Gas-Phase Reactor Downcomer Hold-Up for Agglomerate Prevention
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Solution Overview
Problem
Gas-phase alpha-olefin polymerization processes, especially those using highly active catalysts, face challenges with the formation of agglomerates or deposits on reactor walls due to inadequate heat dissipation, leading to quality reduction and process shutdowns, particularly during ethylene homopolymerization or copolymerization.
Innovation Solution
A gas-phase polymerization process involving a multizone circulating reactor with a riser unit for upward fluidization and a downcomer for downward densified polymer particle flow, where the hold-up of polymer particles in the downcomer is between 55 wt.% to 80 wt.% of the total, and the use of a barrier fluid to manage pressure and composition differences between the riser and downcomer zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If highly active catalysts are used for ethylene polymerization, then productivity is improved, but formation of agglomerates and deposits on reactor wall increases
Solution Approach 1:
The reactor is divided into multiple zones (riser and downcomer sections) with different flow conditions. The riser provides upward fluidization for active polymerization, while the downcomer provides downward densified flow for heat dissipation and preventing agglomerate formation, allowing high productivity without deposits
Solution Approach 2:
Different regions of the reactor are provided with different local conditions: the riser has high gas velocity and upward flow for intensive polymerization, while the downcomer has lower velocity and downward flow for heat management. This local differentiation allows maintaining high overall productivity while preventing harmful effects in specific zones
2Productivity
If heat of polymerization is not dissipated adequately, then productivity is maintained, but local hot spots are formed leading to quality reduction
Solution Approach 1:
The downcomer acts as an intermediary zone between the high-energy riser and the discharge system. It provides a transition region where polymer particles are densified and heat is dissipated before particles leave the reactor, preventing hot spots while maintaining productivity
Solution Approach 2:
The system uses gas flow dynamics (pneumatics) to control heat dissipation. The upward gas flow in the riser and downward particle flow in the downcomer create efficient heat transfer without mechanical moving parts, allowing adequate heat dissipation at high productivity
3Duration of action of stationary object
If agglomerates and deposits are formed, then polymerization process continues, but plugging of product discharge system occurs leading to shutdown
Solution Approach 1:
Instead of the conventional upward-only flow, the system uses downward flow in the downcomer section. This inverted flow direction prevents agglomerates from accumulating and moving toward the discharge system, eliminating plugging issues and enabling continuous reliable operation
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 reduces the formation of agglomerates, maintains polymer quality, and prevents reactor plugging, allowing for continuous operation by effectively managing heat and polymer distribution within the reactor, thereby enhancing productivity and flexibility in polymer composition.
Implementation Method 1
a riser unit wherein growing polymer particles flow upwards under fluidization, fast fluidization or transport conditions
Implementation Method 2
a downcomer wherein growing polymer particles flow downward in a densified form
Implementation Method 3
the formation of such chunks or deposits occurs when the generated heat of polymerization is not dissipated adequately and local hot spots are formed
Data Source
AI summary
A process for preparing an ethylene polymer including the step of homopolymerizing ethylene or copolymerizing ethylene with one or more comonomers in a gas-phase polymerization reactor including a riser unit wherein growing polymer particles flow upwards under fluidization, fast fluidization or transport conditions and a downcomer wherein growing polymer particles flow downward in a densified form, wherein the hold-up of polymer particles in the downcomer is from 55 wt. % to 80 wt. % of the total hold-up of polymer particles in the gas-phase polymerization reactor.