Multistage Olefin Polymerization Transfer Device
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Solution Overview
Problem
Existing multistage gas-phase polymerization processes face challenges in continuously transferring polymer particles from an upstream reactor to a downstream reactor without altering the gas composition, leading to discontinuous operation, polymer agglomeration, and fluctuations in polymer bed levels, which affect the quality of the produced polymer.
Innovation Solution
A transfer device comprising a gas/solid separation chamber and a pair of lock hoppers that operate intermittently in parallel, where one hopper is continuously filled with polymer and the other is pressurized with the reaction gas mixture from the downstream reactor, allowing for continuous transfer of polymer particles by a combination of pressure and gravity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a direct discharge of polymer from upstream reactor to downstream reactor is performed, then the transfer operation is simple, but the polymerization conditions in downstream reactor cannot be maintained due to substantial amount of gases and dissolved hydrocarbons
Solution Approach 1:
The transfer device is segmented into multiple functional chambers: a first chamber for receiving polymer with reaction gases, a second chamber for compressing polymer, and a third chamber for degassing. This segmentation allows each chamber to perform a specific function, effectively separating the polymer transfer function from the gas removal function, thus preventing downstream reactor contamination while maintaining relatively simple overall device structure
Solution Approach 2:
The transfer device acts as an intermediary system between upstream and downstream reactors. It introduces an intermediate processing stage where polymer is compressed and degassed before entering the downstream reactor, thereby mediating the transfer process to prevent direct contamination of downstream reactor with reaction gases and hydrocarbons
2Loss of substance
If polymer is degassed and compressed in multiple vessels with tortuous path, then gas removal is effective, but polymer aggregates and chunks are generated compromising plant operation
Solution Approach 1:
Compression is performed as a preliminary action before degassing. By compressing the polymer in the second chamber first, the polymer particles are compacted and their inter-particle spaces are reduced, which prevents subsequent agglomeration during the degassing process in the third chamber. This preliminary compression action eliminates the harmful effect of polymer aggregation that occurs when degassing is performed first in conventional multi-vessel systems
3Productivity
If periodic transfer operations are performed, then polymer can be transferred between reactors, but continuous transfer is not achieved leading to operational discontinuities
Solution Approach 1:
The transfer device operates through periodic cyclic actions involving sequential opening and closing of valves to control polymer flow between chambers and to downstream reactor. This periodic valve operation enables continuous polymer transfer by maintaining a steady cycle of compression and discharge, eliminating the discontinuities associated with batch-wise transfer operations while keeping the device structure relatively simple
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
Ensures a continuous and reliable transfer of polymer particles between reactors, maintaining different polymerization conditions and preventing contamination of the downstream reactor, thus optimizing the quality and consistency of the polymer produced.
Implementation Method 1
a gas/solid separation chamber in which said reaction gas mixture is removed from the polymer
Implementation Method 2
the other one is continuously pressurized by means of a gas comprising the reaction mixture coming from said downstream reactor
Implementation Method 3
allowing for continuous transfer of polymer particles by a combination of pressure and gravity
Data Source
Figure 1
AI summary
A process for the multistage polymerization of olefins comprising a gas-phase polymerization carried out in at least two serially connected gas-phase reactors, the continuous discharge of polymer and gas reaction mixture from an upstream reactor into a transfer device and the continuous feeding of polymer from said transfer device to a downstream reactor, said transfer device comprising: a) a separation chamber in which said gas reaction mixture is removed from the polymer; b) at least a couple of lock hoppers working intermittently in parallel, where one of said lock hoppers is continuously filled with the polymer coming from step a), while simultaneously the other one is continuously pressurized by means of a gas comprising the reaction mixture coming from said downstream reactor.