Slurry Transfer Line Segmentation for Polymerization
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Solution Overview
Problem
The transfer of slurry phase olefin polymers between reactors is challenging due to fouling and sedimentation issues in the transfer line, particularly when producing polymers with different properties, as it requires careful design to maintain reliable flow across varying operating conditions, and increasing velocity can lead to unacceptably high pressure drops.
Innovation Solution
The process involves separating the slurry stream into two flows, recycling the first flow upstream of the separation point, and passing the second flow into the downstream reactor, with the flow separation located more than halfway along the transfer line, thereby minimizing the length of the transfer line operating at a lower flow rate and reducing fouling and sedimentation risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the velocity of the polymer-containing slurry is increased to prevent sedimentation and fouling in the transfer line, then the reliability of polymer transfer is improved, but the pressure drop through the transfer line increases unacceptably
Solution Approach 1:
The transfer line is segmented into two distinct sections: a first section from the first reactor to the flow separation point, and a second section from the flow separation point to the second reactor. The slurry flow is also segmented into a first flow (recycled) and a second flow (passed to second reactor). This segmentation allows different flow rates in different sections, optimizing both reliability and pressure drop.
Solution Approach 2:
Different sections of the transfer line are assigned different flow rate characteristics. The first section (majority of the line) operates at a higher flow rate to prevent sedimentation and fouling, while the second section (shorter distance) operates at a lower flow rate to minimize pressure drop. This local optimization of flow quality resolves the contradiction between reliability and pressure drop.
2Reliability
If a smaller diameter line is used to increase the velocity of the slurry stream, then the reliability of polymer transfer is improved, but the pressure drop along the line becomes unacceptably high
Solution Approach 1:
The transfer line is divided into two sections with different flow rate requirements. The first section uses a diameter optimized for higher velocity to prevent sedimentation, while the second section uses a diameter optimized for lower pressure drop, resolving the contradiction between reliability and pressure drop.
Solution Approach 2:
Different sections of the transfer line have different diameter specifications tailored to their specific functional requirements. The first section has a smaller diameter to achieve higher velocity and prevent fouling, while the second section has a larger diameter to reduce pressure drop, applying local quality optimization.
3Adaptability or versatility
If the transfer line is made relatively long to connect two reactors separated by significant distance, then the adaptability of the plant configuration is improved, but the effect of variations in pressure drop under differing transfer flows is increased
Solution Approach 1:
The long transfer line is segmented into a first section (majority of the length) and a second section (shorter distance to the second reactor). This segmentation allows the first section to be designed for stable high-velocity flow to minimize pressure drop variations, while the second section accommodates the distance requirement with minimal impact on overall pressure drop sensitivity.
Solution Approach 2:
Different sections of the long transfer line are designed with different flow rate characteristics. The first section maintains high flow rate to reduce pressure drop sensitivity to flow variations, while the second section accepts lower flow rate, thereby reducing the overall effect of pressure drop variations despite the long line length.
Data Source
Figure 1~2
AI summary
A process for transferring a slurry stream containing polymer through a transfer line from a first polymerisation reactor to a second polymerisation reactor is disclosed, wherein prior to entry from the transfer line into the second polymerisation reactor, the slurry stream is separated into two flows and the first flow is returned to the first reactor whilst the second flow passes into the second reactor, the length of the transfer line between the first reactor and the location of the flow separation being more than that between the second reactor and the location of the flow separation.