System for producing carbon fibers from multipurpose commercial fibers

A system for producing carbon fibers, comprising:

• a precursor fiber tow source comprising polyacrylonitrile precursor filaments, the filaments comprising 87-97 mole % acrylonitrile, and comprising less than 0.5 mole % of accelerant functional groups, the filaments being no more than 3 deniers per filament, the filaments being provided by the precursor fiber tow source in tows of at least 150,000 deniers per inch width, wherein the precursor fiber tow source is configured such that the filaments are arranged into precursor fiber tows comprising between 3000 and 3,000,000 filaments, and wherein the precursor fiber tow source is configured such that the filament count is between 100,000 and 3,000,000 filaments per inch width;
• an oxidation and stretching oven, the oxidation and stretching oven receiving the precursor fiber tows and comprising a heater for applying heat to the precursor fiber tows and an oxygen inlet for contacting the precursor fiber tows with oxygen while stretching the precursor fiber tows at least 10% to produce oxidatively stabilized precursor fibers;
• and,
• a carbonization furnace for heating and carbonizing the oxidatively stabilized precursor fibers to produce carbon fibers, wherein the system comprises a first carbonization furnace and a second carbonization furnace.