Olefin Polymerization Vent Column and Lock Hopper Cross-Ties
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Solution Overview
Problem
Gas phase olefin polymerization systems face challenges in pressure control and hydrocarbon recovery, with direct venting of nitrogen being economically unattractive and environmentally problematic, and existing product recovery systems inefficiently managing gas losses.
Innovation Solution
A gas phase polymerization system with a reactor recycle loop, flare, vent column, and product discharge system including lock hoppers and cross-ties, where reactor overhead is processed to separate olefin monomer from carrier gas, and carrier gas is managed through strategic valve operations to minimize nitrogen venting and optimize hydrocarbon recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If direct venting of nitrogen is used to control pressure, then pressure control is achieved, but hydrocarbon recovery is lost and environmental impact increases
Solution Approach 1:
The venting function is segmented into two separate pathways: (1) a product recovery system that handles polymer discharge and associated gas, and (2) a dedicated vent column that handles excess nitrogen removal. This segmentation allows the system to recover hydrocarbons through the product recovery system while separately managing nitrogen venting through the vent column, thereby resolving the contradiction between pressure control and hydrocarbon recovery.
Solution Approach 2:
The vent column acts as an intermediary device between the reactor and the atmosphere. It provides a dedicated pathway for nitrogen to be removed from the system without directly venting the entire reactor effluent (which contains valuable hydrocarbons). The vent column receives gas from the reactor, separates nitrogen from hydrocarbons, and vents only the nitrogen portion, thus serving as a mediator that enables pressure control while preserving hydrocarbon recovery.
2Stress or pressure
If direct venting of nitrogen is used to control pressure, then pressure control is achieved, but economic attractiveness decreases
Solution Approach 1:
The venting function is segmented into two separate pathways: (1) a product recovery system that handles polymer discharge and associated gas, and (2) a dedicated vent column that handles excess nitrogen removal. This segmentation allows the system to recover hydrocarbons through the product recovery system while separately managing nitrogen venting through the vent column, thereby resolving the contradiction between pressure control and hydrocarbon recovery.
Solution Approach 2:
The system implements selective discarding and recovering: the product recovery system recovers and reuses hydrocarbon-rich gas streams, while the vent column selectively discards only the nitrogen portion that must be vented for pressure control. This approach maximizes economic attractiveness by recovering valuable hydrocarbons while minimizing the loss of nitrogen through targeted venting operations.
3Productivity
If conventional product recovery systems are used, then polymer discharge is achieved, but gas loss and nitrogen removal efficiency are reduced
Solution Approach 1:
The venting function is segmented into two separate pathways: (1) a product recovery system that handles polymer discharge and associated gas, and (2) a dedicated vent column that handles excess nitrogen removal. This segmentation allows the system to recover hydrocarbons through the product recovery system while separately managing nitrogen venting through the vent column, thereby resolving the contradiction between pressure control and hydrocarbon recovery.
Solution Approach 2:
The vent column operates continuously to remove nitrogen from the system, providing continuous pressure control without interrupting the polymer discharge operations. This continuous action ensures that nitrogen is constantly removed while the product recovery system handles polymer discharge, maintaining both productivity and efficient gas management simultaneously.
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 improves pressure control by reducing nitrogen venting and hydrocarbon losses, enhancing the efficiency of gas phase olefin polymerization processes while minimizing environmental impact.
Implementation Method 1
The first portion of the reactor overhead in the reactor recycle loop can be supplied to the vent column. The first portion of the reactor overhead can be contacted with a stripping medium within the vent column to remove at least a portion of the olefin monomer to produce a vent column overhead rich in the carrier gas and lean in the olefin monomer and a vent column bottoms rich in the olefin monomer and lean in the carrier gas.
Implementation Method 2
transferring polymer product and reactor gas from the reactor to (1a) the upstream lock hopper of the first pair of lock hoppers and equilibrating the pressure therebetween or (1b) the upstream lock hopper of the second pair of lock hoppers and equilibrating the pressure therebetween
Implementation Method 3
Gas phase catalytic polymerization of olefins is the predominant technology used to produce polyolefin resins. The catalysts used in the process are contained in solid substrate particles from which the polymer chains grow. Gas phase olefin polymerization technology often employs a fluidized bed, where the particles are fluidized by a gas stream also containing the reactants
Data Source
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AI summary
A process for producing an olefin polymer employs a gas phase polymerization reactor in fluid communication with a vent column and a product discharge system. The discharge system can include first and second pairs of lock hoppers, where each pair includes an upstream lock hopper connected by a valve to the reactor and a downstream lock hopper connected by a valve to the upstream lock hopper and by a further valve to a product recovery system, and where a first cross-tie can be provided between the upstream lock hoppers of the first and second pairs of lock hoppers and a second cross-tie can be provided between the downstream lock hoppers of the first and second pairs of lock hoppers. Upon reaching the vent column's maximum removal capacity, additional gas can be removed from the reactor by reducing the frequency of opening the second cross-tie between the downstream lock hoppers.