Ethane recovery and ethane rejection methods and configurations
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Solution Overview
Problem
Current natural gas processing systems face inefficiencies and high energy consumption when switching between ethane recovery and ethane rejection operations, particularly in achieving high propane recovery levels, due to limitations in existing configurations and methods that are optimized for single modes of operation.
Innovation Solution
The proposed solution involves flexible plant configurations and methods that allow for changing the top reflux stream between residue gas and deethanizer overhead, and varying the feed gas split ratios between two feed exchangers, with the demethanizer operating at higher pressures during ethane recovery and lower pressures during ethane rejection, to achieve high propane and ethane recovery rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If higher expansion ratio is used across the turbo-expander to achieve lower temperature, then ethane recovery is improved, but column pressure decreases and residue gas compression horsepower requirements increase
Solution Approach 1:
The patent implements dynamic operation modes that allow the NGL plant to switch between ethane recovery and ethane rejection configurations. During ethane recovery mode, the system operates with higher expansion ratios and lower column pressures to maximize ethane recovery. During ethane rejection mode, the system adjusts to different expansion ratios and maintains higher column pressures to preserve propane recovery, thereby dynamically adapting to different operational requirements and avoiding excessive energy consumption in each mode
Solution Approach 2:
The patent changes key operating parameters including column pressure, expansion ratio, and reflux configuration based on the desired operational mode. By adjusting these parameters, the system optimizes ethane recovery when needed while minimizing energy consumption and maintaining propane recovery when operating in ethane rejection mode
2Manufacturing precision
If lower demethanizer pressure is used to achieve higher ethane recovery, then ethane recovery is improved, but the system becomes more prone to CO2 freezing problems
Solution Approach 1:
The patent dynamically adjusts the demethanizer operating pressure based on the operational mode and feed gas composition. During ethane recovery mode with stable feed composition, the system operates at lower pressures to maximize ethane recovery. When CO2 content increases or during ethane rejection mode, the system raises the operating pressure to prevent CO2 freezing while maintaining acceptable ethane recovery levels through adjusted reflux configurations
3Manufacturing precision
If NGL plant is optimized for single mode of operation, then ethane recovery or propane recovery is improved in that mode, but energy efficiency and recovery levels drop significantly when switching modes
Solution Approach 1:
The patent designs the NGL plant with universal functionality to perform both ethane recovery and ethane rejection operations effectively. The system incorporates configurable reflux streams, adjustable column pressures, and flexible expansion ratios that enable it to adapt to different operational modes without significant performance degradation, making it a multi-functional facility that can respond to varying market demands
Solution Approach 2:
The patent implements dynamic operational modes that allow the plant to switch between ethane recovery and ethane rejection configurations. The system adjusts key parameters including column pressure, expansion ratio, and reflux configuration based on the desired mode of operation, thereby maintaining high efficiency and recovery levels in both modes without requiring substantial reconfiguration
4Manufacturing precision
If additional rectification column is added to achieve high ethane recovery, then ethane recovery is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing demethanizer column multi-functional by implementing configurable reflux streams and adjustable operating parameters. Instead of adding a separate rectification column, the system achieves high ethane recovery by optimizing the demethanizer's operation mode and reflux configuration, thereby avoiding increased device complexity while maintaining the capability to switch between different operational modes
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 propane recovery of at least 99% and ethane recovery of at least 95% during both ethane recovery and rejection operations, reducing energy consumption and eliminating the need for residue gas recycle, thereby enhancing operational flexibility and economic efficiency.
Implementation Method 1
the feed gas is cooled and partially condensed by heat exchange with process streams
Implementation Method 2
The remaining vapor portion is letdown in pressure in a turbo-expander, resulting in further cooling and liquid formation
Data Source
AI summary
Contemplated plants for flexible ethane recovery and rejection by allowing to switch the top reflux to the demethanizer from residue gas to the deethanizer overhead product and by controlling the flow ratio of feed gas to two different feed gas exchangers. Moreover, the pressure of the demethanizer is adjusted relative to the deethanizer pressure for control of the ethane recovery and rejection.