Deicing

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An Aeroflot Airbus A330 being deiced at Sheremetyevo International Airport Aeroflot Airbus A330-200 de-icing Pereslavtsev.jpg
An Aeroflot Airbus A330 being deiced at Sheremetyevo International Airport
Econ Salt Spreader Econ Salt Spreader.jpg
Econ Salt Spreader

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.

Contents

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

Roadways

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

Ice build up in train brakes jeopardizes braking efficiency. Icy train brake.jpg
Ice build up in train brakes jeopardizes braking efficiency.

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

A U.S. C-37B VIP jet gets deiced before departing Alaska in January 2012 A U.S. Army C-37B aircraft transporting Army Chief of Staff Gen. Raymond T. Odierno, gets de-iced before it departs Joint Base Elmendorf-Richardson, Alaska.jpg
A U.S. C-37B VIP jet gets deiced before departing Alaska in January 2012

Ground deicing of aircraft

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

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

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

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

Organics

Environmental impact and mitigation

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

Related Research Articles

<span class="mw-page-title-main">Brine</span> Concentrated solution of salt in water

Brine is water with a high-concentration solution of salt. In diverse contexts, brine may refer to the salt solutions ranging from about 3.5% up to about 26%. Brine forms naturally due to evaporation of ground saline water but it is also generated in the mining of sodium chloride. Brine is used for food processing and cooking, for de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as desalination, so it requires wastewater treatment for proper disposal or further utilization.

<span class="mw-page-title-main">Sodium chloride</span> Chemical compound with formula NaCl

Sodium chloride, commonly known as table salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. Sodium chloride is the salt most responsible for the salinity of seawater and of the extracellular fluid of many multicellular organisms. In its edible form, it is commonly used as a condiment and food preservative. Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and chlorine compounds used as feedstocks for further chemical syntheses. Another major application of sodium chloride is deicing of roadways in sub-freezing weather.

<span class="mw-page-title-main">Propylene glycol</span> Chemical compound

Propylene glycol (IUPAC name: propane-1,2-diol) is a viscous, colorless liquid, which is nearly odorless but possesses a faintly sweet taste. Its chemical formula is CH3CH(OH)CH2OH. As it contains two alcohol groups, it is classed as a diol. It is miscible with a broad range of solvents, including water, acetone, and chloroform. In general, glycols are non-irritating and have very low volatility.

<span class="mw-page-title-main">Calcium chloride</span> Chemical compound

Calcium chloride is an inorganic compound, a salt with the chemical formula CaCl2. It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide.

<span class="mw-page-title-main">Black ice</span> Thin coating of glazed ice on a surface

Black ice, sometimes called clear ice, is a thin coating of glaze ice on a surface, especially on streets. The ice itself is not black, but visually transparent, allowing the often black road below to be seen through it. The typically low levels of noticeable ice pellets, snow, or sleet surrounding black ice means that areas of the ice are often next to invisible to drivers or people walking on it. Thus, there is a risk of slippage and subsequent accident due to the unexpected loss of traction.

<span class="mw-page-title-main">Magnesium chloride</span> Inorganic salt: MgCl2 and its hydrates

Magnesium chloride is an inorganic compound with the formula MgCl2. It forms hydrates MgCl2·nH2O, where n can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in nature, have a variety of practical uses. Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form most readily available.

An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, allowing higher coolant temperature. However, all common antifreeze additives also have lower heat capacities than water, and do reduce water's ability to act as a coolant when added to it.

<span class="mw-page-title-main">Freezing-point depression</span> Process in which adding a solute to a solvent decreases the freezing point of the solvent

Freezing-point depression is a drop in the maximum temperature at which a substance freezes, caused when a smaller amount of another, non-volatile substance is added. Examples include adding salt into water, alcohol in water, ethylene or propylene glycol in water, adding copper to molten silver, or the mixing of two solids such as impurities into a finely powdered drug.

<span class="mw-page-title-main">Water softening</span> Removing positive ions from hard water

Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extends the lifetime of plumbing by reducing or eliminating scale build-up in pipes and fittings. Water softening is usually achieved using lime softening or ion-exchange resins, but is increasingly being accomplished using nanofiltration or reverse osmosis membranes.

<span class="mw-page-title-main">Snow removal</span> Job of removing snow

Snow removal or snow clearing is the job of removing snow after a snowfall to make travel easier and safer. This is done both by individual households and by governments, institutions, and commercial businesses.

Compass Minerals International, Inc is a public company that, through its subsidiaries, is a leading producer of minerals, including salt, magnesium chloride and sulfate of potash. Based in Overland Park, Kansas; the company provides bulk treated and untreated highway deicing salt to customers in North America and the United Kingdom and plant nutrition products to growers worldwide. Compass Minerals also produces consumer deicing and water conditioning products, consumer and commercial culinary salt, and other mineral-based products for consumer, agricultural and industrial applications. In addition, Compass Minerals provides records management services to businesses throughout the United Kingdom.

<span class="mw-page-title-main">Ice protection system</span> Aircraft system which prevents the formation of ice on outside surfaces during flight

In aeronautics, ice protection systems keep atmospheric moisture from accumulating on aircraft surfaces, such as wings, propellers, rotor blades, engine intakes, and environmental control intakes. Ice buildup can change the shape of airfoils and flight control surfaces, degrading control and handling characteristics as well as performance. An anti-icing, de-icing, or ice protection system either prevents formation of ice, or enables the aircraft to shed the ice before it becomes dangerous.

In ground deicing of aircraft, aircraft deicing fluid (ADF), aircraft deicer and anti-icer fluid (ADAF) or aircraft anti-icing fluid (AAF) are commonly used for both commercial and general aviation. Environmental concerns include increased salinity of groundwater where de-icing fluids are discharged into soil, and toxicity to humans and other mammals.

<span class="mw-page-title-main">Sodium formate</span> Chemical compound

Sodium formate, HCOONa, is the sodium salt of formic acid, HCOOH. It usually appears as a white deliquescent powder.

Calcium magnesium acetate (CMA) is a deicer and can be used as an alternative to road salt. It is approximately as corrosive as normal tap water, and in varying concentrations can be effective in stopping road ice from forming down to around −27.5 °C (−17.5 °F) (its eutectic temperature). CMA can also be used as an H2S capture agent.

<span class="mw-page-title-main">Winter service vehicle</span> Vehicle used to clear snow and ice

A winter service vehicle (WSV), or snow removal vehicle, is a vehicle specially designed or adapted to clear thoroughfares of ice and snow. Winter service vehicles are usually based on a dump truck chassis, with adaptations allowing them to carry specially designed snow removal equipment. Many authorities also use smaller vehicles on sidewalks, footpaths, and cycleways. Road maintenance agencies and contractors in temperate or polar areas often own several winter service vehicles, using them to keep the roads clear of snow and ice and safe for driving during winter. Airports use winter service vehicles to keep both aircraft surfaces, and runways and taxiways free of snow and ice, which, besides endangering aircraft takeoff and landing, can interfere with the aerodynamics of the craft.

<span class="mw-page-title-main">Cooling bath</span> Liquid mixture used to maintain low temperatures

A cooling bath or ice bath, in laboratory chemistry practice, is a liquid mixture which is used to maintain low temperatures, typically between 13 °C and −196 °C. These low temperatures are used to collect liquids after distillation, to remove solvents using a rotary evaporator, or to perform a chemical reaction below room temperature.

Calcium nitrite is an inorganic compound with the chemical formula Ca(NO
2)
2. In this compound, as in all nitrites, nitrogen is in a +3 oxidation state. It has many applications such as antifreeze, rust inhibitor of steel and wash heavy oil.

Soil stabilization is a general term for any physical, chemical, mechanical, biological, or combined method of changing a natural soil to meet an engineering purpose. Improvements include increasing the weight-bearing capabilities, tensile strength, and overall performance of unstable subsoils, sands, and waste materials in order to strengthen road pavements.

<span class="mw-page-title-main">Ground deicing of aircraft</span> Ground deicing of aircraft

In aviation, ground deicing of aircraft is the process of removing surface frost, ice or frozen contaminants on aircraft surfaces before an aircraft takes off. This prevents even a small amount of surface frost or ice on aircraft surfaces from severely impacting flight performance. Frozen contaminants on surfaces can also break off in flight, damaging engines or control surfaces.

References

  1. 1 2 Miguel 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. PMID   23202646.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ↑ Fischel, Marion (2001). Evaluation of selected deicers based on a review of the literature. Colorado Dept. of Transportation. OCLC   173668609.
  3. ↑ Amanda Rabinowitz (February 25, 2008). "Beets Part of New Recipe to Treat Icy Roads". National Public Radio.
  4. ↑ Richard J. Brennan (January 21, 2012). "Beet juice melts ice from winter roads". Toronto Star .
  5. ↑ Post, Rachael (March 3, 2014). "The alternatives to salt for battling ice: cheese, beets and ash". The Guardian.
  6. ↑ "About Magic Salt". 2007. Archived from the original on 2009-06-05.
  7. ↑ "Thermal Energy Storage in ThermalBanks for under runway heating". ICAX Ltd, London. Retrieved 2011-11-24.
  8. ↑ Nosonovsky, M.; Hejazi, V. (2012). "Why superhydrophobic surfaces are not always icephobic". ACS Nano. 6 (10): 8488–8913. doi:10.1021/nn302138r. PMID   23009385.
  9. ↑ 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.
  10. ↑ 2012 Autumn & Winter Season (Drivers' Briefing). London, UK: First Capital Connect. September 2012.
  11. 1 2 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.
  12. ↑ "Airport Deicing Effluent Guidelines". EPA. 2021-02-10.
  13. ↑ 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.
  14. ↑ Tom Gibson (September 2002). "Let the Bugs Do the Work". Progressive Engineer. Archived from the original on 8 February 2011. Retrieved 21 February 2011.
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