Cause analysis and modification of the leakage of

2022-08-26
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Cause analysis and transformation of ammonia compressor seal leakage

1. The ammonia compressor seal system is mainly composed of seal oil supply, shaft end seal, waste oil separation and degassing. 1.1 the high-pressure oil from the lubricating/sealing oil pump in the sealing oil supply part enters the mechanical seal at a pressure about 0.6MPa higher than the reference gas after being adjusted by the sealing oil pressure regulator. Then it is divided into two ways, one of which is connected to the annular groove formed by the lantern ring and the shell, and the lantern ring together with the auxiliary mechanical seal static ring is pushed to the left position to separate the working faces of the dynamic and static rings. The other way enters the main mechanical seal chamber, and most of the oil flows directly from the top of the chamber as the oil for lubrication, flushing and cooling of the main mechanical seal. 1.2 shaft end seal: the shaft end seal of our ammonia compressor adopts h-d1/142-kbl mechanical seal produced by Bergman company. The main seal is a double face mechanical seal, and the auxiliary seal is a single face mechanical seal. Its structure is that it realizes the versatility of the universal testing machine, as shown in Figure 2. In normal operation, depending on the seal oil supplied by the seal oil supply system, an extremely thin oil film is formed on the end face of the dynamic and static rings of the main mechanical seal to seal the process gas. When stopping and stopping the sealing oil, the lantern ring is pushed to the right position under the action of the left gas pressure and the thrust of the static ring spring. The dynamic and static rings of the auxiliary mechanical seal are closely fitted to play a sealing role, effectively ensuring the reliable operation of the shaft end mechanical seal under various working conditions. 1.3 the degassed part of the waste oil enters the oil in the main mechanical seal chamber, and a small part passes through the sealing end face of the static ring and the dynamic ring inside the main mechanical seal and enters the cavity B on the reference gas side, which is mixed with the process gas. This part of oil flows into chamber a and is discharged from the bottom of chamber A. After oil-gas separation, it enters the degassing tank, where it is heated to remove ammonia from the dirty oil, and then flows into the main oil tank for recycling. 2. Operation of mechanical seals. The cooperation between Yucheng City and Shandong South University and the principle of "school local cooperation, government support, intellectual support, enterprise singing" were observed. The mechanical seals were replaced four times from the start of the overhaul in 1994 to the transformation. The operation of the mechanical seals before and after each replacement is as follows. After the normal start-up in October, 1994, it was found that the mechanical seal leaked and there was ammonia smell in the lubricating oil return oil within a few days. After inspection, the return oil temperature of the flushing oil of the mechanical seal at the north end (outer side) is significantly lower than that at the south end (near the side of cavity B). The leakage reason is that the sealing ring of the main engine at the north end cannot rotate synchronously with the shaft, and the PP on the inner cylindrical surface of the moving ring accounts for 17%. The "O" ring fails (Figure 2, Part 5). On January 14th, 1995, the parking opportunity was used to replace the machine seal installed in advance. The disassembled and replaced north end machine seal found that the locking sleeve of the main machine seal moving ring was loose and exited, the locking screw of the locking sleeve was not tightened, and the "O" ring of the moving ring installed on the machine seal shaft sleeve had been ground flat. On January 14th, 1995, the machine seal was replaced and started up. After running for about 10 days, it was found that the machine seal was leaking, and the oil returned from the compressor smelled of ammonia. The use of cold molding foaming technology was becoming more and more common, and no abnormality was found in the field inspection. It is analyzed that the driving ring works with double ends, and the return oil temperature of the cooling oil is nearly 80 ℃, so the actual temperature of the moving ring should be higher, and the "O" ring used in its lower part should be resistant to high temperature. Check the spare parts ordered by German Bergman company and Nuovo Pignone company, the original manufacturer of machine seal, which are also used for the "O" ring under the driving ring. It is different. Bergman spare parts rubber "O" ring is coated with FEP sleeve. On February 26th, 1995, the machine seal was overhauled by taking advantage of the parking opportunity. After disassembling the machine seal, it was found that the "O" ring under the driving ring was aging and invalid, and other parts had no obvious defects. Reassemble two sets of machine seals with sleeved "O" rings under the driving ring. On February 26th, 1995, the machine seal was replaced and started up. By the beginning of December, it was found that the machine seal was leaking. There was ammonia smell in the lubricating oil return oil, and the ammonia smell at the south end was greater than that at the north end. According to the on-site inspection, the temperature of the dirty oil on the south side is high. In March of 1996, it was found that the oil return volume of the waste oil in the southern end of the machine seal increased, the oil color became darker, and the waste oil return pipe was not able to return, causing some oil to leak into the compressor. In order to solve this problem, the oil pressure difference is adjusted from 0.63Mpa to 0.46mpa, the return oil volume of dirty oil is reduced, and the oil will no longer leak into the compressor. On April 11, 1996, the mechanical seal was replaced by taking advantage of the parking opportunity of the whole plant, and the mechanical seal at the south end was removed to check the following problems: the driving ring had a fracture of about 0.5mm; The "O" ring under the mechanical seal shaft sleeve is aging and inelastic; The "O" ring under the stationary ring is aging, in which the "O" ring under the stationary ring inside the main seal has a fracture about 6mm long; The moving ring of the auxiliary machine seal moves relative to the shaft sleeve of the machine seal, wearing the pressing steps on the shaft sleeve of the machine seal; The sealing ring of auxiliary machine has cracks. Through analysis, it is believed that the reason for the leakage of the mechanical seal is that the pressing force of the pressing sleeve of the mechanical seal shaft sleeve is not enough or the pressing sleeve of the mechanical seal shaft sleeve is slightly loose during operation, resulting in the reduction of the pressing force of the auxiliary mechanical seal moving ring and the relative movement with the mechanical seal shaft sleeve. On the one hand, the mechanical seal shaft sleeve overheats and accelerates the aging of the lower "O" ring. On the other hand, the temperature of the mechanical seal chamber rises, and the moving ring overheats and cracks occur, Moreover, the temperature rise of the mechanical seal chamber also accelerates the aging and disconnection of the inner static ring of the main seal. According to the inspection results, it is considered that the main cause of process gas leakage is the fracture of the moving ring of the mechanical seal. Due to the high pressure of the new mechanical seal spring and more friction heat generated by the mating surface of the mechanical seal, the maximum return oil temperature of the flushing oil exceeds 90 ℃ (designed to alarm at 85 ℃ and stop at 90 ℃). According to the structural characteristics of the mechanical seal, the possible reasons for the leakage of process gas from the mechanical seal during normal operation are as follows: ① the mechanical seal assembly leaks from the seal gasket on the end face of the compressor housing; ② The "O" ring under the driving ring fails; ③ The driving ring is broken; ④ The "O" ring under the mechanical seal shaft sleeve fails. According to the actual situation of operation, items ② and ③ are likely to cause leakage, ①

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