Natural Gas NGL and Nitrogen Separation Without Recompression
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Solution Overview
Problem
Existing natural gas processing systems face challenges in efficiently removing nitrogen and recovering Natural Gas Liquids (NGLs) while minimizing capital and operating costs, particularly when dealing with wide ranges of inlet nitrogen concentrations and gas volumes.
Innovation Solution
The integration of heat transfer and process streams between NGL and nitrogen removal sections eliminates the need for recompression, utilizing a High Pressure Rectifier and expander/compressor unit to maintain sufficient pressure for nitrogen removal without additional compression, and employs strategic cooling and heat exchange to enhance NGL recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If expander technology is used to reduce inlet pressure from 800 psig to 300 psig for NGL removal, then NGL extraction efficiency is improved, but the gas stream requires additional recompression to 500 psig or higher before nitrogen removal, increasing capital and operating costs
Solution Approach 1:
The patent combines the nitrogen removal function with the NGL extraction process by integrating a nitrogen rejection unit into the demethanizer column. This merging eliminates the need for separate recompression equipment and steps, as the integrated system maintains sufficient pressure throughout the NGL extraction process while simultaneously removing nitrogen from the overhead stream
Solution Approach 2:
The demethanizer column is designed to perform multiple functions: NGL extraction, nitrogen rejection, and overhead stream processing. By making the column universal, it handles both NGL removal and nitrogen separation in a single unit, eliminating the need for additional compression equipment that would otherwise be required between separate processing stages
2Reliability
If a complete stand-alone nitrogen rejection unit is installed to remove large percentages of nitrogen, then nitrogen removal capability is improved, but capital costs and operating costs increase significantly
Solution Approach 1:
The nitrogen rejection function is merged with the existing demethanizer column rather than installing a separate stand-alone nitrogen rejection unit. This integration allows the system to achieve effective nitrogen removal while avoiding the significant capital costs associated with complete stand-alone nitrogen rejection facilities
Solution Approach 2:
The patent removes nitrogen from only the overhead stream of the demethanizer column rather than processing the entire gas stream through a full nitrogen rejection unit. This partial action approach achieves sufficient nitrogen removal to meet specifications while avoiding the excessive capital and operating costs of treating the complete stream
3Reliability
If nitrogen is removed from the overhead stream of the demethanizer column, then nitrogen content in sales gas is reduced, but ethane recovery in the NGL product stream decreases
Solution Approach 1:
The patent applies nitrogen rejection locally to specific portions of the overhead stream rather than treating the entire stream uniformly. By selectively removing nitrogen from portions of the overhead stream while maintaining other portions for NGL recovery, the system achieves nitrogen specification compliance while maximizing ethane recovery in the NGL product stream
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 capital costs by one-third, achieves 90-95% ethane recovery, and ensures 99% purity in the vented nitrogen stream, with the processed sales gas containing less than 4% nitrogen, thereby optimizing the efficiency and cost-effectiveness of the natural gas processing system.
Implementation Method 1
utilizing expander technology to reduce the inlet pressure from approximately 800 psig down to a pressure level of near 300 psig upstream of the nitrogen removal/rejection process
Implementation Method 2
Heat exchange between process streams is utilized to cool and heat various streams throughout the system
Implementation Method 3
The Joule-Thomson valve reduces the pressure of the gas stream and utilizes the Joule-Thomson effect to cool the gas stream
Data Source
AI summary
A system and method for removing nitrogen and producing a high pressure methane product stream and an NGL product stream from natural gas feed streams where at least 90%, and preferably at least 95%, of the ethane in the feed stream is recovered in the NGL product stream. The system and method of the invention are particularly suitable for use with feed streams in excess of 5 MMSCFD and up to 300 MMSCFD and containing around 5% to 80% nitrogen. The system and method preferably combine use of strategic heat exchange between various process streams with a high pressure rectifier tower and the ability to divert all or a portion of a nitrogen rejection unit feed stream to optionally bypass a nitrogen fractionation column to reduce capital costs and operating expenses.