EP2286034A2

EP2286034A2 - Method, filling station and storage holder for providing grit

Info

Publication number: EP2286034A2
Application number: EP09727133A
Authority: EP
Inventors: Hans Barvelink
Original assignee: SCHUITEMAKER MACHINES BV
Current assignee: SCHUITEMAKER MACHINES BV
Priority date: 2008-04-02
Filing date: 2009-04-02
Publication date: 2011-02-23
Also published as: WO2009123456A2; NL2001432C2; WO2009123456A3

Abstract

For providing grit (3) to be distributed over a road surface, water and grit (3) are mixed and ground into a slurry (29) containing a solution (19, 19') of a portion of the grit (3) and a portion (18, 18') of the grit (3) in solid form. The slurry is stored in a filling station and for transferring to a distribution vehicle (1) each time at least a portion of the stored slurry (29) is loaded from the filling station to the distribution vehicle (1). A filling station, a slurry, a method of distribution and a storage holder for use in connection therewith are also described.

Description

Title: Method, filling station and storage holder for providing grit, method for distributing grit and grit-containing slurry

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a method, a filling station and a storage holder for providing a grit to be distributed over a road surface. The invention further relates to a method for distributing slurry over a road surface and to a slurry which contains grit and can be obtained with a method and/or from a filling station and/or storage holder according to the invention.

Iciness of roads and other asphalting is preferably preventively combated, and, when this is impossible, ice, snow and/or freezing is curatively removed from the road surface as rapidly as possible, optionally after mechanical operations such as snow ploughing or snow brushing. It is known for this purpose to spread a solid, granular material (typically NaCl), indicated hereinafter as grit, from a gritting truck. Here, a problem is that especially with preventive spreading, the dry grit is blown from the road surface by the wind and passing vehicles and ends up on the roadside. It is known to moisten the grit during spreading so that it adheres to the road surface better. A customary ratio is 30% liquid (brine solution) to 70% grit in solid form. However, this requires complex apparatuses with limited result for moistening the salt sufficiently intensively given a required large variation in spreading flow rate due to variation in required spreading width, spreading density and driving speed. Insufficiently mixed solid and liquid grit results in an irregularly distributed thawing action and loss of grit as it does not, in part, adhere properly. In turn, this results in reduced efficiency, in that additional grit is to be applied as compensation. A further problem when spreading grit in granular form is that the grain size distribution of the grit influences the distribution of the grit. On average, relatively large particles spread sideways end up farther sideways than relatively small particles spread sideways. To distribute the grit uniformly and to prevent it from ending up on the roadside, it is therefore important that the grain size distribution of the grit is within a narrow range. However, such grit is relatively expensive and special measures, such as adding anti-lumping agent, are required to prevent the effective granule size distribution from changing due to lumping during storage.

It is also known to dissolve the salt in water prior to spreading and to spray the thus obtained saline solution over the road surface. However, here the problem arises that only a limited amount of salt can be dissolved in water, so that the solution can contain relatively little salt. As a result, the thawing action of such a solution is limited, in particular when the solution is further diluted with water already present on the road surface, possibly in the form of snow or ice, or ending up on the road surface as precipitation. A further drawback of the use of a saline solution as thawing agent is that it penetrates snow and ice only poorly and that the solution flows from the road surface easily.

In addition to preventing iciness, spreading substances such as salt over a road surface can also serve other purposes. For instance, through application of salt such as calcium chloride a hygroscopic and hence, through moisture retention, somewhat sticky layer can be provided on a road surface, to which fine dust adheres. Thus, the fine dust emission of traffic can be limited.

From German Auslegeschrift 1 188 639 and Dutch patent 125 310 it is known to add water to the salt prior to spreading, so that a pulp is obtained. It is further described to constantly stir the thus obtained pulp and then to apply it to the asphalting to be treated by means of the spreading apparatus. This direction of development has not been pursued in practice. In the German Auslegeschrift 1 279 707 it is described that the problem then arose that after spreading the remaining pulp could not be stored well in the vehicle because it needs constant stirring and the proposed solution to this problem was storing the salt and the water separately in the spreading vehicle and mix it during the spreading route.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a solution which enables effective and efficient distribution of grit over a road surface by allowing a uniform and controllable distribution of the grit in a simple manner over the road surface to be treated. According to the invention, this object is achieved by carrying out the provision of the grit in a manner as laid down in claim 1 and by carrying out the prevention of the iciness in a manner as laid down in claim 8. The invention can also be embodied in a filling station according to claim 12 or a storage holder according to claim 21 which are especially designed for carrying out the method according to claim 1. The invention can further be embodied in a slurry according to claim 20 which is especially suitable to be provided by the method according to claim 1 and from a filling station according to claim 9 or a storage holder according to claim 21 and which is especially suitable for use in the method according to claim 8. As, prior to spreading, the grit is prepared and held ready in the filling station as a slurry to be delivered, the grain size distribution in the slurry can be well controlled, so that a relatively homogeneous grain size distribution can be guaranteed. When submerged in liquid, non-dissolved granules of the grit appear to exhibit relatively little tendency to lump. Furthermore, a slurry (unlike a pulp) can easily be agitated with some regularity so that the grit is easily manageable and also when preserved longer, lumping can be prevented in a simple manner.

The storage holder is also suitable for storing and dispensing unsaturated grit solutions, so that in particular with preventive gritting operations when only a slight frost is expected, the storage holder can also be used for the purpose of treating a road surface with only a liquid grit solution.

A further additional advantage is that the gritting trucks need not be equipped for the initial mixing of the grit with water and the gritting trucks need only be loaded with one substance: slurry or a liquid instead of water and a solid grit. This enables loading to be more rapid, safer and cleaner.

In the dependent claims, special design aspects of the invention are laid down.

Further aspects, effects and details of the invention appear from the following description of exemplary embodiments, in which reference is made to the drawing.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a schematic overview of an example of a filling station according to the invention and of a distribution vehicle with a storage holder according to the invention;

Fig. 2 is a top plan view of a mixing holder of the filling station according to Fig. 1; Fig. 3 is a schematic representation of a slurry according to the invention in agitated and non-agitated condition;

Fig. 4 is a schematic representation of an exploded side view of a storage holder of the filling station according to Fig. 1; and

Fig. 5 is a schematic representation of an exploded side view of the storage holder of the distribution vehicle according to Fig. 1.

DETAILED DESCRIPTION

In Figs. 1 and 2, an example of a filling station according to the invention is represented. The filling station is a station with which distribution vehicles 1 for spreading or otherwise distributing grit over a road surface can be filled with grit before driving a gritting route and spreading the grit over the road surface, for instance preventively or for melting snow and/or ice already present. The grit can also serve for effecting other properties of the road surface such as stickiness.

The filling station according to this example is equipped with a silo 2 for storing and dispensing a grit 3, such as salt or a mixture of sand and salt, in granular form. The silo 2 has a valve 4 which is reciprocally movable in directions indicated with an arrow 5 for opening and closing a passage 6 in a bottom end of the silo 2. The filling station can be provided with weighing means for determining the amounts of water and solid grit that are dispensed or are still to be dispensed.

Below the opening 6 in the silo 2 there is a mixing holder 7 with a mixing element 8, according to this example in the form of a mixing screw, coupled to a motor 9 for driving rotation of the screw 8 about its central axis. In the mixing holder 7 is also present an approximately semi-conical screen 10 which, if the screw 8 turns to the right, allows for the creation of a circulating flow through the mixing holder 7 as indicated with arrows 11 - 14. This flow is strongest adjacent a downstream end of the screw 8, where it is provided with grinding blades 15 for grinding or breaking salt lumps. Via a water supply line 16 with a valve 17, water can be introduced into the mixing holder 7. After the valves 5 and 17 have been open for a suitable time, in the mixing holder 7 there is an amount of grit 18 and an amount of water 19 in which already a portion of the grit may have been dissolved. After the screw 8 has been switched on for some time the grit 18 and the water 19 are intensively (and preferably) homogeneously mixed into a slurry which contains a portion of the grit and a portion of the grit 18 in solid form. Depending on the ratio of liquid and solid material in the slurry, this will be liquid to a greater or lesser extent. The mixing holder 7 is connected, via a transfer channel 20 of which an inlet is connected to a lower portion of the mixing holder 7 and a recirculation channel 23, to an optional storage holder 21 for storing the slurry. The slurry in the storage holder 21 is indicated with reference numeral 29. The recirculation channel 23 is connected to a first three-way valve 25 with which the transfer channel 20 and a discharge channel 26 link up. The recirculation channel 23 extends through a second three-way valve 27 with which also a filling channel 24 links up.

The filling station is further equipped with a filling apparatus for filling the distribution vehicle 1 with at least a portion of the slurry 29 in the storage holder 21. Here, the distribution vehicle 1 can be completely or partly filled, depending on, for instance, the amount of road surface to be treated and the required application thicknesses. According to example, the filling device is formed by the filling channel 24 which can communicate, via the second three- way valve 27 and a portion of the recirculation channel 23 located upstream thereof, with a pump 22 included in the recirculation channel 23. A downstream part of the filling channel 24 extends through a filling hose 28. The discharge channel 26 linking up with the first three-way valve 25 has an inlet in a lower part of the storage holder 21. According to this example, the inlet links up with a lowest point of the storage holder 21 so that all slurry 29 (with the exception of any slurry that may adhere to walls of the storage holder 21) can be discharged. The storage holder 21 is provided with a ventilation and aeration opening to prevent at least excessive excess pressure and reduced pressure, respectively, in the storage holder 21.

To the slurry pump 22 are connected portions of the recirculation channel 23 located upstream and downstream thereof. The recirculation channel 23 terminates into the inner space of the storage holder 21 for recirculating at least a portion of slurry 29 pumped from the inner space by the slurry pump 22.

An aeration channel 30 terminates into the discharge channel 26 and is connected to an aeration pump 31, according to this example a (centrifugal) compressor for blowing air, via the aeration channel 30 and the discharge channel 26, into the inner space of the storage holder 21.

When the slurry pump 22 is stationary, after a brief period of time, the slurry 29 will turn to a condition as represented in Fig. 1, where the grit 18' present in solid form has settled towards the bottom and the liquid 19' forms a layer above the grit 18' in solid form and is furthermore present in intermediate spaces between the granules of the solid portion of the grit 18'.

In order to prevent formation of lumps, the slurry 29 is periodically agitated. Furthermore, prior to and during pumping slurry 29 across to a distribution vehicle, the slurry 29 can be agitated to improve the homogeneity and pumpability of the slurry 29.

According to this example, agitation is carried out by first introducing air or gas into a lower portion of the storage holder 21. Owing to the rising air bubbles, a solid portion 18' of the slurry 29 is whirled up and, at least for an important part, brought into a suspended condition in the solution 19'. As, according to this example, the air or gas is introduced via an upstream part of the discharge channel 26, here, also solid grit which has settled in this part of the discharge channel is dislodged.

Then, according to this example, the slurry is agitated further through recirculation thereof. Here, the slurry is discharged from the inner space of the storage holder 21 and returned into the inner space. Here, optionally, a portion of the slurry can be discharged permanently for instance for filling the gritting truck 1.

Thereupon, for recirculation of the slurry 29, according to this example, the pump 22 is switched on while the first valve 25, via which the recirculation channel can be brought into communication with either the discharge channel 26 or the transfer channel 29, is in a position of recirculation. In the recirculation position, the discharge channel 26 communicates via this first valve 25 with the recirculation channel 23 while the second valve 27 is in a position in which the portions of the recirculation channel located upstream and downstream thereof mutually communicate. As a result, slurry 29 is circulated from the storage holder 21 via the discharge line 26 and the recirculation channel 23. This operative condition of the storage holder 21 is represented in Fig. 4. The recirculation channel 23 terminates into a lower portion of the inner space of the storage holder 21 (preferably lower than 25% of the height of the storage holder) which is further equipped with a guide surface 32 for allowing slurry to flow into the inner space of the storage holder 21 with a horizontal component of movement. As a result, the solid fraction of the slurry 29 is effectively whirled up in a lower part of the inner space of the storage holder 21. Furthermore, a stirring effect is obtained, further promoting a uniform distribution of the solid fraction of the slurry 29 within the storage holder 21.

The guide surface could form part of an inner wall surface of the recirculation channel or of a branch of the recirculation channel. However, according to this example, the guide surface 32 is designed as a distribution surface located downstream of the outflow opening of the recirculation channel 23 for receiving slurry flowing in a flow direction from the recirculation channel, and facing the recirculation channel 23 for changing the flow direction of the slurry coming from the recirculation channel 23.

Thus, it is effected in a simple manner that the flow direction of the outflowing slurry is deflected in different directions so that a stirring effect is obtained which is distributed better over the inner space of the storage holder 21. When the three-way valves 25, 27 are set for allowing slurry to pass from the transfer channel 20 to the recirculation channel 23 and from the portion of the recirculation channel 23 on the upstream side of the three-way valve 27 to the portion of the recirculation channel 23 on the downstream side of the second three-way valve 27, the slurry can be pumped by the pump 22 in the recirculation channel 23 from the mixing holder 7 to the storage holder 21. Preferably, this takes place while the screw 8 rotates and thus keeps the solid fraction of the grit 18 at least for the larger part suspended in the solution.

If the pump 22 is switched on while the first three-way valve 25 is in a position in which the discharge channel 26 communicates with the recirculation channel 23 and in which the second valve 27 in the recirculation channel 23 is in a position in which the portion of the recirculation channel 23 located upstream thereof communicates with the filling channel 24, slurry is pumped from the storage holder 21 to the vehicle 1. The second valve 27 in the recirculation channel 23 can also be put into a position in which the portion of the recirculation channel 23 located upstream thereof communicates both with the portion of the recirculation channel 23 located downstream thereof and with the filling channel. In that case, a portion of the slurry pumped by the pump 22 to the valve 27 is led to the vehicle 1 and another portion of the slurry pumped by the pump 22 to the valve 27 is recirculated to the inner space of the storage holder 21.

By storing the grit as component of a slurry, it appears that a uniform grain size distribution of the portion of the grit which is in solid form can be maintained in a reliable manner. Furthermore, the slurry present in a premixed form can rapidly be transferred from a filling station. As processing a substantially dry grit and water into a slurry is carried out in a filling station, the distribution vehicle needs not be designed for mixing grit and water into a slurry (as is the case with separate storage holders and dosing means for water and grit), but it suffices when in the distribution vehicle provisions are present for remixing the slurry sufficiently to enable a uniform distribution of the solid fraction of the grit.

As the grinding elements 15 are located in the mixing holder 7, grinding the grit is carried out during mixing whereby large parts are reduced into smaller parts, in the water and lumping after grinding is effectively prevented. This effect can also be achieved if the grinding provisions are placed such that the ground grit is introduced into the water immediately after grinding.

For filling the distribution vehicle with a slurry with a constant composition, it is further advantageous if filling the slurry to the distribution vehicle 1 is carried out while the slurry is being agitated in the storage holder 21.

To prevent lumping, it is further advantageous when the storage holder 21 is equipped with provisions for agitating the stored slurry. As the stored slurry is agitated at least periodically, lumping is further prevented. According to the example shown, this is carried out by circulating the slurry by pumping it around in the above-described manner.

Here, the fact that the provisions for agitating the stored slurry comprise a pump 22, lines 23, 24, 26 and valves 25, 27 designed for recirculating slurry in a condition of agitation from the storage holder 21 and for pumping slurry in a condition for filling from the storage holder to the distribution vehicle 1 is advantageous, because the pump 22 can be deployed for supplying, discharging and for agitating slurry.

With the filling station according to this example, a further increase of the efficiency is achieved in that the pump 22, the lines 20, 23, 24, 26 and the valves 23, 25, 29 are designed such that the pump 22 can also be used for pumping the slurry from the mixing holder 7 to the storage holder 21.

For transferring the slurry from the distribution vehicle 1 to the storage holder 21, a branch of a dispensing channel of the distribution vehicle can be connected to the recirculation line 23. This allows for slurry leftover after spreading of slurry from the distribution vehicle 1 to be transferred from the distribution vehicle 1 to the storage holder 21 of the filling station. Optionally, the slurry holder of the distribution vehicle can be rinsed so that no grit in solid form remains behind therein which may cake upon prolonged storing. Within the framework of the invention, it is also possible to transfer the slurry directly from a mixing holder, such as the mixing holder 7, to a vehicle. As a separate buffer holder 21 is provided, a large amount of slurry can be loaded into distribution vehicles in a relatively short period of time. This is of special importance with suddenly occurring iciness.

The filling station is further equipped with a water supply line 34 with a valve 35 and a flowmeter 36 therein. In the filling channel 26, also, a flowmeter 37 is included. The flowmeters 36, 37 are coupled to the valve 35 for regulating the flow rate through the valve 35. If it is desired to fill the distribution vehicle 1 with a slurry with a water/solid matter ratio having a larger water portion than the water portion of the slurry in the storage holder 21, the valve 35 can be opened in a dosed manner for mixing in water in a dosed manner during the filling of the distribution vehicle 1.

In order to maintain the slurry in the storage holder 21 and the distribution vehicle 1 in a good condition for a longer period of time and in particular prevent lumping of the grit in a simple manner, it is advantageous if the volume percentage of solid matter in the slurry is less than 70% or is at least such that a layer of liquid stands above the grit in solid form. For easy agitation of the slurry, it is further advantageous if the volume percentage of solid matter in the slurry is less than 70%, for instance less than 30, 50 or

60%. In this context, the solid matter is understood to mean the portion of the grit in solid form present in the slurry.

An example of such a slurry is schematically represented in Fig. 3, where, on the left hand side, a slurry 29 in non-agitated condition is represented and, on the right hand side, a slurry 29 in agitated condition is represented. The amount of water in the slurry is so great that when it is not agitated for some time, above a layer 18' of settled solid particles, a layer of liquid 19' is formed which consists of water and grit dissolved therein. The volume of this layer of liquid above the layer of settled particles is, after a standing period sufficient for the solid particles to settle and/or float up, preferably at least approximately 30% of the total volume of the layer of the settled particles including the volume of the liquid between the settled particles of the layer. The above-described amounts of water are of importance for allowing, in agitated condition, sufficient space between the floating particles. As a result, the solid particles in the slurry are easily fluidized in which condition the slurry is furthermore sufficiently thinly liquid to be easily pumped and spread. Here, preferably, the slurry has a composition, also during spreading, as described hereinabove.

The amount of salt to be applied per surface unit to a road surface depends on the expected temperature, the expected precipitation and the amount of salt already present. If little salt is to be applied, it may be advantageous for a uniform distribution of the salt to apply only liquid with salt dissolved therein as is known per se. However, when significantly more salt is desired without the application of more liquid, within the framework of the present invention, a slurry can be applied which contains only a small amount of salt in solid form, for instance five volume percent or more, depending on the expected conditions.

Within the framework of the invention as laid down in the claims, several other embodiments than the embodiments described here by way of example are possible. For instance, instead of from a silo 2, the grit can be also brought from a stock into a mixing holder differently, for instance by means of a shovel, and the grinding elements can be located in a grinding station upstream of the mixing holder. Further, the solid particles in the slurry can also contain non-dissolvable particles such as sand. Instead of or in addition to sodium salt, also other salts, such as calcium and magnesium salts and/or thawing means such as sugars or alcohols can be incorporated into the slurry. In Fig. 5, a storage holder 51 of the distribution vehicle 1 according to Fig. 1 is represented in further detail. The storage holder 51 is composed of four storage holder portions 51-1, 51-2, 51-3 and 51-4. Depending on the desired capacity and the size of the storage holder portions, the storage holder can be composed of more or fewer storage holder portions.

The storage holder portions 51-1, 51-2, 51-3, and 51-4 and the channels for filling, agitating, recirculating and dispensing slurry are designed in a similar manner as the holder 21 and the associated channels 20, 23, 24, 26 for filling, agitating, recirculating and dispensing slurry.

A transferring channel 50 with a connecting coupling 70 to which the filling hose 28 (see Fig. 1) can be connected, is coupled via a first three-way valve 55 to a recirculation channel 53 and to recirculation channel branches 53-1, 53-2, 53-3 and 53-4 located downstream of valves 68-1, 68-2, 68- 3 and 68-4 to the storage holder portions 51-1, 51-2, 51-3 and 51-4. Aligned with the first three-way valve 55 is also a discharge channel 56. Discharge channel branches 56-1,56-2, 56-3 and 56-4 located upstream of valves 69-1, 69-2, 69-3 and 69-4 are connected to the discharge channel 56. The recirculation channel 53 extends through a slurry pump 52 and a second three- way valve 57 with which also a dispensing channel 54 aligns. In the dispensing channel 54, a flow meter 69 and a regulating valve 71 for controlling the dosage of the discharge of slurry are included. Preferably, dosing is settable as density distribution per unit of road surface while the regulating valve 71 is controlled depending on the set density, the flow rate measured by the flow meter 69 and the momentary driving speed. The discharge channel 54 terminates above a distributing disk 72 which is rotatable about an axis 73 for distributing the slurry also in cross direction over a desired releasing width. The branches 56-1, 56-2, 56-3, 56-4 of the discharge channel 56 aligning with the first three-way valve 55 each have an inlet in a lower portion of one of the storage holder portions 51-1, 51-2, 51-3 and 51-4. According to this example too, the inlets link up with lower portions of the storage holder portions 51-1, 51-2, 51-3 and 51-4, so that the slurry can be discharged, besides any slurry that may adhere to walls of the storage holder 51. Portions of the recirculation channel 53 located upstream and downstream of the slurry pump 52 align therewith. The branches 53-1, 53-2, 53-3 and 53-4 of the recirculation channel 53 each terminate into the inner space of one of the storage portions 51-1, 51-2, 51-3 and 51-4 for recirculating at least a portion of the slurry pumped by the slurry pump 52 from the inner space of the respective storage holder portion 51-1, 51-2, 51-3 and 51-4.

Downstream of valves 62-1, 62-2, 62-3 and 63-4, aeration channel branches 60-1, 60-2, 60-3 and 60-4 are connected to an aeration channel 60, which branches each terminate into one of the branches 56-1, 56-2, 56-3 and 56-4 of the discharge channel 56 and which, at least with the respective valves 62-1, 62-2, 62-3, 62-4 open, communicate with an aeration pump 61, according to this example a centrifugal compressor, for blowing air, via the aeration channel 60 and the branches 56-1, 56-2, 56-3 and 56-4 of the discharge channel 56, into the inner space of the storage holder portions

51-1, 51-2, 51-3 and 51-4. Furthermore, a branch 60.5 of the aeration channel 60 links up, downstream of the slurry pump 52 and the second three-way valve 57, with the recirculation channel 53.

Furthermore, upstream of the valves 78-1, 78-2, 78-3 and 78-4, respectively, an upper discharge channel 74 having branches 74-1, 74-2, 74-3 and 74-4 aligns with the discharge channel 56. The branches 73-1, 73-2, 73-3, 73-4 each have an upstream end designed as a flexible helically proceeding hose 76 with an inlet end coupled to a float 75 for taking in liquid at the surface on which the float 75 floats. The slurry pump 52, the aeration pump 61 and all shown valves 55,

57, 56-1, 56-2, 56-3, 56-4, 62-1, 61-2, 61-3, 61-4, 68-1, 68-2, 68-3, 68-4, 69-1, 69-2, 69-3, 69-4, 78-1, 78-2, 78-3, 78-4 are coupled to a control 77 for controlling the pump 52 and the compressor 61 as well as the positions of the valves. For filling the storage holder 51, the first three-way valve 55 is brought in a position in which the filling channel 50 communicates with the recirculation channel 53, and the second three-way valve 57 is brought into a position in which the portions of the recirculation channel 53 upstream and downstream thereof mutually communicate and the dispensing channel 54 is closed off. Furthermore, one or more of the valves 68-1, 68-2,68-3, 68-4 in the recirculation channel are brought into a position that allows slurry to pass to the branches 53-1, 53-2, 53-3, 53-4 connected thereto. Here, the pump 52 can be activated or left to run in neutral when the pressure for moving the slurry provided by the pump 22 of the filling station (Fig. 1) is sufficient. By successively opening the valves 68-1, 68-2, 68-3, 68-4 or, from a condition where they are open simultaneously, closing them when the respective compartments are full, the storage holder 51 can be filled until all compartments are full. It is also possible to wholly or partly fill only one or more of the compartments when the amount of slurry to be distributed is smaller than the capacity of the storage holder 51. By activating the aeration pump 61 and alternately operating preferably only one or optionally several of the valves 62-1, 62-2, 62-3, 62-4 for selectively bringing one or more of the aeration branches 60-1, 60-2, 60-3, 60-4 into communication with the aeration pump 61, each time, agitation can take place in only one or several, respectively, of the compartments formed by the storage holder portions 51-1, 51-2, 51-3, 51-4. This allows for effecting agitation with a relatively small output.

Besides via the aeration branches 60-1, 60-2, 60-3, 60-4 of the aeration channel 60, blowing in air can also be carried out via the recirculation channel 53. Here, the air to be blown in is led to one ore more inner spaces of the storage holder portions 51-1, 51-2, 51-3, 51-4 via the branch 60-5 of the aeration channel 60 and via one or more of the valves 68-1, 68-2, 68-3, 68-4 with which links up a branch 53-1, 53-2, 53-3, 53-4 of the recirculation 53. By selectively opening one or more of the corresponding valves 62-1, 62-2, 62-3, 62-4, 68-1, 68-2,68-3,68-4 in the aeration channel 60 and in the recirculation channel 53 for allowing air to pass to the respective branches 53-1, 53-2,53-3, 53-4, 60-1, 60-2, 60-3 and 60-4, simultaneously, blowing in air via the aeration channel 60 and via the recirculation channel 53 can be carried out. However, it is also possible that air is blown in exclusively via the aeration channel 60 or via the recirculation channel 53 or that air is blown into one compartment via the aeration channel 60 while air is blown into another compartment via the recirculation channel 53.

For effectively whirling up solid particles in lower portions of the compartments of the storage holder 51, and in particular in the branches 56-1, 56-2, 56-3, 56-4 of the discharge channel 56, it is advantageous to each time blow in air exclusively via the aeration channel 60 because as a result, air can be blown in at great pressure in the branches 56-1, 56-2, 56-3, 56-4 of the discharge channel 56. After that, for further homogenisation of the slurry, blowing in of air is regulated via the recirculation channel 53.

To prevent deposits of grit in solid form in the channels after spreading has stopped without a compartment being fully emptied or after recirculation, it is also possible, after spreading or recirculation, to briefly carry out recirculation in a recirculation sense, whereby liquid is withdrawn from the upper area of a compartment and is returned to the respective compartment, via the discharge channel 56 and the respective branch 56-1, 56-2, 56-3, 56-4. What is achieved in this manner is that grit in solid form is rinsed from the channels before the liquid comes to a standstill in the channels. Naturally, this technique can also be utilized with a storage holder not divided into compartments. In that case, recirculation takes place in opposite recirculation direction through the inner space of this storage holder. For the life span of these provisions it can also be beneficial to rinse with clean water after use.

Thereupon, for further homogenisation of the slurry, slurry can be recircuiated by pumping it away via the respective branch(es) 56-1,56-2, 56-3, 56-4 of the discharge channel and returning it, at least partly, to the respective compartment of the storage holder 51, by bringing the first and second three- way valve 55 and 57 in positions for allowing the slurry to flow to and through the recirculation channel 53 and by opening the one of the respective valves 68-1, 68-2, 68-3, 68-4 in the recirculation channel 53. Here, blowing in air can be stopped or continued optionally with reduced output. This latter is advantageous to prevent clogging of the discharge channel 56 with slurries with a relatively small liquid portion. As recirculation can also be carried out each time for one compartment at the time, to this end, a relatively limited output is sufficient too.

Thus, to prevent lumping and to bring the slurry in a homogeneous condition for the purpose of dispensing, the blowing in of air and recirculation of slurry can be carried out per compartment. It is also possible to pump slurry from one compartment to the other.

In preparation to the distribution of slurry over a road surface when the vehicle is driving, the slurry is whirled up in one of the compartments by blowing in air as described hereinabove. Then, slurry from the compartment is recirculated, also as described hereinabove. Thus, a condition is reached where slurry is present in an agitated, relatively homogenous condition in the respective compartment, the discharge channel 56 and the recirculation channel 53 and is recirculated by a pump 52. By then bringing the three-way valve 57 into a position in which at least a portion of the slurry that reaches the second three-way valve 57 is forced into the dispensing channel 54, a slurry flow is effected towards the spreader 72 which is held in rotation about the axis 73 and the slurry is spread in width-direction of the road surface. As the grain size of the solid particles in the slurry is within a relatively narrow range, the distribution of slurry over the road surface can be controlled well. Furthermore, the slurry adheres to the road surface better than grit and salt moistened during spreading while, on the other side, it does not contain so much liquid that an important amount of the slurry flows from the road surface. If application of thawing agent with a limited density is desired, for instance because a road surface is treated only additionally and/or because the road surface is treated preventively in anticipation of slight frost and little precipitation and/or freezing, it can be advantageous to only spread liquid with thawing agent dissolved therein over the road surface. This can be carried out with the storage holder 51 according to this example, by adjusting the valves 69-1, 69-2, 69-3, 69-4 in the discharge channel 56, the first three-way valve 55 and the second three-way valve 57 to have the upper discharge channel 74 communicate with the discharge channel 54, closing the valves 68-1, 68-2, 68-3, 68-4 in the recirculation channel 53 so that no liquid is recirculated. By opening one or more of the valves 78-1, 78-2, 78-3, 78-4 in the upper discharge channel 74 it can be effected that the pump 52, when it is switched on, supplies liquid via a hose 76 in the respective compartment from the surface of the non- agitated slurry which is present in a condition having liquid 19' above the components in solid form 18' as is represented on the left hand side in Fig. 4. The float 75 drops with the sinking of the liquid surface, until the particles in solid form are reached or, when they are not present in the compartment, until the bottom of the compartment is reached. A special advantage of the use of inlet openings coupled to floats is that liquid can be dispensed while soluble slurry components in solid form are present in the storage holder, without these being carried along too. This allows, in turn, as long as sufficient soluble slurry components in solid form are present in the storage holder, to refill the storage holder 51 with only water and to then still obtain a solution and a slurry with thawing agent. Within the framework of the invention, many other elaborations are possible than the above described elaborations discussed by way of example. For instance, the valves for selectively closing the various branches can be designed as seals in the branches instead of, as in the example shown, as three-way valves with which the branches link up. The various channels can be designed as passages through lines, but also be formed completely or partly by passages through other bodies, such as sockets and valve housings. The inner spaces of the storage holder portions can be designed, instead of as compartments of a storage holder, also as inner spaces of several separate storage holders. For the purpose of detaching settled grit in solid form, instead of or in addition to an aerator, also a stirrer can be utilized. Then, driving the stirrer is preferably carried out such that when stirring is started, the stirrer is initially moved slowly and is then accelerated. If to this end, several transmissions are used in the drive of the stirrer, furthermore, upon starting the stirrer, a relatively large output is available to detach any grit in solid form that may lump.

Grinding the grit in solid form so that excessively large grains and lumps are reduced can possibly be achieved without using separate grinding provisions. For instance, when circulating the slurry, depending on the type of pump used, in many cases the effect is already obtained as especially larger particles are reduced in the slurry.

Claims

1. A method for providing grit (3) to be distributed over a road surface, comprising: at the location of a stationary filling station mixing water and grit (3) into a slurry (29) containing a solution (19, 19') of a portion of the grit (3) in the water and a portion (18, 18') of the grit (3) in solid form; and transferring at least a portion of the slurry (29) from the filling station to a distribution vehicle (1).

2. A method according to claim 1, further comprising grinding the grit (3) immediately prior to or during mixing.

3. A method according to claim 1 or 2, wherein the stored slurry (29, 29) is periodically agitated.

4. A method according to any one of the preceding claims, wherein filling the distribution vehicle (1) with the slurry (29) is done from a stock of the slurry (29) while this is being agitated.

5. A method according to any one of the preceding claims, wherein agitating the slurry (29) and filling the distribution vehicle (1) is done by means of the same pump (22).

6. A method according to any one of the preceding claims, further comprising spreading the slurry (29) from the distribution vehicle (1) and, after spreading, transferring surplus slurry (29) from the distribution vehicle (1) to the filling station or to another filling station.

7. A method according to any one of the preceding claims, wherein the volume percentage of solid matter (18, 18') in the slurry (29) is less than 70%.

8. A method for distributing grit over a road surface, comprising spreading from a driving distribution vehicle (1) a slurry (29) containing a liquid, a first portion of a grit (3) dissolved in the liquid and a further portion (18, 18') of the grit (3) in solid form.

9. A method according to claim 8, wherein the slurry is located in compartments (51-1, 51-2, 51-3, 51-4) of a storage holder (51) of the distribution vehicle (1) and wherein the slurry is agitated each time only in a subset of said compartments (51-1, 51-2, 51-3, 51-4).

10. A method according to claim 3 or 9, wherein the agitating comprises introducing air or gas into a lower portion of the storage holder (21; 51).

11. A method according to claim 10, wherein the air or gas is introduced into a discharge channel (26; 56) Unking up with a lower portion of the storage holder (21; 51) and wherein then slurry is recirculated by pumping it away via the discharge channel (26; 56) and at least partly returning it to the storage holder (21; 51).

12. A filling station for providing grit (3) to be distributed over a road surface, comprising: a mixing holder (7) with a mixing element (8) for mixing water and grit (3) into a slurry (29) containing a liquid (19') containing a portion of the grit (3) dissolved in the liquid and a portion (18', 19') of the grit (3) in solid form; and a filling apparatus (22, 23, 24, 26, 27, 28) for transferring at least a portion of the slurry (29) to a distribution vehicle (1).

13. A filling station according to claim 12, further comprising a storage holder (21) and a transfer channel (20) for transferring slurry (29) from the mixing holder (7) to the storage holder (21), wherein the filling apparatus (22, 23, 24, 26, 27, 28) is designed for transferring slurry (29) from the storage holder 921) to the distribution vehicle (1).

14. A filling station according to claim 12, wherein the filling apparatus is designed for transferring slurry (29) directly from the mixing holder to the distribution vehicle.

15. A filling station according to any one of claims 12-14, further comprising a grinding element (15) upstream of or in the mixing holder (7).

16. A filling station according to any one of claims 12-15, further comprising a storage holder (21) equipped with provisions (22, 23, 25, 26, 27, 30, 31, 32) for agitating the stored slurry (29).

17. A filling station according to claim 16, wherein the provisions for agitating the stored slurry (29) comprise a pump (22), lines (23, 26) and valves (25, 27) which are designed for recirculating slurry (29) in an agitation position from the storage holder (21) and for pumping slurry (29) in a filling position from the storage holder (21) to the distribution vehicle (1).

18. A filling station according to claim 17, wherein the pump (22), at least a part of the lines (23, 26) and the valves (25, 27) are also designed for transferring slurry (29), in a transferring position, from the mixing holder (7) to the storage holder (22).

19. A filling station according to any one of claims 12-18, wherein the storage holder (21) is provided with a connection for transferring slurry (29) from the distribution vehicle (1) to the storage holder (21).

20. A slurry containing a saturated solution (19, 19) of water and a portion of a grit (3) dissolved therein and a portion (18, 18') of the grit (3) in solid form, wherein the volume percentage of matter in solid form in the slurry (29) is less than 70%.

21. A storage holder with an inner space for storing therein a slurry (29) containing a solution (19, 19') of a portion of a grit (3) and a portion (18, 18') of the grit (3) in solid form, which storage holder is equipped with: a discharge channel (26; 56, 56-1, 56-2, 56-3, 56-4) with an inlet in a lower area of the storage holder (21; 51); an aeration channel (30; 60, 60-1, 60-2, 60-3, 60-4) terminating into the discharge channel (26; 56); a slurry pump (22; 52) for pumping slurry through the discharge channel (26; 56, 56-1, 56-2, 56-3, 56-4) in a direction away from said inlet; and an aeration pump (31; 61) connected for blowing air or gas into said inner space via the aeration channel (30; 60, 60-1, 60-2, 60-3, 60-4) and the discharge channel (26; 56).

22. A storage holder according to claim 21, further comprising: at least two storage holder portions (51-1, 51-2, 51-3, 51-4) each having one of said inner spaces, which inner spaces are at least partly separated from each other; at least two discharge channels (56-1, 56-2, 56-3, 56-4) each having an inlet in a lower area of one of said inner spaces; and at least two aeration channels (60-1, 60-2, 60-3, 60-4), each terminating into the at least one discharge channel (60); wherein at least: the slurry pump (22; 52) for pumping slurry through the discharge channels (56-1, 56-2, 56-3, 56-4) via a valve structure (69-1, 69-2, 69-3, 69-4) is connected for selectively bringing the slurry pump(52) into communication with one of the discharge channels (56-1, 56-2, 56-3, 56-4); or wherein the aeration pump (61) is connected via a valve structure (62-1, 62-2, 62-3, 62-4) for selectively bringing the aeration pump (60) into communication with one of the aeration channels (60-1, 60-2, 60-3, 60-4).

23. A storage holder according to claim 21 or 22, further comprising a recirculation line (23; 53) connected to said slurry pump (22; 52) and terminating into said inner space for recirculating at least a portion of slurry pumped by the slurry pump (22; 52) from said inner space.

24. A storage holder according to claim 23, wherein the recirculation channel (23; 53) terminates into a lower portion of said inner space, further comprising a guide surface (32) for causing slurry to flow out into the inner space of the storage holder (21; 51) with a horizontal component of movement.

25. A storage holder according to claim 24, wherein the guide surface (32) is designed as a distribution surface which is located downstream of an outflow opening of the recirculation channel (23; 53) for receiving slurry flowing in a flow direction from the recirculation channel (23; 53) and which faces the recirculation channel (23; 53) for changing the flow direction of the slurry coming from the recirculation channel (23; 53).