Continuous Settling Leg Transfer in Loop Reactor Polymerization
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Solution Overview
Problem
Existing olefin polymerization processes face challenges with pressure fluctuations and inefficiencies in continuous polymer slurry removal from loop reactors, leading to issues like gas bubbles, reactor control perturbations, and the need for complex separation processes.
Innovation Solution
A process involving two connected loop reactors with at least one continuously open settling leg for continuous transfer of polymer slurry, allowing control of the number and flow rate of settling legs to optimize residence time and separation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If settling legs operate on a batch principle to discharge polymer slurry, then product recovery is achieved, but pressure fluctuations occur in the loop reactor
Solution Approach 1:
The patent applies the continuity principle by operating settling legs continuously rather than in batch mode. The first settling leg operates continuously to transfer polymer slurry from the first loop reactor to the second loop reactor, eliminating the start-stop operation of batch discharge. This continuous operation maintains steady pressure in the first reactor while the second settling leg handles periodic discharge to the flash tank, thus resolving the pressure stability issue while maintaining productivity.
2Quantity of substance
If settling legs discharge accumulated polymer slurry periodically, then solids concentration is increased, but gas bubbles are created at high monomer concentration
Solution Approach 1:
The patent segments the settling leg operation into two distinct functions: the first settling leg operates continuously with lower discharge rate to maintain reactor pressure stability and avoid gas bubble formation, while the second settling leg handles periodic high-rate discharge to achieve high solids concentration. This segmentation allows each settling leg to operate in its optimal mode without generating harmful gas bubbles.
3Stability of the object's composition
If continuous product take off is implemented, then pressure fluctuations are reduced, but diluent and monomer separation becomes necessary
Solution Approach 1:
The patent uses the second loop reactor as an intermediary between the first loop reactor and the flash tank. The first settling leg continuously transfers polymer slurry to the second loop reactor, which acts as a buffer and separation zone. This intermediary approach allows continuous operation in the first reactor (maintaining pressure stability) while enabling periodic discharge from the second reactor, thus reducing the immediate separation complexity at the first reactor outlet.
4Loss of time
If multiple settling legs are used for continuous transfer, then residence time can be optimized, but device complexity increases
Solution Approach 1:
The patent implements dynamic control of settling leg operation by allowing operators to adjust the number of settling legs in service based on process requirements. The system can operate with one or both settling legs active, enabling flexible adjustment of residence time and transfer rate. This dynamic configuration optimizes residence time for polymer quality while avoiding the fixed complexity of permanently installed multiple settling legs.
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 approach enhances operability and reliability by minimizing pressure fluctuations, avoiding polymer stagnation, and improving the separation of olefin polymer, reactants, and diluent, while maintaining constant operating conditions.
Implementation Method 1
withdrawing polyolefin slurry comprising solid olefin polymer particles and diluent from said first reactor and introducing the withdrawn particles into the second loop reactor, by means of one or more settling legs provided on said first reactor
Data Source
AI summary
A process for the preparation of a polyolefin is disclosed. The process includes introducing one or more olefin reactants, diluents and polymerization catalyst into a first loop reactor, and while circulating the olefin reactants, diluents and polymerization catalyst in the first loop reactor. The method includes polymerizing the one or more olefin reactants to produce a polyolefin slurry comprising liquid diluent and solid olefin polymer particles. The method includes withdrawing polyolefin slurry comprising solid olefin polymer particles and diluent from the first reactor and introducing the withdrawn particles into a second loop reactor, by means of one or more settling legs provided on the first reactor, wherein each settling leg has an inlet connected to the first reactor and an outlet connected to the second reactor by means of a transfer line wherein at least one settling leg is continuously open allowing continuous transfer of solid olefin polymer particles from the first loop reactor to the second loop reactor. The process further comprises controlling the continuous transfer of solid olefin polymer particles from the first loop reactor to the second loop reactor by at least one continuously open settling leg.