|Content Type||Conference Paper|
|Title||Oxidizer use in Refinery Chemical Cleaning: Selection Considerations and Case Histories|
|Authors||Chris H. Spurrell, Chevron USA; Ronald A. Kenyon, Delta Tech Service Inc.|
|Source||CORROSION 2006, March 12 - 16, 2006 , San Diego Ca|
|Copyright||2006. NACE International|
The chemical cleaning techniques used in petroleum refineries often call for the use of oxidizers. When properly applied oxidizers can facilitate the overall cleaning while also improving health and safety factors and reducing environmental impacts. Oxidizers are reactive chemicals and must be selected and applied properly. This paper discusses several of the more commonly used oxidizers, their characteristics, costs, effectiveness' and other peculiarities. Case histories point out some of the consequences of improper use.
The idea of oxidation is at once both intimidating and trivial. As a chemical technology the combination of fuels and oxidizers goes back many hundreds of years. The Red-Ox reaction is the bane of first year college chemistry. In a petroleum refinery oxidation can be as boring as watching a pipe rust or as exciting as lighting a furnace. Oxidation is also inescapable and perfectly natural. Given enough time even the largest refinery will end up as rust, carbon dioxide and water.
Oxidation as an intentional step in chemical cleaning and decontamination is a fairly recent idea which has been driven by health, safety and environmental concerns and regulations. It?s these same concerns and regulations, as well as refinery processing needs, which has introduced widespread use of oxidizers. A survey of one major West Coast refinery showed that oxidizers have been used for: odor control, effluent toxicity reduction, microbiological control, sulfide removal, phenol removal, chemical cleaning, metal passivation, corrosion control, COD (Chemical Oxygen Demand) reduction, land farm fertilizer, microbiological nutrient and H2S scavenger.
So while the use of oxidizers in chemical cleaning and decontamination is expanding into new areas, there are many precedents for oxidizer use in refineries.
The use of oxidizers is not without risk. These are reactive and sometimes unstable chemicals, which if misapplied, can and have had dramatic, even fatal consequences. The following discussion is intended to promote the sharing of technology. As A. E. Newman once said: Learn from the mistakes of others, ?cause you?ll never live long enough to make them all yourself.
Chlorine, Bleach (NaClO) and halogen donors
Chlorine and solutions of the hypochlorite ion probably represent the longest history of oxidizer use in oil refineries. Cooling towers have long used chlorine or sodium hypochlorite. Even with the advent of chlorine donors like halogen-substituted hydantoins or cyanurates, the water chemistry of the oxidizer is the same once it becomes the free halogen or hypohalite ion. In cooling water applications the halogens, at fractional ppm concentrations, are acting as toxins. Still, it is well known that at higher concentrations chlorine can be used to burn out microbiological deposits and provide a measure of chemical cleaning.
With chlorine being the least expensive, most common and easily available oxidizer it has been used in refineries to oxidize pyrophoric iron and neutralize foul smells, especially those sulfur related, and has been specified to destroy certain catalyst sulfiding agents. It has been used in large scale chemical cleaning operations but not without certain risks and liabilities
All the common chlorine sources have the risk of generating a toxic atmosphere. There is a nearly quantitative release of chlorine (or bromine) in an acidic environment. With typical industrial strength bleach, the vapor space of the container will almost always exceed hazardous concentrations.
The reactions of hypohalite salts involve more than simple oxidation. Halogenation also can be a major reac
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