Process of removing ice, snow, or frost from a surface
Deicing
is the process of removing
snow
,
ice
or
frost
from a surface.
Anti-icing
is 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 of
heat
; by use of dry or liquid chemicals designed to lower the
freezing point
of water (various
salts
or
brines
,
alcohols
,
glycols
); or by a combination of these different techniques.
Application areas
[
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]
Roadways
[
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]
In 2013, an estimated 14 million tons of salt were used for deicing roads in North America.
[1]
Deicing of roads has traditionally been done with salt, spread by
snowplows
or
dump trucks
designed to spread it, often mixed with
sand
and
gravel
, on slick roads.
Sodium chloride
(rock salt) is normally used, as it is inexpensive and readily available in large quantities. However, since
salt water
still freezes at ?18 °C (0 °F), it is of no help when the temperature falls below this point. It also has a tendency to cause
corrosion
,
rusting
the
steel
used in most vehicles and the
rebar
in 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 as
calcium chloride
and
magnesium chloride
, which not only depress the freezing point of water to a much lower temperature, but also produce an
exothermic reaction
. They are somewhat safer for
sidewalks
, 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 as
sugar beet
refining or the
distillation
process that produces
ethanol
.
[3]
[4]
Other organic compounds are
wood ash
and a deicing salt called
calcium magnesium acetate
made from roadside grass or even kitchen waste.
[5]
Additionally, mixing 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 that
superhydrophobic
surfaces capable of repelling water can also be used to prevent ice accumulation leading to
icephobicity
. However, not every superhydrophobic surface is icephobic
[8]
and the method is still under development.
[9]
Trains and rail switches
[
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]
Trains and
rail switches
in 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 the
brakes
,
suspension
and
couplers
that 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 example
PTC 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
[
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]
Ground deicing of aircraft
[
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]
On the ground, when there are freezing conditions and
precipitation
, 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 various
aircraft deicing fluids
to 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
[
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]
Ice 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
[
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]
Deicing operations for airport pavement (
runways
,
taxiways
,
aprons
,
taxiway bridges
) may involve several types of liquid and solid chemical products, including
propylene glycol
,
ethylene glycol
and 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
Urea
mixtures 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 to
ammonia
after application, and it has largely been phased out at U.S. airports. In 2012 the
U.S. Environmental Protection Agency
(EPA) prohibited use of urea-based deicers at most commercial airports.
[12]
Deicing chemicals
[
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]
All 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 an
exothermic
dissolution
reaction that allows for an even stronger melting power. The following lists contains the most-commonly used deicing chemicals and their typical
chemical formula
.
Salts
[
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]
Organics
[
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]
Environmental impact and mitigation
[
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]
Deicing salts such as
sodium chloride
or
calcium chloride
leach into natural waters, strongly affecting their salinity.
[1]
Ethylene glycol and propylene glycol are known to exert high levels of
biochemical 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 of
dissolved oxygen
(DO) in the
water column
are consumed when microbial populations decompose propylene glycol.
[13]
: 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 municipal
sewage treatment
plant or a commercial wastewater treatment facility.
[11]
: 68?80
[14]
See also
[
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]
References
[
edit
]
- ^
a
b
Miguel Canedo-Arguelles, Ben J. Kefford, Christophe Piscart, Narcis Prata, Ralf B.Schaferd, Claus-Jurgen Schulze (2013). "Salinisation of Rivers: An Urgent Ecological Issue".
Environmental Pollution
.
173
: 157?67.
doi
:
10.1016/j.envpol.2012.10.011
.
PMID
23202646
.
{{
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.
OCLC
173668609
.
- ^
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 from
the original
on 2009-06-05.
- ^
"Thermal Energy Storage in ThermalBanks for under runway heating"
. ICAX Ltd, London
. Retrieved
2011-11-24
.
- ^
Nosonovsky, M.; Hejazi, V. (2012). "Why superhydrophobic surfaces are not always icephobic".
ACS Nano
.
6
(10): 8488?8913.
doi
:
10.1021/nn302138r
.
PMID
23009385
.
- ^
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
.
PMC
3709168
.
PMID
23846773
.
- ^
2012 Autumn & Winter Season (Drivers' Briefing). London, UK: First Capital Connect. September 2012.
- ^
a
b
Technical 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.
- ^
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 from
the original
on 8 February 2011
. Retrieved
21 February
2011
.
External links
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]