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Electrostatic Precipitator Dry and Wet Fly Ash Treatment ESP System

Advantages of electrostatic precipitator

1. Efficient dust removal: electrostatic precipitator equipment can efficiently remove pollutants in particulate matter and smoke, and its efficiency can reach more than 99%. This is also one of the main reasons why it is widely used.
2. Low energy consumption, low operating costs: compared with other dust removal technologies, electrostatic precipitator requires relatively low energy, low operating costs, and it does not need to consume too much auxiliary materials.
3. Wide range of application: electrostatic precipitator technology can deal with various types of pollutants, whether it is smoke, particulate matter, volatile organic matter or soot, etc., can be effectively controlled and treated.
4. Stable and reliable work: electrostatic precipitator equipment has simple structure, easy operation, stable and reliable operation, so it is often used in the control scene of particles and dust with high requirements.

    The working principle of electrostatic precipitator

    The working principle of electrostatic precipitator is to use high voltage electric field to ionize the flue gas, and the dust charged in the air stream is separated from the air stream under the action of the electric field. The negative electrode is made of metal wire with different section shapes and is called discharge electrode.

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    The positive electrode is made of metal plates of different geometric shapes and is called the dust collecting electrode. The performance of electrostatic precipitator is affected by three factors, such as dust properties, equipment structure and flue gas velocity. The specific resistance of dust is an index to evaluate the electrical conductivity, which has a direct influence on the efficiency of dust removal. The specific resistance is too low, and it is difficult for dust particles to remain on the dust collecting electrode, causing them to return to the air stream. If the specific resistance is too high, the dust particle charge reaching the dust collecting electrode is not easy to release, and the voltage gradient between the dust layers will cause local breakdown and discharge. These conditions will cause the efficiency of dust removal to decline.
    The power supply of electrostatic precipitator is composed of control box, booster transformer and rectifier. The output voltage of the power supply also has a great influence on the dust removal efficiency. Therefore, the operating voltage of electrostatic precipitator should be kept above 40 to 75kV or even 100kV.
    The basic structure of electrostatic precipitator consists of two parts: one part is the body system of electrostatic precipitator; The other part is the power supply device that provides high voltage direct current and the low voltage automatic control system. The structure principle of electrostatic precipitator, the high voltage power supply system for the booster transformer power supply, dust collector pole ground. The low voltage electric control system is used to control the temperature of the electromagnetic hammer, ash discharge electrode, ash delivery electrode and several components.

    The principle and structure of electrostatic precipitator 

    The basic principle of electrostatic precipitator is to use electricity to capture the dust in the flue gas, mainly including the following four interrelated physical processes: (1) ionization of the gas.  (2) the charge of dust.  (3) The charged dust moves towards the electrode.  (4) Capture of charged dust.
    The capture process of charged dust: on the two metal anode and cathode with large curvature radius difference, through high voltage direct current, maintain an electric field sufficient to ionize the gas, and the electrons generated after gas ionization: anions and cations, adsorb on the dust through the electric field, so that the dust obtains charge. Under the action of electric field force, the dust with different polarity of charge moves to the electrode with different polarity and is deposited on the electrode, so as to achieve the purpose of dust and gas separation.

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    (1) Lonization of gas
    There are a small number of free electrons and ions in the atmosphere (100 to 500 per cubic centimeter), which is tens of billions of times worse than the free electrons of conductive metals, so the air is almost non-conductive under normal circumstances. However, when the gas molecules obtain a certain amount of energy, it is possible that the electrons in the gas molecules are separated from themselves, and the gas has conductive properties. When under the action of a high voltage electric field, a small number of electrons in the air are accelerated to a certain kinetic energy, which can cause the colliding atoms to escape electrons (ionization), producing a large number of free electrons and ions.
    (2) The charge of dust
    The dust needs to be charged to separate from the gas under the action of electric field forces. The charge of dust and the amount of electricity it carries are related to the particle size, electric field strength and residence time of dust. There are two basic forms of dust charge: collision charge and diffusion charge. Collision charge refers to the negative ions being shot into a much larger volume of dust particles under the action of electric field force. Diffusion charge refers to the ions making irregular thermal motion and colliding with dust to charge them. In the particle charging process, collision charging and diffusion charging exist almost simultaneously. In the electrostatic precipitator, the impact charge is the main charge for the coarse particles, and the diffusion charge is secondary. For fine dust with diameter less than 0.2um, the saturation value of collision charge is very small, and the diffusion charge accounts for a large proportion. For dust particles with a diameter of about 1um, the effects of collision charge and diffusion charge are similar.
    (3) Capture of charged dust
    When the dust is charged, the charged dust moves towards the dust collecting pole under the action of electric field force, reaches the surface of the dust collecting pole, releases charge and settles on the surface, forming a dust layer. Finally, every once in a while, the dust layer is removed from the dust collecting pole with mechanical vibration to achieve dust collection.
    The electrostatic precipitator consists of a dedusting body and a power supply device. The body is mainly composed of steel support, bottom beam, ash hopper, shell, discharge electrode, dust collecting pole, vibration device, air distribution device, etc. The power supply device consists of a high voltage control system and a low voltage control system. The body of the electrostatic precipitator is a place to achieve dust purification, and the most widely used is the horizontal plate electrostatic precipitator, as shown in the figure:
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    The shell of the dedusting electrostatic precipitator is a structural part that seals the flue gas, supports all the weight of the internal parts and the external parts. The function is to guide the flue gas through the electric field, support the vibration equipment, and form an independent dust collection space isolated from the external environment. The material of the shell depends on the nature of the flue gas to be treated, and the structure of the shell should not only have sufficient stiffness, strength and air tightness, but also consider corrosion resistance and stability. At the same time, the air tightness of the shell is generally required to be less than 5%.
    The function of the dust collecting pole is to collect the charged dust, and through the impact vibration mechanism, the flake dust or cluster-like dust attached to the plate surface is removed from the plate surface and falls into the ash hopper to achieve the purpose of dust removal. The plate is the main component of the electrostatic precipitator, and the performance of the dust collector has the following basic requirements:
    1) The distribution of electric field intensity on the plate surface is relatively uniform;
    2) The deformation of the plate affected by temperature is small, and it has good stiffness;
    3) It has good performance to prevent dust from flying twice;
    4) The vibration force transmission performance is good, and the vibration acceleration distribution on the plate surface is more uniform, and the cleaning effect is good;
    5) flashover discharge is not easy to occur between the discharge electrode and the discharge electrode;
    6) In the case of ensuring the above performance, the weight should be light.

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    The function of the discharge electrode is to form an electric field together with the dust collecting electrode and generate corona current. It consists of a cathode line, a cathode frame, a cathode, a hanging device and other parts. In order to enable the electrostatic precipitator to operate for a long time, efficiently and stably, the discharge electrode should have the following characteristics:
    1) Solid and reliable, high mechanical strength, continuous line, no drop line;
    2) The electrical performance is good, the shape and size of the cathode line can change the size and distribution of the corona voltage, current and electric field intensity to some extent;
    3) Ideal volt-ampere characteristic curve;
    4) The vibration force is transmitted evenly;
    5) Simple structure, simple manufacturing and low cost.
    The function of the vibration device is to clean the dust on the plate and the pole line to ensure the normal operation of the electrostatic precipitator, which is divided into anode vibration and cathode vibration. Vibration devices can be roughly divided into electromechanical, pneumatic and electromagnetic.
    The airflow distribution device makes the flue gas into the electric field evenly distributed and ensures the dust removal efficiency required by the design. If the distribution of air flow in the electric field is not uniform, it means that there are high and low speed areas of flue gas in the electric field, and there are vortices and dead angles in some parts, which will greatly reduce the dust removal efficiency.

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    The air distribution device is composed of a distribution plate and a deflector plate. The function of the distribution plate is to separate the large-scale air flow in front of the distribution plate and form a small-scale air flow behind the distribution plate. The flue baffle is divided into a flue baffle and a distribution baffle. The flue baffle is used to divide the air flow in the flue into several roughly uniform strands before entering the electrostatic precipitator. The distribution deflector guides the inclined air flow into the air flow perpendicular to the distribution plate, so that the air flow can enter the electric field horizontally, and the electric field to the air flow is evenly distributed.
    The ash hopper is a container that collects and stores dust for a short time, located under the housing and welded to the bottom beam. Its shape is divided into two forms: cone and groove. In order to make the dust fall smoothly, the Angle between the ash bucket wall and the horizontal plane is generally not less than 60°; For paper alkali recovery, oil-burning boilers and other supporting electrostatic precipitators, due to its fine dust and large viscosity, the Angle between the ash bucket wall and the horizontal plane is generally not less than 65°.
    The power supply device of electrostatic precipitator is divided into high voltage power supply control system and low voltage control system. According to the nature of flue gas and dust, the high voltage power supply control system can adjust the working voltage of the electrostatic precipitator at any time, so that it can keep the average voltage slightly lower than the voltage of spark discharge. In this way, the electrostatic precipitator will obtain as high a corona power as possible and achieve a good dust removal effect. Low voltage control system is mainly used to achieve negative and anode vibration control; Ash hopper unloading, ash transport control; Security interlock and other functions.
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    Characteristics of electrostatic precipitator

    Compared with other dedusting equipment, electrostatic precipitator has less energy consumption and high dust removal efficiency. It is suitable for removing 0.01-50μm dust in the flue gas, and can be used for occasions with high flue gas temperature and high pressure. The practice shows that the larger the gas volume treated, the more economical the investment and operation cost of electrostatic precipitator.
    Wide pitch horizontal electrostatic precipitator technology
    HHD type wide-pitch horizontal electrostatic precipitator is a scientific research result of introducing and learning from various advanced technologies, combining with the characteristics of industrial kiln exhaust gas conditions, in order to adapt to the increasingly strict exhaust gas emission requirements and WTO market standards. The results have been widely used in metallurgy, electric power, cement and other industries.
    Best wide spacing and plate special configuration
    The electric field strength and plate current distribution are more uniform, the drive speed can be increased by 1.3 times, and the specific resistance range of the collected dust is expanded to 10 1-10 14 Ω-cm, which is especially suitable for the recovery of high specific resistance dust from sulfur bed boilers, new cement dry method rotary kilns, sintering machines and other exhaust gases, to slow down or eliminate the anti-corona phenomenon.
    Integral new RS corona wire
    The maximum length can reach 15 meters, with low corona current, high corona current density, strong steel, never broken, with high temperature resistance, thermal resistance, combined with the top vibration method cleaning effect is excellent. The corona line density is configured according to the dust concentration, so that it can adapt to the dust collection with high dust concentration, and the maximum allowable inlet concentration can reach 1000g/ Nm3.
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    Corona pole top strong vibration
    According to the ash cleaning theory, the top electrode powerful vibration can be used in mechanical and electromagnetic options.
    The yin-yang poles hang freely
    When the exhaust gas temperature is too high, the dust collector and corona pole will expand and extend arbitrarily in the three dimensional direction. The dust collector system is also specially designed with heat-resistant steel tape restraint structure, which makes the HHD dust collector have high heat-resistant capability. The commercial operation shows that HHD electric dust collector can withstand up to 390℃.
    Increased vibration acceleration
    Improve the cleaning effect: The dust removal of the dust collecting pole system directly affects the dust collection efficiency, and most of the electric collectors show a decline in efficiency after a period of operation, which is mainly caused by the poor dust removal effect of the dust collecting plate. The HHD electric dust collector uses the latest impact theory and practice results to change the traditional flat steel impact rod structure into an integral steel structure. The structure of the side vibration hammer of the dust collecting pole is simplified, and the hammer dropping link is reduced by 2/3. The experiment shows that the minimum acceleration of the dust collecting pole plate is increased from 220G to 356G.
    Small footprint, light weight
    Due to the top vibration design of the discharge electrode system, and the unconventional creative use of asymmetrical suspension design for each electric field, and the use of the shell computer software of the United States Environmental Equipment company to optimize the design, the overall length of the electric dust collector is reduced by 3-5 meters in the same total dust collection area, and the weight is reduced by 15%.
    High assurance insulation system
    In order to prevent condensation and creepage of the high voltage insulation material of the electrostatic precipitator, the shell adopts the heat storage double inflatable roof design, the electric heating adopts the latest PTC and PTS materials, and the hyperbolic reverse blowing and cleaning design is adopted at the bottom of the insulation sleeve, which completely prevents the prone failure of the dew creepage of the porcelain sleeve.
    Matching L-C high system
    High voltage control can be controlled by DSC system, upper computer operation, low voltage control by PLC control, Chinese touch screen operation. High voltage power supply adopts constant current, high impedance DC power supply, matching HHD electric dust collector body. It can produce superior functions of high dust removal efficiency, overcoming high specific resistance and handling high concentration.
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    Factors affecting the effect of dust removal

    The dust removal effect of the dust collector is related to many factors, such as the temperature of the flue gas, the flow rate, the sealing state of the dust collector, the distance between the dust collection plate and so on.
    1. Temperature of flue gas
    When the flue gas temperature is too high, the corona starting voltage, the electric field temperature on the corona pole surface and the spark discharge voltage all decrease, which affects the dust removal efficiency. The temperature of flue gas is too low, which is easy to cause the insulation parts to creepage due to condensation. Metal parts are corroded, and the flue gas discharged from coal-fired power generation contains SO2, which is more serious corrosion; Dust caking in the ash hopper affects ash discharge. The dust collecting board and corona line were burned deformed and broken, and the corona line was burned off due to long-term ash accumulation in the ash hopper.
    2.Velocity of smoke
    The velocity of excessively high flue gas cannot be too high, because it takes a certain amount of time for the dust to deposit on the dust collecting pole of the island after being charged in the electric field. If the flue gas wind speed is too high, the nuclear power dust will be taken out of the air without settling, and at the same time, the flue gas velocity is too high, which is easy to cause the dust that has been deposited on the dust collecting plate to fly twice, especially when the dust is shaken down.
    3. Board Spacing
    When the operating voltage and the spacing and radius of the corona wires are the same, increasing the spacing of the plates will affect the distribution of the ionic current generated in the area near the corona wires and increase the potential difference on the surface area, which will lead to the decrease of the electric field intensity in the area outside the corona and affect the dust removal efficiency.
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    4. Corona Cable spacing
    When the operating voltage, corona radius and plate spacing are the same, increasing the corona line spacing will cause the distribution of corona current density and electric field intensity to be uneven. If the corona line spacing is less than the optimal value, the mutual shielding effect of electric fields near the corona line will cause the corona current to decrease.
    5. Uneven air distribution
    When the air distribution is uneven, the dust collection rate is high in the place with low air velocity, the dust collection rate is low in the place with high air velocity, and the increased dust collection amount in the place with low air velocity is less than the reduced dust collection amount in the place with high air velocity, and the total dust collection efficiency is reduced. And where the airflow speed is high, there will be a scouring phenomenon, and the dust that has been deposited on the dust collection board will be raised again in large quantities.
    6. Air Leakage
    Because the electric dust collector is used for negative pressure operation, if the joint of the shell is not tightly sealed, cold air will leak into the outside, so that the wind speed through the electric dust removal increases, the flue gas temperature decreases, which will change the dew point of the flue gas, and the dust collection performance decreases. If the air is leaked into the air from the ash hopper or ash discharge device, the collected dust will be generated and then fly, so that the dust collection efficiency is reduced. It will also make the ash damp, adhere to the ash hopper and cause the unloading of ash is not smooth, and even produce ash blocking. The loose seal of the greenhouse leaks into a large number of high temperature hot ash, which not only greatly reduces the dust removal effect, but also burns out the connection lines of many insulation rings. The ash hopper will also freeze the ash outlet due to air leakage, and the ash will not be discharged, resulting in a large amount of ash accumulation in the ash hopper.
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    Measures and methods to improve the efficiency of dust removal

    From the point of view of the dust removal process of electrostatic precipitator, the efficiency of dust removal can be improved from three stages.
    Stage one: Start with the smoke. In electrostatic dust removal, the dust trapping is related to the dust's own parameters: such as the specific resistance of the dust, dielectric constant and density, gas flow rate, temperature and humidity, the voltammetry characteristics of the electric field and the surface state of the dust collecting pole. Before the dust enters the electrostatic dust removal, a primary dust collector is added to remove some large particles and heavy dust. If cyclone dust removal is used, the dust passes through the cyclone separator at a high speed, so that the dust-containing gas spirals downward along the axis, the centrifugal force is used to remove the coarser particles of dust, and the initial dust concentration into the electric field is effectively controlled. Water mist can also be used to control the specific resistance and dielectric constant of the dust, so that the flue gas has a stronger charging capacity after entering the dust collector. However, it is necessary to control the amount of water used to remove dust and prevent condensation.
    The second stage: Start with soot treatment. By tapping the dust removal potential of electrostatic dust removal itself, the defects and problems in the dust removal process of electrostatic dust collector are solved, so as to effectively improve the dust removal efficiency. The main measures include the following:
    (1) Improve the uneven gas flow velocity distribution and adjust the technical parameters of the gas distribution device.
    (2) Pay attention to the insulation of the dust collection system to ensure the material and thickness of the insulation layer. The insulation layer outside the dust collector will directly affect the temperature of the dust collecting gas, because the external environment contains a certain amount of water, once the temperature of the gas is lower than the dew point, it will produce condensation. Due to condensation, dust adheres to the dust collecting pole and corona pole, and even shaking cannot effectively make it fall off. When the amount of adhering dust reaches a certain degree, it will prevent the corona pole from producing corona, so that the dust collection efficiency is reduced, and the electric dust collector can not work normally. In addition, the condensation will cause corrosion of the electrode system and the shell and bucket of the dust collector, thus shortening the service life.
    (3) Improve the sealing of the dust collection system to ensure that the air leakage rate of the dust collection system is less than 3%. The electric dust collector is usually operated under negative pressure, so attention must be paid to sealing in use to reduce air leakage to ensure its working performance. Because the entry of external air will bring the following three adverse consequences: (1) Reduce the temperature of the gas in the dust collector, it is possible to produce condensation, especially in the winter when the temperature is low, causing the problems caused by the above condensation. ② Increase the electric field wind speed, so that the residence time of dusty gas in the electric field is shortened, thus reducing the dust collection efficiency. (3) If there is air leakage at the ash hopper and ash discharge outlet, the leaking air will directly blow up the dust that has been settled and lift into the air stream, causing serious secondary dust lifting, resulting in reduced dust collection efficiency.

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    (4) According to the chemical composition of the flue gas, adjust the material of the electrode plate in order to increase the corrosion resistance of the electrode plate and prevent plate corrosion, resulting in short circuit.
    (5) Adjust the vibration cycle and vibration force of the electrode to improve corona power and reduce dust flying.
    (6) Increase the capacity or dust collection area of the electrostatic precipitator, that is, increase an electric field, or increase or widen the electric field of the electrostatic precipitator.
    (7) Adjust the control mode and power supply mode of the power supply equipment. The application of high frequency (20 ~ 50kHz) high voltage switching power supply provides a new technical way for the upgrading of electrostatic precipitator. The frequency of high-frequency high-voltage switching power supply (SIR) is 400 to 1000 times that of conventional transformer/rectifier (T/R). Conventional T/R power supply, often in the case of serious spark discharge can not output large power. When there is a high specific resistance dust in the electric field and produce a reverse corona, the spark of the electric field will further increase, which will lead to a sharp decline in the output power, sometimes even down to tens of MA, seriously affecting the improvement of dust collection efficiency. The SIR Is different, because its output voltage frequency is 500 times that of conventional power supplies. When the spark discharge occurs, its voltage fluctuation is small, and it can produce almost smooth HVDC output. Therefore, the SIR Can provide greater current to the electric field. The operation of several electrostatic precipitators shows that the output current of the general SIR Is more than 2 times that of the conventional T/R power supply, so the efficiency of the electrostatic precipitator will be significantly improved.
    The third stage: start from the exhaust gas treatment. You can also add three levels of dust removal after electrostatic dust removal, such as the use of cloth bag dust removal, can be more thoroughly remove some small particles of dust, improve the purification effect, in order to achieve the purpose of pollution-free emissions.

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    This is a parGD type electrostatic precipitator technology introduced in Japan's original electrostatic precipitator technology, through digestion and absorption of the successful experience of the domestic industry, developed a series of GD type electrostatic precipitator, widely used in metallurgy, smelting industry.

    In addition to the characteristics of other types of electrostatic precipitators with low resistance, low energy consumption and high efficiency, the GD series has the following points:
    ◆ Air distribution structure of air inlet with unique design.
    ◆ There are three electrodes in the electric field (discharge electrode, dust collecting electrode, auxiliary electrode), which can adjust the polar configuration of the electric field to change the electric field state, so as to adapt to the dust treatment with different characteristics and achieve the purification effect.
    ◆  negative - positive poles free suspension.
    ◆ Corona wire: no matter how long the corona wire is, it is composed of a steel pipe, and there is no bolt connection in the middle, so there is no failure to break the wire.agraph

    Installation requirements

    ◆ Check and confirm the acceptance of the bottom of the precipitator before installation. Install the components of the electrostatic precipitator according to the requirements of the Installation instructions of the electrostatic precipitator and the design drawings. Determine the central installation base of the electrostatic precipitator according to the confirmation and acceptance foundation, and serve as the installation base of the anode and cathode system.

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    ◆ Check the flatness, column distance and diagonal error of the base plane
    ◆ Check the shell components, correct the transportation deformation, and install them layer by layer from the bottom to the top, such as the support group - bottom beam (installed ash hopper and electric field internal platform after passing the inspection) - column and side wall panel - top beam - inlet and outlet (including distribution plate and trough plate) - anode and cathode system - top cover plate - high voltage power supply and other equipment. Ladders, platforms, and railings can be installed layer by layer in the installation sequence. After each layer is installed, check and record according to the requirements of the Installation instructions of Electrostatic Dust Collector and the design drawings: for example, after the installation of flatness, diagonal, column distance, verticality, and pole distance, check the air tightness of the equipment, repair welding of the missing parts, check and repair welding of the missing parts.
    Electrostatic precipitator is divided into: according to the direction of the air flow is divided into vertical and horizontal, according to the precipitation pole type is divided into plate and tube type, according to the removal method of dust on the precipitation plate is divided into dry wet type. 
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    This is a paragrapMainly applicable to Iron and steel industry: used to purify the exhaust gas of sintering machine, iron smelting furnace, cast iron cupola, coke oven. Coal-fired power plant: electrostatic precipitator for fly ash of coal-fired power plant.
    Other industries: The application in the cement industry is also quite common, and the rotary kilns and dryers of the new large and medium-sized cement plants are mostly equipped with electric dust collectors. Dust sources such as cement mill and coal mill can be controlled by electric dust collector. Electrostatic precipitators are also widely used in the recovery of acid fog in the chemical industry, the treatment of flue gas in the non-ferrous metallurgy industry and the recovery of precious metal particles.h

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