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Control and management scheme of air flows in inner space of steel silo during grain storage

Introduction


The most unfavorable storage conditions inside a metal silo develop in the upper part of the bulk­grain. If the relative humidity of the air in the silo is higher than the relative humidity of the outside air, it is recommended to provide ventilation of the grain space [1].

At low air filtration rates, moisture desorbed from the grain settles on the surface of the grain mass, which leads to its humidification [2].
In order to avoid moisture sedimentation on the surface of the grain mass, it is necessary to ventilate it at filtration rates ensuring the removal of moisture outside the silo [3].

Research results


It was proposed to regulate the amount of forced air by changing the mass of the ventilated grain. This method does not require capital expenditures, but requires some knowledge of air flow control. The smaller the mass of grain is, the greater the air flow is needed. A volume of air is calculated to provide a critical filtration rate in the most loaded central part of the silo [4]. Critical speed is understood as its minimum value that ensures the removal of moisture outside the granary.

The air moves unevenly inside the grain mass. Near the walls of the silo, the air has a higher speed comparing to the central part. This is justified by the difference in the height of the grain layer: in the center the layer is higher than that near the walls. The height difference occurs due to the loading of the silo through one hole in the center of the roof, a conical bulk-grain is formed in the silo. The plot of air velocities at the boundary of exit from the grain mass from the center to the wall can be described by the following formula:







Figure 1. Technological diagram of a large-capacity steel silo for grain storage with air flow control and management in its inner space

Figure 2 shows plots of air filtration rates from the center to the wall in two silos with a diameter of 12.5 meters (R = 6.25 m) with a capacity of 2000 tons and a diameter of 28.3 meters (R = 14.15 m) with a capacity of 10,000 tons respectively. For example, a silo with a diameter of 12.5 m shows the air rate in the center of 0.039 m/s, and near the wall of 0.046 m/s, the difference is 0.007 m/s. While a silo with a diameter of 28.3 m has the air rate in the center of 0.034 m/s, the same speed near the wall of 0.046 m/s, the difference is 0.012 m/s. For a silo with a diameter of 12.5 m, the filtration rate of 0.007 m/s corresponds to the air flow of 3000 m3/h. For a silo with a diameter of 28.3 m, the filtration rate of 0.012 m/s corresponds to the air flow rate over 27000 m3/h. To compensate uneven air distribution, additional energy costs are required.


Figure 2. Plots of air velocities on the surface of the grain mass in silos with a diameter of 12.5 m and 28.3 m with a height of the bulk-grain near the walls of 15 m and 20 m, air pressure in the lower part of the bulk-grain is 3000 Pa.


The required critical filtration rate in the center of the silo is ensured by supplying air in a volume corresponding to the value of the average weighted rate and at a bottom pressure, corresponding to the critical rate in the center [5]. The maximum air pressure in the lower part of the grain is calculated by the formula:



Substituting expression (3) into formula (2), we obtain the following dependence for calculating the average weighted filtration rate.


The coordinate of the average weighted filtration rate was calculated using formulas (4) and (5) for large-capacity steel silo (LCSS) with a diameter of 8-40 meters with equal heights of the grain layer and the silo wall of 15-20 meters. The coordinate does not practically depend on the height of the wall; it changes in silos of various diameters [6]. The values of the coordinate obtained by the calculation for LCSS with different diameters are presented in table 1.
 
Table 1. Coordinate values of the average weighted air filtration rate in silos of various diameters.
 
In order to prevent the development of the grain self-heating process, it is recommended to equip the inside space of the grain mass by the temperature monitoring system with an alarm or a device for automatically turning on fans when the temperature rises above 7 °C for 2 to 3 days with two or more sensors [7]. If there is a risk of self-heating of the grain mass, its ventilation is carried out under any weather conditions [8].
 

Conclusion

The technology of safe active ventilation of grain in steel silos is as follows:
  1. The LCSS is equipped with an air pressure measuring instrument. A diffonometer is installed outside to measure the pressure drop of the air in the grain layer with a thickness of 2.5 to 3.5 meters. The lower pressure take-off point is at least 1 meter from the air distribution grill of the silo.
  2. In LCSS, grain storage with a moisture content of not more than 14% is allowed. Ventilation is allowed with outside parameters excluding additional moisture of the grain. The outside temperature should be lower than the grain temperature by at least 5 °C.

References

[1]  Gadpayle K A, Fulekar M H, Bhattacharyya R and Pal M 2018 Additional N supply improves
grain yield in Triticale better than wheat under elevated CO2 environment Indian Journal of Plant Physiology Synth 23(3) 502-506
[2]  Alghabari F, Ihsan M Z 2018 Effects of drought stress on growth, grain filling duration, yield
and quality attributes Bangladesh Journal of Botany Synth 47(3) 302-312
[3]  Solis J, Gutierrez A, Mangu V, Baisakh N and Linscombe S 2018 Genetic mapping of
quantitative trait loci for grain yield under drought in rice under controlled greenhouse conditions Frontiers in Chemistry 102-106
[4]  Bhatta M, Belamkar V, Baenziger P S and Morgounov A 2018 Genome-wide association study
reveals novel genomic regions for grain yield and yield-related traits in drought-stressed synthetic hexaploid wheat International Journal of Molecular Sciences Synth. 19(10) 23-32
[5]  Kaliyan N, Morey R V and Wilcke W F 2005 Mathematical model for simulating headspace and
grain temperatures in grain bins American Society of Agricultural Engineers 1634-1637
[6]  Zhang Y, Li C and Ma X 2014 Experiment and numerical simulation of layer resistance
parameters in dryer Nongye Jixie Xuebao Synth. (7) 216-221
IOP Conf. Series: Materials Science and Engineering 775 (2020) 012089 doi:10.1088/1757-899X/775/1/012089
[7]  Stankevych G, Kats A and Vasilyev S 2018 Investigation of hygroscopic properties of the spelt
grain Technological audit and production reserves 37-41
[8]  Vasiliev A N, Budnikov D A, Gracheva N N and Smirnov A A 2018 Increasing efficiency of
grain drying with the use of electroactivated air and heater control Handbook of research on renewable energy and electric resources for sustainable rural 255-282


I A Kechkin1, V A Ermolaev2, K D Buzetti1, A I Romanenko1 and E A Gurkovskaya1
  1. Federal State Budget Educational Institution of Higher Education «K.G. Razumovsky Moscow State University of technologies and management (the First Cossack University) », 73, Zemlyanoy Val, Moscow, 109004, Russia
  2. Plekhanov Russian University of Economics, 36, Stremyanny lane, Moscow, 117997, Russia
 
published:
IOP Conf. Series: Materials Science and Engineering 775 (2020) 012089
doi:10.1088/1757-899X/775/1/012089
 
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