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Comment by mytailorisrich | Hacker News Reader

The story with coal is that it has been replaced mostly by natural gas. Probably a lot to do with the shale gas boom.

I wonder, does nat gas release less CO2 per MWh or sth? Because coal is mostly carbon, which can only get burnt to CO2, but eg methane is one carbon, four hydrogens per molecule. Still mostly carbon by weight I guess...

It does. The gas often comes together with crude oil, which is getting burnt elsewhere anyways, so gas is not a saviour. It's more of a "subsidy" of oil.

Yes, apparently natural gas emits almost 50% less CO2 than coal.

It is also cleaner. Emissions are pretty much pure CO2 whereas coal also emits other compounds, e.g. sulfur, and particulates. This even includes a level of radioactive elements. So it is very polluting.

Methane is also a very potent greenhouse gas.

According to 2019 EIA figures (https://www.eia.gov/todayinenergy/detail.php?id=48296), Natural gas plants in the US release about 43% the CO2 per unit energy of US coal plants. This is both because of higher energy per unit CO2 (would be about 56% per MJ or Btu or whatever) and better conversion efficiency. The highest thermal efficiency possible from a modern CCGT plant running at its ideal output is something like 60%, as there is a second steam cycle capturing the heat from the exhaust of the first turbine for more electricity. The numbers given for the efficiency of the fleet of gas plants in that article translate to about 44%, and 32% for coal.

In principle yes, but methane leakage over the natgas supply chain eats that advantage up.

Interesting, can you recommend a source on this?

The science is still ongoing: https://climate.mit.edu/ask-mit/how-much-does-natural-gas-co...

Just an anecdote, but I once reported (by phone to the local gas company) a smelly local gas pipeline/junction that I noticed after cycling by on the road the next to it, so the leak could not have been all that small. I then reported it some weeks later because the smell was still just as strong (but still "faint" at the distance to the road).

Apparently no one cares about the little leaks everywhere (or they cannot be fixed cheaply). Later on I noticed that other gas pipeline junctions -- the type that are scattered around subdivisions -- often smelled faintly of gas. I wonder if these small leaks can be avoided with better engineering or if perfectly sealed pipe fittings in the outdoors are impractical.

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