Justification of the parameters of a pneumatic conveyor for active ventilation of soybean during storage

The article proposes a methodology for studying the productivity (capacity) and power consumption of a pneumatic conveyor for active ventilation of soybeans in container-modular storage in farms and the factors affecting them. In determining the parameters of the pneumatic conveyor, the physical and technological characteristics of the grain (soybean) are taken into account. The proposed methodology is based on the method of classical calculation for selecting a pneumatic conveyor with nominal parameters, which is necessary not only for transportation, both vertically and horizontally, but also for active ventilation of grain in containers during storage. The purpose of the methodology is to select a specific pneumatic conveyor for container-modular equipment for soybeans storage in the conditions of farms in Kazakhstan.


1Introduction
Soybean storage can be short-term (temporary) and long-term. The first one is calculated in days or months (one to three) in duration, while the second one lasts from several months to several years. Both short-term and long-term storage should be organized in a way that there are no losses in weight (except for unavoidable ones) and, even more so, losses in quality.
In practice, two ways of storing grain are used: in tare (in bags) and in bulk (in stores, hoppers, silos).
Storage in tare is used only for some batches of seed: elite seeds, beans, seeds containing essential oils, small-grain seeds, corn seeds, beets, sunflower. This method of storage is more expensive, but it must be used in certain cases to prevent the loss of grain and seed in mass and quality [1].
The main method of soybean storing is storage in bulk [1]. This storage method has such disadvantages as the absence of air flow through the entire volume of the grain mass, as a result of which "dead zones" are formed which are devoid of airflow, leading to clumping and moistening of the grain, which leads to significant grain losses. In addition, rodents and birds eating grain also increase losses.
In [2] a modular equipment for grain storage with active ventilation, eliminating these drawbacks, is proposed. The main idea of this work is that standard containers for the transportation of goods with a capacity of 10-80 cubic meters are used as containers for grain (soybean) storage. Each module consists of a selected container, pneumatic conveying aggregate, pipelines, and control and monitoring instruments.
Equipment for grain storage with active ventilation, includes a hopper for grain storing, characterized in that the hopper is made in the form of a vertically situated container, while its lower part (bottom) is made conical at an angle of at least 40° with a lower hole connected to the pneumatic conveyor through a nozzle and on the inner side, on three equidistant levels along the height of the container, are placed humidity sensors, which are fixed on the steel pipes, and a sensor control and monitoring panel is installed on the outer side of the container.
In Fig. 1 a sketch of the equipment is presented. The main component of the equipment is a pneumatic conveyor consisting of a conveying aggregate (a blower and a supply cyclone (multicyclone) with filter), pipelines, and cyclones-unloaders, designed for suck-blow vertical or horizontal conveying of soybean or any other cereal crop over considerable distances [3].
The equipment for grain storage with active ventilation performs three cycles: loading, venting and unloading and operates as follows: Loading of grain ( Fig.1) into an equipped container 2 from a vehicle 3 is carried out by a pneumatic conveying aggregate 1 through a loading pipeline 9, then through a vertical pipeline 7 into a cyclone 5, where the air-grain flow is separated into air, which is removed through a nozzle 15, and into grain, which is settled down in container 2 for storage. The gate valve in the lower part of the cyclone 5 is driven by an electric motor.
Active ventilation of grain in container 2 is carried out in a closed circle with the pneumatic conveying aggregate 1 from the lower nozzle (with rotary valve) 12 of the container through a two-way valve 14, then through the vertical pipeline 7, the cyclone 5, and returns to the storage container 2.
Unloading of grain from the storage container is made from its lower nozzle by the pneumatic conveying aggregate 1, through the two-way valve 14, a pipeline 8 through a cyclone 6 into a vehicle 3 [2]. 1pneumatic conveying aggregate; 2container; 3vehicle from where the grain is loaded and where it is unloaded; 4mechanical transmission for the conveyor driving (if any); 5 and 6grain separating (discharging) cyclones-unloaders; 7pipeline for active ventilating or loading; 8pipeline for unloading; 9pipeline (hose) for loading of grain mass; 10humidity sensors; 11two-way valve; 12lower nozzle; 13 -Sensor control and monitoring panel; 14two-way valve; 15 and 16nozzles (with filters) for removal of air flow from the cyclones.
The aim of this article is to propose a methodology for studying and justifying the parameters and operating modes of the pneumatic conveyor, taking into account the physical characteristics of the material, during storage and active ventilation of soybeans by the proposed technology and determining its optimal parameters.

Calculation of the equipment
For the calculation of the pneumatic conveyor, the given in [4] method (calculation method of the suction equipment) is assumed. This is a classical method of selecting a pneumatic conveyor with nominal parameters, which is necessary not only for transportation, but also for active ventilation of grain in storage containers.

Flow rate calculation
Calculations are based on equipment with a 40-ton container and where all material (soybeans) in it should be shifted for 10 hours. So, a specified (real) mass flow rate (capacity, productivity) of the pneumatic conveyor is adopted as G sp = 4 t/h. The estimated (ideal) mass flow rate G is determined as follows [5]:

Pipeline calculation
The estimated air velocity v (m/s) in the pipeline is determined by the following formula [5]: where spe v -velocity of the material particles (for soybean v spe = 15), m/s; k -coefficient of sustainable conveying, depending on the material properties (for grain k = 1.2 ÷ 1.5).
The estimated air velocity in the pipelines of the interdepartmental pneumatic conveying systems is taken according to a solids loading ratio (particle mass loading = mass flow rate of particles/mass flow rate of air)  of the air-grain flow as follows: v = 20 m/s for  up to 0.5 kg/kg; v = 22 m/s for  more than 0.5 kg/kg; The value of  for interdepartmental pneumatic conveying systems is assumed up to 3.5 kg/kg (for bran, animal feed, and flour) and 3.5 ÷ 5 kg /kg for grain [5,6]. For soybean, the more appropriate value is  = 3.6 kg/kg. Also, the solids loading ratio (particle mass loading) of the air-grain flow can be determined by the following formula: The estimated volumetric flow rate in the pipeline is determined from formula (3) as follows: Theoretically required diameter of a circular pipeline bore is calculated by the following formula [7]: The diameter of pipeline bore is rounded to the nearest larger or smaller value D, according to the current GOST for pipes and determine the cross-section area of the pipeline given by 2 Then the volumetric flow rate of air in the pipeline is From the operating work of such equipment, it follows that when choosing the diameter of the pipeline it is necessary to observe a ratio of 100 to 1, that is, at 10m of the pipeline height, the diameter should be equal to 0.1 m. Accordingly, in our case the diameter of the pipeline should be within 80-145 mm.
However, the validity of these calculations must be verified empirically, which is supposed to be done in our further studies.

Pressure drop calculation
The pressure drop (loss) in the pneumatic conveyor H pt is determined by the following formula [ where Н cars -pressure drop in the blower and in the gravity flow pipe (lower nozzle); Н rec -pressure drop in the receiver; Н o -the amount of pressure drop to accelerate velocity of fed into a pipeline material to it conveying velocity (acceleration of the material) and to retrieve (redress) the air-grain flow velocity after bends; Н fr.v. , Н fr.h -the amount of pressure drop of friction during the movement of the air-grain flow in straight vertical and horizontal sections of the pipelines; Н b -the amount of pressure drop in bends; Н v.c -pressure drop during the vertical conveying; Н c.u -pressure drop in a cyclone-unloader; 1) Since the value of the pressure drop P cars is small, it can be taken Н cars = 150 Pa.
2) The pressure drop (loss) in the receiver is determined by the following formula: where  rec -loss factor, depended on the type of receiver;  rec =  a = 1.2 kg/m 3air density at the receiver inlet, kg/m 3 ; v rec -air velocity in the receiver, m/s. In the equipment in question, a receiving device of the "Nozzle" type is selected, for which  rec = 0.7 [9].
The air velocity in the receiver is determined by the following formula [9]: where F and F rec -cross-sectional area of the pipeline and the receiver pipe, m 2 . For approximate calculation it is allowed to take F = F rec.
3) The amount of pressure drop to equalize the velocities of the material and air (acceleration of the material) and to retrieve (redress) the air-grain flow velocity after bending is determined by the following formula: Pressure drop to equalize the velocities of the material and air (acceleration of the material) is determined by the following formula: where G -conveyor capacity, t/h; i -pressure drop corresponding to the acceleration of 1 ton of material in the initial section of the pipeline [9,10], Pa/(t/h), given by: where M = 0.324 -coefficient for coarse materials (soybean); v -air velocity, m/s; D -pipeline diameter, m. Ppressure drop to retrieve (redress) the air-grain flow velocity after bends is determined by the following formula: . .
where n -number of bends. The pressure drop after each bend j is given by: where ycoefficient depending on the size of the central angle of the bend (Fig. 2), the ratio of the radius of the bend curvature to the diameter of the pipeline and the length of the straight section behind the bend. Usually, a bend radius is adopted ten times pipeline diameter (r = 10D) [6]. In this case for elbow bend (α = 90º) y = 0.4; For the equipment in question whit two elbow bends (Fig. 1) 4) The pressure drop from friction during the conveying of the air-grain flow in straight vertical (H fr.v ) and horizontal (H fr.h ) sections of the pipeline is determined by the following formulaе where Н cl -pressure drop of clean air flow; K v and K h -empirical coefficients. Friction pressure drop of clean air flow is determined by the following formula: where  -empirical pipeline friction coefficient determined by Nikuradze's formula: where δpipe wall roughness, m. For usually used for grains (including soybean) pipes the wall roughness is accepted  = 0.2·10 -3 m [11].
The coefficient К v for soybean is given by: where The coefficient K h for soybean is given by: where A hcoefficient, for grain A h = 150; 5) The pressure drop in a bend (Fig. 2) Н b is determined by the following formula: where H b.cl -pressure drop (loss) of clean air flow in the bend; K b -bend loss factor given by: where r -radius of curvature of center axis of the bend (r = 10D in the equipment in question); В and m -empirical coefficients. For air-grain flow [4]: В =620 and m = 0.15 for flow from horizontal to vertical direction and В = 550 and m = 0.23 for flow from vertical to horizontal direction; The pressure drop of clean air flow in the bend H b.cl is given by: where  b and  b -empirical coefficients from [4]:  b = 1 for elbow bend (α=90º, Fig 2); ξ b = 0.36 for pipe diameter D = 119…125 mm. 6) Pressure drop during vertical conveying is determined by the following formula: where S -height of the vertical section (S = 10 m in the equipment in question). gearth acceleration, m/s 2 .

Fig. 2.
Elbow bend of the pipeline for active ventilation (pos. 7 in Fig.1) with α=90º 7) Pressure drop in a cyclone-unloader. As unloading device a cyclone separator is chosen by the air-flow rate Q c.u and air velocity v c.u at its inlet nozzle. The needed cross-section area F c.u is given by [12,13] .
where F c.u -cross-section area of the inlet pipe of cycloneunloader, m 2 ; Q c.uvolumetric flow rate of inlet air, m 3 /h; v c.u -velocity of inlet air, m/s. When determining Q c.u , a change in the air condition along the conveyor pipeline should be taken into account: . .
where  -air density at the inlet of the pipeline;  c.u -air density at the inlet of the cyclone-unloader, which is given by: .
Pressure drop in the pipeline H pl is calculated from formula (8) for a respective branch of the conveyor as follows: .
where Н o -the amount of pressure drop to accelerate velocity of material fed into a pipeline to its conveying velocity (acceleration of the material) and to retrieve (redress) the air-grain flow velocity after bends (see formula (12)); Н fr.v. , Н fr.h -the amount of pressure drop from friction during the movement of the air-grain flow in the straight vertical and horizontal sections of the pipelines (see formulae (18) and (19)); Н b -the amount of pressure drop in the bends (see formula (25)); Н v.c -pressure drop during the vertical conveying (see formula (28); By choosing the inlet air velocity v c.u , the required crosssection area F c.u is determined, and a cyclone type is selected. For the equipment in question v c.u = 22.86 m/s and F c.u = 0.017 m 2 . Hence a cyclone type ЦР-400, with F c.u = 0.018 m 2 (D = 400 mm), from [3] is selected. Pressure drop (loss) in the cyclone-unloader is determined by the following formula: where ξ c.d -loss factor, depended on the type of cyclone;  c.u -air density at the inlet of the cyclone-unloader, given by formula (31). For the chosen cyclone (ЦР-400) ξ c.d = 3.7 and ρ c.u =1.1 kg/m 3 .

Rotary valve calculation
In the equipment in question, feeding devices are installed to seal the opening through which the material is fed to or unloaded from the conveyor [14]. In our case, (Fig. 1
After following in formula (34) the rotor's speed can be obtained: The typical speed according to [6] is 20 rpm, which coincides with the producer's recommendation for 15 ÷ 30 rpm.

Supply cyclone calculation
A supply cyclone is selected according to the volume rate of air flow Q s.c entering the cyclone and the air velocity v b.c in its inlet. The required cross-sectional size of the inlet F s.c (in m 2 ) is determined as follows [13,15]: The air flow volumetric rate Q s.c is determined as follows: is a coupling, and equal to 0.95 in case of a belt transmission;  bear = 0.99bearing efficiemcy.
After the abovementioned calculations the blower is chosen. For the conveyor in question Q = 1380 m 3 /h. Transmission efficiency is considered  tr = 0.95; According calculation the blower can be selected.

Nozzle choice
Nozzles with filters (pos. 15 and 16 in Fig. 1) for the removal of air flow from the cyclones-unloaders are chosen by the air flow rate Q c.ds which depends on the volume flow rate Q c.u , of the cyclone inlet air flow (see formula 30). It may be considered .
. The proposed methodology makes it possible to choose the main parameters and modes of operation of the pneumatic conveyor for soybeans and on this basis to choose the optimal pneumatic conveying aggregate for the proposed modular equipment for soybeans storage with active ventilation.
The proposed methodology allowed to establish that, the optimal bore of the pipeline should be no more than 125 mm, as a result of which the power consumption of the electric drive is reduced by 3-5%. Accordingly, the total cost of equipment is reduced.

Conclusion
An innovative way for soybean storage with active ventilation is proposed.
A methodology for studying the productivity (capacity) and power consumption of a pneumatic conveyor of soybeans is proposed. The influencing factors are considered. Their variation allows for the choice of a conveying aggregate with optimal parameters.
The methodology is applied (as an example) for the calculation of pneumatic conveying equipment for container-modular storage with active ventilation of soybeans in farms.