Reason condensate pump thrust bearing temperature analysis and processing
Analysis of the condensate pump bearing temperature of the reasons put forward appropriate countermeasures, and achieved satisfactory results. Keywords: thrust bearing high temperature treatment of two 125MW units in Changxing Power Plant a total of four sets of 12NL-160 type condensate pumps are vertical multistage centrifugal tube bag. Manufactured by Shanghai water pump factory. Its design and technical specifications flow Q = 355m3 / h, head H = 158m, speed n = 1500r / min. 4 condensate pumps in operation since 1992, the year of the hot season, appear to be bearing return oil temperature close to or above 70 ℃ phenomenon, caused by wear of thrust bush, serious or even bush-burning. Often forced to switch to the backup pump to run, and even affect the normal operation of the entire unit. Especially when in March 1999, bearing return oil temperature is as high as 68 ℃. The ambient temperature was only about 20 ℃, the temperature rise of up to 48 ℃, more than the normal requirements of manufacturers. Therefore, these pumps a detailed examination, and made improvements, and achieved good results. 1 Cause Analysis and Countermeasures since the existence of fault from the production after, and after overhaul failed to eliminate, so you can rule out the causes and factors of the equipment itself caused overhaul. After analysis of the following two reasons: (1) the difference between the pump bearing cooling effect of the pump bearings lubricated by the oil cooling, oil cooler and through the built surface cooling. The cooler material is copper, a cooling medium is circulating water. Poor cooling effect there are two reasons. First, the wall surface cooler fouling, poor heat transfer. Second, the small amount of cooling water. Replace the cooler can be taken to improve the cooling water and the cooling water pipe diameter increases pressure and methods for these two points, respectively. (2) the pump thrust bearing actual stress too much bearing temperature rise is mainly due to the thrust plate and thrust tile caused by friction. The size of this friction force depends directly on the force of the thrust bearing. Temperature description of thrust bearing force is too large. So make the bearing temperature drop should try to reduce the stress on the thrust bearing. Since the water pump is unidirectional, the pressure lower than the pressure of the suction side of the impeller side of the drain, thereby generating a pressure difference, toward the suction side is formed on both sides of the impeller of the axial thrust. Jointly borne by the axial thrust balance drum and thrust bearings. Therefore, by increasing the force and reduce the balance drum impeller axial thrust of ways to reduce the force of the thrust bearing. Balance drum works by generating a pressure differential across the impeller opposite direction of the force to balance the axial thrust generated by the pump. It is calculated as follows: F = 10 Pπ (R2-r2) where P- pressure, m; R- balance drum outer diameter, cm; r- balance drum inner diameter, cm. As can be seen from the formula, as long as the increase in the balance of the outer diameter of the drum can be achieved to increase the role of axial thrust. An apparatus according to their own circumstances, you can insert the original balance drum outside a circle, the outer diameter increases 12mm, 561 kg theoretical increase endurance. Pressure pump axial thrust formed on both sides of impeller calculated empirical formula is: F = 9.8 nkH1γπ (R12-R22) where F- pump axial force, N; n- number of pump impeller; H1 - Single-stage head, m; severe γ- liquid, kg / m3; R1- mouth ring radius, m; R2- water pump impeller hub radius, m; k- coefficient ratio transfer speed and experience related. As can be seen from the formula, as long as the reduced lift H1, you can decrease the axial thrust. We have carefully checked the actual operating parameters of the pump, we found slightly higher 19.6 kPa head than the design value, the flow in the unit full load conditions still margin. Thus, the car can take a small impeller method for reducing the outlet pressure of the pump impeller according to the law of turning, thereby reducing the axial thrust of the pump. The pump has five impellers, in order to avoid a greater impact on the pump flow, small car last stage impeller. The calculation is as follows :( pump outlet pressure decreases 19.6 kPa) First calculate the ratio of the speed of the pump: where D '= 334 mm; turning to be met after H'- pressure, m; impeller diameter D'- after turning, mm; D- original impeller diameter, mm; impeller diameter D should be turning quantity, D-D '= 345-334 = 11 mm; can consider turning 10 mm. The effects of the implementation of the method to be implemented later in the overhaul, respectively, before and after the implementation of several methods was not as effective. One method, which is a small rear wheel, put into operation from the point of view, better results after take. There was no significant change in the flow rate, and head down to 155m, the current drops from the original 340 A 330A, can fully meet the needs of the unit running at full capacity. In July and August during the high temperature, the ambient temperature is 35 ℃, bearing oil temperature is only 56 ℃. Temperature 19 ℃, fully meet the requirements of not greater than 25 ℃ specified by the manufacturer. Under the premise to ensure the normal operation of the pump, but also improves the pump's economy.
