Double-effect evaporator for sodium chloride with a processing capacity of 2 tons per hour

I. Project Background

A large pharmaceutical company generates approximately 50 tons of high-concentration sodium chloride wastewater daily during its active pharmaceutical ingredient (API) production process. This wastewater has a salt content as high as 8%–12% and contains small amounts of organic residues. Direct discharge would cause serious environmental pollution, while traditional treatment methods are energy-intensive and prohibitively expensive to operate. The company urgently needs a high-efficiency, stable, and economical evaporation and crystallization system to achieve resource recovery of sodium chloride and wastewater reduction.

After extensive technical evaluation, our company designed and constructed a double-effect evaporator system for sodium chloride with a processing capacity of 2 tons per hour, successfully achieving the dual goals of zero wastewater discharge and industrial salt recovery.

II. Process Scheme

This system adopts a double-effect co-current evaporation process. The core equipment includes a first-effect evaporator, a second-effect evaporator, a condenser, a crystallization separator, and a centrifugal dehydrator unit.

The first-effect evaporator uses live steam as a heat source to heat the sodium chloride wastewater to boiling, generating secondary steam. The second-effect evaporator uses the secondary steam generated in the first effect as a heat source to continue evaporating the concentrated liquid. The system operates with two effects in series, utilizing steam heat energy in a cascade manner, resulting in approximately 45% energy savings compared to single-effect evaporation.

Wastewater, after preheating, enters the first effect, where its concentration gradually increases to near saturation. It then enters the second effect for further concentration, reaching supersaturation before entering the crystallizer. The crystal slurry is dewatered by a centrifuge, producing sodium chloride crystals with a moisture content of less than 3%. The mother liquor is returned to the system's front-end for recycling.

To address the interference of small amounts of organic matter in the wastewater, the system incorporates a pre-treatment unit of flocculation sedimentation and activated carbon filtration, effectively removing suspended solids and some organic impurities. This ensures long-term stable operation of the evaporator and prevents scaling and foaming issues.

III. Equipment Parameters

1. Processing Capacity: 2 t/h (Sodium Chloride Wastewater)

2. Feed Salt Content: 8%~12%

3. Discharge Moisture Content: ≤3%

4. Evaporation Method: Double-Effect Co-current Evaporation

5. Heat Source: Live Steam (Single Effect) / Secondary Steam (Second Effect)

6. Steam Consumption: Approximately 0.55 t Steam / t Water

7. Cooling Water Circulation Rate: 80 m³/h

8. Crystallized Salt Purity: ≥98.5%

9. Annual Operating Time: 7200 

IV. Operational Results

Since its commissioning, the system has operated stably for over 18 months, with all performance indicators meeting design expectations:

1. Processing Capacity: Under full load, it stably processes 2 tons of wastewater per hour, with a daily processing capacity of 48 tons, matching the company's production pace;

2. Energy Saving Performance: The dual-effect thermal coupling design significantly reduces steam consumption, resulting in a more than 40% reduction in overall operating costs compared to the original single-effect solution;

3. Salt Quality: The produced sodium chloride crystals maintain a stable purity of over 98.5%, with good whiteness, meeting industrial salt standards (GB/T 5462). These can be sold as byproducts or reused in processes such as de-icing and boiler softening;

4. Environmental Compliance: The system achieves full-volume wastewater treatment with no liquid discharge, completely eliminating environmental risks.

V. Project Highlights

1.High Efficiency and Energy Saving: The dual-effect evaporation fully utilizes the latent heat of secondary steam, achieving a steam consumption as low as 0.55 tons/ton of water, placing it at a leading level among similar projects.

2. Strong Anti-interference: The synergistic design of pretreatment and evaporation crystallization effectively copes with fluctuations in influent water quality, ensuring long-term system stability.

3. High Degree of Automation: PLC+DCS integrated control enables fully automated operation of the entire process from feeding, evaporation, crystallization, to salt discharge, minimizing manual intervention and reducing labor intensity.

4. Resource-based Closed-Loop: Sodium chloride in wastewater is converted into marketable products, achieving "waste-to-waste treatment," significantly shortening the investment payback period.

The successful implementation of this project verifies the techno-economic advantages of the dual-effect evaporation process in medium-scale sodium chloride wastewater treatment scenarios. The processing capacity of 2 tons per hour not only meets the company's daily production needs but also reserves flexibility for future capacity expansion.

Our company has been deeply involved in the evaporation crystallization field for many years and can provide various technical solutions such as multi-effect evaporation, MVR evaporation, and forced circulation evaporation according to different water qualities and scales. We welcome inquiries and discussions from all sectors to jointly explore a green and circular development path.