About hot-air driven coffee roasters:
devices of this kind using a hot-air engine as a prime mover for coffee roasting were made in those days, prior to World War I, by three French companies: Alliot, Houades and Hennemann. Manufacturer of the engines was the German company of Hubertus Raab, Zeitz in Saxony. Seller in France were "Les Etablissements Duhamel", Raab's agent in France.
Duhamels 24 pages catalogue from 1909 offered Raab two-cylinder engines of the so-called "Can-Type" in sizes of 1/60HP and 1/30HP driving gas-heated coffee roasters from 0.8 to 4 kilos.
In November 2013 a Houades roaster powered by means of a 50mm bore Raab hot-air engine was auctioned on ebay. Final Price: 3677 Euros (ca. $4000.-), a realistic price, maybe even a bargain due to ist rarity.
All about Raab engines in general and Raabs driving coffee roasters in particular is extensively descrived and depicted in volume 07A of the "compendium" series.
Raab's engines and fans were also offered by the French company Mestre et Blatge prior to the first World War. The fans (identical to those offered by Jost in British colonial India) targeted the "colonial market" in French colonial Africa and Southeast Asia although I have never heard of a Raab/Jost fan coming from those areas.