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5
SULFUR DIOXIDE APPLICATIONS
The following chapter has been excerpted from:
WHITE: HANDBOOK OF CHLORINATION AND ALTERNATE DISINFECTANTS, Third Edition, Copyright 1992
by VAN NOSTRAND REINHOLD COMPANY
This information is included here to indicate the severity of some of the moisture problems possible when using
Sulfur Dioxide (SO
2
). Please note that the failed Vaporizers mentioned in this excerpt were not manufactured by
De Nora Water Technologies.
CAUTION
If using the method of water removal detailed in the excerpt below, possible vacuum damage
may occur to rupture discs without vacuum backing plates diaphragm seals used on
pressure switches and gauges. These devices should be isolated from the system
if they cannot withstand the vacuum levels developed by a dead-ended gas feed system.
Excerpt:
Maintenance: Dechlorination Equipment
Sulfur Dioxide Supply System
General Discussion.
The characteristics of Sulfur Dioxide are so similar to those of Chlorine that almost everything
said about maintenance for Chlorine is applicable to the Sulfur Dioxide system. However, there are some exceptions.
The life of the diaphragm protectors on the vapor and liquid pressure gages in an SO
2
system is much longer than for
Chlorine because of the low vapor pressure of SO
2
(35 psi).
The corrosiveness due to the entrance of moisture is almost the same as that for Chlorine, but this action is different
on different metals. For example, in a Chlorine system, line valves and header valves use Monel trim, but these are
not interchangeable for Sulfur Dioxide. Valves for the latter should have 316 SS trim.
Moisture Problems.
Sulfur Dioxide producers claim that the moisture content does not exceed 40 ppm. However,
White has found that this can escalate to more than 100 ppm when a packager transfers the SO
2
from the producer’s
tank car into the packager’s truck tanker. However, certain packagers have a much better and less corrosive product
than others who may be somewhat careless in their transference of an otherwise acceptable product in a tank car
to their tanker trucks. Recent experience in the San Francisco Bay Area indicate that some of the supplies of Sulfur
Dioxide are more corrosive than Chlorine by a factor of 10 to 1. This suggests lack of moisture control during the SO
2
transfer procedure. Attempts to quantify and monitor the moisture content by the user proved fruitless. However, a
preventative maintenance procedure was worked out by one of the wastewater plant operators.
It is described below.
Preventive Maintenance.
The following procedure requires an vaporizer. It was the failure of three SO
2
Vaporizers
which inspired this procedure. It will boil off any excess moisture that may accumulate in the supply system.
Once every day or once every three days, depending upon the SO
2
usage, the Vaporizer under consideration
should be shut down by closing the inlet liquid line. The sulfonator vacuum relief line should be plugged and the
sulfonator be allowed to operate so as to create a vacuum within the SO
2
Vaporizer container vessel. The moisture
that may collect in the supply system will always float upon the liquid SO
2
in the Vaporizer container vessel. Therefore,
withdrawing all of the liquid SO
2
in the Vaporizer is step number 1. Step number 2 is the boiling off of the moisture in
the container vessel by pulling a vacuum through the sulfonator while maintaining a temperature of 160°F - 180°F in
the SO
2
Vaporizer water bath.
Содержание Capital Controls 71V3B Series
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