Miscellaneous Mechanical Components
The important information in this chapter is summarized below.
Demineralization of water is one of the most practical and common
methods used to remove dissolved contaminates. Dissolved impurities
in power plant fluid systems can generate corrosion problems and
decrease efficiency due to fouled heat transfer surfaces. Demineralizers
(also called ion-exchangers) are used to hold ion exchange resins and
transport water through them. Ion exchangers are generally classified
into two groups: single-bed ion exchangers and mixed-bed ion
A demineralizer is basically a cylindrical tank with connections at the
top for water inlet and resin addition, and connections at the bottom for
the water outlet. The resin can usually be changed out through a
connection at the bottom of the tank. The resin beads are kept in the
demineralizer by upper and lower retention elements, which are strainers
with a mesh size smaller then the resin beads.
The water to be purified enters the top at a set flow rate, flows down
through the resin beads where the flow path causes a physical filter
effect as well as a chemical ion exchange. The chemistry of the resin
exchange is explained in detail in the Chemistry Fundamentals
There are two types of demineralizers, single-bed and mixed-bed.
Single-bed demineralizers have resin of either cation or anion exchange
sites. Mixed-bed demineralizers contain both anion and cation resin.
All demineralizers will eventually be exhausted from use. To
regenerate the resin and increase the demineralizer's efficiency, the
demineralizers are regenerated. The regeneration process is slightly
different for a mixed-bed demineralizer compared to the single-bed
demineralizer. Both methods were explained in this chapter.