Demineralizers also called ion- exchangers. Demineralizers are used in power plants which uses fluids. It is used to eliminate the impurities from fluids. This is most common method to remove impurities dissolved in a fluid. This facility increases the overall efficiency of the plant by preventing the corrosion formation and heat loss.
The demineralizers bears the ion exchange resins and also the transportation of fluid through them.

What Is Demineralizer System

Demineralizer is a cylindrical shaped system in which inlet and outlet port is attached. In the cylinder one port for resin is also connected. At the top of the cylinder the inlet port for water and at the bottom of the cylinder the outlet port is situated. There would be the retention elements to keep the resin beads in the demineralizer. The resin can be altered at bottom by the connections. To purify the water, it is forced in the inlet port at the top of the cylinder to flow through the resin beads. Appropriate flow rate should be maintained for better purification. In the flow path the purification process will be processed and the desired result in the form of purified water will come through the outlet of the tank.

There are two types of demineralizer-

1. Single-Bed demineralizer
2. Mixed bed Demineralizer

Single Bed Demineralizers

In the single-bed demineralizer both cation or anion type of resin beads can be used. In a power plant a series of two single-Bed demineralizers can be used. In the series, first cation bed and then anion bed would be placed. Hydrogen ions and hydroxyl ions are used to substitute the impurities from water. The impurities can be exchanged by hydroxyl ions in the cation bed and in the anion bed hydrogen ions are used to replace the impurities. After ion exchange these two ions will be combined mutually to form water.

Single bed Regeneration

In the single bed demineralizer regeneration process completes in three crucial steps
Initially the water is pumped from the bottom and forced to go through resin beads. This will remove any unwanted particles and. This water will be thrown out from the system from the inlet valve at the top of the cylinder. Finally water will be pumped in a vessel called waste container. This first step in the process is called backwash

The next step is about regeneration. In this step the sources of cations and anions will be used. The cation source is acid solution and anion source would be caustic solution. These ion sources will be mixed with water coming from the top. Proper ratio of water and acid or caustic solution should be maintained i.e. these solution should be diluted. This water will pass through the resin beads and drained out from cylinder to the waste container.

In the last step the water would be inserted again in the cylinder from the inlet port at the top and then flows through the resin and exit at the outlet port. This step is just to eliminate any residue particles if available in the cylinder. This last step is called rinsing.

Mixed bed Demineralizer

As the name of the system, it is mixed-bed demineralizer in which both resin beads i.e. cation and anion resin beads are mixed together. The capacity to exchange the ions with impurities in mixed-bed demineralizers is better. The mixed bed demineraliser is same as the two single bed demineralizers in series. The water produced after the process in the mixed-bed demineralizer will the more pure than the single bed demineralizers. But the process of mixed bed demineralizer is complex.

Mixed bed regeneration

Mixed bed regeneration process is complicated than the single bed demineralizer.
Same as the single bed demineralizers, in the mixed bed demineralizer backwash is the first step of the process. The water enters from the bottom and drained out from the top of the cylinder to washout the foreign substances.

The second step is known as regeneration step in which caustic solution would be mixed with the water and bring at the top of the cylinder. Below that the anion bed would be placed. In the same way the acid solution would be bring at the bottom of the cylinder and the cation bed would be placed above the entrance of the acid solution. The flow rate of these solution would be maintained same. These solution should be drained out after the successful use of the solution. If the system is exposed to the radioactive substances then the wastes should also be treated as radioactive waste.

After regeneration, the rinsing would be the further step. In which the water is to be introduced in the vessel. In the mixed bed ion exchanger, the rinsing is a two way process so the water would be introduced from both ends of the vessel and any residual impurity would be eliminated.

What is Cation Exchange resin

What is Anion Exchange Resin