Oxygen limit concentration

In most situations it remains necessary to rely on other alternatives. The most rec-ommendable method to prevent the occurrence of dust explosions is inertization. Some details to be observed in its application will be presented in Section 7.4. At this point, some general remarks shall just be made. The highest allowable oxygen concentration is substance specific. Experimental methods for the determination of this limit concentration are well known. In a first approximation it may be assumed, however, that the oxygen limit concentration for organic powders and dusts will not be lower than 8%. For metal dusts this value has to be halved. 

Many finely divided metal powders in suspension in air are potential e] losion hazards, and causes for ignition of such dust clouds are numerous [Hartmann and Greenwald, Min. MetalL, 26, 331 (1945)]. Concentration of the dust in air and its particle size are important fac tors that determine explosibility. Below a lower Umit of concentration, no explosion can result because the heat of combustion is insufficient to propagate it. Above a maximum limiting concentration, an explosion cannot be produced because insufficient oxygen is available. The finer the particles, the more easily is ignition accomplished and the more rapid is the rate of combustion. This is illustrated in Fig. 20-7. 

R. eutropha is actually an autotrophic hydrogen-oxidizing bacterium which can also produce poly(3HB) from C02, H2, and 02 [34]. The critical factor in such autotrophic cultivation processes is to avoid possible gas explosions. Therefore, a recycled gas, closed circuit culture system equipped with several safety features was developed and the oxygen concentration in the substrate gas phase was kept below the lower limit for gas explosions. A bacterial biomass of 91.3 g 1 1 has been achieved and the poly(3HB) content reached up to 67% per cell dry weight under these oxygen-limited conditions [35]. 

It is further found that the adiabatic flame temperature is approximately 1300 °C for mixtures involving inert diluents at the lower flammable limit concentration. The accuracy of this approximation is illustrated in Figure 4.19 for propane in air. This approximate relationship allows us to estimate the lower limit under a variety of conditions. Consider the resultant temperature due to combustion of a given mixture. The adiabatic flame temperature (7f ad), given by Equation (2.22) for a mixture of fuel (Xp), oxygen (Xo2) and inert diluent (Xd) originally at 7U, where all of the fuel is consumed, is... 

Odour will return in treated slurry as a result of post treatment fermentation. The concentration of readily fermentable substrates, measured as BOD5, provide an indicator of this problem. In continuous culture without oxygen limitation the BOD5 can be described by a model derived from the Monod (13) model of microbial growth (14). The supernatant BOD5 (g/1) from treatment at 15 to 45°C, was described by equation 3 and the whole BOD5 by equations 4 and 5(15). 

Hg, temperature 148°C., w = 200 cm./sec. It may be seen from Figure 2 that the curve for the C02 accumulation rate versus the CO flow rate is one tending to the limit. As the limit is observed when all oxygen atoms have reacted with CO, the limiting concentration, (C02), will be equal to the initial concentration (O)o. Under given experimental conditions... 

Thus, in admitting CO into the stream containing oxygen atoms, the initial oxygen atom concentration may be determined from the limiting rate of C02 accumulation. Certainly, another substance may be used instead of CO and determination of the oxygen atom concentration could then be made from the limiting rate of the primary product accumulation (or of the sum of primary products). But one must be certain that the formation of these products does not proceed by a chain mechanism. 

It will be noted that nitrogen atoms are a good example of atoms the disappearance of which is hindered by untreated molybdenum.44 Calculated data and simple considerations show that the curve for accumulation of secondary products yielded by a reaction of primary radicals with molecules is not different from the primary product curve. This is due to the fact that only one oxygen atom participates in the formation of secondary products. Since the reactivity of a primary radical is such that it is converted into a stable molecule before reaching the trap, its presence may be detected. It will be noted also that while the limiting concentrations of primary and secondary products (when these are the only ones) are equal to the initial concentration atoms, the maximum concentrations of quadratic and cubic products are not higher than one-half and one-third, respectively, of this concentration. 

To find out whether the given primary or secondary product, or the sum of these, is formed by a single step, or by a chain of conversions, the limiting primary product concentration should be compared with the initial oxygen atom concentration determined from CO. If these are equal, this is an indication that the primary product is formed by a nonchain mechanism. 

Athletes, Alligators, and Coelacanths Glycolysis at Limiting Concentrations of Oxygen... 

In contrast, )n mixtures with excess hydrogen and deficient oxygen, the concentration ratio of the deficient component (oxygen) at both limits (upward and downward) is close to unity. 

Prior to the fermentations, the pH of the different hydrolysate samples was adjusted to 5.5 with NaOH (5 M). All fermentations were carried out under oxygen-limited conditions in 55-mL glass vessels containing 50 mL of medium of which 47.5 mL was hydrolysate (or, alternatively, an aqueous glucose solution for reference fermentations). The vessels were sealed with rubber stoppers and equipped with cannulas for outlet of C02. The hydrolysates were supplemented with nutrients as previously described (20). Fermentations of 35 g/L of glucose and nutrients but no hydrolysate were used for reference. The flasks were inoculated to an initial cell mass concentration of 2.0 g/L dry wt and incubated at 30°C with stirring. The fermentations were run for 36 h. Samples of 200 pL were taken after 0,2,4, 6, 8,10, 24, and 36 h. 

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