Materials & Design for High-Chloride/High-TDS
Industrial wastewater with high levels of chloride and total dissolved solids (TDS) presents one of the toughest challenges for evaporation and crystallization systems. Corrosion, fouling, and scale formation can rapidly degrade performance and shorten equipment life if the system is not carefully engineered. To achieve long-term reliability, material selection, hydraulics, and process control must all be integrated from the earliest design stage.
Whiting Equipment Canada and its licensee, Swenson Technology, bring decades of experience in engineering evaporation and crystallization systems that perform reliably in the harshest industrial environments—including high-chloride wastewater treatment and zero-liquid-discharge (ZLD) applications.
Corrosion Mechanisms
Chloride-rich waste streams accelerate multiple corrosion mechanisms, particularly pitting, crevice corrosion, and stress-corrosion cracking. Chloride ions disrupt the passive oxide layer that normally protects stainless steels, especially at elevated temperatures and concentrations typical in evaporators.
Other constituents, such as calcium, magnesium, and sulfate, further exacerbate the problem by forming deposits that create localized corrosion cells. Managing these mechanisms requires both robust metallurgy and design strategies that minimize stagnant zones and promote uniform flow.
Alloys & Coatings
Selecting suitable high chloride wastewater evaporator materials is central to system longevity. For moderate-chloride brines, super-austenitic stainless steels such as 254 SMO (UNS S31254) or 904L often provide adequate protection due to their high molybdenum and nitrogen content.
At chloride concentrations exceeding 20,000 ppm, or where elevated temperatures persist, designers typically consider duplex stainless steels (e.g., 2205, 2507) or nickel-based alloys such as Hastelloy C-276 and Inconel 625. For extreme chloride or mixed-acid environments, titanium and zirconium can be justified despite higher initial cost because of their long-term resistance to localized attack.
In certain sections—especially vapor ducts, tube sheets, or external surfaces—fluoropolymer coatings or thermal spray barriers can further extend life, particularly when used to isolate dissimilar metals and reduce crevice formation.
Velocities & Hydraulics
Designing internal velocities and circulation rates is critical to balancing heat transfer efficiency and scale control. In falling-film evaporators, maintaining turbulent film flow (Re > 4000) minimizes deposition and ensures even heat distribution. Forced-circulation evaporators, used for high-solids or crystallizing duties, rely on robust pumps to maintain bulk velocities that keep solids suspended.
Whiting and Swenson systems are engineered to match hydraulic conditions to the chemistry of the brine. Pilot testing plays a key role in defining these parameters—generating data on fouling tendencies, scaling thresholds, and pump shear limits—so that commercial systems operate safely below critical supersaturation levels.
Fouling & Scaling Control
High-TDS wastewater systems inevitably face precipitation of salts such as sodium chloride, calcium sulfate, and silica. Effective crystallizer design allows these solids to form in a controlled environment where they can be separated, rather than plating onto heat-transfer surfaces.
Key strategies include:
- Seeded crystallization, to promote uniform particle growth.
- Optimized supersaturation profiles, controlled through gradual cooling or staged evaporation.
- Chemical conditioning, using antiscalants or pH adjustment to suppress nucleation.
- Scheduled cleaning, guided by real-time monitoring of pressure drop and heat-transfer coefficients.
Swenson’s pilot facilities are specifically used to study fouling and scaling behavior, allowing engineers to refine these controls before full-scale deployment.
Inspection & Life
Even the best materials require a proactive maintenance plan. Equipment exposed to chloride brines should incorporate:
- Accessible inspection ports for non-destructive examination (e.g., ultrasonic thickness gauging).
- Corrosion coupons or electrical resistance probes to track wall-loss trends.
- Replaceable liners or sacrificial anodes in high-attack regions.
Whiting’s philosophy— “Built to Perform. Designed to Last.”—reflects the emphasis on inspection-ready design and lifecycle reliability. Systems are configured for decades of service through intelligent material selection, modular construction, and planned maintenance intervals.
Specification Checklist
When specifying systems for high-chloride or high-TDS service, process engineers typically evaluate:
- Chloride concentration and temperature range of the feed stream.
- Material compatibility, including alloys, coatings, and weld filler metals.
- Expected solids loading and particle size distribution.
- Flow regime (laminar vs. turbulent) and circulation pump head.
- Access for cleaning and inspection (removable tube bundles, CIP systems).
- Corrosion monitoring provisions and documentation requirements.
- Life-cycle cost analysis, incorporating energy, maintenance, and replacement intervals.
This checklist serves as the foundation for ensuring operational reliability and predictable OPEX throughout the system’s lifetime.
Case Example
In a fertilizer manufacturing facility handling chloride-laden by-product streams, a forced-circulation evaporator constructed in duplex stainless steel and equipped with removable tube bundles demonstrated a five-year run without major corrosion events. Minor scale deposition was mitigated through monthly acid cleaning and the use of a phosphate-based antiscalant.
While the case is representative rather than client-specific, it illustrates how proper material selection, flow design, and chemical conditioning can dramatically extend asset life in severe chloride environments.
(Illustrative example for demonstration purposes only.)
Conclusion
Handling high chloride wastewater evaporator materials correctly is not just a question of selecting corrosion-resistant metals—it’s about integrated design. Whiting Equipment Canada and Swenson Technology combine advanced materials engineering, proven hydraulic design, and pilot-scale testing to ensure reliable evaporation and crystallization in even the most corrosive service conditions.
To discuss material selection, pilot testing, or a complete evaluation of your high-TDS wastewater challenges, contact Whiting Equipment Canada’s engineering team. We can help develop a design strategy that minimizes corrosion risk, optimizes performance, and extends system life. Contact us to discuss your requirements.
