Wet flue gas desulfurization desulfurization of coal-fired power plants in the main process, and a wet electrostatic precipitator after the addition of two dust wet desulfurization apparatus. Current domestic mainstream wet electrostatic precipitator according to electrode materials can be divided into three kinds: metal plate wet electrostatic precipitator, a wet ESP plates and the flexible conductive FRP wet electrostatic precipitator. According to incomplete statistics, the number of wet electrostatic precipitators in domestic coal-fired power plants of 300MW or above has exceeded 40, of which the number of metal plate wet electrostatic precipitators accounted for the majority. Metal plate wet electrostatic precipitator is a wet electrostatic precipitator technology for domestic and foreign power plants. It is also used in the United States and Japan.
In this paper, only the main structure of the metal plate wet electrostatic precipitator is summarized and analyzed. For convenience of description, the metal plate wet electrostatic precipitator is a wet type electrostatic precipitator.
1. Principle of wet electrostatic precipitator
In the principle of dust collection, the wet electrostatic precipitator is no different from the dry electrostatic precipitator. It is to deliver high pressure to the electric field space. After the space gas is ionized, the dust particles and the droplet particles in the flue gas are charged by the electric field force. Move to the dust collecting pole and gather on the dust collecting pole.
2. Type and composition of the structure of the wet electrostatic precipitator
The wet electrostatic precipitator structure (Fig. 1) is basically the same as the dry electrostatic precipitator. It is a typical horizontal single-layer structure metal plate wet electrostatic precipitator. The anode plate adopts a parallel hanging metal plate, and the cathode can adopt a top hanging type or a side hanging type according to the actual situation of the project, and the rest also includes a lower supporting steel frame, a ash bucket, a casing, an inlet and outlet horn, and an airflow uniform device. , high voltage systems, etc. The projects using this type of wet electrostatic precipitator include Guohua Sanhe Power Plant and Guohua Dingzhou Power Plant.
The biggest difference between the wet electrostatic precipitator and the dry electrostatic precipitator lies in the difference of the flue gas working fluid. The dry electrostatic precipitator flue gas is dry flue gas, the flue gas temperature is high, and the flue gas does not contain fog droplets. The wet type electrostatic precipitator is saturated wet flue gas, the flue gas temperature is low, the flue gas contains a large number of mist droplets, and the traditional vibrating cleaning is replaced by spray cleaning in the cleaning method.
Therefore, the wet electrostatic precipitator adds a sprinkler system and a water supply and drainage system that supplies water to the spray cleaning system. Since the wet electrostatic precipitator operates internally with saturated wet flue gas, in order to prevent the saturated wet flue gas from being exposed to cold condensation on the inner wall of the supporting insulator, the supporting insulator is cracked or even exploded, and the wet electrostatic precipitator also increases the hot air of the insulator incubator. The purge system acts as a heating and airtight.
The biggest challenge facing the large-scale application of wet electrostatic precipitators today is the narrowing of the site, because the layout of the tailgate of domestic coal-fired boilers is generally very compact, and the power plant is not considered to be equipped with a wet electrostatic precipitator during planning, so the site layout is more difficult. The wet electrostatic precipitator of the profiled structure described below can solve these problems.
(1) Double-layer double-structure wet electrostatic precipitator (Fig. 2)
In essence, it is the same as the horizontal single-layer wet electrostatic precipitator. It can be regarded as a superposition of two horizontal wet scrubbers to reduce the floor space. It is a wet electrostatic precipitator adapted to narrow site conditions. The upper and lower layers are independent systems, and there is a partition system in the middle of the upper and lower layers to separate the upper and lower layers. The projects of the wet electrostatic precipitator with double-layer complex structure include Huadian Zibo Power Plant, Datang Huangdao Power Plant, and Ningxia Power Investment Xixia Thermal Power Plant.
(2) Wet electrostatic precipitator with vertical structure (Fig. 3)
This is also a wet electrostatic precipitator adapted to the conditions of a small power plant. The imported horn is at the top of the precipitator, and the flue gas enters from the upper part and the lower part is discharged. Shanghang Ruixiang Paper and Shanghai Changxing Island No. 2 Power Plant have adopted this type of wet electrostatic precipitator.
3, wet electrostatic precipitator body structure material application
Since the wet electrostatic precipitator is placed in the wet desulfurization process, its flue gas working fluid is saturated wet flue gas, the flue gas temperature is low, and the flue gas contains a large amount of acid mist, which is highly corrosive. Therefore, attention should be paid to the consideration of the choice of materials for contact between the body and the flue gas.
Structurally speaking, ordinary carbon steel is usually used inside the casing. In order to prevent corrosion, the inner surface of the casing needs to be coated with anticorrosive materials, generally glass scales.
The anode plate works in a corrosive environment package, and its surface needs to have strong corrosion resistance. At the same time, the connection point which is easy to cause corrosion should be minimized, because if the plate fails, it will not only disturb the electric field, but also generate sparks. , causing a decline in dust removal performance. Since the wet electrostatic precipitator is equipped with a continuous spray system, a water film can be formed to cover the surface of the electrode, and the circulating water has been neutralized by alkali, thereby greatly reducing corrosion. In such an environment, 316L stainless steel can be used as the electrode material. .
The cathode line, the cathode frame and the internal pipe of the spray system have the same working environment as the anode plate, and the corrosion resistance should be higher than other components. At the same time, because the surface is easy to cause dust condensation and local corrosion is faster, the cathode wire should also be at least the same material as the anode plate.
Other internal parts, due to irregular shape, difficult construction of anti-corrosion, uncontrolled quality of anti-corrosion construction, therefore, SUS316L stainless steel or equivalent materials are also available.
4. Influence of the structure of the wet electrostatic precipitator on the dust removal efficiency
There are many factors affecting the dust removal efficiency of the wet dust collector. Only the influence of the structure of the wet electrostatic precipitator on the dust removal efficiency will be discussed below.
4.1 pole matching system
As the core component of the electrostatic precipitator, the anode and cathode have an important influence on the dust removal efficiency.
The anode plate is one of the core components of the wet electrostatic precipitator. Whether its structure is favorable for forming a uniform water film, whether it can eliminate the "channel flow" phenomenon of the general plate, it must be considered when designing the plate structure of the wet type electrostatic precipitator. of. Nowadays, environmental protection equipment suppliers at home and abroad have their own designs in such as wind-proof trench structure and board surface structure, and they can achieve good results through actual project demonstration.
In the choice of the cathode line type, because it is in an environment that may be affected by the water film coating, it is preferable to adopt a polar line type with low halo voltage and easy rinsing, which effectively prevents the droplet from staying on the needle tip and ensures the needling The discharge capacity and the line type that reduces droplet corrosion. The wet electrostatic precipitator is the same in principle as the conventional dry electrostatic precipitator. The cathode wire type is used and improved on the cathode type of the conventional dry electrostatic precipitator. The cathode line type of the current mainstream wet electrostatic precipitator mainly has Acupuncture lines, thorn lines, etc., have their own advantages and disadvantages. The needle line has strong discharge performance, but has many consumables and high production cost. The discharge performance of the thorn line is not strong in the needle line, but the production cost is low, the consumables are small, and the weight is light, and the body load is reduced. Therefore, it is necessary to comprehensively consider its discharge characteristics and economy.
4.2 Air distribution
Among the factors affecting the purification efficiency of the electrostatic precipitator, whether the airflow is uniformly distributed in the electric field also has a great influence on the dust removal efficiency.
The uniformity of the distribution of the electric dust removal airflow mainly depends on the correct selection of the ratio of the flue section to the cross section of the precipitator and the arrangement of the airflow uniformity device and the choke device. The airflow uniform device has various structural forms, and the punching plate and the punching plate are one of the most widely used effective forms, as shown in FIG. The orifice plate design should be based on the flue layout of the power plant, and the airflow distribution simulation test should be carried out according to the principle of geometric similarity and dynamic similarity. Through the computer simulation test and the airflow distribution model test, the opening ratio, the pore size and the number of layers of the perforated plate are obtained. In order to guide the design of the flue layout and the guide vanes, etc., to ensure that the internal airflow of the wet scrubber is stable on the premise of meeting the site conditions.
At the same time, the inside of the wet dust collector should also be arranged with a flow blocking device to prevent the turbulent flow of the smoke short circuit, so that the uniformity of the flow field inside the dust remover is further optimized, and the flue gas treatment efficiency is further improved.
4.3 sprinkler system
In view of the characteristics of easy corrosion and easy scaling of flue gas after wet desulfurization, the reasonable arrangement of the spray system is to reduce the residence time of SO3 and gypsum slurry on the surface of the wet electrostatic precipitator plate, reduce the corrosion of SO3 on the plate and relieve the plaster. The key to scaling the slurry on the plates. This requires a comprehensive comparison of the water films formed on the surface of the plates according to nozzles of different structures, and combined with different arrangement arrangements to obtain an optimal nozzle structure and an optimal arrangement. In order to ensure a good cleaning effect, the flushing can be carried out in two ways: one is to arrange a fine mist droplet small-flow water film nozzle on the upper part of the anode and cathode, and the fine mist droplet is sprayed and charged to form uniform continuous water on the surface of the anode plate. The second is to arrange a flushing nozzle with a large amount of water sprayed above the nozzle of the water film, and periodically clean the whole electric field to achieve the purpose of cleaning the plate.
5, summary
As the terminal finishing technology equipment in the mainstream atmospheric composite pollutant control technology at home and abroad, the metal plate wet electrostatic precipitator is similar in structure to the dry electrostatic precipitator, with various types and materials, special materials, and perfect system. Good control of PM2.5, acid mist, aerosols, submicron particles, mercury , heavy metals and dioxins.
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