The provision of heat currently accounts for approximately half of UK energy consumption and one third of carbon dioxide emissions. The government has signalled its intentions for affordable low-carbon energy through the Clean Growth Strategy, and achieving this is likely to require almost full decarbonisation of heat in buildings. There are a number of technologies with the potential to play a role in decarbonising heat, including heat networks, heat pumps, hydrogen and biogas, but it is not yet clear which will work best at scale.
There has been an increasing interest in the role hydrogen could play in the decarbonisation of heat in the UK. Hydrogen could be used in the existing natural gas system, either by blending with the natural gas or by converting the gas system completely to hydrogen. This has the potential to significantly reduce carbon emissions, if low carbon methods of producing hydrogen can be developed and delivered at scale.
The main options include Steam Methane Reformation (SMR) combined with the sequestration (capture and long-term storage) of the carbon, or renewables-powered electrolysis of water. This study has sought to understand whether it is even possible to develop domestic gas appliances which achieve the necessary performance and safety when using 100% hydrogen.
For a given delivery pressure, hydrogen and natural gas provide a similar energy flux when injected through a burner and combusted on the other side. However, hydrogen has a greater flammability range than natural gas and a higher flame speed. Gas burners are designed so that the speed of gas flowing through burner ports is greater than the flame speed, in order to limit the flames to the outside of the port. With a greater flame speed, hydrogen is more prone to light-back, where it propagates back upstream, and given its greater flammability range this poses a risk of ignition to any gas mixtures behind the burner.
Domestic natural gas hobs use atmospheric burners that operate by injecting gas, normally from below, into the burner assembly (Figure 1). The jet of gas entrains the surrounding air underneath the burner and this provides some primary aeration before the gas-air mixture flows through holes (ports) around the burner where it is ignited on the outer side. The primary aeration, generated by the momentum of the gas jet, is not sufficient for full combustion and additional air (secondary air) is naturally drawn into the flame as it burns. Switching to hydrogen will require the removal of the primary airflow, as well as any void spaces where combustible gases could accumulate and potentially ignite. The flame failure devices, which detect when gas is flowing but no flame is present, typically take around 30 seconds to respond in natural gas appliances – a significantly faster response time may be required for hydrogen. Ovens and fires differ slightly from hobs in their geometry but work in a similar manner, so similar changes will be required.
Modern condensing boilers use pre-mix burners to mechanically draw in natural gas and mix it to stoichiometric proportions prior to combustion (Figure 2). The latent heat is captured by condensing out water vapour from the exhaust in the heat exchanger and this requires the burner system (and flames) to be downwards facing so that the condensate drips down away from the burner. Pre-mixed burning is likely to be incompatible with hydrogen, as it will be difficult to safeguard the volume of combustible gas mixture behind the burner surface from light-back.
One possibility is to introduce the air to the gas, or perhaps even both gases simultaneously, directly at the burner surface. Unlike the other appliances, boilers use ionisation sensors to detect poor combustion, through the presence of hydrocarbons in the exhaust. These hydrocarbons do not occur when hydrogen is burned and alternative sensors will need to be developed for domestic boilers, perhaps using ultraviolet (UV) or infrared (IR) sensors which are widely used in other industries.
Engagement with domestic gas appliance manufacturers has suggested that new appliances could be made to run on 100% hydrogen. By designing with hydrogen in mind from the outset, manufacturers see no reason why they couldn’t offer similar performance, lifetime and reliability as current natural gas appliances. The adaptation of existing appliances (similar to the approach used in the town gas conversion in the 1970s) is possible, although it is likely that there will be compromises in the performance, as any remaining components will not have been optimised for the higher temperatures.
The development of dual-fuel appliances, which can readily switch between the gas types, could significantly reduce the burden at the point of switchover, although these are likely to require doubling up of certain components and this would result in larger sizes and higher production costs. In the context of a single gas changeover, ‘hydrogen-ready’ appliances may be an attractive middle ground. Analogous to HD ready televisions, these appliances could developed with hydrogen in mind but temporarily back-fitted to run on natural gas up to the point of changeover. If a switchover occurred a simple, or even standardised conversion kit could be used to readily convert these appliances.
The government is seeking more evidence on the feasibility of hydrogen for domestic heat. As well as this study, it has commissioned the Hy4Heat programme to develop the first generation of domestic hydrogen appliances and investigate the safety case for the use of hydrogen downstream of the meter, in preparation for a potential experimental trial. The full Frazer-Nash report on the feasibility of hydrogen appliances is available on the BEIS website.
Stephen Livermore is a Chartered Mechanical Engineer at Frazer-Nash Consultancy. He undertakes thermo-fluid analysis of industrial processes and the built environment as well as broad multi-disciplinary research projects. He has a PhD in modelling of naturally ventilated buildings and a strong interest in the development of technologies for decarbonising heat.
Visit the UK’s dedicated jobsite for engineering professionals. Each month, we’ll bring you hundreds of the latest roles from across the industry.
Sounds like a lot of hassle – why not just use electric like the rest of the continent. We need to find the simplest solutions not the most complex. A child would tell you that…
Because H2 can be used to store lots of renewably generated energy which would otherwise be wasted (but still paid for by the taxpayer via curtailment payments), and the gas grid is quite elastic in storage capacity. The simplest solution is not to change anything. Problem with that is that a lot of us want our kids to survive…
It might be better to consider switching solely to electricity for domestic heating/cooking and use hydrocarbon gas — and/or hydrogen — for electricity generation.
I follow your (safety) thinking Ed, but that would place an enormous extra demand on the National Grid and local supply networks.
The issue with using the existing gas network for energy delivery is the much higher demand in the winter; with peaks of approximately 5-6x the normal electricity demand. This means 5-6x the electricity infrastructure needed to carry this heating energy, on top of ongoing electrification of transport. Building 5x the countries’ electricity supply for these peak demands also represents a very high cost. Cheaper to keep the infrastructure thats already in place, and just replace boilers etc.
The Renewable Heat Incentive (RHI) already encourages those who do not have gas supplied to use Heat Pump Technology to replace oil fired boilers. Modern heat pumps have a coefficient of performance (COP) between 3 and 4.5 so the electic energy demand is less than a third of the required heat. If heat pumps were to be the preferred ‘large scale’ option, then by Daniel Williams’ unsubstantiated figure for peak gas demand, the capacity of the electricity infrastructure would only need to be (at most) doubled.
Granted, although the low flow temperature 50 degrees max, of Heat Pumps means it is only really any good for underfloor systems in very well-insulated or newbuild low heat loss buildings. Not really a viable option for thousands of draughty, odl victorian terraced homes
I am happy with the analysis made by Dr. Livermore on the topic of hydrogen flames. It might not be well known, but USAF had intended back in the 1970’s, I think to develop a hydrogen fueled jet engine. They intended to operate with premix conditions. They soon found out (at the lab stationed on Wright-Patterson AF base) that pressure condition of 10 bar was sufficient to detonate the stoichiometric mixture every single time, without further inducement. Bad day had by the apparatus. I believe the thinking is 100% correct that removing any form of premix condition is a great idea. For that matter, why do you insist on an actual flame? Why not have the combustion take place at the surface of catalyst (as in a catalytic burner), and then you can tell from the incandescent surface that heat is being generated. It is time to turn the burner box inside out? I love the idea of a condensing (boiler), this way the fuel burn may even lead to potable water?
I was led to believe that hydrogen would seep out of normal metal gas pipes. Is there any data to quantify this? If the hydrogen was produced by solar power in Spain, how much would be lost if piped back to the UK?
I’m old enough to remember when the domestic gas supply was Hydrogen + Carbon monoxide, then we were converted to Natural gas.
I like your idea of a catalytic burner; this should overcome the problem of the (almost) invisible flame when using hydrogen. I’ve no idea if a suitable catalyst exists, but I’ve no doubt that one of our readers will!
Hydrogen would clearly be a first class fuel if it could be produced economically. The cost of producing and moving hydrogen is likely to be enormous, even compared with coal+CCS based electricity however. Does the author have any current costs for production of hydrogen?
Regarding the environmental implications, apart from NOx there is the issue of leakage-hydrogen build up in the upper atmosphere, an unknown quantity I believe!
Not sure about production cost at large scale, but purchase price is ~£4/kg if you buy it for a lab, and the companies supplying to fuel cell vehicle users seem to have settled on ~£8/kg. I think that is more driven by a need to be on par with petrol. The cost question always comes up but everyone seems to have forgotten about the gas grid already being in place (for the last 100 years?), and about the fact that we are often paying renewable generating capacity to shut down because there is either no demand or too much supply. Turn it all in to H2 and it’s effectively free.
Those of riper years will probably remember what were called barrage balloons! Large objects (made by a firm based in Southend called Airbourne Industries (the ‘estate’ is still there, though the factory has long gone) that were supposed to keep Luftwaffe planes at altitude so that they did not ‘bomb’ so accurately. The fabric for these amazing items was woven from 100’s (very thin -like gents’ handkerchief fabric) cotton count (there were few if any synthetic filaments in the late 30s) -and then coated: it was the case that the molecules/atoms of Hydrogen and helium (and there was very little of this available outside the USA, ‘cos they held the world supply!) are so small that they literally did not notice the woven structure as they passed so easily through it! The earliest air-ships had a similar issue: hence the use of ‘bladders’ (as in pig, cow, etc) to contain the lift gases of these earliest lighter-than air products. Is there something here for hydrogen ‘transfer’ pipes?
Since Hydrogen doesn’t exist is large stores ready to use it has to be created, typically by consuming electricity. This process is not very efficient. Heating and cooking directly with the electricity is better. The only advantage converting to Hydrigen gives is some ability to store the Hydrogen and allow consumption at a different time from creation but there are alternative ways of doing this with Electricity than conversion to Hydrogen.
We should be ramping down the gas system, not expending large sums of money to convert it to Hydrogen.
I wonder whether conversion to hydrogen is being considered purely because so much has been invested in the promotion and installation of combi boilers in recent decades. Conversion from gas to electric heating is going to be at considerable cost so modification to the existing natural gas network is probably cheaper. The point about demand times, though, is well made. Evening demand for heat energy in the winter is well beyond an electricity only solution. But maybe hydrogen production as a form of energy storage may solve this. Not efficiently, and would probably require grid upgrades, but I am surprised this option didn’t make the report.
Change is necessary or make gas less pollution, Electricity costs are high a change would need to be done area to area. IT SHOULD BE DONE DONE FREE, like the change from coal to natural gas. The cost of change will be high poor people could not pay for the the change, coumcils and housing associations and landlords will not to pay for the change. I would like a CHP hydrogen boiler, every home to supply electricity, with the higher heat saving money add solar and it could cost almost nothing to run. Who going to pay for the change?
As a gas engineer, you find hydrogen in radiators, created in poorly maintained heating systems. Could an iron and water reactor, combined with electrolysis to accelerate the process be used? Aeration of the water tends to help the process. Just get the iron to rust quickly and capture the hydrogen. Sounds so simple lol
This link is to a commercially available catalytic hydrogen hot water system. Would be interested if anyone knows the current bottle price of H2 vs LPG or Natural Gas. As many have said, economics will drive the change, i’m just wondering where we are at.
I like the sound of it. Sounds like a lot of development will be needed but i can see it being the best alternative to NG IF enough hydrogen can be made without being a pollutant itself and i think reading around the matter that has to be a bigger consideration than even the adaptation of appliances which before even reading this article I had an idea would be possible. But for all this to happen in the timr frame we have would need masdive cooperation between energy suppliers and government and the industry and a big commitment to it. But as i said before the green production of hydrogen is the elephant in the room and to my mind dosent seem to be sorted.
I understand that Orkney has so much excess non-fossil-fuel-generated electricity that it is using the surplus electricity to produce hydrogen for export. This problem of excess production of non-fossil-fuel electricity seems likely to become a more widespread problem for Scotland, as the planned installation of an interconnector .to Norway suggests. For adoption of hydrogen fuel for central heating wouldn’t it be cheaper and safer to install bottled/tanked hydrogen outside each early adopter’s house, rather than to try to convert the gas pipeline network?
I believe the hydrogen isn’t being exported, at least not at present. Electricity is being exported via existing links, however.
British Gas researcher told me that steel pipes would be embrittle by carrying hydrogen. But also found out yesterday that 250,000 Japanese homes are using hydrogen boilers, presumably fuel cell. I am keen to evaluate trends and future tariffs, domestic disruption etc. There seems to be precious little accessible overview information to Jo public to allow decisions about replacing a gas boiler, or improving insulation in existing homes for that matter.
We wrote about the use of domestic fuel cells in Japan in this feature:How the hydrogen economy could make a comeback
Ian Downie I’m old enough to remember when the domestic gas supply was Hydrogen + Carbon monoxide, then we were converted to Natural gas. Cost always has been and always will be the main driver.
I had no idea, so looks like been there and going back? With the addition nano aluminium powder to reduce mass, and the conversion of natural gas & methane through carbon capture to H?If not boilers then vehicle, the entire range from cars,trucks, trains, ships & planes. Hydrogen is a wonder fuel isn’t it?
By decoupling hydrogen supply investment from use, the investment requirements and deployment risk profile of hydrogen adoption is substantially reduced. This lays the foundations for hydrogen-based deeper carbon savings via fuel cells, low carbon dispatchable electricity generation – enabling use of more intermittent renewables – as well as potentially full gas network conversion.
Mark Allen Engineering Limited Registered Office: Mark Allen Group, St Jude's Church, Dulwich Road, London, SE24 0PB Registered in England No. 11569365
2kw Solar Wind Inverter
Hot Water Heat Pump, Swimming Pool Heat Pump, Geothermal Heat Pump - Itenity,https://www.itenity.com/