This article looks at how custody transfer for hydrogen is now possible thanks to new-generation measurement technologies.
Though custody transfer is a term typically associated with the oil and gas industry, custody transfer of hydrogen is an increasingly common practice as hydrogen becomes ever more important in the energy mix.
Hydrogen custody transfer has several unique challenges that must be overcome to ensure the process is effective, safe, and highly accurate, whether on-site, exchanging hands, or crossing borders. Hydrogen, despite having significant potential, is a relatively nascent industry that embraces new technologies. These new technologies can ensure that best practices are set into custody transfer procedures from the outset.
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Chiefly because it can be combusted without producing any pollutants, hydrogen is a promising option for future energy needs. Clean or green hydrogen is generated through an electrolysis process using renewable electricity and produces little-to-no carbon emissions. The emergence of such green hydrogen is an area where technology is helping to reduce carbon impact and bring down renewable energy costs.
As more renewable energy sources are brought online, there are more opportunities to reduce emissions, as well as create a valuable byproduct, in the development of green hydrogen. This can, in turn, help to accelerate further efforts to lower society’s carbon footprint.
Huge Cross-Sector Potential
There are varied potential applications for hydrogen. For instance, it can be used as a clean combustion fuel in industry, replacing natural gas. Along with a wide range of other manufacturing processes, it may also be used in primary metal production and the manufacture of semiconductors and fuel cells.
Hydrogen is a viable fuel for road vehicles and is increasingly featured as an eco-friendly alternative for aerospace and shipping. Using existing networks, hydrogen can be blended with natural gas for water and space heating in buildings, while it can also be used as a way of storing renewable energy.
The economy for storing, transporting, and trading hydrogen as a resource will grow rapidly as the rollout of hydrogen as an energy source becomes more widespread. Therefore, in custody transfer, accurate flow measurement is crucial. Precision can be hard to maintain when operating in harsh field conditions, and even minor errors can potentially create a high financial impact.
A minor misreading can spiral into a major error over time and potentially undermine confidence in the process. It is vital that this is avoided for a growing industry like hydrogen.
The Fundamental Challenges of Handling Hydrogen
Hydrogen is often pressurized when stored and is usable in two physical states — gas or liquid. Metering must be highly accurate and able to handle high flow rates thanks to its low energy density compared to natural gas.
Hydrogen is also the smallest observed molecule in the universe, which can result in a higher likelihood of leakage. As hydrogen is odorless, it can be difficult to detect. Using traditional technologies, accurate measurement of hydrogen flow is a challenge.
The regulatory landscape must be robust to ensure standardization across market and countries to facilitate the increased adoption of hydrogen. As differing regulations and standards may apply, custody transfer across borders is a particular challenge.
In navigating the challenges of the growing hydrogen industry, collaboration between countries, regions and organizations will be fundamental. The American Gas Association (AGA) standard, in response, details the calculations required for measurement of hydrogen in normal conditions, and calculations in the field are certified against this standard.
Complexity of Custody Transfer Arrangements
The issue in this respect is that so-called ‘normal conditions’ rarely occur. Though the physics of pure hydrogen are well understood, in custody transfer, hydrogen can often be mixed with other gases (such as natural gas) which adds an additional layer of complexity.
Therefore, operators need to use the calculations as set out in the standard in addition to gaining an understanding of happenings inside the pipe, to ensure a ‘true’ reading of hydrogen quantities.
As stated, small errors can have a significant financial impact. Therefore, it is essential to ensure that measurements are as accurate as possible. An investment in advanced measurement equipment today will reap benefits through the reduced error rate.
As false reports can potentially have a significant effect on the market, influencing stock and commodity prices, customers must also have confidence in the measurement system.
A wide range of factors can cause measurement errors, including incorrectly calibrated equipment, human error, flow computers with incorrect algorithms, flawed or faulty measurement equipment, and drifting analog inputs. Problems can also result from inadequate maintenance of measurement systems.
It is vital to remember that a single mistake can render an entire custody transfer meaningless, so the stakes are particularly high to ensure that measurement is as precise as it can be.
New and Emerging Hydrogen Measurement Technologies
This is where a flow computer comes into play. When combined with Coriolis mass flow measurement, a flow computer provides a more precise picture of the true conditions and considers key variables, including the presence of other gases.
Widely considered to be one of the most accurate and cost-effective measurement techniques, Coriolis mass flow measurement has been used for many years in oil and gas custody transfer applications. The advantages it offers also render it a logical choice for the measurement of hydrogen.
Operating on the mass flow measurement principle, Coriolis meters are prized for their ability to measure multiple attributes over sustained periods with little maintenance requirements and high repeatability. A wide range of medium characteristics, including aggregate state, conductivity, and density, can be measured by the latest generation of devices from manufacturers such as ABB, with an accuracy to 0.1% in direct mass flow measurement.
Other measurement values can be inferred from the fluid density, mass flow rate and temperature measurements taken by a Coriolis meter, such as volumetric flow rate and percent concentration. Therefore, a single Coriolis meter can carry out the work of multiple instruments, reducing costs by minimizing the need for separate devices, while also limiting maintenance.
A flow computer is an electronic device that takes inputs from the pressure and temperature sensors as well as the flowmeter to compute a correct volume flow. The flow computer, in this sense, acts as the cash register of a hydrogen custody transfer application.
In real time, the software is used to validate field signals continuously and intelligently and raise an error condition so that appropriate actions may be taken when the measurement fails. In many cases, depending on the root cause, it can detect an error and warn the operator, but also correct the mismeasurement incident semi-automatically or even fully automatically and regenerate the flow calculation results, in near real-time, without contributing any further uncertainty.
This has the effect that mismeasurement incidents are now resolved in seconds, rather than weeks, which can save significant amounts of time when compared to manual resolution of issues. Paperwork can therefore be filled out swiftly and correctly, removing complexity and barriers from the custody transfer process.
Produced from materials originally authored by Danny Knoop from ABB.
This information has been sourced, reviewed and adapted from materials provided by ABB Measurement & Analytics.
For more information on this source, please visit ABB Measurement & Analytics.