High-frequency power supply technology plays a significant role in flue gas quenching and tempering in electric dust removal
The 125MW unit of a power plant is equipped with a dual-chamber three-field electric precipitator with a dust removal efficiency of 99.2%. According to the design of coal type, the dust concsentration at the outlet of the unit is less than 140mg/m3. It was put into operation in 2003, and each electrostatic precipitator is equipped with 6 sets of rectification. With the aging of existing dust collector equipment and the improvement of national emission standards, electric dust removal can no longer meet new environmental requirements. It is expected that through the upgrading and upgrading of the electrostatic precipitator, the discharge level of the dust collector will be reduced to below 45mg/m3, and the smoke dust emission concentration of the flue gas will be below 30mg/m3 after being cleaned by the desulfurization tower, reaching the “Air Pollutant Emission Standard for Thermal Power Plants” （ GB13223-2011） requirements.
1 Determination of the preliminary transformation plan
1.1 transformation plan options
At present, in the context of the improvement of the national environmental protection policy, the original electrostatic precipitators of coal-fired power plants basically need to be upgraded and rebuilt, and there are many ways to transform them.
1.1.1 Electrostatic precipitators are still used after the transformation, mainly in the following three types:
（1） Adjusting and increasing the internal pole spacing and type of the original electrostatic precipitator;
（2） increasing the electric field at the tail;
（3） Replace the power supply to increase the electric field strength.
1.1.2 Transformed into electric bag composite dust collector
1.1.3 transformed into a pure bag filter
The 125MW unit has insufficient room for adding electric field at the tail of the original dust collector and changing to the electric bag composite dust collector. These two schemes cannot be used.
Therefore, only the electrical integrated upgrade mode of the electrostatic precipitator body can be adopted or converted into a pure cloth bag method. However, only the “high-frequency power supply” transformation can not achieve the dust concentration of the dust at the outlet of the dust collector ≤ 45mg / m3, it is proposed to adopt the “high-frequency power + flue gas conditioning” technical program.
1.2 Introduction to the transformation plan
After multiple research and comparison of various technologies, the following two options were determined and the two solutions were compared.
（1） Transformed into a pure bag filter.
（2） SO3 flue gas quenching and tempering + high frequency power supply transformation.
1.2.1 Transformed into a pure cloth bag
（1） Transformation plan
This program is to transform the original electrostatic precipitator into a pure bag filter, the main methods are as follows:
a） Retain the electrostatic precipitator casing, ash hopper, etc., and transform the internal space of the original three electric fields into a bag filter.
b） Renovate the inlet and outlet ducts of the precipitator and transform them into inlet and outlet ducts suitable for pure bag filters.
c） Install the bag filter and the compressed air pipe system to perform the shock cleaning of the bag filter.
d） The modified bag filter control system is incorporated into the newly added desulfurization DCS, and the three electric field high and low voltage electric control cabinets of the original electric dust removal are removed.
（2） Working principle
When the dust-containing gas passes through the diversion system, due to the sudden drop of the wind speed, the large particle dust in the dust-containing gas naturally settles and separates directly into the ash hopper after the separation of the diversion system, and the remaining dust is guided by the diversion system. With the airflow entering the bag filter area, the dust is completely collected through the barrier, interception and coagulation of the filter bag, the efficiency is up to 99.9%, and the outlet dust concentration is stable below 30mg/m3.
1.2.2 changed to S03 flue gas conditioning + high frequency power supply
This scheme does not need to increase the electric field, retain the original casing, and carry out restorative overhaul of the electric field body. At the same time, a set of flue gas conditioning equipment is added. After the transformation, the first and second electric field power supply systems adopt ALSTOM's world-leading high-frequency power supply SIR and corresponding integrated control system.
（1） Retrofit of the electrostatic precipitator
The main contents of the ontology change include:
a） Keep the inlet and outlet smoke boxes, and replace the airflow distribution board of the air intake box of the dust collector body;
b） replace the trapped corrosion plate of the electrostatic precipitator casing, and increase the strength of the local position;
c） Restorative overhaul of the existing one, two, and three electric field anode and anode systems, replace the damaged cathode limit and anode plates, and adjust the shaft system to achieve the original design conditions.