Digester

Name:
Digester
Detailed information:
A cylindrical metal vessel, used chiefly in the preparation of wood pulp for papermaking, in which lignin is separated from cellulose by chemical means. It operates at approximately 150 psi and 170C. The wood is fed to the digester in the form of chips, and cooking liquor is added. Standard digesters are 12 ft in diameter and 45 ft high, with a wall thickness of 2 inches. These hold about 20 cords of wood, and some are even larger. The cooking cycle varies from 2.5 hr for board stock to 5 hr for bleached paper. Heat supply is by circulating steam and heat exchanger, though some types have direct steam injection. Digesters are designed for both batch and continuous operation. They are also used in reclaiming fabricated rubber products (tires, boot, and shoe, etc.).See Pulp, Paper; Digestion (2).