Looks like there's a problem with your data.lua: on line 10 it tries to do math on the fuel_value values, but those are quoted by strings in prototypes.

Here's the function I use to multiple energies. You'd have to adapt it to do addition, but should be close enough. I suspect this isn't coming up for other people because my mods are setting fuel values on vanilla fluids.

function(energy,mult)
local num = energy:match "[0-9%.]+"
local alpha = energy:match "%a+"
num = num*mult
return (num..alpha)
end

I think when I made this fuel_value may have been a numeric value. In any case, I need to do more examining (and possible retiring, honestly) of this mod and its handling of other fuels in light of all the changes made by simplifying oil.