Continuous Polymer Discharge in Fluidized Bed Reactors
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Solution Overview
Problem
Conventional discharge systems for gas-phase polymerization in fluidized bed reactors operate discontinuously, leading to fluctuations in pressure and flow rate, which negatively impact polymer quality and increase operational costs due to excessive gas recovery and recycling.
Innovation Solution
A continuous pneumatic recycle system using a circulation loop with a vertical standpipe and pneumatic conveyor pipe, allowing polymer powder to form a solid thickening zone for reduced gas discharge and improved particle size distribution, with a discharge valve adjusting to maintain a constant bed level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional discontinuous discharge system with intermediate reservoir and lock mechanism is used, then polymer powder can be discharged from the reactor, but pressure fluctuations and flow rate variations occur which negatively impact polymer quality
Solution Approach 1:
The patent implements a continuous discharge system where polymer powder is continuously removed from the fluidized bed reactor through a discharge conduit equipped with a control valve. This eliminates the discontinuous batch discharge operation, maintaining steady pressure and flow rate conditions throughout the reactor, thereby ensuring consistent polymer quality without the fluctuations caused by lock mechanism operations.
Solution Approach 2:
The patent extracts and eliminates the intermediate reservoir and lock mechanism from the discharge system. By directly connecting the fluidized bed reactor to the discharge conduit and using a control valve for regulation, the system removes the source of pressure fluctuations and flow rate variations, achieving both discharge functionality and operational stability.
2Productivity
If a conventional discontinuous discharge system is used, then polymer can be removed from the reactor, but excessive gas recovery and recycling is required which increases operational costs
Solution Approach 1:
The continuous discharge system maintains a steady state operation where polymer and associated gas are continuously removed at a controlled rate. This eliminates the need for extensive gas recovery and recycling operations that would be required after batch discharge operations, as the continuous removal process allows for more efficient gas management and reduces the volume of gas requiring recovery and recycling.
3Productivity
If a discharge valve is placed in the bottom region of the fluidized bed, then polymer can be discharged continuously, but stagnant zones and local hot spots are created in the fluidized bed
Solution Approach 1:
The patent positions the discharge conduit and control valve in the lower region of the fluidized bed reactor, but designs the system to maintain uniform polymer distribution and flow patterns. By carefully locating the discharge point and using appropriate conduit sizing and control valve characteristics, the system achieves continuous discharge while preventing stagnant zones and local hot spots through proper hydrodynamic design that maintains good mixing and heat distribution in the fluidized bed.
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 significantly reduces the amount of gas discharged with polymer, lowering operational costs and improving polymer bed uniformity and particle size distribution, while maintaining consistent reactor conditions.
Implementation Method 1
a circulation loop comprising a substantially vertical standpipe and a pneumatic conveyor pipe
Implementation Method 2
polymer powder coming from said fluidized bed enters said standpipe forming therein a solid thickening zone
Implementation Method 3
a control valve, interposed between said standpipe and said discharge conduit, for adjusting the mass flow rate of polymer discharged from the reactor
Implementation Method 4
a bed of polymer particles is maintained in a fluidized state by the upward flow of a fluidizing gas
Implementation Method 5
The recycle gas stream is withdrawn from the upper zone of the fluidized bed reactor, cooled by passage through an external heat exchanger and then recycled to the reactor
Data Source
AI summary
A gas-phase process for polymerizing one or more a-olefins in a fluidized bed reactor in the presence of a polymerization catalyst, said fluidized bed reactor being equipped with a fluidization grid arranged at its base, and external means for recycling and cooling the unreacted gas from the top of said reactor to said fluidization grid, the process being characterized by: (i) a continuous pneumatic recycle of polymer by means of a circulation loop connecting said fluidization grid to the upper region of the fluidized bed reactor; (ii) a continuous discharge of polymer from a zone of said circulation loop having a polymer concentration higher than the polymer concentration inside the fluidized polymer bed.