36$ is their cost after reselling the fuel. The 20-30x is the cost to capture and then sequester a ton, with no revenue for this.
FYI, I didn't find the tweets you've linked to to be convincing. One tweet criticizes prometheus because, at the time of the tweet, they had a P.O. box. The other suggests that 'the secret ingredient may be lies.' Now, maybe both tweet authors' criticisms are well-founded. But, rhetorically speaking, the tweets aren't appeals to logic.
To be clear, no, they're not convincing arguments. It's people who know this space and find the claims by prometheus so unbelievable that they make fun of them.
I was quoting this more to illustrate the tone of the discussion. The argument is ultimately: Prometheus makes claims about costs that are very hard to believe, and doesn't provide much evidence that they are true.
Like they recently claimed that they can capture CO2 from the air with 36$, which is like 20-30 times lower than what current best tech can offer, and also lower than what people believe is generally possible.
See some discussion (while snarky, both people know this space well): https://twitter.com/gnievchenko/status/1385357863191814149# https://mobile.twitter.com/rutherdan/status/1385459168107057...