Oxygen concentrators

Flammability limits. A flammable gas will bum in air only over a limited range of composition. Below a certain concentration of the flammable gas, the lower flammability limit, the mixture is too lean to burn, i.e., lacks fuel. Above a certain concentration, the upper flammability limit, it is too rich to burn, i.e., lacks oxygen. Concentrations between these limits constitute the flammable range. 

For trace quantities of less than 100 ppm, the most successful method — and the most costly— is neutron activation. The sample is subjected to neutron bombardment in an accelerator where oxygen 16 is converted to unstable nitrogen 16 having a half-life of seven seconds. This is accompanied by emission of (J and 7 rays which are detected and measured. Oxygen concentrations as low as 10 ppm can be detected. At such levels, the problem is to find an acceptable blank sample. 

This justifies all the work undertaken to arrive at fuel denitrification which, as is well known, is difficult and costly. Moreover, technological improvements can bring considerable progress to this field. That is the case with low NO burners developed at IFF. These consist of producing separated flame jets that enable lower combustion temperatures, local oxygen concentrations to be less high and a lowered fuel s nitrogen contribution to NOj. formation. In a well defined industrial installation, the burner said to be of the low NO type can attain a level of 350 mg/Nm, instead of the 600 mg/Nm with a conventional burner. 

Fig. 1. The relationship between rate of oxygen uptake and dissolved oxygen, concentration where is the critical oxygen concentration.

Provided this equaHty is satisfied and the dissolved oxygen concentration in the weU-mixed Hquid is greater than the critical concentration throughout the bioreactor, then the maximum oxygen demand of the species should be met satisfactorily. Design of the bioreactor must ensure that the above requirements are achieved economically and without damaging the biological species. 

The SORT value when divided by the standard conditions oxygen transfer rate (OTR) given for a mechanical aerator yields the oxygen concentration required for treatment. 

Fillers that contain combined water or carbon dioxide, such as alumina trihydrate, Mg(OH)2, or dawsonite [12011 -76-6] increase fire resistance by hberating noncombustible gases when they are heated. These gases withdraw heat from the plastic and can also reduce the oxygen concentration of the air surrounding the composition. 

The Ohio State University (OSU) calorimeter (12) differs from the Cone calorimeter ia that it is a tme adiabatic instmment which measures heat released dufing burning of polymers by measurement of the temperature of the exhaust gases. This test has been adopted by the Federal Aeronautics Administration (FAA) to test total and peak heat release of materials used ia the iateriors of commercial aircraft. The other principal heat release test ia use is the Factory Mutual flammabiHty apparatus (13,14). Unlike the Cone or OSU calorimeters this test allows the measurement of flame spread as weU as heat release and smoke. A unique feature is that it uses oxygen concentrations higher than ambient to simulate back radiation from the flames of a large-scale fire. 

Because the reaction takes place in the Hquid, the amount of Hquid held in the contacting vessel is important, as are the Hquid physical properties such as viscosity, density, and surface tension. These properties affect gas bubble size and therefore phase boundary area and diffusion properties for rate considerations. Chemically, the oxidation rate is also dependent on the concentration of the anthrahydroquinone, the actual oxygen concentration in the Hquid, and the system temperature (64). The oxidation reaction is also exothermic, releasing the remaining 45% of the heat of formation from the elements. Temperature can be controUed by the various options described under hydrogenation. Added heat release can result from decomposition of hydrogen peroxide or direct reaction of H2O2 and hydroquinone (HQ) at a catalytic site (eq. 19). 

Both CI2 and HCl have been shown to chlorinate hydrocarbons on fly ash particles. Pilot-scale data involving the injection of fly ash from municipal waste combustion (33) show that intermediate oxygen concentrations (4—7%) produce the highest levels of PCDD and PCDF. These data also show significant reductions in PCDD and PCDF emissions with the upstream injection of Ca(OH)2 at about 800°C. 

Obtainable only in modem plants. Average for U.S. plants is 32.8% Total oxygen concentration is 32 mol %. 

Initiators, usually from 0.02 to 2.0 wt % of the monomer, are dissolved in the reaction solvents and fed as a separate stream to the kettle. Because oxygen is an inhibitor of methacrylic polymerizations, its presence is undesirable. When the polymerization is carried out below reflux temperatures, oxygen concentration is lowered by a sparge with carbon dioxide or nitrogen, and a blanket of the inert gas is then maintained over the polymerization mixture. 

Table 4. Maximum Permissible Oxygen Concentrations for Various Substances ...

As for the selectivity of DBO, the higher the reaction pressure and the lower the reaction temperature, the higher the selectivity. As for the reaction rate, the higher the reaction temperature, the larger the rate. Therefore, the industrial operation of the process is conducted at 10—11 MPa (1450—1595 psi) and 90—100°C. In addition, gas circulation is carried out in order to keep the oxygen concentration below the explosion limit during the reaction, and to improve the CO utili2ation rate and the gas—Hquid contact rate. 

Most dry-chemical fire-extinguishing materials also function by inhibiting combustion rather than by cooling or by reducing oxygen concentration. The usual dry-chemical material is a bicarbonate, but some phosphates, eg, ammonium, provide a coating that makes the material suitable for use on fires involving soHd combustibles such as mbber tires, wood, and paper. 

Norrish type I chemistry is claimed to be responsible for about 15% of the chain scission of ethylene—carbon monoxide polymers at room temperature, whereas at 120°C it promotes 59% of the degradation. Norrish I reactions are independent of temperature and oxygen concentration at temperatures above the T of the polymer (50). 

In lower pressure boilers a variety of additional treatments may be appropriate, particularly if the steam is used in chemical process or other nonturbine appHcation. Chelants and sludge conditioners are employed to condition scale and enable the use of less pure feedwater. When the dmm pressure is less than 7 MPa (1015 psia), sodium sulfite may be added direcdy to the boiler water as an oxygen scavenger. It has minimal effect on the oxygen concentration in the system before the boiler. 

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