A vessel used in chemical pulping processes in which wood chips are cooked with chemicals to produce wood pulp for papermaking. The purpose of pulping is to separate fibers of cellulose from other non-fibrous material. The chemicals added to wood chips in the digester (utilizing either the sulfite process or the sulfate—or kraft—process) dissolve most non-fibrous components of wood, such as lignin and hemicellulose, leaving only cellulose and a residual amount of lignin and other substances. Bleaching removes further amounts of these materials. (See Chemical Pulping.)

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