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Petrochemical facilities generate some of the most complex industrial wastewater streams, often containing mixed salts that challenge conventional treatment approaches. When a large petrochemical complex on China’s eastern coast faced mounting pressure to eliminate liquid discharge while recovering valuable chemical byproducts, they selected CONQINPHI to engineer a cutting-edge solution. This case study examines how our 10t/h sodium sulfite MVR evaporator and sodium sulfate MVR evaporator dual-system installation enabled the facility to transition from wastewater discharge to complete resource recovery, establishing a new operational paradigm for the regional petrochemical sector.
The complex, which operates multiple catalytic cracking and sulfur recovery units, produced approximately 200 tons per day of mixed-salt wastewater containing varying ratios of sodium sulfite and sodium sulfate. Environmental regulators had issued a compliance deadline requiring zero liquid discharge within 18 months, while the facility’s management team sought to transform regulatory compliance into a cost-neutral or profitable operation. After evaluating several technology providers, the engineering committee determined that a purpose-built MVR evaporator system from CONQINPHI offered the optimal balance of energy efficiency, operational reliability, and product recovery capability.
The incoming wastewater presented unique separation challenges that demanded sophisticated process design:
• Variable sulfite-to-sulfate ratio: Feed composition shifted between 60:40 and 40:60 depending on upstream sulfur recovery unit performance, requiring flexible system response
• Oxidation sensitivity: Sodium sulfite readily oxidizes to sulfate when exposed to air, complicating product segregation and purity maintenance
• Scaling tendencies: Both salts exhibit inverse solubility characteristics, creating significant scaling risks on heat transfer surfaces
• High total dissolved solids: Feed concentrations reaching 18-22% TDS pushed conventional evaporation technologies to their operational limits
The facility required a robust sodium sulfite MVR evaporator system capable of processing 10 tons per hour while maintaining product segregation sufficient to achieve commercial-grade purity for both recovered salts. Sodium sulfite product needed to meet photographic-grade specifications (≥98.5% purity), while sodium sulfate recovery targeted detergent-grade quality (≥99.0% Na₂SO₄).
Our process development team conducted an eight-week pilot testing campaign to map the crystallization behavior of the mixed-salt system under various thermal and pressure conditions. Based on this data, we engineered an integrated solution featuring:
• Primary sodium sulfite MVR evaporator operating under controlled inert atmosphere to prevent oxidation during concentration and crystallization
• Secondary sodium sulfate MVR evaporator processing the mother liquor from the primary system to recover remaining sulfate values
• Mechanical vapor recompression technology utilizing a high-efficiency centrifugal compressor to recycle vapor energy, minimizing external steam requirements
• Automated oxidation monitoring with real-time dissolved oxygen control maintaining sulfite product integrity
The installed MVR evaporator complex represents one of the most energy-efficient mixed-salt recovery installations in the Asian petrochemical industry. Key technical parameters include:
Parameter | Sodium Sulfite System | Sodium Sulfate System |
Feed capacity | 6,000 kg/h | 4,000 kg/h (mother liquor) |
Evaporation capacity | 5,100 kg/h | 3,400 kg/h |
Product output | 900 kg/h Na₂SO₃ | 600 kg/h Na₂SO₄ |
Compressor power | 315 kW | 220 kW |
Specific energy consumption | 12 kWh/ton evaporation | 13 kWh/ton evaporation |
Product purity | ≥98.7% Na₂SO₃ | ≥99.1% Na₂SO₄ |
Oxidation loss | <0.3% | N/A |
The sodium sulfite MVR evaporator operates under slight nitrogen positive pressure throughout the concentration and crystallization stages, effectively eliminating atmospheric oxygen contact. A proprietary seal design on the centrifugal compressor maintains this inert environment while achieving compression ratios of 1.8:1 with isentropic efficiency exceeding 82%.
CONQINPHI integrated a comprehensive distributed control system managing both MVR evaporator trains with centralized oversight:
• Feedforward composition control adjusting operating parameters based on real-time feed analysis from inline refractometers and conductivity sensors
• Crystal size distribution management through controlled supersaturation programming, optimizing product morphology for downstream handling
• Compressor surge protection with automated anti-surge valve sequencing ensuring stable operation across the full turndown range
• Integrated CIP scheduling with acid, alkali, and oxidative cleaning cycles maintaining design heat transfer coefficients
The entire facility operates with a staff of three operators per shift, a 70% reduction compared to the previous multi-effect evaporation system that required extensive manual intervention.
After 24 months of continuous commercial operation, the dual sodium sulfate MVR evaporator and sodium sulfite MVR evaporator installation has delivered transformative outcomes:
Zero Liquid Discharge Achievement: The complex now recycles 100% of its mixed-salt wastewater internally, completely eliminating discharge to the municipal treatment system. This compliance milestone removed the facility from regulatory enforcement priority lists and secured its operating license renewal without conditions.
Energy Cost Reduction: Compared to the previously evaluated four-effect steam-driven alternative, the MVR evaporator configuration reduces energy operating costs by 68%. Annual electricity costs of $485,000 compare favorably against projected steam costs exceeding $1.5 million for the thermal alternative.
Byproduct Revenue Stream: Recovered sodium sulfite, sold to regional photographic chemical suppliers at $420 per ton, generates $1.35 million annually. Sodium sulfate recovery, directed to the detergent manufacturing sector at $180 per ton, contributes an additional $320,000 in yearly revenue.
Water Recovery: The system produces 8,500 tons per day of high-purity condensate, meeting boiler feedwater specifications and eliminating external freshwater purchases for steam generation.
Operational data confirms exceptional reliability performance. The sodium sulfite MVR evaporator has maintained 96.5% availability, with the single unplanned outage attributed to an external power quality event rather than equipment failure. Compressor maintenance intervals have extended to 8,000 operating hours, exceeding original projections by 25%.
Heat transfer surface scaling has remained within design parameters, with automated cleaning cycles restoring performance without production interruption. Titanium-clad heating elements show no measurable corrosion after two years of exposure to the aggressive sulfite-sulfate environment.
CONQINPHI has established particular expertise in MVR evaporator systems for petrochemical mixed-salt recovery through sustained investment in process research and materials development. Our technical strengths encompass:
• Thermodynamic optimization: Advanced process simulation utilizing proprietary property databases for complex multi-salt systems
• Mechanical vapor compression: In-house compressor design and manufacturing ensuring optimal matching to specific evaporation duties
• Corrosion engineering: Materials selection protocols validated through extensive field exposure testing in sulfite, sulfate, and chloride environments
• Process safety integration: Hazard and operability studies ensuring safe handling of oxygen-sensitive and thermally unstable chemical species
While this installation serves the Chinese domestic petrochemical market, CONQINPHI’s sodium sulfate MVR evaporator and sodium sulfite MVR evaporator technology has been successfully implemented across the Middle East, Southeast Asia, and South America. Our project execution model combines Chinese manufacturing cost efficiency with internationally certified quality systems, delivering European-equivalent engineering at competitive investment levels.
Our regional service network provides responsive technical support, spare parts availability, and performance optimization consulting to ensure long-term operational excellence regardless of installation geography.
Mixed-salt petrochemical wastewater streams represent both a significant environmental challenge and an untapped resource recovery opportunity. CONQINPHI’s process engineering team offers comprehensive evaluation services, from preliminary feasibility analysis through pilot-scale validation, to determine the optimal MVR evaporator configuration for your specific application.
Contact our petrochemical specialists today to discuss your zero-liquid-discharge objectives, mixed-salt recovery requirements, or existing evaporation system upgrade needs. Whether your stream contains sulfites, sulfates, chlorides, or complex organic salts, CONQINPHI delivers the technical expertise and proven execution capability to transform your wastewater liability into a valuable resource asset.
220 meters north of the intersection of Zhanqian Avenue and Lanzhou East Road in Jiaozhou City, Qingdao, Shandong Province, China.
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