Oxygen, excess

Direct-Flame Incinerators. In direct-flame incineration, the waste gases are heated in a fuel-fired refractory-lined chamber to the autoignition temperature where oxidation occurs with or without a visible flame. A fuel flame aids mixing and ignition. Excess oxygen is required, because incomplete oxidation produces aldehydes, organic acids, carbon monoxide, carbon soot, and other undesirable materials. 

Despite all these safeguards to extend the service life of the antifreeze, fluid replacement is requited periodically. Typically, fluids are replaced because of irreversible damage caused by one of four conditions contamination, gel formation because of glycol/siUcate reaction, extensive glycol degradation caused by overheating or excessive oxygen exposure, or inhibitor depletion. 

The first commercial oil-fumace process was put into operation in 1943 by the Phillips Petroleum Co. in Borger, Texas. The oil-fumace blacks rapidly displaced all other types used for the reinforcement of mbber and today account for practically all carbon black production. In the oil-fumace process heavy aromatic residual oils are atomized into a primary combustion flame where the excess oxygen in the primary zone bums a portion of the residual oil to maintain flame temperatures, and the remaining oil is thermally decomposed into carbon and hydrogen. Yields in this process are in the range of 35 to 50% based on the total carbon input. A broad range of product quaHties can be produced. 

Figure 12 contrasts the decrease in conductivity of ETP copper with that of oxygen-free copper as impurity contents are increased. The importance of oxygen in modifying the effect of impurities on conductivity is clearly illustrated. Phosphoms, which is often used as a deoxidizer, has a pronounced effect in lowering electrical conductivity in oxygen-free copper, but Httie effect in the presence of excess oxygen. 

No reaction takes place below 500°C when sodium cyanide and sodium hydroxide are heated in the absence of water and oxygen. Above 500°C, sodium carbonate, sodium cyanamide [19981-17-0] sodium oxide, and hydrogen are produced. In the presence of small amounts of water at 500°C decomposition occurs with the formation of ammonia and sodium formate, and the latter is converted into sodium carbonate and hydrogen by the caustic soda. In the presence of excess oxygen, sodium carbonate, nitrogen, and water are produced (53). 

There has been a growing demand for a lean NO catalyst ia order to decrease the relatively low NO emission of the lean bum engine sufftciendy to meet the future standards. Lean NO catalysts have been developed based on 2eolites (see Molecularsieves). Cu-promoted ZSM-5 2eolite has shown ability to reduce NO ia an exhaust having excess oxygen at an efficiency of 30 to 50% (153). Durability is not proven. Research has revealed that certain hydrocarbons are preferred for the reduction of NO, and that CO and H2 apparentiy do not reduce NO over such lean NO catalysts (154). 

Reactions. The SCR process is termed selective because the ammonia reacts selectively with NO at temperatures >232° C in the presence of excess oxygen (44). The optimum temperature range for the SCR catalyst is determined by balancing the needs of the redox reactions. 

Nitrogen oxide is oxidized with the excess oxygen from tlie previous process phase to form nitrogen dioxide. The reaction is exothermic ... 

References 1 and 2 give target excess oxygen to shoot for as a guide in heater efficiency improvement. Table 1 summarizes the recommended targets. 

Percentage excess oxygen refers to the oxygen left over from combustion and appearing in the flue gas. This... 

Figure 1. Stack loss vs. excess oxygen and stack temperature.

When the operator realized his mistake and restored the gas flow, the reactor contained excess oxygen, and an explosion occurred, not actually in the reactor but in the downstream waste heat boiler. Four men were killed. 

NO, emissions are less dependent on the type of coal burned, and two oxidation mechanisms are associated with the release of NO, into the atmosphere during the combustion process. Thermal NO results from the reaction of nitrogen in the comhustion air with excess oxygen at elevated temperatures, and fuel NO., is a product of the oxidation of nitrogen chemically hound in the coal. 

Consider the combustion of ethane (C H ) in pure oxygen. If 100 lb of ethane are available and 10% excess oxygen is supplied to ensure complete combustion, calculate (1) the amount of oxygen supplied, and (2) compositions of the reactants and products on mass and molal bases. 

Figure 19.2 shows how the production of CO can vary with excess air for two typical burners. It is seen that to limit CO to, say, 50 ppm with burner B, 3 per cent oxygen in the flue is needed, and with burner A, which exhibits better mixing characteristics, only 0.75 per cent excess oxygen is required. It is also seen that the heel in the curve is more pronounced with burner A such that... 

Excess oxygen be available oxygen promotes the SO2 to SO-, reaction. SO additive will only form a metal sulfate from SO,. 

Since most of the regenerators operating in full combustion mode usually operate with 1 % to 3% excess oxygen, the capturing efficiency of SOj - additive is often greater in full combustion than in partial combustion units. 

The unit operating philosophy and its apparent operating limits often dictate unit constraints. For example, limitations on the main column bottoms temperature, the flue gas excess oxygen, and the slide valve delta P often constrain the unit feed rate and/or conversion. Unfortunately, some of these limits may no longer be applicable and should be reexamined. Some of them may have resulted from one bad experience and should not have become part of the operating procedure. 

---