A long time ago, when coal was still the top fuel and renew­able ener­gies were still long from being discussed, Jules Vernes made a predic­tion in his 1874 novel “The Myste­rious Island”: “Water is the coal of the future. The energy of tomorrow is water, broken down using elec­trical energy. The broken-down elements, hydrogen and oxygen, will ensure the earth’s power supply for an indef­i­nite period of time.” Almost 150 years after the French author wrote these words, his vision is still a long way from being achieved. However, given the chal­lenges presented by climate change and the search for new energy sources, hydrogen, as an energy supply, is gaining increased atten­tion from the world of poli­tics, science and industry. After all, the bene­fits are clear: when it is burned, only water is emitted, rather than harmful carbon dioxide.

Using hydrogen in heating systems can signif­i­cantly contribute towards climate protec­tion.

The down­side is that hydrogen almost always appears on earth as a compound. Obtaining it requires a lot of energy. As Jules Vernes outlined, this can be done using elec­trol­ysis, allowing water to be broken down into hydrogen and oxygen using elec­tricity. This means that the fuel can only be climate-neutral if the elec­tricity used comes from climate-friendly sources. This is where renew­able ener­gies come in.

Devel­oping them will make it ever more neces­sary to store excess energy that cannot be fed imme­di­ately into the grid over longer periods of time. After all, the wind and sun do not answer to levels of demand. This climate-friendly elec­tricity can be used in power-to-gas plants to produce hydrogen, for example. As house­holds produce a large propor­tion of CO₂ emis­sions, using hydrogen in heating systems could signif­i­cantly contribute towards climate protec­tion. Producing it is still very costly, but the heating tech­nology sector is raring to go.

Hydrogen is gaining ground

Figure 1: The basic prin­ciple of the fuel condensing boiler also works with hydrogen, but only if the compo­nents are adapted accord­ingly. Hydrogen burns differ­ently to natural gas. (Photo | ebm-papst)

Enriching natural gas with four to six percent hydrogen is already permitted, depending on the gas char­ac­ter­istic values as per process sheet G260 from DVGW (the German asso­ci­a­tion for gas and water). But would it be possible to switch entirely to hydrogen? Several projects are under way to answer just that. For example, the British govern­ment has launched a program called “Hy4Heat” to deter­mine which tech­nical and logis­tical hurdles need to be over­come in order to grad­u­ally increasing the propor­tion of hydrogen. Doing so would have a partic­u­larly posi­tive effect, consid­ering that 80 percent of house­holds in Great Britain rely on gas, which is a partic­u­larly high amount when compared with the inter­na­tional average.

The country’s third largest city Leeds is plan­ning to move part of its gas network to 100 percent hydrogen in the medium term. Similar ideas can be found on the conti­nent, or more precisely in the Nether­lands. Here, resources from natural gas fields will soon be depleted. In Rozen­burg, Rotterdam there are already field tests in place with 100 percent hydrogen enrich­ment. Yet, when it comes to power-to-gas plants, Germany is the country leading the way again. In test plants, researchers are inves­ti­gating how to generate as much hydrogen as possible with the least amount of energy usage, and there are various studies on converting gas pipe lines into hydrogen pipes lines. In a nutshell: the market is on the move.

Chal­lenges for manu­fac­turers

That is why several manu­fac­turers are working on preparing their condensing units for clean energy supplies (Fig. 1). The aim is to achieve this with as few tech­nical and construc­tional changes as possible. The good news is that the current oper­ating prin­ciple can remain the same. However, due to the char­ac­ter­is­tics of hydrogen, several issues have been to consid­ered: leak require­ments, the compat­i­bility of mate­rials and, most impor­tantly, its flam­ma­bility.

Taking leaks into account, hydrogen is the lightest of all chem­ical elements with the lowest density. It has a higher perme­ability than natural gas through elas­tomers and plas­tics and, due to its slightly lower dynamic viscosity, it has a slightly higher leak rate than natural gas. The tight­ness of the compo­nents in the fuel condensing boiler must be adapted accord­ingly and moni­tored with rele­vant checks. The compat­i­bility of the mate­rials must also be checked, and the flam­ma­bility requires partic­ular atten­tion (see table). The flame speed is eight times higher than with methane, meaning that manu­fac­turers cannot work with the same burners.

The pres­sure loss increases and the power of the blower has to be opti­mized. Mostly impor­tantly, it has to be ensured that the igni­tion does not happen too late. Hydrogen is very reac­tive and ignites a lot better than methane. There­fore, the combus­tion controller has to factor in shorter igni­tion times. Another sticking point is that the usual flame measure­ment proce­dures using ioniza­tion cannot be imple­mented when checking and moni­toring the combus­tion. As a result, heater manu­fac­turers have to test new sensors or ther­mo­cou­ples.

Table: Comparing the prop­er­ties of hydrogen, methane and propane.

Another key issue is that hydrogen has a smaller lower heating value than methane but its Wobbe index, impor­tant for the inter­change­ability of fuel gas, is almost as high. For an optimum mixture in the venturi, the gas/air ratio controls have to be adapted accord­ingly. As a result, the inter­ac­tion between the gas blowers, venturi and gas valve is of great impor­tance.

NRV 118 ready for H₂

Figure 2: The “NRV 118 – Hydrogen” is ideally suited to hydrogen use. (Photo | ebm-papst)

The NRV 118 (Fig. 2) from ebm-papst is already designed for use with a hydrogen propor­tion of up to 10 percent without changes being required. The engi­neers at the Land­shut site put the estab­lished NRV 118 composite system through several inves­ti­ga­tions and initial field tests to check its suit­ability for hydrogen. The result: with some changes, the composite system can be adapted for use with 100 percent hydrogen. The require­ment for the tight­ness of the gas valve and blower was increased and the plas­tics and metals used were checked for their suit­ability.

Another benefit became clear: thanks to special pre-mixture equip­ment, the NRV 118 is ideally suited to hydrogen use. The “pre-fan-mix” gas blower compen­sates for the lower Wobbe index and hydrogen’s smaller lower heating value in the suction oper­a­tion. There is no need for more complex control lines. Further­more, higher modu­la­tions can be run because the gas valve can be opti­mally controlled by nega­tive pres­sure.

Figure 3: It is still a vision, but hydrogen could replace natural gas in the future and take over heat gener­a­tion as a climate-neutral fuel. (Illus­tra­tion | ebm-papst)

All in all, this means that manu­fac­turers can count on the “NRV 118 Hydrogen” when using 100 percent hydrogen. It will be some time before the clean fuel can be used exten­sively for heating (Fig. 3). Yet, if devel­op­ments in science, poli­tics and industry continue as they are, Jules Vernes’ fictional vision may become a reality before long.