Polypropylene Pellet Purging via Preheating to Prevent Heat Runaway
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Solution Overview
Problem
Current polypropylene pellet venting processes face challenges in achieving low FOG values due to 'heat runaway' caused by cold pellets re-crystallizing and becoming sticky, leading to agglomeration and equipment blockages, and require more extreme conditions to meet stringent emission standards.
Innovation Solution
A method involving preheating polypropylene pellets to 60-135°C and maintaining them in a purge vessel at 100-140°C with a counter-current flow of purge gas, ensuring a residence time of at least 24 hours, which stabilizes the process and reduces volatile emissions effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cold polypropylene pellets are fed to a purge vessel operating at high temperature, then the purging process can remove volatile materials, but the cold pellets will re-crystallise and release heat of crystallisation causing the pellets to become sticky and form agglomerates that block the purge vessel or piping system
Solution Approach 1:
The patent applies preliminary action by preheating the cold polypropylene pellets before feeding them to the purge vessel. This preliminary heating step prevents the pellets from re-crystallising and releasing heat of crystallisation, thereby avoiding the formation of sticky agglomerates and equipment blockages while maintaining effective purging of volatile materials
2Manufacturing precision
If more extreme conditions in terms of temperature and residence time are used to meet strict FOG requirements, then the FOG value can be reduced, but the process stability deteriorates and equipment blockages become more likely
Solution Approach 1:
The patent uses preliminary action by preheating pellets before they enter the purge vessel, which prevents re-crystallisation and heat runaway. This allows the use of extreme temperature and residence time conditions needed for low FOG values without compromising process stability or causing equipment blockages
Solution Approach 2:
The patent applies parameter changes by controlling the temperature of pellets before and during the purging process. By preheating pellets to a specific temperature range and maintaining controlled temperature conditions in the purge vessel, the process achieves low FOG values while preventing the sticky behavior that would occur with uncontrolled temperature changes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves a stable and economically feasible process for producing polypropylene pellets with FOG values of at most 250 µg/g, maintaining process stability and quality without significant fluctuations, and preventing equipment blockages.
Implementation Method 1
maintaining the pellets in said purge vessel while directing a flow of at least 10 Nm3/hour of purge gas counter-currently to the flow of the pellets through said purge vessel
Implementation Method 2
preheating polypropylene pellets, preferably to a temperature of from 60 to 135°C in the preheating step a)
Implementation Method 3
removing volatile materials from the polypropylene pellets
Data Source
AI summary
Method for continuously preparing polypropylene pellets having reduced low-molecular weight volatile organic compounds, the method comprising the steps of • a) preheating polypropylene pellets, • b) feeding the preheated polypropylene pellets of step a) to a purge vessel and maintaining the pellets in said purge vessel while directing a flow of at least 10 Nm3 purge gas per hour per m3 of polypropylene pellets (Nm3/ m3 pp.hour) through the pellets, • c) removing polypropylene pellets from said purge vessel, wherein the residence time of polypropylene pellets in said purge vessel is at least 24 hours and the polypropylene pellets are maintained at a temperature Tp of from 100 to 140 °C, wherein in the preheating step a) the pellets are preheated to a temperature in the range of Tp - 20°C and Tp + 10°C; wherein the polypropylene pellets have a temperature < 40°C before the preheating step a)