Transfer of Brine

Pumping. Pumpingofbrineisastraightforwardoperation. As noted above, the corrosivity is not high, and brine is essentially an iimocuous fluid. Density and viscosity are higher than those of water, and so power requirements are greater than in water service. These are not huge effects and do not complicate the basic simplicity of brine 

Many different materials of construction are used. More resistant materials and those less likely to contaminate the brine are called for as pH drops, aeration increases, or the application moves closer to the cells. The most basic combination may be ductile iron casings with cast iron impellers. For in-plant service, the impellers may be upgraded to Monel. Where higher resistance is desired, high-chromium alloys (25-5 steels) appear. An example of this type is CD4MCu (27-30% Cr, 3-6% Ni, 0.04% C, 2% Mo + Cu). The ultimate metal, used firequently for pure brine feed and almost exclusively for acidified depleted brine, is titanium. Rubber-lined pumps also appear and, in the smaller sizes, FRP. 

Most designers recommend double mechanical seals, usually unbalanced. Clear water is the best flushing liquid, because there is a possibility of crystallization from concentrated brine within the gland. Seal water may enter the process through the pump seals, and its quality should be chosen with that in mind. The purity of water required depends on the location of a pump within the process. In a membrane-cell plant, only the best grade of water should be used after the ion-exchange step. 

The same constructions are used for cooling brine. This occurs sometimes within the process and sometimes before long-distance transfer of brine for resaturation. In the latter case, cooling may be by interchange, this time with brine returned from the resaturation process. 

In membrane-cell plants, some of the waste heat generated on the cathode side of the cells is often removed by interchanging the circulating caustic with brine. This application favors plate exchangers. With the temperatures involved and the different demands on the two sides of a plate, it is an exacting service, and Hastelloy C or a similarly resistant alloy is required. 

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Pipelines. This section deals only with off-site pipelines used for the longdistance transfer of brine. Some pipelines, especially among the older ones, are cast iron. Newer lines are more frequently carbon steel or even a resistant plastic. 

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