The key to it all is working out how much carbon you have
I guess you are after a fairly rough and ready calcuation from the quality of your data. From Memory Perry's handbook of chemical engineering has some useful emprical calculations for determining the heating values of coal from composition - I would grap these and work backwards to determine the percentage of carbon. Coal is really pretty simple stuff Carbon, Hydrogen, Nitrogen, Sulphur, Oxygen, Water and ash. If you have the lower and upper heating values you should be able to figure out the quantity of carbon and water by guessimating reasonable percentages of the others.
About 97% of carbon (depends on your coal) is converted to CO2 the rest is in the ash
Various coals can differ quite a bit in composition and, therefore, the amount of CO2 emitted from the combustion of coal can differ quite a bit.
That having been said, for a typical coal with a heating value of about 8,000 Btu/pound and having a carbon content of about 48 weight percent and a moisture content of about 30 weight percent and being combusted with 20 percent excess combustion air:
The wet flue gas = 14,000 SCF per million Btu of coal
CO2 in the wet flue gas = 14 volume percent
The dry flue gas = 12,100 SCF per million Btu of coal
CO2 in the dry flue gas = 16 volume percent
where: SCF = standard cubic feet of gas at 60 [°]F and atmospheric pressure.
