Abstract:
A device for laying dust contained in a flow of bulk product during transfer thereof includes a divergent cone onto whose outside surface the product is directed from a feed pipe to form a tubular layer of product. A mounting device holds the cone in the flow of product leaving the feed pipe and at least one device fixed to the mounting device sprays a moistening liquid to moisten the inside envelope of the layer of product. The spray device has at least one central nozzle in a spray moistening area downstream of the cone to moisten the part of the inside envelope of the product layer downstream of the cone. The structure of the device is such that the thickness of the tubular layer of the flow of product can be freely chosen at least until the flow leaves the area, the layer thereafter retaining its hollow annular shape. Applications include laying dust contained in grain when it is transferred into cells of a storage silo.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to handling bulk product such as agricultural produce, in particular grain or other similar products, that can also contain a powder component referred to hereinafter as “dust”. 
     The invention relates more particularly to a device for laying dust contained in a flow of bulk product during transfer thereof. 
     Transfer can be effected in order to fill or empty a silo, a transportation vehicle such as a railroad wagon, truck or grain bulk-carrier ship or a storage heap. The invention finds one particularly useful application in cells of a silo for storing grain and in ducts for transferring grain to a storage area or transport vehicle. 
     The presence of dust in bulk product can be a great nuisance because dust that separates from the product during transfer forms a suspension in the air and can then degrade the cleanliness of the storage place or the environment. In the case of grain silos, the dust can even cause risks of fire or explosion, similar to those associated with coal “dust”, for example. 
     2. Description of the Prior Art 
     In the dust-laying device described in U.S. Pat. No. 2,973,740, a divergent cone is placed in a casing which, as seen in the direction of flow of the product, narrows until the product enters a pipe connected to the dust-laying device. The layer of product formed downstream of the divergent cone is therefore obliged to become narrowed along the inside surface of the casing. This retards the forward movement of the layer, which reduces the flowrate at which the product passes into the dust-laying device. Also, the structure of the above prior art dust-laying device soils readily because as it moves forward the product is confined within an increasingly small space. Finally, the spray device is housed inside the cone and therefore cannot spray directly onto the outside envelope of the layer, but only from the interior of the divergent cone. It is also found that the above prior art device retards the flow of the product downstream of the spray area, which can become completely invaded by the product if the downstream flow is stopped. 
     The object of the invention is to provide a device for laying dust contained in a bulk product which remedies the drawbacks of the prior art dust-laying device. 
     SUMMARY OF THE INVENTION 
     The invention therefore consists in a device for laying dust contained in a flow of bulk product during transfer thereof, the device comprising a divergent cone onto whose outside surface the product is directed from a feed pipe to form a tubular layer of product, a mounting device for holding the cone in the flow of product leaving the feed pipe and at least one device fixed to the mounting device for spraying a moistening liquid to moisten the inside envelope of the layer of product, wherein the spray device comprises at least one central nozzle in a spray moistening area downstream of the cone to moisten the part of the inside envelope of the product layer downstream of the cone and the structure of the device is such that the thickness of the tubular layer of the flow of product can form freely at least until the flow leaves the area, the layer thereafter retaining its hollow annular shape. 
     Thanks to the above features, particularly effective laying of dust is obtained by direct spraying of a moistening liquid onto the tubular layer of bulk product, without forward motion of the layer being retarded. The device can therefore work with a high flowrate and soiling of the device is minimized. Finally, the device makes it possible to spray the moistening liquid onto the outside envelope of the layer of product. 
     Other features and advantages of the invention will become apparent during the course of the following description which is given by way of example only and with reference to the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of a first embodiment of a dust-laying device in accordance with the invention. 
     FIG. 2 is a view of the same device in vertical section, installed in the ceiling of a grain silo, above one of the cells of the silo. 
     FIG. 3 is a perspective view of a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawing, it can be seen that in one preferred embodiment of the invention, more particularly intended to be used in the situation where the bulk product is an agricultural product and especially grain, the dust-laying device comprises a circular casing  1  having a cylindrical inlet  2  at the top, possibly narrowing in the upward direction with a very slight taper. The inlet  2  is designed to be a tight fit in a pipe  3  feeding the bulk product. In the non-limiting example described here, the pipe  3  can be that provided above each storage cell of a grain silo, for example, in which case the dust-laying device is installed so that its axis is vertical or inclined to the vertical. 
     The inlet  2  is connected to an intermediate part  4  of the casing  1  of frustoconical shape and diverging in the direction of flow. The intermediate part  4  is in turn connected to a lower part  5  of the casing  1 , also of frustoconical shape, but the opposite way around to the part  4 , i.e. narrowing in the downstream direction. In one variant the lower part  5  can be omitted. 
     The casing  1  therefore forms a transfer volume for conveying the bulk product from the feed pipe  3  to the cell of the silo above which the dust-laying device is provided. 
     When, as shown here, the dust-laying device must be fixed against the ceiling P of the silo, a horizontal fixing flange  6  is advantageously provided around the pipe  3  to enable such fixing. For angular positioning of the device around its vertical axis, a fixing lug  7  is provided, attached to a pin or the like (not shown) anchored in the ceiling P of the silo. 
     Supporting spacers  9  in the inlet  2  extend radially inwards. There are preferably three spacers at 120° to each other around the axis of the device. The spacers preferably have a section profiled so that it does not impede the flow of product (similar to that of an airfoil) and support a central mounting member comprising an axial hollow shaft  10  whose upper end is closed by an upwardly directed point  10   a  to facilitate the flow of product. 
     One of the spacers  9  also supports a double tube  11  formed of two coaxial tube sections, namely an inner section  11   a  connected to a pressurized liquid supply (not shown) and an outer section  11   b  connected to a compressed air supply (also not shown). 
     A sleeve  12  is screwed onto the hollow shaft  10  and immobilized by a nut  13 . The lower end of the hollow shaft carries one or more spray nozzles  14 . 
     Three holes  15  in the shaft  10  at 120° to each other provide air outlets. 
     The spray nozzle(s)  14  are fed from a pipe  16  inside the shaft  10  and forming an extension of the tube section  11   a . The pipe  16  has an outside diameter such that there is an air passage around it which communicates with the tube section  11   b  and discharges into the internal volume of the casing  1  via the holes  15 . 
     Spray nozzles  17 , which are preferably outside the casing  1 , are provided at the periphery of its lower part  5  or intermediate part  4 , where applicable. These nozzles communicate with the tube section  11   a  feeding a spray liquid via a pipe, not shown, or are fed by a separate pipe (also not shown), which enables separate adjustment of the pressure and the flowrate in the nozzles  14  and  17 . 
     The spray liquid can be water whose wetting power has been improved by adding a surfactant which is of vegetable origin and of foodstuffs or foodstuffs-compatible grade if the bulk product is a food. The quantity of additive, which can be determined by experiment, is preferably from 0.05% to 2% of the quantity of water sprayed. The quantity of water, which can be determined by experiment, is preferably from 0.05% to 2% of the quantity of product passing through the dust-laying device per unit time. 
     Note that other moistening liquids can be used, such as extracts of consumable agricultural products, foodstuffs-compatible mineral oils or vegetable oils, rapeseed oil being one non-limiting example of a liquid of this kind. In this case, the range of proportions of the moistening liquid relative to the quantity of product transferred can be the same as in the case where water is used as the moistening agent. 
     A convergent entry cone or product guide chute  8  can be fixed to the inside of the inlet  2 , as shown in the drawing by way of example. The chute  8  is frustoconical and converges in the direction of product flow. It extends as high as the junction between the inlet  2  and the intermediate part  4  of the casing  1 . A second cone  18  which diverges in the direction of product flow is fixed around the sleeve  12 . Its position can be adjusted relative to that of the inlet  2  or the chute  8 , where applicable, by adjusting the sleeve  12  on the shaft  10 . This adjustment determines the radial clearance d perpendicular to the surface of the cone  18  and therefore the annular passage between the bottom edge of the inlet  2  or the chute  8  and the cone  18 . In this way the thickness of the annular layer of product flowing in the dust-laying device can be precisely adjusted. The cone  18  can also bring about natural aspiration of air through the orifices  15 , which has the advantage of avoiding reduction in the pressure of this air. 
     This is how the dust-laying device works. 
     The bulk product is gravity fed or propelled mechanically through the feed pipe  3  and received in the inlet  2  or in the convergent chute  8  where it is centered relative to the axis of the dust-laying device. 
     It then drops onto the divergent distributor cone  18  on whose outside surface there forms an annular layer of product of variable thickness, FIG. 2 showing the position of the cone corresponding to the smallest thickness that can be obtained. The product is then accelerated by gravity, which contributes to progressively reducing the thickness of the layer and to improving its penetration by the sprayed liquid. 
     After passing beyond the lower edge of the distributor cone  18 , the inside of the layer of product receives a first spray of liquid via the central nozzle(s)  14  and the very fine droplets of this spray provide initial moistening of the dust in suspension in the internal volume of the annular layer of product. As the nozzle(s)  14  spray in an area  7  downstream of the cone  18 , the layer of product is directly moistened by the sprayed product with a high yield. 
     Then, on leaving the lower part  5 , or where applicable the intermediate part  4 , of the casing  1 , the layer of product retains its hollow annular shape and a second stage of moistening is provided by the peripheral nozzles  17  directed toward the outside envelope of the layer of product, where the dust is also moistened. The flow of air through the orifices  15  scavenges the interior space of the annular layer of air and this draws droplets of the moistening liquid through the layer and so encourages the capture of dust, whilst avoiding soiling of the cone  18  and the nozzles  14  by the moistened dust deposited thereon as a result of turbulence. 
     Note that, in order to increase the surface area of contact of the spray with the dust in the bulk product, the cross sections of the various cones of the device, and where applicable of the casing, can be circular, oval, star shaped or polygonal, for example rectangular, it being clearly understood that the above examples are in no way limiting on the invention. 
     Blowing air can have a particular advantage in a grain silo, for example, where the air arriving via the pipe  11 , whether forced in or drawn in by natural aspiration from the cone  18 , can come from inside the silo itself. This avoids excessive influx of air from the outside and most importantly contributes to recycling the dust remaining in suspension in the air in the silo that the device has previously failed to capture. 
     It is even feasible to accelerate the recycling of air from the silo by using a venturi type air injector driven by compressed air to supply air under pressure to the tube section  11   b  to lay dust remaining in suspension, even after filling the silo, i.e. with no grain flowing through the device. This also enables the device to be used to remove dust from the air in the silo even in the absence of flow of product. 
     As it moves forward in the dust-laying device, the thickness of the layer of product can form freely and the layer is not in contact with the parts  4  or  5  of the outside casing  1  at least until it leaves the area Z. It is not subject to any constriction or retardation and can therefore move forward at a high flowrate, and even accelerate due gravity, which reduces its thickness. 
     In an embodiment which is not shown in the drawing, it is possible to omit the convergent inlet cone  8 , in which case the divergent cone  18  has to be fastened to the inlet  2  or the pipe  3 . How to achieve this will be evident to the skilled person. 
     The dust-laying device of the invention can be complemented by freezing protection means and a control system that controls the spray as a function of the presence or absence of bulk product in the chute  8 . Such auxiliary means will be evident to the skilled person and need not be described in detail. 
     FIG. 3 is a perspective view of another embodiment of the invention including the convergent inlet cone  8 , the divergent cone  18 , a central mounting device formed essentially by the hollow shaft  10  and the sleeve  12  carrying the cone  18  and the central spray nozzle(s)  14 . Note that in this case the fins  9   a  which connect the first cone  8  to the shaft  10  are hollow so that they can convey moistening liquid toward the pipe  16  and air through the space formed around it, respectively from tube sections  11   a  and  11   b . Note also that in this variant an inlet like the inlet  2  can be used with or without the cone  8 . Also, the casing  1  is omitted. 
     However, using the casing  1 , with or without its extension  5 , facilitates fixing and protecting the peripheral nozzles  17  and enables the layer of product to be oriented, without excessive divergence, to facilitate the distribution of the product onto the storage heap or into the transport vehicle. 
     The dust-laying device shown in FIG. 3 is designed to be mounted at the end of a bulk product transfer horn, which means that the device can be mobile to transfer product into a transport vehicle, such as a railroad wagon, truck or grain bulk-carrier ship, or onto a product storage heap. It can be manipulated by hand or mounted at the end of a handling rod or a remote-controlled arm.