An anonymous reader quotes a report from Ars Technica: Most hydrogen today is made by exposing natural gas to high heat, pressure, and steam in a process that creates carbon dioxide as a byproduct. In what’s called “gray” hydrogen, all that carbon dioxide is released into the atmosphere. In “blue” hydrogen, facilities capture the carbon dioxide and sell it or store it, usually deep underground. Blue hydrogen is viewed by some as a bridge fuel, a way to build the hydrogen economy while waiting for green hydrogen prices to come down. In the meantime, blue hydrogen is also supposed to pollute less than gray hydrogen, natural gas, or other carbon-intensive fuel sources. Except blue hydrogen may not be low-carbon at all, according to a new peer-reviewed study. In fact, the study says the climate may be better off if we just burned coal instead.
There are essentially two ways to make blue hydrogen, and both rely on steam reformation, the process of using high heat, pressure, and steam that cracks methane and water to produce hydrogen and carbon dioxide. For both approaches, carbon dioxide from steam reformation is captured and stored or used. The difference between the two is whether carbon dioxide is captured from the generators that power the steam-reformation and carbon-capture processes. When you add it all up, capturing carbon from all parts of the process — steam reformation, power supply, and carbon capture — eliminates just 3 percent of greenhouse gas emissions compared with only capturing carbon from steam reformation. The lowest-carbon blue hydrogen had emissions that were just 12 percent lower than for gray hydrogen. Blue hydrogen’s Achilles’ heel is the methane used to produce it. Methane is the dominant component of natural gas, and while it burns more cleanly than oil or coal, it’s a potent greenhouse gas on its own. Over 20 years, one ton of the stuff warms the atmosphere 86 times more than one ton of carbon dioxide. That means leaks along the supply chain can undo a lot of methane’s climate advantages.
In the new study, Robert Howarth and Mark Jacobson, the paper’s authors and two well-known climate scientists, assume a leakage rate of 3.5 percent of consumption. They arrived at that number by scouring 21 studies that surveyed the emissions of gas fields, pipelines, and storage facilities using satellites or airplanes. To see how their 3.5 percent rate affected the results, Howarth and Jacobson also ran their models assuming 1.54 percent, 2.54 percent, and 4.3 percent leakage. Those rates are based on EPA estimates at the low end and, at the high end, stable carbon isotope analysis that isolated emissions from shale gas production. No matter which leakage rate they used, blue hydrogen production created more greenhouse gas equivalents than simply burning natural gas. And at the 3.5 percent leakage rate, blue hydrogen was worse for the climate than burning coal. “Combined emissions of carbon dioxide and methane are greater for gray hydrogen and for blue hydrogen (whether or not exhaust flue gases are treated for carbon capture) than for any of the fossil fuels,” Howarth and Jacobson wrote. “Methane emissions are a major contributor to this, and methane emissions from both gray and blue hydrogen are larger than for any of the fossil fuels.”
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