Aluminum electrolysis cell.

 

The topics associated with structural analyses of electrolysis cells are quite complex, due to the contemporary presence of physical/chemical/magnetical phenomena which interact with each other and that at present are only scarcely understood.

The present researches were focused in studying the mechanical behavior of a series of cells used in the USA and Italy in the production of primary aluminum. A typical electrolysis cell is about 8 meters in length, 4 meters in width and 2 meters in height. The structure is constituted essentially by four components:

·     the potshell.

·     a series of cradles  that act as support to the potshell and as element of contrast against the lateral forces developed during the electrolysis process.

·     the refractory material or thermal lining at the inner side of walls.

·     a set of internal cathodes  that reach a steady-state temperature of about 1000°C.

 

The structural behavior in the mean and long period (the typical lifetime of a cell is four to six years) of life of a cell is dominated by the swelling of cathodes (increase of volume) which transfer of consequence considerable forces to pot walls and cradles. The internal materials are assembled in large unbound blocks. The contact among the various parts (cathodes/lining/potshell/cradles) may exhibit gaps and sliding surfaces. Potshell and cradles may work in elasto-plastic condition for almost all of lifetime.

The swelling caused by the sodium of the electrolytic bath which impregnates the cathodes starting from the external surface, is a complex function of time, temperature, current, depth and local stress state. Some materials of the thermal protection undergo a controlled crushing during the operating life of the cell. Scope of the investigation is that of better understand the structural behavior of the various components and their mutual relation in order to optimize the design and extend the lifetime of cells. In the preparation of the structural model and in the post-processing phase a large use of utility programs in Fortran and in APDL Ansys language has been made.