Reduction zone

SL/RN Process. In the SL/RN process (Fig. 4), sized iron ore, coal, and dolomite are fed to the rotary kiln wherein the coal is gasified and the iron ore is reduced. The endothermic heat of reduction and the sensible energy that is required to heat the reactants is provided by combustion of volatiles and carbon monoxide leaving the bed with air introduced into the free space above the bed. The temperature profile in the kiln is controlled by radial air ports in the preheat zone and axial air ports in the reduction zone. Part of the coal is injected through the centerline of the kiln at the discharge end. The hot reduced iron and char is discharged into an indirect rotary dmm cooler. The cooled product is screened and magnetically separated to remove char and ash. 

Many hazardous waste activity worksites are temporary and are established at remote locations with limited sanitation facilities. Decontamination is conducted either in the contamination reduction zone or the radiological buffer zone, whereas sanitation functions are performed either in the support zone or outside the boundaries of the hazardous waste activities worksite after decontamination has been completed. 

Site H was the only site at which the contractor had implemented comprehensive and effective site control elements. The Site H contractor had established site work zones, a buddy system, and site communication procedures consistent with 1910.120(d). This contractor had also established exclusion zones and contamination reduction zones to control migration of site contaminants to clean areas of the site when work within these areas introduced the potential for exposure to hazardous contaminants. The audit team supported this contractor s use of flexible and temporary work zone boundaries based on monitoring results and hazard determinations. 

Forty-hour training was required for personnel entering the exclusion zone, and additional supervisory training was required for site supervisors. Site control procedures described in the Site C contractor s SSAHP included maintenance of site control logs at each access point, use of red tape or chainlink fencing to demarcate hot zones, and use of the buddy system in all exclusion and contamination reduction zone areas. Site communications relied almost exclusively on visual sighting of employees the plan did not describe the use of two-way radios. This suggested that all employees in hot zones can be observed continuously from the support zones. 

Signiflcant deficiencies in site control procedures existed at Site K. For example, the Site K subcontractor had not established a contamination reduction zone (CRZ), to physically separate the support zone from the exclusion zone, as required in the site plan. 

Subcontractor may perform limited site work (e.g., nonroutine tasks such as surveying, etc.) but may not work in exchision/contamination reduction zones if he meets the following requirements ... 

Contamination reduction zone (CRZ). This is the area where decontamination takes place. 

Contamination Control Line The established line around a contamination reduction zone that separates it from the support zone. 

Finally, another possibility often discussed in the literature is that cation dopants from the electrode may enhance the electronic conductivity of the gas-exposed surface of the electrolyte in the vicinity of the TPB, thereby extending the reduction zone along the electrolyte surface via mixed conduction. The surface exchange rate of oxygen on both YSZ- and rare-earth-doped ceria (as measured by isotope methods) is only about 1 order of magnitude lower than on LSM at 700 Thus, if there were sufficient... 

AGbo > [ AGa0, almost pure metal A is precipitated in the internal reduction zone. The reaction at the front is induced by a point defect flux which stems from the difference in oxygen potentials (point defect concentration) between the internal reaction front and the external surface. The reaction front and surface act as source and sink for the point defect flux. For example, when we assume that (A,B)0 contains transition-metal ions (e.g., (Ni,Mg)0), the defects are cation vacancies and compensating electron holes. The (reducing) external surface acts as a vacancy sink according to the reaction... 

The profile of Mg2+ in Figure 8.25 indicates downward diffusion of this constituent into the sediments. Mass balance calculations show that sufficient Mg2+ can diffuse into the sediments to account for the mass of organogenic dolomite formed in DSDP sediments (Baker and Bums, 1985 Compton and Siever, 1986). In areas of slow sedimentation rates, the diffusive flux of Mg2+ is high, and the pore waters have long residence times. Dolomites form under these conditions in the zone of sulfate reduction, are depleted in 13c, and have low trace element contents. With more rapid sedimentation rates, shallowly-buried sediments have shorter residence times, and dolomites with depleted 13C formed in the sulfate-reduction zone pass quickly into the underlying zone of methanogenesis. In this zone the DIC is enriched in 13C because of the overall reaction... 

The iron oxide circulates between oxidation and reduction zones. The following reactions are typical, of those occurring in the steam-iron reactor section at temperatures in the 1500° to 1600°F range. 

Administer invasive procedures in the Contamination Reduction Zone (on-scene) or Warm Zone (hospital setting) only when it is absoiuteiy necessary. 

The S04 concentration in sediments affects S04 reduction only when concentrations are quite low. The reduction of SOl in marine sediments appears to be zero-order with respect to S04 to concentrations of 2 mM (Boudreau and Westrich, 1984 Goldhaber and Kaplan, 1974). In freshwaters, SO concentrations must be much lower before they limit SO reduction (Bak and Pfennig, 1991 Lovley and Klug, 1983b Sinke et al., 1992). Because freshwater contains very little sot compared to seawater, the importance of SO4 reduction in sediments increases in an estuary as the salinity increases (Capone and Kiene, 1988). Therefore, the vertical extent of the SO4 reduction zone increases substantially as more SO4 becomes available, while the metha-nogenic zone is pushed deeper into the sediment and its contribution to carbon mineralization decreases in importance. 

Anderson R. T., Rooney-Varga J. N., Gaw C. V., and Eovley D. R. (1998) Anaerobic benzene oxidation in the Ee(lll) reduction zone of petroleum-contaminated aquifers. Environ. Set Technol. 32, 1222-1229. 

In the char reduction zone, the pyrolysed pellets are partially transformed to gases through the gasification reactions. The remaining pellets (inert char) and the ashes leave the bed through the grate. This can be expressed as ... 

If the pyrolysis rate is higher than the char consumption, then the pyrolysis front moves up (v/rei O) and the length of the char reduction zone increases If this is the case, the flaming pyrolysis front will climb indefinitely until it reaches the top of the bed and the drying zone almost disappears, Although such operation mode is stable, the radiation from the top of such bed is a significant heat loss. This operation mode is called Top stabilisation mode" and has been modelled by Di Blasi . 

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