Deicingis the process of removingsnow,iceorfrostfrom a surface.Anti-icingis the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prevent adhesion of ice to make mechanical removal easier.
Deicing can be accomplished by mechanical methods (scraping, pushing); through the application ofheat;by use of dry or liquid chemicals designed to lower thefreezing pointof water (varioussaltsorbrines,alcohols,glycols); or by a combination of these different techniques.
Application areas
editRoadways
editIn 2013, an estimated 14 million tons of salt were used for deicing roads in North America.[1]
Deicing of roads has traditionally been done withsalt,spread bysnowplowsordump trucksdesigned to spread it, often mixed withsandandgravel,on slick roads.Sodium chloride(rock salt) is normally used, as it is inexpensive and readily available in large quantities. However, sincesalt waterstill freezes at −18 °C (0 °F), it is of no help when the temperature falls below this point. It also has a tendency to causecorrosion,rustingthesteelused in most vehicles and therebarin concrete bridges. Depending on the concentration, it can be toxic to some plants and animals,[2]and some urban areas have moved away from it as a result. More recent snowmelters use other salts, such ascalcium chlorideandmagnesium chloride,which not only depress the freezing point of water to a much lower temperature, but also produce anexothermic reaction.They are somewhat safer forsidewalks,but excess should still be removed.
More recently, organic compounds have been developed that reduce the environmental issues connected with salts and have longer residual effects when spread on roadways, usually in conjunction with salt brines or solids. These compounds are often generated as byproducts of agricultural operations such assugar beetrefining or thedistillationprocess that producesethanol.[3][4]Other organic compounds arewood ashand a deicing salt calledcalcium magnesium acetatemade from roadside grass or even kitchen waste.[5]Additionally, mi xing common rock salt with some of the organic compounds and magnesium chloride results in spreadable materials that are both effective to much colder temperatures (−34 °C (−29 °F)) as well as at lower overall rates of spreading per unit area.[6]
Solar road systems have been used to maintain the surface of roads above the freezing point of water. An array of pipes embedded in the road surface is used to collect solar energy in summer, transfer the heat to thermal banks and return the heat to the road in winter to maintain the surface above 0 °C (32 °F).[7]This automated form of renewable energy collection, storage and delivery avoids the environmental issues of using chemical contaminants.
It was suggested in 2012 thatsuperhydrophobicsurfaces capable of repelling water can also be used to prevent ice accumulation leading toicephobicity.However, not every superhydrophobic surface is icephobic[8]and the method is still under development.[9]
Trains and rail switches
edit
Trains andrail switchesin Arctic regions can have significant problems with snow and ice build up. They need a constant heat source on cold days to ensure functionality. On trains it is primarily thebrakes,suspensionandcouplersthat require heaters for deicing. On rails it is primarily the switches that are sensitive to ice. High-powered electrical heaters prevent ice formation and rapidly melt any ice that forms.
The heaters are preferably made of PTC material, for examplePTC rubber,to avoid overheating and potentially destroying the heaters. These heaters are self-limiting and require no regulating electronics; they cannot overheat and require no overheat protection.[10]
Aviation
edit
Ground deicing of aircraft
editOn the ground, when there are freezing conditions andprecipitation,deicing an aircraft is commonly practiced. Frozen contaminants interfere with the aerodynamic properties of the vehicle. Furthermore, dislodged ice can damage the engines.
Ground deicing methods include:
- Spraying on variousaircraft deicing fluidsto melt ice and prevent reformation
- Using unheated forced air to blow off loose snow and ice
- Using infrared heating to melt snow, ice, and frost without using chemicals
- Mechanical deicing using tools such as brooms, scrapers, and ropes
- Placing an aircraft in a warm hangar
In-flight deicing
editIce can build up on aircraft in flight due to atmospheric conditions, causing potential degradation of flight performance. Large commercial aircraft almost always have in-flight ice protections systems to shed ice buildup and prevent reformation. Ice protection systems are becoming increasingly common in smaller general aviation aircraft as well.
Ice protection systems typically use one or more of the following approaches:
- pneumatic rubber "boots" on leading edges of wings and control surfaces, which expand to break off accumulated ice
- electrically heated strips on critical surfaces to prevent ice formation and melt accumulated ice
- bleed air systems which take heated air from the engines and duct them to locations where ice can accumulate
- fluid systems which "weep" deicing fluid over wings and control surfaces via tiny holes
Airport pavement
editDeicing operations for airport pavement (runways,taxiways,aprons,taxiway bridges) may involve several types of liquid and solid chemical products, includingpropylene glycol,ethylene glycoland other organic compounds. Chloride-based compounds (e.g.salt) are not used at airports, due to their corrosive effect on aircraft and other equipment.[11]: 34–35
Ureamixtures have also been used for pavement deicing, due to their low cost. However, urea is a significant pollutant in waterways and wildlife, as it degrades toammoniaafter application, and it has largely been phased out at U.S. airports. In 2012 theU.S. Environmental Protection Agency(EPA) prohibited use of urea-based deicers at most commercial airports.[12]
Water agitator deicer
editWater agitators are electric motors put under water that propel up warmer water andagitatethe surface with it to deice aquatic structures on rivers and lakes in freezing temperatures. There are also agitator bubblers that usecompressed air,run through ahose,and released to agitate the water.[13]
Deicing chemicals
editAll chemical deicers share a common working mechanism: they chemically prevent water molecules from binding above a certain temperature that depends on the concentration. This temperature is below 0 °C, the freezing point of pure water (freezing point depression). Sometimes, there is anexothermicdissolutionreaction that allows for an even stronger melting power. The following lists contains the most-commonly used deicing chemicals and their typicalchemical formula.
Salts
edit- Sodium chloride(NaCl ortable salt;the most common deicing chemical)
- Magnesium chloride(MgCl
2,often added to salt to lower its working temperature) - Calcium chloride(CaCl
2,often added to salt to lower its working temperature, attacks concrete) - Potassium chloride(KCl)
- Calcium magnesium acetate(CaMg
2(CH
3COO)
6) - Potassium acetate(CH
3COOK) - Potassium formate(CHO
2K) - Sodium formate(HCOONa)
- Calcium formate(Ca(HCOO)
2)
Organics
edit- Urea(CO(NH
2)
2), a common fertilizer - Agricultural by-products, generally used as additives tosodium chloride
- Methanol(CH
4O), scarcely used on roads - Ethylene glycol(C
2H
6O
2), scarcely used on roads - Propylene glycol(C
3H
8O
2), scarcely used on roads - Glycerol(C
3H
8O
3), scarcely used on roads
Environmental impact and mitigation
editDeicing salts such assodium chlorideorcalcium chlorideleach into natural waters, strongly affecting their salinity.[1]
Ethylene glycol and propylene glycol are known to exert high levels ofbiochemical oxygen demand(BOD) during degradation in surface waters. This process can adversely affect aquatic life by consuming oxygen needed by aquatic organisms for survival. Large quantities ofdissolved oxygen(DO) in thewater columnare consumed when microbial populations decompose propylene glycol.[14]: 2–23
Some airports recycle used deicing fluid, separating water and solid contaminants, enabling reuse of the fluid in other applications. Other airports have an on-site wastewater treatment facility, and/or send collected fluid to a municipalsewage treatmentplant or a commercial wastewater treatment facility.[11]: 68–80 [15]
See also
editReferences
edit- ^abMiguel Cañedo-Argüelles, Ben J. Kefford, Christophe Piscart, Narcís Prata, Ralf B.Schäferd, Claus-Jürgen Schulze (2013). "Salinisation of Rivers: An Urgent Ecological Issue".Environmental Pollution.173:157–67.doi:10.1016/j.envpol.2012.10.011.PMID23202646.
{{cite journal}}:CS1 maint: multiple names: authors list (link) - ^Fischel, Marion (2001).Evaluation of selected deicers based on a review of the literature.Colorado Dept. of Transportation.OCLC173668609.
- ^Amanda Rabinowitz (February 25, 2008)."Beets Part of New Recipe to Treat Icy Roads".National Public Radio.
- ^Richard J. Brennan (January 21, 2012)."Beet juice melts ice from winter roads".Toronto Star.
- ^Post, Rachael (March 3, 2014)."The alternatives to salt for battling ice: cheese, beets and ash".The Guardian.
- ^"About Magic Salt".2007. Archived fromthe originalon 2009-06-05.
- ^"Thermal Energy Storage in ThermalBanks for under runway heating".ICAX Ltd, London.Retrieved2011-11-24.
- ^Nosonovsky, M.; Hejazi, V. (2012). "Why superhydrophobic surfaces are not always icephobic".ACS Nano.6(10): 8488–8913.doi:10.1021/nn302138r.PMID23009385.
- ^Hejazi, V.; Sobolev, K.; Nosonovsky, M. I. (2013)."From superhydrophobicity to icephobicity: forces and interaction analysis".Scientific Reports.3:2194.Bibcode:2013NatSR...3E2194H.doi:10.1038/srep02194.PMC3709168.PMID23846773.
- ^2012 Autumn & Winter Season (Drivers' Briefing). London, UK: First Capital Connect. September 2012.
- ^abTechnical Development Document for the Final Effluent Limitations Guidelines and New Source Performance Standards for the Airport Deicing Category(Report). Washington, D.C.: U.S. Environmental Protection Agency (EPA). April 2012. EPA-821-R-12-005.
- ^"Airport Deicing Effluent Guidelines".EPA. 2021-02-10.
- ^"What to Look for when Buying a Dock De-Icer".
- ^Environmental Impact and Benefit Assessment for the Final Effluent Limitation Guidelines and Standards for the Airport Deicing Category(Report). EPA. April 2012. EPA-821-R-12-003.
- ^Tom Gibson (September 2002)."Let the Bugs Do the Work".Progressive Engineer.Archived fromthe originalon 8 February 2011.Retrieved21 February2011.
External links
edit
Media related toDe-icing of aircraftat Wikimedia Commons
