the synthesis gas is a significant energy demand. This power is provided by natural gas engines, electric motors powered by energy created at the plant or steam driven turbines. Excess synthesis gas contains hydrogen, since there is a stoichiometric excess, unreacted CO and CO2, and CH4 that was not converted in the reformer.
Figure 4-2: Process Components for Synthetic Fuel Production
Producing methanol or FTD from natural gas results produces a fuel with reduced hydrogen content compared to CH4. (While methanol has four hydrogens per carbon, it can be considered a combination of CH2 and H2O for this discussion. Since the composition of the feedstock and fuel differ, a carbon balance must be used to determine the amount of CO2 emitted from synthetic fuel production. This is simply illustrated by the overall reactions for a steam reforming methanol plant.
CH4 + H2O CO + 3 H2 Reforming
CO + 3H2 CH3OH + H2 Methanol synthesis
In practice, equilibrium and reactor volume considerations prevent all of the CO from being converted to methanol. In addition, some of the methane is not converted to CO and hydrogen. Converting CH4 to fuels does however convert a significant fraction of the carbon in methane to fuel. A process is thus characterized by its energy efficiency, energy ration and carbon efficiency. The energy efficiency is the ratio of product output to all energy inputs to the facility (natural gas for reforming, natural gas for compressor engines and electric power). The product output can include fuel, electricity or steam that is exported to other facilities. The energy ratio is simply the fuel output divided