many advantages of this cell the following were cited: [11 reduction of operating cell voltage (5.0 vs 6.3 V); [2] reduction of energy consumption from 18.5 to 13.2 kWh/kg (8.4 to 6.0 kWh/lb) of magnesium; and [3] reduction of graphite anode consumption to a very low level. Although it has not been divulged by Dow, there is a very high probability that this cell or a modern and improved version of it is being used in this advanced production process. A major-size pilot plant based on this process is scheduled for construction in 1980 and the process should be available for full scale production plants later in the decade of the 1980’s. The figure of 38.9 x 10® kcal/Mton (140 x 10® Btu/Ston) Mg is drastically lower than for any of the processes discussed and some estimates are useful in determining whether it is in fact possible. A five-volt cell, as described above, operating at 90% current efficiency, with 10% power conversion loss will require 13,602 kWh/Mton (12,340 kWh/Ston) Mg or 36.1 x 10fi kcal/Mton (130 x 10® Btu/Ston) Mg at the power plant: Five volts is still substantially above the theoretical potential of 3.1 V, leaving room for further improvements. Preparation of an anhydrous feed requires 31.05 x 10® kcal/Mton (111.77 x 10® Btu/Ston) Mg. However, this might be reduced by dehydration in an HC1 atmosphere (Norsk Hydro) to 28 x 10® kcal/Mton (100 x 10® Btu/Ston) Mg. If 2.9 kg chlorine can be credited per kg Mg, the total credit is 16.7 x 10® kcal/Mton (60 x 106 Btu/Ston Mg). Thus, the total energy consumption can be estimated as A lower overall energy use than this would require further reduction in energy for feed preparation and/or electrolysis. Plans have been presented on how energy consumption will be reduced in the Magnetherm process. During the next four years the consumption of all materials is expected to be reduced by no less than 10% and the yield of magnesium increased by reducing losses in the condensation stage and in the melting and refining. Beyond that, and over the next 10 to 12 years, they plan to introduce more energy-efficient ferrosilicon production furnaces, to improve the dolomite and bauxite calcination stage and to build larger and more efficient reduction furnaces. There is no question that the Magnetherm process does hold promise and that the major improvements anticipated by Dow in the bitterns process will need to be made to compete with it in energy consumption. In summary, it can be stated that the producers of primary magnesium are aggressively seeking improvements in the process for producing primary magnesium. A major portion of available research funds are committed to lowering the total energy required to produce magnesium. However, the impetus for development has been and will be economic. Energy plays a more dominant role in development now than previously because of its increasing cost. Cell Design Traditional electrolytic cells have been designed using electrolytes heavier than the molten magnesium. Thus, both chlorine and magnesium rise concurrently to the top of the cell. In addition, the Dow cell consumes graphite at a sufficient rate to require adjustment or feeding of the electrode into the cell. This requirement has made it difficult or impossible to collect chlorine and perhaps contributed also to lowering cell efficiency through recombination of chlorine and magnesium in the
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