Ion exchange demineralization

Acid regenerant infiltration (e.g., H2S04, HC1) from the regeneration of ion-exchange demineralization plant. 

The most widely used techniques for removing dissolved inorganic solids are boiling, addition of washing soda, lime-soda softening, complexation, sodium ion exchange, demineralization, reverse osmosis, electrodialysis, adsorption onto suspended solids, and aeration. 

The two basic deionizer configurations are the two-bed and mixed-bed. Two-bed deionizers have separate vessels for the cation and anion resins. In mixed-bed deionizers, the anion and cation resins are blended in a single vessel. Generally, mixed-bed systems produce higher-quahty water but have a lower total capacity compared with two-bed systems. Figures 3 and 4 are schematics of typical ion exchange demineralization processes. 

One of the most innovative industrial uses of reverse osmosis is at the Petromin Refinery in Riyadh, Saudi Arabia. The refinery takes an unusable municipal wastewater, secondary effluent from the Riyadh sewage treatment plant, and by using lime clarification, filtration, reverse osmosis and ion exchange demineralization, it converts that useless waste into the entire process water requirements for the refinery. Figure 4.16 is the process flow schematic for the refinery water treatment plant. 

Reverse osmosis also has been used to treat municipal water supplies for industrial purposes even though these supplies are generally low in turbidity, suspended solids and dissolved solids. A large number of reverse osmosis systems have been installed in industrial plants to prepare industrial process water with municipal water as the feed source. A significant number of these industrial applications are to either replace ion exchange demineralization or to pretreat municipal supplies prior to ion exchange demineralization. 

Two substances that are frequently of concern in ion exchange demineralization are silica and organics. The organics are frequently present in natural waters as aromatic polycarboxylic acid derivatives known as humic and fulvic acids. Silica may be the limiting factor in the efficiency of the anionic resins, and (particularly in boiler feedwater applications) the lower the concentration before ion exchange demineralization, the better. Reverse osmosis will frequently produce 90% or greater reductions in total silica concentrations. However, performance should be tested on the specific water to be treated since trie results can be variable and the reason for differences between waters is not yet understood. 

Research on specific distillation problems at the Israel Institute of Technology is in its first stages and is not reported here. This work deals with heat transfer in flash distillation units with particular reference to annuli. Older work on solar distillation and ion exchange demineralization of moderately brackish waters was done at the Weizmann Institute of Science (14). 

Use of RO for desalination of seawater for boiler makeup is a typical aj lkation. The availability of diis system has opened up die use of heretofore unavailable water siqiplies, and it has been used by the industry as a pretreatment to ion exchange demineralization. RO acts as an economical rou iing demineralizer, bringing down the overall cost and improving the life of resins and operation of the ion exchange equipment. 

The 163-N facility (Figure 3-17) produced high-quality, demineralized makeup water from filtered river water for the major coolant systems of the N Reactor. Demineralized water has virtually all dissolved and suspended matter removed by ion exchange. Demineralized water was used to prevent mineral deposits that would foul piping systems and to limit the generation of radioactive waste through neutron activation of dissolved and suspended matter (DOE-RL 1990). 

In this method, the measurement of conductance was used to evaluate the total concentration of the dissolved minerals within the raw and treated water or to determine the degree of demineralization of distandard and deionized water. The work presents an expedient conductometric method for assessing Si02 concentration in high-purity water obtained by ion-exchange demineralization. This method can be used for continuous measurements required by accurate kinetic and thermodynamic studies and monitoring automated systems within industrial facilities. 

For such reasons, the dissolved solids content of the water must be kept as close as possible to zero. A large fraction of the water is continuously cleaned up in a bypass circuit containing ion exchange (demineralizer) beds. At start-up, 100 percent of the water may be passed through the cleanup beds. Chlorides and caustic are the most undesirable salts because they are known to cause SCC of the austenitic stainless steels. Dissolved oxygen may be reduced by the methods described previously to a few parts per billion. 

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