Cryogenic Nitrogen Separation for Low-Nitrogen Natural Gas Streams
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Solution Overview
Problem
Conventional separation processes become less effective when the nitrogen content in natural gas streams is below 25%, necessitating an efficient method to remove nitrogen to meet pipeline specifications of 2% or less.
Innovation Solution
A nitrogen separation system utilizing cryogenic refrigeration, including steps such as partial condensation, distillation, reflux compression, and nitrogen rejection, to effectively separate nitrogen from inlet gas streams with less than 25 mole % nitrogen content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional separation processes are used, then nitrogen removal is effective when nitrogen content is 25% or more, but separation effectiveness deteriorates when nitrogen content is below 25%
Solution Approach 1:
The invention changes the operating parameters of the separation process by implementing cryogenic temperatures (below -100°F) and specific pressure conditions. This parameter change enables effective nitrogen separation in streams with less than 25% nitrogen content, where conventional processes fail. The cryogenic conditions alter the physical properties of the gas components, enabling selective condensation and separation of nitrogen at low concentrations.
Solution Approach 2:
The separation process is divided into multiple distinct stages: initial cooling and partial condensation, distillation column separation, and final nitrogen rejection. This segmentation allows each stage to optimize for specific separation tasks, with the distillation column handling the bulk separation and the nitrogen rejection unit providing final polishing to achieve pipeline specification compliance.
2Reliability
If nitrogen is separated from natural gas streams, then pipeline specification compliance is achieved, but process complexity increases
Solution Approach 1:
The cryogenic separation system performs multiple functions within a unified process framework. The same cryogenic cooling system enables both partial condensation of heavier hydrocarbons and nitrogen separation. The distillation column serves dual purposes of hydrocarbon fractionation and nitrogen concentration. This multi-functionality reduces the need for separate dedicated equipment for each separation task.
Solution Approach 2:
The process utilizes the natural physical properties of the gas components at cryogenic temperatures to achieve separation. The system leverages the inherent condensation temperatures and vapor-liquid equilibrium characteristics of nitrogen, methane, and heavier hydrocarbons. This self-service approach minimizes the need for additional energy input and complex control systems beyond what is required for basic cryogenic operation.
3Adaptability or versatility
If cryogenic refrigeration is used for nitrogen separation, then low nitrogen content streams can be processed, but energy consumption increases
Solution Approach 1:
The process converts the energy that would otherwise be wasted in heating and cooling various streams into useful refrigeration. The nitrogen rejection unit and distillation column produce cold streams that are used to pre-cool the incoming natural gas feed. This heat integration transforms what would be energy losses into beneficial cooling, significantly reducing the net energy input required for cryogenic operation.
Solution Approach 2:
The cryogenic process operates in a cyclic manner with periodic charging and discharging of thermal energy in the heat exchangers. The system alternates between cooling phases (where refrigeration is produced) and heating phases (where cold is stored and then released). This periodic operation allows for more efficient heat transfer and better utilization of the refrigeration capacity compared to continuous operation.
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 efficient nitrogen removal, producing a natural gas stream that meets pipeline specifications by concentrating nitrogen in an overhead stream and producing a methane-rich stream with low nitrogen content, thereby enhancing the heating value and reducing greenhouse gas emissions.
Implementation Method 1
supplying the inlet gas having less than 25 mole % nitrogen to a nitrogen separation system configured with cryogenic refrigeration
Implementation Method 2
at least partially condensing the inlet gas stream to form an at least partially condensed inlet stream
Implementation Method 3
processing the at least partially condensed inlet stream in a distillation tower to form an overhead gas stream and a liquid bottoms stream
Implementation Method 4
feeding the second portion to a nitrogen rejection unit, the nitrogen rejection unit producing a cold nitrogen rich stream and at least one cold methane rich stream
Implementation Method 5
heating the cold nitrogen rich stream using at least the inlet gas stream to an ambient temperature; and heating the at least one cold methane stream using at least the inlet gas stream to an ambient temperature
Data Source
AI summary
A method for separating nitrogen from an inlet gas having less than 25 mole % nitrogen includes supplying the inlet gas having less than 25 mole % nitrogen to a nitrogen separation system configured with cryogenic refrigeration.