Continuous Settling Legs for Loop Reactor Pressure Stability
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Solution Overview
Problem
Current olefin polymerization processes in loop reactors face challenges with batch-based settling legs, leading to pressure fluctuations, inefficient separation of polymer, reactants, and diluent, and reliability issues during continuous operation.
Innovation Solution
Implementing a process with continuously open settling legs equipped with pressure control devices, allowing for continuous withdrawal of polymer slurry from the loop reactor, which optimizes residence time and separation efficiency while maintaining stable reactor pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If batch-based settling legs are used for product removal, then the polymer slurry can be discharged from the reactor, but pressure fluctuations occur in the loop reactor
Solution Approach 1:
The patent applies the continuity principle by transitioning from batch-based settling legs to continuous settling legs that operate without interruption. The continuous settling legs maintain a constant liquid level in the reactor and provide continuous product removal, eliminating the periodic pressure fluctuations caused by batch discharge operations. This ensures stable reactor pressure while maintaining productivity.
2Stability of the object's composition
If continuous product take off is implemented, then pressure stability is improved, but the suspension discharged contains large amounts of diluent and monomer requiring subsequent separation
Solution Approach 1:
The patent introduces an intermediary device - the continuous settling leg - that performs partial separation of polymer particles from the diluent-mononer mixture within the reactor system itself. The settling leg allows polymer particles to settle while the liquid phase with dissolved monomer and diluent is continuously removed, reducing the burden on downstream separation equipment and simplifying the overall process.
3Productivity
If batch settling legs are used, then the process operates on a batch principle, but this creates gas bubbles that interfere with circulation pump operation
Solution Approach 1:
The continuous settling leg operates continuously to maintain a steady liquid level and continuous product removal, preventing the accumulation of gas bubbles that occurs during batch discharge operations. This continuous operation ensures the circulation pump operates reliably without gas bubble interference while maintaining productivity.
4Productivity
If batch settling legs are used, then product can be recovered, but the process lacks flexibility during start-up or response to disruptions
Solution Approach 1:
The continuous settling leg provides dynamic operation that can adapt to changing process conditions. During start-up or in response to disruptions, the continuous operation allows for flexible adjustment of discharge rates and liquid levels, enabling the process to respond quickly to changing conditions while maintaining product recovery capability.
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 the operability and reliability of the polymerization process by minimizing pressure fluctuations, optimizing residence time, and improving the separation efficiency of polymer, reactants, and diluent, reducing the complexity of the process and maintaining stable reactor conditions.
Implementation Method 1
settling legs which operate usually on a batch principle to recover the product. Settling in the legs is used to increase the solids concentration of the slurry finally recovered as product slurry
Implementation Method 2
The polymer particles are dried, additives can be added and finally the polymer is extruded and pelletized... transferred to another reactor or discharged to a flash tank, through flash lines, where most of the diluent and unreacted monomers are flashed off and recycled
Data Source
AI summary
A process for the preparation of a polyolefin in a slurry loop reactor provided with settling legs may include introducing olefin reactants, diluents, and polymerization catalyst into the reactor while circulating. The process may include polymerizing the olefin reactants to produce a slurry, continuously withdrawing the slurry, via the settling legs, and transferring withdrawn solid olefin polymer particles to a recovery section. Each settling leg may have an inlet connected to the reactor and an outlet connected to the recovery section. At least one settling leg is continuously open, allowing continuous withdrawal of slurry. Each outlet of the settling legs may be connected to the recovery section by a conduit provided with a pressure control device. The pressure in the reactor may be controlled by operating the pressure control device.