Blowdown Vessel Quenching Layout for Quiet Ethylene Depressurization
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Solution Overview
Problem
High-pressure polymerization processes for polyethylene production face challenges such as rapid ethylene decomposition, excessive temperatures leading to reactor damage, and unsafe depressurization methods that release polymeric material into the atmosphere, causing noise and reducing recovery rates.
Innovation Solution
A high-pressure polymerization system with a reactor blow down system featuring a reactor blow down vessel, release lines with angled outlets, and a vent stack, along with a process that includes quenching the reactor content with an aqueous medium to separate polymer from ethylene and control depressurization, minimizing noise and enhancing recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If emergency expansion valves are used to depressurize the reactor by disposing hot ethylene and hot polymer into the blow down vessel, then the polymerization reactor can be rapidly depressurized, but polymeric material is released into the atmosphere causing noise and reducing recovery rates
Solution Approach 1:
A water seal is introduced as an intermediary medium between the blow down vessel and the atmosphere. The water seal acts as a barrier that prevents polymeric material from being directly released into the atmosphere while still allowing pressure equalization. The gas outlet from the blow down vessel is positioned below the water level in the water seal, creating a liquid barrier that traps and contains the polymeric material, thereby eliminating noise and enabling material recovery.
Solution Approach 2:
The system creates a composite barrier system combining water (liquid phase) and the polymeric material (solid phase) in the blow down vessel. The water seal forms a liquid barrier that interacts with the gaseous and particulate polymer material, creating a composite system where the liquid water traps and contains the solid polymeric material, preventing its release and enabling both noise reduction and material recovery.
2Ease of operation
If the release line outlet is positioned at a high level in the blow down vessel, then gas can escape easily, but polymeric material accumulates and is released through the vent stack
Solution Approach 1:
The solution moves the gas release function to a different spatial dimension by positioning the gas outlet below the water level in the water seal. Instead of releasing gas vertically through a high-level vent stack, the gas is forced to travel horizontally through the water seal, changing the release pathway from a direct vertical path to a path that must pass through the liquid barrier, thereby trapping polymeric material.
Solution Approach 2:
The water seal serves as an intermediary that mediates between the gas release requirement and the polymer containment requirement. By positioning the gas outlet below the water level, the water acts as a mediator that allows gas to pass through while blocking polymeric material, thus satisfying both the need for gas release and the need for polymer recovery.
3Volume of moving object
If the blow down vessel is designed with a small L/D ratio, then the vessel is more compact, but the quenching efficiency and separation performance are reduced
Solution Approach 1:
The water seal introduces a localized region of enhanced liquid-gas interaction at the gas outlet area. By creating a water seal at this specific location, the system provides localized quenching and separation functionality without requiring the entire vessel to be large. The local water barrier provides sufficient quenching and separation performance while maintaining overall vessel compactness.
Solution Approach 2:
The blow down vessel is segmented into functional zones: a quenching zone where hot gas contacts the aqueous medium, a separation zone where polymer material settles, and a water seal zone that provides the final barrier. This segmentation allows each zone to perform its specific function efficiently, achieving reliable quenching and separation in a more compact overall vessel design.
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
The system effectively quenches hot ethylene and polymer, separates components efficiently, and reduces noise during depressurization, improving safety and recovery rates while maintaining operational continuity.
Implementation Method 1
the reactor content made from or containing hot ethylene and hot polymer is disposed into the reactor blow down vessel via one or more emergency expansion valves, thereby quenching the hot gases with water
Implementation Method 2
the vent stack having a constricted section
Data Source
AI summary
A high-pressure polymerization system having a) a polymerization reactor and b) a reactor blow down system having b1) a reactor blow down vessel, having a circular design over a major portion P having a L/D-ratio in the range from 1.75 to 10.0 and containing an aqueous quenching medium, b2) a release line connecting the polymerization reactor with the reactor blow down vessel and having an outlet located above a maximum level for the aqueous quenching medium, b3) a first emergency valve in the release line to open and close fluid communication between the polymerization reactor and the reactor blow down system, and wherein the release line outlet has a joining piece having an angle (α) between the central axis and a tangent at the reactor blow down vessel in the range from 5° to 70° and the reactor blow down vessel has a vent stack containing a constricted section.