Once-through burning

To complete the broad picture of what is meant by burn-out, it is useful to consider further the particular burn-out condition which produces tolerable wall temperatures. Such a condition must occur, for example, in any practical, once-through boiler system, where a change from, for example, liquid water at inlet to superheated steam at outlet takes place in a single heated channel. Normal operation of nuclear reactors beyond burn-out has also been contemplated, and Collier et al. (C5) have described successful experiments with irradiated Zircaloy-clad rods operating continuously beyond burn-out... 

The UT-Austin experimental tests have shown that high (98+ %) carbon combustion efficiency is possible in a fluidized bed combustor burning Texas lignite and operating on a once-through basis. Future tests incorporating recycle of elutriated material will be performed to determine the extent to which this increases carbon efficiency. 

These facts have led to the review and finally the development of an alternative approach and in particular the possibilities of recovering vanadium for metallurgical use. Figure 100 illustrates the principles of the soot ash removal unit. The carbon slurry from the SGP unit is flashed to atmospheric pressure in the slurry tank (a). The slurry is then filtered on an automatic filter (b) to recover a filter cake with about 80% residual moisture and a clear water filtrate. The filter cake is subjected to a controlled oxidation process in a multiple-hearth furnace (c). This type of furnace, which is well established in many industries and specifically in the vanadium industry, allows combustion of the carbon to occur under conditions where the vanadium oxides neither melt nor corrode. This is not an easy task if one considers the problems of burning a high-vanadium fuel oil in a conventional boiler. The product is a vanadium concentrate, which contains about 75% V2O5. Compared to the old naphtha extraction-based recycle system, the new once-through process consists of only two proces-... 

The plutonium cannot be completely burned in a once-through cycle because of fuel burnup limits and the statistical improbability of all plutonium being struck by a neutron. However, with the right fuel choice perhaps 70-95% can be burned. The remaining 5-30% could then be extracted via reprocessing and returned to a reactor. Thus, a fraction of the entire plutonium stockpile could be burned in one concept in a couple of... 

Figure 16.16 is a sketch of a once-through Claus process using a hot gas bypass for reheat. Sufficient air is used to burn one-third of the H2S and all hydrocarbons. Steam usually is generated in the waste heat boiler, where the combustion products are cooled, and sulfur is condensed. The gas must be heated before introduction to the reactor to prevent sulfur condensation in the reactor... 

Fluidized combustion of coal entails the burning of coal particles in a hot fluidized bed of noncombustible particles, usually a mixture of ash and limestone. Once the coal is fed into the bed it is rapidly dispersed throughout the bed as it bums. The bed temperature is controUed by means of heat exchanger tubes. Elutriation is responsible for the removal of the smallest soHd particles and the larger soHd particles are removed through bed drain pipes. To increase combustion efficiency the particles elutriated from the bed are coUected in a cyclone and are either re-injected into the main bed or burned in a separate bed operated at lower fluidizing velocity and higher temperature. 

An explosion may occur if the filament is heated while a3l appreciable amount of air is still present. Furthermore, the heating element will burn out at once if an adequate supply of cyclohexene vapor is not supplied, since the current passing through the wire is far above the normal rating for air. 

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