Electric precipitator is generally the use of DC negative high-voltage gas ionization, corona discharge, and then make the dust charge, and in the strong electric field force, the dust from the gas under the action of the separation of dust removal device, which is characterized by high dust removal efficiency, generally more than 99%, the design efficiency of the highest up to 99.99%, generally ensure that the dust concentration of dust collector outlet 50-100 mg / m 3 resistance, the design efficiency is up to 99.99%, generally guarantee that the dust concentration of 50-100 mg / m3, the design efficiency is up to 99.99%. -100mg/m3 resistance loss is small, generally 49-196Pa, so the fan's power consumption is small, according to the amount of 1000m3 flue gas per hour, the power consumption is about 0.2-0.8KW.h, the amount of flue gas to deal with a large amount of flue gas, flue gas concentration of the adaptability of the better, low operating costs. Low operation cost. However, its one-time investment and steel consumption is large, covers a large area, requires high level of manufacture, installation and operation, is sensitive to flue gas temperature change, the application range is limited by the specific resistance of dust, according to the data record[1]: the most suitable specific resistance range of the electric precipitator is 104-5×1010(-㎝), if it is outside of the range, it needs to take certain technical measures.
Shenyi three four sets of electric precipitator is composed of Czech mechanical part and East Germany's electrical part, due to the design, manufacture, installation, there are unreasonable factors, since the commissioning, the operating parameters have been poor, never reached the design parameters, after many studies and discussions of engineering and technical personnel and experts, and through the mechanical and electrical control system of the technological transformation, although there is an improvement, but still do not reach the value of rated operating parameters. Rated operating parameters. Especially in recent years, with the aging of the equipment, the operating parameters have been unstable, often appear: the secondary voltage is low or even close to zero or rise to a lower voltage will occur flashover; the secondary current can not rise to maintain the low-current operation or the secondary current is unstable and sharp swing and other phenomena. According to our many years of operation, maintenance experience and technical analysis, the reasons and countermeasures affecting the operating parameters of the three-phase electric precipitator of our plant are discussed below.
2. Analysis of the reasons affecting the operating parameters:
2.1 The influence of anti-corona on the operating parameters:
The most suitable dust specific resistance range of the electric precipitator is 104-5×1010(-㎝), and the dust specific resistance of our plant is tested to be 1011-1013 -㎝. The dust specific resistance of our factory is 1011-1013 -㎝ after testing, and it is high specific resistance dust if it exceeds this critical value. The so-called anti-corona refers to the partial discharge phenomenon produced by the high specific resistance dust layer deposited on the surface of the dust collecting pole. When the specific resistance of dust exceeds the critical value of 1010 (-㎝), the performance of the dust collector decreases with the increase of specific resistance. When the specific resistance exceeds 1012-㎝, it is difficult to achieve the desired effect by using the conventional electrostatic precipitator. This is because if the dust deposited on the dust collection pole is a good conductor, it does not interfere with the normal corona discharge, but if it is a high specific resistance dust, the charge is not easily released. As deposited on the dust collection pole dust layer thickens, the release of charge is more difficult. At this time, on the one hand, due to the dust layer failed to release all the charge, its surface still has the same polarity with the corona pole, it will exclude the subsequent charge dust. On the other hand, due to the dust layer charge release is slow, so the formation of a large potential gradient between the dust. When the dust layer in the electric field strength is greater than its critical value, in the dust layer of the pore space between the local breakdown, resulting in the opposite polarity of the corona polarity of the positive ions, resulting in positive ions will be to the corona pole movement, and the corona area of negatively charged particles. The result is a substantial increase in current and voltage reduction. Operating parameters and for the instability, electric dust removal performance deteriorated significantly.
The performance of electric precipitator exceeds the critical value 1010 (-㎝) with the specific resistance increases and decreases can also be argued according to Ohm's theorem: the current through the dust with a certain resistance of the voltage drop is
△U = j * Rs= j * póR (V) [2]
Where: j - current density in the layer of dust (A/cm)
The current density in the corona area is the same as that in the corona area, but it is not as large as that in the corona area. /cm)
óR--thickness of dust layer (cm) p--specific resistance (-㎝)
The voltage acting between the electrodes is Ug=U-△U= U -j póR (v)
U-electrical precipitator applied voltage
From the above formula, it can be seen that: if the specific resistance of the dust is not too high, the dust layer deposited on the dust collection pole of the voltage drop on the space voltage Ug can be ignored. But with the rise of specific resistance, if more than the critical value of 1010 (-㎝), the dust layer of the voltage △ U becomes very large, to a certain extent, resulting in local breakdown of the dust layer, and spark discharge, that is, usually referred to as the main reason for the impact of the operation parameters of the electric precipitator case study
Anti-corona phenomenon.
In summary, the most obvious effects of anti-corona on current-voltage characteristics are:
a). Reduction of the spark discharge voltage, resulting in a lower secondary voltage;
b). Formation of stable anti-corona traps and the occurrence of sudden changes in current or discontinuity, so that the operating parameters and for instability
c). The maximum corona current is greatly increased, and the secondary current is several times the normal current value when a spark discharge is about to occur.
The measures to prevent and attenuate the reverse corona are [3]: try to reduce the specific resistance of the dust so that the dust layer is not punctured. The main methods are the following:
The flue gas conditioning treatment. (Among them are: humidification treatment; chemical tempering treatment)
The use of high-temperature electric precipitator.
The use of wide-pitch electric precipitator.
4)Adoption of high-pressure pulse power supply system is the most effective means to completely eliminate anti-corona and solve the problem of high specific resistance dust is not easy to capture. Its simple principle is in the DC voltage on the basis of falling plus the action time is very short pulse voltage. The DC voltage is the critical corona voltage, and the pulse voltage ionizes the gas to produce corona current. This kind of power supply method can control the corona current by changing the frequency and width of pulse voltage without reducing the electric field voltage. The product of corona current density and specific resistance of the dust layer deposited on the dust collecting pole will always be lower than the breakdown voltage of the dust layer, thus avoiding the phenomenon of anti-corona completely. At the same time will also make the energy consumption of the electric precipitator greatly reduced, with great economic benefits. The United States, Japan, Denmark and other countries have long been successfully run and has confirmed the actual use of the effect. It is the development and application direction of our country's electric precipitator.
Shenyi dust collector dust specific resistance by environmental protection equipment factory test for 1011-1013 -㎝, is high specific resistance dust, is not conducive to the collection of dust, the operation of the electric field often occurs within the phenomenon of anti-corona, due to the frequent discharge, a serious impact on the operation of the parameters of the elevated. According to this condition and combined with solving other problems of our dust collector, in the past few years, #5 and #8 electric precipitators have been reformed with wide spacing, the same pole distance has been increased from 300mm to 400mm, and the operating voltage has been increased from 30KV to 45KV, and at the same time, high voltage micro-computer control has been adopted, and the operating parameters have been improved, which has prevented and weakened the phenomenon of reverse corona to a large extent, but it still hasn't been completely eliminated. #6, #7 electric precipitator has not been reformed, with the aging of the equipment, not only the anti-corona phenomenon occurs from time to time, but also exposed the corona line fat and anode plate dust accumulation, seriously affecting the stability of operating parameters and improve, to be made in the future for a comprehensive transformation.
2.2 Influence of corona line fatness and anode plate dust accumulation on operation parameters:
The finer the corona line is, the stronger the corona is, but because a small amount of dust particles in the ionic zone around the corona pole get positive charge, they move to the negative polarity of the corona pole and deposit in the corona line, and if the adhesion of dust is very strong, it is not easy to vibrate it down, and so the more the corona line is set, the more the corona line is filled with dust. If the dust has strong adhesion, it is not easy to be vibrated down, so the dust on the corona line is more and more, i.e. the corona line becomes thicker, which greatly reduces the effect of corona discharge, and this is the corona line hypertrophy; the dust with strong adhesion is sometimes also piled up on the anode plate. The above two situations will make the operating parameters significantly lower. The main reasons for this are as follows:
1) When the dust collector is under low load or stops running, the temperature of the electric dust is low with the dew point, and water or sulfuric acid condenses between the dust particles and between the dust particles and the electrodes, dissolving their surfaces, and when the dust collector is running again, the dissolved material solidifies or crystallizes, producing a large adherence.
2) Adhesion due to the nature of the dust, exploring the use of suitable coal to solve.
3) part of the pole plate, pole wire corrosion is serious, adsorbed on the surface of the dust vibration is not easy to remove, although the use of furnace shutdown opportunity to replace part of the cathode wire, but the corrosion of the anode plate need to wait until the overhaul can be replaced.
4) air leakage so that cold air from the inspection door, flue, expansion joints, insulation casing, etc. into the electric field, will not only increase the flue gas treatment capacity, but also due to the temperature drop in the emergence of condensate, resulting in corona electrode ash fat, insulation casing creeping and corrosion and other consequences.
5) vibration strength is not enough or vibration failure, resulting in corona line hypertrophy and anode plate dust accumulation, affecting the current voltage. We found in daily practice: when the current and voltage decreased significantly, by adjusting the microcomputer does not work, suspend the electric field for a few minutes
(vibration continues to run) and put back into the current and voltage increased significantly, and after a few minutes of operation parameters and return to the original state, fully explains the vibration strength is not enough. 98 years for the anode vibration of the two fields **** with a set of prone to commit the problem of the card on the #6 dust collector, after the double side vibration transformation. After the transformation of double-side vibration, after long-term operation observation, we found that not only the faults of the card are obviously reduced, but also the corona line is fat and the anode plate dust accumulation can be greatly improved.
2.3The influence of corona occlusion on operation parameters:
When the dust-containing gas passes through the electric field space, the dust particles collide with the free ions and are charged, and then there are two forms of charge in the dust collector---ion charge and particle charge. Therefore, the corona current on the one hand is formed due to the movement of gas ions, on the other hand is formed by the movement of dust particles, but the dust particle size and mass are much larger than the gas ions, so the gas ions for the movement of hundreds of times the speed of dust ions (gas ions, the average speed of 60-100 m / s, and dust ions, the speed of less than 60 m / s), so that the formation of corona current from the dust ions The corona current formed by dust ions only accounts for 1-2% of the total corona current, with the increase in the concentration of dust in the flue gas, the number of dust ions also increased, so that the corona current formed by dust ions is not large, but the formation of space charge is very large, close to the gas ions formed by the space charge, serious inhibition of the corona current, so that the dust particles can not get enough charge, so that the secondary current decreased significantly, if the concentration of dust If the dust concentration is too large, the current may tend to zero, so that the operating parameters decreased significantly, the dust collection effect deteriorated significantly, this phenomenon is known as corona occlusion. The main reasons for this are as follows:
1) the concentration of dust in the flue gas is large. According to our observation for many years found that: three-phase electric precipitator sometimes due to different coal quality dust concentration is large, electric precipitator current and voltage are affected to different degrees, (especially the first and second current drop is especially obvious) under the ash bucket amount is very large, the dust collection effect deteriorates; the same conditions of the electric precipitator, do not make high-voltage microcomputer electronic control system and vibration of microcomputer electronic control system of any adjustments, and sometimes the current and voltage is very high, under the ash bucket amount is normal, indicating that the flue gas concentration of dust is high, the dust bucket amount is very high, and the dust bucket amount is very high. Normal, indicating that the concentration of dust in the flue gas has a great influence on the operating parameters of the electric precipitator.
2) The increase of flue gas flow rate (electric field wind speed) will also produce corona occlusion phenomenon in different degrees. The third phase of the design of the electric precipitator flue gas flow rate of 1.159m/s, if the flue gas flow rate exceeds this parameter, it will certainly affect the operation of the current and voltage increase. The ESP is operating under negative pressure, when the joints of the body are not sealed tightly and leakage, cold air will enter the electric field from the outside, so that the flue gas flow rate through the ESP increases, then the amount of soot staying in the electric field in each unit of time increases, and thus corona occlusion phenomenon occurs to varying degrees, which worsens the operating parameters.
In order to reduce the impact of the concentration of dust in the flue gas, a few years ago, the use of overhaul will be three phases of the electric precipitator corona line from the sawtooth line to the awned line is suitable for capturing high concentrations of dust, after the transformation of corona occlusion phenomenon is significantly reduced; but with the recent years of the dust collector body aging, dust collector to the overhaul cycle due to other reasons and can not be arranged in time for the overhaul, the leakage of air increased failure to thoroughly manage, leading to corona occlusion phenomenon has increased, operation of the secondary current sometimes obviously. Increase in the operation of the secondary current is sometimes significantly reduced, and even make the current tends to zero.
2.4 boiler exhaust temperature and pressure on the impact of operating parameters:
The temperature and pressure of the flue gas affects the corona starting voltage, corona corona electrode surface electric field strength, corona electrode near the space charge density and molecular ions of the effective mobility, etc., temperature and pressure on the performance of some of the impact of the electrostatic precipitator can be analyzed through the flue gas density ò change.
ò=ò0 * T0/T *P/P0 (kg/m3)[4]
ò0--Density of flue gas at T0 and P0 (kg/m3)
T0--Temperature of standard state ( 273 k)
P0--Atmospheric pressure at standard state (101325pa)
T--Actual temperature of flue gas (k )
P- - the actual pressure of the flue gas (pa)
From the above formula: ò parameter with the increase in temperature and pressure decreases and decreases, when ò decrease, corona starting voltage, corona
corona electrode surface electric field strength and spark discharge voltage and so on should be reduced, resulting in the rise of the secondary voltage can not be up. This is because: when ò reduce the effective mobility of ions due to the number of collisions with neutral molecules and increase, because in the case of a certain amount of applied voltage, which will lead to a decrease in the space charge density near the corona electrode and dust collection electrode of the average current increases. The decrease in space charge density near the corona electrode leads to a certain corona current at the surface of the corona electrode with a lower electric field strength, so when ò decreases, in order to maintain a certain average corona current density on the anode plate, the applied voltage must be reduced, resulting in a decrease in operating parameters.
Shenyi three-phase boiler exhaust temperature can reach a maximum of 180 ℃ or so, and the optimal operating temperature of the dust collector is 140 ℃ -150 ℃, in this high temperature operation will have a direct impact on the secondary voltage of the dust collector and the secondary current rise. And the flue gas pressure after previous tests have little effect, so reduce the boiler exhaust temperature is conducive to improve the operating parameters of the electric precipitator.
2.5. High-voltage short-circuit impact on operating parameters:
High-voltage short-circuit directly affects the operating parameters of the electric precipitator, the occurrence of a high-voltage short-circuit, the secondary current I2 rises, the secondary voltage U2 = 0, the corresponding electric field loses the role of dust removal, in order to prevent the short-circuit current burned out of the electric field or damage to rectifier transformer, the corresponding control cabinets must be tightly shut down, can be seen: high-voltage short-circuit impact on the operating parameters of the electric precipitator Parameters of the electric dust removal operation is the most influential. High voltage short circuit phenomenon and the reason mainly has the following aspects:
1) the operation of the electric precipitator when the secondary current I2 rise, secondary voltage U2 drop (sometimes U2=0) there is a major suspicion of high-voltage short circuit; when I2.U2 change value is not large, it is due to the flue gas conditions changed, resulting in the load aggravation, resulting in the external circuit of the voltage drop is reduced, or due to the rectifier variable secondary Output tap position is not appropriate and the electric field insulation is reduced, at this time should be from the electric field body to find out the cause of insulation reduction, adjust the boiler operating conditions, or change the rectifier variable secondary tap position.
2) when the U2 decline is large, the secondary ammeter, secondary voltmeter reverse swing, that is, the secondary voltmeter instantly down to zero, and the secondary ammeter instantaneous large rise, this time is due to the body of the cathode field within the cathode line or anode plate fracture or weld, the anomaly of the distance between the flue gas flow conditions in the small and large, or even a short-circuit (at this time, the I 2 to the table head, U2 = 0) the rectifier noise Large and small, high temperature rise, from the point of view of equipment safety should stop the high-pressure cabinet operation, to be stopped after the furnace to deal with the body of the electric precipitator.
3) I2 is larger than the normal value, U2=0 needle no swing, the reason is mostly:
(1) electric field pole plate, pole line completely short circuit or ash accumulation short circuit, high voltage cable breakdown to ground.
(2) the electric field or cathode insulation vase serious moisture or water insulation is reduced or even to 0, water so that the cathode absolute boom in the operation of the discharge and carbonization of the complete loss of insulation, resulting in a high-voltage short circuit. High pressure vase rupture.
(3) transformer failure.
Shenyi three electric dust due to the aging of some of the equipment, in the operation of the electric field insulation is often low, or even zero or high-voltage cable aging to the ground breakdown phenomenon, a serious impact on the current and voltage parameters in the operation of the electric dust, the urgent need to take advantage of the overhaul of some of the equipment replacement.
2.6 microcomputer control cabinet operating environment and dust collector boosting variable capacity is insufficient on the operating parameters:
Microcomputer control cabinet of the surrounding environment directly affects the microcomputer internal electronic control components can be correct implementation and feedback control, if the electronic control components set too much ash, will inevitably affect the heat dissipation caused by the temperature rises, which mistakenly send signals, a serious impact on the current and voltage parameters in operation. Parameters. Due to the poor sealing of the distribution room during the commissioning and installation, a large amount of dust enters into the distribution room during the operation of electric dedusting, which seriously affects the correct action of the microcomputer control system. Although the regular cleaning has been strengthened, it is far from meeting the needs of microcomputer operation. At present, in addition to #5 electric dedusting distribution room by overhaul and transformation of the environment has improved significantly, #6, #7, #8 electric dedusting distribution room environment in operation is still very bad, urgent need to completely rectify the seal.
The boosting transformer of the electric precipitator has a great influence on the operation parameters, because the mechanical part of Shenyi electric precipitator is made by Czech Republic, while the electric control cabinet and boosting transformer are made by East Germany, and the design did not carry out the strict matching calculation, the dust collection area of the electric precipitator is too large, which is equivalent to that of the electric precipitator of the domestic 300,000 units, and the boosting transformer's capacity is relatively small. When the capacity of the step-up transformer is large enough, the load change has little effect on its output voltage, on the contrary, if the capacity of the step-up transformer is insufficient, the load change has great effect on its parameters. Due to the design of the step-up transformer is not matched with the capacity of the body and the capacity of the step-up transformer is small, so when the current rises, the transformer itself rectifies the silicon pile, the resistor
nylon resistance and the high-voltage cable have great pressure drop, which reduces the voltage of the electric field, so that the voltage and current cannot rise, and the voltage and current cannot rise. Voltage and current can not rise, the parameters can not reach the rated requirements.
The solution is: widen the pole distance, reduce the dust collection area, (#5, #8 dust collector to implement) but this method is also limited by the maximum allowable transformer voltage, the voltage reaches the rated 55KV, the transformer has been overcurrent. Therefore, the fundamental solution is to replace the large-capacity step-up transformer.
3. Conclusion: Through the above analysis, it can be seen that the main reasons affecting the current Shenyi three electric precipitator operating parameters are:
Dust specific resistance. High exhaust temperature.
Part of the pole plate, pole wire corrosion, deformation, spacing change.
Vibration of large strength is not enough.
High-voltage cable aging; wear and tear of the body leakage; part of the insulation box leakage, leakage of rain, insufficient insulation.
The capacity of the boosting variable is insufficient, and the operating parameters do not reach the rated value.
Distribution room sealing is not tight, microcomputer operating environment is poor.
4. Measures and countermeasures: The measures and long-term countermeasures that should be taken for the current situation are:
Selecting the right kind of coal and burning it reasonably, reducing the temperature of exhaust smoke.
Use the opportunity of overhaul to replace corroded and deformed pole plates, pole wires and unqualified high-voltage cables, completely eliminate air leakage, and put in the heat preservation box heating. Completely solve #6, #7, #8 distribution room sealing problem.
All adopt wide pitch, double side vibration transformation (#5, #8 has adopted wide pitch, #6 has adopted double side vibration). Replacement of large-capacity step-up transformer or the use of high-voltage pulse power supply.