15t/h Rubber Additives CBS Wastewater Triple-Effect Evaporation Crystallization System

The 15t/h CBS wastewater triple-effect evaporation and crystallization system is specifically designed for the production wastewater of CBS (N-cyclohexyl-2-benzothiazole sulfenamide), a rubber accelerator. A single unit has an evaporation capacity of 15t/h (360t/d), employing a "triple-effect cross-flow forced circulation + DTB staged crystallization" process. Steam consumption is ≤0.24t/t water, and the byproduct anhydrous Na₂SO₄ has a purity ≥99% and a whiteness ≥88, which can be directly supplied to ion-exchange membrane caustic soda enterprises, achieving zero discharge of CBS wastewater and high-value utilization of salt resources.

I.Influent Characteristics

CBS synthesis employs an alternating acid-base process. The centrifuged mother liquor contains: Na₂SO₄ 180-220 g/L, CBS residue 12000 mg/L, COD 45000-60000 mg/L, color 20000 times, temperature 95℃, pH 3-4, and contains trace amounts of cyclohexylamine and benzothiazole. It is prone to foaming, polymerization, and is highly corrosive.

II.Process and System Composition

1.Pretreatment Unit:Cooling and oil removal (spiral plate + inclined plate oil separator, oil ≤ 30 mg/L) → Neutralization (NaOH + CO₂, pH 6.5) → High-density softening (MgO + PAC, F⁻ ≤ 5 mg/L, Ca ≤ 20 mg/L) → Tubular microfiltration (SDI ≤ 3) → Two-stage preheating (condensate + secondary steam).

2.Triple-Effect Cross-Flow Evaporation:Vacuum gradient -70 → -82 → -90 kPa, evaporation temperature 85 → 73 → 60℃, forced circulation velocity 3.8 m/s, forced scale prevention; cross-flow operation avoids CBS residue enrichment and coking.

3.DTB Fractional Crystallization: The triple-effect output density is 1.30 t/m³. Seed crystals are introduced, and anhydrous Na₂SO₄ precipitates on the low-temperature side (55℃). Centrifugation yields a water content ≤3% and a whiteness ≥88. The CBS-rich mother liquor is returned to the second-effect stage for concentration to 60% (solids content), pumped into the enrichment tank, and periodically sent to the plant's RTO for incineration. The system has no waste liquid discharge.

III.Core Equipment Parameters

1.Total Evaporation: 15t/h (360t/d)

2.Steam Consumption per Unit: 0.24t/t water (triple-effect); MVR interface reserved, ≤0.08t/t water after upgrade

3.Heat Transfer Area: 200m² for first effect, 180m² for second effect, 160m² for triple effect, totaling 540m², with a 20% design margin

4.DTB Crystallizer: Two units, Φ2600×5500mm, material 2507 + rubber lining, crystal slurry density 25-35%

5.Centrifugal Dryer: LW650×2600-N, separation factor 1500, processing capacity 6t/h, product water content ≤0.3%

IV.Performance and Advantages

1.Low Energy Consumption: Triple-effect + DTB + heat pump reuse, steam cost reduced by 50% compared to single-effect; steam consumption is almost "zero" after full MVR upgrade. 

2.Resource Utilization: Na₂SO₄ meets industrial recycling standards, increasing the external sales price from 200 RMB/t to 650 RMB/t; CBS residue calorific value recovery saves 0.8 million tons of coal annually.

3.Stable Operation: Forced circulation + online CIP, annual operating time ≥8000h, equipment availability >98%.

4.Space Saving: Modular steel structure frame, single-story layout, occupying only 400m², 30% less than traditional triple-effect boilers.

5.Intelligent Control: DCS + APC control, multi-variable prediction of evaporation rate, density, and vacuum degree, fluctuation ±2%; remote monitoring via control software.

V.Operational Data (Performance Evaluation)

1.Water Production Rate: ≥85%, condensate TDS≤120mg/L, COD≤50mg/L, color ≤10 times, reused as boiler feedwater.

2.Mixed salt production: Na₂SO₄ 18 t/d, moisture content ≤0.3%, whiteness ≥88, Cl⁻≤0.05%, meeting the requirements for caustic soda feedstock for ion-exchange membranes.

3.Mother liquor treatment: Dry solids production 12 t/d, calorific value 25 MJ/t, RTO incineration recovery steam 1.5 t/h, no waste liquid discharge from the system.

4.Energy consumption indicators: live steam 0.24 t/t water, electricity consumption 20 kWh/t water, cooling water 2.0 t/t water.