Prevention and Treatment of Mist Eliminator Faults - 【 Industry Recommendation 】

July 29, 2023

At present, due to various factors, the frequent failure of the wire mesh mist eliminator causes a large amount of slurry to corrode the chimney and block the clean flue. The large amount of liquid droplets (gypsum rain) emitted from the flue gas seriously endangers the surrounding environment, becoming an urgent problem for flue gas desulfurization in coal-fired units. This article uses system safety analysis methods based on the phenomenon and data of malfunctions in the mist eliminator, analyzes the failure modes of the mist eliminator, and proposes preventive measures to further improve the reliability of the desulfurization system and ensure the operation effect of the flushing system.
Properly shorten the flushing cycle of the mist eliminator and optimize the flushing process. The upward spray frequency of the lower mist eliminator can be increased, while the upward spray frequency of the upper mist eliminator should be reduced. The remaining water should be added to the lower spray of the lower mist eliminator to ensure that the mist eliminator is washed clean. Ensure the flushing water pressure and flow rate, increase the flushing water pressure of the mist eliminator appropriately to around 0.3MPa, and consider the minimum recirculation flow rate; Pressure and flow measurement points are set in the front main pipe of the mist eliminator flushing valve, and flow measurement points are set in the process water outlet main pipe to facilitate monitoring and detection of valve leakage and mist eliminator flushing effect, improving the reliability of the flushing system

Regularly inspect the flushing water valve and electric actuator of the mist eliminator to prevent internal leakage of the valve. For desulfurization devices with flushing water mechanisms located outdoors in cold northern regions, it is necessary to provide external insulation for the flushing platform to improve the reliability of valve and actuator operation

Ensure operating parameters. Improve the operation efficiency of the absorption tower, strengthen the maintenance of the pressure difference gauge of the mist eliminator, optimize the design or replace the pressure difference transmitter of the mist eliminator, and calibrate it regularly. Accurately monitor the changes in the pressure difference of the mist eliminator, and take effective measures in a timely manner if the pressure difference increases to prevent scaling, blockage, and other phenomena of the mist eliminator

Maintain an appropriate operating pH value. An appropriate pH value of the slurry can ensure normal desulfurization efficiency and fully utilize the limestone slurry. The pH value of the absorption tower slurry is maintained between 5.2 and 5.5, resulting in the highest desulfurization efficiency. Excessive limestone slurry input will not only improve the desulfurization efficiency, but also will not fully neutralize limestone due to the H+, H, and SO - generated after SO2 hydration reaction in the reaction, which will increase the solubility product of Ca2+, SO2-, and SO2- in the slurry and the slurry supersaturation, which will aggravate the blockage of the demister, waste limestone, and increase the operating cost. Improve the oxidation degree of Calcium sulfite, reduce the mass fraction of slurry in the absorption tower, strictly control the mass fraction of slurry in the absorption tower, further reduce the mass fraction of slurry in the absorption tower, and control the mass fraction of slurry within 20% on the premise of ensuring the desulfurization efficiency. Reduce the amount of limestone slurry added to the absorption tower, and the slurry concentration supersaturation is high, which will lead to serious scaling

Reduce smoke and dust content. To strengthen the operation adjustment of the dust collector, it is necessary to strictly control the concentration of smoke and dust at the inlet of the desulfurization system. Try to use the designed coal type as much as possible, control the amount of high sulfur and high ash coal. If the coal type is mixed, it is necessary to do a good job in coal mixing and reasonable mixing to prevent centralized combustion of coal with significant deviation from the designed coal quality, and lay the foundation for the safe and stable operation of the desulfurization system. After canceling the flue gas bypass, the desulfurization system and the unit must operate synchronously. As a key component of the absorption tower system, the mist eliminator is more prone to malfunctions and requires high reliability. Using the FMEA system analysis method to analyze the causes, consequences, detectability, frequency, and measures of faults in the mist eliminator, monitoring key points during operation and maintenance, forming early warning and monitoring projects for equipment failures, faults, and other influencing factors in prediction, and proposing targeted preventive measures to comprehensively improve the reliability of the mist eliminator operation and avoid non shutdown accidents