There's a lot of talk about hydrogen.
But is there any kind of genuine marketplace for "normal" household appliances to run on hydrogen instead of natural gas: I mean
Are conversion kits available for COTS natural gas appliances (as they often are for propane)?
Let's presume the supply problem has been solved, and the house has access to appropriate volumes of hydrogen gas.
The title and body of your post have two slightly different questions, to which there are two different answers:
In 2018, the U.K. Department for Business, Energy & Industrial Strategy commissioned a study on the feasibility of using hydrogen in commercial appliances, and published a thorough report: "Appraisal of domestic hydrogen appliances". I'm going to quote extensively from the executive summary, adding some headings and emphasis, to answer the questions.
The study has involved a systematic review of the available literature as well as detailed industry engagement involving 1-2-1 conversations and a discussion workshop. The industry engagement has included appliance and component manufacturers, gas testing bodies, maintenance and servicing contract companies, trade associations and consultancies.
Hydrogen has a significantly higher flame speed, greater flammability range and is likely to burn at a higher temperature than natural gas. These characteristics present significant engineering challenges that particularly affect the burners in all four appliances. Specifically there are concerns with light-back (propagation of flames back through burner), higher NOx emissions and the potential explosion of unburned gas. To mitigate these effects, it maybe necessary to remove the primary aeration, re-size the burner ports (holes) and remove internal cavities where combustible gas mixtures could form. It will also be necessary to select and test materials that are suitable for higher temperature combustion. A number of potential options for new burner technologies have been identified in this study but there is currently no industry-wide consensus on the most feasible burners and further R&D is required.
Another key technical concern is the Flame Failure Device (FFD) which detects the presence of a flame and shuts off the gas supply if it is extinguished. Natural gas boilers use ionisation sensors to detect flames (via the resulting combustion gases)and these cannot be used with hydrogen. Fires, hobs and ovens use thermoelectric FFDs which have a relatively slow reaction time (typically 30 seconds or greater) and this could be a concern for ovens and fires that have enclosed volumes where unburnt gas could build up. Alternatives such as UV and IR sensors are available and used for industrial processes but these will need to be redeveloped to reduce their size and cost. In addition, hydrogen also burns with a pale blue flame that is difficult to see in daylight conditions and this presents aesthetic and safety concerns, particularly for fires and hobs.
Components such as the pipework, heat exchanger and gas valves will require some redevelopment due to the different combustion characteristics of hydrogen but the operational principles will not fundamentally change.
1. Hydrogen-specific appliances:
Overall, the view from stakeholders was that by developing appliances specifically designed for hydrogen (first option), they should be able to match the key features of existing natural gas appliances. This includes appliance efficiency, lifetime, maintenance requirements, size and ease of use.
2. Newly developed natural gas appliances with a hydrogen conversion kit:
The main advantage of adapted appliances (second option) is that the cost is only burdened if there is a switchover during the lifetime of the appliances. However, following such a switch over they may suffer reductions in performance compared to a new hydrogen appliance as they contain components that have not been fully optimised for hydrogen. There are also significant differences in the design and makeup of domestic gas appliances. Even within one appliance type, there are variations in current commercially available appliances and even greater variation in the makeup of the existing stock in domestic installations. Adapting existing natural gas hobs, ovens and fires to hydrogen is possible although would require a conversion kit that is sufficiently universal to fit different product variations. Adapting boilers is again, in theory possible, although given the limited space inside the appliances this will be very challenging from a practical perspective.
3. Newly developed dual-fuel appliances:
For all four appliances, a dual-fuel option that can readily interchange between natural gas and hydrogen without replacing components is in theory possible, but is likely to require doubling up various components including the burner system. This will significantly increase the size and is very unlikely to be accepted by occupants. For this reason, this option has been discounted and has not considered in the detailed options appraisal. In the context of a single gas switchover, Hydrogen Ready dual-fuel appliances are potentially more attractive. These would be designed for hydrogen but back-fitted in the factory to run on natural gas up to, and indeed if, switchover occurs. These appliances would be specifically developed to be easily converted and this could significantly lessen the burden of switchover. By developing these appliances with hydrogen in mind, they also should offer the same performance as new hydrogen appliances. In principle, Hydrogen Ready dual-fuel could offer an attractive compromise between rolling out hydrogen only appliances and adapting current natural gas appliances.
Ultimately, the general view of the industry was that the development of domestic hydrogen appliances would be initially led by new hydrogen only appliances and adaption and dual-fuel options would be developed off the back of these. Also, in the short term, new appliances would be based on existing natural gas products as much as possible to minimise the amount of new innovation required. If the industry and market for hydrogen appliances develop, further R&D may mean that the appliance components start diverging from those used in natural gas systems.
Note that another option which is commercial available is a hydrogen fuel cell. Rather than burning hydrogen in natural gas appliances, with a fuel cell you would use hydrogen to generate heat (for space and/or water heating) and electricity, which would then be used for other appliances such as ovens, ranges, and clothes dryers.
Currently these fuel cells use natural gas as a feedstock, but having a fuel cell which used hydrogen directly would of course be feasible as well, and in theory would cost less to install and operate.
