Two-Column Nitrogen Removal System for Ultra-Low Methane Emissions
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Solution Overview
Problem
Existing natural gas processing systems face challenges in achieving ultra-low greenhouse gas emissions in nitrogen vent streams while maintaining low nitrogen levels in sales gas streams, often requiring high capital and energy expenditures and struggling with carbon dioxide processing at higher concentrations.
Innovation Solution
A two-column fractionating system with efficient heat exchange and reflux mechanisms, including a high-pressure first column and a lower-pressure second column, allows for the production of multiple sales gas streams at different pressures, minimizing methane and nitrogen levels, and accommodating higher carbon dioxide concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single fractionating column is used, then capital expenditures are reduced, but the nitrogen vent stream contains higher methane emissions (3-5% methane)
Solution Approach 1:
The single fractionating column is divided into two separate columns operating at different pressures. The first column (high pressure) removes the bulk of nitrogen, while the second column (low pressure) achieves ultra-low methane emissions in the nitrogen vent stream. This segmentation allows each column to be optimized for its specific function, resolving the contradiction between simplicity and emission reduction.
2Object-generated harmful factors
If a two-column system is used, then methane emissions in nitrogen vent stream are reduced, but capital expenditures and energy requirements increase
Solution Approach 1:
The system uses dynamic pressure differentiation between the two columns, with the first column operating at high pressure (300-500 psig) and the second at low pressure (75-125 psig). This dynamic approach allows the system to achieve ultra-low methane emissions while optimizing energy consumption and capital expenditures by matching each column's operating conditions to its specific separation function.
3Ease of manufacture
If conventional single-column NRU systems are used, then equipment cost is reduced, but greenhouse gas emissions in nitrogen vent stream are higher
Solution Approach 1:
The invention changes the operating pressure parameter between the two columns, with the first column operating at high pressure (300-500 psig) and the second at low pressure (75-125 psig). This parameter change enables the system to achieve ultra-low greenhouse gas emissions (less than 100 ppm methane) while managing equipment costs through efficient heat exchange and reflux mechanisms.
4Stress or pressure
If the NRU column operates at higher pressure, then sales gas pressure is improved, but energy consumption for refrigeration and compression increases
Solution Approach 1:
The system creates equipotentiality in pressure distribution by having the first column operate at high pressure (300-500 psig) to provide high-pressure sales gas directly, while the second column operates at low pressure (75-125 psig) for energy-efficient methane removal. This pressure stratification reduces the need for additional compression energy while maintaining high sales gas pressure.
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 system achieves ultra-low methane emissions in nitrogen vent streams, reduces energy requirements, and enables processing of natural gas with up to 2500 ppm CO2, producing high-purity nitrogen for product use and multiple sales gas streams at optimized pressures.
Implementation Method 1
processing a feed stream containing natural gas through a first fractionating column operating at a first pressure to produce a first bottoms stream and a first overhead stream, the first overhead stream being fed into a second fractionating column operating at a second pressure
Implementation Method 2
A first heat exchanger cools a portion of the feed stream through heat exchange with a first portion of the first column bottoms stream
Data Source
AI summary
A system and method for removing nitrogen from natural gas using two fractionating columns to achieve an ultra-low greenhouse gas content in a nitrogen vent/product stream, while also producing three sales gas streams at different pressures and with low nitrogen content within pipeline specifications. A portion of a low pressure column overhead stream may be compressed and cooled and recycled back to provide reflux to the low pressure column. A system feed stream is cooled upstream of feed a high pressure column, but preferably not separated into streams with varying compositions. A portion of the high pressure column bottoms stream and the low pressure column bottoms stream provides refrigerant to the high pressure column to produce a reflux stream. An amount of methane in a nitrogen vent/nitrogen product stream may be less than 0.01%.