IE43743B1 - Method and apparatus for the long term conservation of grain - Google Patents

Description

The invention relates to a method and apparatus for the long-term conservation of grain on flat storage beds, by means of the supply of air.

In small and medium-size agricultural concerns, it is known to store grain by the flat bed principle, it being assured that the grain was secured from below against absorption of moisture, possibly with a sufficient layer of air between the grain and the bottom of the storage bed, e.g. by using a screen bottom communicating with the ambient air and allowing a continuous exchange of heat and humidity.

This type of storage is possible only up to a maximum of a few tons quantity.

However, the problem is to store large quantities of grain over longer periods, the grain possibly being supplied in freshly harvested form.

In the past, this problem has been resolved by storing the grain in silos or cell stores or in industrial general purpose sheds, the resistance to deterioration being initially brought about in that the grain is brought to about 13.5 to 14% moisture content by artificial drying. In the case of storage of grain with a moisture content of over 14% to 14.5%, it is often necessary, at intervals, to move the grain, for example by shovelling it or shifting it around.

This type of storage must be regarded as unsatisfactory, since it is not only necessary to expend considerable costs, but time and again parts of the grain which is so stored and treated must be eliminated as spoiled. 3 7 4 3 According to the invention, there is provided a method of storing grain in bulk for a long period of time comprising placing the grain on flat storage beds within an enclosed space, blowing through the grain air conditioned to initially dry the grain to a stage at which its water content and temperature is selected to be most suited for its preservation, and thereafter continuously measuring the values of temperature and humidity of the ambient atmospheric air outside the enclosed space, and intermittently blowing outside air through the grain whenever the said values are such as to correspond with those required to produce or maintain the selected temperature and selected water content of the grain at the temperature within the space.

According to the invention also, there is provided apparatus for carrying out the method and containing an enclosure housing flat storage beds to receive the grain to be stored, means for adjusting the temperature of atmospheric air supplied to the blowing means during the initial drying period of the grain, means for treasuring the temperature and humidity of the atmospheric air outside the enclosure, and means for causing the blowing means to operate to blow the outside air through the grain in response to a signal from the measuring means whenever the temperature and humidity of the outside air have the said corresponding values to produce or maintain the said selected tenperature and water content of the grain.

In conjunction with the supply of conditioned atmospheric air as aforesaid, flat storage beds offer an opportunity of effecting the throughflow of air with relatively low power costs, since the resistance 3 7 <* 3 to flow remains within reasonable limits. Furthermore, this method according to the invention provides an opportunity of conserving grain in flat storage beds for prolonged periods, i.e. of limiting to the rnininum or of entirely excluding heating influences of any kind.

The method on which the invention is based resides in the knowledge that a hygroscopic balance is adjusted between the grain and the outside air, or the air (working air) which is supplied in accordance with this method. This hygroscopic balance, by the method according to the invention, is so adjusted that for storing the grain, humidity levels and temperature levels can be achieved which ensure a resistance to deterioration during storage, these levels being subsequently maintained. This hygroscopic balance differs for every type of grain. It is also independent of the air temperature.

For comparison, attention is drawn to the following table which indicates for example the values for the hydroscopic balance between grain and working air for wheat at a temperature of +20°C.

Water content, wheat Atmospheric humidity (in each case as a % at 20°C) After the working air has been allowed to act on the grain for a sufficiently long time, the moisture content of the grain alters to the same value as the corresponding moisture content of the working air.

By the invention, then, it is possible, by supplying relatively dry air to extract the moisture from the grain, preventing at the same time a situation where the supply of relatively moist heat causes an increase in the moisture content of the grain.

If the temperature of the air blown through loosely stored grain is made progressively lower, then the grain is cooled in layers, accompanied by a loss of moisture in the stored grain. If the atmospheric humidity of the working air is for example 60%, and its initial humidity is 15.5%, the grain humidity will be reduced to 13.5% after prolonged ventilation.

In the practice of the invention, then, the drying phase is followed by a conserve cooling operation. These two operations or procedural steps are constantly merging into one another if the drying stage is carried out at diminishing working air temperature until a certain storage temperature is achieved. Then further drying of the grain is gradually achieved by the cooling process, since the air absorbs moisture, which process effects cooling of the grain to a certain amount. But one must take care that a certain humidity of the grain is preserved, e.g. 13.5%.

In the practice of the invention, the grain is brought to a temperature of 8 to 10°C and to a moisture content which ensures resistance to deterioration during storage, and then by correspondingly controlled intermittent ventilation, it is maintained at these levels. <3743 At temperatures of 10°C or below, the growth of the mould and bacteria is greatly retarded. Furthermore, the development of other grain pests is greatly disturbed. The temperature of approximately 10°C corresponds to the long-term average temperature in temperate latitudes, so that this average storage temperature can be maintained with the minimum of energy, and thus cost.

This treatment of the stored grain with through-flowing air, repeated at intervals of time, furthermore ensures the blowing out of any possible deposits of carbon dioxide which may possibly form due to the anaerobic respiratory activity of the grain. Repeated ventilation is necessary also in order to cool the marginal and superficial layers of the stored grain which become heated according to the season.

Approximately 10 to 15 cubic metres of working air per ton of grain may be calculated for ventilation purposes. The through-flow resistance in the loosely poured on grain can be assumed to be 12 to 20 mm ( water gauge) per metre of loosely poured height - according to the type of grain - for a flat storage bed which is ventilated from below.

The bulk height of a quantity of grain in a flat storage bed may be as much as 8 m.

Since it is possible by means of the method described hereinabove to achieve considerable savings on costs of storage, a further development of the invention provides for external air to be fed to the grain in order to conserve it. The outside air is intermittently fed to the grain whenever its temperature and relative humidity in relation to the temperature of the bottom layer of the loose grain, shows levels which 3 7 4 3 correspond to whatever is the target level. Working according to this method makes it unnecessary to condition the air, so long as it is possible for such unprepared external air to be used within the aforesaid limits. Thus, a further lowering in power consumption and thus running costs is made possible.

Therefore, the temperature and the relative humidity of the outside air is expediently measured and this is then used for flowing into the stored grain when the likewise currently monitored temperature and moisture levels of the stored grain require it.

An apparatus for carrying out the method according to the invention and also further procedural steps are explained by way of example in greater detail hereinafter with reference to the accompanying drawings, in which:Figure 1 diagrammatically shows the timing pattern of grain conservation in terms of relative humidity and temperature; Figure 2 shows weather diagrams for one week for temperatures and relative humidity; Figure 3 is a diagrammatic view of a ventilating plant according to the invention; Figure 4 is a diagrammatic view of a control device according to the invention; Figure 5 shows the structure of a ventilating duct.

The upper graph, Figure 1, shows the pattern of relative humidity of stored grain and of air blown through it plotted in respect of a period of two years. The ordinates show the humidity of the grain, and the cross-hatched area indicates the lowering of the humidity. The abscissae represent successive periods of tims in months. The lower graph in Figure 1 shows, for the same period of time, the pattern of temperature 43 of the grain and of the temperature chosen for the air. In the lower graph, the ordinates represent grain temperature and the cross-hatched area shows the temperature loss. In both graphs the dotted lines show the grain condition and the full line, the steady state of the grain in balance with the air blown in.

These illustrations represent the storage of freshly harvested wheat on a flat storage bed, the wheat having a relative humidity of not more than 16% and a temperature of 24°C. For drying the grain, the working air is adjusted to 20°C and a relative humidity of 14.2%, equal to approximately 60% relative humidity. On a basis of the illustrations in Figure 1, it can be seen that where the grain is concerned, ventilation produces a heat-cold exchange with an accompanying extraction of humidity which is dependent upon the condition and volume of the working air. The tenperature of the inblown air is reduced progressively, the target being a final grain temperature of 8 to 10°C and a storage resistance humidity (approximately 14.5%).

It can be seen from the lower graph of Figure 1 that in the summer of the second year the grain temperatures on the surface and in the marginal layers of the stored mass rise again. Afterwards, ventilation using inblown air at 8°C is resumed to produce a cooling effect.

From this time on, both the temperature and also the moisture content of the grain remain at virtually constant levels, so that ventilation is not required again until March of the following year.

The diagrams show that the greatest enerqy cost is entailed in the drying and cooling (initial treatment) of the freshly harvested grain. Subsequently, for further conservation of the stored grain, only a small annual outlay on energy is needed. For this period of further conservation, it should additionally be noted that if ventilation employs outside air, it can in the main be undertaken during the hours of night, so that an additional loading on the power mains during peak usage periods is avoided.

If, according to the foregoing explanation of the method of the invention, outside air is used at temperatures which make it possible to cool the grain, the outside air having a relative humidity of up to 8535, but which can be further dried by being electrically heated, then during the course of the weather cycle, there are adequate periods when these conditions prevail as natural conditions inherent in the outside air. Figure 2 shows the pattern of temperature and humidity of the outside air over one week. In the top illustration in Figure 2, that particular time of the day at which ventilation with outside air could be undertaken purely by taking the temperature into account, is especially marked.

In the diagram in the bottom of Figure 2, above the continuous limit line for 85% relative atmospheric humidity, is shown the zone which might conditionally be used for ventilation purposes. The energy saving zone (energy saving because it renders drying of the air unnecessary) lies below 70% relative humidity and vertical shading is used to identify these periods particularly in the diagrams.

If one compares the superposed zones of the two diagrams, it is evident that there are periods in which both the necessary most favourable temperature and also the most favourable relative humidity of the outside air in relation to the bottom layer of grain are present, so making ventilation with outside air acceptable. All that is inportant then is constantly to observe the temperatures and the relative humidity of the 3 7 4 3 outside air and to operate the ventilating system when the most favourable temperature and mast favourable atmospheric humidity prevail and to stop when one of these conditions or both ceases to be satisfied. This can occur by constantly measuring the temperature and atmospheric humidity of the outside air, the results being indicated on a control panel. An operator can then switch the ventilating system on or off, as the case may be, as soon as the. temperature and relative humidity of the grain, which must also be measured, necessitate such action or when such steps are essential to achieve the particular goal desired.

However, it is advantageous for these limit values and thus the switching-on and switching-off times to be automatically monitored and to provide a control device which is suitable for the purpose. Such a control device is explained hereinafter.

Figure 3 shows for example and purely diagrammatically a plan view of a flat storage bed comprising two conpartments IT and 12 disposed in a storage shed 10. Located in the bottom of this storage shed at regular intervals are ventilation ducts 13. These ventilation ducts are, for each storage bed, connected to air supply ducts 14, 15. Both air supply ducts are fed by a blow-in duct 16, the outlet of which can be connected via a slide valve 17 either to one or other of the air supply ducts, or to both.

Each of the ventilating ducts 13, or groups of ventilating ducts 13, can furthermore be isolated from the air supply duct 14 or 15 by a slide valve. In this way, the supply of air to the ventilating ducts can be controlled in zones. 3 7 4 3 The blow-in duct 16 is fed by one or more air supply blowers 18 having driving motors 19.

The driving motors or the blower are switched on and off automatically by a control device 20.

Located downstream of the air supply blower 78, in the blow-in duct 16, there is a heating and/or cooling device 21. The temperature and humidity of the air blown into the air supply ducts are measure and/or monitored by a remotely indicating instrument 22 connected to the control device 20.

Furthermore, it is possible from the control device 20 to switch on and off air extractor fans 23 located above the storage beds, for example in the roof of the storage shed 10.

The temperature of the grain stored in the stores 11 and 12, is measured by remotely indicating temperature measuring instruments 24.

The temperature of the outside air and the humidity in the outside air are meausred by means of remotely indicating measuring instruments 25, 26.

The measuring instruments 22, 24, 25 and 26 are connected to the control device 20. The measured values can be indicated there or serve as control variables.

As indicated diagrammatically in Figure 3, the air supply ducts 14 and 15 have longitudinally diminishing cross-sections, in order to permit as far as possible regularity of through-flow and thus regularity of air feed to the ventilating ducts 13.

The control device 20 can optionally be equipped for manual control or may be designed for automatic control of the ventilating system.

The automatic control system is explained in greater detail hereinafter with reference to Figure 4. Here, those parts which correspond to those in Figure 3 carry the same reference numerals as in Figure 3.

For automatic control, the control device 20 comprises a control instrument 30 which, in the example illustrated, is provided with an indicating and adjusting scale 31. Furthermore, the control device 20 has a moisture control circuit 32 and a device 33 for setting the temperature which is measured in the grain in a flat storage bed 11 or 12, preferably close to the bottom layer.

The measuring instruments 25 and 26 for ascertaining the temperature and humidity in the outside air are connected to a circuit, adapted to ascertain limit values and located in the control device 30. The actual values are fed to this circuit by the said measuring instruments. The temperature ascertained in the grain by the temperature measuring instrument 24 is fed to the control device via the circuit arrangement 33 which essentially comprises a potentiometer. This value is then used in the control device 30 as a zero value for further processing of the available data (actual values).

According to the time relationship of this measurement on the diagram in Figure 1, so it is possible to adjust the limit values for air temperature as a difference between grain temperature and outside air temperature, by means of pointers 34, 35 on the scale 31 of the control instrument 30. Adjustment of the pointers in Figure 4 to the values -8 and -4 respectively shows that here the limit values of the outside air are adjusted to a temperature range of 10 to 14°C. This means that the air supply blower 18 is switched on via the control device 30 when the temperature measuring instrument 25 reports that the outside air temperature is between 10 and 14°C. For this purpose, the temperature measuring instrument 25 is connected to a circuit for ascertaining limit values and fed by the temperature of the 3 7 4 3 outside air, the zero value of the circuit 33 and the values adjusted by means of the pointers 34 and 35. The temperature of the outside air is indicated by a pointer 36 as a relative value with regard to the grain temperature measured, or the grain temperature may take over the triggering function.

In the same way, the control device 30 contains a circuit for limit value ascertainment connected to operate in conjunction with the aforesaid and switching the air supply blower 18 on and/or off when the relative humidity of the outside air exceeds or falls below the hygroscopic balance in respect of the grain or when the grain temperature has assumed some different level.

The control circuit 32 adjusts the air blown into the ventilating ducts 13 to a likewise pre-selectable value. As soon as the supply air in the blow-in duct 16 exceeds the pre-set value, the heater register 21 is switched on stepwise by this circuit.

Figure 4 shows furthermore the possibility of additional temperature measurement at the marginal or top layers of the stored grain, using a temperature measuring instrument 37.

The control instrument 30 also operates the air extractor fans 23, doing so after a time lag in respect of operation of the supply air blowers 18.

Figure 5 shows one possibility of setting up the ventilating ducts 13 in the cheapest possible way. In the example of embodiment illustrated, ‘*3 7 4 3 these ducts consist of longitudinally serially disposed standard pallets 40 which are provided with a top layer 41 of expanded metal or the like.

The foregoing explanations relate to application to wheat. The basis adopted is an annual average temperature of 10°C.

It is evident that for application to other grain or fodder materials, it may be necessary to take different numerical values into account.

Also, in the same way, when using the method of the invention in countries with higher or lower annual temperatures, a possibly stricter control of the temperature or humidity values indicated in the foregoing by way of example may be required.

Furthermore, in a fixed storage installation a rigid set up may be provided in place of the pallet arrangement shown in Figure E. Such an arrangement would then gonsist of, situated under the floor, an air supply duct from which individual air supply ducts would likewise extend, still under the floor. These air supply ducts can in each case be individually isolated from the main air supply duct. The tops of these ducts may be covered with suitable gratings. By reason of its greater cross-section, the main air supply duct may also serve as an extraction duct. For this purpose, in per se known manner, it would be possible to provide within it a discharge means so that stored grain could be withdrawn from the storage bed from below.

Claims (24)

1. A method of storing grain in bulk for a long period of time comprising placing the grain on flat storage beds within an enclosed space, blowing through the grain air conditioned to initially dry the grain to a stage at which its water content and temperature is selected to be most suited for its preservation, and thereafter continuously measuring the values of temperature and humidity of the ambient atmospheric air outside the enclosed space, and intermittently blowing outside air through the grain whenever the said values are such as to correspond with those required to produce or maintain the selected temperature and selected water content of the grain at the temperature within the space.

2. A method according to Claim 1, wherein for initially drying the grain, dry heated air is supplied to the grain at intervals of time, the temperature of the air being adjusted to decrease over successive stages of treatment.

3. A method according to Claim 1 or 2, wherein the air intermittently supplied to the grain is adjusted to a relative humidity of 50 to 70%.

4. A method according to any one of the preceding claims, wherein the grain is maintained at a temperature of approximately 8 to 10°C and a water content which ensures resistance to storage, of rrom 13 to 15% by weight.

5. Apparauts for carrying out a method according to Claim 1, comprising an enclosure housing flat storage beds to receive the grain to be stored, means for adjusting the temperature of atmospheric air supplied to the blowing means during the initial drying period of the grain, means for measuring the temperature and humidity of the atmospheric air outside the ύ 7 3 enclosure, and means for causing the blowing means to operate to blow the outside air through the grain in response to a signal from the measuring means whenever the temperature and humidity of the outside air have the said corresponding values to produce or maintain the said selected temperature and water content of the grain.

6. Apparatus according to Claim 5, wherein the storage purposes, a flat storage hed is provided with a bulk material height of at least 3 metres, and in that there are in the bottom of the bed air supply ducts which are fed by one or more air supply blowers.

7. Apparatus according to Claim 6, wherein the air supply ducts consist of air feed ducts with distributor ducts disposed downstream of them.

8. Apparatus according to Claim 6 or 7, wherein in each case individual ducts or groups of ducts can be individually isolated.

9. Apparatus according to any one of Claims 6-8, wherein the distributor ducts consist of wooden pallets having open tops covered with expanded metal.

10. Apparatus according to any one of Claims 6-9, wherein the main air supply duct is constructed as an extraction duct.

11. Apparatus according to any one of Claims 6 - 10, wherein heating/ cooling means is disposed in the main air supply duct.

12. Apparatus according to any one of Claims 6-11, wherein a grid system of temperature measuring probes is provided in the apparatus, which has a plurality of temperature measuring devices located at intervals above one another. 4 3 7 4 3

13. Apparatus according to any one of Claims 6 - 12, wherein remotely indicating humidity measuring instruments are located in the air supply ducts.

14. Apparatus according to any one of Claims 6 - 13, wherein remotely reading temperature measuring instruments are located in the air supply ducts.

15. Apparatus according to any one of Claims 6 - 14, wherein a store room for containing the grain has air extractor fans and means by which the fans may be switched on subsequent to the air supply blowers being switched on.

16. Apparatus according to Claim 11, which incorporates an automatic control device which controls the output of the heating/cooling means as a function of a predetermined value of relative atmospheric humidity and the humidity values present in the air supply ducts.

17. Apparatus according to Claim 16, wherein the control device controls the air supply blower..

18. Apparatus according to any one of Claims 6 - 17, which has remote reading measuring instruments for measuring the temperature and the relative humidity of the outside air.

19. Apparatus according to Claim 18, wherein the measuring instruments for measuring the outside air are connected to a control device which controls the switching of the air supply blower and of an air heating means on and off.

20. Apparatus according to Claim 19, wherein the control device has a circuit for ascertaining values of temperature and humidity and which prevents the supply air blower being switched on when temperature ί 3 7 Ί 3 and/or humidity levels in the outside air are above adjustable limit values.

21. Apparatus according to Claim 19 or 20, wherein the control device has a circuit for ascertaining values of temperature and humidity 5 and which allows the supply air blower and the heating means to be switched on only when adjustable limit values of temperature and/or humidity are exceeded in the store room.

22. Apparatus according to Claim 21 as appendant to Claim 20, wherein the circuits for ascertaining values are linked to operate in 10 conjunction with one another.

23. A method of preserving grain substantially as hereinbefore describe! and with reference to Figures 1 and 2 of the accompanying drawings.

24. Apparatus for carrying out a method of preserving grain constructed and arranged substantially as hereinbefore described and 15 shown in Figures 3-5 of the accompanying drawings.