Fluidized Bed Reactor Conical Bottom Design
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Solution Overview
Problem
Existing olefin polymerization processes in fluidized bed reactors face instability and accumulation of polymer particles and agglomerates at the reactor bottom, particularly in reactors without a gas distribution plate.
Innovation Solution
A vertical fluidized bed reactor design with a conical bottom, cylindrical middle, and conical top zones, where fluidization gas is introduced and recycled, forming a fluidized bed with suspended polymer particles, and no fluidization grid, ensuring the superficial gas velocity is below the transport velocity of particles, and using an inlet chamber with a specific gas flow pattern to prevent accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fluidized bed reactor without a gas distribution plate is used for olefin polymerization, then the device complexity is reduced, but polymer particles and agglomerates accumulate at the reactor bottom causing operational instability
Solution Approach 1:
The reactor bottom is designed with a conical shape instead of a flat surface. This curved geometry prevents polymer particles and agglomerates from accumulating at the bottom by facilitating their movement toward the central upflow region, thereby maintaining operational stability without requiring a gas distribution plate
Solution Approach 2:
The reactor is divided into distinct zones: a conical bottom zone for particle circulation, a cylindrical middle zone for fluidized bed polymerization, and a conical top zone for gas-solid separation. This segmentation allows each zone to perform its specific function optimally while preventing accumulation issues
2Quantity of substance
If the superficial gas velocity is increased to improve mixing, then gas-solid mixing is enhanced, but particle transport velocity is exceeded causing particle loss
Solution Approach 1:
The system operates with dynamic gas velocity control where the superficial gas velocity is maintained below the particle transport velocity threshold. This dynamic balance ensures adequate mixing while preventing particle entrainment and loss through the top zone
3Stability of the object's composition
If polymer particles are allowed to accumulate at the reactor bottom, then the fluidized bed can be maintained, but agglomerate formation increases reducing process reliability
Solution Approach 1:
The conical bottom geometry creates a flow pattern that continuously circulates particles upward through the central region. This prevents static accumulation and agglomerate formation at the bottom while maintaining the fluidized bed structure through controlled particle suspension
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 process achieves stable operation with reduced polymer accumulation, improved gas-solid mixing, enhanced heat transfer, and increased polymer homogeneity, reducing the risk of agglomerate formation and allowing for broader particle size distribution without segregation.
Implementation Method 1
a fluidised bed is formed within the reactor where the growing polymer particles are suspended in the upwards rising gas stream
Implementation Method 2
the gas flows from the upper part of the inlet chamber to the lower part thereof and the gas flows from the lower part of the inlet chamber to the bottom zone
Data Source
AI summary
The present invention deals with an olefin polymerisation process. At least one olefin is polymerised in gas phase in a fluidised bed in the presence of an olefin polymerisation catalyst in a polymerisation reactor having a vertical body; a generally conical downwards tapering bottom zone; a generally cylindrical middle zone above and connected to said bottom zone; and a generally conical upwards tapering top zone above and connected to said middle zone. Fluidisation gas is introduced to the bottom zone of the reactor from where it passes upwards through the reactor, and withdrawn from the top zone of the reactor. The gas is then compressed, cooled and returned into the bottom zone of the reactor. A fluidised bed is thus formed within the reactor where the growing polymer particles are suspended in the upwards rising gas stream wherein the superficial velocity of the fluidisation gas is less than the transport velocity of the particles. There is no fluidisation grid in the reactor. The fluidisation gas is passed from an inlet chamber into the bottom zone and the gas flows from the upper part of the inlet chamber to the lower part thereof and the gas flows from the lower part of the inlet chamber to the bottom zone.