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Origin of Parasitic Currents

The simplest explanation for shunt currents is that the electrolytes in the manifolds, or the manifolds themselves if they are metallic, provide parallel paths to the current flowing in the cells. Thus, with few exceptions, some shunt currents will flow in the connecting piping of bipolar cell stacks. As shown in Fig. 5.5 A, the distribution of shunt [Pg.391]

FIGURE 5.5. A. Schematic of the current flow in bipolar electrolyzer. B. Schematic of the distribution of leakage current and manifold current in a bipolar electrolyzer. [Pg.392]

It must be emphasized that this symmetiy exists over all cells connected in series between the negative and positive poles of the rectifier, not just the cells in a single electrolyzer. Thus, if two bipolar electrolyzers are connected in series in a single DC circuit, the bipolar unit cells with the lowest current will typically be those located near the center of the DC circuit, not those cells at the center of the two electrolyzers. Likewise, if each half of a single electrolyzer is connected in a parallel DC circuit, then the bipolar unit cells with the lowest current will be those located in the center of each half of the electrolyzer, not the ones located in the centers of the electrolyzers. It should be mentioned that leakage currents are also present in monopolar cell circuits. However, their magnitude is very small. [Pg.393]

The typical problems associated with shunt currents include  [Pg.393]

Not all the shunt current returns to the electrolyzer. Some leaks from the system and does not take part in electrolysis. Since the production rate depends on the current supplied, there is a production loss caused by shunt currents. In order to accurately determine current efficiency, the actual current received by each cell in the circuit needs to be known. One of the uses of shunt current models, discussed in the next section, is the estimation of the shunt currents as well as the current in each cell. For well-designed chlor-alkali plants, the shunt current loss will usually be less than 2% and frequently less than 1%. The shunt currents that bypass the center cells do no useful electrolysis, but wiU cause IR heating of the electrolytes. For production of molten metals, where shunt cinrent loss could be much higher than 2% because of the high conductivity, such IR heating could be of some benefit, but the economic trade-off between the choice of bipolar and monopolar cells for such an application needs to be carefully considered [8]. [Pg.393]


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