a quick question:
I want to convert between MMBTU and MWh to get at emission factors from energy.
I have the following information:
I use the data given in 40 CFR 98 (see EPA source here) by the EPA and gives me the Stationary Combustion Emission Factors by Energy content (in MMBTUs) for CO2, CH4 and N2O emissions. I convert the CH4 and N2O emissions using the global warming potentials (21 for CH4 and 310 for N20) to CO2eq.
This gives me 94.007 kgCO2eq/MMBTU for coal and 53.112 kgCO2eq/MMBTU for natural gas.
Now that I have CO2eq emissions by a common unit of energy, I use the information I have on a kWh to convert this to kg CO2eq emissions by kWh. A kWh contains 3412 BTUs or 0.003412 MMBTUs of energy. Therefore, a kWh of coal produces 0.3207519 kg CO2eq and a kWh of gas produces 0.1812181 kg CO2eq. (or Therefore, a coal produces 0.32 tCO2eq/MWh and a kWh of gas produces 0.181 tCO2eq/MWh ).
BUT: I have also found information, like here where I get values for a kWh of 0.882 tCO2eq/MWh for Coal or 0.440 tCO2eq/MWh for Gas. These two pieces of information clearly don't square up!!
In essence, I have the information that a country produced 9,028,638 MWh of Coal electricity. With an emission factor of e.g. 0.91 tCO2eq/MWh that would be 8.76 MtCO2eq. But using the other methodology, 9,028,638 MWh would be 28,369,254 MMBTUs and so would be 28,369,254 * (94.007/1000) = 2.6 MtCO2eq
So clearly using the two methodologies, I get two very different results - but I have no clue where I'm going wrong...
Is the emission factor just so different in individual cases?
Thanks for the help!