Turbomachinery for Nitric Acid Plants - MAN Diesel & Turbo

Nitrous gas compressor
For the two-pressure process the
nitrous gas compressor is generally of
the centrifugal type. Where the oxidation
pressures are very low, an axial
compressor can be used similar to
low-pressure plants. For nitrous gas
compressors today impellers of high
flowhandling capacity and, if necessary,
with large exit angles (900 impellers) are
also chosen.
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In designing compressors for nitrous
gas, one must take into account that
this gas
forms ammonium nitrite,
nitrate and HNO3 is poisonous,
is highly corrosive,
allows chemical reactions to take
place during compression.
Therefore, specific design steps have to
be taken and special equipment has to
be installed on the compressor.
The formation of ammonium nitrate deposits,
which under certain circumstances
has an explosive effect, is prevented by
avoiding any dead spaces within the
compressor.
Deposits that may form in the flow
channel are removed by “washing” in
regular intervals.
This is done by spraying steam condensate
into the compressor suction
nozzle. The so-called washing process
is performed during the start-up procedure.
In addition, condensate may be
injected into the machine during normal
operation for about five minutes every
eight hours.
Special nozzles spray the water at
high pressure against the gas stream to
give a uniform and precise distribution
guaranteeing quick evaporation of the
water.