WO2014182226A1

WO2014182226A1 - Train anti-icing system

Info

Publication number: WO2014182226A1
Application number: PCT/SE2014/050550
Authority: WO
Inventors: Anders Larsson
Original assignee: Nordic Ground Support Equipment Ip Ab
Priority date: 2013-05-06
Filing date: 2014-05-06
Publication date: 2014-11-13
Also published as: EP2994354A1; CN205327022U; EP2994354A4; SE1350548A1

Abstract

A train anti-icing system (10) comprises a spray nozzle arrangement (16) for spraying serviceable anti-icing liquid at a treatment temperature onto a vehicle on tracks; a collection tray (18) for collecting spent anti-icing liquid falling from the vehicle; a preparation vessel (62) for preparing serviceable anti-icing liquid to be sprayed onto the vehicle; a spent anti-icing liquid tank (44) for receiving and storing spent anti-icing liquid collected by the collection tray (18); an ingredient tank (54) for storing anti-icing liquid concentrate; a spent anti-icing liquid supply line (66) for supplying spent anti-icing liquid from the spent anti-icing liquid tank (44) to the preparation vessel (62); and an ingredient supply line (64) for supplying anti-icing liquid concentrate from the ingredient tank (54) to the preparation vessel (62).

Description

TRAIN ANTI-ICING SYSTEM

Field of the invention

The present invention relates to a train anti-icing system comprising a spray nozzle arrangement for spraying anti-icing liquid onto a vehicle on tracks and a collection tray for collecting spent anti-icing liquid falling from the vehicle.

Background of the invention

In cold climate, ice build-up on trains is a safety risk, and therefore trains frequently need to be anti-iced. WO 2013/043090 discloses a train anti- icing system for reducing the icing of a vehicle on tracks.

There is a need for a train anti-icing system with reduced operation and maintenance costs.

Summary of the invention

It is an object of the present invention to solve, or at least mitigate, parts or all of the above mentioned problems. To this end, there is provided a train anti-icing system comprising a spray nozzle arrangement for spraying serviceable anti-icing liquid at a treatment temperature onto a vehicle on tracks; a collection tray for collecting spent anti-icing liquid falling from the vehicle; a preparation vessel for preparing serviceable anti-icing liquid to be sprayed onto the vehicle; a spent anti-icing liquid tank for receiving and storing spent anti-icing liquid collected by the collection tray; an ingredient tank for storing anti-icing liquid concentrate; a spent anti-icing liquid supply line for supplying spent anti-icing liquid from the spent anti-icing liquid tank to the preparation vessel; and an ingredient supply line for supplying anti-icing liquid concentrate from the ingredient tank to the preparation vessel. In such a system, energy consumption may be reduced, since de-watering of collected, spent anti-icing liquid to be re-used will not be necessary. This reduces the operating cost. Moreover, compared to prior systems, the interval for re-filling the system may be significantly increased, such that the maintenance cost is reduced.

According to an embodiment, the treatment temperature is between about 10°C and 50°C.

According to an embodiment, the train anti-icing system further comprises a heater configured to heat the serviceable anti-icing liquid of the preparation vessel to the treatment temperature. Heating may be performed inside or outside the preparation vessel, and the serviceable anti-icing liquid may be maintained at an elevated temperature inside the preparation vessel.

According to an embodiment, the train anti-icing system further comprises a heater configured to heat the spent anti-icing liquid of the spent anti-icing liquid tank to a temperature lower than the treatment temperature. By keeping the spent anti-icing liquid at a lower temperature than that required for performing anti-icing, energy is saved. According to an

embodiment, said lower temperature is between -10°C and 0°C. Preferably, said lower temperature is a freeze-preventing temperature. More preferred, said lower temperature is less than 10°C above the freezing point of the spent anti-icing liquid. Heating may be performed inside or outside the spent anti- icing liquid tank.

According to an embodiment, the preparation vessel is smaller than the spent anti-icing liquid tank. By keeping a large portion of the liquid stored in the system at a temperature below the treatment temperature, energy is saved.

According to an embodiment, the train anti-icing system is configured to store the anti-icing liquid concentrate in the ingredient tank at a

temperature lower than the treatment temperature, and preferably unheated. By storing the anti-icing liquid concentrate unheated, or at least at a lower temperature than that required for performing anti-icing, energy is saved.

According to an embodiment, the preparation vessel is smaller than the ingredient tank. Again, by maintaining a large portion of the liquid stored in the system at a temperature below the treatment temperature, energy is saved. According to an embodiment, the train anti-icing system further comprises a controller configured to, if the amount of serviceable anti-icing liquid in the preparation vessel falls below a threshold value, initiate a transfer of a first selected volume of spent anti-icing liquid from the spent anti-icing liquid tank to the preparation vessel; and initiate a transfer of a second selected volume of anti-icing liquid concentrate from the ingredient tank to the preparation vessel. Thereby, the amount and concentration of serviceable anti-icing liquid in the preparation vessel may be maintained within selected boundaries at all times.

According to an embodiment, the train anti-icing system further comprises a glycol concentration sensor configured for sensing the

concentration of glycol of the spent anti-icing liquid in the spent anti-icing liquid tank. Thereby, information from the glycol concentration sensor may be used for determining suitable amounts of liquid to be added to the preparation vessel from the spent anti-icing liquid tank and the ingredient tank,

respectively.

According to an embodiment, the glycol concentration sensor is located outside the spent anti-icing liquid tank, and the train anti-icing system further comprises a spent anti-icing liquid sampling line for transferring a sample of spent anti-icing liquid from the spent anti-icing liquid tank to the glycol concentration sensor; and a serviceable anti-icing liquid sampling line for transferring a sample of serviceable anti-icing liquid from the preparation vessel to the glycol concentration sensor. This facilitates measuring the glycol concentration in each of the preparation vessel and the spent anti-icing liquid tank. Thereby, it is possible to more accurately optimize the mixing of spent anti-icing liquid and anti-icing liquid concentrate into the preparation vessel, and to verify the quality of the serviceable anti-icing liquid in the preparation vessel before spraying onto a vehicle. The anti-icing system may also comprise an anti-icing liquid concentrate sampling line for transferring a sample of anti-icing liquid concentrate from the ingredient tank to the glycol concentration sensor. Thereby, the quality of the anti-icing liquid concentrate may be verified. According to another aspect of the invention, parts or all of the above mentioned problems are solved, or at least mitigated, by a method of anti- icing a vehicle on tracks, the method comprising collecting spent anti-icing liquid and storing it in a spent anti-icing liquid tank; preparing serviceable anti- icing liquid by transferring collected, spent anti-icing liquid from the spent anti- icing liquid tank to a preparation vessel and transferring anti-icing liquid concentrate from an ingredient tank to the preparation vessel; and spraying serviceable anti-icing liquid at a treatment temperature onto the vehicle.

According to an embodiment, the serviceable anti-icing liquid inside the preparation vessel is maintained at the treatment temperature, and the spent anti-icing liquid inside the spent anti-icing liquid tank is maintained at a temperature below the treatment temperature.

According to an embodiment, the method further comprises

maintaining a relatively smaller amount of serviceable anti-icing liquid at treatment temperature in the preparation vessel; and maintaining a relatively larger amount of spent anti-icing liquid below treatment temperature in the spent anti-icing liquid tank.

According to an embodiment, the method further comprises

determining the amount of serviceable anti-icing liquid in the preparation vessel; and based on said determination, initiating a transfer of a first selected volume of spent anti-icing liquid from the spent anti-icing liquid tank to the preparation vessel and initiating a transfer of a second selected volume of anti-icing liquid concentrate from the ingredient tank to the preparation vessel.

According to an embodiment, said first and second selected volumes are selected based on the concentration of glycol of the spent anti-icing liquid in the spent anti-icing liquid tank.

According to an embodiment, the method further comprises

alternatingly sampling the spent anti-icing liquid and the serviceable anti-icing liquid for determining their respective glycol concentrations using a single glycol concentration sensor. Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Fig. 1 is a diagrammatic view in perspective of an train anti-icing system; and

Fig. 2 is a diagrammatic view of a re-circulation plant of the train anti- icing system of Fig. 1.

Detailed description of the exemplary embodiments

Fig. 1 schematically illustrates a train anti-icing system 10 for reducing the build-up of ice on trains. The anti-icing system 10 may be used for de- icing as well as for anti-icing a train, i.e. leaving an ice-repellent coating of anti-icing liquid on the surface of the train during or after de-icing, or without prior de-icing. The system 10 is configured as a drive-through system, i.e. a train 12, arriving on tracks 14 from the upper left corner of Fig. 1 , passes through the system 10 without having to stop during the de-/anti-icing process.

The anti-icing system 10 comprises a spray nozzle arrangement 16 for spraying an anti-icing liquid onto the train 12, and a collection tray

arrangement 18 for collecting spent anti-icing liquid dripping from the train 12. The system 10 may also be provided with a sensor (not shown) for

determining locations, relative to the spray nozzle arrangement 16, of portions of the train 12 to be selectively sprayed, e.g. in the manner described in WO 2013/043090. Thereby, spraying may be focussed onto the train portions most sensitive to icing, such as wheel units.

Typically, a serviceable anti-icing liquid would be a liquid having a freezing point sufficiently below the freezing point of water, such that any anti- icing liquid residues remaining on the train after de-icing will remain in liquid or slush form when the train 12 is again exposed to cold climate. Thereby, anti-icing liquid residues remaining on the surface of the train 12 will prevent snow and ice from attaching to the train 12. Even though not necessary, the anti-icing liquid may optionally be heated when sprayed to the train 12, so as to increase the de-icing efficiency of the liquid when sprayed onto the train 12. Ethylene glycol, propylene glycol, other alcohols, salt, and sugar are the most common anti-icing liquid ingredients in the art, and may be used for preparing serviceable anti-icing liquid, e.g. by mixing with water.

The spent anti-icing liquid may comprise a slush of anti-icing liquid, rain, dirt, ice, and melted ice in the form of water. The collection tray arrangement 18 extends along a relatively short spray zone 20, at which the spray nozzle arrangement 16 is located, and a somewhat longer collection zone 22, along which no substantive spraying of anti-icing liquid occurs. The collection tray arrangement 18 comprises three collection trays 18a, 18b, 18c extending along the rails 14. Two collection trays 18a, 18b extend along the sides of the tracks 14, while a third collection tray 18c extends between the tracks 14. A drain arrangement 26 comprises a set of drains 26a-c located at the bottoms of the respective collection trays 18a-c. The drain arrangement 26 allows spent anti-icing liquid to be collected from the collection tray arrangement 18 and transferred to a re-circulation plant 28, which may be located within a housing formed by e.g. a cargo container 30. Thereby, the anti-icing system 10 may be prepared or assembled at a central site, and quickly transported to and installed at a de-icing site when needed.

Turning now to Fig. 2, only a single tray 18 and a single drain 26 are illustrated. The spray nozzle arrangement 16 comprises a plurality of spray nozzles 36. A valve arrangement 38, comprising a plurality of valves (not illustrated), is operated by a controller 40. The controller 40 controls, via the valve arrangement 38, the flow of anti-icing liquid to different portions of the spray nozzle arrangement 16 in such a manner that different spray patterns may be selectively obtained.

The re-circulation plant 28 (Fig. 1 ) will now be described in more detail.

Collected, spent anti-icing liquid is pumped from the drain arrangement 26, via a filter 42 for removing solid dirt particles, to a spent anti-icing liquid tank 44 for storing spent anti-icing liquid. The spent anti-icing liquid tank 44 is provided with a spent anti-icing liquid temperature sensor 46, for sensing the temperature of the spent anti-icing liquid in the tank 44, and a spent anti-icing liquid tank level sensor 48, for sensing the amount of spent anti-icing liquid in the tank 44. Temperature and level signals from the sensors 46, 48 are transmitted to the controller 40. The controller 40 also controls a spent anti- icing liquid heater 50, which is located outside the spent anti-icing liquid tank 44. Based on the temperature of the spent anti-icing liquid in the spent anti- icing liquid tank 44, spent anti-icing liquid is pumped from the tank 44 to the heater 50, heated by the heater 50, and then returned to the tank 44.

Thereby, the temperature of the spent anti-icing liquid in the spent anti-icing liquid tank 44 may be kept at a freeze-preventing temperature, i.e. above the freezing point of the spent anti-icing liquid, even if the ambient temperature outside the tank 44 falls below the freezing point. By way of example, a spent anti-icing liquid comprising about 75% - 85% water and 15% - 25% propylene glycol has a typical freezing point of between about -5°C and -10°C; for such a spent anti-icing liquid, the controller 40 may be configured to operate the heater 50 when the temperature falls below a lower spent anti-icing liquid limit temperature, which may be between about -10°C and 0°C. A discharge line 52 allows emptying the spent anti-icing liquid tank 44. As an alternative or complement to heating spent anti-icing liquid in a separate heater 50 outside the tank 44, a heater may be located in the tank 44.

The re-circulation plant 28 further comprises an ingredient tank 54 for storing anti-icing liquid concentrate, such as concentrated propylene glycol or highly concentrated salt brine. The ingredient tank 54 is provided with an anti- icing liquid concentrate temperature sensor 56, for sensing the temperature of the anti-icing liquid concentrate in the tank 54, and an ingredient tank level sensor 58, for sensing the amount of anti-icing liquid concentrate in the ingredient tank 54. Again, temperature and level signals from the sensors 56, 58 are transmitted to the controller 40. A refilling line 60 allows topping up the ingredient tank 54 with anti-icing liquid concentrate.

A preparation vessel 62 allows for preparing serviceable anti-icing liquid to be sprayed onto the train 12. The preparation vessel 62 is connected to the ingredient tank 54 via an ingredient supply line 64, which allows pumping anti-icing liquid concentrate from the ingredient tank 54 to the preparation vessel 62. The preparation vessel 62 is also connected to the spent anti-icing liquid tank 44 via a spent anti-icing liquid supply line 66, which allows pumping spent anti-icing liquid from the spent anti-icing liquid tank 44 to the preparation vessel 62. The preparation vessel 62 is provided with a serviceable anti-icing liquid temperature sensor 68, for sensing the

temperature of the serviceable anti-icing liquid in the preparation vessel 62, and a preparation vessel level sensor 70, for sensing the amount of serviceable anti-icing liquid in the preparation vessel 62. Again, temperature and level signals from the sensors 68, 70 are transmitted to the controller 40.

If the amount of serviceable anti-icing liquid in the preparation vessel 62 reaches a lower limit, serviceable anti-icing liquid is prepared in the preparation vessel 62 by pumping selected amounts of liquid to the

preparation vessel 62 from the ingredient tank 54 and the spent anti-icing liquid tank 44, respectively. The respective amounts of anti-icing liquid concentrate and spent anti-icing liquid are selected by the controller 40 such that the resulting mixture in the preparation vessel 62 will hold the desired anti-icing ingredient concentration to form a serviceable anti-icing liquid.

Thereby, anti-icing liquid may be regenerated in a non-evaporative manner. The amounts transferred from the respective tanks 44, 54 may be calculated by the controller 40 based on the signals from the respective level sensors 48, 58. Non-evaporative regeneration may be particularly beneficial in anti- icing systems 10 configured to focus spraying on selected portions along a train 12 which are particularly prone to icing, such as wheel units. This is due to such selective anti-icing systems consuming particularly small amounts of serviceable anti-icing liquid, such that the collected, spent anti-icing liquid will be particularly highly diluted by melt water.

The controller 40 also controls a serviceable anti-icing liquid heater 72, which is located outside the preparation vessel 62. Based on the temperature of the serviceable anti-icing liquid in the preparation vessel 62, serviceable anti-icing liquid is pumped from the preparation vessel 62 to the heater 72, heated, and then returned to the preparation vessel 62. Thereby, the temperature of the serviceable anti-icing liquid in the preparation vessel 62 may be kept at a treatment temperature, i.e. at a temperature suitable for de- icing a train 12, even if the ambient temperature outside the preparation vessel is low. By way of example, a suitable treatment temperature may be between about 10°C and 50°C, and preferably above 20°C. The controller 40 may be configured to operate the heater 72 when the temperature falls below a lower treatment temperature limit, which may be between about 10°C and 50°C. As an alternative or complement to heating serviceable anti-icing liquid in a separate heater 72 outside the preparation vessel 62, a heater may be located in the preparation vessel. Maintaining only the serviceable anti-icing liquid heated to an elevated treatment temperature, while maintaining anti- icing liquid concentrate and spent anti-icing liquid at a lower temperature, saves heating energy. Alternatively, the serviceable anti-icing liquid may be kept at ambient temperature in the preparation vessel, and may be heated elsewhere by a separate heater when it is to be sprayed onto a train 12. Still alternatively, the serviceable anti-icing liquid may be sprayed onto the train 12 without having been heated, i.e. at ambient temperature, for merely forming an ice-repellent coating on the surface of the vehicle.

It may be the case that not all spent anti-icing liquid collected by the collection tray 18 is needed for preparing serviceable anti-icing liquid.

Therefore, from time to time, it may be desired to tap off some spent anti-icing liquid from the spent anti-icing liquid tank 44 via the discharge line 52, to prevent overfilling of the spent anti-icing liquid tank 44. The spent anti-icing liquid tank 44 preferably has a capacity of at least 4 m³ to allow performing a number of anti-icing operations between tapping off. The preparation vessel 62 preferably has a capacity of at least 0,5 m³, which is typically more than sufficient for anti-icing a train. Preferably, the preparation vessel 62 has a capacity of less than 3 m³ in order to limit the heating power required for maintaining the serviceable anti-icing liquid at treatment temperature.

Preferably, the spent anti-icing liquid tank 44 and the preparation vessel 62 are thermally insulated to minimize heat dissipation therefrom. The ingredient tank 54 typically does not need to be substantially heated.

After an anti-icing operation, about 10 - 100 liters of serviceable anti- icing liquid typically remains on the train 12, and is lost from the anti-icing system 10 as the train 12 leaves the anti-icing system 10. Hence, preferably, the ingredient tank has a capacity of at least 1 m³ to allow performing a number of anti-icing operations between refillings via the refilling line 60.

An ingredient concentration sensor 74, for determining the

concentration of an anti-icing ingredient, is connected to the spent anti-icing liquid tank 44 via a spent anti-icing liquid sampling line 76. By way of example, the ingredient concentration sensor 74 may be a propylene glycol concentration sensor. The concentration value determined by the ingredient sensor 74 is transmitted to the controller 40, and may be used by the controller 40 for calculating the ratio of spent anti-icing liquid and anti-icing liquid concentrate to be transferred to the preparation tank 62 for obtaining serviceable anti-icing liquid of the desired ingredient concentration. If using propylene glycol as the anti-icing ingredient, a propylene glycol concentration of the serviceable anti-icing liquid of between 40% and 60% may typically be desired.

The ability to measure the ingredient concentration of the spent anti- icing liquid in the spent anti-icing liquid tank 44 also makes it possible to determine the freezing point of the spent anti-icing liquid in the tank 44.

Thereby, the controller 40 may select the lower limit temperature of the spent anti-icing liquid based on the ingredient concentration of the spent anti-icing liquid. This makes it possible to even further lower the temperature at which the spent anti-icing liquid is stored to a temperature just above the freezing point. The ingredient concentration sensor 74 is also connected to the preparation vessel via a serviceable anti-icing liquid sampling line 76.

Thereby, the ingredient concentration of the serviceable anti-icing liquid inside the preparation vessel may also be determined by the controller 40, e.g. by alternatingly transferring liquid from the preparation vessel 62 and the spent anti-icing liquid tank, respectively, to the ingredient concentration sensor 74. This permits fine-tuning the ingredient concentration of the serviceable anti- icing liquid. The ingredient concentration sensor 74 may also be connected to the ingredient tank 54 via an anti-icing liquid concentrate sampling line (not shown). Thereby, it is possible to verify the quality of the anti-icing liquid concentrate in the tank 54. The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. For example, a single controller 40, performing several different functions, has been disclosed. Clearly, separate controllers may be used for those different functions, such as for operating different heaters. Moreover, a spray nozzle arrangement 16 comprising multiple spray nozzles has been illustrated. As an alternative, the spray nozzle arrangement may comprise only one single spray nozzle. Even though each of the containers 44, 54, 62 has been illustrated as a closed container, any of them could alternatively be an open container. The invention may be used for many different types of vehicles on tracks, such as trams, and is not limited to trains only.

Claims

1 . A train anti-icing system comprising

a spray nozzle arrangement (16) for spraying serviceable anti-icing liquid at a treatment temperature onto a vehicle on tracks (12); and

a collection tray (18) for collecting spent anti-icing liquid falling from the vehicle (12), the train anti-icing system being characterized in comprising a preparation vessel (62) for preparing serviceable anti-icing liquid to be sprayed onto the vehicle (12);

a spent anti-icing liquid tank (44) for receiving and storing spent anti- icing liquid collected by the collection tray (18);

an ingredient tank (54) for storing anti-icing liquid concentrate;

a spent anti-icing liquid supply line (66) for supplying spent anti-icing liquid from the spent anti-icing liquid tank (44) to the preparation vessel (62); and

an ingredient supply line (64) for supplying anti-icing liquid

concentrate from the ingredient tank (54) to the preparation vessel (62).

2. The train anti-icing system according to claim 1 , further comprising a heater (72) configured to heat the serviceable anti-icing liquid of the preparation vessel (62) to the treatment temperature.

3. The train anti-icing system according to any of the previous claims, further comprising a heater (50) configured to heat the spent anti-icing liquid of the spent anti-icing liquid tank (44) to a temperature lower than the treatment temperature.

4. The train anti-icing system according to claim 3, wherein the preparation vessel (62) is smaller than the spent anti-icing liquid tank (44).

5. The train anti-icing system according to any of the previous claims, wherein the system (10) is configured to store the anti-icing liquid concentrate in the ingredient tank (54) at a temperature lower than the treatment temperature, and preferably unheated.

6. The train anti-icing system according to claim 5, wherein the preparation vessel (62) is smaller than the ingredient tank (54).

7. The train anti-icing system according to any of the previous claims, further comprising a controller (40) configured to, if the amount of serviceable anti-icing liquid in the preparation vessel (62) falls below a threshold value, initiate a transfer of a first selected volume of spent anti-icing liquid from the spent anti-icing liquid tank (44) to the preparation vessel (62); and initiate a transfer of a second selected volume of anti-icing liquid concentrate from the ingredient tank (54) to the preparation vessel (62).

8. The train anti-icing system according to any of the previous claims, further comprising a glycol concentration sensor (74) configured for sensing the concentration of glycol of the spent anti-icing liquid in the spent anti-icing liquid tank (44).

9. The train anti-icing system according to claim 8, wherein the glycol concentration sensor (74) is located outside the spent anti-icing liquid tank (44), the system further comprising

a spent anti-icing liquid sampling line (76) for transferring a sample of spent anti-icing liquid from the spent anti-icing liquid tank (44) to the glycol concentration sensor (74); and

a serviceable anti-icing liquid sampling line (78) for transferring a sample of serviceable anti-icing liquid from the preparation vessel (62) to the glycol concentration sensor (74).

10. A method of anti-icing a vehicle on tracks, comprising

collecting spent anti-icing liquid and storing it in a spent anti-icing liquid tank (44);

preparing serviceable anti-icing liquid by transferring collected, spent anti-icing liquid from the spent anti- icing liquid tank (44) to a preparation vessel (62) and

transferring anti-icing liquid concentrate from an ingredient tank (54) to the preparation vessel (62); and

spraying serviceable anti-icing liquid at a treatment temperature onto the vehicle (12).

1 1 . The method according to claim 10, wherein the serviceable anti-icing liquid inside the preparation vessel (62) is maintained at the treatment temperature, and the spent anti-icing liquid inside the spent anti-icing liquid tank (44) is maintained at a temperature below the treatment temperature.

12. The method according to claim 1 1 , further comprising

maintaining a relatively smaller amount of serviceable anti-icing liquid at treatment temperature in the preparation vessel (62); and

maintaining a relatively larger amount of spent anti-icing liquid below treatment temperature in the spent anti-icing liquid tank (44).

13. The method according to any of the claims 10-12, further comprising determining the amount of serviceable anti-icing liquid in the preparation vessel (62); and

based on said determination,

initiating a transfer of a first selected volume of spent anti-icing liquid from the spent anti-icing liquid tank (44) to the preparation vessel (62); and

initiating a transfer of a second selected volume of anti-icing liquid concentrate from the ingredient tank (54) to the preparation vessel (62).

14. The method according to any of the claims 10-13, wherein said first and second selected volumes are selected based on the concentration of glycol of the spent anti-icing liquid in the spent anti-icing liquid tank (44).

15. The method according to claim 14, further comprising alternatingly sampling the spent anti-icing liquid and the serviceable anti-icing liquid for determining their respective glycol concentrations using a single glycol concentration sensor (74).