METHOD AND DEVICE TO SCATTER A PREHEATED MATERIAL ON A SURFACE

Abstract: Method and device to scatter preheated sand, crushed stone, urea, road salt, etc. (12) from a spreading vehicle (1) onto aeroplane runways and roads (4) in order to counteract slipperiness caused by snow, ice, sleet, mud and the like (3) in which preheating of the material (12) is via an electronically controlled LP-gas driven burner (8) in close association with feeding (5, 6, 7) of the material (12) from the spreading vehicle (1) to the surface (4) which is to be treated, in such a fashion that the flames from the burners (8) have direct contact with the material which is to be preheated (12). The process can be remotely controlled (11) from the driver cabin (13) of the spreading vehicle (1). The heating system (8-11) can be conveniently mounted to an existing spreading vehicle.

Description: METHOD AND DEVICE TO SCATTER A PREHEATED MATERIAL ON A SURFACE. There are many situations where it is desirable to counteract slipperiness caused by ice, snow, mud, sleet and the like. This can be done, for example, by salting or sanding. Not least, this applies to aeroplane runways. Here, urea is used in order to "melt" the icecover and sand with a particular grain size to provide good friction, because aeroplanes can not tolerate road salt or sand of the wrong grain size. The sand or urea are spread with a special spreading vehicle. The effectiveness of sanding can be considerably increased if the sand is preheated, because the sand then melts solidly to the icecover on the runway and forms a sandpaper-like surface which provides very good friction against aeroplane wheels during landing and take off. Sand preheating creates the need for methods and devices to heat the sand. In a currently used system, the sand is stored, continuously heated, in a large silo from which the sand is conveyed to the spreading vehicle and placed in the spreader hopper. The heated sand is conveyed within the spreading vehicle and spread out as desired. The above described technique suffers from serious disadvantages. In the first place, it requires large investments for the above mentioned sand silo. Secondly, because the entire mass of sand is kept continuously heated, the sand silo represents a waste of energy which also leads to high costs. Thirdly, the technique is not particularly effective because the sand continuously loses heat from the moment it is loaded onto the spreading vehicle. Our measurements show that, in fact, the sand has only a fraction of its warmth left when it reaches the spot where it is to be scattered. The object of the present invention is to provide a vehicle-borne method and apparatus to scatter a preheated material onto a surface, especially a preheated, granular anti-slip material onto runways and roads, in which the above described drawbacks are avoided and which gives a high safety level and good control and adjustment. An additional object of the invention is to provide a heating device of the above type which admits of simple installation to existing vehicles. A still further object of the invention is to provide a method and apparatus of the above type which is amenable to low costs, as regards material, installation and fuel consumption. According to the invention, these objects are attained in a method and apparatus having the characteristics defined in the patent claims. The invention shall now be described in greater detail in connection with the accompanying sheets of drawings. The drawings are schematic and make no claim to photographic accuracy. Fig. 1 shows a sand spreading vehicle 1 with a store 2 of sand 12 which is fed via a conveyor belt 5 and a sand shaft 6 to a scattering plate 7 which is a rotating disc which centrifugally slings the sand out. The sand then falls onto the surface 4 coated with snow, ice or the like 3 which is to be sanded. The sanding and the sand spreading vehicle are controlled from a driver cabin 13. Fig. 2 shows how the sand shaft 6, in the form of an elongate, narrow tube of rectangular cross section and the scattering plate 7 are centrally mounted at the rear of the spreading vehicle 1. The sand spreading vehicle is not described further here as vehicles of this type are well known. Additionally, there are a number of different variants of such vehicles in existence. Thus the. sand, for example, can be transported with a screw instead of the conveyer belt 5. Furthermore, the sand shaft 6 can have different forms. Still further, the sand spreading vehicle 1 can have more than one scattering plate 7 and more than one sand shaft 6. A plurality of gas burners 8, which heat the sand prior to it falling through the sand shaft 6, are mounted adjacent the outlet for the sand 12, above the sand shaft 6. The elongate, narrow tube-like form of the sand shaft 6 and the consequent confinement of the sand stream to a relatively limited area provide maximal utilization of the capacity of the burners 8. The burners 8 are directed downwardly into the sand shaft 6 such that the flames from the burners 8 are mixed with the flowing sand. As the sand 12 falls through the .sand shaft 6, the sand grains are separated with respect to their distance from each other. The blast effect obtained from the stream of combustion gases from the burners 8 further facilitates this separation process and provides direct contact between the flames and the individual sand grains which gives optimal heat transfer. The flames of the burners 8 follow the sand shaft 6 right down to the scattering plate 7 which provides the sand grains with a maximally long residence time in the hot flame. Additionally, agglomerates of sand grains are split up when they are heated in this fashion. The hot sand grains, charged with heat energy, are immediately scattered by the scattering plate 7 down onto the ground. In this way, the holding time of the sand grains, between heating and contact with the ground is minimized. The heat energy stored in the sand grains is sufficient to solidly melt them onto the surface of, for example, the ice layer on an aeroplane runway. Advantageously, sifted and washed sand having a sand grain diameter of 1 - 3 mm is used for sanding, in accordance with the norms used on Swedish airfields. According to known thermodynamic principles, the greater the surface area/volume of the sand grains, or in other words the smaller their diameter, the easier it is to heat them. However, the sand grains should not be so small that they fail to function well as a coating on, for example, a runway, depending on the grip (the friction coefficient against tyres) and blasting effect of the landing aeroplane. In practical tests, sand grains with a diameter of 1 - 3 mm have shown themselves to function well from all aspects. The gas burners 8 work by the Bunsen principle and are configured to give a relatively long flame. They are supplied with liquified petroleum (LP) gas in the gas phase from a plurality of gas vessels 10 mounted in the vicinity of the gas burners 8. The burner capacity amounts to several hundred kilowatts. For intermittent use of the burners 8, the gas phase of the LP gas can be taken directly from the gas vessels 10 through adiabatic vapourization without too large a decrease in pressure. For greater gas output, forced vapourization should be employed, for example via an LP gas vapourizer using the motor coolant water of the spreading vehicle as an energy supply, or with a temperature-limited LP gas burner warming the LP gas vessels, controlled by a regulator. A reducing valve 9 acts to keep a constant pressure to the burners 8. The reducing valve 9 is adjustable to provide infinitely variable regulation of the capacity of the burners 8. In this way, the heating operation can be suited to different conditions. A magnetic valve 9 controls the gas flow to all of the burners 8. The heating operation, inter alia gas initiation and lighting the burners 8-, can be remotely controlled via an electronic control system 9,11 from a control panel 11 in the driver cabin 13 which also includes status indicators for the heating system e.g. that the gas supply and burners are operating normally. Within the context of the control system 9,11, the heating system 8,9,10,11 is provided with a number of protective functions for protection in the event that a fault should arise and to prevent imperfect end-results: -if any of the burners 8 go out, its flame is reignited automatically; -if reignition is not successful, the gas supply is turned off; -if the conveyor belt 5 stops, the gas supply is turned off; -if the gas supply to the burners 8 is insufficient, the gas supply is turned off. As mentioned earlier, implementation of the presently described technique does not necessitate the acquisition of new sand spreading vehicles. The heating system can be installed on existing sand spreading vehicles of standard configuration without extensive modification. The heating system can also be easily demounted from the sand spreading vehicle, if required. Installation of the heating system on a sand spreading vehicle does require some modifications including the provision of an opening in the sand shaft 6 for the burners 8, supports for the burners, supports for the other components of the heating system, a power supply and a number of mechanical shields • inter alia to protect the sand feed 5, sand shaft 6 and scattering plate 7 from excess temperature. Appropriate measures are readily apparent to those skilled in the art and need not be described further here. Two years of full scale field trials at the Karlstad airfield have demonstrated that the presently described method for sand heating functions outstandingly well. The LP gas consumption has also been very low. Additionally and surprisingly, the above described method has shown itself to also function very well for the spreading of urea, whose effectiveness is considerably enhanced in this fashion. The reaction time for urea to "melt" away ice to a large extent becomes almost immediate whereas in comparison it takes around 15 minutes when non- preheated urea is spread. The method should also be well suited to the spreading of preheated road salt, i.e. the method is not only applicable to aeroplane runways but also, for example, to vehicle roads. The invention is not limited to the above shown applications and embodiment but can be modified within the context of the patent claims given below.

Claims: CLAIMS 1. A process for scattering granular material (12) at raised temperature from a vehicle (1) over a roadway (4), comprising the steps of feeding the granular material fro a supply container (2) in the vehicle to a scattering means (7) via a feed means (6) and heating the granular material during its passage through the feed means, characterized in that combustion gases are caused to flow under pressure, into the upstream portion of the feed means (6) in order to separate and uniformly heat the individual particles in the granular material (12) during its passage to the scattering means and to flow out from the downstream portion of the feed means (6) in order to assist transport of said particles through the feed means (6). 2. A process according to claim 1, characterized in that the combustion gases are caused to flow through the scattering means (7) to further heat the granular material. 3. A process according to claim 2, characterized in that the combustion gases are caused to flow through the outlet of the scattering means (7), together with the granular material (12). 4. Apparatus for scattering granular material (12) at raised temperature from a vehicle (1) over a roadway (4), comprising a supply container (2) for the granular material in the vehicle, scattering means (7) for scattering said material, feed means (6) for feeding said material from the supply container to the scattering mean and heating means (8-10) to heat said material during its passage through the feed means, in which the feed means comprises an essentially vertical shaft, characterized in that the heating means (8-10) comprises a burner assembly having nozzle(s) (8) disposed above, and directed towards, the upstream portion of the feed means (6), and oriented substantially coaxially with the central axis of the feed means. 5. Apparatus according to claim 4, characterized in that the heating means (8-10) comprises more than one burner nozzle (8) and in that the feed means (6) comprises more than one shaft. 6. Apparatus according to claim 4 or 5, characterized by conveying means (5) being disposed in the supply container (2) and extending therefrom to the upstream portion of the feed means (6). 7. Apparatus according to any one of claims 4 to 6, characterized in that the scattering means (7) comprises an essentially horizontally oriented, rotating plate device which is disposed adjacent the downstream portion of each feed means (6). 8. Apparatus according to any one of claims 4 to 7, characterized in that the heating means (8-10) consists of at least one gas burner (8) with accompanying gas vessel (10), an adjustable reducing valve (9) and a magnetic valve (9) arranged to regulate the gas supply to the gas burner(s). 9. Apparatus according to claim 8, characterized by remote control means (9,11) serving to switch on and off the gas supply and to automatically switch off the gas supply when the feed of granular material ceases. 10. Apparatus according to claim 8 or 9, characterized by remote control means which provide, for at least one burner (8), automatic ignition of the flame, monitoring that the flame is burning, monitoring of the fuel supply and automatic switching off of the fuel supply to the burner (8) during malfunction.

Inventors: FORSDAHL SIXTEN, TOERNER HAAKAN, FORSDAHL, SIXTEN, TOERNER, HAAKAN
Applicants: FORSDAHL SIXTEN, TOERNER HAAKAN, FORSDAHL, SIXTEN, TOERNER, HAAKAN
Application year: 1993
Main classification: E01C19
IPC codes: E01C19, E01H10