< Previous20 MOBILE HYDROGEN REFUELLING STATION FLOW METER STANDARD Carl Wordsworth, Head of Water Sector, TÜV SÜD National Engineering Laboratory There are plans for partial or full replacement of natural gas with hydrogen in grids as well as ambitious targets to enhance the production of fuel cell vehicles and the development of hydrogen refuelling stations. These will form the infrastructure of a future hydrogen network. Accurate metering of hydrogen at different points of this network is particularly important, especially when hydrogen is transferred from one party (a seller) to another (a buyer). Fuel cell electric vehicles (FCEV) along with battery electric vehicles (BEV) are currently considered the most promising candidates for the future of transportation. FCEVs are electric vehicles that use hydrogen as their fuel. Hydrogen reacts with oxygen in a reverse electrolysis reaction in their fuel cells to generate the required electricity. This process is free of carbon emissions as the only product of the reaction is water. FCEVs offer significant advantages, especially for larger vehicles such as buses and heavy goods vehicles (HGV). The hydrogen tank of an FCEV (small or large) can be filled in a few minutes compared to the hours needed to charge a BEV. However, increasing the use of FCEVs requires the development of relevant infrastructures such as hydrogen refuelling stations (HRS), technologies such as accurate hydrogen flow meters, and regulations. All of these are in their preliminary stages of development, although growing at a fast pace. Hydrogen is sold based on mass (in kilograms) in Hydrogen Refuelling Stations (HRSs). Accurate billing, however, needs accurate metering of hydrogen which is a challenge at the present time. Liquid fuels, such as petrol and diesel, need to be measured to 0.5% accuracy in the refuelling stations based on the recommendations of the International Organisation of Legal Metrology (Accuracy Class 0.5 based on the document OIML R117). The required accuracy for the measuring system of gaseous fuels, such as compressed natural gas (CNG), is 1.5% (Class 1.5 based on OIML R 119). However, OIML R 119, separates hydrogen from all other types of gaseous fuels and recommends Class 2 and Class 4 (2% and 4% accuracy of the measuring system, respectively) for its measurements. It is expected that many countries will enforce Class 2 of OIML R 119 in the coming years. There are several factors that make the metering of hydrogen challenging at HRSs. Hydrogen has an extremely high gravimetric energy density of 140 MJ/kg. This means that it stores a lot of energy relative to its weight, much more than natural gas (53.6 MJ/kg), diesel (45.6 MJ/kg), and lithium-ion batteries (<5 MJ/kg). In volumetric terms, hydrogen is the least dense of any gas and takes up more space than natural gas and diesel. To improve its bmta.co.ukbmta.co.uk Hydrogen is recognised as playing a crucial role in reducing global carbon dioxide emissions. From transportation to heating homes, hydrogen is already expected to play a significant part in replacing fossil fuels in net zero policies in the UK and around the world. 21 efficiency as an energy carrier, hydrogen is compressed to pressures as high as 700 bar in hydrogen vehicles. In this compressed state, hydrogen occupies about the same space as a battery, for much less weight. Another advantage of hydrogen vehicles is the fast-refuelling time. However, when hydrogen is rapidly compressed to 700 bar, a lot of heat is generated. To stay within safe operating limits, the quickest fuelling protocols pre-cool the gas to -40°C. Hydrogen refuelling stations are therefore required to operate across a wide range of pressures (up to 875 bar) and temperatures (-40 to 60°C). This is particularly challenging from a measurement perspective since the accuracy of most flow meter technologies is adversely affected by extreme pressure and temperature conditions, as well as the transient flow encountered for vehicle filling. To be able to assess the accuracy of hydrogen refuelling stations it is necessary to develop mobile hydrogen standards, that can be transferred to the site of the refuelling station to test the accuracy of the hydrogen dispenser. When considering hydrogen refuelling standards, it is important to consider the measurement accuracies of the mobile standards. For example, personal vehicles typically have fuel tanks ranging from (0.5 to 6kg) total capacity and are classed as light duty. While heavy goods vehicles have much larger tanks (10 to 40kg) and are classed as heavy duty. Therefore, to provide the necessary measurement accuracy for the mobile standards being developed, two systems have been developed. This is required, as the typical way of measuring the flow in the hydrogen mobile standard is to use a gravimetric approach and weigh the mass of the hydrogen being added to the mobile standard. Due to the differences in fuel tank size in the different vehicles, it is difficult to design a system that can provide the necessary measurement accuracy over the full range of possible hydrogen masses required. TÜV SÜD National Engineering Laboratory is part of the National Measurement System and holder of the national standard for flow. We also operate a Flow Programme Project for the Department of Business, Energy, and Industrial Strategy (BEIS). As part of this project, TÜV SÜD undertakes flow metrology research and development aimed at keeping the United Kingdom Figure 1: Light-Duty Mobile Standard Figure 2: Light-Duty Mobile Standard bmta.co.uk22 bmta.co.ukbmta.co.uk at the forefront of the flow metrology arena, as well as determining the future trends and requirements for flow metrology. TÜV SÜD is carrying out the design, build and testing of two mobile hydrogen refuelling station standards. The light-duty vehicle mobile standard is in the process of being commissioned at TÜV SÜD while the heavy-duty standard is undergoing the detailed design stage. The table below shows the differences in hydrogen refuelling for both light and heavy-duty applications. Light DutyHeavy Duty Maximum Pressure700 bar350 bar H 2 Capacity4 – 6 kg30 – 40 kg Pressure Ramp Rate200 bar/minute30 bar/minute Filling Time3 – 5 minutes10 – 15 minutes Figures 1 and 2 show photographs of the light-duty standard developed by TÜV SÜD. Figure 3 shows a schematic of the mobile standard. The schematic shows the hydrogen storage tanks that are used to measure the hydrogen output from the refuelling station. These tanks are located on weigh scales that enable a very accurate measurement of the hydrogen to allow the flow from the refuelling station to be assessed. Figure 3: Schematic of Light-Duty Standard23 The light-duty mobile standard is currently being commissioned and validated so that it can be used to determine and verify the performance of hydrogen refuelling stations in the UK. Currently, there is no capability in the UK to confirm that hydrogen refuelling dispensers meet the regulatory requirement of OIML R-139, so the principal benefit will be to enable this. Figure 4 shows the approach being used for the development of the heavy- duty mobile hydrogen refuelling station standard. Due to the increased requirement for hydrogen storage, as shown in the table, the heavy-duty standard is larger than the light-duty standard. In the heavy-duty standard, three large hydrogen storage tanks are used. Therefore, the system has been designed to operate in a separate container that can be disconnected from the transport vehicle. This has the added advantage that all the necessary power supply, data acquisition equipment, etc do not have to be ATEX-rated, as they can be located outside of any potentially explosive atmosphere. The detailed design of the heavy-duty system is currently being performed and the system is expected to be ready for commissioning in early 2023. Providing both station operators and consumers with confidence in the measurement of the dispensed quantity of hydrogen will help enable the widespread deployment of hydrogen refuelling stations within the UK. This would provide a pathway towards zero emissions at vehicle tailpipes, thus helping to meet the net zero target of the UK Government and ultimately helping to combat climate change. Figure 4: Schematic Showing Heavy Duty System Approach bmta.co.uk24 CLEANING UP THE FUEL OF THE FUTURE Dr Caroline Widdowson, Head of Market Development, Markes International Why hydrogen fuel is important Scientists have shown that to avert the worst impacts of climate change and preserve a liveable planet, the global temperature increase needs to be limited to 1.5°C above pre-industrial levels1. To keep global warming to no more than 1.5°C – as called for in the Paris Agreement 2 – emissions need to be reduced by 45% by 2030 and reach net zero (cutting greenhouse gas emissions to as close to zero as possible) by 2050. Hydrogen fuel has been identified as an alternative energy source to address the challenge of reaching net zero emissions. According to the Hydrogen Council (a global initiative that provides guidance on accelerating the deployment of hydrogen solutions), hydrogen will be able to supply more than 20% of the global energy demand by 2050.3 One example of the use of hydrogen is in hydrogen-fuelled vehicles. An electric motor powers these, but instead of plugging them in to charge like electric vehicles, they produce their own electricity inside an onboard fuel cell. Inside the cell, hydrogen reacts with oxygen in a process called reverse electrolysis. The reaction takes place on a catalyst. The hydrogen comes from one or more tanks built into the vehicle, filled at hydrogen refuelling stations, while the oxygen comes from the ambient air. The only products of the reaction are the electrical energy used to power the vehicle, heat and water. The water is emitted as water vapour, making hydrogen-powered cars emission-free. Contaminants are a problem However, the widespread adoption of hydrogen as a fuel could be challenged by the presence of contaminants that enter the fuel during the production or purification stages or elsewhere along the supply chain. Any impurities may result in substantial degradation of the fuel cell, even at very low concentrations (parts per billion). bmta.co.uk Hydrogen fuel is emerging as a key player in the rapidly growing clean energy market. However, hydrogen can contain impurities, introduced during production, purification and along the hydrogen supply chain, which limit the efficiency of fuel cells and contribute to pollution. With pressure on companies involved in the supply chain to maintain the purity of the hydrogen, they need to be able to detect even the tiniest amounts of impurities. An analytical technique called thermal desorption–gas chromatography-mass spectrometry can identify and quantify a wide range of compounds down to parts per trillion levels in accordance with regulations. Researchers will then be able to pinpoint the exact cause of fuel cell performance issues and find ways to avoid impurities entering the hydrogen supply or removing them.25 bmta.co.uk Hydrogen impurities include volatile organic compounds (VOCs) that interfere with performance, accelerate degradation and sometimes cause permanent damage to fuel cell components: •Hydrocarbons adsorb onto the catalyst’s surface, reducing the surface area, and impeding its ability to work properly. Hydrocarbons break down to release carbon monoxide, which also adsorbs onto the catalyst’s surface. •Sulfur compounds (mainly hydrogen sulfide) bond to the catalyst, deactivating it permanently. •Halogenated compounds can cause irreversible performance degradation of the fuel cell. •Formaldehyde and other aldehyde species such as acetaldehyde are very reactive and can readily decompose to release hydrogen and carbon monoxide, both of which degrade platinum catalysts. International hydrogen fuel quality standards (ISO 14687, EN 17124, ISO 21087, GB/T 37244, ASTM D7892 and SAE J27194–9) specify maximum concentrations of contaminants for commercial fuel cells. Hydrogen producers and suppliers must safeguard hydrogen quality in accordance with these standards by analysing samples for all, or a subset of the contaminants. Four key standards and their contaminant limit levels are listed in Table 1. Table 1: Hydrogen purity standards and associated limit levels. How can such low levels of contaminants be detected and measured? Trace levels of hydrocarbons, sulfur-containing compounds, halogenated compounds and aldehydes can be detected by thermal desorption–gas chromatography- mass spectrometry/other types of detection instruments. Thermal desorption instruments prepare samples for analysis by increasing the concentration of a sample prior to injection into the gas chromatograph. This is called preconcentration. The gas chromatograph then separates the compounds, and the mass spectrometer detects them, producing a chromatogram from which analysts can see which volatile organic compounds are in the sample. There are different ways to prepare samples for hydrogen fuels depending on sample location, stage of the supply chain and priority impurities for measurement. Some analysts will want to see what is in the entire sample – this approach is called a non-targeted approach. The targeted approach involves looking for a specific compound or 26 bmta.co.uk group of compounds and this would be useful for quality control or for fuel cell research and development. There are two ways to take samples for hydrogen fuels: •On-line monitoring of gas streams: Automated, scheduled sampling and analysis from a hydrogen gas stream provides a regular measure of hydrogen supply purity at source and along the supply chain. The hydrogen gas stream is directed into the thermal desorption instrument where the volatile impurities are preconcentrated before injection to the gas chromatograph. Results can be obtained within minutes of taking the samples. •Off-line sampling: Where it is not practical or cost- effective to install a full analytical setup for every sampling point, a special bag, canister or sorbent tube (a small tube containing a sorbent material that traps the volatile compounds of interest), can be used to collect a sample, which is then returned to a laboratory for analysis. There are also different detectors for detecting specific compounds. A mass spectrometer is used for the non- targeted profiling of an entire sample. To target specific chemicals of interest, other detectors can be used. Flame ionisation detectors enable analysts to identify halogenated and hydrocarbon compounds. Sulfur chemiluminescence detectors target sulfur-containing compounds. Electron capture detectors can be used to target halogenated compounds. The detectors can be combined on the same gas chromatograph. Figure 1 shows the sampling methods that can be used for each compound group. Another point to mention is that instruments should be certified as safe to work with hydrogen. Since 2021, a range of Markes International’s thermal desorption instruments has been multi-gas-enabled. ‘Multi-Gas’ is an award-winning technology that enables the user to choose one of three carrier gases (which are used to transfer volatile compounds through the analytical system) – helium, nitrogen or hydrogen. Each multi- gas instrument has been independently evaluated and certified for hydrogen carrier and sample gas so that the full analytical workflow can be safely configured with hydrogen. Putting the method into practice A multi-gas-enabled UNITY–CIA Advantage-xr™ system can be used to sample from on-line gas streams and off-line cylinders and bags. A water removal system – Kori-xr™ – can be added for humid samples. Water in samples is a problem because it can mask some compounds in the analytical data. Also, an ULTRA-xr™ autosampler was added. This enables unattended sampling of up to 100 sorbent tubes in a single sequence. Figure 1: Different types of sampling and analysis methods for hydrogen fuel impurities, highlighting the complementary nature of the different sampling methods.27 bmta.co.uk The system was used with a gas chromatograph and mass spectrometer to analyse a high-volume sample of a 10ppb (parts per billion) standard containing 60 compounds of interest and 50ppm (parts per million) of water (ten times the maximum water content listed in ISO 14687).10 All 60 compounds were identifiable on the resulting chromatogram (Figure 2) and the water was successfully removed (it would have appeared as a large peak on the chromatogram otherwise). Excellent limits of detection (smallest concentration of a measurand that can be reliably measured by an analytical procedure) values were achieved with an average of 16ppt (parts per trillion) across all 60 compounds, with the highest being 88ppt for isopropanol and the lowest being 4ppt for chlorodibromomethane. The values for all compounds are significantly lower than required by standard methods, for example, ISO 14687, which gives a maximum allowable concentration of 2000ppb for total hydrocarbons, 4ppb for total sulfur compounds and 50ppb for total halocarbons. An equally impressive limit of quantitation values was achieved with an average of 54ppt across all 60 compounds, with the highest being 292ppt for isopropanol and the lowest being 15ppt for chlorodibromomethane and tetrachloroethene. The limit of quantitation is the lowest concentration that can be determined with acceptable precision. Figure 2: Total ion chromatogram showing the peaks of interest for the 60 compounds of interest, produced from a high-volume sample of 10-ppb standard in humid hydrogen gas.28 bmta.co.uk Compound-specific detector Measuring total sulfur content is a priority in hydrogen fuel impurity analysis because it is so destructive to the fuel cell, so a sulfur chemiluminescence detector was employed instead of the mass spectrometer in conjunction with the same thermal desorption and gas chromatography setup. The detector is designed to detect sulfur compounds, reducing potential analytical interference from other impurities such as carbon dioxide, allowing for larger sample volumes and enhancing sensitivity for sulfur-containing compounds. Using sulfur chemiluminescence detection with preconcentration on a thermal desorption instrument, it is possible to detect exceptionally low levels of sulfur compounds. The results in Figure 3 show reliable detection and high sensitivity, even at 20ppt, which is far below the required detection limit for sulfur compounds. Conclusions Thermal desorption with gas chromatography-mass spectrometry is a powerful technique that exceeds the requirements of quality standards such as ISO 14687, EN 17124, SAE J2719 and ASTM D7892 for the analysis of VOC hydrogen fuel impurities. The results will give researchers the data they need to be able to find the causes of fuel cell degradation and find ways to remove them. Figure 3: Thermal desorption–gas chromatography–sulfur chemiluminescence data showing six replicate analyses of priority sulfur-containing compounds at 50ppt. References 1.https://www.un.org/en/climatechange/net-zero-coalition. 2.https://www.un.org/en/climatechange/paris-agreement. 3.https://hydrogencouncil.com/wp-content/uploads/2021/11/ Hydrogen-for-Net-Zero.pdf. 4.ISO 14687:2019, Hydrogen fuel quality – product specification, International Organization for Standardization, Geneva, Switzerland, https://www.iso.org/standard/69539.html. 5.ISO 21087, International standard, Gas analysis – Analytical methods for hydrogen fuel – Proton exchange membrane (PEM) fuel cell applications for road vehicles, https://www.iso. org/standard/69909.html. 6.GB/T 37244, Chinese standard, Fuel specification for proton exchange membrane fuel cell vehicles – Hydrogen, https:// www.standardsofchina.com/standard/GBT37244-2018. 7.EN 17124:2022, Hydrogen fuel. Product specification and quality assurance, Proton exchange membrane (PEM) fuel cell applications for road vehicles, European Committee on Standardisation, Bruxelles (2022), https://www. en-standard. eu/une-en-17124-2022-hydrogen-fuel-product-specification- and-quality-assurance-for-hydrogen-refuelling-points- dispensing-gaseous-hydrogen-proton-exchange-membrane- pem-fuel-cell-applications-for-vehicles/. 8.ASTM D7892, Standard test method for determination of total organic halides, total non-methane hydrocarbons, and formaldehyde in hydrogen fuel by gas chromatography/ mass spectrometry, https://www.en-standard.eu/astm-d7892- 22-standard-test-method-for-determination-of-total-organic- halides-total-non-methane-hydrocarbons-and-formaldehyde- in-hydrogen-fuel-by-gas-chromatography-mass-spectrometry/. 9.SAE J2719: Hydrogen fuel quality for fuel cell vehicles, https:// www.sae.org/standards/content/j2719_201109/. 10.Markes International Application Note 165: Optimised hydrogen fuel impurity analysis: identification, measurement and characterisation of volatile organic compounds by TD– GC–MS/SCD. 29 bmta.co.uk If you are reading this newsletter and would like to become a member of the BMTA, please send an email to enquiries@bmta.co.uk, requesting a membership application pack. 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