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In the world of water treatment, the Mixed Bed (MB) unit stands out for its complexity and the meticulous attention it demands during the regeneration process. They are most commonly used in various industries and applications where high-purity water is essential like Power Plants, Pharmaceutical Industry, Electronics and Semiconductor manufacturing, laboratories, food and beverage industry, chemical processing etc. Recently, a client-site faced a challenge where the Mixed Bed outlet silica levels from the demineralization water treatment plant did not meet the prescribed standards. This case study explores how MWTS identified the root causes and implemented effective solutions to resolve the issue.

Observation

The primary observation was that the silica levels at the Mixed Bed outlet were consistently higher than the acceptable limits. This deviation indicated potential issues in the regeneration process of the Mixed Bed unit.

Probable Reasons

Several factors were identified as potential contributors to the elevated silica levels:

  • Inadequate backwashing: Insufficient backwashing can lead to improper separation of cation and anion resins.
  • New resin not subjected to double charge and soaking: This step is crucial for the resin to achieve optimal performance.
  • Improper regeneration procedures (upflow and downflow): Incorrect procedures can affect the efficiency of the ion exchange process.
  • Incorrect sampling methods: Faulty sampling can lead to inaccurate readings and misdiagnosis of the problem.

Corrective Action for Mixed Bed Exchanger

To address these issues, MWTS implemented a series of corrective actions:

  1. Enhanced Backwashing Procedures: The backwashing process was optimized to ensure thorough separation of the cation and anion resins. This step is critical as it sets the stage for effective regeneration.
  2. Double Charging and Soaking of New Resin: New resin batches were subjected to a double charge and soaking process. This ensured that the resins were fully activated and ready for efficient ion exchange.
  3. Standardized Regeneration Procedures: MWTS standardized the regeneration procedures, ensuring that both upflow and downflow processes were correctly followed. This included precise control of regenerant flow rates and contact times.
  4. Accurate Sampling Methods: The sampling methods were reviewed and corrected to ensure accurate monitoring of silica levels. Proper sampling is essential for reliable data and effective troubleshooting.

The Regeneration Process

The Mixed Bed Exchanger contains both cation and anion resins in a single vessel. During regeneration, the resins are separated through backwashing, with the lighter anion resin rising above the cation resin. Regenerating acid is introduced through the bottom distributor, while caustic is introduced through distributors above the resin bed. The regenerating streams intersect at the boundary between the cation and anion resins and are collected through a designated collector. After introducing the regenerants and performing a displacement rinse, air and water are used to mix the resins. Following this, the resins are rinsed, and the unit is prepared for service.

Conclusion

Through meticulous analysis and targeted corrective actions, MWTS successfully resolved the issue of elevated silica levels in the Mixed Bed unit. By enhancing backwashing procedures, ensuring proper resin preparation, standardizing regeneration processes, and improving sampling methods, MWTS restored the Mixed Bed unit to optimal performance increasing the efficiency of production at the demineralization water treatment plant.

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