Design and use of high voltage electrostatic precipitator for ball mill

Foreword

High-voltage electrostatic precipitators are widely used in dust control in cement and other industrial enterprises. A factory has also adopted a high-voltage electrostatic precipitator on the raw material mill and cement mill, which has achieved good environmental treatment effects and certain economic benefits. Here, combined with the practical experience of a plant application, a brief introduction to the design and use of high-voltage electrostatic precipitators.

First, the working principle of high voltage electrostatic precipitator

The dust removal principle of the dust collector is: through external silicon rectifier transformer, convert 380V alternating current into 100kV direct current, input the corona pole in the center of the dust collector cylinder, form a positive and negative electric field with the casing of the dust collector, and pass the corona wire. The burr is discharged, and the gas ionization in the cylinder generates a large amount of positive and negative ions, so that the dust in the electric field region obtains the same electric charge. Under the action of electric field force, the charged dust tends to be opposite to its polarity, and it falls into the ash hopper by its own weight and rapping to achieve the purpose of dust removal.

Second, the dusty dust and dust properties of the mill

The properties of the mill exhaust gas and the composition of the dust particles are shown in Table 1 and Table 2.

Table 1 Properties of mill exhaust

Table 2 Particle composition of mill dust %

Third, the design and calculation of relevant parameters

(1) Determine the treatment air volume Q

The air volume Q to be treated by the high-voltage electrostatic precipitator is determined according to the ventilation amount of the mill. The calculation formula is:

Where: Q-mill ventilation, m ³ /h;

D-mill effective inner diameter, m;

Φ-grinding inner filling coefficient;

Î¥-grinding wind speed, take (0.6 ~ 0.7), m / s;

K-leakage coefficient, take 1.3;

(2) Determination of dust removal efficiency

According to the exhaust gas temperature of the dust collector inlet dust concentration, exhaust gas temperature and outlet dust concentration (should meet the national industrial enterprise dust concentration discharge standard), the following formula can be used:

Where: η-dust removal efficiency, %;

Q-treatment air volume, m ³ /h;

C _out - dust collector outlet dust concentration, g / m ³ ;

C- _in -dust collector inlet exhaust dust concentration, g/m ³ ;

t _out - dust collector outlet exhaust gas temperature, ° C;

t _{into the} dust collector inlet exhaust gas temperature, ° C;

K-Exhaust gas absolute temperature, °C.

(3) Determination of the basic size of the electric field

1. Effective length of electric field

The dust-containing gas should stay in the effective electric field area for a certain period of time, so that the dust is controlled and recovered under the action of the high-voltage electric field force, and the dust removal purpose is achieved. Generally speaking, the longer the residence time of the dust gas in the electric field region, the higher the dust removal efficiency. When designing the electric field structure, the residence time of the dust-containing gas in the electric field region is required to be no less than 10 s, and the effective length of the electric field can be calculated according to the following formula:

L=uT

Where: L- electric field effective length, that is, corona pole effective length, m;

U-wind speed in the electric field, taking 0.7~0.8, m/s,;

The residence time of the T-dust-containing gas in the electric field, s, is preferably 10 s or more.

2, electric field cross-sectional area shape

The shape of the electric field section is generally round, elliptical, rectangular, etc. In our country, a double corona pole oblate with a corona pole spacing of 2 times the electric field radius is used, which consists of two groups, see Figure 1. The actual cross-sectional area of ​​each group of electric fields is calculated according to the following formula:

F=Ï€R ₂ +4R ₂

Where: F- electric field cross-sectional area, m ² ;

R- electric field radius, m;

The use of an oblate electric field structure has the advantages of being able to handle a dust medium having a large viscosity, easy distribution of the air volume, and easy cleaning of the dust on the inner wall of the cylinder.

Figure 1 Schematic diagram of the dust collector

3. Electric field radius

According to the output voltage of the high voltage power supply device is l00kV, the working current is 10mA, and the electric field strength is selected as 2.5 kV/cm, then the electric field radius:

R=U/E

Where: R- electric field radius (ie corona pole spacing), cm;

U-voltage, kV;

E-electric field strength, kV/cm;

(4) Selection of corona wire structure

The corona wire structure of the high-voltage electrostatic precipitator is generally in the form of a straight type, a spring type, and a thorn type.

Considering that the gas temperature of the mill is normal, but the dust concentration is high, and the raw material grinding exhaust gas contains a certain amount of water, so our factory chooses the thorn-type corona wire, the thorn is Φ1.0mm steel, the following is dense distributed. The electric field force distribution of the corona wire structure is uniform, has strong discharge performance, and can improve the dust collecting efficiency of the electric precipitator.

Fourth, the improvement of the cleaning device

The rapping of the corona wire of the high-voltage electrostatic precipitator generally uses the electromagnetic vibrator to radially oscillate, causing uneven vibration under the corona line, and the pole spacing varies greatly, which is easy to cause fluctuation of the field strength and seriously affect the stable operation of the device. . At the same time, the dust that has been shaken produces a radial movement, which intensifies the secondary flight of dust.

The factory changed the rapping device of the corona wire to a small motor controlled by a time relay to drive a set of connecting rods and hammers. When rapping, the corona wire was slightly oscillated downward. In this way, the corona line is consistently vibrated, the distance between the poles is small, the field strength fluctuation is small, and the dust collector is relatively stable. The dust that has been shaken moves in a vertical downward inertia, and the secondary flying of the dust is reduced, and the cleaning effect is better than the radial vibration.

Fifth, the use of results

The high-voltage electrostatic precipitator has been used on the raw mill of our factory for nearly 2 years and has been used on cement grinding for 3 years. The dust control effect is obvious by the relevant departments, as shown in Table 3.

Table 3 Governance effect measurement data

Sixth, operation and use precautions

When the high-voltage electrostatic precipitator is put into operation, normal maintenance, strict management, and correct operation are the key to ensuring long-term stable operation.

(1) After the high-voltage electrostatic precipitator is put into operation, special personnel shall be provided for maintenance and management, and the main parts such as the corona pole, porcelain bottle, insulating sleeve and cylinder wall of the dust collector shall be inspected regularly.

(2) Insulation measures. Whether high-voltage electrostatic precipitators can be used successfully in winter, insulation measures are the most important, especially the insulation in the electric field is more critical. Therefore, the dust collector cylinder of our factory adopts double-layer shell, filled with expanded perlite , with a thickness of l00mm, and the heat preservation effect is better.

For the humidity-containing gas, a high pressure gas temperature is not high raw mill electrostatic precipitator, but also added a set of small coal-fired furnace, and dust in contact with the pipe, so that the necessary heating field region measures to ensure the stability run.

(3) The installation of high-voltage silicon rectifier transformers shall be provided with a high-voltage shielding room (at least a safety fence shall be provided), which is both safe and meets the technical requirements. At the same time, try to make the transformer close to the cylinder of the high-voltage electrostatic precipitator to reduce the loss of secondary voltage and current.

(4) The concentration of dusty gas. The high-pressure electrostatic precipitator treats the concentration of dust-containing gas, and the upper limit is generally 40g/m ³ . When the concentration of the dust-containing gas exceeds this value, the dust collection efficiency will be greatly reduced. Therefore, in the design, if the concentration of the dust-containing gas is high, the secondary dust collection process should be considered. The first stage uses cyclone dust to remove the dust, and the second stage uses high-voltage electrostatic dust to remove dust.

(5) Specific resistance of dust-containing gas. The specific resistivity of the dust medium is an important factor affecting the dust collection effect. Generally, the specific range of the specific gravity of the high-voltage electrostatic precipitator dust is from l04 to 1011 Ω/cm. When it is lower than 104 Ω/cm, corona sealing will occur; when it is higher than l011 Ω/cm, anti-corona will occur, both of which will greatly reduce the dust collection efficiency of the electrostatic precipitator.

(6) When suspending high-voltage electrostatic precipitator, high-voltage electrical control box to be later than the mill stop 10min, humid gas to be discharged electric dust collector region, so that the corona electrode, housing material reduces corrosion of metal, while the Dust gas is discharged to the standard.

(7) Normal use of the cleaning device. The ashing should not be frequent, and the number and time of slamming can be determined according to the dust adsorption situation and the voltage and current drop. Under normal circumstances, the number of slamming is reduced as much as possible to reduce the secondary dust.

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