongoing maintenance costs.

Kill rates will vary with temperature and kind of beasties. I go for
0.1% residual oxygen. To achieve this you will need either oxygen
absorbers, lots of nitrogen from a tank or dewar (apparently more
cost effective where available), or a flow from a nitrogen generator
that is at least as pure as your target (ie 99.9%). Lower purities
may work on some insects and their life stages.

I am not familiar with chemical-based nitrogen generators, however,
there are a number of brands of passive oxygen scavenger, such as
Ageless, that are readily available and inexpensive when purchased
in bulk quantities (full cartons). Using oxygen scavengers is very
easy: one simply places the appropriate quantity of scavengers in a
barrier film bag (along with the infested objects), seals the bag,
and waits.

Nitrogen generators are mechanical devices, with attendant
challenges, but may be very useful when large quantities of
materials are to be disinfested. They can provide anoxic conditions
for larger chambers, or for "chaining" multiple barrier film bags,
and allow for the use of a wider range of barrier films as a good
flow can overcome leakage from the more permeable materials. You
will need an oxygen analyzer to monitor the process. They are
expensive, and are not needed for passive treatments (though lovely
if you have one).

The nitrogen generators that I am familiar with fall into two
categories: filtration using membranes (osmotic separation) and PSA
(Pressure Swing Adsorption) which uses a bed of activated carbon.
Both these techniques operate with a supply of high pressure air to
separate oxygen and moisture from nitrogen.  The high pressure air
is generated by a small (but usually noisy) air compressor.  PSA
units produce a satisfyingly loud pressure release regularly as they
operate. Some folks may find it distracting, but I like it for its
organic quality.

I leave detailed study of the operating principles and devices
currently available to the prospective purchasers, but I can share
the following observations:

The machine's purity of flow is directly related to pressure (and
therefore volume of flow)--greater flows result in lower purity, and
vice versa. This detail is important when comparing different units.

Compressors are likely to be noisy, and will produce heat while
operating. Be aware that they can be isolated at some distance from
the treatment area if this proves a problem. Also note that the
compressor motor will likely need a dedicated electrical supply.
Most of the units I have seen are small enough to be portable, and
need nothing more than a power outlet.

There are many manufacturers who make these units from readily
available components, and supply them to a wide variety of
industries. It is not necessary to purchase a unit designed
especially for museum use. I have been happy with small PSA units
originally designed for producing nitrogen for pubs and restaurants
(to maintain pressure in beer kegs). The only modification needed
for anoxic applications is a simple adjustment that reduces flow
rate (to increase purity), which can be done by the user.

Should you choose a nitrogen generator, be sure that you have good
maintenance and support available. You will be using the top range
of performance to get the purity you need, and this may create more
stress for the units, and you may need the occasional technical
visit.

Jerry Shiner
Keepsafe Microclimate Systems
+1 416-703-4696
+1 800-683-4696


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                  Conservation DistList Instance 27:26
                 Distributed: Monday, December 16, 2013
                       Message Id: cdl-27-26-003
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