Applications of fault diagnosis technology in catalysis

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Applications of Fault Diagnosis Technology in Catalysis I. Introduction A heavy oil catalytic cracking plant with an annual production capacity of 500,000 tons is equipped with over a hundred types of rotating equipment. Ensuring the safe and reliable operation of equipment is of great significance for maintaining safe production and, thereby, helping to achieve our company’s economic targets. During their routine inspections, equipment managers have traditionally relied on conventional inspection methods—such as looking, listening, and touching—to determine the location and severity of faults based on experience. However, it is often difficult to draw accurate conclusions using experience alone in order to precisely identify the location, nature, and cause of faults. With the improvement of our company’s equipment management techniques, especially after introducing the theory and instruments for vibration analysis of equipment failures, through study and practical application, we have come to realize that combining traditional empirical diagnosis with modern instrumental testing and diagnosis holds great significance and practical value in enhancing the equipment management level of the catalysis plant. We have applied simple fault diagnosis techniques, which have yielded significant results in identifying the causes of equipment failures and guiding maintenance work. II. Simple Fault Diagnosis: We use the DZ-5 vibration analyzer for simple fault diagnosis. In other words, by measuring the displacement, velocity, and acceleration of vibrations in rotating equipment and analyzing the test data, it is possible to determine whether the equipment is in a normal, abnormal, or faulty state based on the relationship between the values of the characteristic parameters and the predetermined limits ； The concept of simple diagnosis involves identifying the cause of a fault by analyzing its characteristic frequency, determining the location of the fault, and providing a reference for maintenance work. III. Practical Cases 1) Failures caused by misalignment of equipment couplings: On July 10, 2006, abnormal vibration of pump 210 was detected during routine inspections. Pump 210 is an oil-sealing pump, model: DYII12-50×3, speed: 2950 rpm. The test data is as follows: Front bearing, Rear bearing – P1(S) P1(V) P1(G) P2(S) P2(V) P2(G). Before maintenance: Horizontal direction: 0.1 mm, 24 mm/s, 16 m/s2; Vertical direction: 0.054 mm, 19 mm/s, 15 m/s2. Axial direction: 4 mm/s, 6 m/s2. After maintenance: Horizontal direction: 0.074 mm, 10 mm/s, 7 m/s2; Vertical direction: 0.045 mm, 8 mm/s, 5 m/s2. The vibration speeds of the front and rear bearings of this pump are 24 mm/s and 19 mm/s respectively. According to the international vibration standard ISO2372, the maximum allowable value for the vibration velocity of the bearing housings in this unit is 7.8 mm/s; clearly, the vibration levels are well above this limit ； A frequency analysis of the vibration velocity at point P1 revealed that the first harmonic was 10 mm/s and the second harmonic was 17 mm/s. Clearly, the vibration at the second harmonic is the main issue; a high value for the second harmonic is an indication of poor alignment. Therefore, it was determined that the fault might be due to poor alignment of the coupling. After shutting down the machine for inspection, it was found that the coupling sleeve was too tight and stuck, which affected the alignment of the shafting. After dealing with the coupling sleeve, the machine was restarted, and all vibration parameters decreased significantly; the second harmonic value at point P1 was only 2 mm/s, indicating that the repair was effective. 2) Vibration caused by bearing failure: On May 24, 2005, abnormal vibration and noise were detected in pump 201/2 during a routine inspection. Pump 201/2 is a feed pump, model: 100YII-120×2B, speed: 2950 rpm. To determine the cause of equipment failures and provide a scientific basis for maintenance, the DZ-5 vibration analysis instrument was used to diagnose the faults in the unit. The data before and after maintenance are as follows: Front bearing, Rear bearing: P1(S), P1(V), P1(G), P2(S), P2(V), P2(G). Before maintenance: 0.2–0.3 mm, 24 mm/s, 80 m/s²; 0.1–0.2 mm, 16 mm/s, 100 m/s². After maintenance: 0.06 mm, 7.8 mm/s, 3.5 m/s²; 0.04 mm, 5.6 mm/s, 2.8 m/s². According to the international vibration standard ISO-2372, regarding the requirements for measuring vibration values in rolling bearings and their housings, vibration velocity is used to determine whether the vibration levels are within acceptable limits. Per this standard, the maximum allowable vibration velocity for the bearing housings of this unit is 7.8 mm/s. For the bearing at point P1 of the pump, the vibration displacement, vibration velocity, and vibration acceleration are 0.2–0.3 mm, 24 mm/s, and 80 m/s2 respectively; it can be seen that the vibration velocity at point P1 is well above the allowable limit (the standard value being 7.8 mm/s) ； The sharp fluctuations in displacement between 0.2 and 0.3 mm indicate unstable shock phenomena in the bearing ； In particular, the vibration acceleration has reached 80 m/s2. Based on traditional experience, auscultation reveals significant noise from the bearings, and coupled with the substantial increase in vibration displacement and vibration velocity, it can be preliminarily determined that the bearings may have suffered fatigue damage or even severe destruction; therefore, the bearings must be replaced immediately. Otherwise, a \"shaft binding\" failure may occur within a very short period of time, leading to serious accidents. For the bearing at point P2, the analyses of vibration displacement, vibration velocity, and vibration acceleration are consistent with the results obtained for point P1. During the disassembly inspection on May 24, it was found that the raceways of bearings P1 and P2 suffered severe fatigue spalling damage along the circumferential direction, and the surfaces of the balls also exhibited severe spalling. After replacing the bearings, the vibration displacement, vibration velocity, and vibration acceleration at points P1 and P2 all decreased significantly, indicating that the pump is in good operating condition. Below are photos of the damaged bearings in this unit (Figure 1, Figure 2): Damage to the inner ring of the bearing (Figure 1); Damage to the rolling elements of the bearing (Figure 2). 3) Vibration caused by mechanical looseness. On July 25, 2006, routine inspections revealed that the horizontal vibration speed of the front bearing of pump 208/2 was 9 mm/s. Pump 208/2 is a slurry pump, model: BYJ-150/100, speed: 2950 rpm. For the front and rear bearings: before maintenance, horizontal vibration levels are 0.05 mm, 9 mm/s, 4 m/s2; vertical vibration levels are 0.03 mm, 5 mm/s, 2.5 m/s2. After maintenance, the horizontal vibration levels are 0.04 mm, 7 mm/s, 4.5 m/s2; vertical vibration levels are 0.03 mm, 5 mm/s, 2.5 m/s2. Further tests showed that the vertical vibration speeds of the front and rear bearings were actually 24 mm/s and 13 mm/s respectively. According to the international vibration standard ISO-2372, the maximum allowable value for the vibration speed of the bearing housings in this unit is 7.8 mm/s. A frequency analysis of the vertical vibration velocity at point P1 showed that the first harmonic frequency reached 22 mm/s, which is well above the acceptable limit. The common causes of such a high first harmonic frequency include shaft misalignment, shaft bending, and mechanical looseness. Analyze the cause of the fault following the principle of moving from simplicity to complexity. First, check for mechanical looseness: a vibration velocity in the vertical direction that is much higher than that in the horizontal direction is a typical characteristic of mechanical looseness. Therefore, the vibration may be caused by mechanical looseness, and fastening components such as anchor bolts should be inspected carefully. A shutdown inspection revealed that the bolts securing the bearing housing supports were loose; after tightening them and restarting the equipment, the vertical vibration speeds of the front and rear bearings decreased significantly, and the equipment returned to normal operating conditions. IV. Conclusion By using the DZ-5 vibration analyzer for simple fault diagnosis, we collected over 1,000 measurement values and analyzed more than 10 major and minor faults. This enabled us to diagnose abnormal conditions or faults in a timely and accurate manner, providing scientific guidance for maintenance work. It prevented unnecessary repairs, enhanced the reliability, safety, and efficiency of equipment operation, and contributed to the safe and stable functioning of the system.