I'm not a fan of the way grey hydrogen was written off: That hydrogen is already being produced today by several different refinery processes, and then burned in a furnace because no one else wants it.

So the right way to handle the carbon accounting isn't to assume that all the CO2 produced by the refinery processes count against the hydrogen produced, but rather that the energy that refineries get from burning the hydrogen would be replaced by them burning natural gas instead.

The per-kg energy value of burning H2 is ~2.5x the value of natural gas (refineries generally use LHV for this accounting). But each kg of natural gas that gets burned produces ~2.8 kg of CO2 (because burning replaces the puny hydrogen with relatively larger oxygen atoms).

2.5*2.8 = 7kg of CO2 per kg of H2 taken out of the refinery. Which isn't as big a difference from the 10kg reported in the article as I expected when I set about writing this comment.

I don't disagree with your numbers, but "and then burned in a furnace because no one else wants it" is doing a lot of work.

Why does nobody want it? If it is being burned off because nobody wants it, then it effectively has less value after compressing and delivering it than the natural gas itself (or as you say, they'd be selling it and burning the natural gas instead).

The truth is, you can burn it off and save the cost and trouble of purifying and storing it (which also uses energy and produces carbon), especially when using it in fuel cells requires 99.99% purity. You couldn't just pipe it over to a data center or power plant.

It's worth considering also that not only is the hydrogen that would come out dirtier (because it's being replaced by natural gas), it's also making the natural gas dirtier, because you're burning methane instead of hydrogen to refine it.