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Major gas generation (separation)
technologies are described as below.
For separating nitrogen and oxygen, the major compositions
of air, the optimum method is selected according to
the application map on the right, for a required flow
rate, purity, etc., in consideration of its economical
efficiency. |
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Pressure swing
adsorption type |
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Oxygen or nitrogen is selectively adsorbed with adsorbent. The components adsorbed
under pressure are desorbed by depressurizing. It is
called PSA (Pressure
Swing Adsorption)
because of such repeated pressurizing and depressurizing.
In generating nitrogen gas, high purity nitrogen gas
(about 99 - 99.99%) (containing argon) is separated, using
the difference in adsorption speed between nitrogen
and oxygen.
In addition, higher purity nitrogen (99.999%) can be
achieved in combination with Purifier.
The capacity ranges from 1 NL/min to several 1000 Nm3/h.
Some small-scale equipment is shipped as assembled in
a cabinet, while some large-scale plant is assembled
on the site.
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Membrane method |
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It
uses the filtration effect by hollow fiber membranes.
High purity nitrogen gas (about 95 - 99.9%) is separated,
using the difference in membrane permeability characteristic
between nitrogen and oxygen when delivering high-pressure
air to a membrane module. Among various types of generators,
it is used in where relatively low purity nitrogen is
required comparing with other methods. Once compressed
air enters a hollow fiber membrane, moisture, oxygen,
and CO2, which are permeable through membranes,
passes through the membrane, while nitrogen and argon,
which are not permeable through membranes, are separated
as a product.
The
selectivity of gases is enhanced when the pressure and
temperature of feed air are high.
It is generally shipped as a unit packaged in a cabinet,
which contains a required number of modules (photo on
the above), a bundle of hollow fiber membranes (photo
on the left), according to the required purity and flow
rate of the generated gas. |
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Cryogenic type |
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High
purity gases (more than 99.999%) are extracted using
the difference in boiling point (b.p.) among nitrogen
(b.p.=-195.8oC), oxygen
(b.p.=-183oC), and
argon (b.p.=-185.7oC),
in the liquefied air. It is suitable where
a large amount of high purity nitrogen is required.
A small-scale 150 Nm3/h equipment requires
a space of 10 x 20 m. Kobe steel, Ltd. has been involved
in manufacture of this equipment since 1930s, and has
abundant experience both in and outside Japan.
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