Fuel Gas Composition Control for Constant MWI in LNG Facilities
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Solution Overview
Problem
LNG facilities face operational challenges due to varying fuel gas compositions, leading to increased capital and operating costs, as most gas turbines are designed to operate with fuel gas of constant composition, necessitating either expensive and complex dual-fuel nozzle configurations or inefficient fuel management.
Innovation Solution
Implementing a process that separates natural gas streams into lights and heavies streams, using a fuel gas separator with a hydrocarbon-separating membrane to control fuel gas composition, ensuring consistent Modified Wobbe Index across different operational modes, thereby allowing for the use of simpler gas turbines and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fuel gas management is used without composition control, then operating costs are reduced, but gas turbines cannot operate efficiently due to varying fuel gas composition
Solution Approach 1:
The fuel gas separator divides the predominantly methane stream into two separate streams: a lights stream (containing lighter hydrocarbons and nitrogen) and a heavies stream (containing heavier hydrocarbons). This segmentation allows selective blending to achieve consistent Modified Wobbe Index in the fuel gas supplied to gas turbines, resolving the contradiction between operational efficiency and system complexity.
Solution Approach 2:
The system dynamically adjusts the blending ratio of lights stream and heavies stream based on real-time composition analysis to maintain a constant Modified Wobbe Index. This parameter control ensures gas turbines operate efficiently despite variations in the original predominantly methane stream composition, without requiring complex dual-fuel nozzle configurations.
2Adaptability or versatility
If dual-fuel nozzle gas turbines are used to accommodate varying fuel gas compositions, then operational flexibility is improved, but capital costs and device complexity increase
Solution Approach 1:
The fuel gas separator and composition control system perform preliminary processing of the fuel gas stream before it reaches the gas turbine. By pre-adjusting the Modified Wobbe Index through selective blending of lights and heavies streams, the system eliminates the need for gas turbines to have dual-fuel nozzle configurations, thereby reducing capital costs and device complexity while maintaining operational flexibility.
3Device complexity
If fuel gas composition is not controlled, then system simplicity is maintained, but operational problems occur in gas turbines
Solution Approach 1:
The system employs real-time composition analysis of the predominantly methane stream and adjusts the blending ratio of lights stream and heavies stream accordingly to maintain a constant Modified Wobbe Index. This feedback control mechanism ensures stable gas turbine operation without requiring overly complex manual intervention, achieving a balance between system simplicity and operational stability.
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 stabilizes fuel gas composition, reducing capital and operating expenses by enabling the use of single-nozzle gas turbines and improving operational flexibility in LNG facilities.
Implementation Method 1
separating a first predominantly methane stream into a first lights stream and a first heavies stream in a fuel gas separator
Implementation Method 2
burning a first fuel gas stream comprising at least a portion of the first lights stream in a gas turbine
Data Source
AI summary
An LNG facility employing an enhanced fuel gas control system. The enhanced fuel gas control system is operable to produce fuel gas having a substantially constant Modified Wobbe Index (MWI) during start-up and steady-state operation of the LNG facility by processing one or more intermediate process streams in a fuel gas separator. In one embodiment, the fuel gas separator employs a hydrocarbon-separating membrane, which can remove heavy hydrocarbons and/or concentrate nitrogen from the incoming process streams.