De Nora Capital Controls 71V3B Series Instruction Manual
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Contents
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115.6031.0 - 40 -5 SULFUR DIOXIDE APPLICATIONSThe following chapter has been excerpted from:WHITE: HANDBOOK OF CHLORINATION AND ALTERNATE DISINFECTANTS, Third Edition, Copyright 1992by VAN NOSTRAND REINHOLD COMPANYThis information is included here to indicate the severity of some of the moisture problems possible when usingSulfur Dioxide (SO2). Please note that the failed Vaporizers mentioned in this excerpt were not manufactured byDe Nora Water Technologies.CAUTIONIf using the method of water removal detailed in the excerpt below, possible vacuum damagemay occur to rupture discs without vacuum backing plates diaphragm seals used onpressure switches and gauges. These devices should be isolated from the systemif they cannot withstand the vacuum levels developed by a dead-ended gas feed system.Excerpt:Maintenance: Dechlorination EquipmentSulfur Dioxide Supply SystemGeneral Discussion. The characteristics of Sulfur Dioxide are so similar to those of Chlorine that almost everythingsaid 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 forChlorine 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 differenton different metals. For example, in a Chlorine system, line valves and header valves use Monel trim, but these arenot 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’stank car into the packager’s truck tanker. However, certain packagers have a much better and less corrosive productthan others who may be somewhat careless in their transference of an otherwise acceptable product in a tank carto their tanker trucks. Recent experience in the San Francisco Bay Area indicate that some of the supplies of SulfurDioxide are more corrosive than Chlorine by a factor of 10 to 1. This suggests lack of moisture control during the SO2transfer procedure. Attempts to quantify and monitor the moisture content by the user proved fruitless. However, apreventative 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 SO2 Vaporizerswhich 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 considerationshould be shut down by closing the inlet liquid line. The sulfonator vacuum relief line should be plugged and thesulfonator be allowed to operate so as to create a vacuum within the SO 2 Vaporizer container vessel. The moisturethat 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 SO2 in the Vaporizer is step number 1. Step number 2 is the boiling off of the moisture inthe container vessel by pulling a vacuum through the sulfonator while maintaining a temperature of 160°F - 180°F inthe SO 2 Vaporizer water bath. |
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