THE VACUUM PAN PROCESS

An appreciable amount of Canada's salt is produced by the vacuum pan process. It yields a very high purity salt, fine in texture, and is principally used in those applications where quality is of first importance.

However, through compaction, and crushing, coarse products are produced and thus evaporated salt can be used in any salt application. Vacuum pan production of salt is a very sophisticated process. To the uninitiated it sounds quite simple but it embodies techniques developed from many branches of engineering and science.It involves a knowledge of mining, hydraulics, crystallography, chemistry, electricity, structures, materials of construction and steam generation, evaporation, filtering, drying, crushing, screening and other specific specialties. Basically, the process involves drilling a hole to the salt deposit, which may be at depths of a few hundred to a few thousand feet. This hole is then cased with steel piping to the top of the deposit and a pipe is lowered through the casing to the bottom of the deposit, thus creating a deep well with two fluid passages.

Water is pumped down to the deposit where it dissolves the salt, forming brine, which is then pumped to the surface. The flow can be either down the pipe and up the annulus or down the annulus and up the tubing. This system affords control over the shape of the cavity which control may be required for either extraction purposes or structural reasons.

When the brine is pumped to the surface it is placed in large tanks and chemically treated to prepare it for the evaporation process.

The brine is evaporated in large vessels, called vacuum pans in the salt industry. These evaporators are normally in a line of three, four, or five and each one in the line is under higher vacuum than the preceding one, which means that brine in each pan boils at a lower temperature than its preceding one.

Steam is admitted to the first evaporator, boiling the brine and creating more steam which boils the brine in the second evaporator, and so on.