Spray drying
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2008-06-25T00:39:48Z
12.202.15.46
{{Mergefrom|Spray dryer|date=June 2007}}
'''Spray drying''' is a commonly used method of drying a liquid feed through a hot gas. Typically, this hot gas is air but sensitive materials such as [[Medication|pharmaceuticals]], and [[solvent]]s like [[ethanol]] require [[oxygen]]-free drying and [[nitrogen]] gas is used instead. The liquid feed varies depending on the material being dried and is not limited to food or pharmaceutical products, and may be a [[solution]], [[colloid]] or [[Suspension (chemistry)|suspension]]. This process of drying is a one step rapid process and eliminates additional processing.
The liquid feed is pumped through an [[atomiser]] device that produces fine droplets into the main drying chamber. Atomisers vary with rotary, single fluid, two-fluid, and ultra-sonic designs. These different styles have different advantages and disadvantages depending on the application of the spray drying required. In some instances a Spray Nozzle is used in place of an atomiser for a different dispersion rate.
The hot drying gas can be passed as a co-current or counter-current flow to the atomiser direction. The co-current flow enables the particles to have a lower residence time within the system and the particle separator (typically a cyclone device) operates more efficiently. The counter-current flow method enables a greater residence time of the particles in the chamber and usually is paired with a fluidised bed system.
Spray drying often is used as an encapsulation technique by the food and pharmaceutical industries. A substance to be encapsulated (the load) and an [[Amphiphile|amphipathic]] carrier (usually some sort of modified [[starch]]) are [[Homogenization|homogenized]] as a [[suspension (chemistry)|suspension]] in water (the slurry). The slurry is then fed into a spray drier, usually a tower heated to temperatures well over the boiling point of [[water]].
As the slurry enters the tower, it is atomized. Partly because of the high [[surface tension]] of water and partly because of the [[Hydrophobe|hydrophobic]]/[[Hydrophile|hydrophilic]] interactions between the amphipathic carrier, the water, and the load, the atomized slurry forms [[micelle]]s. The small size of the drops (averaging 100 [[micrometre|micrometer]]s in diameter) results in a relatively large surface area which dries quickly. As the water dries, the carrier forms a hardened shell around the load.
Load loss is usually a function of molecular weight. That is, lighter molecules tend to boil off in larger quantities at the processing temperatures. Loss is minimized industrially by spraying into taller towers. A larger volume of air has a lower average humidity as the process proceeds. By the [[osmosis]] principle, water will be encouraged by its difference in [[fugacity|fugacities]] in the vapor and liquid phases to leave the micelles and enter the air. Therefore, the same percentage of water can be dried out of the particles at lower temperatures if larger towers are used.
The application of the spray drying encapsulation technique is to prepare "dehydrated" powders of substances which do not have any water to dehydrate. For example, instant drink mixes are spray dries of the various chemicals which make up the beverage. The technique was once used to remove water from food products; for instance, in the preparation of dehydrated milk. Because the milk was not being encapsulated and because spray drying causes [[thermal degradation]], milk dehydration and similar processes have been replaced by other dehydration techniques. Skim [[Powdered milk|milk powders]] are still widely produced using spray drying technology around the world, typically at high solids concentration for maximum drying efficiency. Thermal degradation of products can be overcome by using lower operating temperatures and larger chamber sizes for increased residence times.
Recent research is now suggesting that the use of spray-drying techniques may be an alternative method for crystallisation of amorphous powders during the drying process since the temperature effects on the amorphous powders may be significant depending on drying residence times.
== Sources ==
* Chiou, D., Langrish. T.A.G., Braham, R. (2008) The Effect of Temperature on the Crystallinity of Lactose Powders Produced by Spray Drying, Journal of Food Engineering, 86(2), 288-293.
* Chiou, D., Langrish, T.A.G., Braham, R. (2008) Partial Crystallisation Behaviour During Spray Drying: Simulations and Experiments, Drying Technology, 26(1), 27- 38.
* Chiou, D., Langrish, T.A.G. (2007) Crystallisation of Amorphous Components in Spray-Dried Powders, Drying Technology, 25(9), 1423-1431.
* ''Nutritional evaluation of food processing'' second edition (1975), Robert S. Harris, Ph.D. and Endel Karmas Ph.D. (eds)
* Keey, R.B., (1992). Drying of Loose and Particulate Materials, 1st, (pp504). Hemisphere Publishing Corporation,
== External links ==
* {{cite web
| url=http://www.andersonprocessing.com/index.php
| title=Anderson Custom Processing
}}
* {{cite web
| url=http://www.sono-tek.com/
| title=Sono-Tek, Ultrasonic Spray Technology, A World Leader in Spray Drying Accessories
}}
* {{cite web
| url=http://www.marriottwalker.com
| title=Marriott Walker Corporation, A World Leader in Spray Drying Technology
}}
* {{cite web
| url=http://www.niroinc.com/html/drying/fdspray.html
| title=Niro's expertise in spray drying
}}
* {{cite web
| url=http://www.oc-sd.co.jp/english/e03_spraydrying.htm
| title=Short overview on spray drying from Japanese manufacturer
}}
* {{cite web
| url=http://www.hyfoma.com/en/content/processing-technology/food-heat-transfer-cooler-heater/drying/
| title=Spray drying on Hyfoma.com
| publisher=[[Hyfoma]]
}}
* {{cite web
| url=http://www.generalspraydrying.com/
| title=General Spray Drying Services in New Jersey
}}
* {{cite web
| url=http://www.niro.com/ndk_website/niro/cmsdoc.nsf/WebDoc/ndkk5hmc6zSprayDryers
| title=GEA Niro A/S - Authoritative article on Spray Drying
}}
* {{cite web
| url=http://technalysis.us/pharmaceutical_industry.aspx
| title=technalysis.us - CAE spray dryin
}}
* {{cite web
| url=http://www.delavan.co.uk/pdfs/sdx-brochure%20.pdf
| title=Delavan spray drying technologies
}}
* {{cite web
| url=http://www.delavan.co.uk/pdfs/Spray%20Drying%20-%20Technical%20know%20how.pdf
| title=Delavan's technical know how on spray drying
}}
* {{cite web
| url=http://www.luebbers.org
| title= Lübbers - Innovative expert in Spray Drying
}}
* {{cite web
| url=http://www.anhydro.com/content/us/products/dryers/spray_dryers
| title=Anhydro A/S - Leading Experts in Spray Drying
}}
* {{cite web
| url=http://www.dspllc.net
| title=Dietrich's Specialty Processing, LLC
}}
==See also==
* [[Spray Nozzle]]
[[Category:Food industry]]
[[Category:Flavor technology]]
[[Category:Chemical processes]]
[[Category:Unit operations]]
[[Category:Industrial processes]]
[[Category:Pharmaceutical industry]]
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