1. Wet dust collector technology
1.1 Working principle
Wet electrostatic precipitator has been used in foreign power plants for nearly 30 years. As the final control technology of atmospheric composite pollutant control system, it is used to remove soot, gypsum slurry droplets, fine particles PM2.5 and heavy metals after wet desulfurization. Such as a variety of pollutants, the soot emission limit can be controlled below 10mg / Nm3 or even 5mg / Nm3.
The dust removal principle of the wet electrostatic precipitator is the same as that of the dry electrostatic precipitator, and is carried out in three stages of electric field charging, collecting and cleaning. Under the action of DC high voltage, the metal discharge electrode ionizes the gas to charge the surface of the soot and the droplet particles, and the charged particles move to the dust collecting pole under the action of the electric field force and deposit on the dust collecting pole. The wet type electrostatic precipitator is different from the dry type electrostatic precipitator. On the one hand, the collected water mist is self-flowing and cleaning; on the other hand, it is periodically sprayed through the cleaning nozzle installed on the top of the dust collecting pole to complete the dust collecting and discharging. The electrode is thoroughly cleaned.
According to the material of the dust collecting plate, the wet electrostatic precipitator can be divided into three types: metal dust collecting and extremely wet electrostatic precipitator, flexible dust collecting and extremely wet electrostatic precipitator, and conductive glass steel dust collecting and extremely wet electrostatic precipitator.
1.2 Metal dust collecting and extremely wet electrostatic precipitator
The material of the dust collecting pole is mostly stainless steel 316L, and also adopts stainless steel 2205. Its structure type is basically the same as that of the conventional dry type electrostatic precipitator. The anode plate adopts the flat plate structure, the continuous water spray cleaning is used during operation, and the dust collector is horizontally arranged, the smoke is arranged. The gas level is flat. The dust removal efficiency is 70% (one electric field) / 85% (two electric fields), and the design parameters of different manufacturers are slightly different.
1.3 Conductive FRP Dust Collecting Extreme Wet Electrostatic Precipitator
The dust collecting pole material is made of conductive FRP FRP, and the dust collecting pole structure is tubular. The cross-section shape is round, square, regular hexagon, etc., mostly in regular hexagonal shape, modular assembly. The operation adopts a fixed-time spray water cleaning method, and the dust collector is extremely tubular structure, and the vertical arrangement is arranged, and the smoke flow direction is upward, downward, or downward. The dust removal efficiency can reach 70%-90%, and the requirements of different dust removal efficiency can be realized by selecting the flue gas flow rate and adjusting the length of the dust collecting pole.
1.4 Flexible dust collecting and extremely wet electrostatic precipitator
The dust collecting material is made of organic synthetic fiber flexible fabric material, and the dust material which is wetted by the wet flue gas is highly conductive, and collects the mist in the flue gas. On the one hand, the cleaning method is self-flowing cleaning by the uniform water film on the whole surface of the dust collecting plate, and on the other hand, the upper nozzle is used for thorough cleaning. The plate of the precipitator adopts a tubular structure with a square cross section, and the dust collector is vertically arranged, and the flue gas flow direction is upward, downward, or downward.
3. Comparison of economic and technical indicators
Take the new construction of the 2Ã—1000MW unit wet electrostatic precipitator in the second phase of a power plant as an example. The first scheme adopts the metal dust collecting and extremely wet electrostatic precipitator; the second scheme adopts the conductive glass steel dust collecting and extremely wet electrostatic precipitator; the third scheme adopts the flexible dust collecting pole. Wet electrostatic precipitator. The dust removal efficiency of the three is 75%. See Table 2 for system design indicators. Table 3 shows the analysis of infrastructure investment, operation and maintenance costs.
The metal dust collecting and extremely wet electrostatic precipitator is basically dominant in the domestic market, and its technology is mature and the capital investment is low. However, the water consumption and alkali consumption of the technology are relatively expensive. Since the dust collecting pole forms a continuous water film, the inside of the electric field is liable to cause turbulence of the flue gas, and the electric field at the end of the operation is likely to cause the droplet to carry, and the soot emission is unstable.
Conductive FRP dust-collecting and extremely wet electrostatic precipitators have been mainly used in chemical and metallurgical industries in China in the past. In recent years, there have been many successful engineering cases in the power industry. The technology infrastructure investment is slightly higher, operating and maintenance costs are lower. The soot emissions are stable and can achieve less than 5mg/m3 or even lower.
The technical characteristics of the flexible dust collecting and extremely wet electrostatic precipitator are similar to those of the conductive glass fiber reinforced plastic electrostatic precipitator, but the application of this technology is small and the stability needs to be tested. The technology infrastructure investment is small, but the organic synthetic fiber flexible fabric for the anode plate needs to be replaced every six years, and the replacement cost is large. The electric field operating parameters are not high, and the soot emissions are affected by the electric field operating parameters.
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