Polyethylene Separation Vessels with Jet Pump Recycle
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Solution Overview
Problem
High pressure polymerization reactors face inefficiencies in separating polymer from unreacted monomer, leading to residual monomer leakage and high energy consumption for compression, which limits productivity and increases environmental concerns.
Innovation Solution
The use of three or more separation vessels with a jet pump system that recycles off gas from the second separation vessel back to the first, reducing residual monomer in the polymer and decreasing energy consumption by leveraging the product mixture's flow energy to compress the off gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If two separation vessels are used in series, then monomer separation is achieved, but residual monomer in polymer remains high (30-40 wt% ethylene in polymer from first vessel)
Solution Approach 1:
The separation system is divided into multiple stages: a first separation vessel operating at high pressure (200-500 bar) and a second separation vessel operating at low pressure (1-20 bar). This segmentation allows progressive removal of monomer at different pressure levels, achieving both high separation efficiency and low residual monomer content in the final polymer product.
2Productivity
If off gas from low pressure separator is compressed by purge compressor, then monomer is recycled, but energy consumption increases
Solution Approach 1:
The off-gas streams from both the first and second separation vessels are merged into a single recycle stream that feeds back to the reactor inlet. This consolidation eliminates the need for separate purge compressors for each vessel, reducing overall compression energy requirements while maintaining full monomer recycling capability.
3Stress or pressure
If high pressure let down valve is used to reduce pressure, then polymer mixture enters separator, but energy is lost in pressure reduction
Solution Approach 1:
The pressure reduction that occurs through the high pressure let down valve is not treated as wasted energy but is utilized beneficially: the pressure differential created is exactly what drives the phase separation in the first separation vessel, enabling efficient monomer-polymer separation without requiring additional energy input for the separation process.
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 configuration enhances monomer separation efficiency, reduces monomer loss, and decreases energy consumption, allowing for increased polymer production without additional compression capacity, while minimizing environmental impact by reducing vented ethylene.
Implementation Method 1
a jet pump system that recycles off gas from the second separation vessel back to the first, reducing residual monomer in the polymer and decreasing energy consumption by leveraging the product mixture's flow energy to compress the off gas
Implementation Method 2
The first separation vessel, sometimes referred to as the high pressure vessel, has an inlet for the product mixture coming from the high pressure let down valve, an outlet for the separated unreacted monomer gas (referred to as 'off gas') and an outlet in the bottom of the vessel for the polymer
Implementation Method 3
The polymerization of ethylene is an exothermic process which generates heat
Data Source
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AI summary
The invention provides an apparatus and a process for the high pressure polymerization of ethylene, optionally with one or more comonomers, in which unreacted monomer is separated from the polymer in a separation system having at least first, second and third separation vessels and in which off gas from the second vessel is recombined back into the product mixture upstream of the first separation vessel, preferably using a jet pump.