Aufrufe
vor 13 Monaten

PuK - Process Technology & Components 2023

  • Text
  • Harnischcom
  • Maintenance
  • Compressed
  • Monitoring
  • Hydrogen
  • Vacuum
  • Components
  • Compressors
  • Website
  • Valves
  • Pumps
A technical trade magazine with a history of 60 years.

Hydrogen Unafraid of

Hydrogen Unafraid of hydrogen Dipl.-Ing. Norbert Weimer The topic in this paper is the sealing of hydrogen using static flat gaskets made of fibrous materials (FA). Hydrogen is being hailed as the “oil of the future”, underlining how many designers and practitioners will have to become familiar with using it in their construction projects, plant designs, procurement scenarios and assembly activities. This includes determining how to seal components properly when working with hydrogen. The aim of this article is to raise awareness of this issue and provide information to enable proper decision-making for the material selection and the installation situation. One of the most common forms of sealing is static sealing, where the components to be sealed remain immobile in relation to each other. With these connections, considerable pressure is exerted on the sealing material installed between the flanges - the high-pressure seal. To seal properly, the material used must be adaptable and migrate into the roughness of the flange surface as well as compensate for its waviness. Conversely, despite the high forces involved, the material must remain intact - a typical technical compromise. Klinger has developed a manufacturing process to meet this compromise: The calendering process involves processing a mixture of fibres and fillers with elastomer as a binder into a sealing sheet on a hot roller by exerting enormous pressure. The result is a highly resilient seal, typically capable of withstanding loads of over 200 MPa (approx. 2 tonnes per cm²) at room temperature, which has the smallest of pores and allows adaptation to the surface roughness by compressing the pores and the elastomer. Pressing together, e. g. via screws, prevents surface leakage and leakage through the sealing material - the higher the sealing force, the tighter the connection. Leakage requirements for gas supply The DIN-DVGW type test according to DIN 3535-6 of April 2019 specifies corresponding values. The specific Static gaskets - Soft gaskets Fig. 2: Sealing surface and seal leakage rate must be ≤ 0.1 mg/(s x m). For FA gasket materials, a gasket thickness of 2.0 mm, internal pressure of 40 bar and surface pressure of 32 MPa are assumed. The test gas is nitrogen. So far, we have been using fossil media such as natural gas (predominantly methane) and propane and butane as standards for our energy supply. For these gases, the tightness requirements are sufficient - but what about hydrogen? Does hydrogen differ from the usual fuel gases? Fig. 1: Flange with high-pressure seal (Photo © : KLINGER) Hydrogen gas has a low density and the atom has very low spatial expansion. In fact, it is the smallest atom in 16 PROCESS TECHNOLOGY & COMPONENTS 2023

Hydrogen the periodic table of elements. This is why, in theory, it traverses the smallest channels with greater ease than larger atoms. The reality, however, is different, because hydrogen is only atomic when produced and immediately combines with the next hydrogen atom to form the hydrogen molecule H 2 , which can be pictured in the shape of a dumbbell. Nevertheless, the fuel gases having proliferated to date, methane CH 4 (the main component of natural gas), propane C 3 H 8 and butane C 4 H 10 are all clearly larger. Recent years have seen a growing shift in the use of helium (He) rather than nitrogen as the test gas for measuring any leakage from sealed joints. Accordingly, now we have the second-smallest atom in the periodic table of elements as our standard test gas, which is usable to detect the smallest leaks. Rather than being rigid, our gas particles move due to Brownian molecular motion. If we now compare the kinetic diameters of the relevant gas particles, we see that the helium atom and hydrogen molecule are comparable in size. In the table of kinetic diameters (www.arnold-chemie.de ) we see hydrogen H 2 helium He and for methane CH 4 3.8 Å where 1 Å = 0.1 nm 2.3 – 2.9 Å 2.6 – 2.7 Å And what we notice is that hydrogen, although “smaller” than methane, is on a par with our test gas helium, size-wise. Similarly, previous actual comparative measurements have shown that, despite differences in the quantities of hydrogen and helium leaking, they are of the same order of magnitude. One other thing to note about hydrogen is that it burns faster than natural gas, which explains the smaller distances between the burner nozzle and flame in gas burners. As a result, both the flame detection technology and the material selection of the burner nozzle and other parameters have to be adjusted. Furthermore, unlike other gases, hydrogen has a negative Joule-Thompson effect. But none of this is relevant in the context of tightness of connections. What practical experience do you have? Hydrogen has been a common raw material in the chemical industry for many years. According to the VCI, hydrogen is crucial here and forms the starting point of important chemical value chains. Already today, about 12.5 billion cubic metres of hydrogen are used annually in Germany (according to vci.de). The town gas used in the past contained hydrogen up to around 50 %. Hydrogen is not chemically aggressive and does not attack the usual fibre, graphite and PTFE sealing materials used. Ample proof of our strong familiarity with the medium and the fact we have long been successfully implementing corresponding sealing strategies. A look at the potential dangers of hydrogen As with all fuel gases, there is also a risk of unintentional combustion in the form of an explosion with hydrogen. And here, the explosion limits of the various fuel gases must be observed. The lower explosion limit (LEL) in air is 4 vol% for hydrogen and 4.4 vol% for methane - which resembles the figures just mentioned. The upper explosion limits, however, at 77 vol% H 2 and 16.5 vol% CH 4 are poles apart. Within CEN/TC 58 - Safety and control devices for Burners and appliances burning gaseous or liquid fuels - there is working group 15, which handles the subject of hydrogen and prepares information for international standardisation. Among other things, the “CEN/TC 58 WG 15 evaluations 2022-04-14” presentation deals with a comparison of fuel gases methane, propane and butane with hydrogen and hydrogen/natural gas mixtures 20 % to 80 % with a view to gas installation equipment. Gas fixtures installed, like heating system burners, appliances and household devices, offer wide-ranging potential for future hydrogen applications. With all this in mind, the working group performed a hazard assessment, the scope of which included extensive calculations and initial measurements to get a clear picture. The danger from combustible gases is influenced not only by their leakage behaviour but also their ignit ability. So the working group assessed such influences and described them mathematically. Clearly, although the hazard potential of hydrogen exceeds that of natural gas (methane), it remains well below that of propane and butane. Conclusion 1. We have positive experience with our well-known and high-quality fibre-based gaskets sealing materials from a history of safe sealing of hydrogen. 2. Independent leakage measurements also show that we are within the usual ranges for fuel gases with hydrogen. 3. And with the potential explosion hazard in mind, our experience with hydrogen underlines our progress within a familiar framework that has been safely controlled for many years. In sum, therefore, we see no need to fear hydrogen as a future carbon- free energy carrier. Contingent on appropriate design and having professionals in to install, hydrogen can be a safe means of achieving decarbonisation. The hydrogen age is on the horizon! The Author: Dipl.-Ing. Norbert Weimer, KLINGER GmbH, Idstein, Germany PROCESS TECHNOLOGY & COMPONENTS 2023 17

Wählen Sie die gewünschte Fachzeitschrift

fng MAGAZIN - Food · Nonfood · Getränke · Tobacco