When the resin in a softener becomes exchange-saturated, regeneration treatment is required to restore its ion-exchange capacity. The resin regeneration process is categorized into co-current regeneration and counter-current regeneration based on the direction of the brine solution flow. Co-current regeneration occurs when the brine flow direction matches the raw water flow direction during service; counter-current regeneration occurs when these flows oppose each other. Runxin softener regeneration involves four key steps: backwashing, regeneration (brining), displacement (slow rinse), and forward rinsing.
(1) Backwashing Step
After resin exhaustion, backwashing is performed first by introducing water upward through the resin bed. This process:
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Removes trapped suspended solids and broken resin fragments.
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Breaks up resin compaction, loosening the bed for uniform brine distribution during regeneration.
Optimal practice: Use softened water for backwashing; raw water yields inferior results.
Parameters: Backwash flow rate ≈ 10 m/h; Duration: 10–15 minutes.
(2) Regeneration (Brining) Step
Following backwashing, regeneration begins. The process follows the principle of equivalent mass exchange: 1 mol NaCl restores 1 mol exchange capacity of the resin.
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For domestic 001×7 wet resin (total exchange capacity: 2.0 mol/L; wet bulk density: 0.85 kg/L):
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Theoretical salt requirement: 58.5 × 2 / 0.85 = 137.75 g NaCl per kg resin.
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Actual salt consumption for effective regeneration: 2.0–3.5 × theoretical value = 275.5–482 g NaCl per kg resin.
(Use higher value for co-current; lower for counter-current regeneration).
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Relationship between NaCl consumption per mole of resin (salt specific consumption) and regeneration efficiency is shown in Figure 2.8.
Critical parameters:-
Brine concentration: 5%–10%
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Flow rate: 6–8 m/h
Note: Regeneration efficiency is highly sensitive to brine hardness. Use softened water for brine; avoid high-hardness raw water.
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(3) Displacement (Slow Rinse)
This step extends the regeneration process. After stopping brine injection, residual brine remains in the upper vessel and resin pores. To utilize this brine fully and flush out regeneration byproducts:
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Continue injecting clean water at the same flow direction and rate as regeneration.
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This displaces residual brine while further regenerating resin.
Typical volume: 0.5–1 × resin bed volume.
(4) Brine Tank Refill
After brine is consumed, refill the tank with water for the next regeneration.
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At 25°C, saturation occurs at 360 g salt per liter water (26.4% concentration).
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To ensure saturation:
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Dissolution time > 6 hours.
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Maintain sufficient undissolved salt in the tank.
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(5) Forward Rinsing Step
Performed after displacement or before putting a standby unit into service. To eliminate residual brine and regeneration byproducts:
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Rinse the resin bed with clean water in the same direction as service flow.
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Continue until effluent hardness meets specifications.
Typical volume: 3–6 × resin bed volume.