How green is blue hydrogen?
How green is blue hydrogen?
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DOI：
10.1002/ese3.956
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发表时间：
2021-08-12
影响因子：
3.8
通讯作者：
Jacobson, Mark Z.
中科院分区：
文献类型：
--
作者：
Howarth, Robert W.;Jacobson, Mark Z.
氢通常被视为未来脱碳世界的重要能源载体。目前，大多数氢气是通过天然气中的甲烷（“灰氢”）的蒸汽重整生产的，二氧化碳排放量很高。越来越多的人建议使用碳捕获和储存来减少这些排放，产生所谓的“蓝氢”，经常被宣传为低排放。我们在同行评议的论文中进行了第一次努力，以检查蓝色氢的生命周期温室气体排放，其中包括二氧化碳和未燃烧的逸散甲烷的排放。蓝色氢的生产远不是低碳的，它的温室气体排放量相当高，特别是由于挥发性甲烷的释放。对于我们的默认假设（天然气甲烷排放率为3.5%，20年的全球变暖潜力），蓝色氢的总二氧化碳当量排放量仅比灰色氢少9%-12%。虽然二氧化碳排放量较低，但蓝色氢气的逸散性甲烷排放量高于灰色氢气，因为增加了使用天然气为碳捕获提供动力。也许令人惊讶的是，蓝色氢的温室气体足迹比燃烧天然气或煤炭取暖多20%以上，比燃烧柴油取暖多60%左右，这也是我们的默认假设。在天然气甲烷排放率降至1.54%的敏感性分析中，蓝色氢气的温室气体排放量仍大于单纯燃烧天然气，仅比灰色氢气少18%-25%。我们的分析假设捕获的二氧化碳可以无限期储存，这是一个乐观且未经证实的假设。即使这是真的，蓝色氢的使用似乎也很难从气候的角度来证明。
Hydrogen is often viewed as an important energy carrier in a future decarbonized world. Currently, most hydrogen is produced by steam reforming of methane in natural gas ("gray hydrogen"), with high carbon dioxide emissions. Increasingly, many propose using carbon capture and storage to reduce these emissions, producing so-called "blue hydrogen," frequently promoted as low emissions. We undertake the first effort in a peer-reviewed paper to examine the lifecycle greenhouse gas emissions of blue hydrogen accounting for emissions of both carbon dioxide and unburned fugitive methane. Far from being low carbon, greenhouse gas emissions from the production of blue hydrogen are quite high, particularly due to the release of fugitive methane. For our default assumptions (3.5% emission rate of methane from natural gas and a 20-year global warming potential), total carbon dioxide equivalent emissions for blue hydrogen are only 9%-12% less than for gray hydrogen. While carbon dioxide emissions are lower, fugitive methane emissions for blue hydrogen are higher than for gray hydrogen because of an increased use of natural gas to power the carbon capture. Perhaps surprisingly, the greenhouse gas footprint of blue hydrogen is more than 20% greater than burning natural gas or coal for heat and some 60% greater than burning diesel oil for heat, again with our default assumptions. In a sensitivity analysis in which the methane emission rate from natural gas is reduced to a low value of 1.54%, greenhouse gas emissions from blue hydrogen are still greater than from simply burning natural gas, and are only 18%-25% less than for gray hydrogen. Our analysis assumes that captured carbon dioxide can be stored indefinitely, an optimistic and unproven assumption. Even if true though, the use of blue hydrogen appears difficult to justify on climate grounds.