Fraunhofer Institute for Physical Measurement Techniques IPMPhotoacoustic sensor for measuring the hydrogen content of natural gas
»The more hydrogen we blend into natural gas, the lower the calorific value. Our photoacoustic sensor allows us to analyze gas composition much more easily and cost-effectively than before.«
Hydrogen content changes the calorific value of the gas
Natural gas is still used to heat the majority of our homes. But what exactly does it contain? At present, this question can only be answered by using complex, expensive measurement technology to perform spot checks. The matter will become even more pressing, however, as increasing amounts of hydrogen and biogas are fed into the natural gas grid. This changes the concentrations of the individual gas components and, as a result, the calorific value of gas, which is used as the basis for determining gas prices. Methane, which is the main component of natural gas, has three times the calorific value of hydrogen. Gas composition also has an impact on the combustion process. The supply of oxygen must be adjusted to the gas mixture for this process to be as effective as possible.
A compact, cost-effective sensor makes it easier to measure gas concentrations in blends of natural gas and hydrogen.
In the Brennsorik project, Fraunhofer IPM developed a compact, cost-effective sensor for analyzing gas concentrations in blends of natural gas and hydrogen without the complexity and expense of operating a process gas chromatograph.
The sensor works in accordance with the principle of resonant photoacoustics. This involves the gas in a measurement cell being irradiated with pulsed IR light. The gas molecules are excited as they absorb the light, and the resulting heat generates gas-specific acoustic waves that are read out using a MEMS microphone. The team uses IR LEDs with three different wavelengths and a NIR laser to identify the methane, hydrogen, ethane and carbon dioxide components in the gas. Since the concentration of hydrogen as a percentage cannot simply be measured optically, the gas-dependent resonance frequency is measured as a sum parameter. An algorithm incorporating all the measured values is used to calculate the individual concentrations of gases in the gas mixture as percentages. This method can be used to measure both natural gas concentrations and hydrogen concentrations of 0 to 100 percent. The calorific value can be calculated on the basis of the concentration percentages.
Brennsorik (Calorific value sensor technology for blends of natural gas and hydrogen) project, funded by the Fraunhofer-Gesellschaft (SME project)