Working on a radiant heat calculation for CNG exiting a blow down stack (in case it was to flare). Part of the calculation requires the heat content of the gas, and I am unsure of what number to use. 47.8 MJ/kg is the number I am currently using, but I am unsure if this is correct. This number was given as the heat content for CNG (which is what I am considering). However, by the time it is vented, is it not longer considered compressed natural gas? Any ideas on what number I should use, and where is a good directory of heat content values? Thanks.