Of spent melt

Direct Zinc Chloride Hydrocracking of Sub-bituminous Coal and Regeneration of Spent Melt... 

A substantial program was also previously conducted in a batch autoclave unit on the direct hydrocracking of bituminous coal (1) with zinc chloride melts, but no work was done in either batch or continuous units on regeneration of spent melts from direct hydrocracking of coal. 

Various procedures for regeneration of spent melts from metal halide hydrocracking were proposed by Kiovsky and Petzny (14, 15) and by Loth and Wald (16). A number of regeneration procedures were also discussed previously in detail (2). 

The fluid-bed combustion method (2) has been chosen, however, for process development in the regeneration of spent melts from the hydrocracking of coal. In this method, from one to two parts by weight of spent melt is generated for each part of coal fed to the hydrocracking process. The carbonaceous residue, sulfur, and ammonia retained in the melt are burned out with air in a fluidized bed of inert solids. The zinc chloride is simultaneously vaporized, the ash separated from the overhead vapors, and the zinc chloride vapor is condensed as pure liquid for return to the process. 

Molten salt is a technique that has been considered for the destruction of pesticides and other hazardous wastes for several years. In a recent study by Rockwell International for EPA (1 ), the destruction of solid hexachlorobenzene (HCB) and liquid chlordane exceeded 99.99% in a molten sodium carbonate bath at 900 to 1000°C with a residence time of 0.75 s. For the pilot-scale tests, the concentration of HCB and chlordane in the spent melt was < 1 ppm. The HCl concentration in the off-gas was < 100 ppm. 

Polymer immobilization The polymers used in the immobilization of spent materials can be classified into two main categories thermoplastic and thermosetting polymers. The first type is fed in the form of a solid, and then melts upon heating and combines with the waste. On the other hand, thermosetting polymers are supplied in a liquid form and are then polymerized to a solid form, combining with the waste upon heating or in the presence of catalysts. 

The present paper presents batch autoclave data on the direct hydrocracking of a single sub-bituminous coal from the Powder River basin of southeastern Montana. Comparative data were also obtained with the Pittsburgh Seam bituminous coal that was used in the previous work (I). Data on the regeneration of simulated spent melts from such an operation are also given in a continuous bench-scale, fluidized-bed combustion unit. 

The melt used in this work was prepared from the residue of hydrogen-donor extraction of Colstrip coal with tetralin solvent in such a way as to simulate the composition of an actual spent melt. The extraction was conducted in the continuous bench-scale unit previously described (17) at 412°C and 50 min residence time. The residue used was the solvent-free underflow from continuous settling (17) of the extractor effluent. The residue was then precarbonized to 675°C in a muffle furnace. The melts were blended to simulate the composition of a spent melt from the direct hydrocracking of the Colstrip coal by blending together in a melt pot zinc chloride, zinc sulfide, and ammonium chloride, ammonia, and the carbonized residue in appropriate proportions. Analysis of the feed melt used in this work is given in Table I. 

Operation at these mild conditions is of interest where the objective is to produce low sulfur fuel oil in major amounts as a coproduct with gasoline. Previous work showed that 65-80% of the MEK solubles may be recovered from the spent melt by extraction with a fraction of the distillate oil product. The data of Table III, interestingly enough, show that the MEK soluble oil contains less than 0.2 wt % sulfur even when the high sulfur Pittsburgh Seam coal is used as feedstock. 

Fig. 3.25. Heat flux histories following an ELM of 1MJ/m2 with a power flux triangular waveform (curve 1) with ramp-up and ramp-down phases lasting 300 ds each on a 10mm thick W target under an inter-ELM power flux of 10MWm 2. Curves. (1) incident heat flux load (2) conducted heat flux into the material (3) heat flux spent in melting of the material (the evaporation and black-body radiation heat fluxes are comparatively small and not shown). Curve (4) shows the surface target temperature and (5) shows the temperature of the melt layer. Curve (6) shows the vaporized thickness (amplified of a factor of 1000) and (7) the melt layer assuming that no losses of molten material occur during the ELM [3]...

The COt Acceptor Gasification Process is discussed in light of the required properties of the CaO acceptor. Equilibrium data for reactions involving the CO% and sulfur acceptance and for sulfur rejection jit the process requirements. The kinetics of the reactions are also sufficiently rapid. Phase equilibrium data in the binary systems CaO-Ca(OH)t and Ca(OH)jr-CaCOs show the presence of low melting eutectics, which establish operability limits for the process. Data were obtained in a continuous unit which duplicates process conditions which show adequate acceptor life. Physical strength of many acceptors is adequate, and life is limited by chemical deactivation. Contrary to earlier findings both limestones and dolomites are equally usable in the process. Melts in the Ca(OH)2-CaC03 system are used to reactivate spent acceptors. 

Figure 3.55 shows the plots of the times to reach maximum crystallization rate and the maximum crystallization rate, d /dr, as a function of the melting temperature. Both plots show that, at higher melting temperatures, the resulting rate of crystallization is diminished, with the implication that crystal nuclei are destroyed. As seen, under none of the conditions utilized did the overall rate of crystallization of the samples under high stress reduce to those observed for the samples under low stress. Jaffe also found that the time spent in the melt had an effect similar to the melt-temperature level. As the melt time increases, crystallization kinetics slow down. 

In the non-aqueous reprocessing process of spent nuclear fuels by pyrometallurgical and electrowinning methods [1, 2], a spent fuel is dissolved into molten LiCl-KCl or NaCl-CsCI eutectic melt and dissolved uranium and plutonium ions are recovered as metal or oxide. 

Volkovich, VA., Griffiths, T.R., and Thied, R.C. (2003) Treatment of molten salt wastes by phosphate precipitation removal of fission product elements after pyrochemical reprocessing of spent nuclear fuels in chloride melts. J. Nucl. Mater, 323(1), 49-56. 

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