PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR

Description

D21C covers pulping processes that isolate cellulose fibers by chemically or mechanically removing lignin, hemicellulose, and other non-cellulose constituents from raw cellulose-containing feedstocks such as wood, straw, or recycled paper. This subclass encompasses major pulping methods including kraft, sulfite, soda, and mechanical pulping, along with their associated chemical recovery systems for regenerating and recycling pulping liquors. Included are apparatus, equipment, and process control technologies for delignification, cooking, washing, and liquor circulation throughout pulp production facilities. Adjacent classes cover downstream pulp bleaching and paper sheet formation rather than the primary pulp production stage.