Valves installed in challenging polyethylene and polypropylene production applications require additional design considerations to ensure reliability.
Handling of polyethylene and polypropylene powder during the product discharge process is a challenging application for valves. It is characterized by high speed, frequent cycling in the presence of abrasive, intrusive powder particles. Polyethylene and polypropylene producers need solutions that deliver tight sealing performance over a long service life to extend the uptime and productivity of the reactor that supplies their downstream processes.
The production of polyethylene and polypropylene is a licensed process. Within this process, powder is created in a reactor with the addition of a catalyst. This powder is discharged from the reactor for further processing and pelletizing for downstream use. It is during this powder discharge system (PDS) phase that producers face significant challenges in their valve reliability, and ultimately, the productivity of their operations. These process challenges, illustrated in detail below, require superior valve technology to advance producers’ quality and efficiency goals. The blue colored valve icons in the process map below indicate the critical service valves that require priority attention.
Automated valves in powder discharge applications must be capable of operating at high speed and high frequency. Open or close speeds are typically required to be less than 1 second per inch, with more than 600 cycles per day.
This places significant demand not only on valve components but also requires a highly engineered actuator. These actuators must be constructed of hardened materials, optimized springs, bearings and seals. Actuators must also incorporate cushioning to eliminate excessive shock load.
Polyethylene and polypropylene powders can be some of the most challenging media for valves to handle. The fine powder particles can enter cavities between the ball and seat. Over a short period, this powder can accumulate and compact to prevent sealing and even seize the valve.
Poorly designed valves with imprecisely machined components and ineffective seals can accelerate powder accumulation and inevitable valve or actuator failure.
Powder discharge system valve operating conditions combine high speed, frequent cycling with abrasive polyethylene or polypropylene powder particles. These conditions result in component wear being a leading failure mode.
Poorly designed or specified valves in this application will experience scratching of the ball and seat as well as degradation of the bearings, seals and springs. This damage can cause premature failure of the valve that will require downtime and maintenance.
The reliability of your powder discharge system valves is of critical importance to the profitability of your operations. When sealing is ineffective, powder quality is compromised resulting in costly waste and reprocessing. And when these valves fail, the reactor must be shut down which halts downstream processes.
In addition, some spare parts and replacement valves can come at a high cost with long lead times, escalating downtime and maintenance budgets.
Specify these features when upgrading your powder discharge system valves
When deployed in a licensed process, select a valve solution approved by the licensor to ensure the integrity of your process.
Valves proven to perform 700K cycles are the minimum requirement. Emerson has proven its KTM solution to 2,000,000 cycles.
A smart seat designed to remove powder prior to sealing. The wider face reduces ball surface area pressure and improves longevity.
Must be able to perform high speed, high frequency cycles with the component quality and shock absorption to match the valve life.
Must withstand high loads while maintaining tight, vertically aligned engagement between valve and actuator to prevent backlash.
Backup seals are essential to prevent powder infiltration of the seat springs. A 4 point X-shaped seal is superior to a standard O-ring.
An engineered stem seal arrangement is crucial to prevent water ingress and process egress while resisting cycle wear.
For enduring performance, critical components across the full valve package should be hard coated including the ball and actuator cylinder.
