13
Oven
Some canister cleaning systems are incorporated within an oven. The supply
line for the humidified air stream and the line to the vacuum system are
plumbed directly into the oven. In this arrangement the entire canister,
including the valve, will be heated, and this will help remove contaminants if
both the valve and the canister are dirty. Typically, when using heat, it is help-
ful to create steam from the humidified air stream. An oven temperature of at
least 120°C is required, but higher temperatures often are used. Remember
that heat can shorten the lifetime of the Nupro valve on a SUMMA® canister
(see step 3 in Cleaning Method, below).
Space is a concern with oven systems. Most commercial ovens are not very
large and this restricts the number of canisters that can be cleaned at one time.
However, clean-up times are shorter with heat than without heat, so more
cleaning cycles can be completed in a week.
Heat Bands
A band heater placed around the equator of the canister typically will be capa-
ble of heating the canister to approximately 130°C. There is a heat gradient,
and the valve might only receive radiant heat (approximately 70-100°C). In
most sampling situations, however, this lower temperature should be suffi-
cient for effectively removing contaminants from the valve.
Insulated Heat Jackets
Insulated heat jackets can be obtained to surround and heat each canister.
These jackets typically have a silicone or Teflon®-coated fiberglass fabric exte-
rior and a fiberglass insulation interior. Some operate at a fixed temperature;
others can provide variable temperature, up to 400-500ºF. Restek’s heating
jacket, described at right on this page, offers significant advantages over most
other commercial designs, which do not encompass the valve area.
Infrared Heat
An infrared heating system includes an infrared heat source and a reflective
panel similar to the cylinder drying rack on a gas cylinder system. The infrared
source and the reflective panel are placed on opposing sides of the canisters.
Infrared rays from the source heat the canisters; rays that pass the canisters
strike the reflective panel and heat the canisters from the opposing side.
The Cleaning System
The cleaning systemmust provide a humidified air stream and include a good
vacuum source, a cold trap to collect impurities during cleaning, and accurate
gauges to read vacuum and pressure. A heat source is optional, but is highly
recommended in some circumstances, as discussed above. The system can be
designed to clean 4 to 24 six-liter canisters. Figure 8 (page 14) shows an exam-
ple of a “homemade” system designed to clean 24 six-liter canisters. This
design does not employ heat, but a heater easily can be added (see Heat or No
Heat, page 12). It provides a humidified air stream to all canisters and the
roughing pump on the bottom shelf is the vacuum source. This system is
computer operated to minimize labor, but this is not necessary.
Cleaning Method
1. Connect all canisters to the cleaning system, then release any pressure
within any of the canisters. Put the system under vacuum, to evacuate the
canisters. US EPA Method TO-14A/15 recommends evacuating the sys-
tem to 50 mTorr for 1 hour, but a reduced pressure of 23-25" Hg is suffi-
cient for general cleaning.
2. After the canisters have been under vacuum for approximately 1 hour,
pressurize the canisters with humidified air or nitrogen*. Pressurization
will dilute the impurities and the moist air will hydrolyze them.
Pressurize canisters to 5 psig if they will be heated or to 30 psig if they
will not be heated. Proceed to step 3 when the system has equilibrated at
the designated pressure.
The ultimate in controlled heating,
for reliably cleaning your air canisters!
Description
qty.
cat.#
Air Canister Heating Jacket (110 volt)
ea.
24123
Air Canister Heating Jacket
• Closely simulates oven environment—heats
entire canister.
• Two temperature settings, 75°C and 150°C.
• Prevents sample condensation, for accurate sub-
sampling.
• Easily fits canister up to 6 liters.
• Lightweight; comfortable to the touch when
heated.
• Connect up to five Canister Heating Jackets to
one 15 amp circuit.
The Restek Canister Heating Jacket will help you
clean your canisters faster and more efficiently. The
novel design ensures the entire canister, including
the valve, is heated during the cleaning cycle, to
remove contaminants most effectively. It also can
be used to keep the sample heated during aliquot
removal, which helps prevent condensation and
assure accurate data for larger molecules. The two
heat settings let you match the temperature to the
volatility of your sample components. If you try
one in your system, we think you’ll want more.
*
please
note
If you are cleaning SilcoCan
TM
canisters, and will be using heat,
use humidified nitrogen, not air.
