Patent ID: 6210527
Filing Date: 2001-04-03
Classification: D21C

Abstract:
A method of producing bleached wood pulp comprising:digesting wood chips in a digestion stage to produce brownstock pulp and weak black liquor;washing the brownstock pulp and extracting the weak black liquor;introducing the brownstock pulp, after having been washed, into sequential bleaching stages, including oxygen delignification and ozone bleaching stages, to produce a bleached wood pulp product;the oxygen delignification stage utilizing an oxygen containing stream and the ozone bleaching stage utilizing an ozone/oxygen containing stream and producing a waste stream principally containing water vapor, carbon dioxide, ozone, and oxygen;recovering the waste stream and scrubbing the waste stream with an aqueous, sodium sulfide and sodium hydroxide containing solution to remove ozone and carbon dioxide from the waste stream and thereby form a scrubbed stream; andforming the oxygen containing stream for use in the oxygen delignification stage from the at least part of the scrubbed stream.