Dual-Column Nitrogen Rejection for High-CO₂ Natural Gas Streams
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Solution Overview
Problem
Existing nitrogen rejection units (NRUs) for natural gas processing face challenges in efficiently removing nitrogen while managing high carbon dioxide concentrations, leading to equipment blockages, increased energy requirements, and reduced flexibility in handling varying nitrogen levels, especially when processing high nitrogen content streams.
Innovation Solution
A system and method utilizing two fractionating columns where the first column separates methane and heavier hydrocarbons from nitrogen, and the second column further removes nitrogen, with independent temperature control and external reboilers, allowing for higher carbon dioxide tolerance and reduced compression needs, and optionally includes a third column for methane recovery and helium extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional NRU systems are used to remove nitrogen from natural gas, then nitrogen purity in the vent stream is improved, but capital expenditures increase due to additional plant equipment and operating expenditures increase due to refrigeration and compression requirements
Solution Approach 1:
The patent combines nitrogen rejection with NGL extraction into a single integrated process. The first fractionation column performs nitrogen rejection while the second column extracts NGLs, eliminating the need for separate equipment and reducing overall capital expenditures while maintaining nitrogen purity requirements.
Solution Approach 2:
The fractionation columns are designed to perform multiple functions: the first column removes nitrogen from natural gas, while the second column simultaneously extracts NGL components. This multi-functionality reduces the number of dedicated equipment pieces needed.
2Manufacturing precision
If conventional NRU systems are used to remove nitrogen from natural gas, then nitrogen purity in the vent stream is improved, but operating expenditures increase due to refrigeration and compression requirements
Solution Approach 1:
By merging nitrogen rejection and NGL extraction into one integrated process, the patent eliminates redundant refrigeration and compression steps. The heat exchangers and compressors serve dual purposes, reducing overall energy consumption while achieving the required nitrogen purity.
Solution Approach 2:
The integrated process allows continuous operation where the output of one column feeds into the next, maintaining continuous useful action throughout the system. This eliminates idle time and ensures that energy inputs continuously produce valuable outputs (both nitrogen separation and NGL extraction).
3Manufacturing precision
If cryogenic temperatures are used to remove nitrogen, then nitrogen separation is improved, but carbon dioxide freezing occurs causing blockage of process flow
Solution Approach 1:
The patent removes carbon dioxide from the feed stream before it enters the fractionation columns through preliminary action. This prevents CO2 from freezing and blocking the process flow at cryogenic temperatures, while still allowing effective nitrogen separation to occur.
Solution Approach 2:
The system applies preliminary anti-action by removing the harmful substance (carbon dioxide) before it can cause harm (freezing and blockage). This protective measure enables the cryogenic nitrogen separation process to operate without the harmful effects of CO2 precipitation.
4Device complexity
If heat pump configuration is used to link columns, then capital expenditures are reduced, but flexibility in handling varying nitrogen levels is reduced
Solution Approach 1:
The patent employs dynamic control systems that allow the fractionation columns to adapt to varying nitrogen concentrations in the feed stream. By adjusting operational parameters dynamically, the system maintains flexibility and adaptability while using a simplified equipment configuration without heat pump linking.
5Manufacturing precision
If carbon dioxide is removed to maximum levels, then nitrogen rejection efficiency is improved, but loss of substance increases due to removal of valuable components
Solution Approach 1:
The patent selectively extracts only carbon dioxide from the feed stream before nitrogen rejection, leaving valuable NGL components intact. This targeted extraction approach removes the harmful substance (CO2) without unnecessarily removing valuable components that could be recovered and sold as NGL products.
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 enables efficient nitrogen removal from natural gas streams with up to 50% nitrogen and 100 ppm CO2, reducing overall compression requirements by up to 40% and allowing for flexible operation across a wide range of nitrogen concentrations, while producing a suitable processed gas and valuable NGL streams.
Implementation Method 1
processing a feed gas stream containing primarily nitrogen and methane through two fractionating columns to produce a processed natural gas stream
Implementation Method 2
the first column separates methane and heavier hydrocarbons from nitrogen, and the second column further removes nitrogen
Data Source
AI summary
A system and method for removing nitrogen and producing a high pressure methane product stream from natural gas feed streams having wide variations in nitrogen and methane content are disclosed. Optional add-on systems may be incorporated into the nitrogen and methane separation to produce an NGL sales stream to reduce excess hydrocarbons in the nitrogen vent stream, or to recover helium. The system and method of the invention are particularly suitable for use with feed streams in excess of 50 MMSCFD and up to 300 MMSCFD and containing up to 100 ppm carbon dioxide. Typical power requirements for compressing the methane product stream to produce a suitably high pressure stream for sale are reduced according to the systems and methods of the invention.