The pure aluminum pellets must be mixed with water in a controlled fashion, otherwise you just get all your hydrogen gas at once. That defeats the benefit of this solution — not having to store the hydrogen.
To me, that doesn’t sound like ‘modules’ but more like a tank of aluminum pellets and a separate tank of water — then the pellets are added a few at a time into a reaction chamber, water is added, hydrogen gas produced and pumped out to the engine, and finally the water and alumina slurry moved off into a reclaimation tank.
Both the fresh pellets and waste alumina slurry would be so fine as to be ‘pumpable’. So a filling station would suck out the used alumina slurry while it was pumping new aluminum and water into their own separate tanks.
Thanks for the plausible engineering.