The electrostatic precipitator (ESP) is a type of modern industrial dust collecting equipment with a dust removal rate of over 99%.
Its high dust cleaning rate makes it very popular in many industries with large flue gas emissions, such as power generation, cement making, metallurgy, and chemical industry.
As a kind of mechanical equipment, after working for a long time, the dust removal efficiency of an electrostatic precipitator will inevitably decline. This decline in efficiency may be caused by a combination of one or more factors. Therefore, we need to overhaul it regularly to eliminate possible problems and keep its dust removal efficiency at a high level.
Factors That May Affect the Dust Removal Efficiency
The dust removal efficiency of an electrostatic precipitator is related to more than one factor. The temperature and velocity of the flue gas, the sealing state of the precipitator, the spacing between dust collection plates, and some other elements will all impact the dust removal rate.
Temperature of the dust-laden air
A too high airflow temperature will reduce the initial voltage of the corona, the electric field temperature on the surface of the corona electrode during corona onset, and the voltage during spark discharge, which will have an adverse impact on the dust removal efficiency.
And a too low airflow temperature will possibly cause: creepage of insulating parts due to condensation; corrosion of the metal parts; dust agglomeration in the ash hopper. There was an accident case in which the electrostatic precipitator of a cement plant burned the dust collecting curtain deformed and broken due to the long-term ash accumulation in the ash hopper, which buried the dust collecting plate and corona wire in the ash accumulation.
Flow speed of the dust-laden air
The speed of the airflow is better not to be too fast. It takes a certain time for dust to deposit on the dust collecting curtains after being charged in the electric field, if the air flows too fast, the charged dust will be carried out by the airflow before it has time to settle. At the same time, it is easy to cause the secondary flying of the dust deposited on the dust collecting curtains, especially when the dust is knocked down by rappers.
Distance between curtains
When the applied voltage and the spacing and radius of corona lines are the same, increasing the plate spacing will affect the distribution of ion current generated in the adjacent area of corona lines, increase the potential difference on the surface area, reduce the electric field intensity in the outer area of corona and affect the dust removal efficiency.
Spacing between corona wires
The spacing between corona wires has an optimal value that will produce the maximum corona current. When the applied voltage, corona wire radius, and plate spacing are the same, increasing the corona wire spacing will make the distribution of corona current density and electric field intensity uneven. Reducing the spacing will reduce the corona current due to the mutual shielding effect of the electric field near the corona wires.
Velocity distribution of airflow
Uneven velocity distribution of airflow will cause the overall dust collecting efficiency of the ESP to drop.
The electrostatic precipitator is in negative pressure during operation, if the connection of the shell is not tightly sealed, cold air will leak from the outside, increasing the airflow velocity passing through the ESP and reducing the flue gas temperature, which will change the dew point of the flue gas and degrade the dust collection performance. If air is leaked from the ash hopper or ash discharge device, the collected dust on collection plates will be blown again and reduce the dust collection efficiency; it will also dampen the ash and adhere to the ash hopper, resulting in unsmooth ash unloading and even ash blockage.
Measures that can improve the dust removal performance
By tapping the dust removal potential of the ESP and focusing on solving the defects and problems in the dust removal process, the dust removal efficiency can be effectively improved.
We should first find out the cause for the reduction of dust removal efficiency of an ESP, and then take targeted measures to solve the problem and improve the dust collecting rate. Ordinary measures include:
1. Adjust the technical parameter of the air distribution device to improve uneven velocity distribution of airflow.
2. Overhaul the thermal insulation layer outside the dust collection system regularly to ensure that the thermal insulation materials are in good condition and their thickness meets the standard.
3. Enhance the tightness of the dust collection system and ensure that the wind leakage rate of the whole ESP is less than 3%.
4. Flexibly adjust the material of the electrode plate (collection curtain) according to the chemical composition of flue gas to increase its corrosion resistance and prevent short circuits caused by electrode plate corrosion.
5. Properly adjust the rapping cycle and rapping force of the electrode to improve the corona power and reduce the secondary flying of the dust.
6. Add an extra electric field to increase the capacity and dust collection area of the ESP, or increase or broaden the electric field of the electrostatic precipitator. A larger electric field can effectively enhance the dust collecting rate.
7. Adjust the control mode and power supply mode of power supply equipment. The application of high frequency (20 ~ 50KHz) high voltage switching power supply can technically upgrade and improve the efficiency of electrostatic precipitators.