H21: Is Hydrogen a Safe Fuel?

The two most common elements in the universe are hydrogen and stupidity.” – Harlan Ellison

I first learned about H21, the project to convert the fuel gas distribution system in the North of England from natural gas to hydrogen, at a safety conference where I gave a talk on containing hydrogen deflagrations within pressure vessels. After the talk, I was approached by two serious British engineers.  “We heard your talk this morning.”

My first thought was, Have I upset these guys?

“Are you guys going to beat me up?” Beatings are not actually a common feature of process safety conferences, but somehow, I manage to say things on occasion that stir passions.  They laughed, which I took as a good sign.

“No. We just wanted to know what you thought about the safety of the Leeds project.”

The H21 Project

The project aims to convert the existing 3.7 million meter points comprising the cities of Leeds, Bradford, Wakefield, Huddersfield, Hull, Liverpool, Manchester, Teesside, Tyneside, and York from natural gas to hydrogen. The original study, completed in 2016, confirmed the technical and economical feasibility of the project.  Phase 1 of the project is underway now. It is looking at the safety of the project and project managers expect completion of Phase 1 in 2020.

The aim of the project is to reduce emissions of CO2 to the atmosphere, where it acts as a greenhouse gas.  Although natural gas has the smallest yield of CO2 per energy produced of any fossil fuel, it is still more than that produced by burning H2, which yields no CO2 at all.

Producing Hydrogen Still Yields Carbon Dioxide

Burning molecular hydrogen as a fuel does not yield CO2.  Producing hydrogen, however, does.  About 5% of the hydrogen produced in the world is from the electrolysis of brine, which yields caustic and chlorine gas, with hydrogen gas as a by-product.

2NaCl + 2H2O à 2 NaOH + Cl2 + H2

This reaction produces no CO2, but the production of electricity, often at coal-fired plants, does. At some point in the future, the H21 project hopes to convert to hydrogen produce by electrolysis, using renewable sources of electricity to power the reaction.

The bulk of hydrogen production, however, is by steam reforming to produce syngas, followed by the water-gas shift reaction to convert carbon monoxide to carbon dioxide and yield more hydrogen.

CH4 + H2O à CO + 3 H2 (the reforming reaction)

CO + H2O à CO2 + H2 (the water-gas shift reaction)

This is the approach the project is planning to use: converting natural gas (which is primarily methane) to hydrogen and then distributing hydrogen to be used as a fuel. No fewer molecules of CO2 are produced per molecule of methane, but the release will not be dispersed across 3.7 million end users.  The plan is to collect the CO2 at the point of production, pressurize it, and then inject it deep into the North Sea, where they expect it will be sequestered.

The sequestration they are counting on presumably involves the conversion of CO2 to carbonic acid, H2CO3, and its salts, the bicarbonates and carbonates.  This will undoubtedly impact seawater chemistry and seems bound to cause acidification.  While I doubt the H21 project will make an appreciable difference to the seas, widespread adoption of this approach may very well shift the environmental problem from the atmosphere to the oceans.  If the H21 project is successful, it will be important to quantify the effect before widespread adoption, just to avoid unintended consequences.

“Town Gas”

This is not the first time that hydrogen has been distributed for use as a fuel. In the nineteenth and early twentieth centuries, cities throughout the industrialized world used something called “town gas”. Town gas was made locally from coal. It was a form of syngas, so it was mostly a mixture of hydrogen and carbon monoxide.  This was back in the day when sticking one’s head in the oven was a way to commit suicide. Typically, the cause of death was by carbon monoxide poisoning, rather than by simple asphyxiation with hydrogen or methane.

Fortunately, this new project is doing more on the gas production side, so the safety issues associated with distribution will not involve the distribution of carbon monoxide. Mostly, the concern is with the hazards of hydrogen.

Hydrogen is Dangerous—Thank You, Captain Obvious

You don’t have to be a Led Zeppelin fan to know that hydrogen is dangerous.  Images of the 1937 Hindenburg disaster in Lakehurst, New Jersey, the result of a fire and then hydrogen explosion, are among the most iconic photographs in history. In addition to being flammable, hydrogen is not air, meaning that it is a simple asphyxiant.

Except for its flammability, which is a pretty desirable characteristic for a fuel, and its fundamental inability to support respiration among us oxygen breathers, however, hydrogen has some wonderful properties.  Hydrogen is not a carcinogen and is otherwise non-toxic.  Likewise, its single combustion product—water vapor—is also innocuous.

On the other hand, hydrogen molecules are very small and so can diffuse into other materials with ease, especially at elevated temperatures. The presence of diffused hydrogen in metals can “cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials.” Even at ambient temperatures, hydrogen is more difficult to contain than other gases. The H21 Phase 1 studies focus on whether existing infrastructure will be more likely to leak when pressurized with 100% hydrogen rather than natural gas.

Hydrogen vs. Methane

The flammability properties for hydrogen are typically more extreme than for methane: the lower explosive limit is lower, the upper explosive limit is much, much higher, the minimum ignition energy is much, much lower. The only thing hydrogen has going for it in terms of safety, when compared to methane, is a slightly higher autoignition temperature.

H2 CH4
LEL 4.0% 5.4%
UEL 75% 17%
MIE 0.017 mJ 0.28 mJ
AIT 585 C 537 C

The environmental benefit of distributing hydrogen fuel instead of natural gas to end users seems obvious. It is just as obvious that the safety risk posed by distributing hydrogen is higher than that posed by distributing natural gas. While higher, it is difficult to say in advance by how much. Is it enough higher to matter? It will take experience at the scale of H21 to sort that out.

Let’s See the H21 Project Go Forward

This project is the sort of innovation that may have a very positive impact on reducing the level of CO2 in the atmosphere and so have a positive impact on slowing climate change and global warming. I am grateful that the consortium in the North of England are pursuing this. Innovation means change, and change means new hazards and new risk. By the same token, there are measures that can mitigate the hazards associated with producing hydrogen, with distributing hydrogen, and with sequestering carbon dioxide.

If ever there was a time for a management of change process, this is it. The project team seem determined to do this right. I am confident, or at least hopeful, that even in their zeal to push the project forward, the project organizers are already taking all of these concerns into account.

 

This blog is based on an earlier version, “A New Hydrogen Disaster? The Leeds Experiment”, posted on 23-Nov-2017 by Elsevier in Chemicals & Materials Now!

 

By | 2019-08-08T14:23:25+00:00 August 8th, 2019|Chemicals, Gas|0 Comments

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