System and method for separating wide variations in methane and nitrogen
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Solution Overview
Problem
Existing nitrogen removal systems from natural gas streams face challenges such as high capital and operating costs, limited flexibility in handling varying nitrogen concentrations, and increased greenhouse gas emissions due to inefficiencies in cryogenic processing and heat management.
Innovation Solution
A system comprising two fractionating columns with independent condenser and reboiler duties, where the feed stream is split and processed to separate nitrogen from methane, allowing for flexible operation and reduced compression requirements, and incorporating an external reboiler for enhanced control and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a two-column NRU system is used to achieve high nitrogen purity, then nitrogen removal efficiency is improved, but capital expenditures and equipment complexity increase
Solution Approach 1:
The patent extracts the condenser and reboiler functions from the traditional integrated column system and places them as separate, independently controlled units. This allows the second column to operate with independent thermal control, enabling high nitrogen purity without requiring the full complexity of a traditionally integrated two-column system with coupled duties.
Solution Approach 2:
The patent segments the thermal management system by making the condenser and reboiler duties independent of each other. This segmentation allows each unit to be optimized separately, reducing the overall system complexity while maintaining the ability to achieve high nitrogen purity through coordinated but independent control of each segment.
2Manufacturing precision
If cryogenic temperatures are used to remove nitrogen, then nitrogen separation efficiency is improved, but carbon dioxide freezing and process disruption occur
Solution Approach 1:
The patent changes the operational parameters by allowing warmer feed temperatures to the fractionating columns. By operating at less extreme cryogenic temperatures and using independent condenser/reboiler control, the system achieves nitrogen separation without cooling the feed to temperatures that would cause carbon dioxide to freeze and block process flow.
Solution Approach 2:
The patent applies preliminary cooling through the external reboiler and heat exchangers before the feed enters the fractionating columns, but controls this cooling to avoid excessive temperature reduction. This preliminary action prepares the feed for efficient separation while maintaining temperatures above the carbon dioxide freezing point.
3Use of energy by stationary object
If the first column overhead stream is used to provide reboiler duty for the second column, then operating expenditures are reduced, but flexibility in handling nitrogen concentration variations decreases
Solution Approach 1:
The patent segments the thermal duties by making the condenser and reboiler operations independent rather than linking them through heat exchange between columns. This segmentation allows each column to be adjusted independently to handle variations in nitrogen concentration while still achieving energy efficiency through separate optimization of each unit's thermal requirements.
Solution Approach 2:
The patent introduces dynamic flexibility by allowing the system to adapt to varying nitrogen concentrations through independent control of condenser and reboiler duties. The system can dynamically adjust each unit's operation based on feed composition changes, maintaining optimal performance across a range of nitrogen concentrations rather than being locked into a fixed duty relationship.
4Manufacturing precision
If nitrogen is removed through conventional NRU processes, then nitrogen content in sales gas is reduced, but compression requirements and operating costs increase
Solution Approach 1:
The patent changes the pressure and temperature parameters through independent condenser/reboiler control, allowing the system to operate at conditions that minimize compression requirements. By optimizing the thermal parameters separately in each column, the system achieves high nitrogen removal efficiency while reducing the compression horsepower needed for the methane 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
The system efficiently removes nitrogen while reducing overall compression needs by up to 40% and increases carbon dioxide tolerance, enabling processing of higher flow rates and wider nitrogen concentration ranges with reduced emissions.
Implementation Method 1
a first heat exchanger for cooling the first feed stream upstream of the first splitter and for cooling the second feed stream upstream of the first fractionating column through heat exchange with the first bottoms stream and the first overhead stream
Implementation Method 2
an external reboiler for cooling the third feed stream upstream of the first fractionating column through heat exchange with the first bottoms stream
Implementation Method 3
a first fractionating column wherein the second feed stream and the third feed stream are separated into a first overhead stream and the first bottoms stream
Implementation Method 4
a second fractionating column comprising a condenser and a reboiler, wherein first overhead stream is separated into a second overhead stream and the second bottoms stream
Implementation Method 5
a second fractionating column comprising a condenser and a reboiler
Data Source
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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.