Abstract |
In December, 1972, The Chesapeake Corporation started up a unique three-stage oxygen bleaching system (D/COD) to produce 272 metric air dry tons per day of 88+ brightness hardwood market pulp. This system cost less than conventional chlorination and offered potential for reducing bleach effluents. Excessive fiber losses from, and stress corrosion of the twin roll press were the most serious operating problems experienced on start-up. These problems were satisfactorily solved. Total effluent BODs and color levels indicated no decrease in BODs and a 36 percent decrease in color over conventional chlorination sequences. With oxygen-stage effluent recycle and complete recovery of a 40 percent reduction in BODs and a 65 percent reduction in color could be realized. Prior to and following the bleach plant start-up certain in-process changes were made, and systems using high-purity oxygen for wastewater treatment and weak BLO were piloted and installed. Also an on-site cryogenic air separation plant was installed to provide low-cost oxygen to these systems. The oxygen plant, waste treatment plant, and BLO systems have operated without major process problems since 1974. |