Things to know 
Plunger, Packing, Lubricant – a complex tribological system in LDPE hyper compressors
 
2. Elementary structure of a plant for high-pressure polymerization of ethylene


Picture 2: The hyper compressor, the “heart” of an LDPE-plant

1 Mixing section 10 High-pressure product separator
2 Primary compressor 11/13 Final separator
3 Secondary compressor 12 Cooler
4 Preheater 14 Low-pressure product separator
5 Reactor 15/17 Final Separator
6 Reactor 16 Cooler
7 Initiator pumps 18 Booster compressor
8 Special control valve 19 Extruder
9 Product cooler 20 Additional extruder

In the hyper compressor, designated as secondary compressor (3) in picture 2, the precompressed ethylene enters 1st stage of the hyper compressor and is pressured to approximately 150 MPa. The 2nd stage increases this to approximately 350 MPa where polymerization can take place.
Within the 1st stage of the hyper compressor solid cemented carbide plungers or plungers with carbide coatings are used. But the 2nd stage is usually only equipped with solid cemented carbide plungers. Use of solid cemented carbide plungers on the primary side is bound to presence of an operation monitoring system on this compressor side. This does not exist in such form particularly on the primary side of older hypers and would have to be back fitted, so safe operation with solid cemented carbide plungers may be possible.) Sealing systems and lubricants are similar in both compression stages.

Running periods of compressor cylinders can be as low as 1000 hours but as high as 13 years [1], depending on pressure load and specific gas composition. After that the plunger needs to be refinished and due to the changed plunger diameter undersized packings will usually be required. According to [2] one third of all production shutdowns on LDPE-plants are caused by hyper compressor failures, 95% of which were due to the failure of cylinder components
Differences between Hot Isostatical Pressing (HIP) and Sinter HIP Procedure
Differences between Hot Isostatical and Sinter HIP
1. Hot Isostatical Pressure
2. Sinter HIP Procedure Pressure

Plunger, Packing, Lubricant – a complex tribological system in LDPE hyper compressors
1. Introduction Pressure
2. Elementary structure of a plant for high-pressure polymerization of ethylene
3. The tribological system
4. Wear process in the tribological system
5. Practical knowledge from a carbide metal producer’s point of view
6. Other partners of the tribological system
7. Outlook
8. Summary
9. Reference
3. The tribological system