Calculation Method for Selection of Roots Blower for Material Conveying

The fans mainly used are Roots vacuum pump and high-pressure blower (vortex pump), which are widely used in the fields of cement, coal and other materials transportation, agricultural grain storage and transportation. In daily use, we usually contact with pressure measurement, such as water level measurement, and pneumatic conveying is usually a problem of transportation distance, so here we talk about the selection and calculation method of pneumatic conveying fans (Roots vacuum pump and high-pressure blower):

1、 Mixture ratio of transport material and gas

Mixing ratio is an important parameter of powder pneumatic conveying device. The more mixing ratio, the more beneficial the transportation capacity is under the same productivity environment. The lower the required pipe diameter, the smaller the volume of separation can be selected. The lower the air volume and air volume consumed by the dust removal equipment, thus reducing the operating cost of the powder pneumatic conveying device. The unit energy consumption is reduced.

Calculation method: M=Gm/Gq... (Gm represents the net weight of materials transported in one hour, Gq represents the proportion of air)

2、 Transportation wind

Under the environment of reliable operation of all conveying pipe sections, when the material pneumatic conveying device has economic operating characteristics, the allowable cyclone speed is the transportation wind force. Generally, there should be 10-20 allowance for higher "economic speed" of transportation wind. Please refer to different transportation equipment commonly used in pipelines. The airflow rate of low-pressure transportation is generally 20m/s, and the airflow rate of high-pressure transportation is generally 8m/s.

3、 Air volume required for transportation

The required air volume is conveyed by materials. To determine the mixing ratio, refer to the formula:

　　Q=(1.1-1.2)G/(M ч) Where: G- Calculated transportation rate, kg/h;

　　 ч—— Gas gravity, under standard atmospheric pressure,=1.2kgm3;

M -- mixing ratio.

4、 Diameter of conveying pipe

Determine the pipe diameter (m) according to the air volume and transportation speed required for the transportation of smoke and dust:

　　D2=4Q/ Л Where: Q – air volume m3/h

V – Wind force m/s

5、 Transport pressure

The pressure of transported gas must exceed the sum of various pressure drops △ P when the material moves in the conveying pipe. These pressure drops include: material pressure drop in the horizontal conveying pipe △ P1, material pressure drop in the vertical conveying pipe △ P2, material pressure drop in the transport elbow △ P3, material pressure drop across the discharger and dust remover △ P4, etc.

1. Wind resistance of horizontal pipeline:

　　△P1=△P11+△P12=( λ 11+M λ 12)(L/D)( ρ V2/2)

Where: △ P1 - pressure drop of pure gas, Pa;

△ P Additional pressure drop caused by material transportation in pipe 1111 (Pa);

　　 λ 11 Gas friction resistance;

　　 λ 12 - Additional friction resistance (determined by experiment)

M – material gas mixture ratio;

L Length of horizontal conveying pipe, m;

D - diameter of horizontal conveying pipe, m;

　　 ρ— Average density of gas, kgm3;

V – flow rate of gas in the pipe, m/s.

2. Wind resistance in vertical conveying pipe:

　　△P2=△P21+△P22=( λ 11+ λ 12)*(H/D)*( ρ V2/2)+ ρ gH+ ρ MgHV/V1

Where, △ P is the pressure drop of the horizontal transportation pipe in the same length day, Pa;

△ P221 Pressure drop caused by overcoming gravity work, Pa;

　　 λ 11 Gas friction resistance;

　　 λ 12 - Additional friction resistance (determined by experiment)

H - vertical pipe height, m;

M – material gas mixture ratio;

L - length of horizontal conveying pipe, m;

D - diameter of conveying pipe, m;

　　 ρ— Average density of gas, kgm3;

V - flow rate of gas in the pipe, m/s;

V1 - vertical movement speed of material, m/s;

G - Gravitational acceleration, m/s2.

3. Air resistance of pipe elbow:

　　△P3=△P31(1+N)=( λ 11+M λ 12)*(L”/D)*( ρ V2/2)*(1+N)

Where, when the pressure drop of △ P horizontal conveying pipe is changed to that of connecting pipe, the pressure drop of horizontal conveying pipe will be reduced. Pa;

Length of bending arc with L curvature radius R, m;

　　 λ 11 Gas friction resistance;

　　 λ 12 - Additional friction resistance (determined by experiment)

M – Material gas mixing ratio:

D – Pipe diameter. m;

　　 ρ— Average density of gas, kgm3;

V - flow rate of gas in the pipe, m/s;

N – Additional scale factors can be obtained by testing.