NDIR Gas Impurity Quantification Using Modulated Reference Dilution
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Solution Overview
Problem
Existing gas detection systems face challenges in accurately distinguishing between utility gas and swamp gas due to the lack of high selectivity between methane and ethane, leading to concentration prediction errors from optically interfering impurities, particularly at varying gas concentrations.
Innovation Solution
A method using gas modulation techniques to measure infrared absorption at different sample gas concentrations, comparing signal amplitudes with pre-recorded calibration functions to assess actual impurity levels, optimizing gas modulation frequencies and dilution to enhance sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gas chromatography or cryogenic separation is used to separate and analyze gas components, then selectivity between methane and ethane is improved, but response time increases to several minutes or more
Solution Approach 1:
The measurement process is segmented into multiple rapid successive measurements at different gas modulation frequencies. Instead of using a single slow separation process, the patent divides the analysis into multiple quick measurements that collectively provide the necessary selectivity and concentration information.
Solution Approach 2:
The patent employs periodic gas modulation at different frequencies to alternately introduce gas samples at varying concentrations into the detector. This periodic action enables rapid sequential measurements that achieve separation-like selectivity without the time delay of physical separation processes.
2Device complexity
If a single NDIR sensor is used for detection, then device complexity is reduced, but the ability to accurately quantify both very low concentrations (ppm level) and very high concentrations (1-100%) is compromised
Solution Approach 1:
The patent makes the measurement system dynamic by varying the gas modulation frequency and sample gas time period ratios during measurement. This dynamic adjustment allows a single sensor to adapt its sensitivity range, enabling accurate measurement across both ppm and percentage concentration levels without requiring multiple fixed sensors.
Solution Approach 2:
The patent changes operational parameters (gas modulation frequency, sample gas time period ratio) to optimize the single NDIR sensor's performance across different concentration ranges. By adjusting these parameters, the same sensor can accurately detect both trace ppm levels and high percentage concentrations.
3Adaptability or versatility
If gas modulation with varying sample gas time periods is used to achieve different concentrations, then measurement capability across wide concentration ranges is improved, but measurement process complexity increases
Solution Approach 1:
The system performs self-calibration and self-assessment by automatically comparing measurements taken at different gas modulation frequencies against pre-stored calibration functions. This self-service approach handles the complexity of multi-concentration measurement automatically without requiring manual intervention or complex external calibration procedures.
Solution Approach 2:
The patent implements feedback by comparing the actual measurement signals against pre-recorded calibration functions that represent expected signal amplitudes for known impurity levels. This feedback mechanism automatically assesses impurity concentrations and compensates for measurement variations, simplifying the overall process despite the dynamic measurement approach.
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
Enables rapid discrimination between utility and swamp gas by compensating for impurity levels, providing accurate concentration predictions across a wide range of gas concentrations in real-time.
Implementation Method 1
Infrared gas analyzers detect infrared radiation passing through a gas sample. The measurement principle is based on the fact that specific gas components absorb infrared radiation.
Implementation Method 2
A typical infrared sensor often used in this type of detector is a non-dispersive infrared absorption detector (NDIR sensor). NDIR sensors measure the amount of infrared radiation in one or several wavelength ranges in the radiation passed through the gas to be analyzed.
Data Source
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AI summary
Method for quantifying the amount of optically interfering gas impurities in a Gas detection system comprising a sample gas inlet (12), a reference gas inlet (14), a gas modulation valve (16) and an infrared absorption gas detector (24) used for analysis of methane or natural gas, wherein the gas modulation valve (16) alternatingly connects the sample gas inlet (12) to the gas detector (24) during a sample gas time period and the reference gas inlet (14) to the gas analyser during a reference gas time period characterized in that the infrared absorption is measured for at least two different sample gas concentrations in the gas detector (24) achieved via respective different ratios of sample gas time period vs. reference gas time period, wherein the amplitudes of the different measurement signals are compared with calibration functions representing the signal amplitude versus the gas concentration of different amounts of interfering gas impurities in methane or natural gas in order to thereby assess the actual gas impurities concentration in the sampled gas.