FLASH EVAPORATORS FOR DESALINATION

In 1940 Aqua-Chem, as a Division of the Cleaver-Brooks Company, entered into a contract with the United States Corps of Engineers to develop a machine to purify water. The program was successful and more than 2250 units were manufactured for use by the Armed Forces throughout the World during World War II. After the War, Aqua-Chem pursued its research in the conversion and purification of saline waters by conducting tests on its own, and in collaboration with the U.S. Government. Substantial technological advances were made which broadened the application of desalination equipment to include commercial applications. These advances were based on a progressive development program of corporate research and development, production and field trials of successively larger evaporators and finally commercial production of a full range of desalting plants.

Flash evaporator in Puerto Rico

These Aqua-Chem units purify over 5 million gallons per day in Puerto Rico, for use in refinery processes.

Large-scale prototype evaporators were built and operated to confirm theoretical assumptions and to obtain actual performance data in lieu of extrapolation.

One of the most significant achievements in this field by Aqua-Chem was the development of the long tube multi-stage flash evaporator. The multi-stage flash evaporator produces distilled water from feedwater by heating it until it is ready to flash. The flashed vapor is drawn to the cooler tube bundle surfaces where it is condensed and collected as distillate. Flashing occurs when heated brine is turbulated in a chamber which is maintained at a lower vapor pressure than that of the entering heated brine. Heat is given up by the brine and a portion converted into vapor until the temperature of the brine reaches the saturation temperature corresponding to the chamber pressure. In other words, the heated brine is flashed off by a pressure reduction. Entrained brine droplets are removed from the vapor by entrainment separators and the pure vapor condenses into distillate on the condenser tubes. The distillation process operates from a low vacuum in the first stage to a high vacuum in the last stage, with stage-to-stage pressure differential being the key to the repeated flashing. Details of the process can be seen in this technical bulletin issued by Aqua-Chem.

The first long tube multi-stage flash evaporating plant was installed by Aqua-Chem in an Oxnord, California power plant in 1959. It was later moved to Santa Catalina Island. It was a 100,000 gallon per day 28 stage flash evaporator.

illustration comparing the two types of battery cases

Unit destined for Kharg Island in Persian Gulf under construction in shop.

Prior to the advent of the flash evaporator, the only large plants for desalination were multiple effect submerged tube units. The flash evaporator enabled the development of high economy, lower cost, and new methods of scale control which made desalination possible in many parts of the world. The long tube principle eliminates the need for a waterbox at each stage thus lowering costs and pumping power requirements. The flash evaporator as opposed to submerged tube greatly reduced the scaling problems associated with seawater evaporation and enabled the use of newer and more effective means of scale control.

As a result of their developments, Aqua-Chem was established as a world leader in the design and manufacture of desalination units, a position it maintained until the sale of Cleaver-Brooks.