Fuel Carbon Ratio and Emissions

Switching a power plant from coal to natural gas cuts CO2 emissions by 40-50%, even before accounting for the gas plant's higher efficiency. The reason is chemistry, not engineering: methane (CH4) has four hydrogen atoms per carbon atom, while coal is nearly pure carbon. Hydrogen burns to water. Carbon burns to CO2. More hydrogen per carbon means more energy from water formation and less from CO2 production.

The hydrogen-to-carbon ratio determines a fuel's CO2 intensity. Methane (CH4) has an H:C ratio of 4:1 and emits about 50 kg CO2 per GJ of energy. Coal has an H:C ratio near 0.5:1 and emits about 88 kg CO2 per GJ. Propane (C3H8) and gasoline (C8H18) fall in between. The progression from coal to oil to gas is a progression toward higher hydrogen content and lower carbon content per unit of energy.

This chemistry is why "coal-to-gas switching" reduces emissions without any new technology: you are burning a fundamentally different molecule.

Worked Example

Compare methane and coal on a per-energy basis:

• Methane (CH4). Burning 1 mole produces 1 mole CO2 (44 g) and releases 890 kJ. CO2 per kJ: 44/890 = 0.049 g/kJ.
• Carbon (coal approximation). Burning 1 mole produces 1 mole CO2 (44 g) and releases 394 kJ. CO2 per kJ: 44/394 = 0.112 g/kJ.

What is the ratio of CO2 emissions per unit energy?

0.112/0.049 = 2.3. Coal emits about 2.3 times more CO2 per unit of energy than methane from chemistry alone. Combined with the efficiency advantage of gas turbines (60% vs. 38%), the real-world emissions reduction is even larger.

The hydrogen-to-carbon ratio is the chemical reason natural gas is a lower-carbon fuel, and why no amount of "clean coal" engineering can close the gap entirely.

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