Nitrogen historic concentration

Prompt NO mechanisms In dealing with the presentation of prompt NO mechanisms, much can be learned by considering the historical development of the concept of prompt NO. With the development of the Zeldovich mechanism, many investigators followed the concept that in premixed flame systems, NO would form only in the post-flame or burned gas zone. Thus, it was thought possible to experimentally determine thermal NO formation rates and, from these rates, to find the rate constant of Eq. (8.49) by measurement of the NO concentration profiles in the post-flame zone. Such measurements can be performed readily on flat flame burners. Of course, in order to make these determinations, it is necessary to know the O atom concentrations. Since hydrocarbon-air flames were always considered, the nitrogen concentration was always in large excess. As discussed in the preceding subsection, the O atom concentration was taken as the equilibrium concentration at the flame temperature and all other reactions were assumed very fast compared to the Zeldovich mechanism. 

Breakpoint chlorination. Breakpoint chlorination is a historical concept where combined chlorine is reoxidized to hypochlorous acid by the addition of an excess concentration of hypochlorous acid. These are collectively referred to as combined chlorine or combined available (CAC) under the assumption that the chlorine can be re-liberated. The model used for nearly all literature cites the interaction between hypochlorous acid and ammonia. In recreational water the amount of hypochlorous acid used for a breakpoint treatment is normally ten times the concentration of the combined chlorine. However, the reaction between hypochlorous acid and more complex nitrogen compounds is not fully reversible. White (1986) showed that breakpoint water containing a mixture of combined chlorine from organic and simple ammonia failed to display the elassic dip of the breakpoint reaction. These waters displayed a plateau concentration below which no further reduction in combined chlorine occurred. The nitrogen compounds in recreational water are introduced in bather waste and from the environment and contain mostly amino acids, peptides, and proteins with little free ammonia. Practical experience has shown that this method will reduce, but not eliminate, the combined chlorine. If repeated breakpoint treatments fail to reduce the combined chlorine to the target level (0.02 to 0.05 ppm CAC) alternate treatments such as oxidation with a potassium monopersulfate or partial water replacement to dilute the chloramines must be used. 

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