Choose Right Water Dealkalization Method for Your System

Water dealkization is important and is the pre-treatment for boiler. It can remove carbonate alkalinity in the feed water before it reaches the boiler. In boiled water, the first limit chemistry parameter is alkalinity. Through reducing alkalinity, it can help to decrease blowdown volumes, increase the concentration cycles and decrease energy consumption. Here we will introduce the alkalinity and why we need to reduce alkalinity and how to produce dealkalization water.

Alkalinity refers to the ability of water to neutralize acids, primarily determined by the concentration of carbonate (CO₃^2-), bicarbonate (HCO₃^-), and hydroxide (OH^-) ions present in the water. It reflects the total amount of substances in the water that can act as acid-base buffers and is typically measured in ppm (parts per million) or mg/L.

Naturally occurring alkalinity in the raw water comes in the form carbonate and bicarbonate. When alkalinity enters the boiler, it breaks down into OH^- and CO₂. CO₂ (gas) are discharged with the steam and forms carbonic acid as the steam condenses (pH<6.0). it the water with alkalinity is untreated, low pH water can corrode the condensate network and pipelines.

Alkaline water can have various negative impacts on industrial production:

• Scaling Issues: High alkalinity water contains carbonate and bicarbonate ions that react with calcium and magnesium ions at elevated temperatures to form precipitates (such as calcium carbonate), leading to scaling in equipment and pipelines, thereby affecting heat exchange efficiency and flow rates.
• Corrosion Risks: Although some alkaline waters can be corrosive, excessive alkalinity may reduce corrosivity, affecting the protective layers of certain metals and increasing equipment wear.
• Product Quality Issues: In industries such as pharmaceuticals, food, and beverages, using high-alkalinity water can adversely affect the flavor, color, and stability of the final products, leading to quality problems.
• Reduced Production Efficiency: Scaling and corrosion issues can result in equipment downtime and increased maintenance costs, thereby lowering overall production efficiency.
• Increased Treatment Costs: To remove alkalinity from water, additional treatment processes (such as dealkalization or softening) may be required, leading to higher overall water treatment costs.

Water dealkalization main adopt ion exchange principles, that is remove the carbonate and bicarbonate ions with SAC, WAC or SBA ion exchange resins to achieve water dealkalization. There are three major method to complete water dealkalization, here we will introduce them for you one by one and give you a comparison to help you find your suitable system and choose the right ion exchange resins.

1. Chloride Anion Dealkalization. Choride cycle method is just like the water softening process, which exchange the harness ions (Ca⁺, Mg⁺, etc.) with Na+ ions in ion exchange. Choride cycle system adopts a strong anion base (SBA) resins to complete ion exchange. Alkalized water with carbonate and bicarbonate enters the tank and passes through the ion exchange resins, the carbonate and bicarbonate are exchanged with Choride ions on the resins. Then the alkalinity is removed and only remain Choride ions in the water. Once the resins are staturated, they need to be regenerated with sodium chloride (NaCl) or salt-caustic combination (NaOH) solution. In this system, it is commonly used combined with SAC (Strong Acid Cation) resins for softening.

   
2. Weak Acid Dealkalization. It is an economical and efficient system which is suitable for the raw water with both alkalinity and hardness. And the hardness level is similar or lesser than the alkalinity level. It is complete the treatment in two processes: one is dealkalization and the other is softening.
   1. Dealkalization and degasifier. The weak acid cations with H⁺ ions can exchange with carbonate and bicabonate associated with the alkalinity. The reaction is as follows:
      Ca(HCO₃)₂ + 2R-H → 2R-Ca + 2H₂CO₃
      H₂CO₃ ←→ H₂O + CO₂
      Then, the generated carbonic acid dissociates into water (H₂O) and carbon dioxide (CO₂), the generated water will be delivered into degassifier to remove carbon dioxide through a countercurrent air stream, also, it can also remove the TDS.
   2. Softening. At this time, the alkalinity and TDS are removed and remaining harness in the water. The hard water will be delivered into softening device (tank with SAC resins) to remove all remaining permanent hardness to generate the qualified boiler water.
   3. Regeneration. When the resins near exhaustion, they should be regenerated. The WAC resins can be regenerated with sulfuric acid and the SAC resins should be regenerated with brine solution.
      

3. Split Stream Dealkalization. This method utilizes two parallel strong acid cation (SAC) reactors. One reactor operates in sodium (Na⁺) form, removing hardness while retaining 100% of alkalinity, while the other operates in hydrogen (H⁺) form, removing all alkalinity but remaining free mineral acidity (FMA). In the nex step, these two streams blend, FMA in the hydrogen cation resins effluent coverts sodium carbonate and bicarbonate alkalinity in the sodium cation resins effluent to carbonic acid. Refer to the following reaction:

   

   Then, the generated carbonic acid dissociates into water (H₂O) and carbon dioxide (CO₂), and they will be delivered into degassifier to remove carbon dioxide through a countercurrent air stream. The final water alkalinity can be controlled by managing the percentage of each mixed water flow.

   

4. Comparative Summary

   Method	Advantages	Disadvantages	Application Scenarios
   Chloride Cycle Dealkalization	Effectively removes alkalinity; suitable for industrial applications	Regeneration may introduce chloride ions; management required	Industrial water treatment; prevents boiler scaling
   Weak Acid Dealkalization	Significant cost advantages; high-quality effluent; no extra ions introduced	Relatively slow processing; limited applicability	Situations with high hardness-to-alkalinity ratios
   Split Stream Dealkalization	Flexible adjustments to effluent alkalinity; high stability and adaptability	Complex system design; requires high control and monitoring	Handling varying water quality; adaptable treatments

Choosing the appropriate dealkalization method is crucial for optimizing water treatment effectiveness, reducing production costs, and ensuring product quality. By understanding the advantages and disadvantages of different processes, industrial enterprises can make informed decisions based on their specific needs.