Effect of flue gas performance and flue gas conditions on the performance of the dust collector
The effect on the electrostatic precipitator
Electrostatic precipitator is the use of dust particles charged in the electric field, and under the action of the electric field force to the principle of dust collector to achieve the purification of flue gas.
1 dust than the resistance. The dust specific resistance refers to the resistance value of the gray layer per unit area and unit thickness. Dust specific resistance is an important factor affecting the dust collection efficiency of the electrostatic precipitator. According to the degree of difficulty of dust collection by electrostatic precipitator, there are three kinds of specific resistance types: high, medium and low. Low- and high-specific resistance dusts are regarded as difficult dust collected by electrostatic precipitators, but the mechanism of influence is different. Low specific resistance dust particles have good conductivity, and once they reach the surface of the collector plate, the negative charge they carry is immediately released. Due to electrostatic induction, a positive charge of the same polarity as the dust collector is obtained. If the repulsive force formed by the positive charge is greater than the adhesion force of the dust particles, the precipitated dust will fall out of the dust collector plate and return to the air flow. When the dust particles of the re-flow air current collide again with the anions in the space, the secondary charge moves back to the dust collection pole. Dust particles move back and forth in this way, forming a jump on the collecting plate, and finally they may be carried out of the electrostatic precipitator by the airflow. High specific resistance dust due to the high specific resistance, dust particles deposited on the dust collector discharge process is very slow, the voltage drop in the dust layer is very large, when the voltage drop reaches a certain level, an abnormal phenomenon occurs, causing the gray layer to hit Wear, and generate spark discharge, the so-called anti-corona phenomenon, the formation of a large number of cations in the dust collector and the material layer, neutralize the oncoming anions, so that increased power consumption, dust removal efficiency is reduced, or even not work. The negatively charged medium-specific resistance dust particles reach the precipitation plate, and the neutralization proceeds at a proper speed, and the dust collection efficiency is high. The middle resistivity is the most ideal area for the dust collector to operate. In this area, the dust collection efficiency is basically not affected by the specific resistance value.
2 The effect of dust properties. Influence of chemical composition of dust: As the content of silicon, aluminum, and calcium in dust increases, the specific resistance increases; the content of alkali metal and iron (Fe3O4) such as potassium and sodium increases, and the specific resistance decreases. Adhesion of dust: High dust adhesion, difficulty in rapping and dust removal, low adhesion, loose ash, and easy secondary dust. The effect of dust particle size: The larger the particle size of the dust, the higher the particle’s gravity, the higher the settling velocity, and the smaller the adhesion, resulting in higher dust collection efficiency. Effect of dust density: The higher the density of dust, the higher the gravity of the particles, the higher the settling velocity, and the higher the dust collection efficiency. The influence of the dust concentration of flue gas: the dust concentration of the flue gas is too high, resulting in corona closure, affecting the performance of the electrostatic precipitator, the dust concentration of the flue gas is too low, the dust is not easy to collect, the concentration is too high or too low, the electric field The dust collection efficiency is reduced, and high-concentration electrostatic precipitators in the kiln will collect 40% to 50% of the dust before entering the electric field.
3 The effect of smoke conditions. The effect of smoke humidity: Smoke humidity mainly affects dust collection efficiency by affecting specific resistance of dust and affecting spark discharge, voltage and volt-ampere characteristics. The water content in smoke increases, the dew point rises, and the specific resistance of dust decreases. The efficiency of the dust collector increases; at the same corona voltage, the corona current decreases as the moisture content of the flue gas increases. Effect of flue gas temperature: When the dust is around 180°C, the specific resistance is the highest. The specific resistance of the dust will drop if the temperature is too high or too low. When the temperature is higher than 250°C, the specific resistance will drop sharply with the temperature rise, and is lower than 100°C. The specific resistance will decrease sharply with decreasing temperature; the temperature of flue gas increases, the breakdown voltage of dust layer decreases, and the efficiency of dust remover decreases; the temperature of flue gas rises, the viscosity of flue gas increases, and the dust escapes from the flue gas and drives it to the collector pole. The flow resistance rises and the drive speed drops. Influence of smoke composition: The content of SO2, O2, H2O, and CO2 in the flue gas is high, which has a favorable effect on the blooming of the discharge electrode.
Impact on bag filter
The bag filter removes gas and dust from the dust-containing gas through the filter bag. The dust is trapped on the outer (inner) surface of the filter bag. The clean gas is collected and discharged to complete the filtration process of the dust-containing gas.
1 Dust affects the resistance. The dust specific resistance has no effect on the collection efficiency of the bag filter.
2 Effect of dust properties. Influence of dust chemical composition: The change in specific resistance due to the different chemical composition of dust has no effect on dust collection efficiency. Adhesion of dust: High dust adhesion, difficulty in dust removal from filter bags, increased cleaning kinetic energy, filter bag life, low adhesion, loose ash, and easy secondary dust. Effect of particle size of dust: The larger the particle size of the dust, the higher the particle’s gravity, the higher the settling velocity, the smaller the adhesion, and the higher the dust collection efficiency. The fine particles with a very small particle size are easy to pass through the filter bag, filter bag, and flower plate gap. . The true density of dust affects: The greater the true density of dust, the higher the particle’s gravity, the higher the settling velocity, and the higher the dust collection efficiency. The influence of the dust concentration of flue gas: The dust concentration of flue gas has no obvious effect on the dust collection efficiency of the bag filter. The bag dust collector reduces the flue gas concentration through pre-dust collection, which can reduce the number of filter bag cleaning and reduce the resistance of the filter. , extend filter bag life.
3 Influence of smoke conditions. The effect of smoke humidity: The humidity level changes the dew point of the flue gas. The high dew point can easily cause condensation, paste bags, and increase resistance. Effect of flue gas temperature: The effect of flue gas temperature depends on the temperature resistance of the filter bag. Effect of smoke composition: Smoke composition has no effect on filtration performance.
Comparison of smoke pretreatment measures
The use of an electrostatic precipitator requires depth conditioning of the flue gas. The specific resistance is not within the proper range and the flue gas should be tempered. The most common and most practical method for conditioning the flue gas from the cement kiln is to spray water mist into the flue gas to reduce the flue gas temperature and avoid the high specific resistance temperature zone. The kiln flue gas should be reduced from 350°C to the optimal temperature of 110°C～150°C suitable for the operation of the electrostatic precipitator.
The use of a bag filter only requires cooling of the flue gas. Although it is also possible to use a water spray mist when using a bag filter, the purpose is only to reduce the temperature, without considering the specific resistance. Glass fiber filter bags can withstand long-term temperature of 260 °C, cooling water consumption less than half of the electrostatic precipitator. Cooling methods include air heat exchanger cooling, cold air cooling, and water heat exchanger cooling.
The running resistance comparison
The electrostatic precipitator has low and stable operating resistance. The operating resistance of the electrostatic precipitator is <300Pa, and the resistance is stable over a long period of time, which is not affected by the cleaning factor.
The bag filter has a high resistance. The development of pulse jet cleaning technology and the promotion and application of high-performance high-temperature resistant filter media have greatly reduced the resistance of bag filter. The resistance of the bag filter of pulse jet kiln bag is less than 1000 Pa. The cleaning effect affects the resistance.
The realization of “zero emission” is easy
It is very difficult for electrostatic precipitators to achieve zero discharge. In an electric field, the finer the particles, the lower the probability of being trapped due to turbulent gas perturbations, and can easily escape from the electrostatic precipitator. The dust particles in the kiln flue gas are fine, and the fine particles less than 10 μm account for about 60%. Although the electrostatic precipitator is an efficient dust collection device, its dust collection efficiency is in an exponential relationship with the area of the dust collector plate. A three-electric field electrostatic precipitator has 80% to 90% of its dust collecting efficiency in the first electric field, and the second three electric fields only collect 10% to 20% of the dust content. In order to achieve a low value of less than 30mg/Nm3 Emission density requires the addition of a fourth-fifth electric field or a large increase in plate area in the electric field.
Bag filter is easy to achieve “zero discharge.” The bag filter removes high-efficiency filter materials, lowers the filtering speed, and improves processing accuracy to improve dust collection efficiency. Although the kiln flue gas contains a large number of fine particles, the use of pulse bag filter can completely control the emission concentration. 10mg/Nm3, close to “zero discharge”.
Prevention and protection measures for accidental discharge
Effect of excessive CO in flue gas:
1 The electrostatic precipitator needs shutdown protection. A CO sampling and analysis system shall be installed at the entrance of the electrostatic precipitator to check the flue gas. If the CO content of the kiln flue gas exceeds 2%, an alarm shall be issued to notify the watchman to take measures when the CO content exceeds 2.5%. At that time, the high-pressure silicon rectifier should be closed to prevent the CO content from exceeding the standard smoke from exploding in the electrostatic precipitator. In a few hours after the ignition of the rotary kiln, the incomplete combustion of fuel often stops the CO content in the kiln exhaust gas from exceeding the standard and stops sending power to the electric field. This situation is accidental discharge.
2 bag filter does not need protection. Excessive CO content does not affect the bag filter and does not require installation of a CO sampling analysis system.
3 Failure of the electrostatic precipitator caused by a failure of the power supply or high-voltage line. When the power supply of the electrostatic precipitator fails to transmit power to the electric field or when the insulator in the high-voltage line trips due to condensation due to “climbing,” etc., the electric field that is not delivered with high voltage is only a passage and is also an accident discharge.
The 4 bag filter caused excessive discharge due to bag breakage. Due to aging, mechanical damage, etc., it can cause bag breakage and cause excessive discharge. The bag filter can measure the bag room where the bag is broken by installing a differential pressure meter.
