Loop Reactor Settling Legs Velocity Control

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Solution Overview

Problem

Current polyethylene production processes in loop reactors result in product slurry with high diluent and reactant concentrations, necessitating elaborate downstream processing and increased production costs.

Innovation Solution

Reducing the circulation velocity of polyolefin slurry by 20-60% in specific horizontal sections of the reactor with settling legs, leading to stratification and increased solid polymer concentration, thereby reducing the amount of diluent and reactants in the withdrawn slurry.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If settling legs are used to increase solid polymer concentration in product slurry, then solid polymer concentration is improved, but the increase is only minor and recycling cost remains high

Engineering Contradiction:

Improvesolid polymer concentrationVSAvoidrecycling cost

Core Design Contradiction:

Quantity of substanceVSProductivity

Solution Approach 1:

The invention changes the circulation velocity parameter in horizontal reactor sections by introducing variable speed drives on circulation pumps. By reducing circulation velocity in horizontal sections where settling legs are located, the slurry has sufficient time to settle and deposit solid polymer particles, significantly increasing product slurry concentration without requiring excessive recycling of diluent.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system transitions from static circulation velocity to dynamic control with variable speed drives. The circulation pump speed is adjusted based on operational requirements, allowing optimization of settling efficiency in horizontal sections while maintaining overall reactor productivity and minimizing recycling costs.

Inventive Principle:

Principle #15Dynamics

2Quantity of substance

If circulation velocity is reduced in horizontal sections with settling legs, then solid polymer concentration in product slurry increases, but circulation time increases

Engineering Contradiction:

Improvesolid polymer concentrationVSAvoidcirculation time

Core Design Contradiction:

Quantity of substanceVSLoss of time

Solution Approach 1:

The reactor circulation system is segmented into different velocity zones. Horizontal sections equipped with settling legs operate at reduced velocity to maximize settling, while vertical sections and other parts of the loop maintain higher velocities to ensure adequate mixing and prevent stagnant zones. This segmented approach optimizes both settling efficiency and overall circulation time.

Inventive Principle:

Principle #1Segmentation

3Productivity

If product slurry is withdrawn continuously without settling legs, then production rate is maintained, but diluent and reactant concentration remains high requiring elaborate downstream processing

Engineering Contradiction:

Improveproduction rateVSAvoiddownstream processing

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The settling legs perform preliminary concentration of solid polymer particles before the slurry enters downstream processing equipment. By reducing circulation velocity in horizontal sections, solid particles settle and are incorporated into the product slurry, pre-concentrating the product and reducing the burden on downstream separation and processing operations.

Inventive Principle:

Principle #10Preliminary action

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 efficiency of settling legs, resulting in a higher solid polymer concentration and lower diluent concentration in the product slurry, minimizing downstream processing needs and reducing production costs.

Implementation Method 1

The circulation velocity of the polyolefin slurry inside said at least one horizontal part of said interconnected pipes provided with one or more settling legs is reduced by at least 20% and at most 60%, compared to the circulation velocity inside the remainder of said loop reactor

Methodology Applied

Scientific EffectStratification: Density Gradient

Implementation Method 2

Settling in the legs is used to increase the solid concentration of the slurry finally recovered as product slurry

Methodology Applied

Scientific EffectSedimentation: Sedimentation

Data Source

PatentUS9296834B2Process for preparing a polyethylene product in a polymerization loop reactor

Publication Date: 2016.03.29 TOTAL RES & TECH FELUY SA

AI summary

A process for preparing polyolefin in a polymerization loop reactor can include feeding olefin monomer, liquid diluent, polymerization catalyst, optionally hydrogen, and optionally olefin co-monomer into the polymerization loop reactor. The process can include polymerizing the olefin monomer and optionally the olefin co-monomer to produce a polyolefin slurry in the polymerization loop reactor. The polymerization loop reactor can include a plurality of interconnected pipes defining a flow path for the polyolefin slurry. The polymerization loop reactor can include one or more settling legs provided on at least one horizontal part of the interconnected pipes. The circulation velocity of the polyolefin slurry inside at least one horizontal part of the interconnected pipes provided with one or more settling legs can be reduced by at least 20% and at most 60% compared to a circulation velocity inside a remainder of the polymerization loop reactor.