Torrefaction process

A method of converting cellulosic feedstock to bio coal comprising:

• Providing a conduit comprising a plurality of linear segments having a linear segment diameter, longitudinal axes and circular circumference, said conduit further having an inlet and an outlet and a plurality of curved segments creating a serpentine structure;
• providing a plurality of tubular sleeves around said linear segments and having longitudinal axes coincident with said longitudinal axes of said linear segments of said conduit creating a plurality of annular spaces, said plurality of tubular sleeves being in fluid communication and having a tubular sleeve inlet and tubular sleeve outlet;
• providing a plurality of mixing elements within a plurality of said linear segments, said plurality of mixing elements having no edges perpendicular to said longitudinal axes of said plurality of linear segments and are sized and positioned within said plurality of linear segments such that no mixing elements are in contact with one another, and are free of nooks and crotches which would otherwise result in fluid hangup and which results in an open region of travel for fluids passing from said conduit inlet to said conduit outlet;
• feeding a cellulosic feedstock carried by a process fluid to said conduit inlet;
• feeding a heating fluid to said tubular sleeve inlet causing said heating fluid to pass within said annular spaces;
• facilitating heat transfer between said heating fluid and said cellulosic feedstock;
• and
• maintaining said cellulosic feedstock and process fluid as a substantially oxygen-free fluid stream for a sufficient time to convert said cellulosic feedstock to said bio coal.