Capacity in the USA Note the installed electric capacity is

Capacity in the USA? (Note, the installed electric capacity is about 1 million MW, and these many plants produce about 4E12 kWh per year.) The new GTCC plants with 60% thermodynamic efficiency burn natural gas (assume it is pure methane). These emit less carbon dioxide into the atmosphere than do coal plants, for the same amount of output electricity produced. How much less - i.e. what is the ratio of [carbon dioxide from GTCC plants / carbon dioxide from coal plants] ? Assume that the coal plant burns pure carbon. Start with plants of the same electrical output (say 1000 MW), and proceed to solve the problem.

Solution

For 100 MW of power production the input energy is given by

Input Energy = 1000 / efficiency   = 100 / 0.6 = 1666.7 MW

Take calorific value of coal as 20 MJ/kg

Take calorific value of methane as 55 MJ/kg

amount of coal required   = 1666.7 / 20    = 83.33 kg/s

amount of methane required   = 1666.7 / 55    = 30.3 kg/s

1 mole of methane produces 1 mole of CO2 on combustion

Therefore mass of CO2 produced from methane   = 44 * 30.3 / 16    = 83.325 kg/s

1 mole of C₁₀₀H₁₀₀S₂ produces 100 CO2

Therefore mass of CO2 produced from coal   = 100 * 44 * 83.33 / 1364 = 268.8 kg/s

Ratio of CO2 production   = 83.325 / 268.8   = 0.31