Some empirical data for air slide chute conveying system design.
Air slide chute conveying system is an extreme form of airtight pneumatic conveying method, which uses low-pressure air to pass through the air slide fabrics to achieve the purpose of powder/particles conveying.
The compressed air disperses after passing through the air slide fabric and enters around the particles, which overcomes the resistance of the particles and air slide fabrics, so that the particles become to fluidization conditions like liquid, then flows by gravity in the tank.
Compared with some mechanical conveying systems, the air slide chute system with the properties of no rotating parts, no noise, convenient operation and management, light equipment weight, low energy consumption, simple structure, large conveying capacity, and easy to change the conveying direction. Very economical equipment for conveying powdery materials and granular bulk solids.
1.Construction and design
The air slide chute is generally slightly inclined to the horizontal plane, and the section is usually designed with square.
The air slide chute combined with upper chute and lower chute, the air slide fabrics installed in the middle to make the air slide chute with two chambers, the powder material flowing in the upper chamber which called the material chamber and the compressed air in the lower chamber which called the air chamber.
The compressed air will be filtered and decompressed to the certain pressure as requested, then enter into the air chamber through the air pipe, and then enter into the material chamber through the air slide fabrics.
The airflow passing through the air slide fabrics and suspends the powder material to be the fluidized state, changing the friction angle of the powder material and even making the material not contact with the air slide fabrics. However, the flow speed of the material is fast, but the frictional resistance with the air slide fabrics is very small.
Finally, the compressed air blended with the powder material will be discharged into the atmosphere through the filter, and the powder material flows out through the discharge port of the air slide chute.
The structural materials of the air slide chute for choice can be carbon steel, aluminum alloy, stainless steel or non-metallic materials.
Air slide fabrics can be made of different materials, such as cotton, polyester, aramid, even fiber glass, basalt and so on. Sometimes also can be designed with microplates, such as the porous ceramic plates, sintered porous plastic plates and so on.
1.2, design and calculation.
The key contents of the design and calculation of the air slide chute conveying system are include the cross-sectional size of the chute, the conveying distance, the inclination angle, the air pressure, the air consumption, and the conveying capacity.
In order to make the material convey normally and stably in the air slide chute, the necessary condition is that the air need to be with a certain pressure and sufficient flow rate
1.2.1, air pressure design
The air pressure is subject to the resistance of the air slide fabrics and the height of the material being conveyed in the powder material chamber.
The air slide fabrics need to be with the sufficient resistance to ensure the air distribution in the material chamber equally.
The air pressure can be determined by the following formula:
P1 is resistance of the air slide fabrics, unit is KPa;
P2 is powder material resistance, unit is KPa;
P3 is the resistance of the pipe lines.
According to the experiences, the air press P always choose between 3.5~6.0KPa, when design, mostly according to 5.0KPa.
The air slide fabric is an important part of the air slide chute conveying system/pneumatic conveying chute, the suitable option of the air slide fabric is the precondition of the perfect performance of the air slide chute conveying system.
The air slide fabrics have to be with the pore side, uniform distribution of the weaving pattern, good air permeability, and the pore size have to be smaller than the particles’ diameter of the powder material being conveyed to prevent the air slide fabrics be blocked.
Under the stable conveying conditions, the air resistance/pressure drop across the air slide fabrics should be greater than the air resistance / pressure drop across the powder material being conveyed, and the pressure drop across the air slide fabrics have to uniform, or the air slide chute convey system may easy to be blocked due to the problem of the air slide fabrics, so the change frequency will be much higher.
The air slide fabrics from Zonel Filtech, we guarantee the good performance in 12month after installation or 18month after delivery, but when exact operating, if the working condition is good, the good performance of the air slide fabrics from Zonel Filtech even can stand more than 4 years, which can save much maintenance cost and time for our clients.
1.2.2, compressed air consumption volume.
The compressed air consumption volume for the air slide chute conveying system is related to the following factors:
The physical properties of the material, the cross-sectional size and length of the launder, the height of the powder material layer, the inclination of the launder, etc.
In order to avoid the air slide fabrics being blocked, the supplied air must be de-watered and de-oiled.
The air consumption of the air slide conveying system/pneumatic conveying chute can be calculated by the following formula:
“q” is the air permeability of the air slide fabric, the unit is m3/m2.h, as usual “q” we choose 100~200;
W is the width of the powder material flow chute;
L is the length of the powder material flow chute.
1.2.3, the capacity of the air slide chute conveying system
The capacity of the air slide chute conveying system was effected by many factors, the formula can be as following:
G=3600 X S.ρ.V = 3600 X W.h.ρ.V
S is section area of the powder material in the air slide chute, unite is m2;
P is air density of the fluidized material, unit is kg/m3;
V is the powder material flowing speed, unit is m/s;
W is the inner width of the air slide chute;
H is the inner height of the air slide chute.
According to the principle of fluid mechanics, the flow of powder materials in the air slide chute is very similar to the calm flow of liquid in the open channel, so the flow velocity of the powder material is related to the inclination of the air slide chute as well as the width of the air slide chute and the power material height in the air slide chute, so:
C is Chezy coefficient, C=√(8g/λ)
R is hydraulic radius, unit m;
“i” is inclination of the air slide chute;
“λ”is the friction coefficient.
The inclination of the air slide chute as usual choose between 10%~20%, i.e. 6~11 degree according to the requirements;
If the powder material chute height is H, as usual the air slide chute width W=1.5H, the powder section height h is 0.4H.
The air slide chute conveying system / pneumatic conveying chute uses low-pressure air to fluidize the material, and uses the inclined component force to move the material forward. It can be widely used in the transportation of various types of air-permeable, dry powdery or granular materials with a particle size below 3~6mm.
It has the advantages of large conveying capacity, especially low power consumption, and its application range is gradually expanding.
But due to the air slide chute is installed obliquely, the conveying distance is limited by the drop , also it is not suitable for upward conveying, so the application of the air slide chute conveying system/pneumatic conveying chute has its limitations.
Edited by ZONEL FILTECH
Post time: Mar-06-2022