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Fact Sheet — Evaporation Evaporation is a natural process for transforming water in liquid form to water vapor in the air. Evaporation depends on local humidity, temperature, and wind. Drier climates generally favor evaporation as a waste management technique. This fact sheet describes several different ways to dispose of produced water through evaporation. The simplest approach to evaporation involves placing produced water in a pond, pit, or lagoon with a large surface area. Water can then passively evaporate from the surface. As long as evaporation rates exceed inflows (including precipitation), produced water will be removed. [insert figure of pond; Caption: evaporation pond; Source: BC Technologies Ltd.]. Evaporation rates depend on the size and depth of the pond and the characteristics of the influent. For example, in semiarid regions, hot, dry air moving from a land surface will result in higher evaporation rates for smaller ponds. The evaporation rate of a solution will decrease when the relative shares of solids and chemicals rise. Produced water can be managed at small onsite evaporation ponds or can be sent offsite to commercial facilities that employ large evaporation basins. Examples of commercial evaporation facilities can be found in Colorado, New Mexico, Utah, and Wyoming (Puder and Veil 2006). One potential problem posed by evaporation ponds stems from their attractiveness to migratory waterfowl. If evaporation ponds contain oil or other hydrocarbons on the surface, birds landing in the ponds could become coated with oil and suffer harm. Covering ponds with netting helps to avoid this problem. [insert photo of netting on pond; caption: evaporation pond covered with netting; Source: U.S. Fish and Wildlife Service] Evaporation rates can be enhanced by spraying the water through nozzles. The nozzles create many small droplets with increased surface areas. In some arid parts of the western United States, this has been done through portable misting towers. These are essentially spray nozzles at the top of vertical pipes. The water is sprayed into the air and evaporates before hitting the ground. However, this practice can lead to salt damage to soil and vegetation. Therefore, misting towers are not currently recommended as a management practice. An experimental project involving sprayed evaporation for managing excess rainwater was conducted at a waste treatment facility on the Gulf Coast. Even in the humid local climate, the mechanical sprayer shown successfully increased evaporation rates. [insert 2 figures of sprayer; caption: Mechanical sprayer used for evaporation; Source: J. Veil, Argonne National Laboratory] Boysen et al. (1999) describe an innovative produced water treatment process combining natural freezing and thawing coupled with evaporation (Freeze/Thaw Evaporation or FTE®). [insert figure of process flow chart; caption: The FTE® process; Source: BC Technologies Ltd.] When the ambient temperature drops below 32°F, produced water is pumped from a holding pond and sprayed onto a freezing pad. As the spray freezes, an ice pile forms. [insert figure of ice pile; caption: Ice pile from spraying produced water in the FTE® process; Source: BC Technologies Ltd.] When the temperature warms, ice on the freezing pad melts. The highly saline brine, identified by its high electrical conductivity, is separated and pumped to a pond where it can be utilized as an additive for drilling fluids. The remaining purified water is then pumped from the freezing pad to a holding pond where it can be stored prior to beneficial reuse or discharge. FTE® does not generate new wastes; and no chemicals are added at any point in this treatment process. Unless artificial refrigeration is employed, this process is limited to cooler climates during the colder times of the year. Most existing FTE® installations are located in Wyoming. However, ponds can be used for spray evaporation in warmer months. References Boysen, J.E., J.A. Harju, B. Shaw, M. Fosdick, A. Grisanti, and JA. Sorensen, 1999, “The Current Status of Commercial Deployment of the Freeze Thaw Evaporation Treatment of Produced Water,” SPE 52700, presented at SPE/EPA 1999 Exploration and Production Environmental Conference, Austin, TX, March 1–3. Boysen, D.B., J.E. Boysen, and J.A. Boysen, 2002, “Creative Strategies for Produced Water Disposal in the Rocky Mountain Region,” presented at the 9th International Petroleum Environmental Conference, Albuquerque, NM, Oct. 22–25. Available at http://ipec.utulsa.edu/Conf2002/boysen_89.pdf. Puder, M.G., and J.A. Veil, 2006, Offsite Commercial Disposal of Oil and Gas Exploration and Production Waste: Availability, Options, and Cost, prepared for U.S. Department of Energy, National Energy Technology Laboratory, Aug., 148 pp. Available at http://www.ead.anl.gov/pub/dsp_detail.cfm?PubID=2006.
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