Polypropylene Fluidized Bed Reactor Condensed Mode Heat Removal
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Solution Overview
Problem
Gas-phase polymerization processes face limitations in production rate due to heat removal constraints, leading to particle buildup and lump formation, which results in reactor downtime for maintenance and reduced catalyst productivity.
Innovation Solution
A continuous process for polypropylene production in a fluidized bed reactor operating in condensed mode, where iso-butane is added to the recycle stream to adjust the dew temperature and composition, reducing stickiness and agglomeration, and incorporating a thermal run-away reducing agent to control catalyst activity and maintain a stable process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the velocity of the recycle gas is increased to remove more heat from the reactor, then the heat removal rate is improved, but the bed becomes unstable and may lift out of the reactor leading to blockage and damage
Solution Approach 1:
The invention changes the physical state parameter of the recycle stream by cooling it below the dew point temperature to form a liquid-containing stream. This phase change enables effective heat removal through vaporization of the liquid component, achieving high heat removal rates without increasing gas velocity to unstable levels. The liquid phase acts as a heat sink that evaporates endothermically, removing heat efficiently while maintaining bed stability.
Solution Approach 2:
The invention utilizes phase transition by cooling the recycle stream below its dew point to condense a portion of the gas into liquid, then reintroducing this liquid-containing stream into the reactor where the liquid vaporizes. This phase change process absorbs heat effectively, enabling high heat removal rates without requiring high gas velocities that would cause bed instability and operational problems.
2Productivity
If the recycle gas is cooled to increase heat removal capacity, then the production rate is improved, but the temperature of the recycle gas is limited by the temperature of industrial cooling water available
Solution Approach 1:
The invention overcomes the cooling water temperature limitation by utilizing phase transition. The recycle stream is cooled to just below the dew point temperature, causing partial condensation into liquid. When this liquid-containing stream is reintroduced into the reactor, the liquid vaporizes endothermically, absorbing heat at a temperature determined by the component composition rather than cooling water temperature. This enables effective heat removal and high production rates independent of cooling water temperature constraints.
Solution Approach 2:
The invention changes the thermal parameter approach by utilizing the latent heat of vaporization during phase change rather than relying solely on sensible heat removal through cooling water temperature differential. By controlling the dew point temperature through composition adjustment, the system achieves effective heat removal at temperatures not limited by cooling water availability, thereby increasing production rate.
3Ease of operation
If conventional cooling methods are used to remove heat of polymerization, then the process is simple to operate, but the maximum production rates are limited
Solution Approach 1:
The invention maintains ease of operation by using the existing recycle gas stream and cooling it to below dew point temperature, then reintroducing it to the reactor. The phase transition of liquid condensation followed by vaporization provides enhanced heat removal capacity that enables higher production rates without complex additional equipment or operational procedures. The process leverages the natural phase behavior of the recycle stream components.
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 increases space-time yield, reduces particle buildup and lump formation, enhances catalyst productivity, and maintains process stability while minimizing reactor downtime.
Implementation Method 1
the liquid portion of which vaporizes when it is exposed to the heat of the reactor
Implementation Method 2
the circulating fluids are compressed using a compressor
Implementation Method 3
the circulating fluids are compressed using a compressor and cooled using a heat exchanger
Data Source
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AI summary
The present invention relates to a process for the continuous preparation of polypropylene in a reactor from propylene and optionally ethylene and/or at least one other oolefin monomer, wherein the reactor comprises a fluidized bed, an expanded section located at or near the top of the reactor, a distribution plate located at the lower part of the reactor and an inlet for a recycle stream located under the distribution plate, wherein the process comprises - feeding a polymerization catalyst to the fluidized bed in the area above the distribution plate - feeding the propylene and the optional at least one other oolefin monomer to the reactor - withdrawing the polypropylene from the reactor - circulating fluids from the top of the reactor to the bottom of the reactor, wherein the circulating fluids are compressed using a compressor and cooled using a heat exchanger, resulting in a cooled recycle stream comprising liquid, and wherein the cooled recycle stream is introduced into the reactor using the inlet for the recycle stream wherein an alkane chosen from the group of iso-butane, n-butane, cyclopropane and mixtures thereof is added to the reactor and wherein the molar composition of the components in the recycle stream is chosen such that the dew temperature of the recycle stream at the reactor pressure is at least 0.10°C below the temperature of the reactor