Countercurrent Exchange in Industrial and Scientific Systems
Countercurrent Chromatography is a method of separation, that is based on the differential partitioning of analytes between two immiscible liquids using countercurrent or cocurrent flow. Evolving from Craig's Countercurrent Distribution (CCD), the most widely used term and abbreviation is CounterCurrent Chromatography or CCC, in particular when using hydrodynamic CCC instruments. The term partition chromatography is largely a synonymous and predominantly used for hydrostatic CCC instruments.
- Distillation of chemicals such as in petroleum refining is done towers or columns with perforated trays. Vapor from the low boiling fractions bubbles upward through the holes in the trays in contact with the down flowing high boiling fractions. The concentration of low boiling fraction increases in each tray up the tower as it is "stripped". The low boiling fraction is drawn off the top of the tower and the high boiling fraction drawn from the bottom. The process in the trays is a combination of heat transfer and mass transfer. Heat is supplied at the bottom, known as a "reboiler" and cooling is done at the with a condenser at the top.
- Liquid-liquid extraction (also called 'solvent extraction' or 'partitioning' is a common method for extracting a substance from one liquid into another liquid at a different 'phase' (such as "slurry"). This method, which implements a countercurrent mechanism, is used in nuclear reprocessing, ore processing, the production of fine organic compounds, the processing of perfumes, the production of vegetable oils and biodiesel, and other industries.
- Gold can be separated from a cyanide solution with the Merrill-Crowe process using Counter Current Decantation (CCD). In some mines, Nickel and Cobalt are treated with CCD, after the original ore was treated with concentrated Sulfuric acid and steam in Titanium covered autoclaves, producing nickel cobalt slurry. The nickel and cobalt in the slurry are removed from it almost completely using a CCD system exchanging the cobalt and nickel with flash steam heated water.
- Lime can be manufactured in countercurrent furnaces allowing the heat to reach high temperatures using low cost, low temperature burning fuel. Historically this was developed by the Japanese in certain types of the Anagama kiln. The kiln is built in stages, where fresh air coming to the fuel is passed downwards while the smoke and heat is pushed up and out. The heat does not leave the kiln, but is transferred back to the incoming air, and thus slowly builds up to 3000 °C and more.
- Cement may be created using a countercurrent kiln where the heat is passed in the cement and the exhaust combined, while the incoming air draft is passed along the two, absorbing the heat and retaining it inside the furnace, finally reaching high temperatures.
- Gasification - the process of creating methane and carbon monoxide from organic or fossil matter, can be done using a Counter-current fixed bed ("up draft") gasifier which is built in a similar way to the Anagama kiln, and must therefore withstand more harsh conditions, but reaches better efficiency.
- In nuclear power plants, water leaving the plant must not contain even trace particles of Uranium. Counter Current Decantation (CCD) is used in some facilities to extract water, totally clear of Uranium.
- Some Centrifugal extractors use counter current exchange mechanisms for extracting high rates of the desired material.
- Some protein skimmers - a device to clean saltwater pools and fish ponds of organic mater - use counter current technologies.
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