July, Causes and Prevention of Packing Fires, p. 34.
I thought the article was very timely and informative and appreciate being a reference for your paper. However, after reviewing the information provided regarding potassium permanganate (especially Table 1), I must provide the following constructive comments.
We know of one specific refinery that has been using permanganate since 1991 with excellent results and has recommended its use to other sites within their organization. I have summarized the actual properties of permanganate below. Unfortunately, one of your sources (www.cheresources.com/ironfires.shtml) contains information on permanganate that is mostly in error and needs to be changed. That site is very pro Zyme Flow and the information should have been confirmed from other independent sources. There is one final item I would like to point out. I think the use of trade names was a bit one sided and may have come across as an endorsement.
Dangerous exotherm possible? No. Permanganate is applied as a solution. The maximum concentration one can get in the field is about 5%, which results in a reaction environment where any heat released from reacting with FeS will only warm the water and not lead to a hazardous condition.
Dangerous gas emission possible? No. A permanganate solution will not react with any hydrocarbons remaining in the unit being cleaned. It will react with the FeS and generate a mixture of sulfur or sulfate and the MnO2 solid material.
Dangerous residue possible? No. The residue is comprised of sulfur, sulfate and inert manganese dioxide
Safe with light hydrocarbons? Yes. It has been used to treat hydrocarbons liquids (such as gasoline) to remove sulfur compounds with no adverse affects. A patent was given to Shell for sweetening hydrocarbons in the early 1960’s.
Liquid application? Yes.
Steam application? Yes. A permanganate solution is stable to heat up to approximately 300º F. Permanganate is suitable for low-pressure steam applications.
pH restrictions? Yes. The pH should remain above 4 but will be effective up to a pH of 12.
Create additional or hazardous sludge? Yes. It will produce sludge in the form of inert manganese dioxide but the sludge is not hazardous.
Penetration ability. Moderate.
Secondary waste-treatment required? No. Permanganate has been commonly added to wastewater treatment plants, collection systems and other locations with no adverse affects.
Corrosive? No. A study performed showed permanganate to be non-corrosive to most materials used in a refinery. A low pH will have more effect on corrosion than a permanganate solution.*
Long shelf life? Yes. Potassium permanganate solid has a stability of > 5 years (we have used material that is over 10 years old with no loss in activity). In solution it can be stable for months depending on the quality of the water.
Handling hazards. As with any oxidant, care must be taken. The solid material is more hazardous than the recommended 3–5% solution used for equipment cleaning. The MSDS information must be read before using any chemical, especially for the first time.
Philip Vella, Ph.D.
Carus Chemical Co., La Salle, Ill..
Authors reply:
Many thanks for your valuable comments. In particular, many thanks for your elaboration on the various items that relate to the use of potassium permanganate in our Table 1. As you stated, Table 1 was extracted from another source (Sahdev et. al.), who attempted to condense a multitude of considerations into a single table. As you correctly pointed out, this type of tabulation is an oversimplification to the multitude of considerations involved in handling potassium permanganate. Your discussion clearly points out that handling potassium permanganate can be done safely provided the user correctly follows the necessary precautions. We have talked to one refiner that counts 125 permanganate washes (none, though, with towers containing structured packings) and have not experienced any safety issues. This refiner, however, is aware of the potential hazards and takes extra care to follow all the safe working procedures.
On the other hand, there have been incidents, even accidents, involving permanganate handling that did not follow good handling practices. We believe that the entries in the table address these. For instance, the question of whether a dangerous exotherm is possible. The Table had a “yes”, and we are aware of instances where this happened when poor or questionable mixing procedures were used. On the other hand, you correctly state that once the correct solution strength (less than 5%) is used an exotherm is unlikely. So a “yes” and a “no” are both correct, depending on whether a correct handling procedure is used. So the answers in the Table relate to situations where the procedures used deviate from good practices, while your answers (which we are grateful for) suggest that when good practices are used, permanganate can be handled safely.
Per our e-mail forum over the last few weeks, the website also appreciated your clarifications and now has both the Table and your clarification.
We want to emphasize that the purpose of our paper was to explore the options available for preventing fires with structured packing, not as an exhaustive instruction on how to apply chemical washes. This would be the subject of another very interesting paper, which is outside of our scope.
While on the subject of fires in structured packings, we have attempted to identify refiners that use potassium permanganate with columns containing structured packings. We have not been able to identify any. We requested references from you. We talked to a few that use permanganate extensively for drums and tray towers, but have not been able to identify any that use it with structured packings. The industry would welcome comments from those who have hands-on experience of permanganate washing structured packings.
Henry Kister
Fractionation Research Inc.,
Design Practices Committee,
* See Nickerson, J. L., Vella, P., "Hazardous Material Decontamination with Potassium Permanganate for Refinery Turnarounds" presented at the Corrosion NACExpo Annual Conference & Exposition, San Diego, Calif., March 22 – 27, 1998.