Heat Transfer Tube Mixing Elements for Steam Cracking
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Solution Overview
Problem
Steam cracking processes in hydrocarbon processing face challenges with coke buildup in heat transfer tubes, leading to increased pressure drops and reduced ethylene formation efficiency, despite existing technologies that attempt to improve heat transfer characteristics.
Innovation Solution
Heat transfer tubes with an inner diameter of 1.85 inches or less and a first helical row of mixing elements separated by a gap of 0.5 inches or greater, promoting turbulence and reducing coke accumulation, thereby maintaining favorable heat transfer coefficients and extending the duration of steam cracking processes before decoking is necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inner diameter of heat transfer tubes is decreased to increase internal surface area-to-volume ratio, then heat transfer efficiency and ethylene selectivity are improved, but pressure drop increases due to coke accumulation
Solution Approach 1:
The tube interior is segmented into multiple lanes (e.g., three lanes) by strategically positioned mixing elements, creating separate flow paths. This segmentation allows coke to accumulate in specific regions (at the ends of mixing elements) while maintaining open channels for hydrocarbon flow, thereby reducing the overall pressure drop while preserving the benefits of smaller tube diameter for heat transfer and selectivity.
2Temperature
If mixing elements are placed close together to enhance turbulence and heat transfer, then heat transfer coefficient is improved, but coke accumulation in gaps increases pressure drop
Solution Approach 1:
Different regions of the tube interior are given different functions: the gaps between mixing elements serve as coke accumulation zones, while the lanes created by the mixing elements serve as hydrocarbon flow channels. This local differentiation allows the system to tolerate coke deposition without significant pressure drop increase, while the mixing elements themselves continue to provide turbulence and enhance heat transfer in the flow lanes.
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 solution effectively reduces pressure drops and prolongs the operational duration of heat transfer tubes, enhancing ethylene formation and reducing the frequency of decoking processes, while maintaining efficient heat transfer characteristics.
Implementation Method 1
The mixing elements promote turbulence of flow through the tube and improved heat transfer coefficients
Implementation Method 2
heat transfer from the tube to the hydrocarbon feedstock
Implementation Method 3
Steam cracking is a commercial method for producing olefins such as ethylene, propylene and butadiene from a hydrocarbon feedstock
Data Source
AI summary
The present disclosure relates to a heat transfer tube including an inner surface and an outer surface. The heat transfer tube further includes a first mixing element and a second mixing element disposed on the inner surface of the tube and projecting inwardly toward a central longitudinal axis of the tube. Adjacent mixing elements are separated by a gap arc distance of about 0.5 inches (1.27 cm) or greater. The first helical row has an angle (Θ) from about 15 degrees to about 85 degrees relative to the central longitudinal axis of the tube. The tube has an inner diameter of about 1.85 inches (4.7 cm) or less.