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Innovative Atmospheric Pressure Desalination


Arizona State University; Tempe AZ.
September 1999

Report #52 - Executive Summary -

A relatively new non-traditional and innovative heat efficient tower process, referred to as Dewvaporation, has been investigated and is now operational at Arizona State University. Dewvaporation technique is a specific process of humidification-dehumidification desalination, which uses air as a carrier-gas to evaporate water from saline feeds and dew form pure condensate at constant atmospheric pressure. The heat needed for evaporation is supplied by the heat released by dew fall condensation on opposite sides of a heat transfer wall. Since only a small amount of external heat is needed to establish temperature differences across the wall and since the temperature of the external heat is versatile, the external heat source can be from waste heat, from solar collectors, or from fuel combustion. The unit is constructed out of thin water wettable plastics and operated at pressure drops of less than 0.1 inches of water.

This bench scale database allows design for and demonstration of this technology at the 1,000 gallons per day capacity. The projected capital cost for the 1,000 gallons (3.79m3) per day unit based on laboratory data has been estimated at $1,397, which includes a water heater, two pumps, one air fan (pumps and fan require 0.46kWh per day electricity), and a manufacturer's gross margin of 30%. Totally inclusive operating costs would be $3.35 per 1,000 gallons of condensate. Lower operating costs of about $1.50 per 1,000 gallons of condensate should be realized by solar energy or atmospheric steam waste heat. The unit dimensions would be 4 feet x 4 feet x 8 feet high (1.22 m x 1.22 m x 2.44 m high).

A test unit was built to study the scaling phenomenom in the Dewvaporation process. No scaling was observed on the heat transfer walls after 2/3 of seawater and simulated seawater were evaporated at 190oF (87.78oC). Evaporation at the air/water interface seems to be the key to scale elimination inherent in this evaporative process.


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For more information about the DWPR program, contact Kevin Price at: Bureau of Reclamation, 86-69000, PO Box 25007, Denver CO 80225; phone (303) 445-2260; or e-mail a message to MPrice@usbr.gov.