Air feeding

The U.S. production of argon is summarized in Table 5. Because argon is a by-product of air separation, its production is ca 1% that of air feed. Total 1988 United States consumption of neon, krypton, and xenon was 36,400, 6,800, and 1,200 m, respectively (88). 

Cycle Diluents. Air process technology uses nitrogen as the diluent gas. The amount of nitrogen that enters the process in the air feed caimot be economically diluted (97). 

We have screened 18 compoimds in single contaminant air feeds, and co-fed in air with TCE [3]. For each run, the initial inlet concentration is first measvired. Then, we allow a dark period during which the contaminated air feed passes... 

Figure 55.4 compares the Raman spectra of the two samples spectra were recorded at 380°C in a 15% O2/N2 stream, on equilibrated catalysts downloaded after reaction. Catalyst VN 1.06 was not oxidized in the air stream, whereas in the case of catalyst PA 1.00 bands typical of a phosphate, ai-VOP04, appeared in the spectrum. These bands were not present in the spectmm of the equilibrated catalyst recorded at room temperature. Indeed, the spectra of the two equilibrated catalysts were quite similar when recorded at room temperature. This result confirms that the surface of catalyst VN 1.06 is less oxidizable than that of catalyst PA 1.00. Therefore, the latter is likely more oxidized than the former one under reaction conditions. A treatment in a more oxidant atmosphere than the reactive n-butane/air feed modifies the surface of catalyst VN 1.06, and leads to the unsteady behavior shown in Figure 55.1. The same treatment did not alter the surface of the equihbrated catalyst P/V 1.00 that was already in an oxidized state under reaction conditions.

Fig. 3. Time variation of the catalyst bed temperature and the relative S03 signal in the stream leaving the cycled bed for composition forcing of the final stage of a S02 converter with an air stream and effluent from the previous stage (a) half cycle with air feed, (b) half cycle with S03/S02 feed. Feed to the system contains 12.4 vol% S02, conversion in the first stage = 90% and t = 26 min, s = 0.5. (Figure adapted from Briggs etal., 1977, with permission, 1977 Elsevier Science Publishers.)...

Component feed vapour air air feed outlet outlet gas acid air feed gas feed acid acid ... 

Component Feed Vapour Air Air Feed Outlet Outlet Gas Acid Air Feed Gas Feed Acid Acid... 

Fig. 6. Polarization of the oxygen separator. Air cathode area = 10 cm2 water temperature = 40 °C air feed = 4 dm3/min.

S02 feed rate = 0.0475 g mole/min Air feed rate = 0.681 g mole/min Reaction rate = 0.0940 g mole S03 produced/ (hr-g catalyst)... 

The fuel cell Rankine cycle arrangement has been selected so that all fuel preheating and reforming are carried out external to the cell and air preheating is accomplished by mixing with recycled depleted air. The air feed flow is adjusted so that no heat transfer is required in the cell or from the recycled air. Consequently, the internal fuel cell structure is greatly simplified, and the requirement for a heat exchanger in the recycle air stream is eliminated. 

If a 25% utilization is required, then the air feed must contain four times the oxygen that is consumed. 

The results show that, at temperatures below 60 °C and an air feed stoichiometry below three, the cathode exhaust is fully saturated (nearly fully saturated at 60 °C) with water vapor and the exhaust remains saturated after passing through a condenser at a lower temperature. In order to maintain water balance, all of the liquid water and part of the water vapor in the cathode exhaust have to be recovered and returned to the anode side before the cathode exhaust is released to the atmosphere. Because of the low efficiency of a condenser operated with a small temperature gradient between the stack and the environment, a DMFC stack for portable power applications is preferably operated at a low air feed stoichiometry in order to maximize the efficiency of the balance of plant and thus the energy conversion efficiency for the complete DMFC power system. Thermal balance under given operating conditions was calculated here based on the demonstrated stack performance, mass balance and the amount of waste heat to be rejected. 

Water Balance, Maximum Air Feed Rate and Implications for Cathode Performance... 

Figure 2.4 Amount of water vapor in the air cathode exhaust at cathode exit point of an operating DMFC stack as a function of stack operating temperature and air feed actual stoichiometry.

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