Zero Liquid Discharge Considerations - EPRImydocs.epri.com/docs/AdvancedCooling... · Zero liquid...
Transcript of Zero Liquid Discharge Considerations - EPRImydocs.epri.com/docs/AdvancedCooling... · Zero liquid...
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Zero Liquid Discharge Considerations
EPRI Advanced Cooling Workshop
Dan CasiraroSalt River Project
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Introduction
• Zero liquid discharge systems reclaim and reuse water that would otherwise be discharged.
• Although a total ZLD system includes all equipment involved with reclaiming all water streams, the brine concentrator and crystallizer are primary focus.
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Introduction
• Zero discharge plants have water balance complexities and challenges
• Changes, excursions, and adjustments at one point in the water balance can have significant impacts at a separate point
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Simplified NGS Water Balance
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Typical BC Layout
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NCG Vent
CrystallizerHeater
Feed
CrystallizerVapor Body
RecirculationPump
CompressionDevice
DewateringDevice
SlurryTank
Solids toDisposal
RecoveredWater
NCG Vent
CrystallizerHeater
Feed
CrystallizerVapor Body
RecirculationPump
CompressionDevice
DewateringDevice
SlurryTank
Solids toDisposal
RecoveredWater
Typical Crystallizer Layout
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NGS Crystallizer
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Crystallizers
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Reasons to Install a ZLD System
• Water is in short supply• NPDES permitting obstacles• Discharge contamination issues• Increased CW blowdown flows due
to PM 2.5 rules
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Design Considerations
• Characterize the water streams.• Determine mass loading.• Determine the final disposition of the
solids.• Optimize ZLD system capacity to the
plant situation.• Specify materials, instrumentation
and controls.
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Solids In Equals Solids Out
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Construction Considerations
• Participate during the performance guarantees.
• Review the proposed control package and upgrade if needed.
• Owner should be involved during new construction.
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Operational Considerations• Surge storage between BC and
crystallizer• BC Blowdown Transfer Pipe / Trench• Process stability influences• Final solids transport• Operator training – Entry-level
position• Process monitoring• Contingency plans
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Process Monitoring
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Process Considerations
• High Boiling Point Rise• Sodium sulfate decahydrate• Sustained Limit Cycle Behavior• Seed recycle system• Condensate quality• High corrosion potential
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Maintenance Considerations
• Operating with a restricted floodbox• Increased deposition potential
• Chloride concentration at saturation• Increased corrosion potential
• Process upsets vs. the maintenance schedule
• Planned maintenance versus emergency maintenance
• Chemical cleaning and routine maintenance
• Resource availability issues
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Environmental Considerations
• ZLD system equipment is considered to be environmental equipment.
• Reclaiming miscellaneous wastes through a ZLD should be planned.
• A ZLD system cycles water to high concentrations possibly cycling an undesirable constituent too high.
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Cost Considerations• Forced evaporation is energy intensive
and expensive.• Reclaim water outside the BC and
crystallizer if possible.• BC costs about $2 - $5 per 1000 gallons.• Crystallizer costs about 10X a BC.• Exotic materials are more expensive.• Complex water reclaim systems require
ponds and operator oversight.
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Conclusions
• Although a ZLD system can be a challenge to design, construct, and operate, it is a viable solution to reclaiming water and eliminating water discharges.
• ZLD systems have unlimited configurations. Flexible configuration creates options.
• ZLD systems constantly evolve.