To Preface:

I am not an engineer or chemist. To the extent of my limited research, this technology is viable. I currently don’t have the knowledge to explain its workings in detail. 

The Agricultural-Biomass-Enrichment-System, or “Agribine” is a collection of chemical concepts that have existed for several decades before the Burnout. Starving, and desperate to provide transportation for the other survivors in his estate, George Endell made a compact device that could process waste biomass (inedible plant matter, wood scraps, feces) into an energy-dense fuel. While the process required a considerable amount of input energy— more than it actually produced— it allowed survivors to produce a usable supply of fuel for their vehicles and industrial projects. The first prototype was equipped on the Hail Mary, widely considered the earliest Frost-Ship to travel in the Passage Lands, and travelled to Rillerman’s compound.

The engineers working for Rillerman and Andolous were able to duplicate the mechanism and make several, improved versions for distribution to other survivors. Each of these new Agribines could comfortably fit in a shipping container and were incredibly easy to maintain. The other survivors who received these new Agribines as part of the Widow’s Passage quickly became Proto-Clans. They made their own replicas and quickly became industrial powers for their region. Most groups recognized the incredible inefficiency of the Agribine and started investing in other energy-solutions. The only exception is the Crude Nations, who continued improving on the technology until they became the Post-Burnout equivalent of a petrol-state.

Even in the 60s, every medium, or larger, group of Frostships has an Agribine with them for emergencies and sentimental purposes.