Fan Facts - Large induced draft fan impeller balancing problems and countermeasures
First, the main causes of the impeller wheel imbalances unbalanced in use can be briefly divided into two types: the impeller and impeller fouling wear. Resulting in both cases with the induced draft fan before dusting installations connected, dry dust removal device causes the impeller to wear the main reason for the imbalance, while the effects of wet dust collector impeller fouling the main causes for the imbalance. Are described below. 1. The wear of the impeller, although the dry dust removing device removes a majority of large particles of dust in the flue gas, but a small number of large particles, and many tiny dust particles along the high temperature, high speed together with the flue gases through the fan, the blades subjected to the continuous constantly scour. Over time, the formation of the blade-like abrasion at the exit leaves. Due to this irregular wear, resulting in an imbalance of the impeller. Further, the surface of the impeller at a high temperature is easily oxidized to form thick oxide scale. These combined forces with the impeller surface oxide is not uniform, some of the effects of scale by vibration or centrifugal force will automatically fall off, which is a cause wheel imbalance. 2. Impeller fouling by wet dust removal device (Venturi Water ESP) cleaned flue gas humidity great, although not in addition to the net of dust particles is small, but a large viscosity. When they are through the fan, in the role of gas vortices will be attracted to the non-working surface of the blade, especially the more serious dust fouling formation in non-face at the entrance and exit, and gradually thickening. When part of the grime off the joint action of the centrifugal force and vibration, balancing the impeller is destroyed, the entire draft fan will produce vibration.
Second, to address the imbalance impeller measures 1. Solution impeller wear on the impeller dry dust caused by wear and tear, in addition to improving the effect of dust precipitator, the most effective method is to increase the impeller wear resistance. Currently, this more sophisticated approach is to thermal spray technology, that means with a special abrasion resistant, high temperature resistant metal or ceramic materials such as a high temperature, high-speed stream of particles is sprayed onto the surface of the impeller blade to form a layer over impeller wear-resistant material itself, a much higher temperature and oxidation resistance of super coat. This will not only reduce the wear and tear caused by the destruction of the impeller balancing, but also reduce the oxide layer caused by an imbalance problem. Selection draft fan, the dry dust should be preferred thermal spray process through the impeller. Use the spraying process without overheating wheel when equipment maintenance, consider impeller thermal spraying. Although this will increase the impeller manufacture or maintenance costs, but to improve the life of the impeller l ~ 2-fold, extending the induced draft fan overhaul cycle. Thereby reducing operating costs induced draft fan and the entire production system, the overall efficiency is very good. 2. Solve impeller fouling (1) spray cleaning: This is a common cleaning methods, sprinkler system installed in the induced draft fan casing, by pipeline, three nozzles (one located at the outlet of the impeller, 2 is located at the entrance) and drainage hole components. Water is generally water pressure of about 0.3MPa. This method is usually still valid. The disadvantage is a longer time for each stop cleaning, descaling several times per month shutdown. Affect the normal use of the unit. (2) high-pressure gas cleaning: The system uses a similar structure with a sprinkler system, but its pipeline of high pressure pipelines, special nozzles and high pressure gas source. This means the blade is fast and effective cleaning, it can be normal in the gaps induced draft fan shutdown, open the high-pressure gas source, only tens of seconds of time to complete cleaning. Because of simple operation, many times a day can not only solve the artificial cleaning laborious, time-consuming problems, but also significantly reduce the production cost of the entire unit. The question is whether the user has a ready-made high-pressure gas source (pressure between 0.8 ~ 1.5MPa, you can use compressed air or nitrogen), otherwise, you need a dedicated high pressure compressor equipment. (3) continuous purge stream cleaning: From a structural perspective, continuous purging device requires no external gas source, which uses exhaust pressure induced draft fan itself, a small amount of smoke (1% to 2% of the rated air volume) from directed to specific internal primer fan nozzle which is located in the import of the impeller, at high speed the flue gas onto the non-working surface of the blade cough, which is continuously purged, it in turn with the induced draft fan starts, Not only will just stick to blow off the dust on the leaves, but also to prevent dust deposition thickened and no downtime cleaning. Wheel balancing machine which is simple structure, small volume changes induced draft fan, anti-fouling effect is very good, is a useful development of new technologies.