Natural gas has been an important source of energy for domestic and industrial use worldwide. Recent trends in energy supply have led to changes in the composition of the supplied gas in many countries. Due to these changes, it becomes even more important to measure the composition of this gas. Especially in small-scale applications a need for in-line measurement technology was detected.
For instance, in the Netherlands in the 1950’s a large natural gas reservoir was discovered near Slochteren which supplied a steady and constant source for many decades. However, production from the Slochteren field is declining and will be stopped in 2030. Therefore, the gas grid has to be fed with gas from different sources.
What natural gas from all sources has in common is that it is composed of methane, usually 75…95%. The rest of the mix typically consists of higher alkanes, like ethane and propane and fractions of nitrogen and carbon dioxide. The exact composition depends on the source of the gas, so when a grid is supplied with a variety of gases the composition will change. Furthermore, other recent trends contribute to the fluctuations in composition.
Trends in gas compositions
Natural gas is very suitable to facilitate in the increasing use of renewable energies. Biogas produced from renewable energy sources in biogas plants can, after proper treatment, be fed into the grid. However, biogas composition will depend on the feedstock, which is not always constant in time.
- For more information about adsorption processes used for purification of bio- or natural gas, read our blog about Biogas Purification Testing.
Another important trend is power to gas or P2G; here electricity, produced from renewable sources like solar or wind, is used to produce a gas as an energy carrier. This can be hydrogen produced with electrolysis, or synthetic methane by combining carbon dioxide and hydrogen produced from electrolysis.
A major factor in renewable energy is the mismatch between supply and demand. As you can imagine solar energy is only being produced during daytime. Transferring electrical energy into chemical energy by producing combustible gases and feeding this in the national grid can help to balance this mismatch by utilizing the large buffer capacity of the available gas networks. Recent research, by for instance Kiwa, has shown that the current gas grid in the Netherlands can handle several tens of percent of hydrogen with limited modifications.
All these factors are leading to increasing changes to the gas composition in the network. Composition and quality are strongly correlated; increasing amounts of inert gases, like nitrogen or carbon dioxide, reduce the amount of energy produced when burned, also known as the calorific value. The presence of hydrogen in natural gas can change flame characteristics, such as temperature and flame speed.
Measuring the composition
With changing chemical compositions it becomes increasingly important to measure calorific value and components. With only a single point of entry, one measurement sufficed to analyse the composition in the downstream network. In the present day grid, networks are more intertwined and have multiple points where gases are blended. At every point of entry, it is necessary to measure the composition, not only for quality control but also for fiscal purposes. In this way, the suppliers can make sure consumers receive the quality they need and are charged for the heating value of the gas rather than the volume they receive.
The current standard for determining gas quality is gas chromatography; this method is very accurate but also slow and expensive. Alternative methods like calorimetry are similarly expensive and have a large footprint, making it hard to implement in small-scale applications.
All these future trends lead to a need for measurement technology that can be used in-line and in small-scale applications. This requires sensors that are compact, cost-effective and preferably measure composition.
New solution for gas property measurement In collaboration with:
- TNO (the Netherlands Organisation for Applied Scientific Research),
- Venne Electronics (a Dutch supplier of electronic products) and
- Dutch gas grid operators Alliander and Gasunie
Bronkhorst is developing a solution for gas property measurement that can be installed in many installations for a wide range of applications.
Probe sensor concept with protective cover removed.
The operational principle of the concept is based on the preferential absorption of gas components on coatings that are applied to interdigitated electrode structures. The absorption is proportional to component concentration and results in a change in electrical properties that can be detected as a variation in capacitance of the coating.
DIE sensor (sensor with a small silicon circuit) with interdigitated electrodes and coatings.
Currently, the concept is being tested in the natural gas network of the Netherlands in close collaboration with grid operators and project partners, Alliander and Gasunie.
Methane concentration in the Dutch national grid measured with the concept and gas chromatograph.
Based on the measured components detected at the different coatings, the calorific value can be calculated, based on the concentration of the measured components. In combination with the integrated pressure and temperature sensor, other key parameters for the characterization of natural gas like; Wobbe Index, Propane Equivalent or combustion air requirement can be determined.
By using these parameters as input for a control system, users can optimize their processes to increase efficiency, reduce pollutants, or manage load. For instance in processes such as:
- Monitoring of gas quality in the national grid
- Process control in the production of biogas/synthetic gas
- Motor management for gas engines and burners
Would you like to learn more about odorization of natural gas? Have a look at our blog ‘How Mass Flow Controllers make our gas smell’
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