Source: Energy & Management Powernews, August 02, 2022
The VDI advises to urgently include hydrogen use in the planning. A subsequent conversion may be uneconomical due to the different degrees of cold.
Four floating and two stationary LNG terminals in Stade and Brunsbüttel are planned in Germany for gas imports. The form in which hydrogen will flow through these facilities in the future - whether liquefied as liquid hydrogen (LH2) or alternatively transformed in the form of green ammonia or green methane, for example - is currently unclear. The Association of German Engineers (VDI) advocates playing it safe and considers the hydrogen capability of LNG facilities to be "indispensable."
The construction of LNG terminals is a long-term investment, it says, so it is imperative to consider the subsequent transit of green gases. A terminal that could be used for liquefied natural gas (LNG) and later for LH2 should ideally be planned and built right away as if it would be operated exclusively with liquid hydrogen.
"A later retrofit is possible, but not economically viable, as too many major components would have to be replaced," the association wrote in a recent statement. The tanks, in particular, would have to deal with significant temperature differences, depending on the flow medium: Liquid natural gas, for example, has a temperature of minus 163 degrees Celcius at landfall, while liquid hydrogen has a temperature of minus 253 degrees Celcius. This places significantly higher demands on thermal insulation and metallic materials, according to the VDI. The association refers to H2-ready steels that are already being used in the LNG sector. If other steels were used, embrittlement and cracks in the material could be expected, it said.
Since hydrogen has a slightly lower calorific value than natural gas - 10.7 megajoules per standard cubic meter (MJ/Nm3) versus 35.7 MJ/Nm3, the heat required for regasification also differs: according to the VDI, LH2 requires heat of 0.35 MJ/Nm3, while LNG requires 0.6 MJ/Nm3. According to the association, it would make sense to make the evaporators for regasification modularly expandable in order to achieve the necessary flexibility in the required heat output.
However, the risk of bad investments remains
In addition, the VDI considers it reasonable to use ambient heat (air, seawater) to heat the gases instead of the heat of combustion. For the larger cooler air and water quantities, however, the environmental compatibility must be examined, for example the influence on the ecosystem concerned. LH2 refrigeration is also very valuable in terms of energy: theoretically, 1.7 times as much refrigeration can be obtained from this refrigeration than from natural gas. In particular, LH2 refrigeration could be put to good use for process refrigeration applications in industry.
However, the association sees a shortcoming in its H2-readiness condition for the planned LNG terminals: should it become apparent in the future that shipping hydrogen in the form of ammonia or green methane is more economical, the additional investments for the hydrogen-readiness of the facilities could prove to be a misinvestment.
Author: Davina Spohn
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