CO2 Emissions from Power Plants That Use Natural Gas

From an US EPA web site:

"The average emissions rates in the United States from natural gas-fired generation are: 1135 lbs/MWh of carbon dioxide, 0.1 lbs/MWh of sulfur dioxide, and 1.7 lbs/MWh of nitrogen oxides. Compared to the average air emissions from coal-fired generation, natural gas produces half as much carbon dioxide, less than a third as much nitrogen oxides, and one percent as much sulfur oxides at the power plant. In addition, the process of extraction, treatment, and transport of the natural gas to the power plant generates additional emissions."

Taking the heat of combustion of methane as -890 , and methane having a molecular weight of 16g/mole, and a kWh as 3600kJ, then 1kWh of heat is generated from the combustion of 4.04 moles of methane. 1 mole of methane makes 1 mole of CO₂ when burnt, and the molecular weight of CO₂ is 44g/mol, so for every 1kWh of heat generated so will be about 178g of CO₂. Erring on the high side, the thermodynamic efficiency of the combustion process could be as high as, say, about 55% in a modern power station, and the generating conversion efficiency of, say, 85%, one might reasonably expect the kWh leaving the power plant to have been associated with the emission of somewhere north of 381g of CO₂ to the environment, and very likely won't be less than that figure.

It looks like we have two good answers here. Yours is about 840 lbs/MWhr vs. the EPA value of 1135 lbs/MWhr averaged over all US natural gas fueled generation. Yours is probably better to use for new capacity predictions.