简述
- Renewables rising: Wind, water and solar power are at the heart of the energy transition. They reduce dependence on fossil fuels and drive decarbonization, making them the cornerstone of a sustainable energy system that can meet growing demand while protecting the climate.
- Gas as a bridge: Despite the rapid expansion of renewables, natural gas will continue to play a crucial role in securing reliable and affordable energy in the coming years. It serves as a bridge technology that ensures stability while cleaner alternatives scale up and become more widely available.
- Hydrogen & storage: To balance the weather-dependent nature of renewables and seasonal shifts in consumption, new solutions are needed. Hydrogen is emerging as a versatile energy source, while advanced storage technologies are essential to store surplus energy and provide stability — bringing the goal of a CO2-neutral supply closer.
Hydrogen in the gas network
The production of hydrogen from renewable energies and the feeding in of the hydrogen into existing gas networks play an important role on the way to a CO2-neutral energy supply. Hydrogen can be produced in locations where there is a high availability of renewable energy. Furthermore, it can be stored and transported to the consumer as an additional energy carrier via the existing gas networks. Hydrogen can be stored and transported at up to 30 vol.% in the existing natural gas distribution network.
The networks for pure hydrogen will initially be expanded regionally. These will then gradually grow together to eventually form larger networks. Estimates for a Europe-wide hydrogen transport network predict that up to 40,000 km of network can be created by 2040.
Effects on gas flow measurement
The ability to reliably and stably measure the flow of natural gas with admixed hydrogen is therefore becoming increasingly important these days. The change in gas composition poses new measurement challenges for the various metering technologies. This is because the added hydrogen affects the properties of the natural gas: the density, viscosity, explosivity, flow rate, and sound velocities of the gas change. This poses completely new challenges for pipelines, compressors, seals, valves, measurement technology, etc., for example in regard to the risk of leaks and explosions or the determination of the calorific value. Gas network operators and gas suppliers are therefore wondering how this will affect the performance of their gas flowmeters.
Ultrasonic flow measurement has set a new standard for reliability, durability, and measurement accuracy in both the natural gas and process gas industries over the past two decades.
Adding a small percentage of hydrogen to natural gas already significantly increases the speed of sound (SOS) of the gas mixture. At 100% hydrogen by volume, it is about three times that of natural gas. The diagrams in Figure 1 show the SOS for natural gas, a hydrogen mixture of 30 vol%, and pure hydrogen.
Figure 1: speed of sound for a typical natural gas (methane content of 90
vol%) and hydrogen admixtures up to 100
This places several requirements on the USM design. Both the natural gas-equivalent measuring range and the required measurement uncertainty must be ensured. This includes reducing the scatter of measured values, reducing cross-sensitivities to pressure, temperature and media fluctuations, and reducing fluid-mechanical effects.
For natural gas with hydrogen admixtures of up to 30 vol%, it is still possible to compensate for this effect.
Figure 2: application example of a FLOWSIC device
Ultrasonic flow measurement: Ready for future requirements as well
The same specifications and requirements - especially with regard to measurement accuracy - can be expected for the future custody transfer measurement of hydrogen admixtures and pure hydrogen as for measurement in natural gas. The ultrasonic gas flowmeters (USM) must be appropriately adapted to the new measuring task.
Dedicated hydrogen transport pipelines will not differ significantly, however, from natural gas pipelines. The requirements are similar to those for today's natural gas meters. For an energy-equivalent transport capacity, either larger nominal diameters or higher flow rates are required in the transport systems. USMs specially designed for hydrogen must therefore permit higher maximum gas velocities.
As USMs can satisfy all the requirements very well, they are ideal for custody transfer flow measurement in future transport and distribution networks, whether for hydrogen admixtures or pure hydrogen.
The advantages of flow measurement using a USM are:
- Wide range of nominal diameters (DN50 to DN1400)
- High measuring span of ≥ 1:100
- Non-blocking, no pressure loss
- No mechanical moving parts, no pulsation
- Higher flow rates with hydrogen
- Transferability of the calibration to other media
In addition to classification according to hydrogen content, USMs can also be differentiated according to their use in process gas applications, in transport networks, and in distribution networks:
Gas Quality Indicator (GQI): Determination of the hydrogen content
In addition to the primary measured values and the required high accuracy, ultrasonic gas flowmeters (USM) offer further advantages: Thanks to the implementation of a “gas quality indicator” (GQI) in the USM, this device offers the ability to detect changes in the gas composition via the value of the speed of sound (SOS). Even small changes in hydrogen content can be detected very accurately due to the extremely high SOS of hydrogen. If the reference gas composition or its SOS (without hydrogen) is known, it is also possible to very accurately determine the hydrogen content. The device compares the measured SOS value with the reference SOS value. Assuming that any difference is solely attributable to the hydrogen admixture, the hydrogen content can be determined directly. The approximation is done via an empirical formula implemented in the firmware of the USM.
Summary
Ultrasonic gas flowmeters have been successfully used for more than 20 years to measure the quantity of gas in a wide range of applications. This includes applications for gases with different hydrogen contents. The devices used in these applications, as well as others from the FLOWSIC product family, have already been adapted and approved for the fiscal metering of natural gases with a hydrogen content of up to 30% by volume. Operators of gas networks can follow the trend of feeding regenerative produced hydrogen into existing gas networks, and transporting and storing the hydrogen - without additional investment in new gas flowmeters.
The diagnostic options of the USM allow not only a quantitative measurement but also a qualitative determination of the gas. The device therefore provides a supplementary analysis method for hydrogen. This can replace costly analytical techniques for hydrogen determination, such as extractive gas chromatography, in some applications.
For already installed devices, an inspection of the device condition is recommended to evaluate the impact of feeding in up to 30% hydrogen. The effect of aging, installation conditions, or the pressure regulator should also be checked. The Service department at Endress+Hauser can assist with this evaluation.
