Small Diameter Furnace Tubes for Ethane Cracking
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Solution Overview
Problem
Conventional ethane cracking systems with larger diameter radiant tubes and low coil outlet pressures result in high capital and process costs due to low gas density and high volumetric flowrates, and increased coking rates, which are exacerbated by the need for larger and more costly compressors and equipment for processing the effluent.
Innovation Solution
Operating ethane steam cracking at elevated coil inlet and outlet pressures in small diameter furnace coils, with pressures ranging from 200 kPa-g to 520 kPa-g, while maintaining a coking rate comparable to low pressure operations by reducing temperatures and using resistant materials, such as nickel-chromium alloys with alumina barrier layers, to mitigate coke formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If larger diameter radiant tubes are used with low coil outlet pressures, then conventional ethane cracking can be performed, but capital and process costs increase due to low gas density and high volumetric flowrates requiring larger compressors and equipment
Solution Approach 1:
The patent changes the operating pressure parameter from conventional low pressure (≤150 kPa-g outlet) to elevated pressure (200-520 kPa-g outlet), which increases gas density and reduces volumetric flowrate, thereby reducing compressor size and capital costs while maintaining cracking effectiveness through small diameter tubes
2Reliability
If larger diameter radiant tubes are used with low coil outlet pressures, then conventional cracking can operate, but coking rates increase requiring more frequent maintenance and larger equipment
Solution Approach 1:
The patent changes the tube diameter parameter from conventional large diameter (7-16 cm) to small diameter (≤6.0 cm, preferably 2.0-5.0 cm), which reduces the surface area available for coke formation and allows operation at elevated pressures that reduce coking rates through improved heat transfer and reduced residence time
Solution Approach 2:
The patent employs composite material structures with coke-resistant inner linings or coatings in the small diameter radiant tubes, combining base tube material with protective layers that resist coke adhesion and facilitate easier coke removal, thereby reducing maintenance frequency
3Productivity
If elevated coil outlet pressures (200-520 kPa-g) are used in small diameter coils, then gas density increases and equipment size decreases, but coking rates may increase without temperature reduction
Solution Approach 1:
The patent simultaneously changes multiple parameters: reduces tube diameter to ≤6.0 cm and increases outlet pressure to 200-520 kPa-g, which together enable operation at elevated temperatures without increased coking because the small diameter provides superior heat transfer that prevents localized hot spots where coke forms
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 reduces the number of stages and size of downstream equipment, decreases energy requirements, and maintains once-through conversion and selectivity rates for ethylene production, thereby lowering capital and operating costs while minimizing coking issues.
Implementation Method 1
using resistant materials, such as nickel-chromium alloys with alumina barrier layers, to mitigate coke formation
Implementation Method 2
nickel-chromium alloys with alumina barrier layers
Implementation Method 3
steam cracking of ethane to form ethylene
Implementation Method 4
Operating ethane steam cracking at elevated coil inlet and outlet pressures in small diameter furnace coils, with pressures ranging from 200 kPa-g to 520 kPa-g
Data Source
AI summary
Systems and methods are provided for performing ethane steam cracking at elevated coil inlet pressures and/or elevated coil outlet pressures in small diameter furnace coils. Instead of performing steam cracking of ethane at a coil outlet pressure of ˜22 psig or less (˜150 kPa-g or less), the steam cracking of ethane can be performed in small diameter furnace coils at a coil outlet pressure of 30 psig to 75 psig (˜200 kPa-g to ˜520 kPa-g), or 40 psig to 75 psig (˜270 kPa-g to ˜520 kPa-g). In order to achieve such higher coil outlet pressures, a correspondingly higher coil inlet pressure can also be used, such as a pressure of 45 psig (˜310 kPa-g) or more, or 50 psig (˜340 kPa-g) or more.