Target excess oxygen

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

Permanently mounted oxygen recorder Oxygen recorder with remote manual 4.5 5.0 

In an operating plant, the air rate can be adjusted at fixed heat output (constant steam rate for a boiler) until minimum fuel rate is achieved. This is the optimum so long as the warnings below are heeded. 

Reference 3 speaks of controlling the excess air at 10% for plants having highly variable fuel supplies by using gas density to control air/fuel ratio. Reference 3 gives the following equations relating theoretical air and density. 

Equation (1), die fuel gas equation, does not hold for unsaturated hydrocarbons, but for small percentages of unsaturates the error is not serious. 

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Operating a process heater simply to achieve a minimum excess oxygen target in the flue gas can waste a great deal of energy. The proper way to adjust O2 to a heater is to target for the point of absolute combustion, as shown in Figure 15-5. The point of absolute combustion is defined as that air rate that maximizes heat recovery to the process. That is, either a decrease or an increase in the combustion air supply will reduce heat absorbed in the heater. 

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine production), copper-zinc superoxide dismutase (free radical detoxification), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+2) to cuprous (Cu+1) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+2 in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical O2, which induces lipoperoxidation (Aaseth and Norseth 1986). 

For growth under an excess of oxygen, an increase of the reactive gas partial pressure leads to a reduction in the deposition rate, which is independent of the substrate temperature. This results from the oxidization of the target, since the metallic particle current density j(Zn) is reduced by the low sputtering yield of the oxidized target. 

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