We continue our discussion to do with Sustainable Aviation Fuels (SAFs). Previous posts in this series are,
The basic idea behind the Sustainable Aviation Fuel (SAF) initiative is that the fuel is manufactured from plant materials such as corn. The crop absorbs carbon dioxide (CO2) as it grows. When the SAF is burned in an airplane’s engine it creates an equivalent amount of CO2 that is emitted to the atmosphere and then ‘recycled’ to the growing crops. It is this overall process that is deemed to be sustainable.
As we discuss, in the post Sustainable Aviation Fuels: Land Use, one of the many drawbacks to the SAF project is that large amounts of land are required to grow the corn or other crop needed to manufacture the biofuel. One way around this difficulty is to use vegetation that is currently treated as waste. A recent article in Hydrocarbon Processing magazine ― Scaling up SAF production with Fischer-Tropsch technology ― describes how one company is planning on doing this. Instead of growing a crop such as corn in order to manufacture SAF, this company uses sugar cane waste (bagasse) provided by farms in the State of Louisiana.
The Fischer-Tropsch (F-T) process uses large amounts of energy in order to convert biomass into biofuel. The following steps in the process required the addition of heat.
Gasification of the biomass.
The production of syngas.
The F-T process itself generates heat, which can be used in other parts of the process.
Product refining.
The heat for these process steps currently is supplied by natural gas and other fossil fuels. Until biofuels, or some other form of renewable energy is used to provide the needed energy it is disingenuous to claim that Sustainable Aviation Fuels are truly sustainable.
