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Due to the particularity of the process medium in the synthetic butyl rubber device, the mechanical seal of the reactor stirring frequently leaks. This article describes how a factory reduced the leakage rate of the mechanical seal by adding a throttling bush at the front end of the mechanical seal and arranging a reasonable flushing scheme. In the previous article, we have explained the causes of the leakage phenomenon，so this article will further talks about the tackling measures and results.
Tackling Measures:
On the basis of not changing the mechanical seals' structures, make after measurement some respective throttling bushs on the outer ends of the mechanical seals' gland plates to form restricted tight gaps around the sleeves (or shafts) and arrange clean flushing materials.
The requirements for the layout of the flushing materials were: 1. The flushing materials were compatible and close to the materials in the kettles, and mostly were chosen from reaction solvent or diluent.2. The temperatures of the flushing materials were similar to the temperatures of the materials in the kettles, so that after PLAN32 were put to function, there will be no strong mass transfers or heat transfers, which will affect the reactions. 3. Check whether the matching clearance between the throttling bush and the shaft and the flushing volume of the flushing materials were appropriate. The greater the clearance between the throttle bush and the shaft, the greater the amount of flushing required. And on the contrary，too smaller matching clearances may easily cause wear of the shafts and bushings or increase the flushing pressures of PAN32s. In addition, the operating temperatures and the material selections of the throttling bushes also affect the selection of the matching clearances. 4. Throttle bushing can be made into labyrinth seal or spiral seal. The following table shows the selection plans of the factory mentioned above for the flushing materials and the matching clearances between the throttling bushes and the shafts.
On the basis of not changing the mechanical seals' structures, make after measurement some respective throttling bushs on the outer ends of the mechanical seals' gland plates to form restricted tight gaps around the sleeves (or shafts) and arrange clean flushing materials.
The requirements for the layout of the flushing materials were: 1. The flushing materials were compatible and close to the materials in the kettles, and mostly were chosen from reaction solvent or diluent.2. The temperatures of the flushing materials were similar to the temperatures of the materials in the kettles, so that after PLAN32 were put to function, there will be no strong mass transfers or heat transfers, which will affect the reactions. 3. Check whether the matching clearance between the throttling bush and the shaft and the flushing volume of the flushing materials were appropriate. The greater the clearance between the throttle bush and the shaft, the greater the amount of flushing required. And on the contrary，too smaller matching clearances may easily cause wear of the shafts and bushings or increase the flushing pressures of PAN32s. In addition, the operating temperatures and the material selections of the throttling bushes also affect the selection of the matching clearances. 4. Throttle bushing can be made into labyrinth seal or spiral seal. The following table shows the selection plans of the factory mentioned above for the flushing materials and the matching clearances between the throttling bushes and the shafts.
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Effect after modification:
1. The modifying measures by adding the throttling bushes greatly reduced the leakage rates of the mechanical seals of the above-said agitators and prolongd the service lives of the mechanical seals. In 2012 (before transformation), the polymerization kettles leaked 13 times, and in 2013 (after transformation), it was 2 times; The degassing kettles and the stripping kettles leaked 7 times in 2012 (before the transformation), and in 2013 (after the transformation) no leakage occurred.
2. The reduction of maintenance times reduced the maintenance costs. Comparing maintenance costs of the polymerization kettles, degassing kettles, and stripping kettles in 2012 and 2013 including the costs of disassembly and assembly of the polymerization kettles for cold preservation and the maintenance & replacement of the spare parts of the mechanical seals of each kettle, the cost saving was about 630,000 yuan.
3. For polymerization kettles, degassing kettles, and stripping kettles, the maintenance method of adding a throttling bush is much easier to overhaul the pumping shaft and replace the shaft cap seal, thus improving the maintenance efficiency.
Through repeated practice, we realized that the root cause of the leakage of the mechanical seals of the plant was the deterioration of the lubrication and cleaning conditions of the primary seals. The simple method of adding a throttling bush and adding flushing before the mechanical seal solves this problem, and it has been popularized in the stirred tank of highly corrosive materials in the halogenated butyl units.
