HPD® Evaporation and Crystallization
The CoLD® Process
Unique Zero Liquid Discharge (ZLD) System for Treatment of Wastewater from Coal-Fired Generation
Flue Gas Desulfurization (FGD) and Integrated Gasification Combined Cycle (IGCC) processes produce large volumes of saline wastewater containing toxic and hazardous constituents. Physical, chemical, and biological treatment methods can reduce the concentrations of these pollutants, but the volume and salinity of the wastewater is unchanged. Evaporation and crystallization, a proven method of treating these wastewaters, have been used for over forty years in the power industry to achieve zero liquid discharge (ZLD).
CoLD Eliminates Pre-Treatment & Addition of Chemicals
Veolia Water Technologies has applied proven process designs based on HPD® Industrial Crystallization Technology and successfully utilized in the salt, fertilizer, and chemical industries to develop a simple and robust process to separate the wastewater from coal-fired power plants into clean water and a stable, non-hazardous solid for disposal and/or re-use.
The CoLD® Process is a simple and economical approach to ZLD. It requires no chemical treatment of the wastewater and generates no additional sludge for disposal. The CoLD® Process is an ideal solution to address stricter water reuse standards, mandated ZLD, and increasing regulation of discharge limits of total dissolved solids (TDS) facing the power industry.
Coal-Fired Wastewater Chemistry
|Wet Limestone FGD Purge||IGCC Process Wastewater|
Wastewater from wet limestone scrubbing contains toxins and hazardous constituents such as metals, mercury, and selenium. It is composed mainly of chloride salts of calcium and magnesium, and is saturated in calcium sulfate.
IGCC wastewater is comprised of toxic and corrosive components such as chlorides, ammonia, organic acids, cyanides, sulfides, and heavy metals including mercury and selenium.
Limitations of Conventional Methods
Conventional thermal processes for FGD and IGCC waste streams require clarification and extensive pre-treatment of the wastewater with lime, soda ash, caustic, and other chemicals to replace the calcium, magnesium, and ammonium ions in the wastewater with sodium ions in order to produce a crystalline solid to achieve ZLD.
In some cases, a final drying step is necessary to produce a stable solid suitable for disposal. Pre-treatment equipment includes chemical feed/storage facilities, solids settling or filtration equipment, and sludge dewatering equipment.
These additional facilities increase the footprint of the ZLD system as well as the capital costs and overall maintenance. The logistics of unloading, storing, and preparing chemicals and dewatering and transporting sludge for disposal substantially increase the OPEX.
The CoLD Process Overcomes Challenges of Coal-Fired Wastewater
The CoLD Process is operated at low temperature. The chemistries of FGD and IGCC wastewaters favor the formation of many hydrates and double salts which precipitate at low concentrations as the temperature of the solution is lowered.
When concentrating the waste stream at low temperature, dissolved solids will crystallize at relatively low concentration, without the need for chemical pretreatment and resulting sludge production.
Benefits of the CoLD Process
- Achieves Zero Liquid Discharge (ZLD) on difficult coal-fired wastewaters
- Lowest CAPEX and OPEX
- No chemical pre-treatment or sludge production
- Produces clean water for reuse and stable solids for disposal
- Simple, robust process with high reliability and availability
- Operating experience in other industries