Integrating Evaporation & Crystallization for ZLD
Zero Liquid Discharge (ZLD) represents the highest standard of water stewardship in process industries — capturing, concentrating, and ultimately recovering every drop of wastewater. For facilities dealing with brines, battery-metal wastewaters, or other complex chemistries, effective ZLD evaporation crystallization integration transforms what was once a disposal problem into a resource-recovery opportunity.
Whiting Equipment Canada (WEC), through its partnership with Swenson Technology, delivers integrated evaporation and crystallization systems that align process efficiency with long-term operational resilience. Each system is engineered to operate under the harshest industrial conditions and tailored to the client’s specific chemistry, throughput, and purity goals.
Process Architecture
Every successful ZLD system begins with a clear understanding of the feed chemistry and the thermodynamic pathways available for water and solute recovery. The process architecture typically follows a staged progression:
- Pre-concentration — Falling-film or forced-circulation evaporators remove bulk water while maintaining thermal efficiency.
- Secondary concentration or crystallization — Additional evaporator effects or cooling stages promote nucleation and growth of crystalline salts.
- Mother liquor recycling or purge — Liquor remaining after crystallization is recycled upstream or purged to manage impurity buildup.
- Solid recovery and packaging — Dewatering, washing, and drying systems isolate solids for reuse or safe disposal.
At every stage, design modeling and simulation are used to understand solubility limits, boiling-point elevation, and phase equilibria, ensuring that heat and mass balances align with both product recovery and sustainability goals.
Mother Liquor Handling
In an integrated ZLD system, the mother liquor stream—the concentrated solution remaining after crystal separation—defines both the process yield and purity. Whiting and Swenson’s engineering approach prioritizes efficient impurity removal while maximizing lithium or salt recovery.
Bench and pilot testing quantify crystal yield, purity, and washing efficiency, providing data to fine-tune recycle ratios and purge volumes. In practice, mother liquor can be partially recycled through the evaporator system, where advanced thermodynamic control minimizes scaling risks. The remainder is treated as a managed purge to maintain steady-state impurity concentrations.
Energy Integration
Energy optimization remains central to ZLD evaporation crystallization integration. Each effect, compressor, or heat exchanger must be evaluated for steam economy, heat recovery potential, and power cost.
Whiting and Swenson systems employ the following strategies:
- Thermodynamic modeling to match evaporator duty to available utilities and to identify opportunities for multi-effect or mechanical vapor recompression (MVR) configurations.
- Pinch analysis to integrate waste heat from adjacent plant operations, such as dryer exhaust or reactor cooling water.
- Custom control logic that adjusts duty cycles in real time to maintain target concentration with minimum energy input.
When properly implemented, integrated systems can reduce total energy consumption by 30–40% compared with non-integrated, stand-alone evaporators and crystallizers (based on published ZLD case data in the industrial water treatment sector).
Solids Management
The solid phase is both a process output and a critical operational concern. In ZLD systems, solids may include sodium, calcium, lithium, or sulfate salts — each with unique density, crystal habit, and handling requirements.
Pilot data from Swenson’s facilities are used to determine:
- Settling and washing characteristics
- Centrifuge or filter sizing for dewatering
- Optimal recycle and purge ratios to prevent salt accumulation in the mother liquor
Proper solids management extends to conveying, drying, and packaging systems — all of which must be designed for corrosion resistance, dust control, and operator safety.
Controls & Safety
The complexity of an integrated ZLD plant requires coordinated process control. Whiting’s control philosophy, derived from decades of metallurgical and chemical systems design, uses a PLC/SCADA architecture with advanced operator interfaces. Touch-screen HMIs provide a unified view of flows, temperatures, and phase transitions across evaporation and crystallization trains.
Safety is built into every subsystem: pressure-relief protection, automated level monitoring, and emergency quench systems for high-temperature sections. The company’s mechanical and control engineers collaborate to ensure redundancy in both power and communication pathways, minimizing downtime risk.
Case: Battery-Metal Wastewaters
Battery-metal refining and lithium processing offer near-perfect applications for ZLD. Here, evaporators concentrate sulfate- and chloride-rich wastewaters, while crystallizers recover valuable salts like Li₂SO₄ or Na₂SO₄. Each lithium source — whether brine or hard rock — introduces unique impurities that dictate the configuration of the evaporation and crystallization units.
Whiting and Swenson have decades of relevant experience, supplying crystallization systems for lithium hydroxide monohydrate (LiOH·H₂O), lithium carbonate (Li₂CO₃), and lithium sulfate (Li₂SO₄) production. The same principles of purity control and thermal efficiency apply to ZLD integration, ensuring closed-loop water use and maximum product recovery.
(Case details are representative of industry practice, not specific project disclosures.)
Startup Checklist
A typical ZLD system commissioning roadmap includes:
- Pre-startup review – Verify all instrumentation calibration and confirm line flushing to remove debris.
- Controlled heat-up – Ramp utilities to steady-state temperatures, avoiding thermal shock in high-alloy exchangers.
- Feed introduction – Start dilute feed and gradually increase concentration while monitoring scaling indicators.
- Mother liquor sampling – Collect samples for impurity and density analysis to confirm recycle setpoints.
- Crystal cutpoint verification – Adjust residence time and agitation to achieve the target particle size.
- Full load validation – Confirm solids flow, heat balance, and control system interlocks under continuous operation.
This structured startup process ensures operational reliability, stable purity, and predictable recovery performance.
Conclusion
ZLD evaporation crystallization integration offers a proven, scalable path to eliminate liquid discharge while improving material recovery. By combining Whiting Equipment Canada’s mechanical engineering depth with Swenson Technology’s thermal process expertise, operators gain systems that not only meet environmental compliance goals but also deliver measurable ROI through energy efficiency and resource reuse.
To explore ZLD integration strategies for battery-metal or industrial wastewater streams, contact Whiting Equipment Canada’s process engineering team. We can assist with modeling, material selection, and pilot-scale testing to define a pathway toward full ZLD compliance and sustainable operations.
