Roots Blower It is a positive displacement compression fan, the core component of which is a rotor system including a driving shaft, a driven shaft, an impeller and a gear. It has been widely used in many fields such as petrochemical, electric power, smelting, food and sewage treatment due to its simple structure, no need of lubricating oil in the fan cavity, and smooth operation. Roots blower is one of the key equipment of the wet desulfurization process in power plants. When the limestone gypsum wet desulfurization method is adopted in the boiler system of thermal power plants, most of the Roots blower is used to blow sufficient air into the absorption tower to oxidize calcium sulfite in the slurry of the absorption tower, so as to generate calcium sulfate dihydrate that is easy for post-treatment. The stability of Roots blower operation directly affects the normal operation of the desulfurization system and the emission of environmental protection standards.
The three blade Roots blower produced by Changsha Blower Works is adopted. The model is ASF300, the rated current is 49.4A, and the setting temperature of bearing online monitoring tripping is 98 ℃. In actual operation, the current of Roots blower is 43A, which is higher than its long-term normal operation value (30~32A). In winter, the room temperature is low, and the Roots blower operates well (when the room temperature is 5 ℃, the front bearing of Roots blower is about 80 ℃). In summer, when the room temperature reaches above 30 ℃, the front bearing of Roots blower exceeds the set tripping temperature as the room temperature rises. In order to avoid tripping, the crew added spray water on the casing to cool down as an emergency treatment measure, but the sanitary condition was poor during operation, which did not fundamentally solve the problem.
Disassembly inspection In order to fundamentally solve the problem of high current bearing temperature of Roots blower, we carried out disassembly inspection. Before the disassembly inspection, we found the causes from the blower itself and speculated that there might be the following four possibilities: (1) The internal clearance of the fan changes, and the impeller may have slight friction with the wallboard, which leads to high fan output and high current, and the heat generated by friction is transferred to the bearing, leading to bearing heating;
(2) The bearing itself has problems;
(3) The large clearance fit between the bearing and the shaft as well as the bearing chamber causes serious heating;
(4) The quality of lubricating oil in the bearing chamber is poor, and the oil film cannot be formed during the high-speed operation of the bearing. The bearing roller has slight dry friction, which causes serious heating.
After disassembly, the comparison with the speculation is as follows:
(1) The internal clearance of the fan has changed since the last overhaul. The clearance between the driving impeller and the front wall panel is 0.30mm, less than 0.40~0.60mm. There are slight friction marks on the front wall panel, which may cause bearing heating;
(2) After disassembly, the quality of the bearing is good, no wear of rollers and raceways is found, and the cage is intact without wear. The cause of the bearing problem is eliminated;
(3) The fitting part between the shaft and the inner ring of the bearing is severely worn, and the shaft and the inner ring of the bearing have become a clearance fit with large clearance, which may cause heating;
(4) The oil level in the bearing chamber is relatively high. When the grease is discharged for inspection, it is found that the color of the grease is relatively black. It is judged that the bearing has a high temperature for a long time, and the grease is liable to deteriorate at high temperatures. The lubricating performance of the deteriorated grease will decline, which can further cause bearing heating and form a vicious cycle. After checking the fan impeller, it is found that the impeller is in good condition without signs of wear. Considering that there is no dynamic balancing machine, due to limited conditions, it is reinstalled without dynamic balancing test; After the inspection of the fan gear, it was found that the original material of the gear was 20CrMnTi alloy steel, the material was good, the gear was not worn or broken in use, and the gear was not adjusted; There is an oil slinger at each bearing in the oil tank of the bearing chamber, which is fixed at the end of the impeller. With the rotation of the shaft, the oil is thrown onto the bearing to fully lubricate the bearing. Two oil slinger plates are damaged, and two oil slinger plates are made again with 3mm thick steel plates according to the original size of the oil slinger plates;
Check the locking plate of the fan bearing locking nut. It is found that the locking plate has been used for many times and has failed to prevent the locking nut from loosening. To prevent the bearing locking nut from loosening during operation, replace all the failed locking plates; Check that there is a lot of water rust in the cooling water pipe of the oil tank shell of the bearing chamber, inject dilute oxalic acid solution after shaking it, pour out oxalic acid after it fully reacts, inject fresh water again, clean it, and ensure that the cooling water loop is unblocked. 2 Preliminary treatment 2.1 The treatment scheme sprayed the bearing wear. After spraying, the bearing inner ring and the shaft had a tight fit of 0.02 mm. Although the bearing was not damaged, from the perspective of long-term operation, two sets of FAG manufacturer's C0 clearance 22224 bearings and two sets of NU324 bearings were replaced. The grease inside the bearing chamber was replaced again. After enduring long-term high temperature, There was aging phenomenon, and all of them were replaced with fluororubber materials to ensure that no lubricating oil leakage occurred during operation, and the internal clearance of Roots blower was readjusted.
