Optimization design and application of insulation for low and low temperature and wet electrostatic precipitator
2016-04-06 15:35:01
Abstract: at present, the low temperature wet electrostatic precipitator technology has become the mainstream technology of flue gas in coal-fired power plants to achieve "low emission". Low temperature and wet electric dust collector insulation level in the very great degree is by the surface condition of the insulator, the extent and intensity of surface charge accumulation, charged particles motion and surface coverings (acid dew and water film medium) determined. This paper deeply studies and discusses the factors of the influence of high electric insulation performance, proposed low temperature and wet electrostatic precipitator (ESP) insulation performance optimization method, and introduces the low temperature EP insulation retrofit example.
Keywords: low temperature wet electrostatic precipitator; electrostatic precipitator; surface creepage insulation; optimization; anti dew insulator
0 Introduction
"Energy-saving emission reduction" is a basic policy of China's economic development at present, priority among priorities is "12th Five-Year" work plan. Coal-fired power plant in order to achieve coal consumption decreased 8 grams of standard coal / kW? H, in the boiler flue arranged heat exchanger, heat in the flue gas set
For them, used for the two time, to save energy.
Along with the coal-fired power plant flue gas "ultra low emission" voice intensified, people to achieve ultra-low emission technology more and more attention. In order to achieve ultra low emission requirements, SO3 can be used with tiny dust and easy agglomeration charged characteristic of dust
Low efficiency, low temperature (below 90 DEG C) ESP came into being. In addition, still can use wet electrostatic precipitator technology. At low temperature, wet electrostatic precipitator technology has become the mainstream technology of flue gas in coal-fired power plants to achieve "low emission".
In the electrostatic precipitator, the DC insulator and the AC insulator are different, which should be mainly considered along the surface of the insulator surface discharge, that is, the surface of the. According to the operation experience of electric dust collector for many years, 80% of the fault is an electrical fault, 90% of the electrical fault is insulation fault, and insulation fault in the vast majority of insulator surface creepage caused by, which is the core problem of electrostatic precipitator insulator inevitable, and low ESP inlet flue gas temperature below the acid dew point, wet electric dust collector working in the saturated wet flue gas environment, especially cause height to take seriously.
1 the main factors affecting the insulation performance of DC high voltage electric field
1.1 surface charge accumulation affects insulator surface discharge
Due to the insulator surface in the presence of electric field normal component, when the DC voltage applied for a certain period of time (several minutes to several days), insulator table charge accumulates on the original electric field distortion may occur along the surface discharge [1].
Figure 1 for the Japanese Mitsubishi company K.Nakanishi, et al A.Yoshioka[2] of solid and the middle cylindrical insulator model applied a series of DC voltage and get the insulator surface breakdown voltage as a function of charge density
When the insulator is in a direct current electric field for a long time, the accumulation of the surface charge will decrease the discharge voltage along the surface. For example, in the SF6 0.44MPa gas pressure can withstand the 600kV voltage of the insulator after a few hours after the DC voltage, the discharge voltage to 300kV[3]. It can be seen that the surface charge accumulation is an important factor that affects the performance of DC insulation.
1.2 free conducting particle effects of DC insulation conductive particles in the performance of the dust attached to the surface of the insulator, will become the insulator flashover path, shortening the distance along the surface discharge, greatly reduces the flashover voltage of insulator. Attachment in insulator on the surface of the conductive particles come in a variety of shapes, dimensions, there are a few to a few tens of microns powder, also have a few millimetres in aggregate. Experimental studies have confirmed that the effect of these conductive particles on the flashover voltage of insulators is related to the particle size, shape and location of the insulator. Located in the middle position of the supporting insulator, when particles made of 3mm length increased to 6 mm, the flashover voltage drop about 25%[4]; on the insulator surface in the same position, if the particle length of axial and coaxial electric field in the same direction, then the insulation level decreased significantly; if they are perpendicular to each other, the flashover voltage is not affected [5]. When entering the electrostatic precipitator of the high temperature fume (as ever burning coal-fired power plant flue gas temperature is controlled in more than 120 DEG C), the conductive particles were isolated, scattered state, through the movement attached on the surface of the insulator and a mess of random distribution, then the insulation level decreased obviously; if the flue gas temperature dropped to near or below the acid dew point temperature, SO3 will condensation and adsorption on the surface of the insulator, the formation of creepage channel. Similarly, in wet electrostatic precipitator, if the insulator surface is covered with water film, it will form a climbing channel.
It can be seen that when the conductive material in the DC electric field is attached to the insulator surface, it will become another important factor that affects the high voltage insulation performance of DC electric field.
2 insulation optimization method for low and low temperature and wet electrostatic precipitator
2.1 reasonable choice of enough distance to climb
Low temperature and wet electrostatic precipitator (ESP) insulation design goal is will the creeping discharge voltage increased to pure gas gap breakdown voltage level, so that insulation breakdown occurs in gas medium, rather than along the surface of the insulator. Therefore, it is necessary to choose an adequate distance to climb.
When designing the insulator size, we must pay attention to the distance between the high voltage electrode and the ground along the insulator surface. The surface of the insulator is very important, dry surface and attached fog surface, and cover the surface water film of the same. It is possible to understand the material (smoke and dust) on the surface of insulator, and to understand the resistance value of the dust, as the basis of the design.
Operation experience shows that in dry flue gas condition, when the high and medium specific resistance dust, the unit voltage (unit of kV) of the anti crawling distance of 0.3 inches to 0.4 inches, that is, 7.6mm ~ 10.2mm[7]. According to the working voltage 72kV meter, the surface of the electric dust collector in the general coal-fired power plant is 500mm ~ 700mm.
It is obvious that the creeping distance in the dry flue gas can not meet the requirements of the low temperature and wet ESP, especially for the insulation performance and the choice of the distance from the wet flue gas. To ensure insulation property, wet flue gas under the condition of the surface of the insulator climbing electrical distance should be dry flue gas state climb electrical distance of 1.5 times to 2 times, the unit voltage of anti climbing electric distance 15mm/kV to 20mm/kV. According to the total working voltage 72kV, general wet electric dust collector with the surface of the insulator climbing electric distance appropriate 1000mm ~ 1400mm, and low operating voltage, the creepage distance can be reduced.
The surface of the insulator can always be kept dry, and the surface of the insulator can be crawled under the condition of dry flue gas if the exposed insulator or the common insulator are used for heating and heat preservation and hot blast cleaning. Practice has proved that the insulator can be applied to low temperature electric dust collector, wet ESP and electric mist precipitator.
2.2 optimize the structure of the electric field, so that the distribution of the field intensity is uniform.
The distribution of the electric field strength of the DC insulator is different from that of the AC insulator, the electric field strength of the AC insulator is distributed according to the capacitance, and the electric field strength of the DC insulator is influenced by the resistance of the insulator. The variation of electric field on insulator surface with surface resistance is more obvious than that of volume resistance, and this kind of change is non-linear. Changing the distribution of the electric field and the electric field can make the electric field on the insulator surface more uniform, so as to reduce the electric field strength around the insulator.
Figure 2 and figure 3 are the design of low temperature electric precipitator for a coal-fired power plant, the design of the equivalent circuit and the electric field strength of the insulator.
Transformation of the former total field intensity E0 all added to the supporting porcelain sleeve, supporting porcelain sleeve height 600mm, rated voltage 72kV, each kV climb electrical distance 8.3mm. If reduce the flue gas temperature below the dew point, the porcelain wall. It was lack of insulation.
As shown in Figure 3, when the transformation of 1 plus porcelain wall bushing in the cover plate on the maximum creepage distance reached 1050mm. The total and strong E0 respectively by E1 and wall porcelain bear bear E2, greatly reducing the burden of insulated porcelain sleeve. Figure porcelain bushing and bushing are arranged coaxially, porcelain sleeve installed in the electrostatic precipitator roof beam (electrode), porcelain high voltage end of the cover plate and the bushing flange with other potential composed of intermediate electrode, through the wall bushing axle core cathode boom as the high-voltage electrode.
In the electric field E between the porcelain sleeve inner wall and wall bushing at the lower part of the outer sleeve is actually composed of E12 and E22, E12 and E22 for coaxial electric field and in the opposite direction, e set = E22-E12, visible, so arrangement porcelain sleeve of field strength is reduced due to E12 and E22 offset each other, the adsorption of charged particles on insulator surface in lost power and unable to migrate, avoid insulator surface along the surface discharge.
Also in the electric field between the porcelain sleeve and the lower part of the cathode hanger, due to E0 cut to the direction of the electric field component and E12 and point to the electrode, electric field near the electrode has been strengthened. In this way, it is may prevent charged particles enters the porcelain sleeve, so that the insulation conditions are improving.
2.3 the anti exposed insulator
Anti dew type insulator of 2.3.1 for low temperature electric dust collector
For low temperature and low electric dust collector, in order to prevent creepage dew insulator, using hot air blowing measures and preventing dew insulator type two kind of one of the measures. Insulator with internal heating body, also known as heat type anti dew type insulator.
1) anti dew type support porcelain insulator
The material of the dew proof type supporting porcelain insulator is 95 porcelain, and the inner is provided with a heating body, and the structure of the diagram is shown in Figure 4. 4 hanging point of low temperature electric dust collector with 4 lifting points of a power supply district is provided with an anti exposed supporting porcelain bushing insulator.
The exposed type supporting porcelain insulator can be directly exposed to the smoke, the unique dew prevention effect and the compact insulation structure can significantly improve the reliability of the internal high voltage insulation of the electric dust collector. The dew proof insulated porcelain sleeve is composed of an upper part and a lower part of a circular cylinder.
Compressive strength of high (>2000MPa), high temperature insulation performance is good, 500 DEG C volume resistivity can still keep in 4 x 1010 ohms & dot; cm2/cm, thermal shock resistance of wide temperature range (>700 DEG C), corrosion resistance, anti-aging, and other advantages.
Heating body directly installed in a dew proof type insulated porcelain sleeve at the lower part of the trench, heat from the heating body was mostly anti dew type insulating porcelain jacket direct absorption, and quickly delivered to the dew proof type insulated porcelain sleeve, outer surface, so that the surface to maintain a certain temperature. Heating body power and voltage: 1200W, 220V. In the room temperature environment, when the power supply 3 hours later, the inner wall temperature of the ceramic sleeve can be reached and kept at 120 degrees Celsius. If the temperature of the inner wall of the ceramic sleeve is up to and maintained at more than 150 degrees Celsius in the hot flue gas of 90 to 80 centigrade. When the moisture in the wet flue gas or acid dew has not yet come into contact with the porcelain cover, it is emitted by the surface of the heat evaporation, so that the surface is always kept dry insulation environment.
2) anti dew type pull rod insulator
The proof type pull rod insulator is composed of an external anti dew insulated pull rod and an internal heat generating body. Can be directly exposed in the flue gas. With high tensile strength (rated tensile load 100kN), high temperature insulation performance, thermal shock resistance of the temperature
A wide range (>700 C), corrosion resistance, anti-aging and other advantages.
Heater installed directly in a dew proof type insulation pull rod groove, heat from the heating body was mostly anti revealing an insulated pull rod directly absorbed, and quickly delivered to an insulated pull rod, outer surface, the surface to maintain a certain temperature. Heating body power and voltage: 250W, 36V. 3 hours after the power supply is switched on and a dew proof type insulation pull rod hair heater warming effect and the function and a dew proof type insulating porcelain jacket heating is the same.
Anti dew type pull rod insulator can be used for hanging with a total weight of 10 tons of cathode frame, low temperature ep a power supply zone four hanging points insulation were installed 3 dew proof type insulation pull rod and a dew proof supporting porcelain insulator, its installation, as shown in Figure 6. Dew type pull
Rod insulator can also be used for anti swing support of the side part of the cathode frame.
Anti dew type insulator for 2.3.2 used in wet electric dust collector
For wet electric dust collector, the dew proof supporting porcelain insulator and a dew proof type pull rod insulators to prevent creepage dew insulator, but its structure and installation method with low temperature and low electrostatic precipitator is slightly different. In addition, the anti dew type post insulator and the dew proof type anti swing insulator can also be used.
1) proof type post insulator
The dew proof type post insulator is composed of an external insulation support and an internal heat generating body, which can be directly exposed in the smoke. With high compressive strength, high temperature insulation performance, wide temperature range of thermal shock resistance (>700 DEG C), corrosion resistance, anti-aging, and other advantages.
The heating body directly installed in the insulating pillar at the bottom of the groove, heat from the heating body most of insulating pillar direct absorption, and quickly delivered to the insulation inside the pillar, outer surface, so that the surface to maintain a certain temperature. Heating body power and voltage: 250 W ~ 300W, 36V. The power supply is switched on for 3 hours and a dew proof type insulating pillar hair heater heating effect and effect and low temperature EP dew proof type insulating porcelain jacket heating is the same.
A dew proof type pillar insulator generally use 2 in each group, installed in the electric dust collector at the top of the lift cathode hanger, but also from the side of the cathode frame out of the cantilever beam, four dew pillar type installed at the two sides of the electric dust remover main body frame, carrying a cathode frame. Dew
The schematic diagram of the installation of the type post insulator is shown in Figure 7, and the local figure is shown in Figure 8.
In order to better prevent moisture, the outer surface of the dew type post insulator is designed to be under the umbrella skirt (wing), as shown in figure 9. Wing umbrella below the 45 degree line within the scope of the surface for the rain shielding surface, design the unfolded length should not be less than insulators dry state climbing electrical distance.
2) anti dew type anti swing insulator
The cathode frame of the wet electrostatic precipitator is covered with water, and the insulator is the horizontal installation, and it is particularly important to prevent moisture. The installation of anti swing insulator is shown in figure 10.
Outdoor insulator should be equipped with waterproof cover to prevent spray water directly sprayed on the surface of insulator.
The metal accessories used for the wet electrostatic precipitator shall be all stainless steel, in order to prolong the service life.
3 Optimization of insulation structure in the application of low temperature electric precipitator
3.1 transformation scheme
Huaneng Nanjing power plant 300MW #2 unit after the transformation of low temperature electric dust collector, electrostatic precipitator inlet flue gas temperature in the following points. Due to the decline of the flue gas temperature, electric precipitator insulator surface there condensation, resulting in surface creepage, insulation failure is to ensure safe operation
, porcelain heating continuous cast, will face the following problems: a simple continuous cast heater can effectively avoid the occurrence of creepage phenomenon remains to be to run the test of practice; second, large power consumption, porcelain heating by electric heating, total power of 150KW, if
Continuous cast, power consumption of large, three is porcelain repair cost is bound to increase (electric heater and porcelain bottles continuously cast with easily damaged and in need of replacement); the fourth is online unit operation, replace the damaged insulator and the heater both unsafe, is not easy. It is necessary for the insulation of water
Improve the level of upgrading.
Due to the lower temperature of the electric precipitator, to better test the actual effect, select one of the partition of the power supply for insulation transformation, and as a test electric field. ESP each electric cathode framework in addition by 4 to porcelain suspended and insulation, but also on the cathode rapping
The four or five electric field is also arranged at the lower part of the cathode frame. Therefore, this test in addition to the electric dust precipitator suspension way to transform, but also to deal with the rotating shaft insulator and anti swing insulator to improve synchronization.
Transformation scheme is as follows:
Based on (1) of the original ordinary industrial porcelain insulation and support, each industrial porcelain bushing installation of a dew proof type wall bushing and the insulator total creepage distance 1000mm, increases the creepage electrical distance method to avoid and solve the inner wall of the porcelain bottle creepage problem.
Specific transformation steps:
1 before the installation of the anode and cathode frame should be measured mutual position and space distance, and make a good record;
2) with a hook lifting tool cathode frame beams, the nut, the cathode frame lifting 1~5mm;
3) the removal of the original on the cover, will lengthen short and tighten and welded cathode hanger, burning. Attention should be made to the insulation porcelain sets of protection, welding slag, sparks and so on shall not splash to the surface of the porcelain, so as to avoid damage to the insulation porcelain sets;
4) and then press the order on the cover, asbestos gasket, wall bushing, cushion, gland and nuts etc installation;
5) tighten large nut, will enhance the removal tool. Then the adjustment nut cathode frame height, the cathode frame of restitution. The height of the top of the cathode hanger and the top of the insulator chamber must be more than 200mm;
6) the final access to high voltage power supply. Welding in gland terminals connected to the high voltage power line, power connector must be good available bolts and firmly pressed contact, but also be used welding welding. But if the welding is used, we should also pay attention to protect the porcelain insulator.
After the transformation of the structure as shown in figure 11.
(2) to change the vibration of the rotating shaft insulator into a large distance from the insulator, the distance increased to more than 1000mm.
(3) the 8 metal clamping arms of the lower insulating plate of the lower part of the cathode frame are replaced with 95 porcelain insulating arms, so that the electric distance of the lower part of the anti swing insulator is also increased to more than 1000mm.
3.2 effect
The renovation work was completed in early 2014 10, after the insulation of the transformation of the electric field of the two voltage significantly increased, compared with the adjacent electric field, the operating voltage is higher, indicating that the electric field insulation is good. After six months to actually run, proved that the transformation effect is good.
It can be seen that the insulation structure is capable of working in the wet flue gas environment of the low temperature electric dust collector. Don't even have to put into operation the electric heater, the insulator can maintain the normal operation, the energy saving effect is remarkable. It is estimated that the 300MW unit for electric dust collector is concerned,
Can save electricity 1 million 100 thousand degrees per year.
4 conclusions
This paper deeply studies and discusses the factors of the influence of high electric insulation performance, proposed low temperature and wet electrostatic precipitator (ESP) insulation performance optimization method, and introduces the low temperature EP insulation retrofit example. Main conclusions are:
(1) low temperature, wet electric dust collector insulation level in the very great degree is by the surface condition of the insulator, the extent and intensity of surface charge accumulation, charged particles motion and surface coverings (acid dew and water film medium) determined.
(2) to ensure that the insulation performance of low temperature and low and wet electrostatic precipitator (ESP), need to increase the insulator climbing electrical distance, wet flue gas under the condition of the surface of the insulator climbing electrical distance should be dry flue gas state climb electrical distance of 1.5 times to 2 times, the unit voltage of anti climbing electric distance 15mm/kV to
20mm/kV. According to the working voltage, the surface of the insulator can be climbed.
(3) by changing the structure of the electric field, the reasonable arrangement of the resistance and the electrode can make the electric field on the insulator surface more uniform, so as to reduce the electric field strength around the insulator.
(4) anti exposed insulator is simple in structure, low in energy consumption and good in reliability. For low temperature and low electrostatic precipitator, the dew proof supporting porcelain insulator, anti dew type pull rod insulator and a dew proof type wall bushing insulators to prevent creepage insulator condensation and wet electric dust collector can also
The proof type post insulator and the dew proof type anti swing insulator, namely, the insulating pull rod.
(5) the proof insulator has been applied to the #2 furnace 300MW unit in Huaneng Nanjing power plant, which is verified by the application of the modified project of the low temperature electric dust collector. The two voltage of the electric field after insulation is significantly increased, the effect is good.
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(转载自《北极星节能环保网》）