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Burning hydrogen releases a little more energy than burning carbon, correct?
And methane is CH4, but coal is mostly C, correct?
So shouldn't burning pure carbon release five times the CO2 (Assuming combusting carbon releases the same energy as hydrogen), or even six times per unit energy 'released'/'created' by the power plant (since hydrogen is more energy-dense per unit mass than carbon)?
When you do these calculations be sure to keep track of your units and the actual reactions you are considering.
Burning methane is not the same as burning the same amount of carbon plus twice the amount of dihydrogen. You need to check the specific heats of combustion and you need to make sure you keep track of the units used to measure the heat produced in the reaction (per mol, per kg or per mol of carbon dioxide?).
The heat of combustion (assuming all products are at STP) for carbon is 393 kJ/mol and for methane it is 889 kJ/mol. Both reactions produce the same amount of carbon dioxide if combustion is complete. So burning methane produces about 2.3 times as much heat per mole of carbon dioxide as burning pure carbon (anthracite coal will be close to this).
Well, burning H2 releases 4.7 times the heat of an equivalent weight of carbon, according to the table given by MaxW.
The heat given by methane is 1.84 times as much as bituminous coal, but the CO2 is only 0.75 as much.
So, burning bituminous coal would release 1.83/0.75 = 2.45 times as much CO2.
