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In order to detect natural gas leaks in the built environment, the gas in the public distribution network is odorised. To maintain at least the same level of safety, hydrogen in the public distribution network will also have to be odorised. The final choice of the odorant for hydrogen has not yet been made, but there are good arguments for choosing tetrahydrothiophene (THT), which is also used in natural gas. The big advantage is that people in the Netherlands are familiar with the smell of THT and also link it to gas leakages. However, the disadvantage is that this odorant contains sulfur, which means that the use of odorised hydrogen is not possible in all end-user applications without pre-cleaning the gas.
Work package 2 of the Hydelta program investigated the effect of sulfur-containing odorants on the various end use applications. This is based on an odorant concentration of 10-40 mg THT/m3(n), corresponding to 3.5-14.5 mg S/m3(n), as specified for natural gas in the Dutch Ministerial Regulation on Gas Quality. A literature study was conducted for the study and additional discussions were held with manufacturers. The following applications have been considered:
- Central heating and hot water boilers;
- Kitchen appliances;
- Gas engines;
- gas turbines;
- Fuel cells;
- Feedstock and industry;
- Other applications, such as decorative fireplaces, outdoor heaters and patio heaters.
The impact of other gas quality parameters, the maturity and (economic) feasibility of the applications and the options for cleaning fell outside the scope of this study.
The results have shown that no insurmountable problems are to be expected for combustion equipment, such as central heating and hot water boilers, kitchen appliances, ornamental fireplaces, outdoor stoves and patio heaters, and gas engines when using hydrogen that is odorised with a sulfur-containing odorant, such as THT.
While these applications are relatively robust for low concentrations of sulfur (<14.5 mg S/m3(n)) in the hydrogen, fuel cells are very sensitive to these impurities. The presence of sulfur in the hydrogen leads to irreversible damage to the fuel cell. This is an accumulating process, which already occurs at sulfur concentrations of 1 ppm (1.4 mg S/m3(n)).
The development of hydrogen-driven gas turbines is still in full swing. Little is therefore currently known about the hydrogen specification ultimately required for gas turbines. In principle, gas turbines fall under ISO 14687 grade B, with a specified sulfur concentration of 10 molppm, corresponding to approximately 14 mg S/m3(n). This concentration corresponds to the maximum specification that currently applies to natural gas distributed in the Netherlands. It is known from the past that natural gas-fired turbines are suitable for this sulfur load. It is up to the suppliers to make the gas turbines still to be developed suitable for this sulfur load.
For feedstock applications, where the hydrogen is used directly in the production process, impurities such as sulfur are highly relevant. These processes are so specific that no general statements can be made about the maximum permissible sulfur content in hydrogen. It is expected, however, that additional cleaning will have to be applied, as is now also the case for odorised natural gas.
It should be noted that almost all feedstock processes are connected to the high-pressure transport system (HTL). It is expected that, in accordance with the current HTL network, the hydrogen backbone will also not be odorised and the sulfur impact will not be increased. The impact of sulfurous hydrogen will therefore not be an issue for these applications.
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