EP0051008A1 - Process for the slowly deferred continuous cooling of grain - Google Patents

Abstract

Method and apparatus for the slow cooling of grain in which warm grain is introduced into the upper end of a silo and cooling air is introduced at the lower end and is evacuated at an intermediate point between the upper and lower ends of the silo. The warm grain descends through the silo in a non-ventilated space above the intermediate point where the internal moisture is removed, then into a ventilated space where it is cooled by the cooling air and finally to the lower end of the silo from which the cooled grain is extracted.

Description

It is customary to dry the harvested grain in order to remove moisture from it before storage. This operation is carried out, currently, in a continuous manner in dryers working continuously, the grain being introduced into the upper part of the dryer and being taken from its lower part, means being provided for admitting into the dryer first of the hot air, in one or more upper sections, then cold air, in its lower part, in order to cool the grain before its extraction from the dryer.

It is also known to provide, in a dryer of this general type, at least one section in which there is no circulation of air (French patent 821,091, US patent 3,701,203) so that the heat transmitted to the grain in the drying zone (or in a pre-drying zone) can permeate the latter by allowing a rise in temperature of the whole grain.

During this period, there is a migration of interior moisture to the surface in the grain, which promotes drying.

But taking into account the time during which the grain remains in a dryer between its upper inlet orifice and its base, the duration of stay of the grain in these relaxation or drying areas is necessarily very limited and it is in fact too short to allow sufficient migration of moisture from the grain to the surface to make it possible to finish drying to the required degree under the sole effect of cooling air.

It is also known to come out of a grain dryer that is not completely dry and still hot. In such a case, to complete the drying, the calories contained in the grain leaving the dryer are used, ensuring its rest in a cell. During this rest, a drying of the internal moisture of the grain takes place, which undergoes a migration towards the outside or towards the periphery. The phenomenon that occurs can be compared to that occurring in the relaxation zone of a dryer as previously indicated. But it is then significantly longer in duration, which allows a more complete migration of moisture towards the outside of the grain, and consequently an easier extraction of this moisture. After this migration, it suffices to ventilate the grain with a low air renewal rate to complete the drying and cooling.

It results from this known process, called the delayed slow cooling process, in addition to a more homogeneous and more efficient drying, as indicated above, a gain in throughput for existing dryers, a reduction in energy consumption and an improvement in the quality of the grain.

_As it is applied at present, this method however has a certain number of drawbacks. Indeed, it requires the use of several silos equipped with a delayed slow cooling system to follow the functional rhythm of a continuous dryer. In addition, the control of the operation must be rigorous to respect the necessary phases, which requires the training of specialized personnel who must also pay particular attention to the work.

The object of the invention is to remedy the drawbacks of the known method.

The invention is materialized, for this purpose, in a slow delayed cooling process of the grain still hot and still charged with excess moisture taken from a dryer, consisting in ensuring the gradual descent of this grain inside at least a column, first in non-ventilated conditions, then after a descent time corresponding to the time necessary for drying the internal moisture of the grain, to ensure the ventilation of this grain to complete drying and cooling while said grain continues its progression downward inside the column, and taking the dried and cooled grain from the column, intermittently or continuously.

Thus, the general known method of delayed slow cooling is implemented continuously during the progression of the grain in the same column, avoiding the drawbacks resulting from the storage capacity required according to the prior art. Inside the column, the grain is subjected to a very precise treatment sequence, which differs from that of a dryer in that no heating of the grain occurs for drying and that this grain is subjected simply a period of rest or drying, then cooling ventilation.

This process combines the advantages resulting from the removal from a drier of a grain which is not yet dried to the required degree and still hot, with the gain in throughput and the reduction in energy consumption associated therewith, and those resulting from drying. more complete and longer grain, with the advantages of continuous treatment in a device of much smaller dimensions compared to existing installations.

According to a preferred embodiment, the grain is ventilated during its progression through the column by the passage of air against the current with respect to the direction of grain progression. It is thus possible, according to the invention, to admit air in the vicinity of the point of exit of the grain relative to the column, that is to say at the place where the grain is already sufficiently cooled, which avoids the thermal shock of the grain, reducing cracks.

According to another particular feature of this process, ventilation of the grain is carried out under pressure, ensuring the admission of cold air to the vicinity of the point of exit of the grain relative to the column and the evacuation of the air at an intermediate level of this column, chosen according to the drying time required. We can then recover the energy contained in the air evacuated from the column due to the constant enthalpy level of this air, which is saturated and hot and which is practically at the same temperature as the grain after drying. This energy recovery can be done in any desired way, for example by means of a heat exchanger, with condensation of the humidity contained in the air.

Yet another advantage of the process according to the invention lies in the fact that the homogeneity of the dried grain is improved as a result of its regular and continuous progression in the column. Changes in contact are then established between the grains with respect to the neighboring grains, which promotes exchanges with the air and consequently increases the efficiency of ventilation.

The invention also relates to an installation for implementing this process, characterized in that it comprises at least one vertical column through which the grain passes, means for ensuring the admission of the still hot grain coming from a dryer in the upper part of this column in order to keep it always filled, means provided at the base of the column for ensuring the extraction of the dried and cooled grain, means for the admission of cold ventilation air to the base of the said column, and means for the outlet of this ventilation air at an intermediate level over the height of the column, so that the grain undergoes in this column a displacement in principle continuous towards the bottom, with all of first a drying of the humidity in the upper part of the column, then a ventilation completing its drying and cooling in the lower part of this column.

It is already well known in this technique (US Patent 3,701,203, French Patents 821,091 and 912,848, British Patent 647,490) to provide, in a dryer constituted by a column equipped with a arrival of the grain to be dried at its upper part, a cold air intake system provided at the bottom of the column for cooling the grain, this air being exhausted from the column at a point located above this intake . However, dryers of this type, on the one hand are intended for a completely different treatment of the grain, and on the other hand include various means of intake and exhaust of hot air at different levels over the height of the column, so that the combination of means forming the subject of the invention, providing the technical result which it provides, is neither described nor carried out in the prior art.

According to a preferred embodiment, the delayed slow cooling column of the grain is constituted by a cooling silo of modular structure.

This silo can then be supplied with grain from one or more driers, means being provided to keep it constantly filled. One can provide at the base of each silo module a multi-cone system combined with means for controlling the extraction of grain. Such a multi-cone system ensures this extraction in a regular principle in the whole of the straight section of the silo and consequently a descent of the grain in it by horizontal layers.

The means ensuring the extraction of the grain at the base of the column may include pneumatically or other hatches, programmed in an appropriate manner, or else devices such as conveyor screws.

One can judiciously provide, at the base of each cone, a tube joining the sheath of a conveyor screw driven at low speed in a controlled manner to ensure the metering of the grain extraction. This screw can itself be connected to a high-speed collecting screw which ensures the evacuation of the grain downstream of the installation, for example for its storage.

According to a variant, a tube starting from the base of each cone can lead directly into the sheath of an evacuation conveyor screw, with the interposition of a lock, a damper or similar device associated with flow regulation means to control the evacuation flow of the grain by this tube.

Such extraction and evacuation systems with screws have the advantage of a small overall height, linked to a reduction in the cost of the supports.

Furthermore, the combination of two screws to form the extractor system constitutes a substantially sealed assembly, which ensures that the seal is maintained during extraction. According to another particularity, in the case of a multi-cone system with extractors of the type mentioned above, it is possible to provide means allowing an independent adjustment of the extraction flow rates by lines at the base of the dryer, to take account in particular wall effects, with a view to obtaining uniform extraction over the section of the silo.

According to yet another particularity, the base of each module is profiled so as to provide a sheath for passage and distribution of the cold air admitted, combined with means for entry of this air into the lower part of the grain. Thus, in the case of a multi-cone system as indicated above, an air distribution duct can be provided between the conical or pyramidal outlets directed downwards and caps or deflectors can be placed above the upper perforated part of this sheath to allow the transfer of air to the grain, without penetration of the latter inside the sheath. Each sheath can be made judiciously in the manner of a beam supporting the grain of the silo.

The invention also relates to a composite installation comprising one or more driers and a column for slow, delayed and continuous cooling of the grain as described above, as well as means connecting the base of the drier (s) to the top of this column for feeding grain in such a way that the grain, still hot and still insufficiently dried, taken out in driers, undergoes in this delayed slow cooling column first a drying stage without ventilation, then a cooling ventilation.

The description which follows, given with reference to the appended drawings, given without limitation, will allow a better understanding of the invention.

Fig. 1 is a schematic elevational view of a slow delayed cooling installation of the continuous grain according to the invention.

Fig. 2 is a view taken in a plane perpendicular to that of FIG. 1.

Fig. 3 is a plan view of the lower part of a module.

Fig. 4 is a sectional view through the line IV-IV in FIG. 3.

Fig. 5 is a partial schematic view showing the base of a module of the installation.

Fig. 6 is a view similar to FIG. 5, but looking in a direction offset by 90 °.

Fig. 7 is a view similar to FIG. 6 but corresponding to an alternative embodiment.

There is shown in Figs. 1 and 2 an embodiment of a slow delayed cooling installation of the continuous grain according to the invention. This installation comprises a silo generally designated by the reference 1, having a modular construction and providing chambers or columns 2 for cooling the grain.

This silo is combined in its upper part with a grain feed device, indicated diagrammatically at 3 in FIGS. 1 and 2, capable of bringing grain to the silo from a grain dryer for example. There are judiciously provided devices for controlling the level of the grain in the silo and a regulating device, these devices possibly being of a type known per se.

According to the invention, there are provided towards the base of the silo cold air supply and distribution ducts indicated in 4, which will be described in more detail below and which ensure a uniform air distribution throughout the base of the silo. These ducts 4 are supplied from fans 5.

At an intermediate level of the silo, there is provided a duct system 7 forming an air collector which intercepts and evacuates towards the outside at 6 (Fig. 2) the drying and cooling air having entered the silo by sheaths 4.

There is shown in more detail on the. Fig. 3 and 4 the lower part of the silo, with the air intake means.

These Figs. 3 and 4 show a module generally designated by 8, with its support posts 9 and four cones 10 directed downwards for the outlet of the grain, the outlet orifices being indicated at 10a.

The central part of the module is formed by the air inlet sheath 4, which constitutes a beam supporting the weight of the grain which is in the silo. Side parts 11 also constituting support beams complete the modular structure of the base of this silo.

As shown in Figs. 3 and 4, the upper part of the central sheath 4 has the shape of a roof, and there are provided towards the top of this part air outlet orifices, 12. This part provided with orifices 12 is covered with a cap 13 supported at a certain distance from the sheath 4 so that, as indicated by arrows in particular in FIG. 4, the air passing through this sheath 4 and exiting through the orifices 12 is deflected by the cap 13 to go up inside the grain substantially at the right of the flow orifices 10a of the discharge cones of the module.

The sheath 4 ensuring the routing of air in a module communicates with the sheath 4 of the next module after the assembly of the modules, by rectangular orifices formed in the end flanks of the base, visible at 14 in FIG. . 2. This communication appears in FIG. 1.

We see that we thus obtain, for the base of the silo, a self-supporting structure which fulfills three different functions. Indeed, this structure supports the grain, avoiding a conventional beam with I and H profiles. It also allows simultaneous extraction by multi-cones in the entire horizontal cross section of the silo, in a way ensuring a descent of the grain in horizontal layers, which subjects all the fractions of the grain to uniform slow cooling. Finally, by the ducts and caps described, it constitutes a ventilation and air injection network in the grain, with a direct distribution from one module to another.

We have shown in Figs. 5 and 6 a preferred embodiment of the extraction system. The elements already visible in Figs. 3 and 4 have been designated here by the same references. It can be seen that each orifice 10a of an extraction cone 10 is extended downwards by a tube 15 to which another tube 16 is connected with the interposition of a flexible and watertight seal 17 which allows the deformations while avoiding leakage d 'air. This tube 16 is in turn connected by a versatile connector 18 to a first sheath 19 in which is mounted a conveyor screw rotating at low speed. The speed of rotation of this screw is regulated by a motor-variator which can be for example of mechanical or electronic type, which makes possible a precise dosage of the extraction of the grain.

There is provided, below this first sheath 19, another sheath 20 connected to the previous one by fittings 21 and in which is mounted a high-flow collecting conveyor screw, ensuring the evacuation of the grain for example to a post of storage.

We see in particular on examining FIG. 6, in which arrows indicate the direction of grain transport by the screws, that the grain of the upper sheath at low flow rate falls after a very short journey in the lower sheath at high flow rate. It should also be noted that the directions of transport in the two sheaths could be the same instead of being opposite.

This arrangement of the extraction and evacuation system makes it possible to obtain a low overall height and it can be supported by bases as indicated at 22 in FIG. 5. This low height results in an appreciable gain on the cost of the posts and the bracing irons are avoided because of the embedding of the lateral posts over the entire height of the bases. In addition, a two-screw extraction system of this type constitutes a substantially sealed extractor, which maintains the seal during extraction.

We will now describe the overall operation of a slow cooling silo continuously differed according to the invention.

In Figs. 1 and 2, the grain embankment coming from a dryer and brought in by the feed device 3 is indicated at 23. The silo is filled with grain over its entire height. It is easy to see that it takes place through the cones 10 and tubes 15, 16, at the base of the silo, a sample of a certain amount of grain, depending on the speed of the screws 19. The mass of the grain then undergoes in the silo a progressive displacement downwards by horizontal layers. The screw speed can be adjusted according to the required residence time of the grain in the silo.

During operation, the fans 5 send the entire base of the silo, via the ducts 4, cold air ensuring the cooling and the end of the drying of the grain. This air which penetrates into the base of the silo rises inside the mass of the grain and it is intercepted and evacuated to the outside by the duct system 7 located at an intermediate level.

Thus, in the upper part of the silo, the grain is not subjected to the effect of drying air. It therefore undergoes during its entire downward progression in the upper part of the silo a drying effect of internal humidity, similar to that obtained during its rest in a cell. When the grain arrives, during its descent, at the intermediate level of the duct system 7 and crosses it, it begins to undergo the effect of air which will complete its drying and cooling.

Since cold air is introduced into the silo through its base, just upstream of the extractors, this cold air comes into contact with grain which is in principle completely cooled, which avoids any thermal shock for the grain. As it progresses upwards inside the grain, this air heats up coming into contact with increasingly hot grain, and the air leaving the silo is approximately at the grain temperature at the end of the drying stage. The air escaping to the outside can then be treated to recover the calories it contains, with condensation of humidity.

We have shown in FIG. 7 an alternative embodiment of grain extraction means at the base of the silo. In this case, a tube 23 is connected to the base of the orifice 10a of the cone 10, this tube here being in two parts with the interposition of a flexible seal 24. This tube 23 is extended downwards by a nozzle 25 connecting to a lock body 26. An outlet nozzle 27 starting from this lock body 26 joins the sheath 28 of a collecting screw.

A rotary lock of known type is mounted in the lock body 26. It is rotated by a shaft 29 whose speed is adjusted as a function of the output flow of the grain and consequently of the residence time of the grain in the silo .

The overall operation of a silo thus equipped is the same as before.

Modifications can be made to the embodiments described, in the field of technical equivalences, without deviating t _er of the invention. Thus, as indicated above, the means for removing the grain could be constituted by valves, pneumatic with register, which can be controlled all together or one after the other according to an opening rhythm determined here again as a function of the required residence time. for the grain inside the silo.

Claims (12)

1. A slow delayed cooling process of the grain still hot and still charged with excess moisture taken from a dryer, characterized in that it ensures the progressive descent of this grain inside at least one column first in non-ventilated conditions, then after a descent time corresponding to the time necessary to dry the internal moisture of the grain, this grain is ventilated to complete drying and cooling while said grain continues to progress downward to inside the column, and the dried and cooled grain is taken from this column intermittently or continuously. 2. Method according to claim 1, characterized in that the ventilation of the grain is ensured during its progression in the column against the current with respect to the direction of progression of this grain. 3. Method according to claim 2, characterized in that the ventilation of the grain is carried out by ensuring the admission of cold air in the vicinity of the point of exit of the grain relative to the column and the evacuation of the air at an intermediate level in this column, chosen according to the drying time required. 4. Method according to claim 2 or 3, characterized in that the heat energy contained in the air discharged from the column is recovered. 5. Installation for implementing the method according to any one of claims 1 to 4, characterized in that it comprises at least one vertical column through which the grain passes, means for ensuring the admission of the grain to the part upper part of this column in order to keep it always filled, means provided at the base of the column for ensuring the extraction of the dried and cooled grain, means for admitting cold ventilation air to the base of said column, and means for the outlet of this ventilation air at an intermediate level over the height of the column, so that the grain undergoes in this column a displacement in principle continuous towards the bottom with first of all a drying of the humidity in the upper part of the column, then a ventilation completing its drying and its cooling in the lower part of this column. 6. Installation according to claim 5, characterized in that the column receiving the grain is constituted by a silo of modular structure. 7. Installation according to claim 5 or 6, characterized in that there is provided at the base of the column or silo a multi-cone system for the simultaneous extraction of the grain by this base, in principle in the whole of the horizontal cross section of the column or silo, each discharge cone being connected to a tube in which is preferably inserted a flexible compensation joint, this tube opening into an upper sheath in which is mounted a low flow conveyor screw, this sheath being itself connected at at least one point and preferably at multiple points to a lower discharge sheath containing a high flow conveyor screw. 8. Installation according to claim 7, characterized in that means are provided for adjusting the speed and the iébit of the conveyor screws. 9. Installation according to claim 5 or 6, characterized in that there is provided at the base of the column or silo a multi-cone system for the simultaneous extraction of grain by this base, in principle in the whole of the horizontal straight section of the column or silo, each extraction cone being connected to a sheath of evacuation conveyor screw by a tube system in which is inserted a lock or an equivalent device, the means being provided for adjusting the flow through: ette lock or similar device. .0.Installation according to claim 5, characterized in that the base of the modular type silo is constituted by a self-supporting structure comprising, for each module, a sheath air intake forming a beam, provided in its upper part with air outlet holes and capped at a certain distance by a cap deflecting this air in the direction of the extraction cones, this beam and this cap supporting the grain filling the column or silo. 11. Installation according to claim 10, characterized in that communications are established for the ducts between the different modules, for a uniform distribution of air throughout the horizontal cross section of the column or silo. 12. Composite installation characterized in that it comprises one or more dryers and a column of slow delayed continuous cooling of the grain according to any one of claims 5 to 10, as well as means connecting the base of the dryer (s) to the top of this column for its grain supply, in such a way that the grain, still hot and still insufficiently dried, sampled in the driers, undergoes in this column of delayed slow cooling, first drying without ventilation, then cooling ventilation.

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