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A New Hydrogen Disaster? The Leeds Experiment
Posted on November 23rd, 2017 by Mike Schmidt in Chemical Manufacturing Excellence
“The two most common elements in the universe are hydrogen and stupidity.” – Harlan Ellison
I recently attended the Mary Kay O’Connor Process Safety Center International Symposium, where I gave a talk on design criteria for containing hydrogen deflagrations within pressure vessels. It went well enough, with some questions seeking clarification and other questions intended to show off how much the questioner knew. Later, during a break, 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 Leeds City Gate Project
Leeds is one of the largest cities in the U.K. It is contemplating a project to convert the existing natural gas network to 100% hydrogen. The executive summary of the phase 1 work describes the feasibility, both technically and economically. I understand that the phase 2 study will describe the safety implications.
The aim of the project is to reduce emissions of CO2 to the atmosphere, where it acts as a greenhouse. 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 H2, however, does. About 5% of the H2 produced in the world is from the electrolysis of brine, which yields caustic and chlorine gas, with hydrogen gas as a by-product.
This reaction produces no CO2, but the production of electricity, often at coal-fired plants, does.
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 CO2 and yield more H2.
This is the approach the Leeds experiment proposes: 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 is not distributed. The plan is to collect the CO2, 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 Leeds 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 Leeds experiment is successful, it will be important to quantify the effect before widespread adoption, just to avoid unintended consequences.
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.
Hydrogen is not a carcinogen and is otherwise non-toxic. Likewise, its single combustion product—water vapor—is also innocuous. Although not toxic, hydrogen is not air, so it is a simple asphyxiant.
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.”
The experiment in Leeds is called the H21 Leeds City Gate project. In the executive summary, they make a point of reminding the public that this is not the first time that hydrogen has been distributed for use as a fuel. Earlier in the city’s history, and throughout the industrialized world, cities used something called “town gas.” Town gas was made from coal—it was a form of syngas, so it contained hydrogen and high concentrations of 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 CO poisoning, rather than by simple asphyxiation with hydrogen or methane. Fortunately, the project is addressing that, so the safety issues associated with distribution will not involve the distribution of CO.
Mostly, the concern with hydrogen will be because of its flammability.
Hydrogen vs. Methane
There is no mention at all in the executive summary comparing the safety of distributing hydrogen instead of 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.
Let’s See the Leeds Experiment Go Forward
I cannot imagine that the risk posed by distributing hydrogen is less than that posed by distributing natural gas. While the risk is likely higher, I don’t know by how much. Is it higher enough to matter? It will take experience at the scale of a city to sort that out, which is exactly the scale of the experiment being suggested for the city of Leeds.
I would like to see the experiment in Leeds go forward. This 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 people of Leeds are considering 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 hydrogen. If ever there was a time for a management of change process, this is it. 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.
All opinions shared in this post are the author’s own.
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Principal, Bluefield Process Safety, LLC
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