Loop Reactor Heat Transfer via Biot Number Control
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Solution Overview
Problem
In polymerization reactor systems, maintaining controlled temperature is challenging due to exothermic reactions, leading to overheating, fouling, and plugging issues, which affects the quality of polyolefins like polyethylene and polypropylene produced by slurry polymerization.
Innovation Solution
The process involves maintaining an internal Biot number below 3.0 in a loop reactor by optimizing the slurry film coefficient, thermal conductivity of the reactor wall, and circulation velocity to ensure effective heat transfer, using a continuous tubular shell with a high thermal conductivity ratio and circulating the slurry at velocities above 9 m/s to manage heat transfer resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the slurry circulation velocity is increased to improve heat transfer, then the heat removal efficiency is improved, but the energy consumption and mechanical stress on the reactor system increases
Solution Approach 1:
The patent optimizes the slurry circulation velocity by maintaining specific Biot number ranges (0.1 < Bi < 10) and velocity ranges (0.1 < u < 10 m/s) to achieve effective heat transfer while avoiding excessive energy consumption. This parameter optimization resolves the contradiction by finding the optimal operating window where heat removal efficiency is maximized without proportionally increasing energy input.
Solution Approach 2:
The patent employs temperature monitoring and control systems that continuously measure the slurry temperature and adjust the circulation velocity accordingly. When temperature approaches the polyolefin melting point, the system increases circulation velocity to enhance heat removal. This feedback mechanism ensures energy is used only when needed, resolving the contradiction between heat removal efficiency and energy consumption.
2Temperature
If the reactor wall thermal conductivity is increased to improve heat transfer, then the heat removal capability is improved, but the reactor wall thickness must be reduced which compromises structural strength
Solution Approach 1:
The patent employs reactor walls with composite structures that combine materials of different thermal conductivities and mechanical strengths. The wall may consist of an inner layer with high thermal conductivity for heat transfer and an outer layer with high strength for structural integrity. This composite approach resolves the contradiction by allowing effective heat removal while maintaining the necessary structural strength.
Solution Approach 2:
The reactor wall is divided into multiple layers or zones with different thermal and mechanical properties. The segmentation allows the inner surface to optimize for heat transfer (higher thermal conductivity) while the outer structure maintains structural strength. This layered approach resolves the contradiction between heat transfer capability and structural strength.
3Temperature
If the slurry film coefficient is decreased to reduce heat transfer resistance, then the temperature control is improved, but the slurry flow pattern becomes less turbulent which may affect mixing quality
Solution Approach 1:
The patent optimizes the slurry film coefficient by controlling the Biot number within a specific range (0.1 < Bi < 10) and adjusting circulation velocity (0.1 < u < 10 m/s). These parameter changes achieve effective heat transfer (improved temperature control) while maintaining sufficient turbulence for adequate mixing. The optimized parameters resolve the contradiction by finding the window where both temperature control and mixing quality are satisfied.
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 effectively controls temperature, preventing overheating and fouling, thereby ensuring the production of polyolefins with desired properties by balancing heat transfer resistances through the slurry film, reactor wall, and coolant film.
Implementation Method 1
The slurry in the loop reactor forms a slurry film having a slurry film coefficient along an inner surface of the shell
Implementation Method 2
a ratio of the thermal conductivity to the thickness is greater than or equal to about 700 W·m -2
Implementation Method 3
The slurry has a velocity of greater than about 9 m/s (30 ft/s) during the circulating
Implementation Method 4
contacting at least a portion of an exterior surface of the loop reactor with a coolant fluid
Implementation Method 5
the coolant fluid forms a coolant film having a coolant film coefficient along an exterior surface of the loop reactor
Implementation Method 6
the polymerization process is exothermic, and the heat generated must be removed from the reactor
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A process comprises polymerizing an olefin monomer in a loop reactor in the presence of a catalyst and a diluent, and producing a slurry comprising solid particulate olefin polymer and diluent. The Biot number is maintained at or below about 3.0 within the loop reactor during the polymerizing process. The slurry in the loop reactor forms a slurry film having a film coefficient along an inner surface of the reactor wall, and the film coefficient is less than about 500 BTU•hr-1•ft-2•F-1.