Electrolyzer Technologies General

All membrane electrolyzers have common general design features such as vertical arrangement of membranes, stacked elements, and usage of similar materials of construction. Nevertheless, there are quite substantial differences in the cell design. 

As membrane development allows increasing current densities, electrolyzer internals have to meet the related effects. Essential design targets are the minimization of 

Structural voltage losses, homogenization of electrolyte concentration and temperature, and measures to counter problems related to the increased gas evolution. 

All the technology cell suppliers claim that their cells can operate at current densities greater than 5 kA m with an energy consumption of 2,000-2,100 kW hr ton of caustic at 5 kA m . They also claim that their designs have addressed and solved many of the problems observed during their operation. Details are in their publications and promotional literature. 

The key component of a membrane cell is the ion-exchange membrane, which determines the performance characteristics of the ceU, reckoned in terms of cell voltage, current efficiency, product purity, and the active life of the cell. The ion-exchange membrane operates best if it maintains its dimensional and structural integrity in the cell during startup, shutdown, and operation. It is essential that the membrane is fully stretched in the cell without any folds or wrinkles and is not subjected to physical wear or fluttering. Furthermore, the entire surface of the membrane should be exposed to a constant flux of sodium ions and water molecules during operation. 

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Two cases were examined for the production of water electrolysis. Data were taken from Reference (1) and adjusted to mid-1979 levels in accordance with Table 1. The costs of "current technology" electrolysis were averaged in Reference (1) from information provided by Lurgi, Electrolyser Corp., General Electric, and Teledyne Isotopes. An advanced electrolyzer design, based upon the General Electric Solid Polymer Electrolyte (SPE) design, was also addressed as the second case. 

Detailed shutdown procedures vary significantly among technologies. The above should be considered general principles, and the procedures recommended by electrolyzer suppliers should be followed carefully. Some of the differences in procedures are worth highlighting here ... 

We mentioned in Section 1.3 some important industrial applications of electrolysis—in the chloralkali industry, metal winning and refining, and organic electrosynthesis. As indicated in Section 1.2, we do not intend to describe electrochemical processes in detail, since there are many books on electrochemical technology. We will discuss the design of individual reactors, with emphasis on modularized, general purpose flow electrolyzers. We will classify reactors by their mode of operation. 

Electrolyzers and fuel cells generally do not perform well in the reverse mode to that for which they have been optimized, with the probable exception of SO technology (Figure 2.22). Thus, to cany out a local function of storage and release of electrical energy, it will also generally be necessary to combine a fuel cell... 

In the case of low-temperature technologies, both modes of operation are exothermic, and it is therefore possible to wonder abont how to make profitable nse of the produced by electrical and/or thermal cogeneration, which noticeably complexifies the system. In the case of high temperature technologies, it can be envisaged to store the heat lost in fuel cell mode and exploit it in electrolyzer mode, which is generally endothermic. 

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