‘Best of’ IWC
Webinar Series
The Best of IWC Webinar Series is a great way to preview the high quality technical content presented at the International Water Conference®.
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Past Webinars
Topic: MLD, ZLD and Brine Management
Date: June, 2022
IWC 21-33: Xcel Cherokee near ZLD Wastewater Treatment System Design Considerations
Paul Brandt, Burns & McDonnell
Given new NPDES permit limits for chlorides, sulfates, total inorganic nitrogen (TIN) and other constituents for the plant’s common outfall. Meeting the new chloride and sulfate concentrations became the limiting factor for technology selection and compliance. Wastewater produced at the plant includes cooling tower blowdown, reverse osmosis (RO) system reject, stormwater, and other miscellaneous plant wastewaters. Due to the new NPDES limits, Xcel Energy, with the assistance of Burns & McDonnell, determined that a near-ZLD wastewater treatment system was the best option for the plant to replace an existing conventional clarification system. Treated water from the new system is returned to the plant for reuse and concentrated brine is routed to new evaporation ponds. Various options were evaluated in the study phase to help select the most economical treatment configuration including: Makeup water softening, High efficiency reverse osmosis, Nanofiltration, Closed-circuit reverse osmosis, Forward osmosis, Ultra-high pressure reverse osmosis, Membrane electrodialysis, Osmotically enhanced reverse osmosis, Mechanical vapor 15
recompression evaporator, Forced circulation crystallizer, Alternative thermal evaporator designs, Evaporation ponds, Waste heat cooling tower, Bypass evaporator spray dryer, Operational changes, Discharge to a nearby POTW facility
The wastewater system ultimately selected and designed includes:
Equalization ponds, High rate softening clarification, Multimedia filtration, Closed circuit reverse osmosis with 98% recovery of wastewater for reuse, Evaporation ponds for concentrated brine wastewater, Filter press for sludge dewatering, Required startup in Fall of 2021
The WWT project is currently under construction and is planned to complete startup at the end of 2021. This paper will cover the following aspects of the study and detailed design phases of the wastewater treatment system:
- Study phase options considered and drivers for the near ZLD system selected.
- Process description and design considerations/limitations of equipment selected.
- Operational changes to reduce wastewater flow requiring treatment.
- Challenges of elevated TOC in wastewater, effects on selected wastewater equipment, and TOC removal methods evaluated.
- Challenges and recommendations of locating new equipment in existing water treatment building
- Methodical approach to evaporation pond selection/sizing.
Paul Brandt is a Senior Chemical Engineer with Burns & McDonnell. His 15 years of power industry experience include water and wastewater aspects of various systems such as: physical/chemical/biological treatment with ZLD for wet scrubber blowdown, demineralized water treatment, air quality control equipment, bottom ash handling, and CCR pond closures.
IWC 21-34: Power Plant Water Balance Tool Optimizes Load Leveling and Achieves ZLD
Dan Carey, Ph.D., P.E., Worley
Orlando Utilities Commission (OUC) operates two coal fired boilers in the Stanton Energy Center. OUC has recently announced they will repower both units with natural gas in 2025 and 2027. The plant is a zero-liquid discharge (ZLD) facility. The repowering will bring its own challenges to the ZLD operation. During periods of high net rainfall (particularly the summer) water levels in wastewater storage ponds are limited by evaporating water in the FGD scrubbers and disposal of gypsum. If the plant’s units are not operated at sufficient capacity factors, FGD scrubber evaporation and gypsum disposal are limited.
OUC had a need for a water balance model that could be operated by onsite personnel. There were several goals for the model including:
- Forecasting future conditions to guide dispatch and maintain ZLD;
- Understanding the effects to the salt balance on ability to reuse water;
- Predicting flue gas stack evaporation and salt balance for coal firing and future transition to gas firing of boilers at varying capacity factors and combinations of coal and gas;
- Ability to update data with actual date for past operation to improve accuracy of future operations;
- A non-proprietary model that plant personnel can use without outside support;
- Simple inputs and operation.
A Microsoft Excel model was created to predict pond storage volumes, chloride and TDS concentrations. FGD evaporation is correlated to capacity factors, temperature, humidity, barometric pressure, and fuel properties. Evaporation rates for mixtures of coal and natural gas were calculated using an inhouse model and graphed for the non-proprietary model. The model includes use of reverse osmosis and evaporation for disposal of water and salts. Inputs include capacity factors, process flows, and constituents, rainfall, and environmental conditions. Several examples of model runs will be provided.
The model was calibrated with historical data; results confirm monthly flows and pond volumes are accurate to +/- 5% over a year. The user inputs 12 months of operating data to predict future conditions. The model offers monthly outputs and finer adjustments on operation. For example, FGD purge rate, gypsum cake solids water content, pond level control, and RO system operation may be adjusted for each month.
OUC has found the model useful in optimizing dispatch decisions and maintaining ZLD requirements. Methods used in this interactive water balance tool may be helpful for other facilities to maintain water balance across a system, track water quality for reuse applications, and test new operating conditions.
Dr. Carey has over 11 years of experience in biological and chemical wastewater treatment in industrial, municipal, and academic settings. At Worley, he serves as an environmental process engineer; his primary role is consulting and design in oil refineries, power plants, chemical manufacturing, and other industries.
Historical Papers
As an offering of the high quality technical content presented at the IWC, please review these historical papers from IWC-past. Technical Papers from more recent conferences, and our archived history, can be found here. Check back often, as content will be updated on a regular basis.
Please click on title to download paper
IWC 95-02: A COMPARISON OF A SELECTIVE RESIN WITH A CONVENTIONAL RESIN FOR NITRATE REMOVAL
G.L. Dimotsis, Sybron Chemicals Inc., Birmingham, NJ and F.X. McGarvey, Sybron Chemicals Inc., Birmingham, NJ
IWC 09-36: Steam Generation Using Produced Water: Lessons Learned
Martin R. Godfrey, Nalco Company, Naperville, Illinois
Keywords: Produced Water, OTSG, Evaporator, Steam Generation, SAGD
Prepared Discussion for IWC 09-36:
Discusser: Melonie Myszczyszyn, CNRL Facilities Engineer, Alberta, Canada
IWC 07-24: Equipment Design Considerations for Lime and Ion Exchange Treatment of Produced Water in Heavy Oil Extraction
Robert Holloway, Holloway Associates, Etobicoke, Ontario, Canada
Gordon Page, Page Technology Ltd., Calgary, Alberta, Canada
Prepared Discussion for IWC 07-24:
John E. Fair, P.Eng., Fair Canada Engineering Ltd., Calgary, Alberta
Author’s Closure for IWC 07-24:
Robert Holloway, Holloway Associates, Etobicoke, Ontario, Canada
Gordon Page, Page Technology Ltd., Calgary, Alberta, Canada