Case Study: Three-Effect Evaporation Treatment of Sodium Sulfate-Containing Wastewater from a Chemical Plant

Project Background

A large-scale fine chemical enterprise generates a significant volume of wastewater containing sodium sulfate during its production process, with a daily treatment capacity of 30 tons and a sodium sulfate concentration ranging from 12% to 18%. This wastewater is characterized by high salinity and strong corrosivity; direct discharge would cause severe environmental pollution. The client’s existing treatment process suffered from excessive energy consumption and inconsistent salt quality, failing to meet increasingly stringent environmental regulations and reuse standards.

Solution

Following an on-site water quality analysis and a comprehensive evaluation of potential process technologies, we designed a custom three-effect forced-circulation evaporation system for the client. The solution utilizes a counter-current feed and co-current salt discharge configuration, which maximizes the utilization of residual heat from the secondary steam in each effect, thereby significantly reducing overall steam consumption. To address issues such as scaling at high concentrations and non-uniform crystal size, the evaporators are equipped with an in-line cleaning system and a seed-induced crystallization system, ensuring stable, long-term operation.

Core Equipment Configuration

The complete system comprises a first-effect falling-film evaporator, second- and third-effect forced-circulation evaporators, a crystallization separator, a centrifugal dewatering unit, and a vacuum system. The heating chambers and the main bodies of the separators are constructed from 2205 duplex stainless steel, providing effective resistance against the combined corrosive effects of chloride and sulfate ions. The system is managed by a fully automated PLC control unit, which monitors liquid levels, temperatures, densities, and vacuum degrees in real-time, enabling unattended operation.

Process Highlights

The three-effect series design reduces live steam consumption to approximately one-third of that required for single-effect evaporation, keeping steam consumption below 0.35 tons per ton of water evaporated. Secondary steam generated in the second and third effects serves as the heat source for the subsequent effect, while the secondary steam from the final effect is recovered via a surface condenser; the resulting condensate meets the standards for process reuse. After centrifugal separation, the sodium sulfate crystals have a moisture content of less than 3%, with whiteness and purity levels meeting the standards for "Grade I" industrial products—making them suitable for direct sale or reuse in production.

Project Outcomes

Since its commissioning, the system has operated continuously for over 18 months, processing more than 10,000 tons of sodium sulfate-containing wastewater annually and recovering over 3,600 tons of solid sodium sulfate. The client’s steam costs have decreased by 62% year-on-year, and near-zero liquid discharge (NZLD) has been achieved, resulting in annual savings of over one million yuan in pollutant discharge fees and raw material procurement costs. This system now serves as a model unit for wastewater resource recovery at the client’s facility.

To receive a customized evaporation solution tailored to your specific operating conditions, please contact our technical team for a complimentary water quality analysis and process design service.