We have discussed about Demin Plant in the last article, still remember right? Well softener is...
Demin Plant is a process of reducing TDS content by exchanging cations in water with H+ ions and anions with OH- ions in ion exchange resin.
The following are the types of resins based on the type of ions exchanged:
- Strong Acid Cation (SAC) resin à all cations: Ca2+, Mg2+, Na+, K+, etc.
- Weak Acid Cation (WAC) machines à cation hardness related to alkalinity
- Strong Base Anion (SBA) machine à all anions: SO42-, CO32-, Cl-, SiO2, etc.
- Weak Base Anion (WBA) machines àfree mineral acids: HCl, H2SO4, HNO3
The choice of equipment in a Demin plant depends on the desired input TDS and output TDS. The simplest form consists of SAC Exchanger - SBA Exchanger. Some options that can be done to achieve the desired output TDS, are as follows:
- Adding Degassifier between SAC and SBA, if the HCO content is 3> 1 meq/l and the flowrate capacity is large, so that the SBA load is lighter
- Add WAC before SAC if weak cation content is significant
- Adding WBA before SBA if weak anion content is significant
- Add Mixed Bed Exchanger (SAC and SBA resins combined in one vessel) if the desired output TDS quality is smaller than 5 mg/l. .
So to design a good demin plant, it all starts with complete feed water analysis data, flowrate, and desired running/cycle time. Complete water analysis data is required to calculate the number of cations and anions to be exchanged, cation and anion load, resin volume, and so on.
- Cation load = Flowrate (l/h) x cycle time (h) x cation amount (meq/l)
- Anion load = Flowrate (l/h) x cycle time (h) x number of anions (meq/l)
- Operating exchange capacity of resin is usually 60-90% of total exchange capacity of resin
- Cation resin volume = Cation load / Operating exchange capacity of cation resin
- Anion resin volume = Anion load / Operating exchange capacity of anion resin
- Hydraulic loading (BV/h) = Flowrate (m3/h) / Resin volume (m3) à typical 8-40 BV/h
After saturation the resin must be regenerated to restore its ion exchange capability. Cation resins are regenerated using HCl or H2SO4, while anion resins are regenerated using NaOH. Based on the direction of regeneration flow there are 2 kinds of systems used: co-flow and counter flow. Co-flow means that the regeneration flow is in the same direction as the operating flow, while counter flow means that the regeneration flow is in the opposite direction to the flow at the time of operation.
The design of a good demin plant is based on the design of the plant.
A good demin plant design not only takes into account low manufacturing costs, but also takes into account optimal operational costs such as consumption of chemicals, electricity, labor and replacement of consumables and spare parts. For more details about this Demin Plant, please contact and discuss further with our engineering team.
Thus our article this time, hopefully useful. See you in the next article.
