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John O | October 2017

New filter improves power plant water consumption for cooling


Researchers at Sandia National Laboratory (Albuquerque, N.M.) have developed a new silica filter for the coolant in power plants to reduce the amount of freshwater that plants consume by increasing the number of times that a cooling tower can be reused and recycled.

 


Tina Nenoff, Pat Brady, and former post-doc student Koroush Sasan researched how hydrotalcite can filter silica out of cooling tower water at power plants. (Randy Montoya)

 

This solution helps address the growing issue of water consumption by power plants, which has risen, according to a report from Sandia, to about 500 billion gallons per day.

 

Silica buildup is a significant factor in the ability for power plants to reuse cooling towers. Silica is a naturally-occurring substance in freshwater and forms scales on turbines, boilers, heat exchangers, pipes, and more, which leads to equipment failure, inability to transfer heat, and costly repairs.

 

“The cost to treat and recycle water used at power plants is estimated to be 1.5 to 2 times the cost of freshwater, often because of the high price of current silica removal methods,” the article added.

 

Over two years, Sandia researchers worked with hydrotalcite, which is layered with aluminum hydroxide, and found that it could remove nearly 90 percent of accumulated silica in recycled water and could be reused for five cycles.

 

Students at the University of New Mexico assisted the researchers with scale-up analysis on hydrotalcite to determine the real-world cost and energy savings from this new filter.

 

The research was recently published in the Journal of Water Process Engineering. The abstract read:

 

“Dissolved silica is ubiquitous in impaired waters, a fouling agent in desalination membranes, resistant to existing antiscalants, and difficult to remove from power plant feed waters, thereby inhibiting long term reuse of industrial water. Herein we report a systematic materials study of an inorganic anion exchanger, hydrotalcite (HTC, (Mg6Al2(OH)16(CO3)•4H2O)), for the highly selective removal of silica from aqueous solutions.

 

“HTCs exist in two different forms: crystalline uncalcined and calcined (550 °C) phases. Variables studied in ion-exchange studies include pH, HTC concentration, duration and selectivity with competing anions. Results indicate calcined HTC effectively removes silicate anion from different waters including simulated concentrated cooling tower water (CCTW), and waters with high concentration of competing ions, such as SO42− and Cl.

 

“The non-optimized HTC can be easily regenerated and recycled. Calcined HTC has a silica adsorption capacity of 45 mg SiO2/g HTC. The single path flow through (SPFT) studies indicate that using ∼1.1 g/L calcined HTC effectively removes >90% of the dissolved silica from the CCTW. A pseudo-second order kinetic model was fit the experimental data of calcined HTC.

 

“Data is supported by Fourier transform infrared (FTIR), Thermogravimetric-Mass analyses (TGA-MS), Energy dispersive spectroscopy (EDS) and powder X-ray diffraction (XRD).”

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