Monday, July 18, 2016

Could the UK's gas grid be converted to hydrogen?

[NOTE: An earlier version of this piece appeared on 13 July on The Fifth Estate. This version has been updated.]

A new study claims converting the UK gas grid to carry hydrogen instead of natural gas will help to meet the UK’s carbon reduction targets and is technically feasible without much disruption to consumers. It proposes Leeds as a pilot city, but there are still major problems to be overcome before it can go ahead.

The proposal is called the H21 Leeds City Gate and the report has been produced by the North of England’s gas distributor, Northern Gas Networks, which is clearly worried by what could happen to its assets down the line, as the country reduces its greenhouse gas emissions by 80 per cent of 1990 values by 2050, which is the target.

It commissioned Kiwa Gastec, Amec Foster Wheeler, and Wales & West Utilities to assess the prospects for converting the gas network to take hydrogen instead of natural gas for cooking in heating, beginning in Leeds and eventually covering the entire UK.

The study is backed by no less than four other recent reports, all making the case for using the existing gas grid, which serves almost half the UK population, for either biogas or hydrogen or a combination.
A UK-wide conversion of the grid to hydrogen gas could, it’s claimed by H21, reduce greenhouse gas emissions associated with domestic heating and cooking – currently over 30 per cent of the UK’s total emissions – by a minimum of 73 per cent, as well as supporting decarbonisation of transport and local electricity generation.

The report argues that a hydrogen gas grid could use the existing underground natural gas pipe network, and that household appliances can be converted to run on hydrogen with far less disruption and expense than converting to renewable energy sources.

Dan Sadler, H21 project manager at Northern Gas Networks, said: “Households won’t be required to buy new appliances. The conversion process will be similar to that carried out in the 1960s and ’70s when 40 million appliances across 14 million households were converted from town gas to natural gas. We’d have special teams, working street by street to make the conversion as smooth as possible for customers with minimal impact in the homes and the highways.”

H21 says the project would be funded the same way as happened during that first conversion. This would allow the costs to be paid back over time and, alongside energy efficiency measures, would have a minimal impact on household energy bills.

Household appliances will, however, need to be upgraded or modified.

Pure hydrogen embrittles many pipeline steels causing cracking and many pipes are made of iron, but they are slowly being changed to polypropylene at a cost of around £1 billion (AU$1.75b) a year. This cost is spread across consumer bills.

NGN is proposing that Leeds, the UK’s third largest city, is used as a prototype test bed, and the conversion would take place from 2026-29. If successful, there would be a rollout across the UK, implemented at the pace required.

The government has cautiously welcomed the report as a contribution to the debate on Britain’s energy future.

John Loughhead, the chief scientific adviser at the Department for Energy and Climate Change, said: “Meeting the challenge of the Climate Change Act is a huge technical and business challenge. The H21 Leeds City Gate project has usefully explored one possible contribution to meeting this challenge. DECC, and wider UK government, are looking forward to seeing the full findings of the project in the final report.”

The Leeds proposal has received backing from local authorities and businesses including Leeds City Council, the Leeds City Region LEP and Tees Valley Unlimited LEP.

Councillor Lucinda Yeadon, Leeds City Council’s executive member for environment and sustainability, said: “Transforming Leeds into a hydrogen city would be a bold step. It could play a crucial role in how we heat and power our homes in the future alongside other sustainable energy sources.”

NGN is asking for £70-100 million to take the project to the next stage.

Big hurdles

There are several problems with NGN’s proposal besides replacing the pipes, to do with the energy content of hydrogen, and the process of obtaining it.

NGN is proposing the hydrogen be derived from North Sea natural gas with the carbon dioxide removed and placed securely back under the sea so that it doesn’t contribute to global warming.

But at present there is no proof this can work or will be cost-effective. 

Let’s look at this a little more closely.

Most hydrogen in the lithosphere is bonded to oxygen in water. Over 90 per cent of today’s hydrogen is mainly produced by a process called steam reforming, which uses fossil fuels – natural gas, oil or coal – as a source of the hydrogen. The carbon dioxide is removed and vented to the atmosphere.

Hydrogen produced from gas this way is two to three times the cost of the original fuel.

Of course, the energy content of hydrogen is less than that of the original fuel. The claimed energy efficiency for natural gas reforming is 75 per cent. Furthermore, by weight, a unit of hydrogen contains around three times more energy than natural gas or petrol:

  • Hydrogen: 33.33 kWh/kg
  • Natural gas: (82-93 per cent methane): 10.6-13.1 kWh/kg
  • Petrol: 12.0 kWh/kg
  • Methane: 13.9 kWh/kg
But natural gas is 7.857 times more dense than hydrogen, and we buy it by volume. Since natural gas carries 41.7 per cent less energy per unit of weight, you’d need to pipe to people’s homes just over three times as much volume of uncompressed hydrogen for them to get the same amount of energy, so the pipes will be under greater pressure to compensate.

Then there’s the climate change problem. The global warming potential of producing hydrogen using the steam reforming process is 13.7kg CO2-e per kg of hydrogen produced. Coal gasification, another major production method, delivers even worse emission levels.

A typical steam methane reforming hydrogen plant with a production rate of one million cubic metres of hydrogen a day produces 0.3-0.4 million standard cubic meters of CO2 a day, which is normally vented into the atmosphere.

To fully attain the benefits of using hydrogen, we must therefore either produce it from renewable energy – or capture and store somewhere the carbon dioxide removed during steam reforming – a process called carbon capture and storage. H21 is proposing the latter.

The renewables option

There are at least eight sustainable ways of producing hydrogen. Electrolysis of water is the cheapest but currently is much more expensive, around US$1500/kWh.

A comparison of photoelectrochemical (PEC) and photovoltaic-electrolytic (PV-E) ways of producing hydrogen with low CO2 and CO2-neutral energy sources indicated that base-case PEC hydrogen is not currently cost-competitive with electrolysis using electricity supplied by nuclear power or from fossil-fuels in conjunction with carbon capture and storage.

They are currently an order of magnitude greater in cost than electricity prices with no clear economic advantage to hydrogen storage as of yet.

A number of possibly cheaper technical breakthroughs are in the wings but we don’t yet know if and when they will be commercially viable.

Analysts at the US National Renewable Energy Laboratory who have looked into the feasibility of hydrogen, assume that 53kWh are required for an electrolyser to produce a kilogram of hydrogen (remember that’s 33kWh when converted), so we’d need a lot of renewable energy to create all the hydrogen to feed the grid.

It might just be more effective to send the electricity straight there and use it directly for heating and cooking.

The CCS option

The H21 proposal has been welcomed by Scottish Carbon Capture & Storage, a research partnership that includes the British Geological Survey, whose director, Stuart Haszeldine, called steam reforming with carbon capture and storage “the least cost method of generating the large amounts of hydrogen required”.

So he is right. Except that no one knows how much it will cost.

The H21 report points towards the very few existing CCS projects in the US and elsewhere – but these operate under very different conditions.

Ever since CCS was first proposed over 15 years ago, I have been sceptical that it could work. It has always been seen as a get-out-of-jail card to permit business as usual in terms of fossil fuels and energy use while seeming to tackle climate change.

Every single deadline and target to get economically viable demonstration and proof-of-concept projects off the ground has been missed in Europe.

This crucial hurdle needs to be overcome – perhaps by backing a completely different and sustainable route to making the hydrogen, or by using the carbon dioxide removed as a feedstock for fuels, chemistry and polymers.

This is called Carbon Storage and Utilisation (CCU).

CCU for the production of fuels, chemicals and materials has emerged as a possible complementary alternative to CO2 storage, but the report does not mention it. Nor do the two other reports on adapting the gas network produced last week.

"CCS is basically a non-profit technology, where every step is costly. CCU however has the potential to produce value-added products that have a market and can generate a profit." says Dr Lothar Mennicken, German Federal Ministry of Education and Research.

The report CCU in the Green Economy from The Centre for Low Carbon Futures shows CCU can be profitable with short payback times on investment.

It says: "Although only a partial solution to the CO2 problem, under some conditions using CO2 for CCU rather than storing it underground can add value as well as offsetting some of the CCS costs."

But what are the life-cycle carbon emissions of hydrogen production using SMR plus CCS/CCU?

The latest UK government estimated LCA CO2 emission figures for NG combustion are 184.45 g/kWh plus 24.83 g/kWh emitted by the supply system, totalling 209.28 g/kWh.

But this depends on the gas source: e.g., liquefying natural gas in Qatar, transporting it in refrigerated ships, transporting it in special depots, reclassifying and compressing it into the transmission system can add around another 20 g/kWh, totalling 230 g/kWh.

The carbon footprint of SMR+CCS has been evaluated as 269 g/kWh using the lowest 184.45g/kWh figure above and assuming an efficiency for the process of 68.4%. But applying this to the more accurate lifecycle figure for NG of 230 g/kWh obtains 336.26 g/kWh.

If 90% of the carbon dioxide emitted by combustion is captured by CCS or CCU this still leaves [184.45/0.687] x 0.1 + 20 + 24.83 g/kWh = 71.68g/kWh emissions of carbon dioxide equivalent gases – a not insignificant amount.

H21Leeds puts the figure higher, at 85.83g/kWh. Hardly zero carbon – so H2 generation by renewable energy + electrolysis might be a necessary option in the future.

So, for the time being H21 is an interesting dream – but we must wait to see if it can become a reality.

David Thorpe is the author of:

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