Demineralization
Demineralization or deionization is the process of removing mineral salts from water by using the ion exchange process. With most natural water sources it is possible to use demineralization and produce water of a higher quality than conventional distillation. Demineralization involves two ion exchange reactions. Initially, the Cation such as calcium magnesium & sodium are removed by Hydrogen ion (H+). The salts thus converted into their respective acids by this exchange. The acidic water is then passed through an anion exchange where the anions such as sulphates chlorides etc, are removed by Hydroxyl (OH-) ions. Ion exchange is an equilibrium reaction, which is reversible. In the Hydrogen Cation exchange resins the cation group shows a greater affinity for other Cations in preference to Hydrogen ions. This is reversed when the resin bed gets exhausted of Hydrogen ions & is regenerated with a strong acid the reverse process taking place because of Hydrogen ions being present in high concentration in the regenerant acid (either HCl or H2SO4). The anion exchange resins contain active amine groups & the OH radical replaces the anions like SO4 & Cl. There are two types of anion exchange resins, namely strong basic (SBA).
The strong basic anion exchange resin is regenerated with Sodium Hydroxide (Caustic Soda) is regenerated with Sodium Carbonate (Soda Ash) or Caustic Soda, to remove suspended solids, chlorine, CO2, dissolve minerals like sulphate, chloride, nitrates of calcium, magnesium and sodium and mainly dissolve & colloidal silica . Our main aim is to produce high purity water for high pressure boilers.
The following equations will give an indication of the reaction involved during service Cycle.
DM Reaction during service:
R-H + Na+ R-Na + H + for CATION
R-OH + Cl– R-Cl + OH– for ANION
H+ + OH– = H2O
When the supply of exchangeable ions within the resin is exhausted the treated water quality deteriorates & the resin requires regeneration i.e. re-conversion into the operating form the cation exchange resins with mineral acid such as Hydrochloric Acid or Sulfuric acid. The strongly basic anion exchange resins are regenerated with Sodium Hydroxide (Caustic Soda) with either Caustic Soda or Sodium Carbonate; the processes are as below:
DM Regeneration reactions:
R-Na + H + = R-H + Na+ for Cation
R-Cl + OH– = R-OH + Cl– for Anion
Basic Water Chemistry
Raw water and Impurities
Water as it occurs in nature “pure”, and whatever be the source, always contains impurities either in solution or in suspension. The determination of these impurities makes analysis of water necessary and removal and control of these impurities make water treatment essential.
Sources
The various sources of water can be broadly classified as:
a) Rain water
b) Surface water (Rivers, Streams, Ponds, Lakes, and Reservoirs)
c) Ground water (springs, Shallow Wells and Deep Wells) Of the above, logically, rain water is the purest but even this collects and dissolves atmospheric gases. Further, once in contact with the earth’s crust, the rainwater will gradually dissolve various materials.
Impurities
The major impurities of waters can be classified in three main groups:
1) Non-ionic and undissolved
2) Ionic and Dissolved
3) Gaseous
1) Non ionic Impurities
These are mainly turbidity, salt, mud, dirt and other suspended matter; microorganisms, bacteria and other organic matter, oil and corrosion products. It goes without saying that drinking water and most industrial water supplies should be clear and organic-free.
2) Ionic and dissolved impurities
Any salt which dissolved in water solids into positively charged Cations and negatively charged Anions and since these permit the water to conduct electricity, these salts are called electrolytes. Some of the most common cations in water are Calcium, Magnesium, and Sodium and Iron rarely Ammonium Manganese. These Cations are associated with Anions like Bicarbonates, Carbonates, Hydroxides (the sum of which is termed as Alkalinity), Sulphates and Chlorides. Presence of Nitrates and Phosphates is normally not very common. In the water treatment field, the preferred method of expression of these dissolved impurities is in terms of Equivalent Calcium Carbonate, abbreviated to “as CaCO3”. This is because Calcium Carbonate is a good common denominator as it has a molecular weight of 100, which facilitates calculations. temperatures and pressures. Even in lower pressure boilers, it could form a very hard type of scale by acting as a binding agent.
3) Gaseous Impurities
Of the atmospheric gases found in naturally occurring waters, only two, Carbon Dioxide and Oxygen are the main causes of many corrosion problems.
Removal of Impurities
Our major concern is industrial water treatment, whereby, water used directly or indirectly in an industrial process is made suitable for that particular application. The use of water in boilers for steam generation is an obvious industrial use. Depending on the process, varying degrees of purity of treated water are required. For example, a textile processing unit will require soft and clear water for process use; a chemical plant or electronic components manufacturing unit will require ultra-pure water containing total dissolved impurities not exceeding 0.5mg/litre or less.
Operating Principle
A Typical two-bed Demineralised Water plant or DM Plant consists of FRP/MS Rubber lined Pressure vessels connected in series along with its internal fittings. The first unit consists of high capacity strongly acidic cation exchange resin, which converts positive ions of salt and replaces them with hydrogen ions to form respective acids, which are absorbed in next vessel by strongly basic anion exchange resin. The water obtained by this process shows conductivity less than 20 µ S / cm at 250 C and total dissolved solids less than 10 ppm.
Further high purity water can be achieved by Mixed Bed Deionisers, which are designed to produce high purity treated water. They can be used as polishing units after two bed DM Plant to obtain high purity water. Mixed Bed Deionisers are single column units, filled with strongly acidic cation and strongly basic anion exchange resins mixed together.
De-gasifiers
Degassifier unit is a part of a DM Plant In which, we offer a full range of degassers to suit the packaged /custom-made Demineralisation Plants [DM Plants]. Degassers when installed downstream of the cation unit removes the carbon dioxide, thereby reducing the load on the Anion unit. This results in cost savings by way of reduced chemical consumption. Standard units comprise of a tower in mild steel rubber lined / FRP construction along with a blower and transfer pump in stainless steel construction. Additional pump and blowers are offered as options.
Mixed Bed De-mineralisers
Mixed bed de-mineralisers are used on the downstream of the DM unit to achieve high purity levels in the treated water. We confer packaged and custom-built mixed bed de-mineralisers. These mixed bed units comprise of a single vessel with a mixture of cation and anion resins and are offered with complete service and regeneration piping, self supportive skid foundation and chemical tanks for regeneration.
Condensate Polishing
A condensate polisher is a device used to filter water condensed from steam as part of the steam cycle. Our superior condensate polishing ion exchange resins excel in capturing corrosion products in the condensate stream. This polishing typically involves ion exchange technology for the removal of trace dissolved minerals and suspended matter. It is generally used as part of a power plant’s condensate system and prevents premature chemical failure and deposition within the power cycle which would have resulted in loss of unit efficiency and possible mechanical damage to key generating equipment.
Fully Automatic Rapid Flow Two Bed DM Plants
Fluid Systems Offer Skid Mounted, PLC Controlled Two Bed Fully Automatic Rapid DM Plants incorporating state-of-the-art counter flow ion exchange technology previously available only in large, purpose-designed plant. The operational cycle of these rapid-regeneration, packaged units is controlled by volume throughput, which is pre-programmed into the PC according to the type of feed water. The ion exchange resins are never fully exhausted ensuring optimum deionised water production at all times.
Regeneration takes just 30 minutes – after a minimum service cycle of two hours – minimizing the need for both standby plant and the storage of large volumes of water. As regeneration of the cation and anion beds is simultaneous, the effluent streams are largely self-neutralising, reducing waste disposal costs and environmental impact.