Real-Time LNG Methane Number Calculation via Liquid Phase Sensors
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Solution Overview
Problem
Current methods for calculating the methane index of liquefied natural gas (LNG) in on-board tanks are inefficient and costly, as they rely on gas phase composition measurements, which differ from the liquid phase composition, leading to inaccurate predictions and potential engine knocking issues.
Innovation Solution
A method using three sensors to measure temperature, density, and pressure of the liquid phase LNG, combined with nonlinear optimization algorithms, to approximate the methane index with a margin of error less than 5%, thereby addressing the composition variability and cost issues of existing techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gas phase composition measurement methods are used to calculate methane index, then measurement precision can be achieved, but the results do not correspond to actual liquid phase composition leading to inaccurate predictions
Solution Approach 1:
The patent changes the measurement parameter from gas phase composition to liquid phase composition. By measuring the liquid phase composition directly using density and temperature parameters, the system obtains accurate methane index values that reflect the actual fuel composition injected into the engine, resolving the discrepancy between gas phase measurements and actual liquid phase properties
Solution Approach 2:
The patent replaces complex gas phase analysis systems with simpler liquid phase measurement systems. Instead of using expensive optical sensors or chromatography to analyze gas phase composition, the system uses straightforward density and temperature measurements of the liquid phase, substituting a more reliable and cost-effective measurement approach
2Measurement precision
If optical measurement by spectrometry is used to determine gas phase composition, then precision on heavy hydrocarbons is achieved, but cost increases significantly
Solution Approach 1:
The patent replaces expensive optical sensors and spectrometry equipment with inexpensive density and temperature sensors. These simpler sensors can be easily installed in LNG tanks and provide sufficient measurement precision without the high cost and complexity of optical measurement systems
Solution Approach 2:
The patent extracts the essential measurement parameters (density and temperature) from the complex gas phase composition analysis. By focusing only on these two key liquid phase parameters, the system achieves the necessary measurement precision while eliminating the need for expensive optical measurement equipment
3Device complexity
If calculation by empirical correlation with temperature and pressure sensors is used, then cost is reduced, but manufacturing precision is compromised as sensors must be adapted for LNG
Solution Approach 1:
The patent changes from using pressure sensors to using density sensors. Density is a more suitable parameter for LNG characterization as it directly reflects composition changes. This parameter substitution eliminates the need to adapt pressure sensors for LNG use while maintaining measurement accuracy
Solution Approach 2:
The patent uses readily available density and temperature sensors that can be directly applied to LNG tanks without requiring specialized adaptation. These off-the-shelf sensors provide the necessary measurement capability without the cost and complexity of customized sensor solutions
4Measurement precision
If chromatography measurement is used to determine composition, then accurate composition analysis is achieved, but device size and cost make it unthinkable for on-board tanks
Solution Approach 1:
The patent extracts the essential composition information from complex chromatography analysis by using simple density measurements of the liquid phase. This extraction approach provides sufficient composition data for methane index calculation without requiring bulky and expensive chromatography equipment
Solution Approach 2:
The patent replaces complex chromatography instrumentation with simple density and temperature sensing systems. This substitution enables accurate composition analysis in a compact form factor suitable for on-board LNG tanks, eliminating the need for large, expensive laboratory-style equipment
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 allows for accurate, real-time calculation of the methane index with high precision, reducing the risk of engine knocking and enhancing the stability and efficiency of LNG fuel systems.
Implementation Method 1
a layer of natural gas (11) in the liquid state (1) defined at an instant t given by its temperature T(t) and its density ρ(t), said layer of natural gas (11) being in equilibrium with a layer of natural gas (12) in the gaseous state (g)
Data Source
AI summary
The invention relates to a method for calculating in real time the methane number of a liquefied natural gas contained in a tank, in particular in an on-board tank.